Phosphorylation of the Multidrug Resistance Associated Glycoprotein

Wilfredo Mellado, Susan Band Horwitz

Research output: Contribution to journalArticlepeer-review

99 Scopus citations


Drug-resistant cell lines derived from the mouse macrophage-like cell line J774.2 express the multidrug resistant 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 µM 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 [γ-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.

Original languageEnglish (US)
Pages (from-to)6900-6904
Number of pages5
Issue number22
StatePublished - 1987
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry


Dive into the research topics of 'Phosphorylation of the Multidrug Resistance Associated Glycoprotein'. Together they form a unique fingerprint.

Cite this