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

P-glycoproteins are responsible for multidrug resistance in tumor cell lines and are thought to have a physiologic role in exporting cellular metabolites. We now report that a P-glycoprotein gene in the H region of the trypanosomatid protozoan Leishmania confers resistance to heavy metals when present in multiple copies. The Leishmania H region is frequently amplified in drug-resistant lines and is associated with metal resistance. Leishmania expression vectors were used to introduce multiple copies of segments of the Leishmania major H region into wild-type L. major promastigotes. Only constructs bearing a segment of L. major DNA containing the P-glycoprotein lmpgpA conferred arsenite resistance. Deletional analysis of the arsenite-resistant construct mapped resistance to the lmpgpA protein coding region. Lines expressing lmpgpA showed resistance to arsenite and trivalent antimonials, but not to pentavalent antimonials, zinc, cadmium, or the typical multidrug-resistant P-glycoprotein substrates vinblastine and puromycin. Transfection of the Leishmania tarentolae P-glycoprotein homologue ltpgpA resulted in a similar resistance profile. Thus, these pgpAs represent a functionally distinct group of P-glycoproteins which exhibit a substrate specificity similar to prokaryotic heavy metal pumps. Additionally, several arguments suggest that pgpAs may play a role in the susceptibility of Leishmania to clinically utilized antimonials.
 ...
PMID:Heavy metal resistance: a new role for P-glycoproteins in Leishmania. 168 Aug 61

The mdr gene, which encodes an energy-dependent multidrug efflux pump termed P-glycoprotein, is expressed in some normal human and rodent tissues, including the adrenal gland, kidney, liver, colon, small intestine, and brain and testis capillary endothelial cells. Because of the important role played by the multidrug transporter in determining sensitivity of normal tissues and resistance of cancers to chemotherapeutic drugs, we and others have been determining the environmental factors which regulate expression of the mdr gene. In previous studies, expression of the human MDR1 gene has been shown to be regulated by heat shock, arsenite, and cadmium in a kidney carcinoma cell line, and mdr RNA is dramatically elevated in rat liver after partial hepatectomy or treatment of the animals with cytotoxic agents. We have now investigated the genetic response of the mdr gene to acute cytotoxic insults in rodent and human tissue culture cells. Following exposure to several drugs, most of which are known to be substrates for the multidrug transporter, mdr RNA levels were found to increase substantially in the rodent cells, but not the human cells. Furthermore, RNA levels for topoisomerase II, an intracellular target for these drugs, decreased in the rodent cells. These results suggest a complex pattern of regulation of mdr RNA levels, depending on animal species and cell type, and possible coordinate regulation with topoisomerase II RNA levels.
 ...
PMID:Regulation of mdr RNA levels in response to cytotoxic drugs in rodent cells. 170 76

The multidrug transporter, initially identified as a multidrug efflux pump responsible for resistance of cultured cells to natural product cytotoxic drugs, is normally expressed on the apical membranes of excretory epithelial cells in the liver, kidney, and intestine. This localization suggests that the multidrug transporter may have a normal physiological role in transporting cytotoxic compounds or metabolites. In the liver, hepatectomy or treatment with chemical carcinogens increases expression of the MDR1 gene which encodes the multidrug transporter. To evaluate conditions which increase MDR1 gene expression, we have investigated the induction of the MDR1 gene by physical and chemical environmental insults in the renal adenocarcinoma cell line HTB-46. There are two strong heat shock consensus elements in the major MDR1 gene promoter. Exposure of HTB-46 cells to heat shock, sodium arsenite, or cadmium chloride led to a 7- to 8-fold increase in MDR1 mRNA levels. MDR1 RNA levels did not change following glucose starvation or treatment with 2-deoxyglucose and the calcium ionophore A23187, conditions which are known to activate the expression of another family of stress proteins, the glucose-regulated proteins. The levels of the multidrug transporter, P-glycoprotein, as measured by immunoprecipitation, were also increased after heat shock and sodium arsenite treatment. This increase in the level of the multidrug transporter in HTB-46 cells correlated with a transient increase in resistance to vinblastine following heat shock and arsenite treatment. These results suggest that the MDR1 gene is regulatable by environmental stress.
 ...
PMID:Heat shock and arsenite increase expression of the multidrug resistance (MDR1) gene in human renal carcinoma cells. 196 74

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.
 ...
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

Acquired resistance to tetraplatin [d,1-trans-1,2-diaminocy-clohexane tetrachloroplatinum (IV)] has been generated in vitro in the human ovarian carcinoma cell line PXN94; the derived line, PXN94tetR, was 24-fold resistant to tetraplatin. Intracellular tetraplatin accumulation was reduced in PXN94tetR compared with PXN94 by an average of 1.3-fold across the concentration range 1-100 microM (2 hr exposure). There was no significant difference in glutathione levels between the 2 cell lines. PXN94tetR was 1.6-fold more resistant to cadmium chloride than PXN94, suggesting that metallothionein levels may be elevated. However, no significant difference was observed between PXN94 and PXN94tetR in the levels of total platinum bound to DNA or DNA interstrand cross-links immediately after tetraplatin exposure (10-100 microM x 2 hr). There was also no significant difference between the 2 cell lines in the rate of removal of total platinum or interstrand cross-links from DNA following 2 hr exposure to 25 microM tetraplatin. Hence the major mechanism of acquired tetraplatin resistance in PXN94tetR appears to be increased tolerance of platinum-DNA adducts. PXN94tetR was partially cross-resistant to the bifunctional alkylating agents melphalan, chlorambucil and mitomycin C. Partial cross-resistance was also observed to Adriamycin, bleomycin, etoposide, 5-fluorouracil and vinblastine; however, no elevation in P-glycoprotein levels was apparent in PXN94tetR. No cross-resistance was observed to taxotere. PXN94tetR was partially cross-resistant to cisplatin, carboplatin and several novel cis platinum complexes. In contrast, resistance was completely circumvented by the novel trans platinum complex JM335 [trans ammine (cyclohexylamine) dichloro dihydroxo platinum (IV)].
 ...
PMID:Circumvention of acquired tetraplatin resistance in a human ovarian carcinoma cell line by a novel trans platinum complex, JM335 [trans ammine (cyclohexylamine) dichloro dihydroxo platinum (IV)]. 792 6

The aim of this study was to characterize two cis-diamminedichloroplatinum(II) (CDDP) resistant cell lines established from human larynx carcinoma HEp2 cells through repeated treatments with increased CDDP concentrations. CK2 cells obtained by continuous treatments were more resistant to CDDP than CA3 cells obtained by acute treatments. The examination of growth characteristics showed that both CDDP resistant cells had doubling times identical to that of the parental cells, but had lower plating efficiency. The possible involvement of glutathione (GSH), glutathione transferases (GST), metallothioneins, P-glycoprotein and drug accumulation in CDDP resistance was examined. Glutathione contents were elevated in both CDDP resistant lines. However, neither GSH nor GST were involved in CDDP resistance. This was demonstrated by simultaneous incubation of parental and CDDP resistant cells with CDDP and specific inhibitors of GSH and GST alpha and pi (buthionine sulfoximine and ethacrinic acid). Similarly, verapamil, an inhibitor of P-glycoprotein, did not influence the sensitivity of parental and resistant cells to CDDP. As compared to the parental cells, CK2 cells became resistant and CA3 cells became sensitive to cadmium, indicating increased level of metallothioneins in CK2 cells, and reduced level in CA3 cells. Measurements of platinum contents in parental and CDDP resistant cells after 1, 3 and 6 hours exposure to 70 mumol CDDP showed reduction in platinum accumulation after each exposure time in CK2 cells, and after 6 hours exposure in CA3 cells. This study identified decreased platinum accumulation as an important mechanism of CDDP resistance in human larynx carcinoma cells.
 ...
PMID:Human larynx carcinoma cells resistant to cis-diamminedichloroplatinum(II): mechanisms involved in the resistance. 793 85

We have previously identified and characterized a novel member of the ATP-binding cassette superfamily of transport proteins, multidrug resistance protein (MRP), and subsequently demonstrated that its overexpression is sufficient to confer multidrug resistance on previously sensitive cells (Cole et al., Science (Washington DC), 258: 1650-1654, 1992; Grant et al., Cancer Res. 54: 357-361, 1994). In the present study, we have transfected two different eukaryotic expression vectors containing MRP complementary DNA into HeLa cells to study the pharmacological phenotype produced exclusively by overexpression of human MRP. The drug resistance patterns of the two MRP-transfected cell populations were similar. They were characterized by a moderate (5- to 15-fold) level of resistance to doxorubicin, daunorubicin, epirubicin, vincristine, and etoposide, and a low (< or = 3-fold) level of resistance to taxol, vinblastine, and colchicine. The transfectants were not resistant to 9-alkyl anthracyclines, mitoxantrone, or cisplatin. The MRP-transfected cells were also resistant to some heavy metal anions including arsenite, arsenate, and trivalent and pentavalent antimonials but were not resistant to cadmium chloride. Accumulation of radiolabeled vincristine was reduced by 45% in the MRP-transfected cells and could be restored to the levels found in sensitive cells by depletion of ATP. Rates of vincristine efflux did not differ greatly in the sensitive and resistant cells. The cytotoxic effects of vincristine and doxorubicin could be enhanced in a dose-dependent fashion by coadministration of verapamil. Cyclosporin A also increased vincristine toxicity but had less effect on doxorubicin toxicity. The degree of chemosensitization by verapamil and cyclosporin A was similar in MRP-transfected cells and in cells transfected with the vector alone, suggesting that sensitization involved mechanisms independent of MRP expression. Verapamil and cyclosporin A caused a modest increase in vincristine accumulation in the resistant cells but did not restore levels to those of the sensitive cells. Taken together, these data indicate that drug-resistant cell lines generated by transfection with MRP complementary DNA display some but not all of the characteristics of MRP-overexpressing cell lines produced by drug selection in vitro. They further demonstrate that the multidrug resistance phenotype conferred by MRP is similar but not identical to that conferred by P-glycoprotein and includes resistance to arsenical and antimonial oxyanions.
 ...
PMID:Pharmacological characterization of multidrug resistant MRP-transfected human tumor cells. 795 21

We previously found that human cervix carcinoma HeLa cells irradiated with multiple fractions of gamma rays (0.5 Gy daily, five times per week over 6 weeks) become resistant to cis-dichlorodiammineplatinum(II) (cis-DDP), methotrexate (MTX) and vincristine (VCR), but retain the same sensitivity to gamma rays or UV light. In the present report attempts were made to elucidate the mechanisms by which these cells have acquired resistance to cis-DDP and VCR. The sensitivity to different drugs was measured by modified MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) method. Neither buthionine sulfoximine (BSO) nor ethacrinic acid were able to reverse the resistance of preirradiated cells to cis-DDP. Therefore, neither the increased levels of glutathione nor glutathione transferase seem to be involved in resistance to cis-DDP. Preirradiated cells did show resistance to cadmium, indicating the increased levels of metallothioneins in these cells. Resistance of preirradiated cells to vincristine was abolished by the addition of verapamil, indicating that resistance to this drug may depend on the increased expression of plasma membrane P-glycoprotein. It was concluded that mechanisms of resistance of preirradiated cells to cytostatics are multifactorial and involve at least the increased levels of metallothioneins and changes in the plasma membrane. Acquired resistance to cytotoxic drugs induced by preirradiation may be the reason for the reduced response to these drugs after radiation treatment of certain tumors.
 ...
PMID:Multifactorial molecular mechanisms are involved in resistance of preirradiated human cervix carcinoma cells to cis-dichlorodiammineplatinum (II) and vincristine. 810 78

We report the characterization of the pfmdr2 gene which is a gene related to the P-glycoprotein family but with a somewhat different structure than the mdr genes. Based on DNA sequence analysis of genomic clones, we have discovered that the pfmdr2 gene has 10 predicted transmembrane domains and a single ATP-binding site. In a homology search using GenBank sequences, we discovered that the pfmdr2 gene has a significant homology with the hmt1 gene in yeast. The yeast hmt1 gene is involved in cadmium resistance and is hypothesized to transport cadmium containing complexes from the cell. We have further characterized the pfmdr2 gene expression by northern analysis and discovered that it is expressed in a stage-specific manner, only at the trophozoite stage and not in ring stages. We have prepared a rabbit antibody to a recombinant fusion protein expressing a portion of the pfmdr2 coding region. In IFA analysis, this antibody stains trophozoites and not ring stages. Western analysis reveals a protein of approximately 110 kDa which is consistent with the size of the predicted open reading frame based on DNA sequence analysis. Based on this analysis and previous work, there is no evidence for a change in pfmdr2 expression in drug-resistant versus drug-sensitive parasites.
 ...
PMID:Characterization of the pfmdr2 gene for Plasmodium falciparum. 791 76

In vitro, overexpression of the human multidrug-resistance protein (MRP) causes a form of multidrug resistance similar to that conferred by P-glycoprotein, although the two proteins are only very distantly related. Studies with MRP-enriched membrane vesicles have demonstrated that the protein can bind and transport cysteinyl leukotrienes, as well as some other glutathione conjugates, with high affinity. In contrast, there is no direct evidence of the ability of MRP to bind or transport unmodified forms of the drugs to which it confers resistance. To facilitate studies of the physiological function(s) of MRP and its ability to cause multidrug resistance in vivo, we cloned and characterized the mRNA specifying its murine homolog. The murine MRP mRNA encodes a protein of 1528 amino acids that is 88% identical to human MRP. Although detectable by Northern blotting at variable levels in a wide range of tissues, in situ hybridization experiments revealed that MRP mRNA expression in some tissues is cell-type specific. High levels of the mRNA were detected in epithelia lining bronchi and bronchioles, as well as stage-specific expression in the seminiferous epithelium of the testes. Comparison of the predicted hydropathy profiles of human and murine MRP suggests a highly conserved membrane topology, the most distinctive feature of which is an extremely hydrophobic NH2-terminal region containing five or six potential transmembrane sequences. This structural feature is shared with the sulfonylurea receptor and the yeast cadmium factor 1 but is not present in members of the superfamily, such as the cystic fibrosis transmembrane conductance regulator and P-glycoproteins. Finally, we used overlapping cDNAs to construct an episomally replicating murine MRP expression vector that was stably transfected into HeLa cells. MRP-Transfected cell populations expressed markedly elevated levels of a 180-190-kDa protein that cross-reacted with a polyclonal antiserum raised against a peptide that is completely conserved in murine and human MRPs. The MRP transfectants also displayed increased resistance to vincristine (5-6-fold) and doxorubicin (< 2-fold).
 ...
PMID:Structure and expression of the messenger RNA encoding the murine multidrug resistance protein, an ATP-binding cassette transporter. 864 56


1 2 3 4 Next >>