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)

The multidrug resistance phenotype is found to be frequently associated with the overexpression of proteins which lead to a decrease of drug accumulation within human tumor cells. A 170 kDa membrane glycoprotein which is related to the overexpression of the mdr1 gene is inserted in the plasma membrane and pumps the cytotoxic drugs out of the cells. The aim of this work was to study the morphological modifications of resistant CEM/VLB 100 cells relative to their parental drug-sensitive ones and the detection of the ultrastructural localization of P-glycoprotein at the cytoplasmic level. Using a scanning electron microscope, CEM resistant cells showed wide smooth protrusions while CEM sensitive cells showed microvilli and fine folds. With transmission electron microscopy, an enhanced secretory system was observed in CEM resistant cells: both electron transparent and electron opaque vesicles were associated with the Golgi system, revealed by wheat germ agglutinin-colloidal gold labelling. These vesicles were the binding site of C 219 and MRK 16 antimembrane glycoprotein antibodies, and some of them were determined to belong to the lysosomal system after PTA staining. These vesicles may be an additional way to decrease the cellular uptake of drugs in multidrug resistant cells. Moreover, some nuclear and nucleolar modifications were also observed. These observations show that MDR has wide morphological features which concern several organelles.
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PMID:Ultrastructural changes related to multidrug resistance in CEM cells: role of cytoplasmic vesicles in drug exclusion. 941 88

Strictly speaking, multidrug resistance (MDR) describes the experimental observation of cross resistance to various structurally unrelated cytotoxic agents in laboratory models of cancer. These drugs have in common their origin as natural products, and in 1985 the basis of this MDR was established as the over-expression of a membrane glycoprotein, called P-glycoprotein (Pgp), which acts as a drug efflux pump actively depleting intracellular drug concentrations in resistant tumour cells. Since then, MDR has arguably taken on a second meaning, i.e. 'misunderstood drug resistance', through the understandable, but mistaken assumption by many scientists and some clinicians that the clinical observation in cancer patients treated with chemotherapy of resistance to a wide range of cytotoxic drugs (either as a primary or acquired property) inevitably involves the same mechanism. At present, the evidence from clinical studies to support such a notion is clearly lacking, particularly in solid tumours. However, increased Pgp expression has been observed in a number of clinical situations, and its relevance requires further elucidation. Current data indicate that increased Pgp expression represents an adverse prognostic factor, for reasons which may be quite unrelated to developing drug resistance. Experimentally, MDR can be reversed by simultaneous treatment with a number of non-cytotoxic agents which competitively inhibit Pgp function. Despite the reservations outlined, numerous clinical trials of this approach have been conducted. The results have generally been negative in solid tumours, although some have been more promising in haematological cancers. The most recent studies have used more potent modulating agents, such as the cyclosporin analogue, PSC833. Interpretation of data from these trials is complicated by pharmacokinetic interactions between the target cytotoxic drug and the modulating agent. Randomized trials are now underway in a number of tumour types; thus a clearer picture of the clinical relevance of MDR should emerge over the next few years.
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PMID:Multidrug resistance: clinical relevance in solid tumours and strategies for circumvention. 980 54

P-glycoprotein (P-gp), a plasma membrane glycoprotein associated with the multidrug resistance phenotype, is responsible for the ATP-dependent efflux of various amphiphilic drugs. Using membrane vesicles prepared from the multidrug resistant cell line DC-3F/ADX, we studied the perturbation of the basal (i.e. in the absence of drug) and verapamil-dependent P-gp ATPase activities induced by various detergents, at non-solubilizing, as well as at solubilizing, concentrations. The progressive membrane solubilization with increasing detergent concentration was monitored by light scattering and centrifugation experiments. For non-solubilizing detergent concentrations, all tested detergents except DOC induced a partial inhibition of P-gp ATPase activity, which was not correlated with the amount of the various tested detergents incorporated in the membranes. Analysis of the verapamil-induced P-gp activation reveals that P-gp ATPase activity is differently modulated by the various detergents at non-solubilizing concentrations. Thus, specific interactions between P-gp and detergents are more likely to occur rather than a global membrane perturbation. After solubilization by the various tested detergents, the basal P-gp ATPase activity was virtually completely inhibited, except in the presence of CHAPS which was able to preserve this activity at a level comparable to that measured in native membranes. However, the verapamil-induced P-gp ATPase activation was lost during P-gp solubilization by CHAPS, but recovered after dilution of CHAPS below its critical micellar concentration. These observations indicate specific interactions between P-gp and CHAPS molecules within the mixed micelles. On the whole, our data evidencing specific interactions P-gp/detergents are consistent with the location of the drug transport sites on P-gp transmembrane domains.
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PMID:Effects of detergents on P-glycoprotein atpase activity: differences in perturbations of basal and verapamil-dependent activities. 992 70

P-glycoprotein (Pgp) is a plasma-membrane glycoprotein that confers multi-drug resistance (MDR) on cells and displays ATP-driven drug pumping. The possible contribution of calpain-mediated proteolytic pathways to the functional regulation of the Pgp molecule was evaluated using K562/DXR, MDR cells. N-Acetyl-L-leucyl-L-leucyl-norleucinal was effluxed by Pgp, but N-benzyloxycarbonyl-L-leucyl-L-leucinal (zLLal), an inhibitor of calpain, retarded the degradation of Pgp leading to accumulation of the molecule largely at the cell surface membrane. Treatment with brefeldin A did not obstruct the zLLal-induced Pgp accumulation. NH4Cl increased the cytoplasmic Pgp level, with a slight to significant decrease at the cell surface membrane. Ubiquitin-ELISA and western blot analysis confirmed that the Pgp molecule, which accumulated mainly at the cell surface, was ubiquitinated. However, lactacystin did not show any accumulation of Pgp in either the cytoplasm or the cell surface membrane, suggesting that the proteasome did not participate in the phenomenon. Additionally, the Pgp was limitedly proteolyzed by calpain into two 98 kDa and 69 kDa, fragments within one minute. Despite the increased accumulation of Pgp at the cell surface after treatment with calpain inhibitor, the cytoplasmic doxorubicin level of the cells treated with a calpain inhibitor was higher than that of non-treated cells and approached that of parental cells. These results indicated that calpain involved Pgp turnover and that calpain inhibition induced ubiquitinated Pgp-accumulation mainly at the cell surface membrane with a reduction in its own functions suggesting that the modulation of Pgp-turnover involves MDR-reversal by another approach.
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PMID:Calpain inhibitor causes accumulation of ubiquitinated P-glycoprotein at the cell surface: possible role of calpain in P-glycoprotein turnover. 1049 48

P-glycoprotein (Pgp), the so-called multidrug transporter, is a plasma membrane glycoprotein often involved in the resistance of cancer cells towards multiple anticancer agents in the multidrug-resistant (MDR) phenotype. It has long been recognized that the lipid phase of the plasma membrane plays an important role with respect to multidrug resistance and Pgp because: the compounds involved in the MDR phenotype are hydrophobic and diffuse passively through the membrane; Pgp domains involved in drug binding are located within the putative transmembrane segments; Pgp activity is highly sensitive to its lipid environment; and Pgp may be involved in lipid trafficking and metabolism. Unraveling the different roles played by the membrane lipid phase in MDR is relevant, not only to the evaluation of the precise role of Pgp, but also to the understanding of the mechanism of action and function of Pgp. With this aim, I review the data from different fields (cancer research, medicinal chemistry, membrane biophysics, pharmaceutical research) concerning drug-membrane, as well as Pgp-membrane, interactions. It is emphasized that the lipid phase of the membrane cannot be overlooked while investigating the MDR phenotype. Taking into account these aspects should be useful in the search of ways to obviate MDR and could also be relevant to the study of other multidrug transporters.
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PMID:Analysis of the tangled relationships between P-glycoprotein-mediated multidrug resistance and the lipid phase of the cell membrane. 1063 98

MRP1 is a 190-kDa membrane glycoprotein that confers multidrug resistance (MDR) to tumor cells. MRP1 is characterized by an N-terminal transmembrane domain (TMD(0)), which is connected to a P-glycoprotein-like core region (DeltaMRP) by a cytoplasmic linker domain zero (L(0)). It has been demonstrated that GSH plays an important role in MRP1-mediated MDR. However, the mechanism by which GSH mediates MDR and the precise roles of TMD(0) and L(0) are not known. We synthesized [(125)I]11-azidophenyl agosterol A ([(125)I]azidoAG-A), a photoaffinity analog of the MDR-reversing agent, agosterol A (AG-A), to photolabel MRP1, and found that the analog photolabeled the C-proximal molecule of MRP1 (C(932-1531)) in a manner that was GSH-dependent. The photolabeling was inhibited by anticancer agents, reversing agents and leukotriene C(4). Based on photolabeling studies in the presence and absence of GSH using membrane vesicles expressing various truncated, co-expressed, and mutated MRP1s, we found that L(0) is the site on MRP1 that interacts with GSH. This study demonstrated that GSH is required for the binding of an unconjugated agent to MRP1 and suggested that GSH interacts with L(0) of MRP1. The photoanalog of AG-A will be useful for identifying the drug binding site within MRP1, and the role of GSH in transporting substrates by MRP1.
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PMID:Glutathione-dependent binding of a photoaffinity analog of agosterol A to the C-terminal half of human multidrug resistance protein. 1130 32

The human MDR1-encoded transporter is a 170-kDa plasma membrane glycoprotein [P-glycoprotein (P-gp)] capable of binding and energy-dependent extrusion of structurally diverse organic compounds and drugs. P-gp seems to play a significant role in uptake, distribution, and excretion of many different drugs. To determine whether common polymorphic forms of P-gp are likely to alter function of P-gp, we characterized five known MDR1 coding polymorphisms (N21D, F103L, S400N, A893S, and A998T) using a vaccinia virus-based transient expression system. Cell surface expression of wild-type P-gp was time-dependent over a time course of 5.5 to 34.5 h; highest expression was obtained by 22 to 26.5 h after infection/transfection, indicating that a semiquantitative assay for P-gp expression levels was possible. HeLa cells stained with the P-gp specific monoclonal antibodies MRK-16 and Western blots probed with C219 revealed similar cell surface expression for the polymorphisms and for wild-type protein. Time-dependent P-gp pump function maximal at 22 h after infection/transfection was demonstrated for the following MDR1 fluorescence substrates: 4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-pentanoic acid, succinimidyl ester (bodipy-FL)-verapamil, bodipy-FL-vinblastine, calcein-AM, bodipy-FL-prazosin, bisantrene, and bodipy-FL-forskolin, but not for daunorubicin. Transport studies of all tested substrates indicated that the substrate specificity of the pump was not substantially affected by any of the tested polymorphisms. Cell surface expression and function of double mutants including the more common polymorphisms (N21D-S400N, N21D-A893S, and S400N-A893S) showed no differences from wild-type. These results demonstrate that the common MDR1 coding polymorphisms result in P-gps with a cell surface distribution and function similar to wild-type P-gp.
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PMID:Functional characterization of coding polymorphisms in the human MDR1 gene using a vaccinia virus expression system. 1206 48

Overexpression of a 170kD membrane glycoprotein, P-glycoprotein (Pgp), which acts as an energy dependent efflux pump for cytotoxic drugs is believed to be one of the factors that is responsible for clinical drug resistance. Recent studies suggest that Pgp is also responsible for the intracellular transport of cholesterol from the plasma membrane to the endoplasmic reticulum. Leukemic cells from patients with acute myelogenous leukemia have an elevated uptake of low density lipoprotein (LDL) when compared with white blood cells from healthy individuals. Since elevated LDL receptor expression and multidrug resistance are both common events in leukemic cells, we investigated LDL receptor expression in sensitive and drug resistant human leukemic cell lines. We found a 2- to 10-fold higher uptake of LDL in five out of five drug resistant K562 cell lines. All three drug resistant HL60 cell lines studied also had higher uptake than the parental cells. The LDL receptor expression in vincristine resistant Pgp positive K562 cells was less sensitive to downregulation by sterols than in parental cells. There was no selective effect of the Pgp inhibitor PSC-833 or other Pgp modulators on LDL receptor activity in Pgp positive cells. Since also resistant Pgp, multidrug resistance protein 1, and breast cancer resistance protein negative cells exhibited an elevated LDL receptor activity, we conclude that overexpression of these proteins is not the mechanism behind the elevated LDL uptake in the drug resistant leukemic cell lines. The findings are of interest for the concept of using lipoproteins as carriers of cytotoxic drugs in cancer treatment.
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PMID:Elevated uptake of low density lipoprotein by drug resistant human leukemic cell lines. 1211 Mar 76

P-glycoprotein (P-gp) is a plasma membrane glycoprotein that confers multidrug resistance on cells by virtue of its ability to exclude cytotoxic drugs in an ATP-dependent manner. The most commonly considered hypothesis is that P-gp acts as an ATP-driven drug-export pump, the mechanism of which is not understood in detail. Therefore, a tremendous effort is being made to find out modulator molecules to inhibit P-gp. We have been developing flavonoid derivatives as a new class of promising modulators using a new in vitro rational-screening assay based on measurements of the binding-affinity toward the C-terminal nucleotide-binding domain (NBD2) of P-gp. This review is focused on our results obtained with a variety of flavonoids. Structure-activity relationships of flavonoids as potential MDR modulators are reported.
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PMID:Recent advances in the discovery of flavonoids and analogs with high-affinity binding to P-glycoprotein responsible for cancer cell multidrug resistance. 1221 May 57

P-glycoprotein (P-gp) is a plasma membrane glycoprotein that can cause multidrug resistance (MDR) of cancer cells by acting as an ATP-dependent drug efflux pump. The regulatory effects of the small GTPases Rab5 and RalA on the intracellular trafficking of P-gp were investigated in HeLa cells. As expected, overexpressed enhanced green fluorescent protein (EGFP)-tagged P-gp (P-gp-EGFP) is mainly localised to the plasma membrane. However, upon cotransfection of either dominant negative Rab5 (Rab5-S34N) or constitutively active RalA (RalA-G23V) the intracellular P-gp-EGFP levels increased approximately 9 and 13 fold, respectively, compared to control P-gp-EGFP cells. These results suggest that Rab5 and RalA regulate P-gp trafficking between the plasma membrane and an intracellular compartment. In contrast, coexpression of constitutively active Rab5 (Rab5-Q79L) or dominant negative RalA (RalA-S28N) had no effect on the localisation of P-gp-EGFP. Furthermore, the intracellular accumulation of daunorubicin, a substrate for P-gp, increased significantly with an increased intracellular localisation of P-gp-EGFP. These results imply that it may be possible to overcome MDR by controlling the plasma membrane localisation of P-gp.
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PMID:The small GTPases Rab5 and RalA regulate intracellular traffic of P-glycoprotein. 1752 4


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