Phosphorylation of the multidrug resistance associated glycoprotein.
Drug-resistant cell lines derived from the mouse macrophage-like cell line J774.2 express the multidrug resistance phenotype which includes the overexpression of a membrane glycoprotein (130-140 kilodaltons). Phosphorylation of this resistant-specific glycoprotein (P-glycoprotein) in intact cells and in cell-free membrane fractions has been studied. The phosphorylated glycoprotein can be immunoprecipitated by a rabbit polyclonal antibody specific for the glycoprotein. Phosphorylation studies done with partially purified membrane fractions derived from colchicine-resistant cells indicated that (a) phosphorylation of the glycoprotein in 1 mM MgCl2 was enhanced a minimum of 2-fold by 10 microM cAMP and (b) the purified catalytic subunit of the cAMP-dependent protein kinase (protein kinase A) phosphorylated partially purified glycoprotein that was not phosphorylated by [gamma-32P]ATP alone, suggesting that autophosphorylation was not involved. These results indicate that the glycoprotein is a phosphoprotein and that at least one of the kinases responsible for its phosphorylation is a membrane-associated protein kinase A. The state of phosphorylation of the glycoprotein, which is a major component of the multidrug resistance phenotype, may be related to the role of the glycoprotein in maintaining drug resistance.
Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461.
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Mellado
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Horwitz
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D004351:Drug Resistance; D008264:Macrophages; D008562:Membrane Glycoproteins / Q000235:genetics*; D051379:Mice; D010710:Phosphates / Q000378:metabolism; D010761:Phosphorus Radioisotopes; D010766:Phosphorylation
D008562:Membrane Glycoproteins; D010710:Phosphates; D010761:Phosphorus Radioisotopes; D000255:Adenosine Triphosphate