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)

Expression of P-glycoprotein (P-gp), the product of multidrug resistance gene(s), was investigated in primary cultures of normal adult rat hepatocytes. Levels of P-gp mRNAs determined by Northern blotting and of P-gp measured by immunoblotting increased in parallel with time in culture. As in normal liver, P-gp was found to be localized on the membrane of bile canaliculus-like structures. This increased expression of P-gp was associated with decreased intracellular retention of doxorubicin, which could be restored by compounds such as verapamil and cyclosporin; doxorubicin (and also vincristine) was more cytotoxic to early than to late cultures. As in preneoplastic and neoplastic liver, overexpression of P-gp in cultured hepatocytes was associated with differential changes in drug-metabolizing enzymes, including increased glutathione S-transferase 7-7. Functional P-gp over-expression was observed in the absence of xenobiotic exposure or cell division; it could be linked to cellular stress occurring during cell isolation and plating. Increased expression of P-gp was blocked by actinomycin D, indicating its dependence on increased transcription, while cycloheximide led to a superinduction suggesting negative regulation by a protein factor.
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PMID:Overexpression of the multidrug resistance gene product in adult rat hepatocytes during primary culture. 134 83

We have investigated the polarity of the efflux of the intracellular pH fluorochrome 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF) from layers of epithelial Madin-Darby canine kidney (MDCK, Strains I and II) and human intestinal (Caco-2, HCT-8 and T84) cells grown on porous membranes. In Strain I MDCK cells, BCECF efflux was effectively reduced by indomethacin (50% inhibition with 100 microM) and 5-nitro-2-(3-phenylpropyl-amino)-benzoate (NPPB; 50% inhibition with 10 microM). Replacement of external Cl- with bromide, iodide or nitrate did not alter BCECF efflux, while substitution with methanesulphonate resulted in a small but significant reduction. All five cell lines form confluent epithelial layers when grown on porous membranes. Efflux of BCECF from Strain I MDCK epithelial layers into the apical solution was approximately three times greater than into the basal solution. Addition of indomethacin to the apical solution attenuated efflux into the apical but not the basal solution, while basal indomethacin was effective against basal efflux. NPPB has a similar specificity of action. Adrenaline, a stimulant of electrogenic Cl- secretion, did not alter the pattern of BCECF efflux. BCECF efflux was also polarized, with apical efflux greater than basal efflux, in MDCK Strain II and Caco-2 epithelial layers. In contrast, BCECF efflux into the basal and apical media was equivalent in layers formed from HCT-8 and T84 cells. However, indomethacin reduced efflux in all five epithelial lines, although the relative sensitivities of the apical and basal efflux rates to indomethacin varied, as did the sensitivity to the sidedness of application of indomethacin. In MDCK and HCT-8 epithelial layers, transepithelial vinblastine secretion mediated by P-glycoprotein was not inhibited by indomethacin. The data are consistent with the hypothesis that BCECF efflux is a manifestation of a novel ATP-dependent xenobiotic secretory efflux mechanism in renal and gastrointestinal epithelia. The factors regulating the polarity of BCECF efflux, both the indomethacin-sensitive and -insensitive components, have yet to be elucidated.
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PMID:Polarized efflux of 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein from cultured epithelial cell monolayers. 151 Jun 94

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 in-vitro pharmacokinetics of vincristine (VCR) in normal rat colonic mucosa were studied. Two complementary approaches were adopted using an explant organ-culture system. Firstly [G-3H]vincristine (3HVCR) accumulation, retention and efflux were characterized under basal conditions and compared with measurements made either under energy-depleted conditions, or in the presence of VRP. Secondly, a histological method--the postmetaphase index (PMI)--was used to compare the sensitivity of explants to VCR in the presence or absence of verapamil (VRP). This latter technique involves the measurement, by counting, of the proportion of mitotic figures escaping from metaphase arrest. The studies yielded the following results: 3HVCR accumulation in colonic mucosa showed no evidence of saturability up to the maximum dose studied (130 nM), at a dose of 52 nM accumulation was enhanced in energy-depleted conditions by a factor of 1.8, and in the presence of VRP (6.6 microM) by a factor of 1.4. In the presence of VRP (6.6 microM) retention of 3HVCR was increased by a factor of 1.3 and efflux was reduced by a factor of 0.8 after 2 hr. VRP (6.6 microM) reduced the PMI of colonic mucosal epithelial cells exposed to 11 nM VCR from 18.8% to 11.4% (i.e. 40% reduction) indicating sensitization of the cells to this property of VCR. These results provide evidence that the sensitivity of normal colonic mucosa to vincristine is, at least in part, regulated by drug transport. Qualitatively our observations resemble those described in multidrug resistance. Given that P-glycoprotein has been demonstrated by several groups in colonic mucosal cells, the results support a normal role for this membrane transport molecule in the protection of intestinal cells from plant alkaloids and other xenobiotic agents ingested in the diet.
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PMID:Modulation by verapamil of vincristine pharmacokinetics and sensitivity to metaphase arrest of the normal rat colon in organ culture. 200 97

In a set of four increasingly multidrug-resistant variants of SW-1573 human lung tumor cells, the pHi (i.e., steady-state cytosolic pH) increased up to 0.44 U as a function of the level of doxorubicin resistance. The elevated pHi in the most resistant (2,000-fold) variant dropped to the control level upon addition of verapamil, a known inhibitor of P-glycoprotein activity. These data suggest that, in the absence of xenobiotic substrates, P-glycoprotein activity can affect cellular pHi. This finding may be important for the elucidation of the physiological function of this protein.
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PMID:Increased cytosolic pH in multidrug-resistant human lung tumor cells: effect of verapamil. 256 4

P-glycoprotein (PGP), responsible for multidrug resistance (MDR) in cancer cells, is normally expressed in kidney proximal tubules and mesangium. PGP expression and function were studied in human mesangial cell cultures. MDR1 gene expression was demonstrated by reverse transcription-polymerase chain reaction. PGP expression was determined using MRK16 monoclonal antibody and its function was assessed by the efflux of rhodamine-123 (R123). R123 efflux had a half time of 25 +/- 5 s. Efflux was inhibited by cyclosporin A (10 microM), verapamil (10 microM), and vinblastine (100 microM) with half times of 380, 535, and 312 s, respectively. Incubation with MDR1-antisense oligonucleotide decreased R123 efflux (half time = 304 s). Verapamil, cyclosporin A, and PSC-833 augmented the cytotoxicity of Adriamycin by reducing the 50% maximal growth-inhibitory dose from 730 nM to 130, 110, and 90 nM, respectively. We conclude that human mesangial cells express MDR1 and demonstrate xenobiotic transport inhibitable by several known PGP substrates. Concomitant exposure of mesangial cells to PGP-transported drugs causes intracellular accumulation of toxic PGP substrates and ultimately damages the mesangial cells.
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PMID:Expression and function of P-glycoprotein in human mesangial cells. 752 96

P-glycoprotein (pgp), the protein product of the multidrug resistance (mdr) gene family, can confer a multidrug resistance (mdr) phenotype to cells in which it is expressed. One member of the pgp family, pgp2, is located on the hepatocyte biliary pole where it may have a role in biliary excretion. Using primates we sought to determine if mdr gene expression and pgp levels were affected by xenobiotics excreted via the bile in man. Five drugs were studied in male and female rhesus monkeys: erythromycin, rifampicin, tamoxifen, diethylstilbesterol (DES), and probenecid. For each xenobiotic, with the exception of DES, an increase in mdr2 mRNA was observed. The results suggest that expression of mdr2 is responsive to xenobiotics, or their metabolites, that require biliary excretion. We speculate that the mdr2 gene may be a member of a class of xenobiotic responsive genes coding for proteins that actively excrete xenobiotics and/or their metabolites into the bile.
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PMID:In vivo induction of liver P-glycoprotein expression by xenobiotics in monkeys. 764 23

The vectorial transport of xenobiotics across the hepatocyte is mediated by various transport and transfer proteins that differ in ligand specificity and function. The influx of xenobiotics from the blood across the sinusoidal membrane of the hepatocyte can occur through passive or active transport processes. Once in the cell, xenobiotics can be sequestered by intracellular transfer proteins that prevent refluxing of the chemical back through the sinusoidal membrane. Transfer proteins may also facilitate the localization of the xenobiotics within the cell to sites of metabolism (i.e., the endoplasmic reticulum) or elimination (i.e., the canalicular membrane). Intracellular transfer proteins include glutathione S-transferases, fatty acid-binding proteins, and 3 alpha-hydroxysteroid dehydrogenase. Intracellular nuclear transfer proteins have also been identified that facilitate the transfer of chemical carcinogens from the cytoplasm into the cell nucleus. Several active transport proteins exist on the canalicular membrane of the hepatocyte that mediate the efflux of chemicals from the cell into the biliary canaliculus. Xenobiotic efflux proteins include the multispecific organic anion transporter, that eliminates xenobiotics that have undergone conjugation with glutathione, glucuronic acid, and possibly sulfate; and, P-glycoprotein, an active transporter that actively effluxes a variety of structurally diverse xenobiotics. Induction of P-glycoprotein by the amplification of its gene has been identified as a major cause of resistance of tumor cells to the toxicity of a variety of anti-cancer drugs. The hepatic induction of P-glycoprotein may also contribute to acquired resistance of organisms to environmental toxicants. Continued elucidation of xenobiotic transport and transfer processes at the cellular levels will significantly advance our understanding of processes involved in xenobiotic toxicity and acquired resistance to chemical toxicity.
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PMID:Hepatic vectorial transport of xenobiotics. 790 59

Cellular drug resistance is believed to involve P-glycoprotein-related drug efflux as well as xenobiotic detoxification. In the present study, we analyzed five human melanoma cell lines with 1- to 6-fold doxorubicin resistance for doxorubicin retention and MDR-1 and GST pi gene expression. All the cell lines had high doxorubicin retention, and efflux blockers such as trifluoperazine and verapamil did not have a major effect on drug retention or cytotoxicity. Even though all the cell lines carried the MDR-1 and GST pi genes, gene amplification was not associated with drug resistance. Both laser flow cytometry and immunoperoxidase staining showed high expression of C-219 reactive P-glycoprotein in some of the resistant cells which was not accompanied by either high drug efflux or sensitivity to doxorubicin efflux blockers.
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PMID:Doxorubicin resistance in human melanoma cells: MDR-1 and glutathione S-transferase pi gene expression. 809 41

The curative potential of chemotherapy for a number of tumor types has been obscured by the fact that many patients initially have striking remissions but later relapse and die. At the time of relapse many patients manifest resistance to a wide array of structurally unrelated antineoplastic agents, hence the term multidrug resistance (MDR). Other tumor types, such as those arising in the colon, kidneys, liver, and lungs, tend to exhibit poor response to available cytotoxic drugs. The MDR phenomenon includes cross-resistance among the anthracyclines (doxorubicin, daunorubicin), the epipodophyllotoxins (etoposide, teniposide), the vinca alkaloids (vinblastine, vincristine), taxol, and other compounds. In vitro studies in cell culture indicate that this form of resistance is associated with amplification or overexpression of the mdr1 gene. The mdr1 gene codes for the expression of a cell surface protein, P-glycoprotein (P-gp), which acts as an energy-dependent efflux pump that transports drugs associated with MDR out of the cell before cytotoxic effects occur. The protein is expressed in normal human tissues such as the gastrointestinal tract, liver, and kidneys, where it is thought to serve as an excretory pathway for xenobiotic drugs and toxins. Preliminary studies demonstrated the presence of P-gp in tumor samples from patients with acute leukemia, multiple myeloma, lymphomas, and a variety of solid tumors. A number of drugs are able to reverse MDR, including calcium-channel blockers, phenothiazines, quinidine, antimalarial agents, antiestrogenic and other steroids, and cyclosporine. Limited results from clinical trials with small numbers of patients suggest that the addition of verapamil, diltiazem, quinine, trifluoperazine, or cyclosporine to chemotherapeutic regimens has the potential to reverse MDR; however, toxicities limit their clinical usefulness. A number of trials are under way to identify more active and less toxic modulators of MDR.
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PMID:Molecular targets in oncology: implications of the multidrug resistance gene. 809 38


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