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)

Studies were undertaken to identify the protein kinase(s) responsible for P-glycoprotein phosphorylation in multidrug-resistant (KB-V1) human carcinoma cells and to elucidate the functional role of phosphorylation. P-glycoprotein migrated on sodium dodecyl sulfate gels with apparent Mr 150,000 and is termed P150. When KB-V1 membrane vesicles were incubated with [gamma-32P] ATP, P150 was phosphorylated by an endogenous kinase that exhibited properties of membrane-inserted protein kinase C (PKC). Both membrane-bound P150 and purified P150 served as effective substrates for highly purified rat brain PKC which incorporated approximately 0.6 mol of phosphate/mol of P150. Enzyme assays showed that KB-V1 cells exhibit 4-fold higher PKC activity compared with the drug-sensitive KB-3 cell line. The basal phosphorylation of P150 observed in 32P-labeled cells was increased 2-fold by phorbol ester (PMA) treatment and reduced 30% by treatment with the isoquinolinsulfonamide H-7. Phosphopeptide maps of partially digested P150, phosphorylated either in vitro with PKC or in intact 32P-labeled control or PMA-stimulated cells, were indistinguishable from one another. Drug accumulation assays revealed that PMA treatment of KB-V1 cells significantly reduced [3H]vinblastine accumulation induced by verapamil or by tetrandrine. The results suggest that PKC is primarily responsible for P150 phosphorylation in KB-V1 cells and that phosphorylation may play a modulatory role in the drug transport process.
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PMID:Protein kinase C phosphorylates P-glycoprotein in multidrug resistant human KB carcinoma cells. 197 May 71

HL60 cells exhibiting a 140-fold increase in resistance to vincristine contain three surface membrane proteins with molecular weights of 210,000 (P210), 180,000 (P180), and 150,000 (P150) which are highly phosphorylated in vivo and in an in vitro system in the presence of Mn2+ and [gamma-32P]ATP. These phosphorylated proteins are either absent or present in very low levels in membranes of drug-sensitive cells. Growth of the vincristine-resistant isolate in the absence of drug results in a decrease in the level of resistance and a major reduction in the phosphorylation of P210 and P180. The phosphorylation of P150 is not altered in the revertant which still exhibits substantial levels of resistance. Further studies show that P210 and P180 are highly reactive with a monoclonal antibody against P-glycoprotein. These two proteins are present in only very low levels in revertant cells. The monoclonal antibody exhibits no reactivity with P150. In HL60 cells isolated for a 25-fold increase in vincristine resistance proteins reactive with P-glycoprotein monoclonal antibody are essentially absent. P150 is however highly phosphorylated in these cells. Additional experiments using lectin binding of 32P-labeled proteins demonstrates that P150 has properties distinct from P210 and P180. Analysis of drug uptake patterns in the vincristine-resistant isolates and the revertant shows that resistance is related to a reduced intracellular accumulation of drug. Reduced accumulation of vincristine is also found in HL60 cells isolated for resistance to Adriamycin. These cells are devoid of P-glycoprotein but contain phosphorylated P150. These results suggest that proteins P150, P180, and P210 may contribute to multidrug resistance in HL60 cells through a mechanism which involves reduced cellular accumulation of drug. P180 and P210 are structurally related whereas P150 is distinct from these two proteins.
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PMID:Mechanisms of multidrug resistance in HL60 cells: evidence that a surface membrane protein distinct from P-glycoprotein contributes to reduced cellular accumulation of drug. 289 87