ABCMdb

ABCG2 p.Arg482Met

Predicted by SNAP2:	A: D (91%), C: D (85%), D: D (95%), E: D (95%), F: D (91%), G: D (95%), H: D (95%), I: D (85%), K: D (85%), L: D (91%), M: D (85%), N: D (95%), P: D (95%), Q: D (95%), S: D (91%), T: D (91%), V: D (91%), W: D (95%), Y: D (95%),
Predicted by PROVEAN:	A: D, C: D, D: D, E: D, F: D, G: D, H: D, I: D, K: D, L: D, M: D, N: D, P: D, Q: D, S: D, T: D, V: D, W: D, Y: D,

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[hide] A mutation hot spot in the Bcrp1 (Abcg2) multidrug... Cancer Res. 2002 Apr 15;62(8):2294-9. Allen JD, Jackson SC, Schinkel AH
A mutation hot spot in the Bcrp1 (Abcg2) multidrug transporter in mouse cell lines selected for Doxorubicin resistance.
Cancer Res. 2002 Apr 15;62(8):2294-9., 2002-04-15 [PMID:11956086]

Abstract [show]
The recent identification of mutations at arginine 482 (R482) in human Breast Cancer Resistance Protein (BCRP) in two drug-selected cell lines largely explains some discrepancies observed in the cross-resistance profiles of human cell lines overexpressing this multidrug transporter. We find that each of three mouse cell lines independently selected for resistance to the anthracycline doxorubicin also acquired mutations in the cognate mouse transporter Bcrp1 exclusively at R482. Although the mouse Bcrp1 amino acid substitutions (M or S) are distinct from those seen in the human cell lines (G or T), they all have similar consequences: (a) greater resistance to anthracyclines (and bisantrene); (b) relatively lower resistance to topotecan; (c) greatly enhanced efflux of the dye rhodamine 123. The ready selection of R482X mutations seen in vitro might also occur in tumors treated with anthracyclines. Thus, it is noteworthy that the efficacy of Bcrp1 inhibitors applicable in vivo was not markedly affected by the presence of the mutations. We found that the Bcrp1 mutations all occurred after previous amplification and overexpression of the wild-type gene under doxorubicin selection; wild-type Bcrp1 is evidently able to mediate substantial resistance to anthracyclines, and this was confirmed in Bcrp1-transduced cell lines. These observations emphasize the general importance of the arginine at amino acid 482 for substrate specificity of the transporter, while reminding us that unmutated Bcrp1 remains a potential source of resistance to anthracyclines and a potential factor in anthracycline pharmacokinetics. The same is most likely true of human BCRP, given its profound similarities to mouse Bcrp1.

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146 Clearly, the mouse Bcrp1 R482M and R482S mutants confer enhanced resistance to anthracyclines compared with the wild-type transporter. Login to comment
149 Resistance to topotecan was at least 10-fold lower, relative to the anthracyclines and bisantrene, in the 88.6-derived R482M and R482S mutant lines, as was found for the human R482G mutant (13). Login to comment
150 In this context it is also noteworthy that cell lines carrying either the R482M or R482S Bcrp1 mutants showed greatly reduced (and Ko143-reversible) accumulation of the dye rhodamine 123 (Fig. 3C), as was observed previously for the R482G and R482T mutants of human BCRP (13). Login to comment
144 Clearly, the mouse Bcrp1 R482M and R482S mutants confer enhanced resistance to anthracyclines compared with the wild-type transporter. Login to comment
147 Resistance to topotecan was at least 10-fold lower, relative to the anthracyclines and bisantrene, in the 88.6-derived R482M and R482S mutant lines, as was found for the human R482G mutant (13). Login to comment
148 In this context it is also noteworthy that cell lines carrying either the R482M or R482S Bcrp1 mutants showed greatly reduced (and Ko143-reversible) accumulation of the dye rhodamine 123 (Fig. 3C), as was observed previously for the R482G and R482T mutants of human BCRP (13). Login to comment

[hide] Overexpression of wild-type breast cancer resistan... Cancer Res. 2002 Sep 1;62(17):5035-40. Volk EL, Farley KM, Wu Y, Li F, Robey RW, Schneider E
Overexpression of wild-type breast cancer resistance protein mediates methotrexate resistance.
Cancer Res. 2002 Sep 1;62(17):5035-40., 2002-09-01 [PMID:12208758]

Abstract [show]
Previously, we have reported that a multidrug-resistant, mitoxantrone (MX)-selected cell line, MCF7/MX, is highly cross-resistant to the antifolate methotrexate (MTX), because of enhanced ATP-dependent drug efflux (E. L. Volk et al., Cancer Res., 60: 3514-3521, 2000). These cells overexpress the breast cancer resistance protein (BCRP), and resistance to MTX as well as to MX was reversible by the BCRP inhibitor, GF120918. These data indicated that BCRP causes the multidrug-resistance phenotype. To further examine the role of this transporter in MTX resistance, and in particular the role of amino acid 482, we analyzed a number of BCRP-overexpressing cell lines. MTX resistance correlated with BCRP expression in all of the cell lines expressing the wild-type transporter, which contains an Arg at position 482. In contrast, little or no cross-resistance was found in the MCF7/AdVp1000 and S1-M1-3.2 and S1-M1-80 cell lines, which contain acquired mutations at this position, R482T and R482G, respectively. Concomitantly, the greatest reduction in MTX accumulation was observed in the MCF7/MX cells (BCRP(Arg)) as compared with cells expressing the Thr and Gly BCRP variants. Furthermore, the reduction in drug accumulation was sensitive to BCRP inhibition by GF120918. In conclusion, we have demonstrated a novel role for BCRP as a mediator of MTX resistance and have provided further evidence for the importance of amino acid 482 in substrate specificity.

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154 Similar results were also seen in murine Bcrp1 R482M and R482S mutants (32). Login to comment
153 Similar results were also seen in murine Bcrp1 R482M and R482S mutants (32). Login to comment

[hide] Characterization of drug transport, ATP hydrolysis... J Biol Chem. 2002 Dec 13;277(50):47980-90. Epub 2002 Oct 8. Ozvegy C, Varadi A, Sarkadi B
Characterization of drug transport, ATP hydrolysis, and nucleotide trapping by the human ABCG2 multidrug transporter. Modulation of substrate specificity by a point mutation.
J Biol Chem. 2002 Dec 13;277(50):47980-90. Epub 2002 Oct 8., 2002-12-13 [PMID:12374800]

Abstract [show]
The overexpression of the human ATP-binding cassette half-transporter, ABCG2 (placenta-specific ABC transporter, mitoxantrone resistance-associated protein, breast cancer resistance protein), causes multidrug resistance in tumor cells. An altered drug resistance profile and substrate recognition were suggested for wild-type ABCG2 and its mutant variants (R482G and R482T); the mutations were found in drug-selected tumor cells. In order to characterize the different human ABCG2 transporters without possible endogenous dimerization partners, we expressed these proteins and a catalytic center mutant (K86M) in Sf9 insect cells. Transport activity was followed in intact cells, whereas the ATP binding and hydrolytic properties of ABCG2 were studied in isolated cell membranes. We found that the K86M mutant had no transport or ATP hydrolytic activity, although its ATP binding was retained. The wild-type ABCG2 and its variants, R482G and R482T, showed characteristically different drug and dye transport activities; mitoxantrone and Hoechst 33342 were transported by all transporters, whereas rhodamine 123 was only pumped by the R482G and R482T mutants. In each case, ABCG2-dependent transport was blocked by the specific inhibitor, fumitremorgin C. A relatively high basal ABCG2-ATPase, inhibited by fumitremorgin C, was observed in all active proteins, but specific drug stimulation could only be observed in the case of R482G and R482T mutants. We found that ABCG2 is capable of a vanadate-dependent adenine nucleotide trapping. Nucleotide trapping was stimulated by the transported compounds in the R482G and R482T variants but not in the wild-type ABCG2. These experiments document the applicability of the Sf9 expression system for parallel, quantitative examination of the specific transport and ATP hydrolytic properties of different ABCG2 proteins and demonstrate significant differences in their substrate interactions.

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23 Interestingly, in some drug-selected mouse cell lines, mutation of the equipositional amino acid in mouse ABCG2 occurred, causing altered drug resistance profiles for the mutant variants R482S and R482M (21). Login to comment

[hide] Breast cancer resistance protein (BCRP/ABCG2) indu... Mol Pharmacol. 2003 Jan;63(1):65-72. Wang X, Furukawa T, Nitanda T, Okamoto M, Sugimoto Y, Akiyama S, Baba M
Breast cancer resistance protein (BCRP/ABCG2) induces cellular resistance to HIV-1 nucleoside reverse transcriptase inhibitors.
Mol Pharmacol. 2003 Jan;63(1):65-72., [PMID:12488537]

Abstract [show]
Breast cancer resistance protein (BCRP/ABCG2) is a novel member of ATP- binding cassette transporters, which induce multidrug resistance in cancer cells. We found that a high level of BCRP expression in CD4+ T cells conferred cellular resistance to human immunodeficiency virus type-1 (HIV-1) nucleoside reverse transcriptase inhibitors. The cell line MT-4/DOX 500 was established through the long-term culture of MT-4 cells in the presence of doxorubicin (DOX) and had reduced sensitivity to not only DOX but also zidovudine (AZT). MT-4/DOX 500 cells showed reduced intracellular accumulation and retention of DOX and increased ATP-dependent rhodamine 123 efflux. The cells were also resistant to several anticancer agents such as mitoxantrone, 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin, and 7-ethyl-10-hydroxycamptothecin. AZT was 7.5-fold less inhibitory to HIV-1 replication in MT-4/DOX 500 cells than in MT-4 cells. Furthermore, the anti-HIV-1 activity of lamivudine was severely impaired in MT-4/DOX 500 cells. In contrast, the antiviral activity of non-nucleoside reverse transcriptase inhibitors and protease inhibitors was not affected in the cells. MT-4/DOX 500 cells expressed glycosylated BCRP but not P-glycoprotein (ABCB1), multidrug resistance protein 1, 2, or 4 (ABCC1, -2, or -4), or lung resistance-related protein. In addition, the BCRP-specific inhibitor fumitremorgin C completely abolished the resistance of MT-4/DOX 500 cells to AZT as well as to DOX. An analysis for intracellular metabolism of AZT suggests that the resistance is attributed to the increase of ATP-dependent efflux of its metabolites, presumably AZT 5'-monophosphate, in MT-4/DOX 500 cells.

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194 Our preliminary analysis for the full-length BCRP cDNA identified the R482M mutation in MT-4/DOX500 cells (data not shown). Login to comment

[hide] Single amino acid substitutions in the transmembra... Int J Cancer. 2003 Dec 10;107(5):757-63. Miwa M, Tsukahara S, Ishikawa E, Asada S, Imai Y, Sugimoto Y
Single amino acid substitutions in the transmembrane domains of breast cancer resistance protein (BCRP) alter cross resistance patterns in transfectants.
Int J Cancer. 2003 Dec 10;107(5):757-63., 2003-12-10 [PMID:14566825]

Abstract [show]
Breast cancer resistance protein (BCRP) is a member of ATP-binding cassette transporters that has an N-terminal ATP binding domain and a C-terminal transmembrane domain (TM). Expression of wild-type BCRP confers resistance to multiple chemotherapeutic agents such as mitoxantrone, SN-38 and topotecan, but not to doxorubicin. We made 32 BCRP mutants with an amino acid substitution in the TMs (7 E446-mutants in TM2, 15 R482-mutants in TM3, 4 N557-mutants in TM5 and 6 H630-mutants in TM6) and examined the effect of the substitutions on cellular drug resistance. PA317 cells transfected with any one of the 7 E446-mutant BCRP cDNAs did not show drug resistance. Cells transfected with any one of the 13 R482X2-BCRP cDNAs (X2 = N, C, M, S, T, V, A, G, E, W, D, Q and H, but not Y and K) showed higher resistance to mitoxantrone and doxorubicin than the wild-type BCRP-transfected cells. Cells transfected with N557D-BCRP cDNA showed similar resistance to mitoxantrone but lower resistance to SN-38 than the wild-type BCRP-transfected cells. Cells transfected with N557E-, H630E- or H630L-BCRP cDNA showed similar degrees of resistance to mitoxantrone and SN-38. Estrone and fumitremorgin C reversed the drug resistance of cells transfected with R482-, N557- or H630-mutant BCRP cDNA. Cells transfected with R482G- or R482S-BCRP cDNA showed less intracellular accumulation of [3H]mitoxantrone than the wild-type BCRP-transfected cells. These results suggest that E446 in TM2, R482 in TM3, N557 in TM5 and H630 in TM6 play important roles in drug recognition of BCRP.

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13 A doxorubicin-resistant human breast cancer cell line MCF-7 AdVp3000 and a mitoxantrone-resistant human colon carcinoma cell line S1-M1-80 expressed R482T- and R482G-BCRP, respectively and showed high resistance to mitoxantrone and doxorubicin.5,6,13 Doxorubicin-resistant murine fibroblast cell lines also expressed R482M- or R482S-BCRP and showed high resistance to mitoxantrone and doxorubicin.14 We recently identified the substitution R482M in a doxorubicin-resistant human T cell line MT-4/DOX500.23 We made 32 mutant BCRP cDNAs with an amino acid substitution in the TMs and examined the effect of the substitutions on cellular drug resistance. Login to comment
64 PA/R482N, PA/R482C, PA/R482M, PA/R482S, PA/R482T, PA/R482V, PA/R482A, PA/R482G, PA/R482E PA/R482W and PA/R482D (Group 2) showed higher degrees of resistance to mitoxantrone than to SN-38. Login to comment
135 MCF-7 AdVp3000 established by treating MCF-7 cells with 3 ␮g/ml of doxorubicin and 5 ␮g/ml of verapamil overexpressed R482T-BCRP.5,13 S1-M1-80 established by treating human colon carcinoma S1 cells with 80 ␮M mitoxantrone overexpressed R482G-BCRP.6,13 These resistant cells exhibited high resistance to doxorubicin and mitoxantrone.5,6,13 We found recently that MT-4/DOX500 cells established by treating human T cell MT-4 cells with 500 ng/ml of doxorubicin overexpressed R482M-BCRP.23 Two doxorubicin-resistant murine fibroblast lines 88.6/D800-A and 88.6/D800-B overexpressed R482M-BCRP and R482S-BCRP, respectively.14 Another doxorubicin-resistant cell line KOT52/D800 from mouse fibroblasts co-expressed wild-type BCRP and R482M-BCRP.14 In addition to anthracyclines and mitoxantrone, cells transfected with R482-mutant BCRP cDNAs also showed high resistance to methotrexate.28 Theoretically, 9 FIGURE 6 - Accumulation of [3 H]mitoxantrone in R482-mutant BCRP transfectants. PA/WT2, PA/R482G and PA/R482S were mixed populations of the transfected cells established after the 2-step selection with 120 ng/ml methotrexate and 1 ng/ml mitoxantrone. Login to comment
147 Cells transfected with R482G- (GGG), R482M- (ATG), R482T- (ACG), or R482S- (AGT and AGC) BCRP cDNA showed greater resistance to mitoxantrone and doxorubicin than PA/WT2 (Fig. 2). Login to comment
148 As described above, human drug-resistant cell lines MCF-7 AdVp3000, S1-M1-80, MT-4/DOX500 and a mouse drug-resistant line 88.6/D800-B overexpressed R482T- (ACG), R482G- (GGG), R482M- (ATG) and R482S- (AGT) BCRP, respectively.5,6,13,14,23 The other possible mutations are R482W (TGG) and R482K (AAG). Login to comment
149 PA317 cells expressing R482W- BCRP (PA/R482W) showed somewhat higher levels of resistance to mitoxantrone and doxorubicin than PA/WT2, but the resistance levels were lower than those in PA/ R482G, PA/R482M, PA/R482T and PA/R482S. Login to comment
163 Group 2 members (PA/R482N, PA/R482C, PA/R482M, PA/R482S, PA/R482T, PA/R482V, PA/ R482A, PA/R482G, PA/R482E PA/R482W and PA/R482D) showed higher degrees of resistance to mitoxantrone than to SN-38. Login to comment

[hide] Mutations at amino-acid 482 in the ABCG2 gene affe... Br J Cancer. 2003 Nov 17;89(10):1971-8. Robey RW, Honjo Y, Morisaki K, Nadjem TA, Runge S, Risbood M, Poruchynsky MS, Bates SE
Mutations at amino-acid 482 in the ABCG2 gene affect substrate and antagonist specificity.
Br J Cancer. 2003 Nov 17;89(10):1971-8., 2003-11-17 [PMID:14612912]

Abstract [show]
Recent studies have shown that mutations at amino-acid 482 in the ABCG2 gene affect the substrate specificity of the protein. To delineate the effects of these mutations clearly, human embryonic kidney cells (HEK-293) were stably transfected with wild-type 482R or mutant 482G and 482T ABCG2. By flow cytometry, mitoxantrone, BODIPY-prazosin, and Hoechst 33342 were found to be substrates of all ABCG2 proteins, while rhodamine 123, daunorubicin, and LysoTracker Green were transported only by mutant ABCG2. In cytotoxicity assays, all ABCG2 proteins conferred high levels of resistance to mitoxantrone, SN-38, and topotecan, while mutant ABCG2 also exhibited a gain of function for mitoxantrone as they conferred a four-fold greater resistance compared to wild type. Cells transfected with mutant ABCG2 were 13- to 71- fold resistant to the P-glycoprotein substrates doxorubicin, daunorubicin, epirubicin, bisantrene, and rhodamine 123 compared to cells transfected with wild-type ABCG2, which were only three- to four-fold resistant to these compounds. ABCG2 did not confer appreciable resistance to etoposide, taxol or the histone deacetylase inhibitor depsipeptide. None of the transfected cell lines demonstrated resistance to flavopiridol despite our previous observation that ABCG2-overexpressing cell lines are cross-resistant to the drug. Recently reported inhibitors of ABCG2 were evaluated and 50 microM novobiocin was found to reverse wild-type ABCG2 completely, but only reverse mutant ABCG2 partially. The studies presented here serve to underscore the importance of amino-acid 482 in defining the substrate specificity of the ABCG2 protein and raise the possibility that amino-acid 482 mutations in human cancers could affect the clinical application of antagonists for ABCG2.

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133 Mutations at amino-acid 482 have included R482G and R482T in human cancer cells; R482S and R482M in mouse fibroblast lines (Honjo et al, 2001; Allen et al, 2002); and a recently reported R482M mutation in a doxorubicin-selected human T-cell line (Wang et al, 2003). Login to comment
152 The findings presented here parallel those of Allen et al, (2002), who described two mutations, R482M and R482S, in mouse fibroblast cells lacking functional Mdr1, Mdr2, and Mrp1. Login to comment

[hide] Multidrug resistance in cancer chemotherapy and xe... Curr Med Chem Anticancer Agents. 2004 Jan;4(1):31-42. Han B, Zhang JT
Multidrug resistance in cancer chemotherapy and xenobiotic protection mediated by the half ATP-binding cassette transporter ABCG2.
Curr Med Chem Anticancer Agents. 2004 Jan;4(1):31-42., [PMID:14754410]

Abstract [show]
ABCG2, also termed BCRP/MXR/ABCP, is a half ATP-binding cassette (ABC) transporter expressed on plasma membranes. ABCG2 was independently cloned from placenta as well as cell lines selected for resistance to mitoxantrone or anthracyclines. ABCG2 consists of a nucleotide-binding domain (NBD) at the amino terminus and a transmembrane domain (TMD) at the carboxyl terminus and it is postulated to form a homodimer to perform its biological functions. Over-expression of ABCG2 in cell lines confers resistance on a wide variety of anticancer drugs including mitoxantrone, daunorubicin, doxorubicin, topotecan and epirubicin. The expression of ABCG2 has been implicated in multidrug resistance (MDR) of acute myeloid leukemia and some solid tumors. In addition, ABCG2 can transport several fluorescent dyes or toxins. ABCG2 is found to be expressed in epithelial cells of intestine and colon, liver canaliculi, and renal tubules, where it serves to eliminate the plasma level of orally administered anticancer drugs as well as ingested toxins. ABCG2 is found to be highly expressed in placenta and the luminal surface of microvessel endothelium blood-brain barrier where it may play a role in limiting the penetration of drugs, such as topotecan from the maternal plasma into the fetus and from blood to brain. A variety of inhibitors for ABCG2 including GF120918 may prove useful for sensitizing cancer cells to chemotherapy or altering the distribution of orally administered drug substrates of ABCG2. Interestingly, ABCG2 is also expressed highly in hematopoietic stem cells. However, the function of ABCG2 in stem cells is currently unknown, although it may provide protection to stem cells from a variety of xenobiotics.

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106 However, no polymorphism at amino acid 482 was identified to correspond to the Arg482 Gly, Arg482 Met, or Arg482 Thr mutation that has been identified in drug selected cell lines. Login to comment

[hide] ABCG2 -- a transporter for all seasons. FEBS Lett. 2004 Jun 1;567(1):116-20. Sarkadi B, Ozvegy-Laczka C, Nemet K, Varadi A
ABCG2 -- a transporter for all seasons.
FEBS Lett. 2004 Jun 1;567(1):116-20., 2004-06-01 [PMID:15165903]

Abstract [show]
The human ABCG2 (ABCP/MXR/BCRP) protein is a recently recognized ABC half-transporter, which forms homodimers in the plasma membrane and actively extrudes a wide variety of chemically unrelated compounds from the cells. This protein protects our cells and tissues against various xenobiotics, with a crucial role in the intestine, liver, placenta, and the blood-brain barrier. Moreover, ABCG2 seems to have a key function in stem cell protection/regulation, and also in hypoxic defense mechanisms. Widely occurring single nucleotide polymorphisms in ABCG2 may affect absorption and distribution, altering the effectiveness and toxicity of drugs in large populations. At the clinics, overexpression of ABCG2 in tumor cells confers cancer multidrug resistance to a variety of newly developed anticancer agents. On the other hand, specific substrate mutants of ABCG2 are advocated for use as selectable markers in stem-cell based gene therapy.

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119 The mutants having R482G or R482T (R482M or R482S in the mouse abcg2) showed altered substrate specificity as compared to the wild-type protein, i.e., they conferred increased mitoxantrone or doxorubicin (DOX) resistance and rhodamine 123 transport capacity (see Fig. 2, [42,43]). Login to comment

[hide] Induction of cellular resistance to nucleoside rev... Biochem Pharmacol. 2004 Oct 1;68(7):1363-70. Wang X, Nitanda T, Shi M, Okamoto M, Furukawa T, Sugimoto Y, Akiyama S, Baba M
Induction of cellular resistance to nucleoside reverse transcriptase inhibitors by the wild-type breast cancer resistance protein.
Biochem Pharmacol. 2004 Oct 1;68(7):1363-70., 2004-10-01 [PMID:15345326]

Abstract [show]
Breast cancer resistance protein (BCRP/ABCG2) is a novel member of ATP-binding cassette transporters, which induce multidrug resistance in cancer cells. We previously reported that a high level of BCRP expression in CD4(+) T cells conferred cellular resistance to nucleoside reverse transcriptase inhibitors (NRTIs) of human immunodeficiency virus type 1 (HIV-1). However, this BCRP was found to have a mutation of Arg to Met at position 482 (BCRP(R482M)). The present study demonstrated that the wild-type BCRP (BCRP(WT)) also conferred cellular resistance to NRTIs. MT-4 cells (a CD4(+) T-cell line) highly expressing BCRP(WT) (MT-4/BCRP) were generated and the expression of BCRP(WT) was confirmed by genotypic and phenotypic analyses. Compared to the parental MT-4 cells, MT-4/BCRP cells displayed resistance to zidovudine (AZT) in terms of antiviral activity as well as drug cytotoxicity. In addition, other NRTIs were also less inhibitory to HIV-1 replication in MT-4/BCRP cells than in MT-4 cells. Significant reduction of intracellular AZT accumulation was observed in MT-4/BCRP cells. An analysis for intracellular metabolism of AZT suggested that the resistance was attributed to the increased efflux of AZT and its metabolites in MT-4/BCRP cells. Furthermore, the BCRP-specific inhibitor fumitremorgin C completely restored the reduction of AZT in MT-4/BCRP cells. These results indicate that, like BCRP(R482M), BCRP(WT) also plays an important role in cellular resistance to NRTIs.

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2 However, this BCRP was found to have a mutation of Arg to Met at position 482 (BCRPR482M). Login to comment
32 This BCRP was found to have a mutation of Arg to Met at position 482 (BCRPR482M). Login to comment

[hide] Single amino acid (482) variants of the ABCG2 mult... Biochim Biophys Acta. 2005 Feb 1;1668(1):53-63. Ozvegy-Laczka C, Koblos G, Sarkadi B, Varadi A
Single amino acid (482) variants of the ABCG2 multidrug transporter: major differences in transport capacity and substrate recognition.
Biochim Biophys Acta. 2005 Feb 1;1668(1):53-63., 2005-02-01 [PMID:15670731]

Abstract [show]
The human ABCG2 protein is an ATP binding cassette half-transporter, which protects our cells and tissues against various xenobiotics, while overexpression of ABCG2 in tumor cells confers multidrug resistance. It has been documented that single amino acid changes at position 482 resulted in altered drug resistance and transport capacity. In this study, we have generated nine Arg-482 mutants (G, I, M, S, T, D, N, K, Y) of ABCG2, and expressed them in insect cells. All ABCG2 variants showed cell surface expression and, in isolated membranes, an ABCG2-specific ATPase activity. When methotrexate accumulation was measured in inside-out membrane vesicles, this transport was supported only by the wild-type ABCG2. In intact cells, mitoxantrone was transported by all ABCG2 variants, except by R482K. Rhodamine 123 was extruded by most of the mutants, except by R482K, Y and by wild-type ABCG2. Hoechst 33342 was pumped out from cells expressing the wild-type and all Arg-482 variants, but not from those expressing R482K and Y. Our study demonstrates that the substrate specificity of the Arg (wild-type) form is unique and that amino acid replacements at position 482 induce major alterations in both the transport activity and substrate specificity of this protein.

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29 The mutants, containing R482G, T or M (R482M or S in the mouse abcg2), showed altered substrate specificity [22-24]. Login to comment
48 The two internal complementary primer pairs containing the specific mutation were: 5V-tta tta cca atg atc atg tta cc-3Vand 5-Vgg taa cat gat cat tgg taa taa-3V (R482I), 5V-tta tca gat cta tta ccc atg-3Vand 5V-gg taa cat cat cat ggg taa t-3V(R482M), 5V-ta ccc atg tcg atg tta cca a-3Vand 5V-t tgg taa cat cga cat ggg ta-3V(R482S), 5V-cc atg gac atg tta cca tcg att ata-3V and 5V-tat aat cga tgg taa cat gtc cat gg-3V (R482D), 5V-atg tta cca tcg att ata ttt acc-3Vand 5V-cc atg aat atg tta cca tcg att ata-3V (R482N), 5V-tta tta cct atg aag atg tta-3V cc and 5V-gg taa cat ctt cat agg taa taa-3V(R482K) and 5V-tta tta cct atg tac atg tta cc-3Vand 5V-gg taa cat gta cat agg taa taa-3V (R482Y). Login to comment

[hide] Single nucleotide polymorphisms modify the transpo... Cancer Chemother Pharmacol. 2005 Aug;56(2):161-72. Epub 2005 Apr 19. Morisaki K, Robey RW, Ozvegy-Laczka C, Honjo Y, Polgar O, Steadman K, Sarkadi B, Bates SE
Single nucleotide polymorphisms modify the transporter activity of ABCG2.
Cancer Chemother Pharmacol. 2005 Aug;56(2):161-72. Epub 2005 Apr 19., [PMID:15838659]

Abstract [show]
Single nucleotide polymorphism (SNP) analyses of the ABCG2 gene have revealed three nonsynonymous SNPs resulting in the amino acid changes at V12M, Q141K and D620N. To determine whether the SNPs have an effect on drug transport, human embryonic kidney cells (HEK-293) were stably transfected with full length ABCG2 coding wild-type or SNP variants of ABCG2. In 4-day cytotoxicity assays with mitoxantrone, topotecan, SN-38 or diflomotecan, cells transfected with wild-type R482 ABCG2 showed IC50 values up to 1.2-fold to 5-fold higher than cells expressing comparable levels of Q141K ABCG2, suggesting that the Q141K SNP affects drug transport. FTC-inhibitable mitoxantrone efflux normalized to ABCG2 surface expression as assayed by the anti-ABCG2 antibody 5D3 was significantly lower in cells transfected with Q141K ABCG2 than in those transfected with wild-type R482 ABCG2 (P = 0.0048). Values for V12M and D620N ABCG2 were comparable to those for wild-type R482 ABCG2. The vanadate-sensitive ATPase activity of ABCG2 was assayed in Sf9 insect cells infected with wild-type or SNP variants of ABCG2. Basal ATPase activity in cells transfected with Q141K ABCG2 was 1.8-fold lower than in cells transfected with wild-type ABCG2, but was comparable among cells expressing wild-type, V12M or D620N ABCG2. Confocal studies of ABCG2 localization revealed higher intracellular staining in the Q141K transfectants than in cells transfected with wild-type or V12M ABCG2. Decreased transport of Hoechst 33342 was observed in Sf9 cells expressing V12M ABCG2; however, this was not true in HEK-293 cells expressing V12M ABCG2. These results suggest that the Q141K SNP affects the transport efficiency of ABCG2 and may result in altered pharmacokinetics or drug-resistance profiles in clinical oncology.

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25 Wang et al. have also identified an R482M mutation in a doxorubicin-resistant human T-cell line [47]. Login to comment

[hide] The ABC transporter Abcg2/Bcrp: role in hypoxia me... Biometals. 2005 Aug;18(4):349-58. Krishnamurthy P, Schuetz JD
The ABC transporter Abcg2/Bcrp: role in hypoxia mediated survival.
Biometals. 2005 Aug;18(4):349-58., [PMID:16158227]

Abstract [show]
ABC (ATP-binding cassette) transporters have diverse roles in many cellular processes. These diverse roles require the presence of conserved membrane spanning domains and nucleotide binding domains. Bcrp (Abcg2) is a member of the ATP binding cassette family of plasma membrane transporters that was originally discovered for its ability to confer drug resistance in tumor cells. Subsequent studies showed Bcrp expression in normal tissues and high expression in primitive stem cells. Bcrp expression is induced under low oxygen conditions consistent with its high expression in tissues exposed to low oxygen environments. Moreover, Bcrp interacts with heme and other porphyrins. This finding and its regulation by hypoxia suggests it may play a role in protecting cells/tissue from protoporphyrin accumulation under hypoxia. These observations are strengthened by the fact that porphyrins accumulate in tissues of the Bcrp knockout mouse. It is possible that humans with loss of function Bcrp alleles may be more susceptible to porphyrin-induced phototoxicity. We propose that Bcrp plays a role in porphyrin homoeostasis and regulates survival under low oxygen conditions.

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115 The mutants having R482G or R482T (R482M or R482S in the mouse Bcrp) showed altered transport properties as compared to the wild-type protein (Honjo et al. 2001; Allen et al. 2002). Login to comment

[hide] ABCG2 harboring the Gly482 mutation confers high-l... Cancer Res. 2005 Sep 15;65(18):8414-22. Shafran A, Ifergan I, Bram E, Jansen G, Kathmann I, Peters GJ, Robey RW, Bates SE, Assaraf YG
ABCG2 harboring the Gly482 mutation confers high-level resistance to various hydrophilic antifolates.
Cancer Res. 2005 Sep 15;65(18):8414-22., 2005-09-15 [PMID:16166320]

Abstract [show]
ABCG2 is an ATP-binding cassette transporter that confers resistance to various chemotherapeutic agents. Recent studies have established that an Arg (wild-type) to Gly mutation at amino acid 482 in ABCG2 alters substrate specificity. Here, we explored the role of this G482 mutation in antifolate resistance using a clinically relevant 4-hour drug exposure. Stable transfectants overexpressing the mutant G482 transporter displayed 120-, 1,000-, and >6,250-fold resistance to the antifolates methotrexate, GW1843, and Tomudex, respectively, relative to parental human embryonic kidney cells. Moreover, although overexpressing equal transporter levels at the plasma membrane, G482-ABCG2 cells were 6-, 23-, and >521-fold more resistant to methotrexate, GW1843, and Tomudex, respectively, than R482-ABCG2 cells. In contrast, upon a continuous (72-hour) drug exposure, both the G482- and R482-ABCG2 cells lost almost all their antifolate resistance; this result was consistent with the inability of ABCG2 to extrude long-chain antifolate polyglutamates. Ko143, a specific and potent ABCG2 inhibitor reversed methotrexate resistance in both G482- and R482-ABCG2 cells. Consistently, whereas the pool of free methotrexate in parental human embryonic kidney cells was prominent after 4 hours of transport with 1 micromol/L [3H]methotrexate, in R482- and G482-ABCG2 cells, it was minimal. Furthermore, G482-ABCG2 cells contained marked decreases in the di- and triglutamate species of [3H]methotrexate at 4 hours of incubation with methotrexate and in the tetra- and pentaglutamates at 24 hours. These changes were not associated with any significant decrease in folylypoly-gamma-glutamate synthetase activity. These results provide the first evidence that the G482-ABCG2 mutation confers high-level resistance to various hydrophilic antifolates.

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22 Sequencing of the Abcg2 gene in these drug-resistant cell lines identified two mutations, R482M and R482S. Login to comment

[hide] The role of the human ABCG2 multidrug transporter ... Cancer Lett. 2006 Mar 8;234(1):62-72. Epub 2005 Dec 7. Cervenak J, Andrikovics H, Ozvegy-Laczka C, Tordai A, Nemet K, Varadi A, Sarkadi B
The role of the human ABCG2 multidrug transporter and its variants in cancer therapy and toxicology.
Cancer Lett. 2006 Mar 8;234(1):62-72. Epub 2005 Dec 7., 2006-03-08 [PMID:16337740]

Abstract [show]
The human multidrug resistance ABC transporters provide a protective function in our body against a large number of toxic compounds. These proteins, residing in the plasma membrane, perform an active, ATP-dependent extrusion of such xenobiotics. However, the same proteins are also used by the tumor cells to fight various anticancer agents. ABCG2 is an important member of the multidrug resistance proteins, an 'ABC half transporter', which functions as a homodimer in the cell membrane. In this review, we provide a basic overview of ABCG2 function in physiology and drug metabolism, but concentrate on the discussion of mutations and polymorphisms discovered in this protein. Interestingly, a single nucleotide mutation, changing amino acid 482 from arginine to threonine or glycine in ABCG2, results in a major increase in the catalytic activity and a wider drug recognition by this protein. Still, this mutation proved to be an in vitro artifact, produced only in heavily drug-selected cell lines. In contrast, at least two, but possibly more polymorphic variants of ABCG2 were found to be present in large human populations with different ethnic background. However, currently available experimental data regarding the cellular expression, localization and function of these ABCG2 variants are strongly contradictory. Since, the proteins produced by these variant alleles may differently modulate cancer treatment, general drug absorption and toxicity, may represent risk factors in fetal toxicity, or alter the differentiation of stem cells, their exact characterization is a major challenge in this field.

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80 The cDNA sequence analysis of the MCF-7/AdVP3000 human breast cancer cell line and the S1M1-80 human colon cancer cell line revealed that in these cell lines, each showing anthracycline resistance and an ability to extrude rhodamine 123, a single amino acid change occurred at position 482, resulting an R482T (c.1445GOC) mutant in the MCF-7/AdVP3000 cell line, an R482G replacement (c.1444AOG) in S1M1-80 cells, and an R482M substitution (c.1445GOT) in the MT-4/DOX500 human T cell line [27,41,54]. Login to comment
81 Moreover, in the 88.6/D800-A, 88.6/D800-B and KOT52/ D800 mouse fibroblast cell lines, an R482M (KOT52/D800 and 88.6/D800-A cells) and an R482S (88.6/D800-B cells) mutation was observed, with a similar, anthracycline resistant phenotype [42]. Login to comment

[hide] The nature of amino acid 482 of human ABCG2 affect... Protein Sci. 2006 Jul;15(7):1597-607. Ejendal KF, Diop NK, Schweiger LC, Hrycyna CA
The nature of amino acid 482 of human ABCG2 affects substrate transport and ATP hydrolysis but not substrate binding.
Protein Sci. 2006 Jul;15(7):1597-607., [PMID:16815914]

Abstract [show]
Several members of the ATP-binding cassette (ABC) transporter superfamily, including P-glycoprotein and the half-transporter ABCG2, can confer multidrug resistance to cancer cells in culture by functioning as ATP-dependent efflux pumps. ABCG2 variants harboring a mutation at arginine 482 have been cloned from several drug-resistant cell lines, and these variants differ in their substrate transport phenotype. In this study, we changed the wild-type arginine 482 in human ABCG2 to each one of the 19 other standard amino acids and expressed each one transiently in HeLa cells. Using the 5D3 antibody that recognizes a cell surface epitope of ABCG2, we observed that all the mutants were expressed at the cell surface. However, the mutant ABCG2 proteins differed markedly in transport activity. All of the variants were capable of transporting one or more of the substrates used in this study, with the exception of the R482K mutant, which is completely devoid of transport ability. Six of the mutants (R482G, R482H, R482K, R482P, R482T, and R482Y) and the wild-type protein (R482wt) were selected for studies of basal and stimulated ATPase activity and photoaffinity labeling with the substrate analog [125I]iodoarylazidoprazosin. Whereas these seven ABCG2 variants differed markedly in ATPase activity, all were able to specifically bind the substrate analog [125I]iodoarylazidoprazosin. These data suggest that residue 482 plays an important role in substrate transport and ATP turnover, but that the nature of this amino acid may not be important for substrate recognition and binding.

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30 Recently, another ABCG2 variant was found to have a mutation of arginine to methionine at position 482 in a doxorubicin-resistant CD4+ T-cell line (Wang et al. 2003). Login to comment

[hide] Human multidrug resistance ABCB and ABCG transport... Physiol Rev. 2006 Oct;86(4):1179-236. Sarkadi B, Homolya L, Szakacs G, Varadi A
Human multidrug resistance ABCB and ABCG transporters: participation in a chemoimmunity defense system.
Physiol Rev. 2006 Oct;86(4):1179-236., [PMID:17015488]

Abstract [show]
In this review we give an overview of the physiological functions of a group of ATP binding cassette (ABC) transporter proteins, which were discovered, and still referred to, as multidrug resistance (MDR) transporters. Although they indeed play an important role in cancer drug resistance, their major physiological function is to provide general protection against hydrophobic xenobiotics. With a highly conserved structure, membrane topology, and mechanism of action, these essential transporters are preserved throughout all living systems, from bacteria to human. We describe the general structural and mechanistic features of the human MDR-ABC transporters and introduce some of the basic methods that can be applied for the analysis of their expression, function, regulation, and modulation. We treat in detail the biochemistry, cell biology, and physiology of the ABCB1 (MDR1/P-glycoprotein) and the ABCG2 (MXR/BCRP) proteins and describe emerging information related to additional ABCB- and ABCG-type transporters with a potential role in drug and xenobiotic resistance. Throughout this review we demonstrate and emphasize the general network characteristics of the MDR-ABC transporters, functioning at the cellular and physiological tissue barriers. In addition, we suggest that multidrug transporters are essential parts of an innate defense system, the "chemoimmunity" network, which has a number of features reminiscent of classical immunology.

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804 Interestingly, the same phenomenon was observed in the case of the mouse Abcg2 protein; drug selection induced a mutation exactly at the same position (R482M or R482S in the mouse Abcg2), similarly altering the substrate handling of this ortholog (5). Login to comment

[hide] Antibody binding shift assay for rapid screening o... Eur J Pharm Sci. 2012 Jan 23;45(1-2):101-9. Epub 2011 Nov 17. Telbisz A, Hegedus C, Ozvegy-Laczka C, Goda K, Varady G, Takats Z, Szabo E, Sorrentino BP, Varadi A, Sarkadi B
Antibody binding shift assay for rapid screening of drug interactions with the human ABCG2 multidrug transporter.
Eur J Pharm Sci. 2012 Jan 23;45(1-2):101-9. Epub 2011 Nov 17., [PMID:22115866]

Abstract [show]
The ABCG2 multidrug transporter protein has been identified as a key player in cancer drug resistance and xenobiotic elimination, as its actively transported substrates include anticancer drugs, intermediates of heme metabolism, xenobiotics, and also drug conjugates. Several transported substrates at higher concentrations, and some anticancer agents even at low concentrations directly inhibit the ABCG2 transporter, thus it is difficult to provide estimation for pharmacologically important ABCG2-dependent interactions. In addition, as documented here, in mutant variants of the transporter, inhibitors of the wild-type ABCG2 may become actively transported substrates. In this paper we describe a rapid in vitro assay to identify transport modulation by measuring the cell surface interaction of a conformation sensitive monoclonal antibody (5D3) with ABCG2 in intact cells. As documented, in conjunction with membrane ATPase, transport and cytotoxicity measurements, this assay provides a reliable estimate of concentration-dependent modulation of ABCG2 by newly emerging pharmacophores. A high-throughput, 96-well plate assay platform is also provided.

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18 The mutants, containing R482G, T (or R482M or S in the mouse Abcg2), showed altered substrate specificities. Login to comment