Growth factor-stimulated protein synthesis is inhibited by sodium orthovanadate

The study of intracellular signaling pathways has been aided by the use of sodium orthovanadate, a cell-permeable inhibitor of tyrosine phosphatases. However, long-term addition of sodium orthovanadate is often cytotoxic. In this study we demonstrate that the growth factor-mediated increase in the r ate of protein synthesis was inhibited by sodium orthovanadate. This effect of sodium orthovanadate was dose-dependent, with an IC50 of 40 muM and max imal inhibition obtained at 100 muM. As a consequence, the fetal bovine ser um-mediated induction of the immediate-early genes, c-Fos and MKP-1, at the protein level was inhibited by orthovanadate. Orthovanadate's ability to a ttenuate protein synthesis was partially reversible, and was no longer evid ent when the agent was added 6 h after addition of growth factor to cells. Analysis of several elements of signaling pathways which are known to regul ate protein synthesis in a positive manner (p42/p44 MAPK, AKT and p70 S6K s timulation, and hyperphosphorylation of PHAS-I) were not inhibited but rath er were stimulated by orthovanadate. Thus, sodium orthovanadate is a potent inhibitor of growth factor-stimulated protein synthesis independent of p42 /p44 MAPK or PI3K-p70 S6K activation.