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)

P-glycoprotein is a cell membrane transport protein in various human tissues that acts as an efflux pump, apparently to protect normal cells from environmental toxins. It is also a mechanism used by some cancer cells to resist chemotherapy. The gene responsible for P-glycoprotein is partially defined. Agents that inhibit the protein in tumors may make chemotherapy more effective and less toxic.
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PMID:Multidrug resistance due to P-glycoprotein. 196 65

Chinese hamster pgpl P-glycoprotein (Pgp) is a membrane transport protein that causes multidrug resistance (MDR) by actively extruding a wide variety of cytotoxic agents out of cells. It may also function as a peptide transporter and as a chloride channel. Previously, we have shown that hamster pgpl Pgp is expressed in more than one topological form and that the generation of these structures is modulated by charged amino acids flanking the predicted transmembrane (TM) segments 3 and 4. Different topological structures of Pgp may be involved in different functions. In this study, we examined the role of cytoplasmic components in cell-free translation systems in modulating the topologies of Pgp. By using rabbit reticulocyte lysate (RRL) and wheat germ extract (WGE) expression systems, we showed that WGE contains a soluble, heat-labile, high molecular weight fraction that regulates the membrane topology of truncated Pgp molecules. These results and our previous findings indicate that the membrane topology of a mammalian polytopic membrane protein may be regulated both by the amino acid sequence of the protein and by soluble cytoplasmic component(s). We speculate that Pgp expressed in various cell types may have different topological structures modulated by specific cytoplasmic factors.
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PMID:Involvement of cytoplasmic factors regulating the membrane orientation of P-glycoprotein sequences. 761 15

A major problem in cytostatic treatment of many tumours is the development of multidrug resistance (MDR4). This is most often accompanied by the overexpression of a membrane transport protein, P-glycoprotein, and its encoding mRNA. In order to reverse the resistant phenotype in cell cultures, we constructed a specific hammerhead ribozyme possessing catalytic activity that cleaves the 3'-end of the GUC sequence in codon 880 of the mdr1 mRNA. We demonstrated that the constructed ribozyme is able to cleave a reduced substrate mdr1 mRNA at the GUC position under physiological conditions in a cell-free system. A DNA sequence encoding the ribozyme gene was then incorporated into a mammalian expression vector (pH beta APr-1 neo) and transfected into the human pancreatic carcinoma cell line EPP85-181RDB, which is resistant to daunorubicin and expresses the MDR phenotype. The expressed ribozyme decreased the level of mdr1 mRNA expression, inhibited the formation of P-glycoprotein and reduced the cell's resistance to daunorubicin dramatically; this means that the resistant cells were 1,600-fold more resistant than the parental cell line (EPP85-181P), whereas those cell clones that showed ribozyme expression were only 5.3-fold more resistant than the parental cell line.
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PMID:Reversion of multidrug resistance in the P-glycoprotein-positive human pancreatic cell line (EPP85-181RDB) by introduction of a hammerhead ribozyme. 791 21

P-glycoprotein (pgp) is a membrane transport protein that causes multidrug resistance (MDR) by actively extruding a wide variety of cytotoxic agents out of cells. It may also function as a peptide transporter, a volume-regulated chloride channel, and an ATP channel. Previously, it has been shown that hamster pgp 1 Pgp is expressed in more than one topological form and that the generation of these structures is modulated by charged amino acids flanking the predicted transmembrane (TM) segments 3 and 4 and by soluble cytoplasmic factors. Different topological structures of Pgp may be related to its different functions. In this study, we examined the effects of translation temperature on the membrane insertion process and the topologies of Pgp. Using the rabbit reticulocyte lysate expression system, we showed that translation at different temperatures affects the membrane insertion and orientation of the putative TM3 and TM4 of hamster pgp 1 Pgp in a co-translational manner. This observation suggests that the membrane insertion process of TM3 and TM4 of Pgp molecules may involve a protein conducting channel and/or the interaction between TM3 and TM4, which act in a temperature sensitive manner. We speculate that manipulating temperature may provide a way to understand the structure-function relationship of Pgp and help overcome Pgp-related multidrug resistance of cancer cells.
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PMID:Co-translational effects of temperature on membrane insertion and orientation of P-glycoprotein sequences. 881 6

Phosphatidylcholines (PC) are secreted into the bile via a membrane transport protein(s). Recently, evidence for ATP-dependent mdr2-encoded PC transport as well as for carrier-mediated PC transport had been reported. Therefore, we investigated whether mdr2 P-glycoprotein is involved in the transport of a water-soluble short chain phosphatidylcholine analogue L-alpha-dibutyroyl-PC (diC4PC) induced by expression of liver mRNA in Xenopus laevis oocytes. Expression of mouse and rat mdr2 cRNA did not result in diC4PC net uptake in Xenopus laevis oocytes. By contrast oocytes showed a similar carrier-mediated uptake activity for diC4PC after injection of mouse, rat and human liver total mRNA (Km 7.7, 9.6, and 11.6 mM). Antisense inhibition of mdr2 mRNA expression increased diC4PC uptake induced by total liver mRNA from mouse and rat. The present data prove the existence of a specific mRNA for a non-mdr2-coded cell membrane PC carrier in mouse, rat, and human liver which exhibits similar transport affinity for diC4PC as the PC carrier in rat liver canalicular membranes.
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PMID:Expression of a non-MDR2-coded liver phosphatidylcholine membrane transport protein in Xenopus laevis oocytes. 907 Feb 63

The intracellular location of the MDR1 gene product, known as P-glycoprotein (P-gp), has been detected by flow cytometry in 3 stabilized human melanoma cell lines which had never undergone cytotoxic drug treatment and did not express P-gp on the plasma membrane. In addition, MDR1 mRNA expression was revealed by RT-PCR in the same cell lines. Immunofluorescence microscopy, performed by using the same 2 monoclonal antibodies (MM4.17 and MRK-16) as employed in the flow-cytometric analysis, revealed the presence of P-gp intracytoplasmically, in a well-defined perinuclear region. Double immunofluorescence labelling and immunoelectron microscopy strongly suggested the location of the transporter molecule in the Golgi apparatus. The same observations have been obtained on a primary culture from a metastasis of human melanoma. Analysis of the expression of another membrane transport protein, the multidrug-resistance-related protein (MRP1), showed that it was present in the cytoplasm of all the melanoma cell lines examined. MRP1 also showed Golgi-like localization. The study by laser scanning confocal microscopy on the intracellular localization of the anti-tumoral agent doxorubicin (DOX) during the drug-uptake and -efflux phases, indicated the Golgi apparatus as a preferential accumulation site for the anthracyclinic antibiotic. P-gp function modulators (verapamil and cyclosporin A) were able to modify DOX intracytoplasmic distribution and to increase drug intracellular concentration and cytotoxic effect in melanoma cells. On the contrary, MRP1 modulators (probenecid and genistein) did not significantly influence either DOX efflux and distribution or the sensitivity of melanoma cells to the cytotoxic drug.
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PMID:Detection of P-glycoprotein in the Golgi apparatus of drug-untreated human melanoma cells. 950 34

Resistance to anthelmintics that are used to control parasite populations in domestic animals has become a serious problem worldwide. The development of resistance is an evolutionary process that leads to genetic changes in parasite populations in response to drug exposure. The anthelmintic ivermectin is known to bind to the human membrane transport protein, P-glycoprotein, and P-glycoprotein-deficient mice treated with ivermectin have shown signs of neurotoxicity. P-glycoprotein is believed to be involved in the multidrug resistance phenotype seen in some human cancers and for drug resistance in some protists. We have examined the genetic variation of a P-glycoprotein homologue from the nematode Haemonchus contortus to see if an association exists between specific alleles of this gene and survival to exposure to ivermectin or moxidectin. Two parasite strains passaged without drug treatment and three strains, subjected to anthelmintic selection and derived from the unselected strains, were examined. Allelic variation in the unselected strains showed this locus to be highly polymorphic. chi 2 analyses of allele frequencies showed significant differences between the unselected and the drug-selected derived strains. In all three drug-selected strains, an apparent selection for the same allele was observed. These findings suggest that P-glycoprotein may be involved in resistance to both ivermectin and moxidectin in H. contortus.
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PMID:Selection at a P-glycoprotein gene in ivermectin- and moxidectin-selected strains of Haemonchus contortus. 980 12

The plasma membrane transport protein P-glycoprotein (P-gp) is expressed by subsets of both CD4+ and CD8+ T cells in mice. The proportion of T cells that express P-gp goes up with age, and the P-gp-expressing subset of the CD4 memory population is hyporesponsive in many in vitro assays. The significance of P-gp expression for T cell function has not been well established, although several reports have suggested that it may promote cytokine export and/or cytotoxic T cell function. To elucidate which T cell functions may require P-gp, we have compared a variety of responses using T cells from wt and P-gp knockout mice. Protein expression and rhodamine-123 efflux studies revealed that peripheral T cells exclusively utilize the mdr1a-encoded isoform rather than the homologous mdr1b or mdr2 isoforms. Comparisons of T cells from mdr1a+/+ and mdr1a-/- mice showed no differences in proliferation or in secretion of IL-2, IL-4, IL-5, IL-10, or IFN-gamma in response to polyclonal stimulation. Moreover, mdr1a-/- T cells produced strong allospecific cytotoxic responses comparable to those of wt T cells. Our results show that P-gp is not a necessary component of peripheral T cell functional responses. Further investigation will be needed to determine the significance of P-gp expression in T lymphocytes.
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PMID:mdr1a-encoded P-glycoprotein is not required for peripheral T cell proliferation, cytokine release, or cytotoxic effector function in mice. 1045 1

To clarify the function of the multidrug transporter P-glycoprotein in mast cells we used the green fluorescent compound Bodipy-FL-verapamil, which is a substrate of P-glycoprotein. This compound is also transported by Multidrug Resistance-related Protein (MRP), another membrane transport protein expressed in many tumour resistant cells as well as in normal cells. When rat peritoneal mast cells were incubated with Bodipy-verapamil, a rapid uptake of this compound was observed. Pretreatment with modulators of P-glycoprotein activity, such as verapamil and vinblastine, increased Bodipy-verapamil intracellular concentrations. In addition, Bodipy-verapamil efflux from these cells was rapid and also inhibited by verapamil and vinblastine. In contrast, no effect was observed when cells were treated with agents, such as probenecid and indomethacin, that are known inhibitors of MRP. Methylamine and monensin, substances that modify the pH values in the granules, were able to lower the concentrations of Bodipy-verapamil. Microscopical observations, conducted in both rat and beige mouse mast cells, demonstrated that the fluorochrome accumulated in the cytoplasmic secretory granules. RT-PCR performed on rat peritoneal mast cells revealed the presence of MDR1a and MDR1b mRNAs; on the contrary, MRP mRNA was not expressed. Mast cells were further treated with the fluorescent probe LysoSensor Blue, a weak base that becomes fluorescent when inside acidic organelles. This substance accumulated in mast cell granular structures and its fluorescence was reduced either by treatment with P-glycoprotein modulators or with agents that disrupt pH gradients. In conclusion, these data further confirm the presence of an active P-glycoprotein, but not of MRP, in rat peritoneal mast cells. These findings, coupled with previous ultrastructural data, lend further support to the assumption that this protein is located on the mast cell perigranular membrane. The functional role of P-glycoprotein in these cells is at present unclear, but a possible involvement in the transport of molecules from the granules to the cytosol can be hypothesized. Alternatively, this protein might be indirectly implicated in changes of pH values inside secretory granules.
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PMID:Expression and function of P-glycoprotein and absence of multidrug resistance-related protein in rat and beige mouse peritoneal mast cells. 1156 38

We had shown previously that the novel, marine, anticancer compound dehydrothyrsiferol (DHT) does not modulate P-glycoprotein (P-gp) dependent drug efflux. Many chemotherapeutics with clinical impact are substrates for the structurally distant related membrane transport protein MRP1 (multidrug resistance-associated protein 1). Thus, we were interested in analysing the behaviour of DHT and control compounds in specific drug transport of MRP1 overexpressing cells. We established a fluorescence based drug efflux system for specific, functional detection of interference of a test compound in MRP1 mediated drug extrusion. Briefly, MRP1 overexpressing HL60/Adr cells were incubated to uptake and then efflux fluorescent 5(6)-carboxyfluorescein diacetate (CFDA), rhodamine 123 (Rh123), or 3,3-diethylocarbocyanine iodide (DiOC2), respectively. Changes in cell fluorescence intensity after coincubation with the compound of interest were determined by flow cytometry. MRP1 mediated efflux of CFDA was analysed in the presence of DHT, the known substrates genistein, probenecid, and the specific inhibitor MK-571. To exclude unknown P-gp related interference in drug transport, efflux of the fluorescent P-gp substrate DiOC2 and specific inhibition by cyclosporin A (CsA) were analysed. Cytotoxicity of DHT in resistant HL60/Adr cells was found to be even superior to that in the parental HL60 leukaemia cell line. Consequently, DHT did not interfere in MRP1 mediated drug transport. In contrast to DiOC2, rhodamine 123 was not specifically effluxed by P-gp but also by MRP1. Therefore, we propose the MRP1 specific CFDA efflux model as a screening and/or excluding system for MRP1 substrates. Together with previous data our results suggest DHT to be an interesting candidate for further investigation directed towards a drug development regimen.
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PMID:Dehydrothyrsiferol does not modulate multidrug resistance-associated protein 1 resistance: a functional screening system for MRP1 substrates. 1237


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