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)

Increased expression of P-glycoprotein, a plasma membrane glycoprotein of relative molecular mass (Mr) 170,000 (170K), occurs in a wide variety of cell lines that exhibit pleiotropic resistance to unrelated drugs. The presence of P-glycoprotein in human cancers refractory to chemotherapy suggests that tumour cells with multidrug resistance can arise during malignant progression. We have discovered striking homology between P-glycoprotein and the HlyB protein, a 66K Escherichia coli membrane protein required for the export of haemolysin (protein of Mr 107K). P-glycoprotein can be viewed as a tandem duplication of the HlyB protein. The hydropathy profiles of the two proteins are similar and reveal an extensive transmembrane region resembling those found in pore-forming plasma membrane proteins. The C-terminal region of P-glycoprotein and the HlyB protein contain sequences homologous to the nucleotide-binding domains of a group of closely related bacterial ATP-binding proteins. We propose a model for multidrug resistance in which P-glycoprotein functions as an energy-dependent export pump to reduce intracellular levels of anticancer drugs.
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PMID:Homology between P-glycoprotein and a bacterial haemolysin transport protein suggests a model for multidrug resistance. 287 68

170-180-kDa membrane glycoprotein (P-glycoprotein) associated with multidrug resistance is involved in drug transport mechanisms across the plasma membrane of resistant cells. From sequence analysis of cDNAs of the P-glycoprotein gene, it is postulated that the active drug-efflux pump function may be attributable to the protein. However, purification of the P-glycoprotein while preserving its enzymatic activity has not been reported. In this study, we have purified the P-glycoprotein from the human myelogenous leukemia K562 cell line resistant to adriamycin (K562/ADM) by means of one-step immunoaffinity chromatography using a monoclonal antibody against P-glycoprotein. The procedure was simple and efficiently yielded an electrophoretically homogeneous P-glycoprotein sample. By solubilization with 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate, the purified P-glycoprotein was found to have ATPase activity. This ATP hydrolysis may be coupled with the active efflux of anticancer drugs across the plasma membrane of multidrug-resistant cells.
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PMID:Purification of the 170- to 180-kilodalton membrane glycoprotein associated with multidrug resistance. 170- to 180-kilodalton membrane glycoprotein is an ATPase. 289 11

HL60 cells exhibiting a 140-fold increase in resistance to vincristine contain three surface membrane proteins with molecular weights of 210,000 (P210), 180,000 (P180), and 150,000 (P150) which are highly phosphorylated in vivo and in an in vitro system in the presence of Mn2+ and [gamma-32P]ATP. These phosphorylated proteins are either absent or present in very low levels in membranes of drug-sensitive cells. Growth of the vincristine-resistant isolate in the absence of drug results in a decrease in the level of resistance and a major reduction in the phosphorylation of P210 and P180. The phosphorylation of P150 is not altered in the revertant which still exhibits substantial levels of resistance. Further studies show that P210 and P180 are highly reactive with a monoclonal antibody against P-glycoprotein. These two proteins are present in only very low levels in revertant cells. The monoclonal antibody exhibits no reactivity with P150. In HL60 cells isolated for a 25-fold increase in vincristine resistance proteins reactive with P-glycoprotein monoclonal antibody are essentially absent. P150 is however highly phosphorylated in these cells. Additional experiments using lectin binding of 32P-labeled proteins demonstrates that P150 has properties distinct from P210 and P180. Analysis of drug uptake patterns in the vincristine-resistant isolates and the revertant shows that resistance is related to a reduced intracellular accumulation of drug. Reduced accumulation of vincristine is also found in HL60 cells isolated for resistance to Adriamycin. These cells are devoid of P-glycoprotein but contain phosphorylated P150. These results suggest that proteins P150, P180, and P210 may contribute to multidrug resistance in HL60 cells through a mechanism which involves reduced cellular accumulation of drug. P180 and P210 are structurally related whereas P150 is distinct from these two proteins.
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PMID:Mechanisms of multidrug resistance in HL60 cells: evidence that a surface membrane protein distinct from P-glycoprotein contributes to reduced cellular accumulation of drug. 289 87

An overexpression of plasma membrane 170-180 kDa P-glycoproteins is consistently found in multidrug-resistant (MDR) cell lines. In this study MRK-16, a monoclonal antibody (mAb) reacting with P-glycoprotein is used to study the putative functional role of this protein in vincristine (VCR) and daunorubicin (DNR) cellular accumulation in the MDR human ovarian carcinoma cell line 2780AD. We established that this cell line is highly cross-resistant to vincristine and daunomycin, related to a greatly reduced drug accumulation. Verapamil (Vp) (8 microM) caused a 3.6-fold increase in DNR as well as VCR accumulation. Exposition of 2780AD cells to MRK-16 led to an increase of 30% in cellular accumulation of VCR, both in normal growth medium as well as in medium without added glucose and with sodium azide, which largely depleted cellular ATP levels. No increase in DNR accumulation was found under these conditions. However, in the presence of 8 microM Vp, MRK-16 increased not only VCR but also DNR accumulation with about 30%. The relative increase of DNR accumulation was constant in a concentration range of 0.2-4 microM DNR. These data indicate that mAbs against P-glycoprotein might potentiate the action of calcium antagonists like Vp to increase cellular anthracycline accumulation.
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PMID:Increase of daunorubicin and vincristine accumulation in multidrug resistant human ovarian carcinoma cells by a monoclonal antibody reacting with P-glycoprotein. 289 43

The Mr 170,000 to 180,000 membrane glycoprotein associated with multidrug resistance (P-glycoprotein) is involved in drug transport mechanisms across the plasma membrane of multidrug-resistant cells. We have recently reported the purification of P-glycoprotein. The purified P-glycoprotein was found to have an ATPase activity, which might be coupled with the active efflux of anticancer drugs. In the present study, we have further studied the properties of the P-glycoprotein ATPase activity by an immobilized enzyme assay procedure using a P-glycoprotein-antibody-Protein A-Sepharose complex. GTP was also hydrolyzed by the P-glycoprotein, although less efficiently than ATP. The ATPase activity of P-glycoprotein had an optimal pH range around neutrality (pH 6.5-7.4). The detergent concentration of 3-[(3-cholamidopropyl)dimethyl-ammonio]-1-propane sulfonate used for protein solubilization was essential for enzyme recovery. Maximum activity was obtained when 0.1-0.2% 3-[(3-cholamidopropyl)dimethyl-ammonio]-propane sulfonate was used, while higher concentrations markedly inhibited the ATPase activity. The ATPase activity was dependent on Mg2+; maximum activity was obtained at 2-10 mM. Manganese and cobalt could substitute for magnesium as ionic cofactors. Divalent cations such as Ca2+, Zn2+, Ni2+, Cd2+, and Cu2+ inhibited the Mg2+-catalyzed ATP hydrolysis. N-Ethylmaleimide and vanadate inhibited the ATPase activity, while sodium azide or ouabain had no effect. Anticancer agents such as vincristine and Adriamycin did not affect the enzyme activity. In contrast, verapamil and trifluoperazine, agents which inhibit active drug efflux and restore drug sensitivity in resistant cells, caused an increase in the P-glycoprotein ATPase activity suggesting that P-glycoprotein might be the target molecule of these agents.
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PMID:Characterization of the ATPase activity of the Mr 170,000 to 180,000 membrane glycoprotein (P-glycoprotein) associated with multidrug resistance in K562/ADM cells. 290 Jun 77

MDR1 gene encodes a membrane glycoprotein (P-glycoprotein) that acts as a energy-dependent pump to transport antitumor drugs out of the cells. P-glycoprotein, 1280 amino acids long, consists of two homologous parts of approximately equal length. The protein has binding sites for ATP, antitumor drugs and calcium channel blockers. MDR1 gene is expressed tissue-specific in human normal adrenal, kidney, liver and colon. The normal function and transcriptional regulation of this gene are also discussed.
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PMID:[The multidrug-resistance gene MDR1]. 290 31

The brown gene of Drosophila melanogaster is required for deposition of pteridine pigments in the compound eye and other tissues. We isolated a ca. 150-kilobase region including brown by microdissection and chromosome walking using cosmids. Among the cDNAs identified by hybridization to the cosmids, one class hybridized to a genomic region that is interrupted in two brown mutants, bw and In(2LR)CK, and to 2.8- and 3.0-kilobase poly(A)+ RNAs which are altered in the mutants. Nucleotide sequencing of these cDNAs revealed that the two transcripts differ as a consequence of alternative poly(A) addition and that both encode the same predicted protein of 675 amino acids. Searches of available databases for amino acid sequence similarities detected a striking overall similarity of this predicted protein to that of the D. melanogaster white gene. The N-terminal portion aligned with the HisP family of membrane-associated ATP-binding proteins, most of which are subunits of active transport complexes in bacteria, and to two regions of the multidrug resistance P-glycoprotein. The C-terminal portion showed a structural similarity to integral membrane components of the same complexes. Taken together with earlier biochemical evidence that brown and white gene products are necessary for uptake of a pteridine precursor and genetic evidence that brown and white proteins interact, our results are consistent with suggestions that these proteins are subunits of a pteridine precursor permease.
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PMID:The brown protein of Drosophila melanogaster is similar to the white protein and to components of active transport complexes. 314 12

Resistance of human cancer cells to multiple cytotoxic hydrophobic agents (multidrug resistance) is due to overexpression of the "MDR1" gene, whose product is the plasma membrane P-glycoprotein. Plasma membrane vesicles partially purified from multidrug-resistant human KB carcinoma cells, but not from drug-sensitive cells, accumulate [3H]vinblastine in an ATP-dependent manner. This transport is osmotically sensitive, with an apparent Km of 38 microM for ATP and of approximately equal to 2 microM for vinblastine. The nonhydrolyzable analog adenosine 5'-[beta, gamma-imido]triphosphate does not substitute for ATP but is a competitive inhibitor of ATP for the transport process. Vanadate, an ATPase inhibitor, is a potent noncompetitive inhibitor of transport. These results indicate that hydrolysis of ATP is probably required for active transport of vinblastine. Several other drugs to which multidrug-resistant cell lines are resistant inhibit transport, with relative potencies as follows: vincristine greater than actinomycin D greater than daunomycin greater than colchicine = puromycin. Verapamil and quinidine, which reverse the multidrug-resistance phenotype, are good inhibitors of the transport process. These results confirm that multidrug-resistant cells express an energy-dependent plasma membrane transporter for hydrophobic drugs, and establish a system for the detailed biochemical analysis of this transport process.
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PMID:ATP-dependent transport of vinblastine in vesicles from human multidrug-resistant cells. 336 66

1. P-glycoprotein, the protein product of the multidrug resistance (MDR1) gene, has ATP-dependent transporter activity. It has been suggested that P-glycoprotein may also function as a volume-regulated chloride channel or chloride channel regulator. To assess the chloride channel function of P-glycoprotein, we examined swelling-activated chloride conductances in Xenopus oocytes injected with human MDR1 cRNA. 2. Functional expression of P-glycoprotein in Xenopus oocytes was confirmed using Western blot analysis and by assessing transport of the P-glycoprotein substrate, calcein AM. 3. Endogenous, swelling-activated chloride conductances were virtually absent by the time P-glycoprotein expression was confirmed. Thus, this expression system afforded the advantage of assessing putative MDR1-associated chloride currents in the absence of background currents. 4. The currents activated by hypotonic shock (50%) in both MDR1-injected and control (water-injected) oocytes were not significantly different. The swelling response was due in part to the activation of a potassium-selective conductance which could be inhibited by barium. No chloride-selective currents were activated by hypotonic shock in the presence or absence of barium. Therefore, we conclude that P-glycoprotein expression does not produce a swelling-activated chloride conductance in the Xenopus oocyte expression system.
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PMID:Failure of P-glycoprotein (MDR1) expressed in Xenopus oocytes to produce swelling-activated chloride channel activity. 747 31

The nucleotide sequence of the Bacillus licheniformis bacitracin-resistance locus was determined. The presence of three open reading frames, bcrA, bcrB and bcrC, was revealed. The BcrA protein shares a high degree of homology with the hydrophilic ATP-binding components of the ABC family of transport proteins. The bcrB and bcrC genes were found to encode hydrophobic proteins, which may function as membrane components of the permease. Apart from Bacillus subtilis, these genes also confer resistance upon the Gram-negative Escherichia coli. The presumed function of the Bcr transporter is to remove the bacitracin molecule from its membrane target. In addition to the homology of the nucleotide-binding sites, BcrA protein and mammalian multidrug transporter or P-glycoprotein share collateral detergent sensitivity of resistant cells and possibly the mode of Bcr transport activity within the membrane. The advantage of the resistance phenotype of the Bcr transporter was used to construct deletions within the nucleotide-binding protein to determine the importance of various regions in transport.
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PMID:Bacillus licheniformis bacitracin-resistance ABC transporter: relationship to mammalian multidrug resistance. 747 93


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