Estrogen receptor is associated with protein and phospholipid kinase activities

The ability of immunopurified estrogen receptor from MCF-7 cells, incubated with [Y-32P]-ATP, to conduct its own phosphorylation and to phosphorylate phosphatidylinositol and 1,2-diacylglycerol was investigated. SDS gel electrophoresis analysis of the phosphorylated products revealed three major labeled phosphopeptides with molecular weights of 57, 47 and 43 kilodaltons. Other polypeptides were detected although in much smaller amounts. When the phosphorylation system was supplemented in vitro with phosphatidylinositol, phosphatidylinositol-4-P, or 1,2-diacylglycerol and the 32P-lipids were analyzed by thin layer chromatography, PI, but not 1,2-diacylglycerol, was converted in part to 32P-phosphatidic acid and phosphatidylinositol-4-32P. Phosphatidylinositol-4-P was also phosphorylated to phosphatidylinositol-4,5-32P. An estrogen receptor-negative cell line (MDA) produced negligible 32P-polypeptides and 32P-lipids under identical conditions used for MCF-7 cells.