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)

Multidrug resistance phenotypes in human tumours are associated with the overexpression of the 170 kDa P-glycoprotein encoded by the multidrug resistance 1 (MDR1) gene, and also with that of the non-P-glycoprotein-mediated multidrug resistance gene, MRP, which encodes a 190 kDa membrane ATP-binding protein. We have previously reported that overexpression of MRP appears to be responsible for spontaneous multidrug resistance in some human glioma cell lines (Abe et al., Int. J. Cancer, 58, 860-864, 1994). In this study, we investigated whether chemosensitising agents of P-glycoprotein-mediated multidrug resistance such as verapamil, a biscoclaurine alkaloid (cepharanthine), and a dihydropyridine analogue (NIK250) could also reverse multidrug resistance in human glioma cells. The glioma cell lines were the two MRP-expressing cell lines, T98G and IN500, an MDR1-expressing cell line, CCF-STTG1, and the MRP1 MDR1-non-expressing cell line, IN157. Verapamil and NIK250 almost completely reversed drug resistance to vincristine, etoposide and doxorubicin in T98G cells, while they also reversed drug resistance to vincristine and etoposide, but only partially to doxorubicin in IN500 cells. Cepharanthine as well as verapamil and NIK250 reversed vincristine resistance in CCF-STTG1 cells, but cepharanthine only partially reversed drug resistance in T98G and IN500 cells. The cellular accumulation of [3H]etoposide increased about 2- and 3-fold compared with control in T98G cells in the presence of verapamil and NIK250 respectively. Furthermore, the release of doxorubicin from the nuclei of T98G cells was blocked by NIK250. However, NIK250 and verapamil caused no apparent increase in vincristine accumulation in T98G cells. NIK250 or verapamil might exert inhibitory effects upon MRP function, resulting in a reversal of MRP-mediated spontaneous multidrug resistance in cultured human glioma cells.
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PMID:Chemosensitisation of spontaneous multidrug resistance by a 1,4-dihydropyridine analogue and verapamil in human glioma cell lines overexpressing MRP or MDR1. 764 Feb 27

P-glycoprotein (Pgp or multidrug-resistance protein) shows drug-stimulated ATPase activity. The catalytic sites are known to be of low affinity and specificity for nucleotides. From the sequence, two nucleotide sites are predicted per Pgp molecule. Using plasma membranes from a multidrug-resistant Chinese hamster ovary cell line, which are highly enriched in Pgp, we show that vanadate-induced trapping of nucleotide at a single catalytic site produces stably inhibited Pgp, with t 1/2 for reactivation of ATPase activity of 84 min at 37 degrees C and >30 h at 4 degrees C. Reactivation of ATPase correlated with release of trapped nucleotide. Concentrations of MgATP and MgADP required to produce 50% inhibition were 9 and 15 microM, respectively, thus the apparent affinity for nucleotide is greatly increased by vanadate-trapping. The trapped nucleotide species was ADP. Divalent Cation was required, with magnesium, manganese, and cobalt all effective: cobalt yielded a very stable inhibited species, t1/2 at 37 degrees C = 18 h. No photocleavage of Pgp was observed after vanadate trapping with MgATP, nor was UV-induced photolabeling of Pgp by trapped adenine nucleotide observed. Vanadate-trapping with 8-azido-ATP followed by UV irradiation caused permanent inactivation and specific labeling of Pgp. Vanadate-induced inhibition was also shown with pure, reconstituted Pgp, with similar characteristics to those in plasma membranes. Vanadate trapping overcomes technical difficulties posed by lack of high affinity nucleotide-binding site(s) or a covalent enzyme-phosphate catalytic intermediate in Pgp. The finding that vanadate trapping of nucleotide at just one site/Pgp is sufficient to give full inhibition at ATPase activity shows that the two predicted nucleotide sites can not function independently as catalytic sites.
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PMID:P-glycoprotein is stably inhibited by vanadate-induced trapping of nucleotide at a single catalytic site. 764 18

In malignant cells multidrug resistance (MDR) is frequently associated with the expression of a 170 KDa P-glycoprotein (P-gp) in the plasma membrane. P-gp acts as an ATP-dependent efflux pump causing a decreased intracellular accumulation of structurally unrelated natural anticancer agents such as anthracyclines. Doxorubicin (DX) resistance is mostly related to the multidrug resistance gene product P-gp. In our experiments the revertant activity of medroxyprogesterone acetate (MPA) in comparison to that of the well known revertant agent verapamil (VRP) was investigated. In vitro tests were carried out on a DX-resistant variant (CG5/DX) obtained in our laboratory from the parental CG5 human breast cancer cell line by continuous exposure to the drug. The ability of MPA to modulate intracellular DX accumulation and to reverse MDR was evaluated. MPA appeared more active than VRP in reversing MDR, suggesting a possible role of this synthetic progestin as chemosensitizing agent in the clinical management of anthracycline-resistant breast cancer.
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PMID:Medroxyprogesterone-acetate reverses the MDR phenotype of the CG5-doxorubicin resistant human breast cancer cell line. 764 52

Glucocorticoid hormones cause apoptosis in the murine T-lymphoma cell line WEHI-7. Glucocorticoid receptors in these cells are cytoplasmic proteins that translocate to the nucleus upon binding hormone. Thus, regulation of cytoplasmic glucocorticoid concentrations controls the level of activated receptors and sensitivity to steroid-induced apoptosis. We found that expression of the mdr1 P-glycoprotein gene produces a reduced accumulation of dexamethasone in WEHI-7 cells. Concomitantly, there is a suppression of dexamethasone-induced changes in transcription and a decrease in steroid sensitivity. P-glycoproteins are known to cause an outward, ATP-dependent transport of a variety of unrelated hydrophobic drugs across the plasma membrane. Our results indicate that glucocorticoid transport by P-glycoproteins depends upon the presence of an hydroxyl group at position 11 of corticosteroids and is enhanced by hydroxyl groups at the positions 16, 17, and 21. The antiprogestin RU486, which contains a dimethyl aminophenyl substitution at the position 11, is not transported by the mdr1 P-glycoprotein. We have found that RU486 is an inhibitor of P-glycoprotein function, indicating that steroid analogs could be useful chemosensitizers in patients undergoing chemotherapy.
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PMID:Expression of the mdr1 P-glycoprotein gene: a mechanism of escape from glucocorticoid-induced apoptosis. 765 29

WEHI-3B/NOVO is a cloned murine leukemia cell line selected for resistance to novobiocin that is cross-resistant to the cytotoxic action of etoposide (VP-16) and to a lesser extent to a variety of other topoisomerase II (topo II)-reactive drugs. We have reported previously (Cancer Res. 52: 2782-2790, 1992) that WEHI-3B/NOVO cells exhibit a pronounced decrease in VP-16 induced DNA-topo II cross-link formation compared to the parental WEHI-3B/S cell line in intact cells, in the absence of a significant difference in the P4 unknotting activity of topo II assayed in nuclear extracts. Because the pattern of cross-resistance was suggestive of a topo II-mediated mechanism, we have ascertained whether a change in topo II can account for the multidrug-resistant phenotype of WEHI-3B/NOVO cells. No differences existed between WEHI-3B/S and WEHI-3B/NOVO cells in topo II mRNA and protein levels, as well as in the amount of topo II associated with the nuclear matrix. Neither sensitive nor resistant cells expressed detectable levels of the MDR1 gene; however, VP-16 accumulation in WEHI-3B/NOVO cells was 3-4-fold less than that present in WEHI-3B/S cells, whereas doxorubicin accumulation was the same in both cell lines. Over the first 60 s, no difference existed in the rate of uptake of VP-16 between parental and resistant cells; however, beyond the first 60 s of incubation, [3H]VP-16 accumulated to a greater extent in parental sensitive cells. Thus, an increased rate of efflux of VP-16 was responsible for the lower steady-state concentration of the drug in resistant cells. The efflux Km for VP-16 in WEHI-3B/NOVO cells was 254.7 microM and the Vmax was 10.4 pmol/s/10(7) cells. In the presence of the inhibitors of energy metabolism, sodium azide and deoxyglucose, the efflux of VP-16 was markedly inhibited; readdition of glucose restored the original efflux rate. Northern blot analyses using the human 10.1 probe for the 3'-terminal region of the multidrug-resistance protein (MRP) cDNA revealed a mRNA species of approximately 6 kb in WEHI-3B/NOVO cells but not in WEHI-3B/S cells. Overexpression was associated with amplification of the cognate gene. To ascertain whether the overexpressed gene in WEHI-3B/NOVO cells was the murine MRP or a different member of the same superfamily of ATP-binding ABC cassette transporters, a 341-bp MRP cDNA probe was generated from a murine genomic library.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Increased rate of adenosine triphosphate-dependent etoposide (VP-16) efflux in a murine leukemia cell line overexpressing the multidrug resistance-associated protein (MRP) gene. 767 Dec 47

The multidrug resistance (mdr1) gene product, P-glycoprotein, is responsible for the ATP-dependent extrusion of a variety of compounds, including chemotherapeutic drugs, from cells. The data presented here show that cells with increased levels of the P-glycoprotein release ATP to the medium in proportion to the concentration of the protein in their plasma membrane. Furthermore, measurements of whole-cell and single-channel currents with patch-clamp electrodes indicate that the P-glycoprotein serves as an ATP-conducting channel in the plasma membrane. These findings suggest an unusual role for the P-glycoprotein.
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PMID:The multidrug resistance (mdr1) gene product functions as an ATP channel. 767 45

The possible role of Cl- currents in regulatory volume decrease processes has been explored in HeLa cells using the whole-cell recording mode of the patch-clamp technique. Cells showed very small currents in voltage-clamp experiments performed with Cl(-)-rich, permeant-cation-free (N-methyl-D-glucamine replacement) intracellular and bathing solutions. Exposure of the cells to hypotonic solutions visibly swelled the cells and activated, reversibly, an outward rectifying Cl- current, which decayed at the most depolarised voltages used. Replacement of extracellular Cl- by a series of halide anions, SCN- and gluconate was consistent with an anion selectivity sequence: SCN- > I- > Br- > Cl- > F- > gluconate. The volume-regulated Cl- current was effectively inhibited by 100 microM 5-nitro-2-(3-phenyl-propylamino)-benzoic acid and by 100 microM 4,4'-diisothiocyanotostilbene-2,2-disulphonic acid, substances known to block Cl- channels in a variety of cells. Chloride current activation by hypotonicity was dependent on the presence of ATP in the intracellular solution and this requirement could be replaced by the non-hydrolysable analogue ATP[gamma S] and Mg(2+)-free ATP. The data suggest that the channels responsible for the current described are involved in the regulatory volume decrease in HeLa cells. The characteristics of this Cl- current are similar to those of the current associated with expression of multidrug resistance P-glycoprotein. Furthermore, the currents in HeLa cells were inhibited rapidly and reversibly by verapamil and 1,9-dideoxyforskolin, which are known to inhibit P-glycoprotein function.
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PMID:Volume-activated chloride channels in HeLa cells are blocked by verapamil and dideoxyforskolin. 767 91

A M(r) 110,000 protein (p110) is overexpressed in P-glycoprotein-negative multidrug-resistant tumor cell lines of different histogenetic origins. These cell lines show an ATP-dependent drug accumulation defect, suggesting the presence of drug transporter molecules different from P-glycoprotein. Immunohistochemical staining with a p110-specific monoclonal antibody (LRP-56) showed that, like P-glycoprotein, the molecule has a high expression in normal epithelial cells and tissues chronically exposed to xenobiotics and potentially toxic agents, such as bronchial cells, cells lining the intestines, and kidney tubules. Staining of LRP-56 is primarily cytoplasmic, in a coarsely granular fashion, indicating that it reacts with a molecule closely associated with vesicular/lysosomal structures. Involvement of p110 in the energy-dependent drug transport process present in the cell lines is unknown.
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PMID:Overexpression of a M(r) 110,000 vesicular protein in non-P-glycoprotein-mediated multidrug resistance. 768 Sep 54

The cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel requires both phosphorylation of its R domain and the presence of nucleoside triphosphates for activation. Our previous work suggested that hydrolysis of nucleoside triphosphates may be required to support channel activity. However, recent studies have suggested that the nonhydrolyzable adenosine triphosphate analogue, 5'-adenylylimidodiphosphate (AMP-PNP), may support some Cl- channel activity in sweat gland duct epithelia in the presence of low ATP concentration and in Cl- channels associated with expression of the P-glycoprotein multidrug resistance transporter. To examine the effect of AMP-PNP, we applied it to the cytosolic surface of phosphorylated CFTR Cl- channels contained in excised, cell-free patches of membrane. We found that preparations of 10 mM AMP-PNP opened phosphorylated CFTR Cl- channels. However, this effect was due to contaminating ATP: high-pressure liquid chromatography analysis of AMP-PNP demonstrated that 10 mM AMP-PNP could contain up to 50 microM ATP, which could account for the observed stimulation of CFTR Cl- channel activity. When contaminating ATP was hydrolyzed with hexokinase, AMP-PNP was unable to support CFTR channel activity. AMP-PNP (10 mM) also failed to attenuate or potentiate the current induced by 0.3 mM ATP. These results suggest that AMP-PNP has no direct effect on CFTR Cl- channels.
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PMID:5'-Adenylylimidodiphosphate does not activate CFTR chloride channels in cell-free patches of membrane. 768 26

Human MDR1 cDNA was introduced into the human cultured cells KB-3-1 and Schizosaccharomyces pombe pmd1 null mutant KN3. The drug sensitivity of KB-G2 and KN3/pgp, expressing human P-glycoprotein, was examined. KB-G2 was resistant to the peptide antibiotics valinomycin and gramicidin D as well as having a typical multidrug resistance (MDR) phenotype. KN3/pgp was resistant to valinomycin and actinomycin D, but not to adriamycin. The ATP-hydrolysis-deficient mutant did not confer KN3 resistance to these antibiotics. Human P-glycoprotein expressed in S. pombe seemed to lack N-glycosylation. The N-glycosylation-deficient mutant, however, conferred a typical MDR phenotype on KB-3-1. These results suggest that human P-glycoprotein functions as an efflux pump of valinomycin and actinomycin D in the membrane of S. pombe.
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PMID:Functional expression of human P-glycoprotein in Schizosaccharomyces pombe. 769 Jul 15


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