Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.6.3.44 (P-glycoprotein)
 13,344 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have transfected a eukaryotic expression vector containing a mdr1 complementary DNA isolated from normal human liver into human BRO melanoma cells to study the drug-resistant phenotype produced by the exclusive overexpression of normal human mdr1 P-glycoprotein. The drug resistance pattern of mdr1-transfected clones includes relatively high resistance to gramicidin D (about 300-fold), vincristine (about 100-fold), and actinomycin D (about 100-fold) and a lower degree of resistance to doxorubicin (about 10-fold), VP16-213 (about 10-fold), and colchicine (about 6-fold). The transfectants did not exhibit resistance to trimetrexate, cis-platinum, mitomycin C, 1-beta-D-arabinofuranosylcytosine, bleomycin, G418, or magainin-2-amide; they were slightly more sensitive to verapamil (2-fold) but not to Triton X-100. As in other multidrug-resistant cell lines, resistance to vincristine could be reversed by verapamil and, more effectively, by cyclosporin A. Chloroquine only marginally increased drug sensitivity in mdr1-transfected cells. Gramicidin D resistance was also reversed by verapamil, suggesting that the mechanism of resistance to this polypeptide antibiotic is similar to that of other drugs transported by P-glycoprotein. Thus, expression of the wild-type mdr1 complementary DNA induces a drug-resistant phenotype similar to that induced by mdr1 complementary DNAs isolated from drug-resistant cell lines with relatively low colchicine resistance. As other cell lines may display a different pattern of drug resistance, it is clear that other resistance mechanisms or cell type-specific factors may modulate the resistance. mdr1-transfected cell lines provide a convenient tool for the identification of P-glycoprotein-mediated phenomena.
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PMID:Multidrug resistance phenotype of human BRO melanoma cells transfected with a wild-type human mdr1 complementary DNA. 196 59

A major form of multidrug resistance results from the overexpression of P-glycoprotein, a 170 kDa membrane protein. Multidrug resistant (MDR) Chinese hamster ovary (CHO) cells and mdrl transfectants displayed cross-resistance to the channel-forming peptide ionophore gramicidin D, which was reversed by various chemosensitizers, thus directly implicating P-glycoprotein as the mediator of resistance. However, gramicidin D was not able to inhibit [3H]azidopine photolabelling of P-glycoprotein. MDR cells were not resistant to other pore-forming ionophores, but showed a modest level of cross-resistance to the mobile ionophore valinomycin. There was no difference in 125I-gramicidin D uptake by resistant and sensitive cells. Resistant cells showed lower 86Rb+ uptake, relative to the drug-sensitive parent. Addition of GmD increased both the rate and the level of 86Rb+ uptake in sensitive cells, but had no effect on MDR cells. MDR cells also showed much lower rates of gramicidin D-dependent 86Rb+ efflux than sensitive cells, and this was greatly increased by verapamil. These results suggest that P-glycoprotein interferes with the formation of ion-conducting gramicidin D channels. In contrast, valinomycin had the same effect on gramicidin D-dependent cation efflux in MDR and sensitive cells. Gramicidin D is thus unique among the ionophores is being a substrate for P-glycoprotein, which appears to greatly reduce the formation of active dimeric channels in the plasma membrane of MDR cells.
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PMID:Interaction of multidrug-resistant Chinese hamster ovary cells with the peptide ionophore gramicidin D. 750 93

It has been proposed that the multidrug resistance (MDR) transporter, P-glycoprotein (P-170), may be physiologically involved in the transport of polypeptides. As a step towards understanding the interaction of P-170 with polypeptides, we isolated various gramicidin-D-resistant mammalian cell lines. Gramicidin D is a hydrophobic pentadecapeptide ionophore that forms proton and alkali metal cation-permeable channels in lipid bilayers. Gramicidin-D-resistant cells displayed a prominent MDR gene amplification, P-170 overexpression, reduced drug accumulation, and consequent resistance to MDR-type cytotoxic agents. Modulators of the MDR phenotype, including verapamil, reserpine and quinidine, rendered these cells sensitive to gramicidin D. Using these cell lines, we established an assay that probes for the intra-membranal interaction between P-170 and gramicidin D. Gramicidin-D channel formation was followed by cellular accumulation of 86Rb+. Ionophore-resistant cells, and other MDR cells, did not show an appreciable increase in 86Rb+ influx rates, in the presence of increasing gramicidin-D concentrations. In contrast, parental cells displayed a dose-dependent increase in the 86Rb+ influx rates. Interestingly, in the absence of serum, gramicidin-D-resistant cells resumed the wild-type, ionophore-dose-dependent increase in 86Rb+ influx rates. MDR modulators caused a resumption of channel formation in ionophore-resistant cells. We conclude that acquisition of the MDR phenotype is an efficient means of cellular protection against gramicidin D. Hence, a new approach is offered in which P-170 interaction with gramicidin D is quantitatively followed by a rapid assessment of the biological activity (i.e. channel formation) of the substrate itself. Possible mechanisms of P-170 interaction with free ionophore monomers, and membrane-associated gramicidin D are discussed.
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PMID:Probing the interaction of the multidrug-resistance phenotype with the polypeptide ionophore gramicidin D via functional channel formation. 751 66

The aim of the present study was to demonstrate that the modulation of P-glycoprotein (Pgp) ATPase activity by peptides, drugs, and chemosensitizers takes place on a common drug pharmacophore. To this end, a highly emetine-resistant Chinese hamster ovary cell line was established, in which Pgp constituted 18% of plasma membrane protein. Reconstituted proteoliposomes, the Pgp content of which was up to 40%, displayed a basal activity of 2.6 +/- 0.45 micromol of Pi/min/mg of protein, suggesting the presence of an endogenous Pgp substrate. This basal ATPase activity was stimulated (up to 5.2 micromol of Pi/min/mg of protein) by valinomycin and various Pgp substrates, whereas, to our surprise, gramicidin D, an established Pgp substrate, was inhibitory. Taking advantage of this novel inhibition of Pgp ATPase activity by gramicidin D, a drug competition assay was devised in which gramicidin D-inhibited Pgp ATPase was coincubated with increasing concentrations of various substrates that stimulate its ATPase activity. Gramicidin D inhibition of Pgp ATPase was reversed by Pgp substrates, including various cytotoxic agents and chemosensitizers. The inhibition of the basal ATPase activity and the reversal of gramicidin D inhibition of Pgp ATPase by its various substrates conformed to classical Michaelis-Menten competition. This competition involved an endogenous substrate, the inhibitory drug gramicidin D, and a stimulatory substrate. We conclude that the various MDR type substrates and chemosensitizers compete on a common drug binding site present in Pgp.
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PMID:Competition of hydrophobic peptides, cytotoxic drugs, and chemosensitizers on a common P-glycoprotein pharmacophore as revealed by its ATPase activity. 862 16