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 the mdr1 gene, encoding the 175 kDa P-glycoprotein, and the gst-pi gene, encoding the anionic isozyme of glutathione S-transferase (GST), have previously been detected in continuous human breast cancer cell lines selected in vitro for resistance to doxorubicin. In this present study we have measured RNA levels of mdr1 and gst-pi in primary human breast tumour biopsies prior to chemotherapy and from tumours which have different inherent responses to doxorubicin treatment, including colon, head and neck squamous cell carcinomas and myeloid leukaemias. Detectable levels of mdr1 mRNA was observed in 25 out of 49 breast tumours, with up to a 100-fold range in expression. A narrower range of gst-pi expression has also been observed in these tumours. Chemosensitivity of cells grown in short-term culture from some of the breast tumours has been measured by an in vitro colony forming assay in the presence of doxorubicin. Comparison of the dose of doxorubicin causing 50% inhibition of growth (ID50) with RNA levels showed that the tumours with high mdr1 expression had high ID50, while the more sensitive explants had low mdr1 expression. These results support a role for mdr1 gene expression in determining the response of human breast cancer cells to chemotherapy.
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PMID:Expression of mdr1 and gst-pi in human breast tumours: comparison to in vitro chemosensitivity. 197 Sep 34

Development of multidrug resistance due to overexpression of P-glycoprotein (Pgp), a cell membrane drug efflux pump, occurs commonly during in vitro selections with adriamycin (Adr). Pgp-mediated drug resistance can be overcome by the calcium channel blocker verapamil (Vp), which acts as a competitive inhibitor of drug binding and efflux. In order to identify other mechanisms of Adr resistance, we isolated an Adr-resistant subline by selecting the human breast cancer cell line MCF-7 with incremental increases of Adr in the presence of 10 microgram/ml verapamil. The resultant MCF-7/AdrVp subline is 900-fold resistant to Adr, does not overexpress Pgp, and does not exhibit a decrease in Adr accumulation. It exhibits a unique cross-resistance pattern: high cross-resistance to the potent Adr analogue 3'-deamino-3'-(3-cyano-4-morpholinyl)doxorubicin, lower cross-resistance to the alkylating agent melphalan, and a sensitivity similar to the parental cell line to vinblastine. The levels of glutathione and glutathione S-transferase are similar in the parental line and the Adr-resistant subline. Topoisomerase II-DNA complexes measured by the potassium-sodium dodecyl sulfate precipitation method shows a 2-3 fold decrease in the resistant subline. The MCF-7/AdrVp cells overexpress a novel membrane protein with an apparent molecular mass of 95 kDa. Polyclonal antibodies raised against the P-95 protein demonstrate a correaltion between the level of expression and Adr resistance. Removal of Adr but not verapamil from the selection media results in a decline in P-95 protein levels that parallels a restoration of sensitivity to Adr. Immunohistochemistry demonstrates localization of the P-95 protein on the cell surface. The demonstration of high levels of the protein in clinical samples obtained from patients refractory to Adr suggests that this protein may play a role in clinical drug resistance.
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PMID:Characterization of adriamycin-resistant human breast cancer cells which display overexpression of a novel resistance-related membrane protein. 197 54

The nucleotide sequence of the mdr1 gene encoding a putative drug efflux pump (P-glycoprotein) is homologous to a class of bacterial membrane-associated transport proteins. These bacterial proteins are part of a multicomponent system that includes soluble periplasmic proteins that bind substrates, channeling them through the membrane in an energy-dependent manner. We have investigated the possibility that a similar multicomponent transport system exists in a multidrug-resistant human MCF-7 breast cancer cell line that was initially selected for resistance to doxorubicin (AdrR MCF-7). AdrR MCF-7 cells overexpress both the mdr1 gene and the pi class isozyme of glutathione S-transferase (GST-pi) (EC 2.5.1.18). The latter is one of several isozymes known to have a ligand-binding function in addition to drug-metabolizing capabilities. Although we have recently shown that transfection of a functional GST-pi expression vector is insufficient to confer resistance to doxorubicin in cells that lack P-glycoprotein expression [Mol. Pharmacol. 36:22-28 (1989)], we examined the possibility that GST-pi interacts with P-glycoprotein to alter multidrug resistance. To do this, we have cloned cDNAs encoding these proteins from AdrR MCF-7 cells, constructed expression vectors containing these two genes, and transfected these vectors sequentially into drug-sensitive MCF-7 cells. The human mdr1 cDNA isolated from AdrR MCF-7 is a variant gene whose sequence differs from that isolated previously from vinblastine-resistant KB cells [Cell 53:519-529 (1989)], resulting in an amino acid substitution of alanine to serine at position 893 (mdr1/893ala). Transfection of eukaryotic expression vectors containing the mdr1 gene isolated from AdrR MCF-7 cells produced a multidrug-resistant phenotype in recipient cells, with a cross-resistance pattern similar to that in the AdrR MCF-7 cells. To determine whether GST-pi expression could augment resistance provided by mdr1, two clones transfected with mdr1, one with high levels (153% of mdr1 RNA in AdR MCF-7 cells) and one with low levels (10% of mdr1 RNA in AdrR MCF-7 cells), were subsequently cotransfected with a GST-pi expression vector and pSVNeo and selected for resistance to G418. Six of these clones contained levels of GST-pi that were 8- to 18-fold greater than GST levels found in mdr1-expressing clones transfected with nonspecific DNA. We found no difference in the degree of resistance to doxorubicin, actinomycin D, and vinblastine between the clones expressing mdr1 only and the clones expressing both mdr1 and GST-pi.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Multidrug resistance in cells transfected with human genes encoding a variant P-glycoprotein and glutathione S-transferase-pi. 197 72

Glutathione S-transferases (GSTs), a family of isoenzymes that play an important role in protecting cells from cytotoxic and carcinogenic agents, can be separated by biochemical and immunologic characteristics into three distinct classes named alpha, mu, and pi. Previous studies have indicated that there is marked heterogeneity in the expression of different GST isoenzymes in different normal and malignant tissues. To better understand the regulation of the human pi class glutathione S-transferase isoenzyme (GST-pi), the tissue distribution of this protein wa studied by an immunohistochemical technique using an anti-GST-pi polyclonal antibody in normal paraffin-embedded human tissues. These studies indicate that there is a broad distribution of GST-pi in normal human tissues and establish a precise localization within the different organs studied. GST-pi was expressed predominantly in normal epithelial cells of the urinary, digestive, and respiratory tracts, suggesting a possible role for GST-pi in detoxication and elimination of toxic substances. Previous studies have indicated that GST-pi and the putative drug efflux pump P-glycoprotein are both overexpressed in multidrug-resistant human breast cancer cells and in xenobiotic resistant preneoplastic rat hyperplastic liver nodules. Results from this study indicate that there are also similarities between the normal tissue distribution GST-pi and that previously reported for mammalian P-glycoprotein, particularly in secretory epithelia. This finding suggests that these two gene products, which have been implicated in the development of resistance to cytotoxic drugs, may be coregulated in normal and malignant cells.
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PMID:An immunohistochemical study of pi class glutathione S-transferase expression in normal human tissue. 197 19

The effects of GSH depletion in a human breast cancer cell line and a multi-drug resistant subline (ADRr) were determined in a number of experimental conditions. The ADRr cells contained lower GSH concentration which cannot be explained solely on the basis of differences in cell kinetics, and yet the rate-limiting synthetic enzyme gamma-glutamylcysteine synthetase was increased 2-fold. Inhibition of GSH synthesis by BSO resulted in more rapid and more pronounced GSH depletion in ADRr compared to the wild-type cells, suggesting that enhanced GSH utilization and efflux in the resistant cells account for the lowered basal concentration. In addition, the gamma-glutamyl moiety salvage enzyme gamma-glutamyltranspeptidase was reduced markedly in the ADRr cell line. Since these cells have overexpression of the efflux pump protein P-glycoprotein, we examined the effects on cellular GSH of inhibition of the pump's function by verapamil. We found that verapamil significantly depleted cellular GSH. In a rat mammary carcinoma cell line selected in Adriamycin for multi-drug resistance, a similar molecular phenotype has been described including diminished cellular GSH concentration. Verapamil treatment of these cells also resulted in significant depletion of cellular GSH. These results are consistent with the recent report that combined treatment of BSO and verapamil has an additive effect on cytotoxicity. It is likely that decreased basal GSH concentration is due to oxidation and conjugation of it in reactions catalyzed by the enhanced peroxidase and GST found in these cells.
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PMID:Glutathione depletion in human and in rat multi-drug resistant breast cancer cell lines. 199 9

The liver is the major organ which eliminates leukotriene C4 (LTC4) and other cysteinyl leukotrienes from the blood circulation into bile. Transport of LTC4 was studied using inside-out vesicles enriched in canalicular and sinusoidal membranes from rat liver. The incubation of canalicular membrane vesicles with [3H]LTC4 in the presence of ATP resulted in an uptake of LTC4 into vesicles. The initial rate of ATP-stimulated LTC4 uptake was about 40-fold higher in canalicular than in sinusoidal membrane vesicles. When liver plasma membrane vesicles were incubated in the absence of ATP, an apparent transient uptake of LTC4 was observed which was temperature-dependent and not affected by the osmolarity. This indicates that LTC4 was bound to proteins on the surface of plasma membrane vesicles. Two proteins with relative molecular weights of 17,000 and 25,000 were detected by direct photoaffinity labeling as major LTC4-binding proteins. One protein (Mr 25,000) was ascribed to subunit 1 (Ya) of glutathione S-transferase which was associated with the membrane. LTD4, LTE4, N-acetyl-LTE4, and omega-carboxy-N-acetyl-LTE4 were also transported into liver plasma membrane vesicles in an ATP-dependent manner with initial rates relative to LTC4 (1.0) of 0.46, 0.11, 0.35, and 0.22, respectively. Mutual competition between the cysteinyl leukotrienes and S-(2,4-dinitrophenyl)-glutathione for uptake indicated that they are transported by a common carrier. Apparent Km values of the transport system for LTC4, LTD4, and N-acetyl-LTE4 were 0.25, 1.5, and 5.2 microM, respectively. The ATP-dependent transport of LTC4 into vesicles was not inhibited by doxorubicin, daunorubicin, or verapamil, or by the monoclonal antibody C219, suggesting that the transport system differs from P-glycoprotein. Liver plasma membrane vesicles prepared from mutant rats deficient in the hepatobiliary excretion of cysteinyl leukotrienes lacked the ATP-dependent transport of cysteinyl leukotrienes and S-(2,4-dinitrophenyl)-glutathione. These results demonstrate that the ATP-dependent carrier system is responsible for the transport of cysteinyl leukotrienes and glutathione S-conjugates from the hepatocytes into bile.
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PMID:ATP-dependent primary active transport of cysteinyl leukotrienes across liver canalicular membrane. Role of the ATP-dependent transport system for glutathione S-conjugates. 217 49

Multidrug resistance (MDR) in an MCF-7 human breast cancer cell line (MCF7/Adr) is associated with decreased drug accumulation and overexpression of P-glycoprotein as well as alterations in the levels of specific drug-metabolizing enzymes, including decreased activity of the phase I drug-metabolizing enzyme aryl hydrocarbon hydroxylase (AHH) and increased expression of the anionic form of the phase II drug-metabolizing enzyme glutathione S-transferase. Since the development of MDR in this MCF-7 cell line is also associated with a loss of estrogen receptors (ER), we have examined the expression of cytochrome P450IA 1, the gene encoding AHH activity, in other breast cancer cell lines not selected for drug resistance but expressing various levels of ER. These studies show that a relationship exists between 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-inducible AHH activity and the ER content in a series of breast cancer cell lines. In these cell lines expression of AHH activity is regulated, at least in part, at the level of P450IA 1 RNA. While TCDD-specific binding proteins (Ah receptors) were found in each of the breast cancer cell lines, there was no apparent relation between the level of nuclear TCDD-binding proteins and the level of TCDD-inducible P450IA 1 expression. Previous studies from our laboratory have described an inverse relationship between levels of the anionic form of glutathione S-transferase and ER in breast cancer.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Relation between cytochrome P450IA1 expression and estrogen receptor content of human breast cancer cells. 246 54

The development of multidrug resistance in MCF7 human breast cancer cells is associated with overexpression of P-glycoprotein, changes in activities of several detoxication enzymes, and loss of hormone sensitivity and estrogen receptors (ERs). We have cloned the cDNA for one of the drug-detoxifying enzymes overexpressed in multidrug-resistant MCF7 cells (AdrR MCF7), the anionic isozyme of glutathione S-transferase (GST pi). Hybridization with this GST pi cDNA, GST pi-1, demonstrated that increased GST pi activity in AdrR MCF7 cells is associated with overexpression but not with amplification of the gene. We mapped the GST pi gene to human chromosome 11q13 by in situ hybridization. Since multidrug resistance and GST pi overexpression are associated with the loss of ERs in AdrR MCF7 cells, we examined several other breast cancer cell lines that were not selected for drug resistance. In each of these cell lines we found an inverse association between GST pi expression and ER content. We also examined RNA from 21 primary breast cancers and found a similar association between GST pi expression and ER content in vivo. GST pi mRNA content in 11 ER-positive tumors (less than or equal to 10 fmol/mg of protein) was significantly different from the GST pi content of 10 ER-negative tumors (P = 0.002; Mann-Whitney Wilcoxon test for two independent samples). The finding of similar patterns of expression of a drug-detoxifying enzyme and of ERs in vitro as well as in vivo suggests that ER-negative breast cancer cells may have greater protection against antineoplastic agents conferred by GST pi than ER-positive tumors.
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PMID:Isolation of the human anionic glutathione S-transferase cDNA and the relation of its gene expression to estrogen-receptor content in primary breast cancer. 284 75

Cloned lines of Adriamycin (ADR)-sensitive and -resistant P388 leukemia have been established, including P388/ADR/3 and P388/ADR/7 that are 5- and 10-fold more resistant than the cloned sensitive cell line P388/4 (Cancer Res., 46: 2978, 1986). A time course of ADR-induced DNA double-strand breaks revealed that in sensitive P388/4 cells, evidence of DNA repair was noted 4 h after removal of drug, whereas in resistant clone 3 and 7 cells repair was observed 1 h after drug removal. The earlier onset of DNA repair was statistically significant (p = 0.0154 for clone 3 cells, and p = 0.0009 for clone 7 cells). By contrast, once the repair process was initiated, the rate of repair was similar for all three cell lines. The level of glutathione transferase activity was determined in whole cell extracts. Enzyme activity (mean +/- SE) in sensitive cells was 9.49 +/- 1.00 nmol/min/mg protein, that in resistant clone 3 cells was 13.36 +/- 1.03 nmol/min/mg, and that in clone 7 cells was 13.96 +/- 1.44 nmol/min/mg; the 1.44-fold increase in enzyme activity in resistant cells was statistically significant (p = 0.01). Further evidence of induction of glutathione transferase was provided by Northern blot analysis using a 32P-labeled cDNA for an anionic glutathione transferase, which demonstrated approximately a twofold increase in mRNA in resistant clone 7 cells. Western blot analysis with a polyvalent antibody against anionic glutathione transferase also revealed a proportionate increase in gene product in resistant cells. Dose-survival studies showed that ADR-resistant cells were cross-resistant to actinomycin D, daunorubicin, mitoxantrone, colchicine, and etoposide, but not to the alkylating agent melphalan; this finding provided evidence that these cells are multidrug resistant. Using a cDNA probe for P-glycoprotein, a phenotypic marker for multidrug resistance, Northern blot analysis showed an increase in the steady state level of mRNA of approximately twofold in resistant clone 3 and 7 cells. Southern analysis with the same cDNA probe showed no evidence of gene amplification or rearrangement. Western blot analysis with monoclonal C219 antibody demonstrated a distinct increase in P-glycoprotein in resistant cells. Efflux of Adriamycin as measured by the efflux rate constant was identical in all three cell lines. Furthermore, the metabolic inhibitors azide and dinitrophenol did not augment drug uptake in either sensitive or resistant cells. These findings suggest that despite the increase in P-glycoprotein, an active extrusion pump was not operational in these cells.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Multifactorial resistance to adriamycin: relationship of DNA repair, glutathione transferase activity, drug efflux, and P-glycoprotein in cloned cell lines of adriamycin-sensitive and -resistant P388 leukemia. 289 75

Increased expression of glutathione-S-transferase isoenzyme pi (GST-pi) may account for drug resistance and treatment failure in hematologic malignancies when alkylating agents like cyclophosphamide, chlorambucil, busulfan and melphalan, or doxorubicin are used. We have studied the expression of GST-pi in peripheral blood lymphocytes of healthy blood donors. In peripheral and bone marrow lymphocytes/blasts of patients with other diseases than hematologic malignancies, and of patients with acute leukemia by using flow cytometry. We studied bone marrow cells of 35 patients diagnosed as having acute leukemia at initial presentation, 16 patients in the refractory stage, 20 in morphological remission and 15 controls. None of the samples obtained in remission contained more GST-pi-positive cells than the controls, whereas 51% of the samples obtained at diagnosis and 56% of those obtained in the refractory stage were GST-pi-positive. The mean proportion of GST-pi-positive cells in the lymphocyte/blast cell gate of bone marrow cells of controls was 2.6% and of patients with acute leukemia studied at diagnosis 16.6%, respectively. We analyzed the samples also for P-glycoprotein expression. There was a significant positive association between GST-pi and P-glycoprotein expression in acute leukemia.
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PMID:Flow cytometric analysis of glutathione-S-transferase-pi in acute leukemia. 751 31


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