Phorbol ester, serum, and rous sarcoma virus transforming gene product induce similar phosphorylations of ribosomal protein S6.

Abstract

The addition of phorbol-12-myristate-13-acetate (PMA), a potent tumor promoter, to serum-starved quiescent chicken embryo fibroblasts (CEF) or C127 murine cells resulted in increased phosphorylation of 40S ribosomal protein S6. The effect of PMA on S6 phosphorylation in quiescent CEF was half-maximal at .apprx. 100 nM and was readily observed at 16 nM. S6 phosphorylation was increased in serum-starved CEF incubated with the diacylglycerol derivative, 1-oleoyl-2-acetylglycerol. S6 phosphorylation in PMA-stimulated, serum-stimulated, and serum-starved Rous sarcoma virus-tranformed CEF was analyzed by phospho-amino acid analysis, 2-dimensional polyacrylamide gel electrophoresis, limited proteolysis with V8 protease and 2-dimensional thin layer electrophoresis of chymotryptic digests. Comparison of S6 phosphorylation of S6 stimulated by PMA, serum or oncogenic transformation with Rous sarcoma virus occurs through common pathways. This is further supported by the observation that the simultaneous addition of PMA and serum to CEF or of either PMA or serum to Rous sarcoma virus-transformed CEF did not significantly further increase the incorporation of phosphate into S6.