ABCMdb

ABCB11 p.Gly982Arg

Reviews:	p.Gly982Arg D
Predicted by SNAP2:	A: D (71%), C: D (80%), D: D (91%), E: D (91%), F: D (91%), H: D (91%), I: D (85%), K: D (91%), L: D (91%), M: D (80%), N: D (80%), P: D (91%), Q: D (85%), R: D (91%), S: D (71%), T: D (80%), V: D (85%), W: D (91%), Y: D (91%),
Predicted by PROVEAN:	A: D, C: D, D: D, E: D, F: D, H: D, I: D, K: D, L: D, M: D, N: D, P: D, Q: D, R: D, S: D, T: D, V: D, W: D, Y: D,

[switch to compact view]
Comments [show]

None has been submitted yet.

Publications
[hide] Bile salt transporters: molecular characterization... Physiol Rev. 2003 Apr;83(2):633-71. Trauner M, Boyer JL
Bile salt transporters: molecular characterization, function, and regulation.
Physiol Rev. 2003 Apr;83(2):633-71., [PMID:12663868]

Abstract [show]
Molecular medicine has led to rapid advances in the characterization of hepatobiliary transport systems that determine the uptake and excretion of bile salts and other biliary constituents in the liver and extrahepatic tissues. The bile salt pool undergoes an enterohepatic circulation that is regulated by distinct bile salt transport proteins, including the canalicular bile salt export pump BSEP (ABCB11), the ileal Na(+)-dependent bile salt transporter ISBT (SLC10A2), and the hepatic sinusoidal Na(+)- taurocholate cotransporting polypeptide NTCP (SLC10A1). Other bile salt transporters include the organic anion transporting polypeptides OATPs (SLC21A) and the multidrug resistance-associated proteins 2 and 3 MRP2,3 (ABCC2,3). Bile salt transporters are also present in cholangiocytes, the renal proximal tubule, and the placenta. Expression of these transport proteins is regulated by both transcriptional and posttranscriptional events, with the former involving nuclear hormone receptors where bile salts function as specific ligands. During bile secretory failure (cholestasis), bile salt transport proteins undergo adaptive responses that serve to protect the liver from bile salt retention and which facilitate extrahepatic routes of bile salt excretion. This review is a comprehensive summary of current knowledge of the molecular characterization, function, and regulation of bile salt transporters in normal physiology and in cholestatic liver disease and liver regeneration.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
631 G238V, E297G, G982R, R1153C, and R1268Q mutations prevent the protein from trafficking to the apical membrane, whereas the G238V mutant seems to be rapidly degraded by proteasomes. Login to comment

[hide] The bile salt export pump. Pflugers Arch. 2007 Feb;453(5):611-20. Epub 2006 Oct 19. Stieger B, Meier Y, Meier PJ
The bile salt export pump.
Pflugers Arch. 2007 Feb;453(5):611-20. Epub 2006 Oct 19., [PMID:17051391]

Abstract [show]
Canalicular secretion of bile salts mediated by the bile salt export pump Bsep constitutes the major driving force for the generation of bile flow. Bsep is a member of the B-family of the super family of ATP-binding cassette transporters and is classified as ABCB11. Bsep has a narrow substrate specificity, which is largely restricted to bile salts. Bsep is extensively regulated at the transcriptional and posttranscriptional level, which directly modulates canalicular bile formation. Pathophysiological alterations of Bsep by either inherited mutations or acquired processes such as inhibition by drugs or disease-related down regulation may lead to a wide spectrum of mild to severe forms of liver disease. Furthermore, many genetic variants of Bsep are known, some of which potentially render individuals susceptible to acquired forms of liver disease.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
160 Their bile flow rate is slightly but not significantly lower in comparison to controls, but the total bile salt output into bile is massively reduced and their liver bile salt concen- S114R G238V V284L* C336S D482G R487H S593R E636G G982R G1004D R1153CD R1268Q E186G E297G R432T I498T I498T T923P A926P R1050C R1128H S194P G260D N519S A1228V V444A K461E M677V R698H PFIC2 BRIC2 acquired cholestasis SNP Fig. 2 Putative secondary structure of Bsep (NT-005403) generated with the TOPO program (http://www.sacs.ucsf.edu/TOPO-run/wtopo.pl). Login to comment

[hide] Prediction of drug-induced intrahepatic cholestasi... Expert Opin Drug Saf. 2007 Jan;6(1):71-86. Sakurai A, Kurata A, Onishi Y, Hirano H, Ishikawa T
Prediction of drug-induced intrahepatic cholestasis: in vitro screening and QSAR analysis of drugs inhibiting the human bile salt export pump.
Expert Opin Drug Saf. 2007 Jan;6(1):71-86., [PMID:17181454]

Abstract [show]
Drug-induced intrahepatic cholestasis is one of the major causes of hepatotoxicity, which often occur during the drug discovery and development process. Human ATP-binding cassette transporter ABCB11 (sister of P-glycoprotein/bile salt export pump) mediates the elimination of cytotoxic bile salts from liver cells to bile, and, therefore, plays a critical role in the generation of bile flow. The authors have recently developed in vitro high-speed screening and quantitative structure-activity relationship analysis methods to investigate the interaction of ABCB11 with a variety of compounds. Based on the extent of inhibition of the bile salt export pump, the authors analysed the quantitative structure-activity relationship to identify chemical groups closely associated with the inhibition of ABCB11. This approach provides a new tool to predict compounds with a potential risk of drug-induced intrahepatic cholestasis.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
120 H2N COOH S56L G238V G260D C336S L339V V444A K461E D482G T923P K930X G982R R1090X R1153C Outside Inside R1268Q A1228VE1186K R1128H R1057X R1050C A926P A865V R698H E636G M677V S593R E592Q N591S R575XA570T Q558H I498T R432T R415Q R299K E297G V284A I206V S194P E186G cholestasis Expert Opin. Drug Saf. (2007) 6(1) Table 1. Login to comment
126 [46] - 22 2767 A→C Thr923Pro BRIC2 [45] - 22 2776 G→C Ala926Pro BRIC2 [45] - 22 2788 A→T Lys930X PFIC2 [43] - 23 2944 G→A Gly982Arg PFIC2 [47] - 23 3148 C→T Arg1050Cys BRIC2 [45] - 23 3169 C→T Arg1057X PFIC2 [35,47] - 24 3213 G→del Frame shift at position 1071 PFIC2 [47] - 24 3268 C→T Arg1090X PFIC2 [47] *Although Jansen et al. [47] reports the S114R variant, amino acid 114 in the wild type is Trp instead of Ser. BRIC2: Benign recurrent intrahepatic cholestasis type 2; del: Deletion; ICP: Intrahepatic cholestasis of pregnancy; NCBI: National Center for Biotechnology Information; PFIC2: Progressive familial intrahepatic cholestasis type 2. Login to comment

[hide] Phenotypic differences in PFIC2 and BRIC2 correlat... Am J Physiol Gastrointest Liver Physiol. 2008 Jan;294(1):G58-67. Epub 2007 Oct 18. Kagawa T, Watanabe N, Mochizuki K, Numari A, Ikeno Y, Itoh J, Tanaka H, Arias IM, Mine T
Phenotypic differences in PFIC2 and BRIC2 correlate with protein stability of mutant Bsep and impaired taurocholate secretion in MDCK II cells.
Am J Physiol Gastrointest Liver Physiol. 2008 Jan;294(1):G58-67. Epub 2007 Oct 18., [PMID:17947449]

Abstract [show]
Progressive familial cholestasis (PFIC) 2 and benign recurrent intrahepatic cholestasis (BRIC) 2 are caused by mutations in the bile salt export pump (BSEP, ABCB11) gene; however, their prognosis differs. PFIC2 progresses to cirrhosis and requires liver transplantation, whereas BRIC2 is clinically benign. To identify the molecular mechanism(s) responsible for the phenotypic differences, eight PFIC2 and two BRIC2 mutations were introduced in rat Bsep, which was transfected in MDCK II cells. Taurocholate transport activity, protein expression, and subcellular distribution of these mutant proteins were studied in a polarized MDCK II monolayer. The taurocholate transport activity was approximately half of the wild-type (WT) in BRIC2 mutants (A570T and R1050C), was substantially less in two PFIC2 mutants (D482G and E297G), and was almost abolished in six other PFIC2 mutants (K461E, G982R, R1153C, R1268Q, 3767-3768insC, and R1057X). Bsep protein expression levels correlated closely with transport activity, except for R1057X. The half-life of the D482G mutant was shorter than that of the WT (1.35 h vs. 3.49 h in the mature form). BRIC2 mutants and three PFIC mutants (D482G, E297G, and R1057X) were predominantly distributed in the apical membrane. The other PFIC2 mutants remained intracellular. The R1057X mutant protein was stably expressed and trafficked to the apical membrane, suggesting that the COOH-terminal tail is required for transport activity but not for correct targeting. In conclusion, taurocholate transport function was impaired in proportion to rapid degradation of Bsep protein in the mutants, which were aligned in the following order: A570T and R1050C > D482G > E297G > K461E, G982R, R1153C, R1268Q, 3767-3768insC, and R1057X. These results may explain the phenotypic difference between BRIC2 and PFIC2.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
13 The taurocholate transport activity was approximately half of the wild-type (WT) in BRIC2 mutants (A570T and R1050C), was substantially less in two PFIC2 mutants (D482G and E297G), and was almost abolished in six other PFIC2 mutants (K461E, G982R, R1153C, R1268Q, 3767-3768insC, and R1057X). Login to comment
19 In conclusion, taurocholate transport function was impaired in proportion to rapid degradation of Bsep protein in the mutants, which were aligned in the following order: A570T and R1050C Ͼ D482G Ͼ E297G Ͼ K461E, G982R, R1153C, R1268Q, 3767-3768insC, and R1057X. Login to comment
139 The positions of 8 PFIC2 mutations (E297G, K461E, D482G, G982R, R1057C, R1153C, 3767-3768insC, and R1268Q) and 2 BRIC2 mutations (A570T and R1050C) are indicated by ଝ and ଙ, respectively. Login to comment
165 Other PFIC2 mutants (K461E, G982R, R1153C, R1268Q, 3767-3768insC, and R1057X) did not show significant TC transport activity. Login to comment
184 Subcellular distribution study revealed that E297G, R1057X, A570T, and R1050C mutants were predominantly located along the apical membrane, whereas the other PFIC2 mutants (K461E, G982R, R1153C, R1268Q, and 3767-3768insC) remained intracellular (Fig. 7). Login to comment
188 Other PFIC2 mutant proteins (K461E, G982R, R1153C, R1268Q, and 3767-3768insC) were unstable and lost all transport activity. Login to comment
245 The mature form of Bsep protein (band C) of K461E, G982R, R1153C, R1268Q, and 3767-3768insC mutants was hardly detected (Fig. 6B) and, consequently, TC transport activity was abolished (Fig. 6A). Login to comment
290 From the view of maintenance of TC transport activity, the mutants could be aligned in the following order: A570T and R1050C Ͼ D482G Ͼ E297G Ͼ K461E, G982R, R1153C, R1268Q, 3767-3768insC, and R1057X. Login to comment

[hide] Update on progressive familial intrahepatic choles... J Pediatr Gastroenterol Nutr. 2008 Mar;46(3):241-52. Alissa FT, Jaffe R, Shneider BL
Update on progressive familial intrahepatic cholestasis.
J Pediatr Gastroenterol Nutr. 2008 Mar;46(3):241-52., [PMID:18376240]

Abstract [show]
Three distinct forms of familial intrahepatic cholestasis are the result of mutations in the ATP8B1, ABCB11, and ABCB4 genes. The pathophysiologies of the latter 2 of these diseases are well characterized and are the result of abnormalities in canalicular excretion of bile acids and phospholipids, respectively. The molecular pathophysiology of the systemic disease associated with mutations in ATP8B1 remains unclear. In all of these diseases, wide variations in clinical phenotypes have been observed. The variability can be ascribed at least in part to predicted genotype:phenotype correlations. Disease- and genotype-specific prognoses and therapeutic approaches may exist, although much more information needs to be ascertained before clinicians can confidently make decisions based on genetic information.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
188 Other common mutations include R575X, R1057X, G982R, C336S, R1153C, D482G, K461E, R1153C, R1268Q, R1090X, G238V, S114R, S593R, del 695, and del 3213 (66,67). Login to comment

[hide] Degradation of the bile salt export pump at endopl... Hepatology. 2008 Nov;48(5):1558-69. Wang L, Dong H, Soroka CJ, Wei N, Boyer JL, Hochstrasser M
Degradation of the bile salt export pump at endoplasmic reticulum in progressive familial intrahepatic cholestasis type II.
Hepatology. 2008 Nov;48(5):1558-69., [PMID:18798335]

Abstract [show]
The bile salt export pump (Bsep) represents the major bile salt transport system at the canalicular membrane of hepatocytes. When examined in model cell lines, genetic mutations in the BSEP gene impair its targeting and transport function, contributing to the pathogenesis of progressive familial intrahepatic cholestasis type II (PFIC II). PFIC II mutations are known to lead to a deficiency of BSEP in human hepatocytes, suggesting that PFIC II mutants are unstable and degraded in the cell. To investigate this further, we have characterized the impact of several PFIC II mutations on the processing and stability of rat Bsep. G238V, D482G, G982R, R1153C, and R1286Q all retain Bsep to the endoplasmic reticulum (ER) to different extents. Except for R1153C, the PFIC II mutants are degraded with varying half-lives. G238V and D482G are partially misfolded and can be stabilized by low temperature and glycerol. The proteasome provides the major degradation pathway for the PFIC II mutants, whereas the lysosome also contributes to the degradation of D482G. The PFIC II mutants appear to be more heavily ubiquitinated compared with the wild-type (wt) Bsep, and their ubiquitination is increased by the proteasome inhibitors. Overexpression of several E3 ubiquitin ligases, which are involved in ER-associated degradation (ERAD), lead to the decrease of both mutant and wt Bsep. Gene knockdown studies showed that the ERAD E3s Rma1 and TEB4 contribute to the degradation of G238V, whereas HRD1 contributes to the degradation of a mutant lacking the lumenal glycosylation domain (DeltaGly). Furthermore, we present evidence that G982R weakly associates with various components of the ER quality control system. These data together demonstrate that the PFIC II mutants except R1153C and DeltaGly are degraded by the ERAD pathway.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
4 G238V, D482G, G982R, R1153C, and R1286Q all retain Bsep to the endoplasmic reticulum (ER) to different extents. Login to comment
11 Furthermore, we present evidence that G982R weakly associates with various components of the ER quality control system. Login to comment
48 The following missense mutants were studied in this work: G238V, D482G, G982R, R1153C, and R1286Q. Login to comment
82 The positions of G238V, D482G, G982R, R1153C, and R1286Q are indicated by star signs in a predicted topology model of rat Bsep. Login to comment
95 As can be seen, there is substantial colocalization between GFP-Bsep and calnexin in mutants that are exclusively core-glycosylated or non-glycosylated, that is, G982R, R1153C, R1286Q, and ⌬Gly. Login to comment
99 Besides different glycosylation pattern, PFIC II mutants were also noticeably expressed at lower levels compared with the wt protein, with D482G, G982R, and ⌬Gly showing the lowest expression (Fig. 2A). Login to comment
119 G982R, R1286Q, and ⌬Gly were degraded over time as indicated by the decrease in the core-glycosylated form (the only form detected), whereas R1153C was relatively stable. Login to comment
122 In contrast, G982R and R1286Q are degraded with a half-life of approximately 1 hour (Fig. 3C). Login to comment
133 Because the proteasome and lysosome provide two of the major degradation mechanisms in the cell, we next examined the contribution of these two pathways to the stability of G238V, D482G, and G982R. Login to comment
156 In contrast, treatment with MG132 significantly stabilized the 170-kDa core-glycosylated form of G982R, D482G, and G238V. Login to comment
158 In contrast, the combination of ammonium chloride, leupeptin, and pepstatin only moderately increases the mature glycosylated form of D482G, while not affecting the expression of G238V or G982R. Login to comment
161 (A) The HEK 293 cells were transfected with the wt GFP-Bsep, G238V, D482G, and G982R. Login to comment
168 The HEK 293 cells were transfected with wt FLAG-Bsep (B) and G982R (C). Login to comment
176 The stabilization of G982R by the proteasome inhibitor was confirmed by pulse-chase studies (Fig. 5C), whereas the expression of wt Bsep is little affected by MG132 (Fig. 5B). Login to comment
183 However, the increase in ubiquitination is moderate for wt Bsep, compared with the mutant proteins G238V, D482G, G982R, and ⌬Gly. Login to comment
218 We transfected HEK cells with wt FLAG-Bsep, G982R and ⌬Gly, and isolated FLAG-Bsep by immunoprecipitation. Login to comment
221 Weak binding was seen between the sugar-binding ER chaperone calnexin and wt Bsep and G982R but not with the nonglycosylated ⌬Gly mutant, as expected. Login to comment
222 The ATPase p97, which extracts the retro-translocated proteins from the ER membrane,20 and a component of the retro-translocation complex HERP21,22 primarily associate with G982R as expected, which is a strong ERAD substrate. Login to comment
246 Taken together, the data from this study show that G238V, D482G, G982R, R1153C, R1286Q, and ⌬Gly mutations cause retention of Bsep in the ER to different extents. Login to comment
250 Mutants such as G982R and R1286Q are degraded with a half-life of approximately 1 hour. Login to comment
263 In addition, G238V, D482G, G982R, and ⌬Gly become relatively more ubiquitinated, compared with wt Bsep, when the function of the proteasome is inhibited, consistent with the notion that these mutant Bseps are misfolded and thus unstable. Login to comment
265 The ERAD substrate G982R interacts with multiple components of the ER quality control system. Login to comment
266 The HEK 293 cells were transfected with wt FLAG-Bsep, G982R, and ⌬Gly. Login to comment
291 Finally, we presented evidence that the ERAD substrates such as Bsep G982R weakly interact with components of the ER quality control system. Login to comment
294 For example, p97 and HERP primarily associate with G982R, which is a strong ERAD substrate (Fig. 5). Login to comment
295 Although calnexin interacts with both wt Bsep and G982R, the ratio of calnexin bound to Bsep is likely to be higher for G982R, because its expression level is lower than wt Bsep. Login to comment

[hide] Missense mutations and single nucleotide polymorph... Hepatology. 2009 Feb;49(2):553-67. Byrne JA, Strautnieks SS, Ihrke G, Pagani F, Knisely AS, Linton KJ, Mieli-Vergani G, Thompson RJ
Missense mutations and single nucleotide polymorphisms in ABCB11 impair bile salt export pump processing and function or disrupt pre-messenger RNA splicing.
Hepatology. 2009 Feb;49(2):553-67., [PMID:19101985]

Abstract [show]
The gene encoding the human bile salt export pump (BSEP), ABCB11, is mutated in several forms of intrahepatic cholestasis. Here we classified the majority (63) of known ABCB11 missense mutations and 21 single-nucleotide polymorphisms (SNPs) to determine whether they caused abnormal ABCB11 pre-messenger RNA splicing, abnormal processing of BSEP protein, or alterations in BSEP protein function. Using an in vitro minigene system to analyze splicing events, we found reduced wild-type splicing for 20 mutations/SNPs, with normal mRNA levels reduced to 5% or less in eight cases. The common ABCB11 missense mutation encoding D482G enhanced aberrant splicing, whereas the common SNP A1028A promoted exon skipping. Addition of exogenous splicing factors modulated several splicing defects. Of the mutants expressed in vitro in CHO-K1 cells, most appeared to be retained in the endoplasmic reticulum and degraded. A minority had BSEP levels similar to wild-type. The SNP variant A444 had reduced levels of protein compared with V444. Treatment with glycerol and incubation at reduced temperature overcame processing defects for several mutants, including E297G. Taurocholate transport by two assessed mutants, N490D and A570T, was reduced compared with wild-type. Conclusion: This work is a comprehensive analysis of 80% of ABCB11 missense mutations and single-nucleotide polymorphisms at pre-mRNA splicing and protein processing/functional levels. We show that aberrant pre-mRNA splicing occurs in a considerable number of cases, leading to reduced levels of normal mRNA. Thus, primary defects at either the protein or the mRNA level (or both) contribute significantly to BSEP deficiency. These results will help to develop mutation-specific therapies for children and adults suffering from intrahepatic cholestasis due to BSEP deficiency.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
68 Continued Exon Nucleotide Change Predicted Protein Effect Location in Protein Associated Phenotype Prevalence or frequency* Any Defect(s) Identified Reference BRIC, 1 family (both hom) 15 c.1757CϾT T586I Adj WB BRIC 1 family (het) No splicing † 15 c.1763CϾT A588V Adj WB PFIC 2 families (both het) No protein 31, 32 15 c.1772AϾG N591S Adj WB SNP-ICP 2.6% 42 15 c.1779TϾA S593R NBF1 PFIC 1 family (het) 29 15 c.1791GϾT V597V NBF1 SNP 2.6% 42 16 c.1880TϾC I627T IC3 PFIC 1 family (het) ‡ 16 c.1964CϾT T655I IC3 BRIC / ICP / DC 1 family (het) Reduced levels of mature protein ‡ 17 c.2029AϾG M677V IC3 SNP 1.6-5.6% 39, 42-45 18 c.2093GϾA R698H IC3 SNP 0.3 - 0.8% 43, 45 18 c.2125GϾA E709K IC3 SNP-PFIC 1 family (het) ‡ 18 c.2130TϾC P710P IC3 SNP-PBC 0.5 - 3.1% 43 20-21 c.2412AϾC A804A TM8 SNP 1.1% 45 20-21 c.2453AϾT Y818F IC4 SNP-PFIC 2 families (hom) Reduced levels of mature protein ‡ 20-21 c.2494CϾT R832C IC4 PFIC 2 families (1 het, 1 consanguineous) Moderate differential splicing 31, 32 20-21 c.2576CϾG T859R IC4 PFIC 1 family (het) 31 22 c.2767AϾC T923P IC5 BRIC 1 family (het) 8 22 c.2776GϾC A926P IC5 BRIC 1 family (het) Mild exon skipping 8 23 c.2842CϾT R948C IC5 PFIC 2 families (both het) Immature protein 31 23 c.2935AϾG N979D TM11 PFIC 1 family (consanguineous) 31 23 c.2944GϾA G982R TM11 PFIC 4 families (1 hom, 1 consanguineous, 2 het) Immature protein 7, 29, 31 23 c.3011GϾA G1004D EC6 PFIC 1 family (hom) 28 24 c.3084AϾG A1028A TM12 SNP-PBC 39.86 - 56.3% Severe exon skipping 8, 43, 45 24 c.3148CϾT R1050C C term BRIC 2 familes (1 hom, 1 het) Immature protein 8 25 c.3329CϾA A1110E Adj WA PFIC 2 familes (both het) Mild exon skipping; immature protein 31 25 c.3346GϾC G1116R WA PFIC / BRIC 1 family (consanguineous) Mild exon skipping ‡ 25 c.3382CϾT R1128C NBF2 PFIC 1 family (consanguineous) Mild exon skipping; immature protein 31 25 c.3383GϾA R1128H NBF2 BRIC 1 family (hom) Mild exon skipping; greatly reduced levels of mature protein 8 26 c.3432CϾA S1144R NBF2 PFIC 1 family (het) Severe differential splicing 29 26 c.3457CϾT R1153C NBF2 PFIC 4 families (2 consanguineous, 2 het) Immature protein 7, 31, 36 26 c.3458GϾA R1153H NBF2 PFIC 4 families (2 consanguineous, 2 het) Severe differential splicing; immature protein 31 26 c.3460TϾC S1154P NBF2 PFIC 1 family (het) Severe differential splicing 31 26 c.3556GϾA E1186K NBF2 SNP 1%-10% Mild exon skipping ‡ 26 c.3589_3590 delCTinsGG L1197G NBF2 BRIC 1 family (het) † 27 c.3628AϾC T1210P Adj ABCm PFIC 1 family (hom) Immature protein 31 27 c.3631AϾG N1211D Adj ABCm SNP-PFIC 1 family (het) ‡ 27 c.3669GϾC E1223D ABCm Prolonged NNH 1 family (het) ‡ 27 c.3683CϾT A1228V Adj ABCm/WB SNP-PBC 0.8% 43 27 c.3691CϾT R1231W Adj ABCm/WB PFIC 1 family (het) Severe exon skipping; immature protein 30, 31 27 c.3692GϾA R1231Q Adj ABCm/WB PFIC 2 families (1 consanguineous, 1 het) No splicing; immature protein 31, 34 27 c.3724CϾA L1242I WB PFIC 1 family (het) 31 28 c.3892GϾA R1268Q¶ NBF2 PFIC 1 family (hom) Immature protein 7 *Prevalence or frequency is quoted depending on how data were presented in the original publication(s). Login to comment

[hide] De novo bile salt transporter antibodies as a poss... Hepatology. 2009 Aug;50(2):510-7. Keitel V, Burdelski M, Vojnisek Z, Schmitt L, Haussinger D, Kubitz R
De novo bile salt transporter antibodies as a possible cause of recurrent graft failure after liver transplantation: a novel mechanism of cholestasis.
Hepatology. 2009 Aug;50(2):510-7., [PMID:19642168]

Abstract [show]
Progressive familial intrahepatic cholestasis type 2 (PFIC-2) is caused by mutations of the bile salt export pump (BSEP [ABCB11]), an ATP-binding cassette (ABC)-transporter exclusively expressed at the canalicular membrane of hepatocytes. An absence of BSEP from the canalicular membrane causes cholestasis and leads to liver cirrhosis, which may necessitate liver transplantation in early childhood. We report on the first case of a child with PFIC-2 suffering from repeated posttransplant recurrence of progressive intrahepatic cholestasis due to autoantibodies against BSEP. These antibodies occurred after transplantation and were detected in the patient's serum and at the canalicular membrane of two consecutive liver transplants. The antibodies were reactive toward the first extracellular loop of BSEP, were of high affinity, and inhibited transport activity of BSEP, thus causing severe cholestasis. The patient had three homozygous, missense changes in the BSEP gene. Their combination resulted in the complete absence of BSEP, which explains the lack of tolerance, a prerequisite of autoantibody formation toward BSEP. The findings illustrate a novel disease mechanism due to a new class of functionally relevant autoantibodies resulting in cholestasis and subsequent liver failure.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
29 Compared to the reference sequence NM_003742 of BSEP (ABCB11), three homozygous missense changes were found: 1331T3C (V444A),17 2453A3T (Y818F), and 2944G3A (G982R)4 (start codon numbered as "1"). Login to comment
81 The patient`s mutations were introduced using the Quickchange-Multisite- mutagenesis kit (Stratagene) and the following primers: 2453A3T (Y818F): 5Ј-ccaatttctacagggatttgcctttgctaaatc- 3Ј; 2944G3A (G982R): 5Ј-cagaaagccaatatttacagattctgctt- tgcctttgc-3Ј. Login to comment
151 However, introduction of G982R alone or in combination with either V444A or Y818F (Fig. 4B) resulted in the retention of BSEPG982R, BSEPV444A/G982R, and BSEPY818F/G982R in the endoplasmic reticulum (ER) in colocalization with the ER marker protein disulfide isomerase. Login to comment
152 Combining all three mutations resulted in nondetectability of BSEPV444A/Y818F/G982R-YFP (Fig. 4C) independent of the cell type used (Supporting Fig. 3). Login to comment
154 Unexpectedly, K165 and K168 immunoreactivity, but no YFP fluorescence, was present in aggresomes of BSEPV444A/Y818F/ G982R-YFP-transfected cells after MG-132 treatment (Fig. 4G,J). Login to comment
165 Bars ϭ 10 ␮m. BSEPV444A/Y818F/G982R-YFP within the ER-associated degradation pathway. Login to comment
166 Furthermore, the apparent loss of YFP fluorescence is suggestive of an incomplete expression or a major folding defect of BSEPV444A/Y818F/G982R-YFP. Login to comment
175 It is of note, that in addition to the G982R and Y818F mutations, the common mutation/polymorphism V444A is necessary for the complete disappearance of BSEP. Login to comment
176 V444A has a high prevalence in the Caucasian population,17 has been linked to the development of drug-induced liver injury,30 and may aggravate cholestatic liver diseases such as intrahepatic cholestasis of pregnan- cy31 or benign recurrent intrahepatic cholestasis.32 Expression of BSEPV444A/Y818F/G982R in hepatic and nonhepatic cell lines was below detectability. Login to comment
184 The presence of G982R and Y818F caused the retention of mutated BSEPY818F/G982R-YFP within the endoplasmic reticulum. Login to comment
185 Combination of all three mutations of the patient (V444A,Y818F,G982R) induced complete absence of mutated BSEPV444A/Y818F/G982R-YFP. Login to comment
188 (G-L) Aggresomes, induced by MG132 in BSEPV444A/Y818F/G982R-YFP-expressing cells, contained immunoreactivity for the BSEP antibodies K165 (I) and K168 (L) but no green fluorescence, suggesting incomplete expression or misfolding of BSEPV444A/Y818F/G982R-YFP. Login to comment

[hide] Polymorphic variants in the human bile salt export... Pharmacogenet Genomics. 2010 Jan;20(1):45-57. Ho RH, Leake BF, Kilkenny DM, Meyer Zu Schwabedissen HE, Glaeser H, Kroetz DL, Kim RB
Polymorphic variants in the human bile salt export pump (BSEP; ABCB11): functional characterization and interindividual variability.
Pharmacogenet Genomics. 2010 Jan;20(1):45-57., [PMID:20010382]

Abstract [show]
OBJECTIVES: Our aims were to identify and functionally characterize coding region nonsynonymous single nucleotide polymorphisms in the hepatic efflux transporter, bile salt export pump (BSEP; ABCB11), and to assess interindividual variability in BSEP expression. METHODS: We identified 24 single nucleotide polymorphisms, including nine nonsynonymous variants, in ABCB11 from genomic DNA of approximately 250 ethnically diverse healthy individuals using denaturing high-performance liquid chromatography analysis and DNA sequencing. Wild type and variant BSEP were generated and functionally characterized for taurocholate transport activity in vitro in HeLa cells using a recombinant vaccinia-based method. BSEP expression was assessed by real-time mRNA analysis, western blot analysis, and immunofluorescence confocal microscopy. RESULTS: For the most part, polymorphisms were rare and ethnic-dependent. In vitro functional studies revealed several rare variants, including 616A>G, 1674G>C, 1772A>G, and 3556G>A, to be associated with significantly impaired taurocholate transport activity while the 890A>G variant trended towards impaired function but was not statistically significant. The 3556G>A variant was associated with reduced cell surface to total protein expression compared with wild-type BSEP. Expression of BSEP by mRNA and protein analysis was determined from a bank of human liver samples. Wide interindividual variability was noted in both mRNA (19-fold) and protein (31-fold) expression levels. The common variant 1331T>C was associated with significantly reduced hepatic BSEP mRNA levels. CONCLUSION: Accordingly, our study indicates there are functionally relevant polymorphisms in ABCB11 which may be of potential relevance in the predisposition to acquired liver disorders such as drug-induced cholestasis.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
138 Functional analysis of bile salt export pump variants A panel of expression plasmids comprising wild-type BSEP, nine nonsynonymous BSEP variants, and two known PFIC2 BSEP missense mutants, 2944G > A (Gly982Arg) and 3457C >T (Arg1153Cys), was constructed for functional studies. Login to comment

[hide] ATP8B1 and ABCB11 analysis in 62 children with nor... Hepatology. 2010 May;51(5):1645-55. Davit-Spraul A, Fabre M, Branchereau S, Baussan C, Gonzales E, Stieger B, Bernard O, Jacquemin E
ATP8B1 and ABCB11 analysis in 62 children with normal gamma-glutamyl transferase progressive familial intrahepatic cholestasis (PFIC): phenotypic differences between PFIC1 and PFIC2 and natural history.
Hepatology. 2010 May;51(5):1645-55., [PMID:20232290]

Abstract [show]
Progressive familial intrahepatic cholestasis (PFIC) types 1 and 2 are characterized by normal serum gamma-glutamyl transferase (GGT) activity and are due to mutations in ATP8B1 (encoding FIC1) and ABCB11 (encoding bile salt export pump [BSEP]), respectively. Our goal was to evaluate the features that may distinguish PFIC1 from PFIC2 and ease their diagnosis. We retrospectively reviewed charts of 62 children with normal-GGT PFIC in whom a search for ATP8B1 and/or ABCB11 mutation, liver BSEP immunostaining, and/or bile analysis were performed. Based on genetic testing, 13 patients were PFIC1 and 39 PFIC2. The PFIC origin remained unknown in 10 cases. PFIC2 patients had a higher tendency to develop neonatal cholestasis. High serum alanine aminotransferase and alphafetoprotein levels, severe lobular lesions with giant hepatocytes, early liver failure, cholelithiasis, hepatocellular carcinoma, very low biliary bile acid concentration, and negative BSEP canalicular staining suggest PFIC2, whereas an absence of these signs and/or presence of extrahepatic manifestations suggest PFIC1. The PFIC1 and PFIC2 phenotypes were not clearly correlated with mutation types, but we found tendencies for a better prognosis and response to ursodeoxycholic acid (UDCA) or biliary diversion (BD) in a few children with missense mutations. Combination of UDCA, BD, and liver transplantation allowed 87% of normal-GGT PFIC patients to be alive at a median age of 10.5 years (1-36), half of them without liver transplantation. CONCLUSION: PFIC1 and PFIC2 differ clinically, biochemically, and histologically at presentation and/or during the disease course. A small proportion of normal-GGT PFIC is likely not due to ATP8B1 or ABCB11 mutations.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
94 ABCB11 Mutations in PFIC2 Patients Family Mutation Allele 1 Mutation Allele 2 Biliary BA (N > 10 mmol/L) BSEP Liver Immunohistochemistry PFIC2 no. 1 p.R1090X p.R1090X 0.02 BSEP À PFIC2 no. 2 p.Y354X p.Y354X 0.02 BSEP À PFIC2 no. 3 p.Y354X p.Y354X 0.19 BSEP À PFIC2 no. 4 p.Y354X p.Y354X na na PFIC2 no. Login to comment
95 5a‡ p.Y354X p.G982R 0.10 BSEP À PFIC2 no. Login to comment
96 5b‡ p.Y354X p.G982R na na PFIC2 no. Login to comment
102 12† p.T1210P p.T1210P 0.11 BSEP À PFIC2 no. 13 c.3213 15 G>A p.A1192EfsX50 na BSEP À PFIC2 no. Login to comment
104 14b† p.I420T p.I1061VfsX34 na na PFIC2 no. 15*,‡ p.A167T p.G1058HfsX38 0.5 BSEP À PFIC2 no. 16* p.R1231W p.I528X na na PFIC2 no. 17 p.M62K p.I112T þ p.R698H 0.10 BSEP À PFIC2 no. 18* p.E297G p.H484RfsX5 0.16 BSEP À PFIC2 no. 19* p.E297G p.I610GfsX45 0.23 BSEP À PFIC2 no. Login to comment
105 20† p.A257G p.G982R na na PFIC2 no. 21* p.I182K c.3213 15 G>A na BSEP À PFIC2 no. 22 p.D549V c.76 13 G>T na na PFIC2 no. Login to comment
107 24† p.R1153C c.3213 14 A>G 0.13 BSEP À PFIC2 no. 25* p.G982R p.Q101DfsX8 0.10 BSEP À PFIC2 no. 26* p.N591S þ p.V597V nf 0.39 BSEP À PFIC2 no. 27* p.G982R p.R1001R na BSEP À PFIC2 no. 28 p.L232CfsX9 nf na BSEP À PFIC2 no. 29 p.W114R nf 0.50 BSEP À PFIC2 no. Login to comment

[hide] The bile salt export pump: clinical and experiment... Semin Liver Dis. 2010 May;30(2):125-33. Epub 2010 Apr 26. Lam P, Soroka CJ, Boyer JL
The bile salt export pump: clinical and experimental aspects of genetic and acquired cholestatic liver disease.
Semin Liver Dis. 2010 May;30(2):125-33. Epub 2010 Apr 26., [PMID:20422495]

Abstract [show]
The primary transporter responsible for bile salt secretion is the bile salt export pump (BSEP, ABCB11), a member of the ATP-binding cassette (ABC) superfamily, which is located at the bile canalicular apical domain of hepatocytes. In humans, BSEP deficiency results in several different genetic forms of cholestasis, which include progressive familial intrahepatic cholestasis type 2 (PFIC2), benign recurrent intrahepatic cholestasis type 2 (BRIC2), as well as other acquired forms of cholestasis such as drug-induced cholestasis (DIC) and intrahepatic cholestasis of pregnancy (ICP). Because bile salts play a pivotal role in a wide range of physiologic and pathophysiologic processes, regulation of BSEP expression has been a subject of intense research. The authors briefly describe the molecular characteristics of BSEP and then summarize what is known about its role in the pathogenesis of genetic and acquired cholestatic disorders, emphasizing experimental observations from animal models and cell culture in vitro systems.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
77 Ubiquitylation is involved in the degradation of receptors, channels, and transporters from the endoplasmic reticulum and cell surface of yeast and higher eukaryotes.86-88 Wang et al, showed for the first time that specific E3 ubiquitin ligases are involved in Bsep degradation.58 Bsep mutants (p.G238V, p.D482G, p.G982R, p.R1153C, and p.R1268Q) were highly ubiquitinated following overexpression of different E3 ubiquitin ligases and were rapidly degraded by proteasomes resulting in shorter half-lives compared with the wild-type protein.58 This study suggests that stabilizing aberrant BSEP proteins by inactivating key E3 ubiquitin ligases might be a novel therapeutic approach, providing that global effects on proteasomal degradation can be avoided. Login to comment

[hide] Living-related liver transplantation for siblings ... Am J Transplant. 2011 Feb;11(2):394-8. doi: 10.1111/j.1600-6143.2010.03397.x. Epub 2011 Jan 10. Shimizu H, Migita O, Kosaki R, Kasahara M, Fukuda A, Sakamoto S, Shigeta T, Uemoto S, Nakazawa A, Kakiuchi T, Arai K
Living-related liver transplantation for siblings with progressive familial intrahepatic cholestasis 2, with novel genetic findings.
Am J Transplant. 2011 Feb;11(2):394-8. doi: 10.1111/j.1600-6143.2010.03397.x. Epub 2011 Jan 10., [PMID:21219577]

Abstract [show]
Progressive familial intrahepatic cholestasis is a syndrome of severe cholestasis progressing to biliary cirrhosis and liver failure that develops in childhood. This report describes two siblings with PFIC-2 who underwent living-related liver transplantation from their genetically proven heterozygous parents. Both patients had normal gamma-glutamyl transpeptidase levels, but showed severe pruritus with sleep disturbance, cholestasis, jaundice and growth failure. Genetic testing of each patient revealed two missense mutations of the bile salt export pump, S901R and C1083Y, which have not previously been associated with PFIC-2. Usual medical treatment failed to improve their clinical symptoms, and the two siblings underwent living-related liver transplantation from their heterozygous parents. The transplants improved their clinical symptoms significantly, and the patients have since shown age-appropriate growth. Electron microscopic findings of the explanted liver of the younger sister revealed dense and amorphous bile, which is characteristic of PFIC-2. In the cases presented here, living-related liver transplantation from a heterozygous donor was associated with better quality of life and improvement of growth, and thus appears to be a feasible option for PFIC-2 patients. Mutation analysis is a useful tool to help decide the course of treatment of PFIC.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
104 The common mutations include E297G, R575X, R1057X, G982R, C336S, R1153C, D482G, K461E, R1153C, R1268Q, R1090X, G238V, S114R, S593R, del 695 and del 3213 (22). Login to comment

[hide] Morphologic findings in progressive familial intra... Am J Surg Pathol. 2011 May;35(5):687-96. Evason K, Bove KE, Finegold MJ, Knisely AS, Rhee S, Rosenthal P, Miethke AG, Karpen SJ, Ferrell LD, Kim GE
Morphologic findings in progressive familial intrahepatic cholestasis 2 (PFIC2): correlation with genetic and immunohistochemical studies.
Am J Surg Pathol. 2011 May;35(5):687-96., [PMID:21490445]

Abstract [show]
Progressive familial intrahepatic cholestasis, type 2 (PFIC2), characterized by cholestasis in infancy that may progress to cirrhosis, is caused by mutation in ABCB11, which encodes bile salt export pump (BSEP). We correlated histopathologic, immunohistochemical, and ultrastructural features in PFIC2 with specific mutations and clinical course. Twelve patients with clinical PFIC2 and ABCB11 mutations were identified, and 22 liver biopsy and explant specimens were assessed. All had hepatocellular cholestasis; most had canalicular bile plugs. At least 1 specimen from every patient had centrizonal/sinusoidal fibrosis, often with periportal fibrosis. Neonatal hepatitis-like features (inflammation, giant cells, necrosis) varied. In 2 of the 5 patients with paired specimens obtained >6 months apart, lobular and portal fibrosis worsened. Transmission electron microscopy (EM) in all 9 patients studied showed canalicular dilatation, microvilli loss, abnormal mitochondrial internal structure, and varying intracanalicular accumulation of finely granular bile. Canalicular staining for BSEP was absent in 10 patients and present in 2 patients, 1 of whom had intermittent symptoms. ABCB11 sequencing of all patients identified 6 novel and 10 previously described mutations, with nonsense, missense, and/or noncoding mutations in the 10 patients without immunohistochemically demonstrable BSEP. Missense and/or noncoding mutations were identified in the 2 patients with demonstrable BSEP, whose clinical course was more indolent. Mutations ending ABCB11 transcription appear linked, through hepatocellular necrosis and fibrosis, to worse outcome. In conclusion, light microscopy and electron microscopy findings in clinical PFIC2 can support diagnosis, but are variable and nonspecific. Therefore, no correlation between specific mutations and histopathology is yet possible.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
143 Immunohistochemical Findings and Genetic Abnormalities Patient BSEP Mutation Type of Mutation(s) 1 Absent c.890A>G (p.E297G)* Missense5,7,10,13,16,19,20 2 Absent c.1723C>T (p.R575X) Nonsense7,19,20 c.2178+1G>T Noncoding region20 3 Present c.1708G>A (p.A570T) Missense20 c.3634G>T (p.V1212F) Missense, predicted deleterious 4 Absent c.3164T>C (p.L1055P)* Missense, predicted deleterious 5 Absent c.3692G>A (p.R1231Q) Missense20 c.2296G>A (p.G766R) Missense20 6 Absent c.2782C>T (p.R928X) Nonsense13 c.3268C>T (p.R1090X) Nonsense5,7,13 7 Present c.3347G>A (p.G1116E) Missense, predicted deleterious IVS 23-8 G-A Noncoding region 8 Absent IVS 16-8 T>Gw Noncoding region10 9 Absent c.2944G>A (p.G982R) Missense5,7,19,20 c.2296G>A (p.G766R) Missense20 10 Absent c.2944G>A (p.G982R) Missense5,7,19,20 c.2296G>A (p.G766R) Missense20 11 Absent c.319T>C (p.C107R) Missense, predicted deleterious c.611+4A>G Noncoding region 12 Absent c.1723C>T (p.R575X) Nonsense7,19,20 c.2178+1G>T Noncoding region20 *Homozygous. Login to comment

[hide] A gene encoding a liver-specific ABC transporter i... Nat Genet. 1998 Nov;20(3):233-8. Strautnieks SS, Bull LN, Knisely AS, Kocoshis SA, Dahl N, Arnell H, Sokal E, Dahan K, Childs S, Ling V, Tanner MS, Kagalwalla AF, Nemeth A, Pawlowska J, Baker A, Mieli-Vergani G, Freimer NB, Gardiner RM, Thompson RJ
A gene encoding a liver-specific ABC transporter is mutated in progressive familial intrahepatic cholestasis.
Nat Genet. 1998 Nov;20(3):233-8., [PMID:9806540]

Abstract [show]
The progressive familial intrahepatic cholestases (PFIC) are a group of inherited disorders with severe cholestatic liver disease from early infancy. A subgroup characterized by normal serum cholesterol and gamma-glutamyltranspeptidase (gammaGT) levels is genetically heterogeneous with loci on chromosomes 2q (PFIC2) and 18q. The phenotype of the PFIC2-linked group is consistent with defective bile acid transport at the hepatocyte canalicular membrane. The PFIC2 gene has now been identified by mutations in a positional candidate, BSEP, which encodes a liver-specific ATP-binding cassette (ABC) transporter, sister of p-glycoprotein (SPGP). The product of the orthologous rat gene has been shown to be an effective bile acid transporter in vitro. These data provide evidence that SPGP is the human bile salt export pump (BSEP).

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
121 One Saudi Arabian family carries 2944 G→A (G982R), which is predicted to replace a glycine with an arginine, thereby disrupting transmembrane span 11. Login to comment
142 The ABC transporter family of proteins is the largest so far iden- Table 1• BSEP mutations found in PFIC patients Nucleotide mutation Amino acid number/ Protein consequence Families mutation 1723 C→T R575X Termination codon in first B2 heterozygous nucleotide binding fold Q homozygous 3169 C→T R1057X Termination codon in second B5 heterozygous nucleotide binding fold 908 del G 303 17 novel amino acids then truncation Family 57 heterozygous 3767-3768 ins C 1256 39 novel amino acids then truncation Family 99 homozygous 890 A→G E297G Glutamate to glycine in the intracellular loop S1, S3, S4B, S5, S6, S7, 38 homozygous between transmembrane spans 4 and 5 S4A, B5, B6, B7, 53, L heterozygous 1381 A→G K461E Lysine to glutamate in first Walker A motif Family 55 homozygous 1445 A→G D482G Aspartate to glycine in first P and 52 homozygous nucleotide binding fold 2944 G→A G982R Glycine to arginine in transmembrane span 11 Family 18 homozygous 3457 C→T R1153C Arginine to cysteine in second C and D homozygous nucleotide binding fold 3803 G→A R1268Q Arginine to glutamine in second J homozygous nucleotide binding fold In each case the nucleotide position in the human coding sequence is given along with details of the predicted protein consequence. Login to comment
236 The endonucleases used were: HphI (E297G), BpmI (K461E), FokI (D482G), AlwNI (G982R), BsrBI (R1153C) and AvaII (R1268Q). Login to comment

[hide] Xenobiotic, bile acid, and cholesterol transporter... Pharmacol Rev. 2010 Mar;62(1):1-96. Epub 2010 Jan 26. Klaassen CD, Aleksunes LM
Xenobiotic, bile acid, and cholesterol transporters: function and regulation.
Pharmacol Rev. 2010 Mar;62(1):1-96. Epub 2010 Jan 26., [PMID:20103563]

Abstract [show]
Transporters influence the disposition of chemicals within the body by participating in absorption, distribution, and elimination. Transporters of the solute carrier family (SLC) comprise a variety of proteins, including organic cation transporters (OCT) 1 to 3, organic cation/carnitine transporters (OCTN) 1 to 3, organic anion transporters (OAT) 1 to 7, various organic anion transporting polypeptide isoforms, sodium taurocholate cotransporting polypeptide, apical sodium-dependent bile acid transporter, peptide transporters (PEPT) 1 and 2, concentrative nucleoside transporters (CNT) 1 to 3, equilibrative nucleoside transporter (ENT) 1 to 3, and multidrug and toxin extrusion transporters (MATE) 1 and 2, which mediate the uptake (except MATEs) of organic anions and cations as well as peptides and nucleosides. Efflux transporters of the ATP-binding cassette superfamily, such as ATP-binding cassette transporter A1 (ABCA1), multidrug resistance proteins (MDR) 1 and 2, bile salt export pump, multidrug resistance-associated proteins (MRP) 1 to 9, breast cancer resistance protein, and ATP-binding cassette subfamily G members 5 and 8, are responsible for the unidirectional export of endogenous and exogenous substances. Other efflux transporters [ATPase copper-transporting beta polypeptide (ATP7B) and ATPase class I type 8B member 1 (ATP8B1) as well as organic solute transporters (OST) alpha and beta] also play major roles in the transport of some endogenous chemicals across biological membranes. This review article provides a comprehensive overview of these transporters (both rodent and human) with regard to tissue distribution, subcellular localization, and substrate preferences. Because uptake and efflux transporters are expressed in multiple cell types, the roles of transporters in a variety of tissues, including the liver, kidneys, intestine, brain, heart, placenta, mammary glands, immune cells, and testes are discussed. Attention is also placed upon a variety of regulatory factors that influence transporter expression and function, including transcriptional activation and post-translational modifications as well as subcellular trafficking. Sex differences, ontogeny, and pharmacological and toxicological regulation of transporters are also addressed. Transporters are important transmembrane proteins that mediate the cellular entry and exit of a wide range of substrates throughout the body and thereby play important roles in human physiology, pharmacology, pathology, and toxicology.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
6508 Nucleotide Change Amino Acid Change In Vitro Function Protein Expression/ Localization ABCB11 BSEP N.D. G238V N.D. Intracellular A890G E297G 2 Intracellular N.D. C336S ↔ Normal G1296C R432T 2 Reduced T1331C V444A ↔ Normal/Reduced A1445G D482G 2 Normal/Reduced G2026T D676Y 2 Reduced G2563A G855R 2 Reduced G2944A G982R 2 Intracellular C3457T R1153C 2 Intracellular G3803A R1268Q 2 Intracellular searchers were able to identify functional roles for Mrp2 using rats lacking this transporter (Eisai hyperbilirubinemic rats on a Sprague-Dawley background and transport-deficient (TR-) on a Wistar background) (Paulusma et al., 1996; Ito et al., 1997). Login to comment

[hide] Apical/basolateral surface expression of drug tran... Pharm Res. 2005 Oct;22(10):1559-77. Epub 2005 Sep 22. Ito K, Suzuki H, Horie T, Sugiyama Y
Apical/basolateral surface expression of drug transporters and its role in vectorial drug transport.
Pharm Res. 2005 Oct;22(10):1559-77. Epub 2005 Sep 22., [PMID:16180115]

Abstract [show]
It is well known that transporter proteins play a key role in governing drug absorption, distribution, and elimination in the body, and, accordingly, they are now considered as causes of drug-drug interactions and interindividual differences in pharmacokinetic profiles. Polarized tissues directly involved in drug disposition (intestine, kidney, and liver) and restricted distribution to naive sanctuaries (blood-tissue barriers) asymmetrically express a variety of drug transporters on the apical and basolateral sides, resulting in vectorial drug transport. For example, the organic anion transporting polypeptide (OATP) family on the sinusoidal (basolateral) membrane and multidrug resistance-associated protein 2 (MRP2/ABCC2) on the apical bile canalicular membrane of hepatocytes take up and excrete organic anionic compounds from blood to bile. Such vectorial transcellular transport is fundamentally attributable to the asymmetrical distribution of transporter molecules in polarized cells. Besides the apical/basolateral sorting direction, distribution of the transporter protein between the membrane surface (active site) and the intracellular fraction (inactive site) is of practical importance for the quantitative evaluation of drug transport processes. The most characterized drug transporter associated with this issue is MRP2 on the hepatocyte canalicular (apical) membrane, and it is linked to a genetic disease. Dubin-Johnson syndrome is sometimes caused by impaired canalicular surface expression of MRP2 by a single amino acid substitution. Moreover, single nucleotide polymorphisms in OATP-C/SLC21A6 (SLCO1B1) also affect membrane surface expression, and actually lead to the altered pharmacokinetic profile of pravastatin in healthy subjects. In this review article, the asymmetrical transporter distribution and altered surface expression in polarized tissues are discussed.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
240 Seven amino acid substitutions in BSEP, linked to PFICII (G238V, E297G, C336S, D482G, G982R, R1153C, R1268Q), have been reported and have been examined using rat Bsep expressed in MDCK (128). Login to comment
241 Five of these mutations resulted in disappearance from the apical surface in MDCK cells (G238V, E297G, G982R, R1153C, R1268R) (128). Login to comment

[hide] Enterohepatic bile salt transporters in normal phy... Gastroenterology. 2004 Jan;126(1):322-42. Kullak-Ublick GA, Stieger B, Meier PJ
Enterohepatic bile salt transporters in normal physiology and liver disease.
Gastroenterology. 2004 Jan;126(1):322-42., [PMID:14699511]

Abstract [show]
The vectorial transport of bile salts from blood into bile is essential for the generation of bile flow, solubilization of cholesterol in bile, and emulsification of lipids in the intestine. Major transport proteins involved in the enterohepatic circulation of bile salts include the hepatocellular bile salt export pump (BSEP, ABCB11), the apical sodium-dependent bile salt transporter (ASBT, SLC10A2) in cholangiocytes and enterocytes, the sodium-dependent hepatocyte bile salt uptake system NTCP (SLC10A1), the organic anion transporting polypeptides OATP-C (SLC21A6), OATP8 (SLC21A8) and OATP-A (SLC21A3), and the multidrug resistance protein MRP3 (ABCC3). Synthesis and transport of bile salts are intricately linked processes that undergo extensive feedback and feed-forward regulation by transcriptional and posttranscriptional mechanisms. A key regulator of hepatocellular bile salt homeostasis is the bile acid receptor/farnesoid X receptor FXR, which activates transcription of the BSEP and OATP8 genes and of the small heterodimer partner 1 (SHP). SHP is a transcriptional repressor that mediates bile acid-induced repression of the bile salt uptake systems rat Ntcp and human OATP-C. A nuclear receptor that activates rodent Oatp2 (Slc21a5) and human MRP2 (ABCC2) is the pregnane X receptor/steroid X receptor PXR/SXR. Intracellular trafficking and membrane insertion of bile salt transporters is regulated by lipid, protein, and extracellular signal-related kinases in response to physiologic stimuli such as cyclic adenosine monophosphate or taurocholate. Finally, dysfunction of individual bile salt transporters such as BSEP, on account of genetic mutations, steric inhibition, suppression of gene expression, or disturbed signaling, is an important cause of cholestatic liver disease.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
117 It is caused by mutations of the BSEP (ABCB11) gene, which is located on chromosome 2q 24.173 Children with PFIC2 do not express BSEP.174 When PFIC2-related BSEP mutations are introduced artificially into rat Bsep and expressed in Madin-Darby canine kidney and Sf9 insect cells, the G238V, E297G, G982R, R1153C, and R1268Q mutations prevent the protein from trafficking to the apical membrane, whereas the G238V mutant seems to be rapidly degraded by proteasomes.175 Whereas mutation C336S affects neither Bsep transport activity nor trafficking, mutations E297G, G982R, R1153C, and R1268Q abolish taurocholate transport activity. Login to comment

[hide] Severe bile salt export pump deficiency: 82 differ... Gastroenterology. 2008 Apr;134(4):1203-14. doi: 10.1053/j.gastro.2008.01.038. Epub 2008 Jan 18. Strautnieks SS, Byrne JA, Pawlikowska L, Cebecauerova D, Rayner A, Dutton L, Meier Y, Antoniou A, Stieger B, Arnell H, Ozcay F, Al-Hussaini HF, Bassas AF, Verkade HJ, Fischler B, Nemeth A, Kotalova R, Shneider BL, Cielecka-Kuszyk J, McClean P, Whitington PF, Sokal E, Jirsa M, Wali SH, Jankowska I, Pawlowska J, Mieli-Vergani G, Knisely AS, Bull LN, Thompson RJ
Severe bile salt export pump deficiency: 82 different ABCB11 mutations in 109 families.
Gastroenterology. 2008 Apr;134(4):1203-14. doi: 10.1053/j.gastro.2008.01.038. Epub 2008 Jan 18., [PMID:18395098]

Abstract [show]
BACKGROUND & AIMS: Patients with severe bile salt export pump (BSEP) deficiency present as infants with progressive cholestatic liver disease. We characterized mutations of ABCB11 (encoding BSEP) in such patients and correlated genotypes with residual protein detection and risk of malignancy. METHODS: Patients with intrahepatic cholestasis suggestive of BSEP deficiency were investigated by single-strand conformation polymorphism analysis and sequencing of ABCB11. Genotypes sorted by likely phenotypic severity were correlated with data on BSEP immunohistochemistry and clinical outcome. RESULTS: Eighty-two different mutations (52 novel) were identified in 109 families (9 nonsense mutations, 10 small insertions and deletions, 15 splice-site changes, 3 whole-gene deletions, 45 missense changes). In 7 families, only a single heterozygous mutation was identified despite complete sequence analysis. Thirty-two percent of mutations occurred in >1 family, with E297G and/or D482G present in 58% of European families (52/89). On immunohistochemical analysis (88 patients), 93% had abnormal or absent BSEP staining. Expression varied most for E297G and D482G, with some BSEP detected in 45% of patients (19/42) with these mutations. Hepatocellular carcinoma or cholangiocarcinoma developed in 15% of patients (19/128). Two protein-truncating mutations conferred particular risk; 38% (8/21) of such patients developed malignancy versus 10% (11/107) with potentially less severe genotypes (relative risk, 3.7 [confidence limits, 1.7-8.1; P = .003]). CONCLUSIONS: With this study, >100 ABCB11 mutations are now identified. Immunohistochemically detectable BSEP is typically absent, or much reduced, in severe disease. BSEP deficiency confers risk of hepatobiliary malignancy. Close surveillance of BSEP-deficient patients retaining their native liver, particularly those carrying 2 null mutations, is essential.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
77 The common mutations E297G, D482G, R575X, R1153C, and R1153H abolish HphI, FokI, FokI, BsrBI, and BsrBI sites, respectively, while G982R creates an AlwNI site. Login to comment
150 Missense Mutations in ABCB11 Nucleotide change Predicted effect Exon CpG site Location Change in: Size Charge Hyd/Pol Shape c.149Tb0e;C p.Leu50Ser 4 No NH2 term Y Y Y c.470Ab0e;G p.Tyr157Cys 6 No TM2 Y Y Y c.725Cb0e;T p.Thr242Ile 8 No TM4 Y Y c.890Ab0e;G p.Glu297Gly 9 No IC2 Y Y Y c.908Gb0e;A p.Arg303Lys 9 No IC2 c.937Cb0e;A p.Arg313Ser 10 Yes IC2 Y Y Y Y c.980Gb0e;A p.Gly327Glu 10 No TM5 Y Y Y c.1168Gb0e;C p.Ala390Pro 11 No TM/NBF Y c.1229Gb0e;A p.Gly410Asp 12 No TM/NBF Y Y c.1238Tb0e;G p.Leu413Trp 12 No TM/NBF c.1388Cb0e;T p.Thr463Ile 13 No Adj Walker A Y Y Y c.1396Cb0e;A p.Gln466Lys 13 No Adj Walker A Y c.1409Gb0e;A p.Arg470Gln 13 Yes Adj Walker A Y c.1415Ab0e;G p.Tyr472Cys 13 No Adj Walker A Y Y Y c.1442Tb0e;A p.Val481Glu 14 No NBF1 Y Y Y c.1445Ab0e;G p.Asp482Gly 14 No NBF1 Y Y c.1460Gb0e;C p.Arg487Pro 14 Yes NBF1 Y Y Y Y c.1468Ab0e;G p.Asn490Asp 14 No NBF1 Y c.1535Tb0e;C p.Ile512Thr 14 No NBF1 Y Y Y c.1544Ab0e;C p.Asn515Thr 14 No NBF1 Y Y c.1550Gb0e;A p.Arg517His 14 Yes NBF1 Y Y c.1621Ab0e;C p.Ile541Leu 14 No NBF1 c.1622Tb0e;C p.Ile541Thr 14 No NBF1 Y Y Y c.1643Tb0e;A p.Phe548Tyr 15 No Adj ABC c.1685Gb0e;A p.Gly562Asp 15 No ABC Y Y c.1708Gb0e;A p.Ala570Thr 15 Yes ABC/Walker B Y c.1763Cb0e;T p.Ala588Val 15 No Adj Walker B Y c.2272Gb0e;C p.Gly758Arg 19 No NBF/TM Y Y Y c.2296Gb0e;A p.Gly766Arg 19 Yes TM7 Y Y Y c.2494Cb0e;T p.Arg832Cys 21 Yes IC3 Y Y Y Y c.2576Cb0e;G p.Thr859Arg 21 No IC3 Y Y Y Y c.2842Cb0e;T p.Arg948Cys 23 Yes IC4 Y Y Y Y c.2935Ab0e;G p.Asn979Asp 23 No TM11 Y c.2944Gb0e;A p.Gly982Arg 23 Yes TM11 Y Y Y c.3086Cb0e;A p.Thr1029Lys 24 No TM12 Y Y Y Y c.3329Cb0e;A p.Ala1110Glu 25 Yes Adj Walker A Y Y Y c.3382Cb0e;T p.Arg1128Cys 25 Yes Adj Walker A Y Y Y Y c.3457Cb0e;T p.Arg1153Cys 26 Yes NBF2 Y Y Y Y c.3458Gb0e;A p.Arg1153His 26 Yes NBF2 Y Y c.3460Tb0e;C p.Ser1154Pro 26 No NBF2 Y c.3628Ab0e;C p.Thr1210Pro 27 No Adj ABC Y c.3691Cb0e;T p.Arg1231Trp 27 Yes ABC/Walker B Y Y c.3692Gb0e;A p.Arg1231Gln 27 Yes ABC/Walker B Y c.3724Cb0e;A p.Leu1242Ile 27 No Walker B c.3892Gb0e;A p.Gly1298Arg 28 No NBF2 Y Y Y NOTE. Login to comment
207 Ten mutations occurred in multiple families: R470Q, R832C,33 R948C, A1110E, and R1231Q53 have now been reported in 2 families; R1090X2 in 3 families; G982R,1,2 R1153C,1,47 and R1153H in 4 families; and R575X in 6 families.1,2,32,45 Six common missense and nonsense changes occurred at non-CpG sites: R520X and A588V33 in 2 European families and E1302X and I541L33,54 in 3 European families each. Login to comment

[hide] Relapsing features of bile salt export pump defici... J Hepatol. 2010 Nov;53(5):981-6. doi: 10.1016/j.jhep.2010.05.025. Epub 2010 Jul 29. Maggiore G, Gonzales E, Sciveres M, Redon MJ, Grosse B, Stieger B, Davit-Spraul A, Fabre M, Jacquemin E
Relapsing features of bile salt export pump deficiency after liver transplantation in two patients with progressive familial intrahepatic cholestasis type 2.
J Hepatol. 2010 Nov;53(5):981-6. doi: 10.1016/j.jhep.2010.05.025. Epub 2010 Jul 29., [PMID:20800306]

Abstract [show]
BACKGROUND & AIMS: PFIC2 is caused by mutations in ABCB11 encoding BSEP. In most cases affected children need liver transplantation that is thought to be curative. We report on two patients who developed recurrent normal GGT cholestasis mimicking primary BSEP disease, after liver transplantation. METHODS: PFIC2 diagnosis was made in infancy in both patients on absence of canalicular BSEP immunodetection and on ABCB11 mutation identification. Liver transplantation was performed at age 9 (patient 1) and 2.8 (patient 2) years without major complications. Cholestasis with normal GGT developed 17 and 4.8years after liver transplantation, in patient 1 and patient 2, respectively, during an immunosuppression reduction period. RESULTS: Liver biopsies showed canalicular cholestasis, giant hepatocytes, and slight lobular fibrosis, without evidence of rejection or biliary complications. An increase in immunosuppression resulted in cholestasis resolution in only one patient. Both patients developed atrial fibrillation, and one melanonychia. The newborn of patient 1 developed transient neonatal normal GGT cholestasis. Immunofluorescence staining of normal human liver sections with patient's sera, collected at the time of cholestasis, and using an anti-human IgG antibody to detect serum antibodies, showed reactivity to a canalicular epitope, likely to be BSEP. Indeed, Western blot analysis showed that patient 2 serum recognized rat Bsep. CONCLUSIONS: Allo-immune mediated BSEP dysfunction may occur after liver transplantation in PFIC2 patients leading to a PFIC2 like phenotype. Extrahepatic features and/or offspring transient neonatal cholestasis of possible immune mediated mechanisms, may be associated. Increasing the immunosuppressive regimen might be an effective therapy.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
69 Patient Gender Patient 1 Female ABCB11 mutations Compound heterozygous c.301delCA p.Q101DfsX8 and c.2944G>A p.G982R with c.1331T>C p.V444A Negative 0.1 mmol/L 9 years SC P Growth failure Cirrhosis Hepatocellular cholestasis Giant hepatocytes Portal inflammation 36 234 N 17 Patient 2 Male Homozygous c.77-19T>A leading to abnormal splicing*: p.Y26Ifs7X Homozygous c.1331T>C p.V444A Negative NA 2.8 years SC P Growth failure Cirrhosis Hepatocellular cholestasis Giant hepatocytes 139 100 76 420 2xN 20 Canalicular BSEP staining Age at LT Indication Native liver histology PT (N >70%) Total bilirubin (N <17&#b5;mol/L) ALT (N <40 IU/L) AFP Serum liver tests at LT GGT (N <60 IU/L) Biliary bile acids (N >10 mmol/L) SC, severe cholestasis; P, pruritus refractory to medical management; PT, prothrombin time; ALT, alanine aminotransferase; AFP; alpha fetoprotein; GGT, gamma-glutamyl transpeptidase; BSEP, bile salt export pump, LT, liver transplantation; NA, not available; *, in silico test predicts abnormal splicing [2]. Login to comment

[hide] The bile salt export pump (BSEP) in health and dis... Clin Res Hepatol Gastroenterol. 2012 Dec;36(6):536-53. doi: 10.1016/j.clinre.2012.06.006. Epub 2012 Jul 12. Kubitz R, Droge C, Stindt J, Weissenberger K, Haussinger D
The bile salt export pump (BSEP) in health and disease.
Clin Res Hepatol Gastroenterol. 2012 Dec;36(6):536-53. doi: 10.1016/j.clinre.2012.06.006. Epub 2012 Jul 12., [PMID:22795478]

Abstract [show]
The bile salt export pump (BSEP) is the major transporter for the secretion of bile acids from hepatocytes into bile in humans. Mutations of BSEP are associated with cholestatic liver diseases of varying severity including progressive familial intrahepatic cholestasis type 2 (PFIC-2), benign recurrent intrahepatic cholestasis type 2 (BRIC-2) and genetic polymorphisms are linked to intrahepatic cholestasis of pregnancy (ICP) and drug-induced liver injury (DILI). Detailed analysis of these diseases has considerably increased our knowledge about physiology and pathophysiology of bile secretion in humans. This review focuses on expression, localization, and function, short- and long-term regulation of BSEP as well as diseases association and treatment options for BSEP-associated diseases.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
185 PFIC BRIC/NFC ICP Other liver diseases Genetic variants without disease association Missense mutations M1V C336S D549V L1055P E135K E137K T87R V43I S701P G19R W342G G556R C1083Y E137K L198P M123T S56L L712L L50S A382G G562D A1110E E186G E297G S194P Q121K A865D M62K R387H A570T S1114R L198P R415Q L198P R128H A865G C68Y A390P L581F G1116E E297G V444A G260D I206V S874P C107R G410D A588V G1116F G374S D482G E297K V284A I939M I112T L413W S593R G1116R A390P N591S V444A G295C R958Q W114R I420T I627T S1120N R432T T655I T510T G295R F959C Y157C D440E E636G R1128C V444A T655I G295S F959V A167T G455E R698C S1144R I498T D676Y R299K T965S A167V K461E S699P R1153C A570T P710P R303K F971L I182K T463I E709K R1153H T586I L827I L339V F971Y M183T Q466K G758R S1154P G648V G855R H423R L1006F M183V R470Q G766R N1173D T655I E1186K V444A N1009H G188W Y472C Y818F T1210P T923P V444D K1145N M217R V481E R832C N1211D A926P V444G I1183T R223C D482G R832H V1212F R948C A459V S226L R487H T859R R1231Q G1004D I468I G238V R487P A865V R1231W R1050C R487L T242I N490D Q869P L1242I G1116R Q546K A257G I498T G877R D1243G R1128H Q558H V284L G499E S901R R1268Q L1197G E592Q E297G I512T R948C A1283V R1231Q V597M R303G N515T N979D G1292V R616G R303K R517H G982R G1298R T619A Q312H F540L G1004D M677L R313S I541L T1029K M677V G327E I541T G1032R R696Q W330R F548Y A1044P R698H Nonsense mutations (premature stop-codons) S25X Y472X Y772X R1090X E96X W493X Q791X V1147X W330X R520X R928X Q1215X Y354X I528X Y1041X R1235X R415X R575X R1057X E1302X R470X Q702X Q1058X Table 1 (Continued) PFIC BRIC/NFC ICP Other liver diseases Genetic variants without disease association Splice site mutations 76 + 3G > T 908 + 1delG 2178 + 1G > T 3057-2A > G Q159Q 77-1G > C 908 + 1G > T 2179-2A > G 3213 + 1delG Q361Q 99-1G > T 908 + 1G > A 2343 + 1G > T 3213 + 4A > G 150 + 3A > C 1435-13 -8del 2343 + 2T > C 3213 + 5G > A 390-1G > A 2012-8T > G 2611-2A > T 611 + 1G > A 2178 + 1G > A R1001R Deletions/insertions/frame shifts Q101Dfs8X L380Wfs18X G648Vfs5X Q1058Hfs38X F959Hfs1X T127Hfs6X A382 A388del K700Sfs12X I1061Vfs34X F959Gfs48X N199Ifs14X P456Pfs24X T919del L1165del L232Cfs9X H484Rfs5X K930Efs92X A1192Efs50X R303Sfs17X I528Sfs21X K930Efs79X T1256Tfs40X V368Rfs27X I610Qfs45X K969 K972del Synonymous variants without disease association R33R F90F L232L I416I G557G I876I A1028A K1145K D36D I134I Y269Y G418G V597V G937G K1070K R52R S136S Q312Q F427F A804A Y981Y T1086T D58D V195V G319G E395E A535A G817G G1004G A1110A The overview shows ࣈ 290 known variants of BSEP on the protein level, except splice site mutations, which are shown on cDNA level. Login to comment

[hide] Biosynthesis and trafficking of the bile salt expo... Mol Aspects Med. 2014 Jun;37:3-14. doi: 10.1016/j.mam.2013.05.001. Epub 2013 May 15. Soroka CJ, Boyer JL
Biosynthesis and trafficking of the bile salt export pump, BSEP: therapeutic implications of BSEP mutations.
Mol Aspects Med. 2014 Jun;37:3-14. doi: 10.1016/j.mam.2013.05.001. Epub 2013 May 15., [PMID:23685087]

Abstract [show]
The bile salt export pump (BSEP, ABCB11) is the primary transporter of bile acids from the hepatocyte to the biliary system. This rate-limiting step in bile formation is essential to the formation of bile salt dependent bile flow, the enterohepatic circulation of bile acids, and the digestion of dietary fats. Mutations in BSEP are associated with cholestatic diseases such as progressive familial intrahepatic cholestasis type 2 (PFIC2), benign recurrent intrahepatic cholestasis type 2 (BRIC2), drug-induced cholestasis, and intrahepatic cholestasis of pregnancy. Development of clinical therapies for these conditions necessitates a clear understanding of the cell biology of biosynthesis, trafficking, and transcriptional and translational regulation of BSEP. This chapter will focus on the molecular and cell biological aspects of this critical hepatic membrane transporter.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
136 When seven PFIC2 missense mutations were expressed in MDCK cells, five of these common mutations (G238V, E297G, G982R, R1153C and R1268Q) were unable to traffic to the apical membrane (Wang et al., 2002). Login to comment
185 In vitro studies using rat Bsep mutants of the human mutations G238V, D482G, G982R, R1153C, and R1268Q all resulted in retention of Bsep in the ER to different extents (Wang et al., 2008). Login to comment
207 A preliminary report from the same group finds that 4-PBA decreases pruritus and serum bile acid concentrations, and improves liver function within 3 months of treatment in 3 PFIC2 children harboring a least one missense mutation (A257V, G982R and T1210P) (Gonzales et al., 2012b). Login to comment

[hide] Ursodeoxycholic acid stabilizes the bile salt expo... J Gastroenterol. 2014 May;49(5):890-9. doi: 10.1007/s00535-013-0833-y. Epub 2013 May 31. Kagawa T, Orii R, Hirose S, Arase Y, Shiraishi K, Mizutani A, Tsukamoto H, Mine T
Ursodeoxycholic acid stabilizes the bile salt export pump in the apical membrane in MDCK II cells.
J Gastroenterol. 2014 May;49(5):890-9. doi: 10.1007/s00535-013-0833-y. Epub 2013 May 31., [PMID:23722250]

Abstract [show]
BACKGROUND: Ursodeoxycholic acid (UDCA) partly exerts choleretic effects by modifying the function of the bile salt export pump (Bsep, ABCB11). UDCA induces insertion of Bsep into the canalicular membrane of hepatocytes; however, underlying mechanisms remain unknown. We aimed to elucidate molecular mechanisms behind UDCA-induced Bsep activation. METHODS: We established MDCK II cells stably expressing both Bsep and Na(+)-taurocholate cotransporting polypeptide, and investigated the effect of UDCA on activity and protein expression of Bsep using these cells. We performed inhibitor study to know the molecules involved in UDCA-induced Bsep activation, and also tested the influence of UDCA on Bsep having a disease-associated mutation. RESULTS: UDCA activated Bsep in a dose-dependent manner. UDCA did not affect Bsep protein expression in whole cell lysates but increased its apical surface expression by extending the half-life from 2.4 to 5.0 h. This effect was specific to Bsep because UDCA did not affect other apical and basolateral proteins, and was independent of protein kinase A, adenylate cyclase, p38(MAPK), phosphatidylinositide 3-kinase, Ca(2+), and microtubules. NorUDCA activated Bsep similar to UDCA; however, cholic acid, taurocholic acid, and tauroUDCA had no effect. UDCA significantly increased the activity of Bsep with a benign recurrent intrahepatic cholestasis 2 mutation (A570T) but did not affect Bsep with a progressive familial intrahepatic cholestasis 2 mutation (G982R or D482G). CONCLUSIONS: We demonstrated that UDCA stabilizes Bsep protein in the apical membrane and increases its activity in MDCK II cells, presumably by retarding the endocytotic process.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
11 UDCA significantly increased the activity of Bsep with a benign recurrent intrahepatic cholestasis 2 mutation (A570T) but did not affect Bsep with a progressive familial intrahepatic cholestasis 2 mutation (G982R or D482G). Login to comment
88 MDCK-Ntcp cells were transfected with an expression vector that contained mutated Bsep, including any of a PFIC2 mutation (G982R or D482G) and a BRIC2 mutation (A570T) [11]. Login to comment
90 Basal Bsep activity was slightly lower in the A570T mutant (80.6 % of the wild-type Bsep activity) and much lower in the G982R (15.3 %) and D482G (18.8 %) mutants compared with that in wild-type Bsep (Fig. 6). Login to comment
93 In contrast, UDCA did not affect the activity of the G982R and D482G mutant proteins. Login to comment
163 The inability of TUDCA to stimulate Bsep activity was unexpected because this molecule has been reported to 0 50 100 150 200 wild-type A570T G982R D482G UDCA - + - + - + - + * ** Bsep activity (%) Fig. 6 The effect of UDCA on mutant Bsep activity. Login to comment
164 MDCK II cells stably expressing wild-type or mutant (A570T, G982R, or D482G) Bsep were incubated in the presence or absence of UDCA (100 lM) for 24 h after preincubation with sodium butyrate (5 mM) for 24 h. Thereafter, these cells were incubated for 1 h at 37 &#b0;C with [3 H]-TC (1 lM) and cold TC (10 lM) in the lower compartment. The intracellular accumulation and transcellular flux of TC were calculated on the basis of the radioactivity in the total cells and apical medium, respectively. Bsep activity was determined by the permeability-surface area product for TC transport across the apical membrane (PSapical), which was calculated as (rate of transcellular TC flux)/(intracellular TC concentration). Login to comment
175 Negligible Bsep activity was observed for the G982R and D482G mutants, which cause PFIC2. Login to comment

[hide] Genetic variations of bile salt transporters. Drug Discov Today Technol. 2014 Jun;12:e55-67. doi: 10.1016/j.ddtec.2014.03.006. Kubitz R, Droge C, Kluge S, Stindt J, Haussinger D
Genetic variations of bile salt transporters.
Drug Discov Today Technol. 2014 Jun;12:e55-67. doi: 10.1016/j.ddtec.2014.03.006., [PMID:25027376]

Abstract [show]
Bile salt transporters directly or indirectly influence biological processes through physicochemical or signalling properties of bile salts. The coordinated action of uptake and efflux transporters in polarized epithelial cells of the liver, biliary tree, small intestine and kidney determine bile salt concentrations in different compartments of the body. Genetic variations of bile salt transporters lead to clinical relevant phenotypes of varying severity ranging from a predisposition for drug-induced liver injury to rapidly progressing end-stage liver disease. This review focuses on the impact of genetic variations of bile salt transporters including BSEP, NTCP, ASBT and OSTalpha/beta and discusses approaches for transporter analysis.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
112 The missense mutations p.G238V, p.E297G, p.G982R, p.R1153C and p.R1268Q all led to a reduced expression at the apical membrane, when expressed in MDCK cells [124]. Login to comment
113 It was shown in vitro that the two BSEP mutations p.Y818F and p.G982R caused intracellular retention of BSEP. Login to comment
137 BSEP/Bsep NTCP ASBT Exon skipping E186G G1116R G319G R1128C T463I R1128H A926P E1186K A1028Aa R1231W A1110E Aberrant splicing E297K R1153H R832C S1154P S1144R No splice product T586I R1231Q Reduced plasma membrane expression E135K A570T I223T E297Gb N591Sb V444A R1050C Intracellular retention Y818F G982R Reduced or absent bile salt transport A570T R432T A64T K314E V98Ic M264V I206V Q558H I223T C144Y P290S E297Gb N591Sb S267F L243P G374S E1186K I279T T262M a A1028A induces significant exon skipping in vitro but probably not in vivo (unpublished data; Dro &#a8;ge, Ha &#a8;ussinger, Kubitz). Login to comment

[hide] Liver transcript analysis reveals aberrant splicin... Mol Genet Metab. 2014 Nov;113(3):225-9. doi: 10.1016/j.ymgme.2014.07.006. Epub 2014 Jul 15. Davit-Spraul A, Oliveira C, Gonzales E, Gaignard P, Therond P, Jacquemin E
Liver transcript analysis reveals aberrant splicing due to silent and intronic variations in the ABCB11 gene.
Mol Genet Metab. 2014 Nov;113(3):225-9. doi: 10.1016/j.ymgme.2014.07.006. Epub 2014 Jul 15., [PMID:25085279]

Abstract [show]
BACKGROUND: Progressive familial intrahepatic cholestasis type 2 (PFIC2) is an autosomal recessive disease due to mutations in ABCB11. ABCB11 encodes the bile salt export pump (BSEP), the major transporter responsible for biliary bile acid secretion, which expression is restricted to hepatocytes. In some patients, molecular analysis of ABCB11 revealed either exonic or intronic variations - including common polymorphisms - predicted to affect splicing according to in silico analysis or in vitro minigene studies. Transcript analysis in liver tissue is the best way to determine whether the variations predicted to affect splicing are deleterious or not. METHODS AND RESULTS: We performed ABCB11 transcript analysis in liver tissue from five PFIC2 patients who had variations which were predicted to either affect splicing or not. Among eleven variants tested, only the silent c.3003A>G variant and the intronic c.3213+4A>G variant led to abnormal splicing as suggested by in silico analysis. CONCLUSION: ABCB11 liver transcript analysis is a useful tool to confirm or invalidate the predicted splicing effect of a silent or intronic ABCB11 variation.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
42 Patient 2 is compound heterozygous for the missense mutation p.Gly982Arg and the silent substitution of unknown significance c.3003ANG (p.Arg1001Arg) in exon 23. Login to comment
44 Patient 4 is compound heterozygous for the non-sense mutation p.Tyr354X and the missense mutation p.Gly982Arg. Login to comment
71 Maternal allele Paternal allele Patient 1 c.3213+4ANG p.Val444Ala&#b0; p.Arg1153Cys p.Val444Ala&#b0; Patient 2 p.Gly982Arg p.Val444Ala&#b0; p.Phe90Phe&#b0; c.3003ANG (silent p.Arg1001) Patient 3 p.Gly1003Glu p.Val444Ala&#b0; p.Ala1028Ala** p.Tyr1041X p.Val444Ala&#b0; Patient 4 p.Tyr354X p.Gly319Gly* p.Met677Val&#b0; p.Ala1028Ala** c.389+8GNA p.Gly982Arg Patient 5 p.Arg1128Cys* p.Val444Ala&#b0; p.Met677Val&#b0; p.Thr1086Thr p.Arg1128Cys p.Val444Ala&#b0; p.Met677Val&#b0; p.Thr1086Thr In bold: disease-causing mutation. In italic: common variation. Login to comment

[hide] Autoimmune BSEP disease: disease recurrence after ... Clin Rev Allergy Immunol. 2015 Jun;48(2-3):273-84. doi: 10.1007/s12016-014-8457-4. Kubitz R, Droge C, Kluge S, Stross C, Walter N, Keitel V, Haussinger D, Stindt J
Autoimmune BSEP disease: disease recurrence after liver transplantation for progressive familial intrahepatic cholestasis.
Clin Rev Allergy Immunol. 2015 Jun;48(2-3):273-84. doi: 10.1007/s12016-014-8457-4., [PMID:25342496]

Abstract [show]
Severe cholestasis may result in end-stage liver disease with the need of liver transplantation (LTX). In children, about 10 % of LTX are necessary because of cholestatic liver diseases. Apart from bile duct atresia, three types of progressive familial intrahepatic cholestasis (PFIC) are common causes of severe cholestasis in children. The three subtypes of PFIC are defined by the involved genes: PFIC-1, PFIC-2, and PFIC-3 are due to mutations of P-type ATPase ATP8B1 (familial intrahepatic cholestasis 1, FIC1), the ATP binding cassette transporter ABCB11 (bile salt export pump, BSEP), or ABCB4 (multidrug resistance protein 3, MDR3), respectively. All transporters are localized in the canalicular membrane of hepatocytes and together mediate bile salt and phospholipid transport. In some patients with PFIC-2 disease, recurrence has been observed after LTX, which mimics a PFIC phenotype. It could be shown by several groups that inhibitory anti-BSEP antibodies emerge, which most likely cause disease recurrence. The prevalence of severe BSEP mutations (e.g., splice site and premature stop codon mutations) is very high in this group of patients. These mutations often result in the complete absence of BSEP, which likely accounts for an insufficient auto-tolerance against BSEP. Although many aspects of this "new" disease are not fully elucidated, the possibility of anti-BSEP antibody formation has implications for the pre- and posttransplant management of PFIC-2 patients. This review will summarize the current knowledge including diagnosis, pathomechanisms, and management of "autoimmune BSEP disease."

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
51 The three mutations/variants Y818F, G982R, and V444A have been found on the same allele in a PFIC-2 patient. Login to comment
52 BSEP with Y818F together with G982R is poorly expressed. Login to comment
87 Sex Age at LTX (years) Zygosity Nucleotide change Predicted (protein) effect BSEP expression (before LTX) BSEP autoantibodies detected Symptom recurrence- time after LTX (years) Triggering factors 1 [22, 63] F 3.5/3.5/4.9 hom hom c.2453A>T c.2944G>A p.Y818F p.G982R Absent (exp) Yes 1/0.4 Graft rejection after first LTX 2 [23] M 5.2 hom c.907A>G p.R303G Absent Yes 12 Unknown 3 [23] F 3.7 com het c.1741C>T IVS12+1G>T a p.L581F abb splic Absent Yes 3.5/5.2/8.1/12.1/13 EBV infection; ࢑ corticosteroids 4 [23] F 2.2 hom IVS17+1T>A a abb splic Absent Yes 2.1/4 Low CsA, switch from Tac to CsA 5 [62, 63] F 9 com het c.301delCA c.2944G>A p.Q101Dfs8X p.G982R Absent NA 3.3/17 ࢑ IS, pregnancy? Login to comment
112 Following this report, similar observations were published (1) K930Efs79X wtBSEP (2) (3) (4) R1050C (7) D482G G374S (6) (5) c.150+3A>C (8) G982R Fig. 2 Different effects of genetic ABCB11 variants on processing and function of BSEP. Login to comment

[hide] Hypothyroidism Associated with ATP8B1 Deficiency. J Pediatr. 2015 Dec;167(6):1334-1339.e1. doi: 10.1016/j.jpeds.2015.08.037. Epub 2015 Sep 15. Li L, Deheragoda M, Lu Y, Gong J, Wang J
Hypothyroidism Associated with ATP8B1 Deficiency.
J Pediatr. 2015 Dec;167(6):1334-1339.e1. doi: 10.1016/j.jpeds.2015.08.037. Epub 2015 Sep 15., [PMID:26382629]

Abstract [show]
OBJECTIVE: To examine whether hypothyroidism is an extrahepatic feature of ATPase, aminophospholipid transporter, class I, type 8B, member 1 (ATP8B1) deficiency. STUDY DESIGN: Children with normal gamma-glutamyltransferase cholestasis (n = 47; 13 patients with ATP8B1 deficiency, 19 with ATP-binding cassette, subfamily B (MDR/TAP), member 11 (ABCB11) deficiency, and 15 without either ATP8B1 or ABCB11 mutations) were enrolled. Clinical information and thyroid function test results were retrospectively retrieved from clinical records and compared. Hypothyroidism was diagnosed by clinical-biochemistry criteria (thyroid function test results). RESULTS: Three out of 13 patients with ATP8B1 deficiency were diagnosed as hypothyroid and 2 as subclinically hypothyroid. The frequency of hypothyroidism and subclinical hypothyroidism was significantly higher than in patients with ABCB11 deficiency (5/13 vs 0/19, P = .006) and in patients without ATP8B1 or ABCB11 mutations (5/13 vs 0/15, P = .013). Thyroid function test results normalized after hormone replacement in all 5 patients, with no relief of cholestasis. CONCLUSIONS: As hypothyroidism can be another extrahepatic feature of ATP8B1 deficiency, thyroid function should be monitored in these patients.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
71 ABCB11 mutations and immunostaining in patients with ABCB11 mutations Patient ID Sex Nucleotide change Amino acid change Mutation origin BSEP expression GGT expression 244 Female c.145C>T/- p.Q49X/- Paternal/- Absent Normal 653 Female c.1197+1G>T/c.1197+1G>T -/- Paternal/maternal Not assessed Not assessed 727 Male c.2782C>T/c.3593A>G p.R928X/p.H1198R Maternal/paternal Not assessed Not assessed 889 Female c.3457C>T/c.3623A>G p.R1153C/p.Y1208C Paternal/maternal Absent Normal 919 Female c.1493T>C/c.1493T>C p.I498T/p.I498T Paternal/maternal Not assessed Not assessed 996 Male c.612-2_4 CTA>TT/- -/- Maternal/- Absent Normal 1022 Male c.212T>A/c.677C>T p.L71H/p.S226L Paternal/maternal Absent Normal 1131 Male c.409G>A/c.2216delC p.E137K/p.P740QfsX6 De novo/paternal Absent Normal 1134 Male c.1760C>G/c.3677G>C p.S587X/p.R1226P Maternal/paternal Absent Absent 1139 Female c.2935A>G/c.3746T>G p.N979D/p.L1249X Not assessed Not assessed Not assessed 1140 Male c.542G>T/c.1370_1372dupGTG p.R181I/p.V458dup Maternal/paternal Not assessed Not assessed 1219 Female c.872T>C/c.3691C>T p.V291A/p.R1231W Maternal/paternal Not assessed Not assessed 334* Female c.2944G>A/- p.G982R/- Not assessed Normal Normal 802* Female c.3458G>A/- p.R1153H/- Not assessed Not assessed Not assessed 862* Male c.634G>A/c.849A>C/c.1638G>T p.A212T/p.E283D/p.Q546H Maternal/maternal/de novo Not assessed Not assessed 864* Male c.1727A>G/- p.N576S/- Paternal/- Normal Normal 1165* Male c.1583T>C/c.1583T>C p.I528T/p.I528T Not assessed Not assessed Not assessed 1167* Male c.334A>G/c.3233T>C p.I112V/p.I1078T Not assessed Not assessed Not assessed 1242* Male c.2783G>A/- p.R928Q/- Not assessed Not assessed Not assessed Bold: Novel mutation. Login to comment