ABCB1 p.Ser671Asn
| Predicted by SNAP2: | A: N (66%), C: D (53%), D: N (66%), E: N (72%), F: N (61%), G: N (66%), H: N (78%), I: N (66%), K: N (78%), L: N (66%), M: N (66%), N: N (78%), P: N (72%), Q: N (78%), R: N (78%), T: N (82%), V: N (66%), W: D (59%), Y: N (61%), |
| Predicted by PROVEAN: | A: N, C: D, D: N, E: N, F: D, G: N, H: D, I: D, K: N, L: D, M: D, N: N, P: D, Q: N, R: D, T: N, V: D, W: D, Y: D, |
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[hide] P-Glycoprotein, Multidrug Resistance and Protein K... Oncologist. 1996;1(4):261-268. Fine RL, Chambers TC, Sachs CW
P-Glycoprotein, Multidrug Resistance and Protein Kinase C.
Oncologist. 1996;1(4):261-268., [PMID:10388000]
Abstract [show]
The multidrug resistant (MDR) phenotype is a well-studied subject that has been recognized as a determinant underlying specific types of drug resistance in human cancer. Although it is clear that the P-glycoprotein plays a major role in MDR, it is not clear whether post-translational modifications such as phosphorylation have any major impact on its modulation. The laboratory of Dr. Bruce Chabner was one of the first to describe increased expression and activity of protein kinase C (PKC) associated with the MDR phenotype. Since that time, a similar correlation has been observed in many other MDR cell lines. Most of these studies have been performed with doxorubicin-selected cells that have acquired MDR and have shown increased PKC activity, mainly for PKC-a isoenzyme. Intrinsic MDR in human renal cell carcinoma lines has been shown to correlate directly with PKC activity, but further studies with intrinsic MDR cell lines are needed before any conclusions can be drawn. More recent evidence suggests that there is a complex biochemical process by which PKC isoenzymes differentially phosphorylate specific serine residues in the linker region of P-glycoprotein which may lead to alterations in P-glycoprotein ATPase and drug-binding functions. To further complicate matters, PKC plays an important role in anti-apoptotic pathways, which can confound the dissection and elucidation of drug-resistance mechanisms. However, these areas are still under active investigation and not fully answered. Further studies are needed to specifically answer the question of whether PKC directly modulates basal and/or drug-stimulated P-glycoprotein function. This manuscript reviews the majority of the literature on PKC and MDR, as well as offers caveats for interpretation of these studies to answer the above questions.
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No. Sentence Comment
96 Mutation of serine 671 to asparagine in the linker region of P-glycoprotein abrogated verapamil and PKC-α-stimulated ATPase activity.
X
ABCB1 p.Ser671Asn 10388000:96:12
status: NEW[hide] Modulation of P-glycoprotein by protein kinase C a... Biochemistry. 1994 Aug 30;33(34):10313-8. Ahmad S, Safa AR, Glazer RI
Modulation of P-glycoprotein by protein kinase C alpha in a baculovirus expression system.
Biochemistry. 1994 Aug 30;33(34):10313-8., 1994-08-30 [PMID:7915139]
Abstract [show]
The modulation of P-glycoprotein by protein kinase C alpha (PKC alpha) was examined in a baculovirus expression system. PGP was phosphorylated in membrane vesicle preparations in vitro only when coexpressed with PKC alpha, and phosphorylation was Ca(2+)-dependent and inhibited by the PKC inhibitor Ro 31-8220. PGP and PKC alpha were tightly associated in membrane vesicles and were coimmunoprecipitated with antibodies against either PGP or PKC alpha. Photoaffinity labeling of membrane vesicles with [3H]azidopine indicated that drug binding to PGP was slightly increased in the presence of PKC alpha. In contrast, PGP ATPase activity was increased by PKC alpha as well as by verapamil, but only PKC-stimulated activity in the presence of verapamil was inhibited by Ro 31-8220. Mutation of serine-671 to asparagine in the linker region of PGP abolished PKC alpha-stimulated ATPase activity, and also inhibited to a lesser degree verapamil-stimulated ATPase activity. These results indicate that PKC alpha in a positive regulator of PGP ATPase activity and suggest that this mechanism may account for the increased multidrug resistance observed in MDR1-expressing cells when PKC alpha activity is elevated.
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No. Sentence Comment
112 To directly determine the dependence of PGP ATPase activity on PKC-mediated phosphorylation, Ser671 was mutated to Asn within a PKC consensus phosphorylation sequence in the linker region of PGP (Figure 6).
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ABCB1 p.Ser671Asn 7915139:112:93
status: NEW117 Ser671Asn mutant exhibiteda similarlevelof ATPaseactivity as wild-type PGP; however,mutant PGP was resistant to the stimulatoryeffectof PKCa on ATPaseactivity, and exhibited an attenuated response to verapamil compared to wild-type PGP.
X
ABCB1 p.Ser671Asn 7915139:117:0
status: NEW[hide] P-glycoprotein, multidrug resistance and protein k... Stem Cells. 1996 Jan;14(1):47-55. Fine RL, Chambers TC, Sachs CW
P-glycoprotein, multidrug resistance and protein kinase C.
Stem Cells. 1996 Jan;14(1):47-55., [PMID:8820951]
Abstract [show]
The multidrug resistant (MDR) phenotype is a well-studied subject that has been recognized as a determinant underlying specific types of drug resistance in human cancer. Although it is clear that the P-glycoprotein plays a major role in MDR, it is not clear whether post-translational modifications such as phosphorylation have any major impact on its modulation. The laboratory of Dr. Bruce Chabner was one of the first to describe increased expression and activity of protein kinase C (PKC) associated with the MDR phenotype. Since that time, a similar correlation has been observed in many other MDR cell lines. Most of these studies have been performed with doxorubicin-selected cells that have acquired MDR and have shown increased PKC activity, mainly for PKC-alpha isoenzyme. Intrinsic MDR in human renal cell carcinoma lines has been shown to correlate directly with PKC activity, but further studies with intrinsic MDR cell lines are needed before any conclusions can be drawn. More recent evidence suggests that there is a complex biochemical process by which PKC isoenzymes differentially phosphorylate specific serine residues in the linker region of P-glycoprotein which may lead to alterations in P-glycoprotein ATPase and drug-binding functions. To further complicate matters, PKC plays an important role in anti-apoptotic pathways, which can confound the dissection and elucidation of drug-resistance mechanisms. However, these areas are still under active investigation and not fully answered. Further studies are needed to specifically answer the question of whether PKC directly modulates basal and/or drug-stimulated P-glycoprotein function. This manuscript reviews the majority of the literature on PKC and MDR, as well as offers caveats for interpretation of these studies to answer the above questions.
Comments [show]
None has been submitted yet.
No. Sentence Comment
97 Mutation of serine 671 to asparagine in the linker region of P-glycoprotein abrogated verapamil and PKC-α-stimulated ATPase activity.
X
ABCB1 p.Ser671Asn 8820951:97:12
status: NEW[hide] Phosphorylation site mutations in the human multid... J Biol Chem. 1997 Sep 12;272(37):23165-71. Szabo K, Bakos E, Welker E, Muller M, Goodfellow HR, Higgins CF, Varadi A, Sarkadi B
Phosphorylation site mutations in the human multidrug transporter modulate its drug-stimulated ATPase activity.
J Biol Chem. 1997 Sep 12;272(37):23165-71., 1997-09-12 [PMID:9287320]
Abstract [show]
In the human multidrug transporter (MDR1), three serine residues located in the "linker" region of the protein are targets of in vivo phosphorylation. These three serines, or all eight serines and threonines in the linker, were substituted by alanines (mutants 3A and 8A) or with glutamic acids (mutants 3E and 8E). The wild-type and mutant proteins were expressed in baculovirus-infected Spodoptera frugiperda (Sf9) ovarian insect cells, and the vanadate-sensitive, drug-stimulated ATPase activity was measured in isolated membrane preparations. The maximum drug-stimulated MDR1-ATPase activity was similar for the wild-type and the mutant proteins. However, wild-type MDR1, which is known to be phosphorylated in Sf9 membranes, and the 3E and 8E mutants, which mimic the charge of phosphorylation, achieved half-maximum activation of MDR1-ATPase activity at lower verapamil, vinblastine, or rhodamine 123 concentrations than the nonphosphorylatable 3A and 8A variants. For some other drugs (e.g. valinomycin or calcein acetoxymethylester) activation of the MDR1-ATPase for any of the mutants was indistinguishable from that of the wild-type protein. Kinetic analysis of the data obtained for the 3A and 8A MDR1 variants indicated the presence of more than one drug interaction site, exhibiting an apparent negative cooperativity. This phenomenon was not observed for the wild-type or the 3E and 8E MDR1 proteins. The dependence of the MDR1-ATPase activity on ATP concentration was identical in the wild-type and the mutant proteins, and Hill plots indicated the presence of more than one functional ATP-binding site. These results suggest that phosphorylation of the linker region modulates the interaction of certain drugs with MDR1, especially at low concentrations, although phosphorylation does not alter the maximum level of MDR1-ATPase activity or its dependence on ATP concentration.
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No. Sentence Comment
158 Ahmad et al. (40) have also presented evidence that exchanging Ser671 to asparagine reduced ATPase activity by about 50% at 10 M verapamil when expressed in Sf9 cells.
X
ABCB1 p.Ser671Asn 9287320:158:63
status: NEW