ABCMdb

ABCB11 p.Gly238Val

Reviews:	p.Gly238Val D
Predicted by SNAP2:	A: N (61%), C: N (57%), D: D (66%), E: D (71%), F: D (71%), H: D (63%), I: D (66%), K: D (80%), L: D (71%), M: D (66%), N: N (53%), P: D (80%), Q: D (66%), R: D (80%), S: N (87%), T: D (66%), V: D (63%), W: D (85%), Y: D (66%),
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,

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[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.

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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.

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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.

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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
121 Nonsynonymous polymorphisms and mutations in the ABCB11 gene NCBI No. Exon Nucleotide Amino acid alteration Phenotype Ref. Position Alteration rs11568361 5 167 C→T Ser56Leu - [102] - 5 341 G→C Ser114Arg PFIC2 [47]* - 6 557 A→G Glu186Gly BRIC2 [45,48] - 6 580 T→C Ser194Pro - [44] rs11568358 7 616 A→G Ile206Val - [102] - 7 695 T→del Frame shift at position 232 PFIC2 [47] - 7 713 G→T Gly238Val PFIC2 [47] - 8 779 G→A Gly260Asp - [44] - 8 851 T→C Val284Ala - [44] rs11568372 8 890 A→G Glu297Gly PFIC2/BRIC2 [35,43,45,47,102] rs2287617 8 896 G→A Arg299Lys - [102] - 8 908 G→del Frame shift at position 303 PFIC2 [35] - 9 1007 G→C Cys336Ser PFIC2 [47] - 9 1015 C→G Leu339Val - [46] - 11 1244 G→A Arg415Gln - [39] - 11 1294 G→C Arg432Thr BRIC2 [43] rs2287622 12 1331 T→C Val444Ala ICP/PFIC2? 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.

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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.

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4 G238V, D482G, G982R, R1153C, and R1286Q all retain Bsep to the endoplasmic reticulum (ER) to different extents. Login to comment
6 G238V and D482G are partially misfolded and can be stabilized by low temperature and glycerol. Login to comment
10 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 (⌬Gly). Login to comment
31 Inhibition of proteasomes also stabilized Bsep G238V, E297G, and D482G when examined in Madin-Darby canine kidney (MDCK) cells and human embryonic kidney (HEK) cells.8,10,13 These findings suggest that the proteasome plays a major role in the degradation of these BSEP mutants in PFIC II patients. 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
90 In contrast, the PFIC II mutants were mostly detected as core-glycosylated proteins, except G238V and D482G, for which a fraction of 190-kDa mature glycosylated form was also observed. Login to comment
96 For G238V and D482G, which are partially core-glycosylated, there is a partial colocalization between GFP-Bsep and calnexin. Login to comment
107 In G238V, the core-glycosylated form disappears while the mature form is not significantly increased, indicating that the core-glycosylated form is degraded over the chase period. Login to comment
124 For G238V and D482G, respectively, only approximately 20% and 40% of the 140-kDa protein is converted to the 160-kDa protein, whereas approximately 50% of the 140-kDa protein is degraded over the 120-minute chase (Fig. 3D). Login to comment
125 These data suggest that the core-glycosylated G238V and D482G have a half-life of approximately 2 hours, which is consistent with the results from the cycloheximide chase studies, which used chase times up to 4 hours (Fig. 3A). Login to comment
127 The Effect of Low Temperature and Chemical on G238V and D482G. Login to comment
128 The data in Fig. 3 suggest that a portion of D482G and G238V can be converted to the mature glycosylated form over time during biosynthesis. Login to comment
129 We next asked whether conditions such as low temperature or chemical chaperones can stabilize D482G and G238V, because these conditions favor protein folding and have been shown to stabilize the misfolded mutant protein CFTR ⌬F508 during its biogenesis.19 Both incubation at low temperature (30°C) and addition of glycerol increases the peripheral, cell surface expression of GFP-tagged D482G and G238V in HEK cells (Fig. 4A). Login to comment
130 This is confirmed by a higher percentage of mature glycosylated form in D482G and G238V in HEK cells under these conditions (Fig. 4B). Login to comment
131 These data together confirm the notion that a fraction of correctly folded D482G and G238V can traffic through secretory pathway, and this fraction is increased under the conditions that favor protein folding. 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
147 Low temperature and glycerol stabilize G238V and D482G. Login to comment
148 (A) The HEK 293 cells were transfected with wt GFP-Bsep, G238V, and D482G. 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
183 However, the increase in ubiquitination is moderate for wt Bsep, compared with the mutant proteins G238V, D482G, G982R, and ⌬Gly. Login to comment
193 To examine whether the ERAD E3s affect the expression of the Bsep mutants, we co-expressed the ERAD E3s HRD1, TEB4, Rma1, or CHIP with the wt Bsep, G238V, and ⌬Gly proteins. Login to comment
194 Increased levels of all the E3s resulted in decreased amounts of G238V and ⌬Gly compared with the mutant expressed alone (Fig. 7A). Login to comment
197 Enhanced ubiquitination of G238V was seen with the other ERAD E3s (data not shown). Login to comment
201 Reduction of TEB4 and Rma1 levels, but not those of CHIP, stabilized G238V. Login to comment
213 These data suggest that TEB4 and Rma1 may function as the E3s targeting G238V for degradation but do not do so for the wt Bsep and ⌬Gly proteins. Login to comment
226 (A) The HEK 293 cells were transfected with wt GFP-Bsep, G238V, and ⌬Gly alone or co-transfected with the cDNAs encoding the ERAD E3s HRD1, TEB4, Rma1, and myc-CHIP. Login to comment
235 (A) The HEK 293 cells were transfected with wt GFP-Bsep, G238V, and ⌬Gly. Login to comment
242 (including digitonin, deoxyBigChap, NP-40, and Triton X-100) and solubilization conditions but could not detect any specific interaction between the endogenous HRD1, TEB4, and Rma1 E3s and Bsep mutant substrates such as G238V and ⌬Gly (data not shown). 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
251 For mutants D482G and G238V, only a portion of immature glycosylated protein can be converted to mature glycosylated protein over the chase period, whereas a large pool of immature glycosylated protein is degraded. Login to comment
252 This suggests that D482G and G238V are partly misfolded. Login to comment
253 This notion is supported by the data showing that conditions favoring protein folding, such as low temperature or the addition of glycerol, stabilize D482G and G238V and increase the fraction of the mature glycosylated form and cell surface expression (Fig. 4). 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
286 In contrast, siRNA-mediated knockdown of endogenous Rma1 and TEB4 stabilizes G238V but not ⌬Gly, whereas the knockdown of HRD1 levels significantly stabilizes ⌬Gly but not R1286Q. 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.

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67 ABCB11 Missense Mutations and SNPs Functionally Analyzed in This Study Exon Nucleotide Change Predicted Protein Effect Location in Protein Associated Phenotype Prevalence or Frequency* Any Defect(s) Identified Reference 4 c.149TϾC L50S NH2 term PFIC 1 family (het) Immature protein 31 5 c.270TϾC F90F EC1 SNP 2.7%-7.7% 43, 45 6 c.403GϾA E135K EC1 BRIC 1 family (het) Reduced levels of mature protein † 6 c.409GϾA E137K EC1 BRIC / ICP 1 family (het) Immature protein ‡ 7 c.500CϾT A167V TM2 PFIC 1 family (hom) Mild exon skipping beta 7 c.557AϾG E186G IC1 BRIC 2 families (both het) Moderate exon skipping; greatly reduced levels of mature protein 8, 37 7 c.580TϾC S194P IC1 SNP-PSC 1.1% 43 7 c.593TϾC L198P IC1 BRIC / ICP / DC 1 family (het) Greatly reduced levels of mature protein # 8 c.713GϾT G238V EC2 PFIC 1 family (hom) 29 8 c.725CϾT T242I TM4 PFIC 1 family (het) 31 8 c.779GϾA G260D TM4 SNP-PBC 0.8% 43 9 c.850GϾC V284L IC2 PFIC 1 family (het) No protein 28 9 c.851TϾC V284A IC2 SNP 0.5% Increased levels of mature protein 43, 45† 9 c.889GϾA E297K IC2 Prolonged NNH 1 family (het) Moderate differential splicing; immature protein ‡ 9 c. 890AϾG E297G IC2 PFIC, BRIC PFIC, 45 families (14 hom, 31 het) BRIC, 4 families (2 hom, 2 het) Greatly reduced levels of mature protein 7, 8, 12, 29-32, 35 10 c.936GϾT Q312H IC2 PFIC 1 family (het) ‡ 10 c.937CϾA R313S IC2 PFIC 1 family (het) 31 10 c.957AϾG G319G TM5 SNP 1.5 - 7.5% Mild exon skipping 42, 43, 45 10 c.980GϾA G327E TM5 PFIC 1 family (het) 31 10 c.1007GϾC C336S TM5 PFIC 1 family (het) 29 11 c.1168GϾC A390P NBF PFIC, BRIC 2 families (both het) Immature protein 31; # 12 c.1129GϾA G410D NBF PFIC 1 family (het) 31 12 c.1238TϾG L413W NBF PFIC 1 family (het) Greatly reduced levels of mature protein 31 12 c.1244GϾA R415Q NBF SNP-ICP 1.3% 42 12 c.1295GϾC R432T NBF BRIC 1 family (het) Reduced levels of mature protein 12 13 c.1331CϾT A444V NBF SNP, ICP, CC, DC, BRIC 43-60% Increased levels of mature protein 8, 28, 37, 39-45 13 c.1381AϾG K461E WA PFIC 1 family (hom) Immature protein 7 13 c.1388CϾT T463I WA PFIC 1 family (het) Mild exon skipping 31 13 c.1396CϾA Q466K Adj WA PFIC 1 family (het) 31 13 c.1409GϾA R470Q Adj WA PFIC 2 families (1 het, 1 consanguineous) Immature protein 31 14 c.1442TϾA V481E NBF1 PFIC 1 family (het) 31 14 c.1445AϾG D482G NBF1 PFIC 22 families (16 het, 6 hom) Severe differential splicing; immature protein 7, 30-32 14 c.1468AϾG N490D NBF1 PFIC 1 family (het) Greatly reduced levels of mature protein; reduction in bile salt transport 31 14 c.1493TϾC I498T NBF1 PFIC / BRIC 1 family (het) 38 14 c.1530CϾA T510T NBF1 SNP-PBC 0.7% 43 14 c.1535TϾC I512T NBF1 PFIC 1 family (het) 31 14 c.1544AϾC N515T NBF1 PFIC 1 family (het) 31, 32 14 c.1440GϾA R517H NBF1 PFIC 1 family (het) No protein 31, 32 14 c.1605CϾT A535A NBF1 SNP 0.3% Slightly reduced levels mature protein 39, 45 14 c.1621AϾC I541L NBF1 PFIC 3 families (1 het, 2 consanguineous) No protein 31-33 15 c.1643TϾA F548Y Adj ABCm PFIC 1 family (het) 31, 32 15 c.1685GϾA G562D ABCm PFIC 1 family (het) 31 15 c.1708GϾA A570T Adj ABCm/WB PFIC, BRIC PFIC, 1 family Greatly reduced levels of mature protein; reduction in bile salt transport 8, 31 Table 1. 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.

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97 6† p.R415X p.R415X na na PFIC2 no. Login to comment
98 7† p.S226L p.S226L na na PFIC2 no. 8 p.G238V p.G238V 0.06 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.

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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.

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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] 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.

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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.

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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.

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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] 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.

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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.

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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

[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.

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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

[hide] Ubiquitin-specific protease 19 regulates the stabi... Exp Cell Res. 2014 Oct 15;328(1):207-16. doi: 10.1016/j.yexcr.2014.07.025. Epub 2014 Aug 1. Nakamura N, Harada K, Kato M, Hirose S
Ubiquitin-specific protease 19 regulates the stability of the E3 ubiquitin ligase MARCH6.
Exp Cell Res. 2014 Oct 15;328(1):207-16. doi: 10.1016/j.yexcr.2014.07.025. Epub 2014 Aug 1., [PMID:25088257]

Abstract [show]
Ubiquitin-specific protease (USP)19 is a recently identified deubiquitinating enzyme (DUB) having multiple splice variants and cellular functions. One variant encodes an endoplasmic reticulum (ER)-anchored DUB that rescues misfolded transmembrane proteins from ER-associated degradation (ERAD), but the underlying mechanism remains to be elucidated. Here, we show that USP19 interacts with the ERAD-associated E3 ubiquitin ligase MARCH6. Overexpression of USP19 delayed the degradation of MARCH6, leading to an increase in its protein level. In contrast, USP19 depletion resulted in decreased expression of MARCH6. We also show that USP19 overexpression reduced ubiquitination of MARCH6, while its knockdown had the opposite effect. In particular, USP19 was found to protect MARCH6 by deubiquitination from the p97-dependent proteasomal degradation. In addition, USP19 knockdown leads to increased expression of mutant ABCB11, an ERAD substrate of MARCH6. Moreover, USP19 is itself subjected to endoproteolytic processing by DUB activity, and the processing cleaves off an N-terminal cytoplasmic region of unknown function. However, elimination of this processing had no evident effect on MARCH6 stabilization. These results suggest that USP19 is involved in the regulation of ERAD by controlling the stability of MARCH6 via deubiquitination.

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52 FLAG-ABCB11G238V was constructed by cloning cDNA fragments encoding human ABCB11 containing a G238V mutation into the KpnI/XbaI sites of p3 FLAGCMV-10. Login to comment
146 Knockdown of USP19 stabilizes mutant ABCB11 It has been shown that MARCH6 promotes degradation of the bile salt export pump (Bsep or ABCB11) containing the G238V mutation, which causes progressive familial intrahepatic cholestasis type II [38]. Login to comment