Phosphorylation of the erbB gene product from an avian erythroblastosis virus-transformed chick fibroblast cell line.

Polyclonal antiserum prepared against the human epidermal growth factor receptor immunoprecipitated four proteins of Mr = 66,000, 68,000, 74,000, and 82,000 from avian erythroblastosis virus-transformed chick embryo fibroblasts (cell line AEV-C23) which seemed to be related to the erbB gene product. The Mr = 66,000 and 68,000 proteins chased into the Mr = 74,000 and 82,000 proteins in pulse-chase experiments. The Mr = 68,000 and 82,000 proteins were found to be phosphorylated primarily on serine and threonine residues and contained minor amounts of phosphotyrosine. Tryptic peptide analysis of these phosphoproteins revealed several major peptides, and treatment of cells with the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate resulted in the appearance of an additional phosphopeptide. 12-O-Tetradecanoyl-phorbol-13-acetate also inhibited growth of AEV-C23 cells in soft agar and in monolayer culture. In vitro phosphorylation of Mr = 68,000 and 74,000 proteins in immunoprecipitates occurred on tyrosine with lesser amounts of phosphoserine and phosphothreonine detected.