Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

The prokaryotic permeases are members of a superfamily of membrane transporters called traffic ATPases, which includes the medically important eukaryotic multidrug resistance (MDR) protein and cystic fibrosis transmembrane regulator (CFTR). Members of this superfamily have extensive sequence and structural similarity, in particular in an ATP-binding motif, and are believed to use ATP to energize translocation of substrates across biological membranes. The prokaryotic histidine permease is well-characterized and serves as a convenient model system. In this review, we highlight some of the biochemical and molecular biological approaches used to study the functional and architectural organization of this permease and relate the results of these approaches to what is known about other traffic ATPases. We have identified specific regions that we believe critical for the function of the histidine permease and propose that the corresponding regions in the eukaryotic traffic ATPases are also important for their function. In light of the fact that CFTR (and possibly the MDR protein) is an ion channel, we compare the properties of channels and transporters; in addition, we discuss the possibility that other members of the traffic ATPases may also have channel-like activity.
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PMID:ATP-dependent transport systems in bacteria and humans: relevance to cystic fibrosis and multidrug resistance. 750 4

We have recently reported that expression in yeast cells of P-glycoprotein (P-gp) encoded by the mouse multidrug resistance mdr3 gene (Mdr3) can complement a null ste6 mutation (M. Raymond, P. Gros, M. Whiteway, and D. Y. Thomas, Science 256:232-234, 1992). Here we show that Mdr3 behaves as a fully functional drug transporter in this heterologous expression system. Photolabelling experiments indicate that Mdr3 synthesized in yeast cells binds the drug analog [125I]iodoaryl azidoprazosin, this binding being competed for by vinblastine and tetraphenylphosphonium bromide, two known multidrug resistance drugs. Spheroplasts expressing wild-type Mdr3 (Ser-939) exhibit an ATP-dependent and verapamil-sensitive decreased accumulation of [3H]vinblastine as compared with spheroplasts expressing a mutant form of Mdr3 with impaired transport activity (Phe-939). Expression of Mdr3 in yeast cells can confer resistance to growth inhibition by the antifungal and immunosuppressive agent FK520, suggesting that this compound is a substrate for P-gp in yeast cells. Replacement of Ser-939 in Mdr3 by a series of amino acid substitutions is shown to modulate both the level of cellular resistance to FK520 and the mating efficiency of yeast mdr3 transformants. The effects of these mutations on the function of Mdr3 in yeast cells are similar to those observed in mammalian cells with respect to drug resistance and transport, indicating that transport of a-factor and FK520 in yeast cells is mechanistically similar to drug transport in mammalian cells. The ability of P-gp to confer cellular resistance to FK520 in yeast cells establishes a dominant phenotype that can be assayed for the positive selection of intragenic revertants of P-gp inactive mutants, an important tool for the structure-function analysis of mammalian P-gp in yeast cells.
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PMID:Functional expression of P-glycoprotein in Saccharomyces cerevisiae confers cellular resistance to the immunosuppressive and antifungal agent FK520. 750 92

The decrease of the intracellular concentration of drug in resistant cells compared to sensitive cells is, in most cases, correlated with the presence, in the membrane of resistant cells, of a 170-kDa P-glycoprotein responsible for an active efflux of the drug. In an attempt to identify mechanism(s) by which multidrug resistance can be circumvented, we have examined the cellular accumulation of 4'-O-tetrahydropyranyl-adriamycin, alone and in conjunction with various ionophores on the one hand and with cyclosporin A on the other hand. The present study was performed using a spectrofluorometric method with which it is possible to follow continuously the uptake and release of fluorescent molecules by living cells, as the incubation of the cells with the drug proceeds. Erythroleukemia K562 cell lines were used. Using experimental conditions in which these ionophores were unable to modify either the intracellular pH, or the transmembrane potential, or to induce an intracellular ATP depletion, we have shown that mobile ionophores as well as cyclosporin inhibit the P-glycoprotein-mediated efflux of 4'-O-tetrahydropyranyl-adriamycin in K562 resistant cells, whereas gramicidin, a channel-forming ionophore, does not. The concentration that must be used to inhibit 50% of the efflux was 0.7 microM for valinomycin, 0.4 microM for nonactin, 0.2 microM for nigericin, 1.1 microM for monensin, 0.4 microM for lasalocid, 1.2 microM for calcimycin and 0.4 microM for cyclosporin. Due to the high toxicity of the ionophores, the observation that they increased 4'-O-tetrahydropyranyl-adriamycin accumulation in the multidrug-resistant cells is not correlated with an effect of these compounds on drug resistance. However, the correlation exists in the case of cyclosporin. From our data showing that lipophilic neutral complexes, formed between carboxylic ionophores and metal ions, are both able to inhibit the P-glycoprotein-mediated efflux of anthracycline we can infer that the lipophilicity but not the cationic charge is an important physical property.
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PMID:Mobile ionophores are a novel class of P-glycoprotein inhibitors. The effects of ionophores on 4'-O-tetrahydropyranyl-adriamycin incorporation in K562 drug-resistant cells. 751 90

The emergence of multidrug resistance in tumor cells is caused by the expression of P-glycoprotein. P-glycoprotein has a unique structure formed by two homologous halves, each encoding six putative transmembrane segments and one nucleotide binding fold. This structural arrangement has been conserved in a large number of eukaryotic and prokaryotic membrane transport systems, which together form the ATP binding cassette superfamily. These membrane transporters act on different groups of substrates in different cell types and organisms. The combined molecular analysis of these proteins has shed light on the mechanism by which P-glycoprotein acts on structurally unrelated groups of chemotherapeutic drugs and has allowed the identification of the protein domain responsible for the common mechanism of transport and recognition of substrate molecules. The function of P-glycoprotein in normal tissues remains intriguing and is discussed in this review.
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PMID:Structural and functional aspects of P-glycoproteins and related transport proteins. 752 12

The aim of this study was to examine the peptide transport activity of a naturally occurring P-glycoprotein such as that present in rat liver canalicular membrane vesicles. The peptide ionophores valinomycin and gramicidin D, which are known substrates of P-glycoprotein, served to monitor the P-glycoprotein activity indirectly as the ATP-dependent uptake of 86Rb+ mediated by these ionophores. Canalicular membrane vesicles proved inherently permeable to K+ ions, which prevented assay of transport ionophore activity. Therefore, P-glycoprotein was extracted from canalicular membrane vesicles and reconstituted into proteoliposomes that are relatively impermeable to cations. P-glycoprotein activity in the proteoliposomes was dependent on ATP hydrolysis since it was not observed with non-hydrolyzable analogs of ATP. Maximal ATP-dependent 86Rb+ uptake occurred at 50 nM gramicidin D and at 500 nM valinomycin thus possibly reflecting higher affinity of P-glycoprotein for gramicidin D. Nigericin, which does not participate in the multidrug resistance phenomenon, did not support an ATP-dependent uptake of 86Rb+. ATP hydrolysis increased the amount of 86RB+ transported into the proteoliposomes. Furthermore, preincubation of the proteoliposomes in the presence of gramicidin D and 86Rb+, allowing for maximal ATP-independent 86Rb+ uptake to occur, did not interfere with subsequent ATP-dependent uptake, indicating the latter to constitute an active transport mechanism. The ATP-dependent component of 86Rb+ uptake occurred neither with liposomes nor with proteoliposomes reconstituted with proteins extracted from sinusoidal vesicles that lack P-glycoprotein. The ATP-dependent uptake was blocked by the known inhibitors of the ATPase activity associated with P-glycoprotein, oligomycin and vanadate, as well as by its established substrates, daunorubicin, doxorubicin, vinblastine, and the tripeptide N-acetyl-leucyl-leucyl-norleucinal. Thus, the reconstituted P-glycoprotein catalyzes the ATP-dependent 86Rb+ uptake that appears to occur by an energy-dependent translocation of the 86Rb(+)-ionophore complex. In this case, the actual substrate of P-glycoprotein is the ionophore-cation complex, which is both hydrophobic and positively charged as are most of the substrates of P-glycoprotein. This is the first demonstration of transport of a naturally occurring polypeptide by proteoliposomes reconstituted with physiologically expressed P-glycoprotein.
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PMID:Transport of polypeptide ionophores into proteoliposomes reconstituted with rat liver P-glycoprotein. 752

A few protein targets were found to display a specific high-affinity interaction with the immunosuppressant cyclosporin A (CsA): cytosolic cyclophilins (CyP)A, B, C, D, E containing from 122 to 174 amino acid residues in a polypeptide chain, and secreted forms of CyP; CyP-40, 40-kDa CsA-binding polypeptide complexed with steroid receptor (SR); CyP-related 150-kDa receptor of natural killer (NK) cells; interleukin 8 (IL-8); actin; a family of molecular chaperones hsp70 and P-glycoprotein (P-GP). All CyPs possess peptidyl-prolyl cis-trans isomerase activity (PPIase) and may serve as ATP-independent molecular chaperone proteins. The CsA-CyP complexes are specific inhibitors of Ca(2+)-and calmodulin-dependent protein phosphatase calcineurin (CaN). The inhibition of CaN blocks the activation of genes of IL-2, IL-2R, IL-4, etc. in T cells. In addition, immunosuppressive and/or antiinflammatory activity of CsA can be executed via CyP-40 and hsp 70 complexed with SR, and following the interaction with CyP-related receptor of NK and with IL-8. CsA binding to CyPC, P-GP and actin may throw light on the biochemical events leading to nephrotoxicity and graft vessel disease, two major side effects produced by CsA. The discovery of the interaction of human immunodeficiency virus type 1 (HIV-1) Gag protein with CyP and effective disruption of this interaction by CsA may be important for our understanding of the pathology caused by this immunosuppressive virus and will inspire therapeutic strategies to nip HIV in the bud. Bacterial immunophilins (ImPs) contribute to the virulence of pathogenic microorganisms. Elucidation of molecular mechanisms of microbial ImPs' action in the pathogenesis of bacterial infections may lead to new strategies for designing antibacterial drugs.
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PMID:Some new aspects of molecular mechanisms of cyclosporin A effect on immune response. 754 42

Multidrug resistance (MDR) in mammalian cells and tumors is associated with overexpression of an approximately 170 kDa integral membrane efflux transporter, the MDR1 P-glycoprotein. Hexakis (2-methoxyisobutyl isonitrile)technetium(I) (Tc-SESTAMIBI), a gamma-emitting lipophilic cationic metallopharmaceutical, has recently been shown to be a P-glycoprotein transport substrate. Exploiting the negligible lipid membrane adsorption properties of this organometallic substrate, we studied the transport kinetics, pharmacology, drug binding, and modulation of P-glycoprotein in cell preparations derived from a variety of species and selection strategies, including SW-1573, V79, Alex, and CHO drug-sensitive cells and in 77A, LZ-8, and Alex/A.5 MDR cells. Rapid cell accumulation (t1/2 approximately 6 min) of the agent to a steady state was observed which was inversely proportional to immunodetectable levels of P-glycoprotein. Many MDR cytotoxic agents inhibited P-glycoprotein-mediated Tc-SESTAMIBI efflux, thereby enhancing organometallic cation accumulation. Median effective concentrations (EC50; microM) were as follows: vinblastine, 13; daunomycin, 55; idarubicin, 65; actinomycin D, 235; colchicine, minimal inhibition; adriamycin, no effect. P-glycoprotein modulators generally demonstrated significantly greater potency (EC50; microM): SDZ PSC 833, 0.08; cyclosporin A, 1.3; verapamil, 4.1; quinidine, 6.4; prazosin, > 300. Modulator-induced enhancement up to 100-fold was observed with Hill coefficients approximately 1, consistent with simple Michaelis-Menten kinetics. Vanadate was an efficacious transport inhibitor, while agents usually not included in the MDR phenotype were without effect. Scatchard analysis showed quinidine to be a noncompetitive inhibitor of P-glycoprotein-mediated Tc-SESTAMIBI transport, indicating allosteric effector sites on P-glycoprotein. The lipid bilayer adsorbing agents tetraphenyl borate and phloretin induced large increases in final Tc-SESTAMIBI accumulation, showing maximal accumulations 2-fold greater than classic MDR modulators and Hill coefficients >> 2. In V79 and 77A cells, modulators of PKC activity altered Tc-SESTAMIBI accumulation, while there was no indication of modulation of P-glycoprotein-mediated Tc-SESTAMIBI transport by hypotonic buffer, extracellular ATP, Cl-, or K+ (membrane potential). While recognized and avidly transported by the P-glycoprotein at buffer concentrations as low as 7 pM, Tc-SESTAMIBI at up to 100 microM only minimally modulated the cytotoxic action of colchicine, doxorubicin, or vinblastine in MDR cells. In conclusion, transport analysis with Tc-SESTAMIBI is a sensitive assay for detecting functional expression of low levels of P-glycoprotein and for the quantitative characterization of transporter modulation and regulation. The biochemical data favor a high Km, high capacity allosterically modulated translocation mechanism for P-glycoprotein-mediated transport of this organometallic cation.
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PMID:Characterization of multidrug resistance P-glycoprotein transport function with an organotechnetium cation. 754 62

Canine lymphoma is a spontaneous, naturally occurring disease that is a model for non-Hodgkin's lymphoma in humans. Chemotherapy with antineoplastics results in a high rate of remission; however, relapse and clinical drug resistance are usually seen within 8-10 months. The P-glycoprotein product of the mdr gene is thought to function as an ATP-driven membrane drug efflux pump and appears to play an important role in tumor cell resistance. To assess the role of mdr gene products in drug resistance in canine lymphoma, membrane preparations of lymphoma cells from 31 dogs with high- or intermediate-grade lymphoma were subjected to Western blotting for detection of P-glycoprotein. In this study, one of 30 samples taken from dogs prior to receiving chemotherapy expressed detectable levels of P-glycoprotein. P-glycoprotein was also detected in biopsy samples from 3 of 8 dogs that had become resistant to chemotherapy. This pattern of expression is similar to that in human non-Hodgkin's lymphoma. These studies suggest that canine lymphoma is a useful model for studying multidrug resistance.
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PMID:The expression of P-glycoprotein in canine lymphoma and its association with multidrug resistance. 755 13

The ATPase activity of P-glycoprotein is inactivated by N-ethylmaleimide (NEM), which is postulated to modify cysteine residues within either of the homology A consensus sequences for nucleotide binding (GNSGCGKS and GSSGCGKS, respectively) (Al-Shawi, M. K., Urbatsch, I. L., and Senior, A. E. (1994) J. Biol. Chem. 269, 8986-8992). To test this postulate as well as determine the contribution of either nucleotide-binding domain to function, a Cys-less mutant was constructed, and then a single cysteine residue was reintroduced back into each nucleotide-binding consensus sequence. We then tested the sensitivity of the ATPase activity of each mutant to covalent modification by NEM. It was found that covalent modification of a single cysteine residue within either nucleotide-binding consensus sequence (Cys-431 and Cys-1074, respectively) with NEM inhibited drug-stimulated ATPase activity of P-glycoprotein. The concentrations of NEM required for half-maximal inactivation of ATPase activity were 7 and 35 microM for mutants Cys-431 and Cys-1074, respectively. In both cases, inactivation of ATPase activity by NEM was prevented by ATP. These results suggest that both nucleotide-binding domains may need to bind ATP to couple drug binding to ATPase activity.
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PMID:Covalent modification of human P-glycoprotein mutants containing a single cysteine in either nucleotide-binding fold abolishes drug-stimulated ATPase activity. 755 32

To study the molecular function of the multidrug-resistance gene product P-glycoprotein, we purified and reconstituted it into liposomes. Twelve detergents were examined in an attempt to solubilize and reconstitute the transport activity of K562/ADM membrane proteins containing P-glycoprotein. We found that transport activity was effective reconstituted after solubilization with cholate, glycocholate and taurocholate. Other detergents, such as CHAPS, Triton X-100 and deoxycholate, diminished the transport activity. The K562/ADM membrane was solubilized by 1% glycocholate, and P-glycoprotein was purified by MRK-16 immunoaffinity column chromatography to a homogeneous single band on sodium dodecyl sulfate/polyacrylamide gel electrophoresis. The purified P-glycoprotein was reconstituted by detergent dialysis into liposomes composed of phosphatidylcholine, phosphatidylethanolamine and phosphatidylserine. The reconstituted P-glycoprotein specifically bound [3H]azidopine and had an ATPase activity that was slightly stimulated when vincristine was added. Furthermore, though its activity was reduced, the reconstituted P-glycoprotein was shown to be an ATP-dependent transporter of vincristine.
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PMID:Reconstitution of purified P-glycoprotein into liposomes. 755 41


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