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)

We have developed a modified rhodamine (Rho) staining procedure to study uptake and efflux in murine hematopoietic stem cells. Distinct populations of Rho++ (bright), Rho+ (dull), and Rho- (negative) cells could be discriminated. Sorted Rho- cells were subjected to a second Rho staining procedure with the P-glycoprotein blocking agent verapamil (VP). Most cells became Rho positive [Rho-/Rho(VP)+ cells] and some remained Rho negative [Rho-/Rho(VP)- cells]. These cell fractions were characterized by their marrow-repopulating ability in a syngeneic, sex-mismatch transplantation model. Short-term repopulating ability was determined by recipient survival for at least 6 weeks after lethal irradiation and transplantation--i.e., radioprotection. Long-term repopulating ability at 6 months after transplantation was measured by fluorescence in situ hybridization with a Y-chromosome-specific probe, by graft function and recipient survival. Marrow-repopulating cells were mainly present in the small Rho- cell fraction. Transplantation of 30 Rho- cells resulted in 50% radioprotection and > 80% donor repopulation in marrow, spleen, and thymus 6 months after transplantation. Cotransplantation of cells from both fractions in individual mice directly showed that within this Rho- cell fraction, the Rho-/Rho(VP)+ cells exhibited mainly short-term and the Rho-/Rho(VP)- cells exhibited mainly long-term repopulating ability. Our results indicate that hematopoietic stem cells have relatively high P-glycoprotein expression and that the cells responsible for long-term repopulating ability can be separated from cells exhibiting short-term repopulating ability, probably by a reduced mitochondrial Rho-binding capacity.
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PMID:Modification of rhodamine staining allows identification of hematopoietic stem cells with preferential short-term or long-term bone marrow-repopulating ability. 756 40

P-glycoprotein 170 (P-gp), the multidrug transport pump, excludes drugs from the interior of cells and is inhibited by agents such as cyclosporin A (CsA), verapamil, and FK-506, which are also substrates for the P-gp pump. This work documents the age- and differentiation-related changes in P-gp on T and B lymphocytes from human blood or spleen, and its absence on most thymus and bone marrow cells. Analysis of rhodamine 123 (Rh123) dye efflux, and its inhibition by cyclosporin A, was used as a quantitative measure of functional P-gp, and reactivity with MRK-16 was used as a measure of P-gp surface expression. The dye efflux and phenotypic expression of P-gp+ PBMC appeared equivalent to that of a moderately drug-resistant cell line, although efflux is prolonged. The sensitivity to inhibition by CsA, cyclosporin G (CsG), and PSC833 of P-gp on PBMC, thymocytes, or T-cell lines varied with apparent cell-type specificity. Normal blood and splenic T- or B-cells included 50-80% of cells with surface P-gp (MRK-16+), which mediated CsA-sensitive dye export. The proportion of P-gp+ T- and B-cells was lowest among children under age 10 years, increased in adulthood, and decreased after age 60. Thymus included 30% of P-gp+ cells mediating CsA-sensitive dye export, including CD3-4-8- progenitors and mature CD3hi CD4+8- or CD4-8+ thymocytes. Mature T-cells in cord or adult blood, spleen, and bone marrow included a large proportion (50-60%) with efficient CsA-sensitive dye export, preferentially among the CD45RA+ subset. Monocytes from all tissue sources, and most bone marrow cells, expressed surface P-gp but retained Rh123, suggesting the absence of a functional dye export mechanism. In vitro mitogen-stimulated PBMC T and B lymphocytes lost P-gp function within 4-24 hr, consistent with the observation that P-gp was reduced on antigen-experienced CD45R0+ T-cells in vivo. Drug export by P-gp may protect lymphocytes from toxic effects of CsA, and may contribute to the immunosuppressive effects of such drugs. The developmentally regulated expression of P-gp function on lymphocytes, and its modulation on activated T- or B-cells, suggest an important role in normal immune development.
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PMID:Multidrug transporter P-glycoprotein 170 as a differentiation antigen on normal human lymphocytes and thymocytes: modulation with differentiation stage and during aging. 763 78

P-glycoprotein (P-gly) is the transmembrane efflux pump responsible for multidrug resistance in tumor cells. The activity of P-gly in mature peripheral lymphocytes is lineage specific, with CD8+ T cells and natural killer (NK) cells expressing high levels as compared to CD4+ T cells and B cells. We have now investigated P-gly activity in immature and mature subsets of mouse thymocytes. Our data indicate that P-gly activity is undetectable in immature CD4-8- and CD4+8+ thymocyte subsets. Among mature thymocytes, P-gly activity is absent in the CD4+ subset but present in the more mature (HSAlow) fraction of CD8+ cells. Furthermore, while thymic CD4-8- T cell receptor (TCR) gamma delta cells have little P-gly activity, a minor subset of CD4-8- or CD4+ TCR alpha beta + thymocytes bearing the NK1.1 surface marker expresses high levels of P-gly activity. Collectively, our results indicate that P-gly activity arises late during thymus development and is expressed in a lineage-specific fashion.
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PMID:Developmentally regulated expression of P-glycoprotein (multidrug resistance) activity in mouse thymocytes. 777 50

P-glycoprotein (Pgp) has been widely associated with the multidrug resistance phenotype. Nevertheless, this protein has been detected in many normal tissues and cells, including liver, kidney, endothelial cells that constitute the hematological barrier of the brain and testes, and cells from the immune system. Many in vitro models have been used to study drugs that modulate Pgp activity and the multidrug resistance phenomenon. In the present work, we investigate the in vivo effects of resistance-modulating agents on lymphoid organs. Rhodamine 123 (Rho123), a well-known Pgp substrate, was administered to mice, and the fluorescence level in thymus and lymph node cells measured. The fluorescence level on these organs showed a dose-dependent response. Cyclosporin A (CSA), Verapamil (VP) and Trifluoperazine (TFP), three resistance-modulating agents, were administered to mice 1 h prior to 1 mg/kg Rho123 administration. Surprisingly, VP (10 mg/kg) and TFP (750 microg/kg) did not modulate Rho123 retention by thymus and lymph node cells. CSA (50 mg/kg) was the only drug that increased the fluorescence level in both organs. These results point out to the need of a wider study on the in vivo effects of resistance-modulating agents in different organs and systems.
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PMID:The in vivo effect of the administration of resistance-modulating agents on rhodamine 123 distribution in mice thymus and lymph nodes. 1037 99

Both p53 and multidrug transporters play important roles in chemoresistance. A transcriptional dependence of the Mdr1 gene promoter by p53 was first established a decade ago, and despite intense study, the p53-Mdr1 relationship still remains vague in vivo. The general model proposes that wild-type p53 down regulates, while mutant p53 up regulates, the Mdr1 promoter. Given that many studies have utilized cancer cell lines, minimal promoters and non-specific cDNA expression for in vitro experiments, we first sought to confirm the model using dermal fibroblasts isolated from the p53-knockout mice. We show that the gene products of the mouse Mdr1 homologue (Mdr1a and Mdr1b), namely P-glycoprotein (P-gp), appear upregulated at both the protein and mRNA levels in p53(-/-) mFbs compared with p53(+/+) cells. We demonstrate that transient transfection of a mouse p53(WT) expression plasmid into short-term primary p53(-/-) fibroblasts can revert P-gp overexpression. The difference in P-gp levels has functional significance in that p53(-/-) fibroblasts are more resistant to doxorubicin and vincristine treatment and this resistance can be attenuated in the presence of the P-gp inhibitor, verapamil. Furthermore, we demonstrate that in kidney, spleen and testis, P-gp expression is elevated in the absence of p53. In contrast, other organs such as heart, liver, lung, brain, thymus and skeletal muscle, show no difference in expression between p53(+/+) and p53(-/-) mice. Thus, our data shows a tissue-specific regulation of P-gp isoforms by p53 in the context of a p53-null mouse model.
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PMID:Regulation of the Mdr1 isoforms in a p53-deficient mouse model. 1237 67

ATP-binding cassette (ABC) transporters play a pivotal role in physiology and pathology. We identified and cloned two novel mRNA isoforms (ABCB 5alpha and ABCB 5beta) of the ABC transporter ABCB 5 in human melanoma cells. The deduced ABCB 5alpha protein appears to be an altered splice variant containing only a putative ABC, whereas the ABCB 5beta isoform shares approximately 70% similarity with ABCB1 (MDR1) and has a deduced topological arrangement similar to that of the whole carboxyl terminal half of the ABCB1 gene product, P-glycoprotein, including an intact ABC. Northern blot, real-time PCR, and conventional RT-PCR were used to verify the expression profiles of ABCB 5alpha/beta. We found that the melanomas included among the NCI-60 panel of cell lines preferentially expressed both ABCB 5alpha and ABCB 5beta. However, ABCB 5alpha/beta expression was undetectable in two amelanotic melanomas (M14 and LOX-IMVI). The expression profile of ABCB 5alpha/beta in all of the other melanomas of the panel was confirmed both by RT-PCR and by sequencing. Neither ABCB 5alpha nor ABCB 5beta expression was found in normal tissues such as liver, spleen, thymus, kidney, lung, colon, small intestines or placenta. ABCB 5alpha/beta mRNAs were also expressed in normal melanocytes and in retinal pigment epithelial cells, suggesting that ABCB 5alpha/beta expression is pigment cell-specific and might be involved in melanogenesis. Our findings indicate that expression of ABCB 5alpha/beta might possibly provide two novel molecular markers for differential diagnosis of melanomas and constitute potential molecular targets for therapy of melanomas.
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PMID:Principal expression of two mRNA isoforms (ABCB 5alpha and ABCB 5beta ) of the ATP-binding cassette transporter gene ABCB 5 in melanoma cells and melanocytes. 1576 Mar 39

The synthetic glucocorticoid dexamethasone (dex) blocks stress-induced hypothalamic-pituitary-adrenal (HPA) activation primarily at the level of the anterior pituitary because multidrug resistance P-glycoprotein hampers its penetration in the brain. Here, we tested the hypothesis that central components of the HPA axis would escape dex suppression under conditions of potent peripheral glucocorticoid action. We subchronically treated rats with low or high doses of dex. The animals were subjected on the last day of treatment for 30 min to a restraint stressor after which central and peripheral markers of HPA axis activity were measured. Basal and stress-induced corticosterone secretion, body weight gain, adrenal and thymus weight, as well as proopiomelanocortin mRNA in the anterior pituitary were reduced in a dose-dependent manner by dex administered either 5 d sc or 3 wk orally. In the brain, the highest dose dex suppressed CRH mRNA and CRH heteronuclear RNA in the paraventricular nucleus (PVN). However, in the peripherally active low-dose range of dex CRH mRNA and heteronuclear RNA showed resistance to suppression, and CRH mRNA expression in the PVN was in fact enhanced under the long-term treatment condition. In the PVN, c-fos mRNA was suppressed by the highest dose of dex, but this effect showed a degree of resistance after long-term oral treatment. c-fos mRNA responses in the anterior pituitary followed those in PVN and reflect central drive of the HPA axis even if corticosterone responses are strongly reduced. The results support the concept that low doses of dex can create a hypocorticoid state in the brain.
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PMID:Low doses of dexamethasone can produce a hypocorticosteroid state in the brain. 1615 Sep 12

Recently, we reported that the ATP-binding cassette transporter 10 (ABCC10), also known as multidrug resistance protein 7 (MRP7), is able to confer resistance to a variety of anticancer agents, including taxanes. However, the in vivo functions of the pump have not been determined to any extent. In this study, we generated and analyzed Abcc10(-/-) mice to investigate the ability of Abcc10 to function as an endogenous resistance factor. Mouse embryo fibroblasts derived from Abcc10(-/-) mice were hypersensitive to docetaxel, paclitaxel, vincristine, and cytarabine (Ara-C) and exhibited increased cellular drug accumulation, relative to wild-type controls. Abcc10(-/-) null mice treated with paclitaxel exhibited increased lethality associated with neutropenia and marked bone marrow toxicity. In addition, toxicity in spleen and thymus was evident. These findings indicate that Abcc10 is dispensable for health and viability and that it is an endogenous resistance factor for taxanes, other natural product agents, and nucleoside analogues. This is the first demonstration that an ATP-binding cassette transporter other than P-glycoprotein can affect in vivo tissue sensitivity toward taxanes.
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PMID:Contribution of Abcc10 (Mrp7) to in vivo paclitaxel resistance as assessed in Abcc10(-/-) mice. 2157 88