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.
Mellado
W
W
Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461.
Horwitz
S B
SB
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