High level of c-fos mRNA accumulation is not obligatory for renewed cell proliferation.

We have examined the expression of the c-fos gene and the formation of inositol phosphates with respect to the reentry of inducible C2 myoblasts into the cell cycle. GI arrested myoblasts were stimulated to proliferate by addition of fresh medium containing either 20% foetal calf serum (FCS) or 1.6 10(-6) M insulin and 7 microM Na+ vanadate. Our results show that renewed proliferation, which occurred in the presence of insulin + vanadate, was neither preceded by increased inositol phosphate formation, nor by high level of c-fos mRNA accumulation, while, as classically observed, FCS induced proliferation was. These results suggest that increased inositol phospholipids breakdown and transient accumulation of c-fos mRNA at a high level, are not obligatory for renewed cell proliferation.