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)

We used a series of P-glycoprotein (P-gp) expressing multidrug-resistant (MDR) cells, developed from human breast cancer MCF-7 cells by exposure to Adriamycin, to investigate the effects of flavonoids on P-gp-mediated efflux mechanisms for chemical carcinogens. We previously showed that MDR cells derived from exposure to Adriamycin are cross-resistant to a chemical carcinogen, benzo(a)pyrene, due to its cellular efflux by the P-gp-mediated putative drug efflux pump. Our current studies extended this observation to another polycyclic aromatic hydrocarbon, 7,12-dimethylbenz(a)anthracene, known to induce mammary tumors in animals. In our attempt to find naturally occurring dietary compounds which may stimulate the P-gp-mediated efflux of carcinogens, we found that certain flavonols, kaempferol, quercetin, and galangin, are potent stimulators of the P-gp-mediated efflux of 7,12-dimethylbenz(a)-anthracene. The increased efflux decreased the cellular burden of 7,12-dimethylbenz(a)anthracene. Since these flavonol compounds are widely distributed in fruits and vegetables, their stimulatory effect on P-gp may be a mechanism relevant to carcinogenesis and the observed lowered cancer risk in humans with higher dietary intake of fruits and vegetables.
Cancer Res 1993 Dec 15
PMID:Flavonol-stimulated efflux of 7,12-dimethylbenz(a)anthracene in multidrug-resistant breast cancer cells. 790 98

Multidrug-resistant cells are thought to maintain low intracellular cytotoxic drug concentration though the active efflux of drugs across the cell membrane. It is presently believed that P-glycoprotein mediates this energy-dependent drug efflux by interacting directly with various lipophilic compounds. In this report, we have used [3H]azidopine in a photoaffinity labeling assay to study the effect of detergents and denaturing agents on P-glycoprotein drug binding in intact cells. Nonionic detergents such as Triton X-100 or Nonidet P-40 at very low concentrations were found to completely abolish azidopine photolabeling to P-glycoprotein and are able to reverse the multidrug resistance phenotype. In contrast, high concentrations of the denaturing agent urea or the zwitterionic detergent 1-[(3-cholamidopropyl)dimethylamino]-1-propanesulfonate did not inhibit azidopine photolabeling to P-glycoprotein. A comparison between verapamil and Triton X-100 revealed that the latter was more effective in inhibiting azidopine photolabeling to P-glycoprotein while verapamil was more effective in potentiating [3H]vinblastine accumulation in drug-resistant cells. Drug transport studies showed that [3H]Triton X-100 accumulated in both drug-sensitive and -resistant cells, and its accumulation was not modulated by excess vinblastine, verapamil, or colchicine. Taken together, these findings suggest that low concentrations of Triton X-100 reverse the multidrug resistance phenotype by inhibiting P-glycoprotein drug binding. In addition, it is also suggested that the site(s) of P-glycoprotein drug binding is localized to sequences found within the lipid bilayer.
Cancer Res 1993 Dec 15
PMID:Effects of nonionic detergents on P-glycoprotein drug binding and reversal of multidrug resistance. 790

The multidrug resistance (MDR) P-glycoprotein (P-gp) is an active transporter associated with chemoresistance of tumor cells. A fundamental aspect not yet entirely clarified is the physiological role of MDR-P-gp in normal mammalian tissues. In this paper we report that multidrug (chemo)resistance is already present in mouse oocytes and early cleavage embryos. Expression of MDR-specific P-gp is detectable by antibody (C219) staining from the primary oocyte onward to the eight-cell embryo. MDR-mRNA is demonstrated in mature oocytes using an Mdr1-specific cDNA probe. Functional activity of P-gp is shown by the efficacy of MDR reversers (verapamil or quinidine) in enhancement of: 1) drug accumulation (daunomycin) in all stages investigated, 2) drug cytotoxicity (daunomycin or mitomycin c-induced developmental impairment) in two-cell embryos cultured for 24 h, and 3) drug cytokinesis-blocking activity (cytochalasin D; our recent findings demonstrate cytochalasins to be substrates for P-gp and to indicate the presence of MDR by their microfilament-disrupting action on cycling cells) in four- and eight-cell embryos cultured for 24 h. Furthermore, functional involvement of P-gp in vivo is demonstrated. Concurrent administration of verapamil increases doxorubicin-induced developmental impairment in the zygote stage during the first cleavage cycle in pregnant females. Results provide evidence that MDR-P-gp has an efficient protective function in early reproduction.
FASEB J 1993 Dec
PMID:P-glycoprotein regulates chemosensitivity in early developmental stages of the mouse. 790 62

To evaluate the role of P-glycoprotein in steroid secretion in adrenal cells, we have used gene targeting to introduce a null mutation into one allele of the mdr1b gene in mouse Y1 adrenal cells. Characterization of both the wild-type and the mutant cell lines revealed the following. 1) The expression of mdr1b is enhanced by steroid hormones, in a feedback regulatory mechanism. Inhibition of steroid biosynthesis by 2-aminoglutethimide blocks the adrenocorticotropin (ACTH)-induced increase in mdr1b mRNA levels. 2) ACTH-stimulated steroid secretion is markedly decreased in the mutant cell line. This decreased steroid secretion in the mutant cells occurs despite an increase in the levels of mdr1b mRNA and P-glycoprotein. Kinetic analyses of vinblastine and daunomycin accumulation in both the wild-type and the mutant cell lines during ACTH-stimulated steroidogenesis show that in the mutant cells both drugs accumulated to higher levels than in Y1 cells, suggesting that the remaining mdr1b allele in the mutant cells is relatively inactive as an exporter of steroids, or that the targeted disruption of the mdr1b allele is associated with other changes in the mutant cells which block ACTH-stimulated steroid secretion.
J Biol Chem 1993 Dec 25
PMID:Targeted disruption of the mouse mdr1b gene reveals that steroid hormones enhance mdr gene expression. 790 3

We have expressed P-glycoprotein (P-gp) encoded by the mouse mdr3 gene in the yeast Saccharomyces cerevisiae and have developed an experimental protocol to isolate and purify inside-out plasma membrane vesicles (IOVs) from these cells. Biochemical characterization of IOVs from control and P-gp-expressing cells isolated by this procedure show that they are greatly enriched for plasma membrane markers, are tightly sealed, and are competent for D-glucose transport. P-gp expression in these vesicles results in the appearance of a specific ATP-dependent and temperature-sensitive transport of the drugs colchicine and vinblastine that is osmotically sensitive. P-gp-mediated drug transport into these IOVs is inhibited by a known P-gp modulator, verapamil, and can be abrogated by prior incubation of the IOVs with an anti-P-gp antibody. A Ser-939-->Phe mutation within the predicted transmembrane domain 11 of P-gp, which is known to modulate its function in mammalian cells, drastically reduces drug transport in IOVs obtained from yeast cells expressing the mutant protein. The successful demonstration of active drug transport into IOVs from P-gp-expressing yeast cells indicates that P-gp can mediate both chemotherapeutic drugs and a-pheromone transport in yeast cells.
Proc Natl Acad Sci U S A 1993 Dec 15
PMID:Functional expression of P-glycoprotein encoded by the mouse mdr3 gene in yeast cells. 790 52

The characteristics of cyclosporin A (CsA) transport across Caco-2 monolayers were investigated. CsA (0.25-5.0 microM) was transported in a time and concentration dependent manner. The total amount of apical (AP) to basolateral (BL) transport was non-linearly related to CsA concentration from 0.25 to 1 microM and was linear from about 1 to 5 microM. Average permeability coefficient (Papp) values obtained in the AP to BL direction showed CsA concentration (0.5 and 5.0 microM) dependence, whereas those of the reverse (BL to AP) process did not. Papp values for the AP to BL direction were also markedly lower. When the P-glycoprotein pump inhibitors, chlorpromazine and progesterone, were included in the transport medium we observed a significant increase in CsA (0.5 and 5.0 microM) transport from the AP to BL direction; transport was decreased in the reverse direction. This study suggests that CsA is transported across Caco-2 cells by passive diffusion, but that a polarized efflux system (presumably a P-glycoprotein pump) located at the apical membrane can attenuate the net AP to BL transport.
Biochem Biophys Res Commun 1993 Dec 15
PMID:Evidence for a polarized efflux system in CACO-2 cells capable of modulating cyclosporin A transport. 790 26

Resistance may limit the clinical usefulness of a variety of chemotherapeutic drugs including mitomycin C (MMC). The MMC-sensitive HT-29 colon cancer cell line and its MMC-resistant subline, HT-29R13, were studied in vitro under aerobic conditions to help characterize the mechanisms associated with MMC resistance. HT-29R13 cells exhibit approximately 2-fold resistance to MMC compared with HT-29 cells and lack the typical multidrug-resistance pattern; resistance is stable in the absence of drug exposure. Levels of glutathione (GSH) and total glutathione-S-transferase (GST) activity were not different between the two cell lines; however, levels of GSH reductase and GSH peroxidase were increased significantly in HT-29R13. Although total GST activity was unchanged, GST-pi and GST-alpha isoenzyme expression as measured using western blot were increased significantly in HT-29R13 compared with HT-29. DT-diaphorase levels and topoisomerase II activity were decreased significantly in HT-29R13. Both cell lines had equal P-glycoprotein expression. Multiple drug resistance mechanisms are present in HT-29R13 including decreased drug activation (decreased DT-diaphorase), increased drug detoxification (increased GST-pi and GST-alpha, GSH reductase, GSH peroxidase), and decreased accessibility of DNA targets (decreased topoisomerase II). Further work will be necessary to determine the degree to which each of these mechanisms contribute to MMC resistance in this model.
Biochem Pharmacol 1993 Dec 03
PMID:Biochemical characterization of a mitomycin C resistant colon cancer cell line variant. 790 34

P-glycoprotein (Pgp) is a polytopic plasma membrane protein thought to function as a drug efflux pump. Two functional groups of Pgp have been identified in mammalian cells. One group (classes I and II) is associated with MDR and the other (class III) is not. Transmembrane (TM) sequences in Pgp have been postulated to be important for determining drug specificity. TM11 and TM12 have been predicted to bind drugs and play an important role in determining drug specificity of MDR-associated Pgps. Whether or not the membrane insertion and orientation of these TM segments differ amongst the different classes of Pgp has not been examined directly. In this study, we showed that membrane insertion and orientation of TM11 and TM12 of the MDR-associated Pgp may differ from the non-MDR-associated Pgp using an in vitro transcription and translation system. Charged amino acids surrounding TM domains are thought to be important in determining the topology of membrane proteins. The positively charged amino acids surrounding TM11 and TM12 of these two forms of Pgp are different. By site-directed mutagenesis we showed that these amino acids may affect the membrane orientation but not membrane insertion of these TMs. These results raise the possibility that a difference in membrane anchorage may be a underlying cause for the functional difference between the two groups of Pgp.
Biochim Biophys Acta 1993 Dec 12
PMID:Membrane orientation of transmembrane segments 11 and 12 of MDR- and non-MDR-associated P-glycoproteins. 790 65

Using degenerate oligodeoxyribonucleotides from conserved regions of the gene family encoding ATP-binding domain of the active transporter, two new Escherichia coli genes were identified. The first of the genes, named mdl (multidrug resistance-like), is located at min 10.2 of the E. coli chromosome and encodes two ATP-binding motifs and two hydrophobic (transmembrane) domains. The ATP-binding domains of mdl show 35-38% amino acid (aa) identity with members of the eukaryotic P-glycoprotein/multidrug resistance family. To date, 25 members of the ATP-transporter/permease gene family have been characterized in E. coli. Comparison of the ATP-binding domains from this family indicates that mdl is part of a distinct subfamily of sequences that includes hlyB, msbA, and cvaB. Gene-disruption studies revealed that mdl is not essential for cell growth. The second open reading frame, named abc (ATP-binding cassette), is located at min 4.9 of the chromosome, encodes a single ATP-binding domain, and is most homologous to ftsE, a cell division control gene of E. coli. The abc gene product also shows aa sequence homology to several E. coli permeases.
Gene 1993 Dec 22
PMID:Cloning and organization of the abc and mdl genes of Escherichia coli: relationship to eukaryotic multidrug resistance. 790 73

Verapamil, cyclosporin A (CsA), the cyclosporin derivative SDZ PSC 833 and the novel cyclopeptolide SDZ 280-446 were tested for their capacity to chemosensitize a P-glycoprotein (Pgp)-expressing multi-drug resistant (MDR) variant of the CEM human T lymphoblastoid cell subline (CCRF ACTD 400+). That MDR-CEM cell subline had been previously selected for MDR by actinomycin D and displayed a very high resistance phenotype: 3700-fold for actinomycin D, 3900-fold for vincristine, 1200-fold for taxol, 1000-fold for daunomycin (DAU) and 400-fold for colchicine. Interestingly, these MDR-CEM cells displayed little chemosensitization by resistance-modulating agents (RMA) which presumably work by inhibiting Pgp function. These MDR-CEM cells displayed virtually no chemosensitization by 1 microM verapamil or 1 microgram/ml (about 0.8 microM) CsA, whereas their chemosensitization for different anti-cancer drugs (ACD) was rather stable (from 51- to 82-fold) with 1 microgram/ml (about 0.8 microM) SDZ 280-446, while being very unbalanced (from 5- to 38-fold) with 1 microgram/ml (about 0.8 microM) SDZ PSC 833. Exposure of the MDR-CEM cells to Pgp-directed RMAs, during their loading with DAU (DAU-loading phase), hardly restored DAU retention: SDZ 280-446 being as poorly active as SDZ PSC 833, and about only 3- and 4-fold more active than CsA and verapamil. In contrast, SDZ PSC 833 treatment of human MDR-KB and MDR-LoVo cell lines under the same conditions could restore most or all the DAU retention shown by the parental (Par) cells, in spite of their high level of resistance. By keeping the MDR-CEM cells in the presence of RMA throughout the experiment (both DAU-loading and DAU-efflux phases), a better DAU retention could be restored by the different RMAs used, their order of relative restoration activity being SDZ 280-446 3- to 4-fold > SDZ PSC 833 3- to 10-fold > CsA 2- to 4-fold > verapamil. Nevertheless, the level of DAU retention restored in the MDR-CEM cells reached a plateau at 50% of the Par-CEM cell level. Therefore, although the MDR-CEM cells expressed easily detectable membranous Pgp molecules and probably used them for DAU efflux, they displayed an additional efflux mechanism that was not sensitive to the Pgp inhibitors.
Anticancer Drugs 1993 Dec
PMID:Atypical multi-drug resistance (MDR): low sensitivity of a P-glycoprotein-expressing human T lymphoblastoid MDR cell line to classical P-glycoprotein-directed resistance-modulating agents. 790


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