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)

First-step Adriamycin (doxorubicin)-resistant mutants of the murine erythroleukemia cell line PC4 were cloned from Adriamycin-containing (10 ng/ml) methylcellulose at a frequency of 3 x 10(-4). They demonstrated 1.6- to 2.4-fold stable resistance to Adriamycin. Most were cross-resistant to etoposide, but not to vincristine, and were without enhanced expression of mdr genes, which code for P-glycoproteins. Two different murine erythroleukemia cell lines, PC4 and C7D, were passaged in suspension culture into stepwise increasing amounts of Adriamycin. No high-level resistant mutants were isolated de novo; cells initially displayed low-level resistance to Adriamycin and etoposide. Two stepwise doublings of the drug concentration were needed before PC4 cells acquired vincristine resistance, but there was no detectable overexpression of mdr or a change in anthracycline uptake. In a subsequent doubling of Adriamycin concentration, the cells showed a further increase in resistance to all three drugs and now a decreased anthracycline accumulation. However, there was still no detectable increase in mdr expression as judged by Northern analysis of poly(A)+ enriched RNA and Western blot analysis of membrane proteins. Only after a fourth doubling of Adriamycin concentration did the cells demonstrate enhanced expression of mdr and P-glycoprotein. Equivalent mutants of C7D were selected, but generally at lower Adriamycin concentrations. Verapamil partially lowered resistance, but failed to restore parental susceptibility in any mutant; it caused an increased uptake in those mutants showing decreased anthracycline accumulation, including those that did not overexpress mdr. This study demonstrated different resistance phenotypes among mutants appearing spontaneously under stepwise drug selection; mutants with vincristine resistance and decreased anthracycline uptake preceded those associated with over-expression of P-glycoprotein.
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PMID:Sequential emergence of distinct resistance phenotypes in murine erythroleukemia cells under adriamycin selection: decreased anthracycline uptake precedes increased P-glycoprotein expression. 197 51

Dolastatin 10, a cytotoxic pentapeptide isolated from the mollusk Dolabella auricularia, exhibits potent antitumor activity. The present studies demonstrated that sublines of murine PC4 and human U-937 leukemia cells expressing a multidrug resistance (MDR) phenotype are cross-resistant to this agent. We also demonstrated that such resistance was reversed by verapamil. While these findings suggested the involvement of the P-glycoprotein (P-gp) in dolastatin 10 resistance, we performed similar studies in a CHO cell line transfected with the human mdr1 cDNA. Expression of P-gp in the transfected cells was associated with resistance to dolastatin 10 by a verapamil-sensitive mechanism. The demonstration that photoaffinity labeling of P-gp was decreased in the presence of dolastatin 10 further supports the interaction of this cytotoxic peptide with P-gp. Taken together, these findings suggest that resistance to dolastatin 10 is conferred, at least in part, by P-gp and that this cytotoxic peptide is a novel member of the MDR phenotype.
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PMID:Role of P-glycoprotein in dolastatin 10 resistance. 791 13

Multidrug-resistant sublines of the murine erythroleukemia cell line PC4 were sequentially selected in increasing vincristine concentrations (5-160 ng/ml). The low- and intermediate-level resistant cell lines, selected in < or = 40 ng/ml of vincristine, demonstrated resistance to Vinca alkaloids and to an epipodophyllotoxin but little or none to an anthracycline. The expression of murine mdr genes, as analyzed by Northern blotting, revealed a baseline expression of murine mdr2 in parental cells that was unchanged in the drug-resistant cell lines. Overexpression of mdr3 was observed only in the highest-level resistant cell line, PC-V160, whereas mdr1 mRNA was not detected in any of the cell lines. The polymerase chain reaction, using mdr3-specific primers, excluded the possibility that low levels of P-glycoprotein expression contributed to the resistance phenotype in the low and intermediate-level resistant cell lines. Northern blot analysis using a human complementary DNA probe for the multidrug resistance-associated protein (MRP) demonstrated overexpression of murine mrp in each of the vincristine-selected sublines. Genomic amplification of the mrp gene was coincident with mrp overexpression. The expression of mrp was also examined in two series of previously characterized doxorubicin-selected cell lines derived from parental PC4 and C7D murine erythroleukemia cells. In contrast to the vincristine-selected cell lines, overexpression of mrp was not detected. These studies demonstrate that, in murine erythroleukemia cells selected for vincristine resistance, overexpression of murine mrp occurred prior to that for murine mdr. In contrast to human MRP, selection for vincristine, but not doxorubicin resistance, resulted in the overexpression of murine mrp.
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PMID:Overexpression of the multidrug resistance-associated protein (MRP) gene in vincristine but not doxorubicin-selected multidrug-resistant murine erythroleukemia cells. 792 5

The multidrug resistance protein (MRP) is a membrane protein that mediates altered transport of cytotoxic drugs. Although MRP overexpression has been described in doxorubicin-selected human tumor cell lines, the murine PC-V10 and PC-V40 cell lines are members of the only reported series of vincristine-selected cell lines that overexpress mrp. Western blotting, using an antiserum developed against human MRP, demonstrated high-level expression of murine MRP primarily in the plasma membranes in each of the vincristine-selected cell lines. Only PC-V160, selected for high level resistance, demonstrated concomitant overexpression of the P-glycoprotein. As compared with parental cells, each of the drug-selected cell lines demonstrated an energy-dependent, decreased net accumulation of vincristine without any changes in the initial rates of vincristine influx. However, there was an enhanced rate of vincristine loss, 2.3-fold from the PC-V40 cell line and 3.9-fold from the PC-V160 cell line. Selective plasma membrane permeabilization with digitonin equalized vincristine accumulation among the parental, the PC-V40, and the PC-V160 cell lines. No intracellular pH differences were detected among the cell lines. Despite high-level MRP expression, daunorubicin accumulation and the rate of daunorubicin loss in the PC-V40 cells were the same as that observed in parental PC4 cells. Fluorescence microscopy demonstrated no difference in the pattern of subcellular daunorubicin accumulation between parental and PC-V40 cells. These studies demonstrate that murine MRP, overexpressed and found predominantly in the plasma membrane of vincristine-selected PC-V40 cells, is associated with an energy-dependent increased efflux of vincristine, but not with efflux or altered distribution of daunorubicin.
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PMID:Increased efflux of vincristine, but not of daunorubicin, associated with the murine multidrug resistance protein (MRP). 893 72

The relationship between mammalian facilitative glucose transport proteins (GLUT) and multidrug resistance was examined in two vincristine (VCR)-selected murine erythroleukaemia (MEL) PC4 cell lines. GLUT proteins, GLUT1 and GLUT3, were constitutively coexpressed in the parental cell line and also in the VCR-selected cell lines. Increased expression of the GLUT1 isoform was noted both in the PC-V40 (a non-P-glycoprotein, mrp-overexpressing subline) and in the more resistant PC-V160 (overexpressing mrp and mdr3) cell lines. Overexpression of GLUT3 was detected only in the PC-V160 subline. An increased rate of facilitative glucose transport (Vmax) and level of plasma membrane GLUT protein expression paralleled increased VCR resistance, active VCR efflux and decreased VCR steady-state accumulation in these cell lines. Glucose transport inhibitors (GTIs), cytochalasin B (CB) and phloretin blocked the active efflux and decreased steady-state accumulation of VCR in the PC-V40 subline. GTIs did not significantly affect VCR accumulation in the parental or PC-V160 cells. A comparison of protein sequences among GLUT1, GLUT3 and MRP revealed a putative cytochalasin B binding site in MRP, which displayed 44% sequence similarity/12% identity with that previously identified in GLUT1 and GLUT3; these regions also exhibited a similar hydropathy plot pattern. The findings suggested that CB bound to MRP and directly or indirectly lowered VCR efflux and/or CB bound to one or both GLUT proteins, which acted to lower the VCR efflux mediated by MRP. This is the first report of a non-neuronal murine cell line that expressed GLUT3.
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PMID:Effect of glucose transport inhibitors on vincristine efflux in multidrug-resistant murine erythroleukaemia cells overexpressing the multidrug resistance-associated protein (MRP) and two glucose transport proteins, GLUT1 and GLUT3. 901 20

In murine erythroleukemia (MEL) A20 cells (grown in 20 ng/ml adriamycin), mutation(s) producing 10-fold adriamycin (doxorubicin) resistance emerged via an unknown mechanism. Exposure of A20 cells to further stepwise increasing concentrations of ADR in combination with MDR modulators (PSC833 and verapamil) aimed to amplify the undetermined A20 mechanism while controlling P-glycoprotein (P-gp) overexpression. The growth of the derived cell lines A30P, A40P and A60P (grown in 30, 40 and 60 ng/ml ADR with PSC833 and verapamil) was initially slow, but eventually reached near WT rates. The new cell lines A30P and A40P were only 1.3- and 1.6-fold more resistant to adriamycin than PC4 A20. Resistance to vincristine was unchanged, but resistance to etoposide (VP-16) was 3.7-fold higher in A40P than A20 (itself 97-fold higher than wild-type). Expression of mdr3 and mrp mRNA tested by RT-PCR showed no increase. Daunorubicin and etoposide accumulation was not different among the cell lines, and no changes were detected in the number of daunorubicin fluorescent lysosomes. In comparison to WT, reduced topoisomerase IIalpha (EC 5.99.1.3) activity (20%) and protein expression (80%) was similar to the parental A20 cells. No mutations in the coding sequence of topoisomerase IIalpha could be located to account for the high etoposide resistance levels. The inhibitor combination of verapamil and PSC833 prevented the emergence of transporter mediated MDR, but not ADR selection of cell lines highly resistant to etoposide.
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PMID:Selection of non-P-glycoprotein mediated high-level etoposide resistant cell lines by adriamycin with P-gp inhibitors. 1646 81