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, encoded by the MDR1 (multidrug resistance) gene, is a transmembrane efflux pump for various lipophilic compounds. MDR1 is expressed in several types of normal human tissues and in a variety of tumors, where its expression has been correlated with resistance to chemotherapy. Some P-glycoprotein-overexpressing multidrug-resistant cell lines contain elevated amounts of protein kinase C (PKC). PKC activation was shown to increase the level of drug resistance in several cell lines, but the functional association of PKC with P-glycoprotein-mediated multidrug resistance remains unclear. We have studied the effects of lymphocyte-activating agents on P-glycoprotein activity in normal human lymphocytes, and found that 12-O-tetradecanoylphorbol-13-acetate (TPA), an efficient agonist of PKC, increased the activity as well as the levels of P-glycoprotein in these cells. TPA also increased P-glycoprotein expression in several cell lines derived from different types of leukemias and solid tumors. The increase in MDR1 gene expression was observed at both the protein and RNA levels. Induction of MDR1 mRNA was apparent as early as two hours after the addition of TPA. Diacylglycerol (DAG), a physiological stimulant of PKC, also increased the expression of MDR1 mRNA and P-glycoprotein. The induction of MDR1 expression by TPA and DAG was suppressed by staurosporine, a protein kinase inhibitor. The results suggest that MDR1 gene expression in different cell types is regulated by a PKC-mediated pathway. This finding has implications for the emergence of multidrug resistance in vitro and in vivo.
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PMID:Activation of MDR1 (P-glycoprotein) gene expression in human cells by protein kinase C agonists. 136 Feb 76

Covalent modification by phosphorylation is a characteristic of the P-glycoproteins expressed in multidrug-resistant cells. This report describes analysis of P-glycoprotein phosphorylation in multidrug-resistant human KB-V1 cells and a study of the relationship of phosphorylation and drug accumulation. In isolated membranes, phosphorylation of P-glycoprotein by purified protein kinase C (PKC) was rapid, and time-dependent dephosphorylation was inhibited by okadaic acid, an inhibitor of type 1 and type 2A protein phosphatases. In 32P-labeled intact KB-V1 cells, P-glycoprotein phosphorylation was stimulated by both 12-O-tetradecanoylphorbol-13-acetate (TPA), an activator of PKC, and okadaic acid. Two-dimensional thin layer tryptic phosphopeptide maps indicated that the sites of phosphorylation were similar in control, TPA-treated, and okadaic acid-treated cells and that they corresponded to those phosphorylated by PKC in vitro. The protein kinase inhibitor staurosporine, and the PKC-selective inhibitors calphostin C and the alkyl-lysophospholipid 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine, inhibited P-glycoprotein phosphorylation in vitro and in intact cells. Drug accumulation assays demonstrated that in KB-V1 cells TPA caused a decrease, whereas staurosporine and calphostin C caused an increase, in accumulation of [3H]vinblastine. These compounds did not significantly alter [3H]vinblastine levels in drug-sensitive KB-3 cells. These results suggest that PKC is chiefly responsible for P-glycoprotein phosphorylation in KB-V1 cells, that membrane-associated protein phosphatases 1 and 2A are active in dephosphorylation of P-glycoprotein, and that phosphorylation of P-glycoprotein may be an important mechanism for modulation of drug-pumping activity.
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PMID:Regulation by phorbol ester and protein kinase C inhibitors, and by a protein phosphatase inhibitor (okadaic acid), of P-glycoprotein phosphorylation and relationship to drug accumulation in multidrug-resistant human KB cells. 137 25

In the present study we have analyzed the involvement of phosphorylation in the function of P-glycoprotein and have also examined sites of phosphorylation along the P-glycoprotein polypeptide chain. The results show that in HL60 cells isolated for resistance to vincristine the protein kinase inhibitor staurosporine induces a major inhibition in the phosphorylation of P-glycoprotein. Further studies show that under the same conditions in which staurosporine inhibits P-glycoprotein phosphorylation there is a concomitant increase in cellular drug accumulation and a major inhibition in drug efflux. Additional studies using pulse-chase experiments show that the P-glycoprotein phosphate groups are metabolically active and that the protein undergoes rapid cycles of phosphorylation and dephosphorylation in the cell. Structural analyses demonstrate that cleavage of 32P-labeled P-glycoprotein at Asp-Pro linkages with formic acid results in the formation of a major phosphorylated peptide of 35 kDa and a minor peptide of 42 kDa. Western blot analysis using site-specific anti-sera against P-glycoprotein suggests that P35 represents a phosphorylated fragment containing P-glycoprotein amino acids 446-744. Analysis of tryptic peptides using site-specific antisera identifies a second major phosphorylated region of P-glycoprotein which contains amino acids 745-1088. These studies thus suggest that phosphorylation plays an important role in the biological activity of P-glycoprotein. The results also indicate that two adjacent internal regions are highly phosphorylated in the P-glycoprotein molecule.
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PMID:Analysis of P-glycoprotein phosphorylation in HL60 cells isolated for resistance to vincristine. 167 14

Cells containing increased levels of the membrane phosphoprotein P-glycoprotein exhibit a multidrug-resistant phenotype. In the present study we have analyzed protein kinases capable of phosphorylating P-glycoprotein in membranes of HL60 cells isolated for resistance to vincristine. Analysis of this system demonstrates that in isolated membranes the protein kinase inhibitor staurosporine greatly reduces P-glycoprotein phosphorylation. In contrast, the kinase inhibitor H-7 does not affect this reaction. Fractionation of solubilized membrane proteins from sensitive and resistant cells on DEAE-cellulose reveals a major protein kinase (PK-1) which exhibits optimal activity in the presence of Mn2+ and histone H1. This enzyme fraction does not contain detectable levels of protein kinase C or cAMP-dependent protein kinase. PK-1 phosphorylation of two endogenous proteins is, however, greatly enhanced in the presence of phosphatidylserine or phosphatidyl-inositol. In reaction mixtures containing Mg2+ or Mn2+ in the absence of phospholipid, PK-1 from resistant cells phosphorylates an endogenous protein of 180 kilodaltons (P180), which exhibits an electrophoretic mobility identical to P-glycoprotein. In parallel experiments with PK-1 from sensitive cells there is no detectable phosphorylation of a P180 protein. P180 phosphorylated by PK-1 from resistant cells is immunoprecipitated by antibody against P-glycoprotein. Additional studies demonstrate that PK-1 is capable of phosphorylating specific synthetic peptides which correspond to the sequence of P-glycoprotein. Peptide phosphorylation occurs at both serine and threonine residues. These studies thus identify a novel membrane-associated protein kinase in HL60 cells which is capable of phosphorylating P-glycoprotein. This enzyme may have an important role in regulating levels of multidrug resistance.
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PMID:Characterization of a membrane-associated protein kinase of multidrug-resistant HL60 cells which phosphorylates P-glycoprotein. 196 66

We established previously that lipopolysaccharide (LPS) can induce the expression of LPS-binding sites on bone marrow cells (BMC). We now report that staurosporine (STP), a glycosylated indolocarbazole alkaloid with potent inhibitory activity for various protein kinases, can induce the same effect. With both agents, the newly expressed LPS receptor was found to be CD14. The STP-induced effect was independent of its protein kinase inhibitory activity because several other protein kinase inhibitors, such as the indolocarbazole K-252a, the bisindolylmaleimide RO-31-8220, the perylenequinone calphostin C, and the isoquinolinesulfonamide H7, did not induce CD14 expression. The observation that the STP analog K-252a with an identical polyaromatic aglycon moiety was inactive yet the analog UCN-01 with an identical glycoside ring was active suggests that the induction of CD14 expression is triggered by the sugar moiety of STP. Three lines of evidence show that the mechanism of CD14 expression induced by STP differs from that induced by LPS: (i) unlike LPS, STP can stimulate BMC from LPS-unresponsive C3H/HeJ mice, (ii) LPS and STP effects are additive at a saturating dose of LPS, and (iii) the protein kinase inhibitor K-252a inhibits the LPS-induced but not STP-induced stimulation. Therefore, our findings show that both a protein kinase-dependent (LPS-induced) and a protein kinase-independent (STP-induced) mechanism can lead to the expression of the LPS receptor CD14 on BMC. We also found that the STP-induced stimulation of BMC is modulated by cyclosporin A, vinblastine, and verapamil. This observation may suggest that the inducible effect of STP could be initiated by its interaction with P-glycoprotein, a membrane pump with drug efflux function that plays a critical role in the multidrug resistance of cancer cells.
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PMID:Lipopolysaccharide and the glycoside ring of staurosporine induce CD14 expression on bone marrow granulocytes by different mechanisms. 938 33