Evidence for the phosphorylation of the type II insulin-like growth factor receptor in cultured cells

Abstract The ATP pools of monolayer cultures of rat embryo fibroblasts and rat liver cells (BRL-3A2) were labeled with [ 32 P]H 3 PO 4 . The type II insulin-like growth factor (IGF) receptor was purified by affinity chromatography on wheat germ lectin-Sepharose and IGF-II-Sepharose columns. A phosphorylated species having the expected size of the type II receptor (Mr=220,000 without reduction, Mr=260,000 with reduction) was identified by sodium dodecyl sulfate polyacrylamide gel electrophoresis and autoradiography. IGF-II stimulated phosphorylation of the type II receptor in BRL-3A2 rat liver cells. Lability of the receptor phosphate bonds to alkaline pH suggests that the bulk of phosphorylation was occurring on serine residues.