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 pathogenic yeast, Candida albicans, is insensitive to the anti-mitotic drug, benomyl, and to the dihydrofolate reductase inhibitor, methotrexate. Genes responsible for the intrinsic drug resistance were sought by transforming Saccharomyces cerevisiae, a yeast sensitive to both drugs, with genomic C. albicans libraries and screening on benomyl or methotrexate. Restriction analysis of plasmids isolated from benomyl- and methotrexate-resistant colonies indicated that both phenotypes were encoded by the same DNA fragment. Sequence analysis showed that the fragments were nearly identical and contained a long open reading frame of 1694 bp (ORF1) and a small ORF of 446 bp (ORF2) within ORF1 on the opposite strand. By site-directed mutagenesis, it was shown that ORF1 encoded both phenotypes. The protein had no sequence similarity to any known proteins, including beta-tubulin, dihydrofolate reductase, and the P-glycoprotein of the multi-drug resistance family. The resistance gene was detected in several C. albicans strains and in C. stellatoidea by DNA hybridization and by the polymerase chain reaction.
Mol Gen Genet 1991 Jun
PMID:Analysis of a Candida albicans gene that encodes a novel mechanism for resistance to benomyl and methotrexate. 206 11

Resistance to chemotherapeutic agents in neoplastic cells is often mediated by expression of P-glycoprotein, which functions as a drug-efflux pump for a broad range of substrates. We have used a combination of patch clamp and video-imaging techniques to examine the expression and drug-efflux function of P-glycoprotein and to determine the possible correlation with swelling-activated chloride channels in drug-sensitive and -resistant cell lines. Two pairs of cell lines were used in these experiments: (a) control NIH-3T3 cells and a corresponding MDR1-transfectant; and (b) control 8226 myeloma cells and a derivative cell line selected for resistance to chemotherapeutic agents. Control cells lacked detectable P-glycoprotein expression based on Western blotting, immunofluorescence staining with a specific monoclonal antibody, and a functional assay of rhodamine-123 (R123) efflux. Resistant cells expressed P-glycoprotein at high levels and rapidly exported R123. During whole-cell recording using either hyperosmotic pipette solution or hypoosmotic Ringer solution, cell swelling was accompanied by Cl- channel opening in all four cell lines. The rates of induction, biophysical properties and magnitudes of Cl conductance (gCl) were indistinguishable between control and corresponding multidrug-resistant cells: gCl reached 0.96 +/- 0.31 (n = 14) and 0.83 +/- 0.31 nS/pF (mean +/- SD; n = 31) in NIH-3T3 and NIH-3T3/MDR cells, respectively; and 0.31 +/- 0.20 (n = 9) and 0.37 +/- 0.22 nS/pF (n = 7) in 8226 and 8226/Dox40 cells, respectively. gCl exhibited moderate outward rectification in symmetrical Cl- solutions, with a rectification ratio of 1.4 at +/- 50 mV. Cl- channels slowly closed during strong depolarization beyond +60 mV. Using video-imaging techniques with SPQ as a fluorescent probe, we monitored Cl(-)-channel opening in intact drug-sensitive and -resistant cells. gCl, measured either with whole-cell recording or SPQ imaging, was blocked by DIDS (voltage-dependent Kd < 50 microM at +40 mV), NPPB (Kd approximately 30 microM), and tamoxifen (complete and irreversible block approximately 10 microM). None of these blockers inhibited R123 efflux. NPPB accelerated R123 efflux, an effect that was mimicked by CCP, a mitochondrial uncoupler. In contrast, verapamil selectively blocked R123 efflux (Kd = 0.3 to 0.5 microM); 10 microM left gCl unaltered. Induction of gCl was not affected by vincristine or doxorubicin in the pipette solution. Moreover, the rate of R123 efflux did not change during cell swelling. We conclude that P-glycoprotein and swelling-activated chloride channels function independently and are separable by expression and by pharmacological sensitivities.
J Gen Physiol 1994 Dec
PMID:Swelling-activated chloride channels in multidrug-sensitive and -resistant cells. 769 67

Overexpression of P-glycoprotein (P-GP) accompanied by multidrug resistance (MDR) to diverse groups of cytostatics was developed by long-term adaptation of mouse leukemic cell line L1210 to vincristine. Two resistant sublines of cells characterized by ID50 values for vincristine 1.05 mg/l (L1210/VCR-1) and 2.3 mg/l (L1210/VCR-2), respectively, were used. The sensitive parental cell line L1210 had the ID50 value for vincristine around 0.01 mg/l. Overexpression of P-GP induced by the adaptation procedure was found to be accompanied by an increase in the mean cell diameter from 10.28 +/- 1.60 microns (mean +/- SD, n = 122) for sensitive L1210 cells to 17.82 +/- 2.59 microns (n = 120) and 37.26 +/- 5.72 microns (n = 121) for L1210/VCR-1 and L1210/VCR-2 resistant cell sublines, respectively. Significant decrease in ability to accumulate [3H]-vincristine from cultivation medium was observed for both resistant cell sublines in comparison to sensitive cells. Accumulation of [3H]-vincristine by sensitive cells is secured only by passive diffusion of the drug across the plasma membrane. Contrary to that, active efflux of drug operating against its diffusion across the plasma membrane should be assumed as a factor influencing the [3H]-vincristine accumulation by resistant cells. Indeed, the time dependence of [3H]-vincristine accumulation by sensitive cells could be fitted using simple monoexponential kinetic dependence in contrast to biexponential kinetic dependences that are necessary for fitting [3H]-vincristine accumulation by both resistant cell sublines. Kinetic analysis of the experimental data indicates that accumulation of [3H]-vincristine by sensitive cells grows to a plateau reflecting probably the equilibrium of drug concentration in the intracellular and extracellular space. On the contrary, accumulation of [3H]-vincristine by both resistant cell sublines was stabilized after an initial growth on a considerably lower level than it was observed for the sensitive cells in the equilibrium.
Gen Physiol Biophys 1994 Aug
PMID:Time dependence of [3H]-vincristine accumulation by L1210 mouse leukemic cells. Effect of P-glycoprotein overexpression. 789 Jan 45

Effect of phorbol myristate acetate (PMA) on P-glycoprotein (P-GP)-mediated vincristine resistance of the multidrug resistant mouse leukemic cell line L1210/VCR was studied by one hour lasting incubation of cells in the presence of PMA, and after three days of cultivation in the presence of the same substance. After the incubation with 100 micrograms.1-1 PMA the accumulation of [3H]-vincristine by the above cells was significantly depressed. Moreover, full reverse of verapamil-induced stimulation of [3H]-vincristine accumulation was observed in the presence of PMA. In contrary, when cells were cultivated three days in the presence of PMA, only slight but non-significant increase of [3H]-vincristine accumulation was observed. Slight increase of vincristine accumulation by cells cultivated in the presence of PMA was also supported by higher sensitivity of these cells to vincristine.
Gen Physiol Biophys 1995 Apr
PMID:Effect of phorbol myristate acetate (PMA) on P-glycoprotein mediated vincristine resistance of L1210 cells. 884 84

Multidrug resistance (MDR) mediated by overexpression of the MDR protein (P-glycoprotein) has been associated with intracellular alkalinization, membrane depolarization, and other cellular alterations. However, virtually all MDR cell lines studied in detail have been created via protocols that involve growth on chemotherapeutic drugs, which can alter cells in many ways. Thus it is not clear which phenotypic alterations are explicitly due to MDR protein overexpression alone. To more precisely define the MDR phenotype mediated by hu MDR 1 protein, we co-transfected hu MDR 1 cDNA and a neomycin resistance marker into LR73 Chinese hamster ovary fibroblasts and selected stable G418 (geneticin) resistant transfectants. Several clones expressing different levels of hu MDR 1 protein were isolated. Unlike previous work with hu MDR 1 transfectants, the clones were not further selected with, or maintained on, chemotherapeutic drugs. These clones were analyzed for chemotherapeutic drug resistance, intracellular pH (pHi), membrane electrical potential (Vm), and stability of MDR 1 protein overexpression. LR73/hu MDR 1 clones exhibit elevated pHi and are depolarized, consistent with previous work with LR73/mu MDR 1 transfectants (Luz, J.G. L.Y. Wei, S. Basu, and P.D. Roepe. 1994. Biochemistry. 33:7239-7249). The extent of these perturbations is related to the level of hu MDR 1 protein that is expressed. Cytotoxicity experiments with untransfected LR73 cells with elevated pHi due to manipulating percent CO2 show that the pHi perturbations in the MDR 1 clones can account for much of the measured drug resistance. Membrane depolarization in the absence of MDR protein expression is also found to confer mild drug resistance, and we find that the pHi and Vm changes can conceivably account for the altered drug accumulation measured for representative clones. These data indicate that the MDR phenotype unequivocally mediated by MDR 1 protein overexpression alone can be fully explained by the perturbations in Vm and pHi that accompany this overexpression. In addition, MDR mediated by MDR protein overexpression alone differs significantly from that observed for MDR cell lines expressing similar levels of MDR protein but also exposed to chemotherapeutic drugs.
J Gen Physiol 1996 Oct
PMID:Are altered pHi and membrane potential in hu MDR 1 transfectants sufficient to cause MDR protein-mediated multidrug resistance? 889 78

The antracyclines induce multiple intracellular effects; however, inhibition of the nuclear enzyme topoisomerase II (TOPO II) is the main mechanism of action. Resistance to anthracyclines in tumor cells is multifactorial. The main mechanisms are: (1) the classic multidrug resistance (MDR) phenotype, which is due to the presence of P-glycoprotein (PGP) in plasma membrane, that is, a "pump" that can extrude a wide range of anticancer drugs. Membrane-active drugs (e.g., verapamil) have been found in vitro to reverse this phenotype. Most clinical studies including chemosensitizers have, however, been disappointing. (2) Non-PGP-mediated MDR: this phenotype is characterized by expression of other proteins in the plasma membrane which are also able to extrude anticancer drugs. (3) Changes in the intracellular distribution of drug: this mechanism has been demonstrated in several cell lines, most often in combination with PGP or non-PGP-mediated resistance. (4) Glutathione transferases (GST) and detoxification mechanisms: these represent a multigene family of enzymes that conjugate glutathione to chemically reactive groups. Direct evidence for a causative role of GST in anthracycline resistance is missing. (5) Alterations in TOPO II (at-MDR): DNA topoisomerases are involved in several aspects of DNA metabolism, in particular genetic recombination, DNA transcription, and chromosome segregation. Low levels of expression or alterations in TOPO II are associated in vitro with resistance. (6) Increased DNA repair: in several cell lines, an increase in the efficacy of DNA repair has been associated with resistance to doxorubicin (DOX). So far, only classic MDR has been shown to contribute to resistance in clinical conditions, whereas evidence for the other mechanisms of resistance is still missing.
Gen Pharmacol 1996 Mar
PMID:Cellular resistance to anthracyclines. 891 38

1. An increase in cell volume activates, in most mammalian cells, a Cl- current, ICl,vol. This current is involved in a variety of cellular functions, such as the maintenance of a constant cell volume, pH regulation, and control of membrane potential. It might also play a role in the regulation of cell proliferation and in the processes that control transition from proliferation to differentiation. This review focuses on various aspects of this current, including its biophysical characterisation and its functional role for various cell processes. 2. Volume-activated Cl- channels show all outward rectification. Iodide is more permeable than chloride. In some cell types, ICl,vol inactivates at positive potentials. Single channel conductance can be divided mainly into two groups: small (< 5 pS) and medium conductance channels (around 50 pS). 3. The pharmacology and modulation of these channels are reviewed in detail, and suggest the existence of an heterogeneous family of multiple volume-activated Cl- channels. 4. Molecular candidates for this channel (i.e. ClC-2, a member of the ClC-family of voltage-dependent Cl- channels, the mdr-1 encoded P-glycoprotein, the nucleotide-sensitive pICln protein and phospholemman) will be discussed.
Gen Pharmacol 1996 Oct
PMID:Volume-activated Cl- channels. 898 Oct 57

The development of chemoresistance is one of the major clinical problems in the therapy of malignant bone tumors in childhood. The expression of membrane-bound P-glycoprotein turned out to be an essential factor in the evidence of resistant tumor cells. To investigate the significance of multidrug resistance in the prognosis of highly malignant osteosarcomas, the immunohistologic expression of P-glycoprotein was investigated in the tumor tissue of 52 patients under special consideration of the histologic subtype. The data were compared with the histologic regression grade in the resection specimen and correlated with clinical data. Formalin-fixed, paraffin-embedded tissue and, additionally, fresh frozen material taken from the primary biopsy were stained using monoclonal antibody JSB1. 29 (55%) of the tumors investigated were P-glycoprotein positive. Considering the response to chemotherapy, no conclusion could be drawn regarding P-glycoprotein expression, regression grade in the resection specimens, and the clinical follow-up. P-glycoprotein was detected in only 52% of the non-responders. A positive reaction was also evidenced in 59% of the patients with high chemosensitivity. A comparison of the histologic subtypes yielded a significant result in the chondroblastic osteosarcomas. 11 of 12 cases showed a strong expression of P-glycoprotein. Most of the cases were non-responders, and using Kaplan-Meier live tables, an unfavorable clinical outcome could be demonstrated. Possibly, chondroblastic tumors have a special position among osteosarcomas because of their differentiation.
Gen Diagn Pathol 1997 Feb
PMID:Expression of P-glycoprotein in high grade osteosarcomas with special emphasis on chondroblastic subtype. 906 77

1. Multidrug resistance (MDR) is a phenomenon originally seen in cultured tumor cells that, following selection for resistance to a single anticancer agent, become resistant to a range of chemically diverse anticancer agents. These MDR cells show a decrease in intracellular drug accumulation due to active efflux by transporter proteins. The transporter best characterized is P-glycoprotein (Pgp). This protein has been identified in many cancers and has been the target for agents able to inhibit its action, thereby reversing resistance. 2. More recently, another transporter, multidrug resistance-associated protein (MRP) has been identified in a number of MDR human tumor cell lines that do not apparently express Pgp. The presence of MRP at the cell surface of these cells is associated with alterations in drug accumulation and distribution. 3. The gene-encoding MRP has been cloned and sequenced and shown by transfection studies to be able to confer resistance and changes in drug accumulation in sensitive tumor cells. The profile of anticancer drugs expelled in the presence of MRP is similar, but not identical, to that of Pgp. 4. MRP has been identified in a number of different types of cancers, but it is not yet clear to what extent it is involved with clinical resistance. Furthermore, resistance modulators useful against Pgp are less effective in reversing MRP-mediated resistance. 5. It is not fully understood how MRP brings about drug efflux, but it is clear that the underlying mechanisms are different from those responsible for Pgp-mediated drug efflux. In particular, glutathione (GSH) is required for the effective expulsion of the anticancer agents. 6. Unlike Pgp, MRP is able to transport metallic oxyanions and glutathione and other conjugates, including peptidyl leukotrienes. Agents that inhibit organic anion transport, such as probenecid, can block MRP activity. 7. Like Pgp, MRP is expressed not only in resistant tumor cells, but also in normal human tissues. These include the epithelial cells lining the airways and the gastrointestinal tract. In cells in normal tissues, MRP appears to be located within the cytoplasm, which may mean that it functions here in a manner slightly different to that in malignant cells. It is now also recognized in cells and tissues from other species, such as the rat and mouse.
Gen Pharmacol 1997 May
PMID:Multidrug resistance-associated protein: a protein distinct from P-glycoprotein involved in cytotoxic drug expulsion. 918 95

One important mechanism by which multidrug resistance is mediated is the mdr1 gene product, P-glycoprotein (Pgp). Even though chemotherapy, in the treatment of high grade central osteosarcoma (hgc-OS), has led to dramatic improvements in survival rate, a certain percentage of patients still show only a poor response to chemotherapy. To further characterize a potential connection between Pgp and chemotherapy as well as the role of Pgp in tumorigenesis of osteosarcoma, we analyzed Pgp-expression in hcg-OS. Immunohistochemistry was performed on 68 hgc-OS samples from 58 patients using the monoclonal antibody JSB-1; in addition, Pgp-expression in normal bone cells was studied in 5 human epiphyseal growth plates. 70.5% of all cases stained positive for P-glycoprotein, while 29.5% of the cases were negative. Cases investigated after chemotherapy showed a higher incidence (82.9%) of positive P-glycoprotein immunostaining than cases prior to chemotherapy (64.4%). The Pgp-expression of 34 biopsies was compared with chemotherapy, as determined at the surgical specimen. In these cases, however, no correlation could be established between P-glycoprotein expression of the biopsy and the later response to chemotherapy. 48.4% of the cases with biopsies, initially positive for Pgp, showed a good response in the surgical specimen, while only 27.2% of Pgp-positive biopsies were later classified as non-responders. In the normally growing skeleton, positive immunostaining was detected in the area of mineralization of epiphyseal growth plates. Osteoclasts, hypertrophic chondrocytes, and cuboidal osteoblasts showed Pgp-expression, while there was a lack of Pgp in the majority of osteocytes and chondrocytes in the resting and proliferating zone. These data therefore suggest that P-glycoprotein expression in hgc-OS resembles, at least in part, the phenotype of active bone cells. These results may explain why P-glycoprotein, by using immunohistochemistry, in biopsies of osteosarcomas is insufficient to predict the response to chemotherapy.
Gen Diagn Pathol 1997 Jun
PMID:P-glycoprotein expression in high grade central osteosarcoma and normal bone cells. An immunohistochemical study. 922 55


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