Cyclic AMP stimulates protein synthesis in L6 myoblasts and its effects are additive to those of insulin, vasopressin and 12-0-tetradecanoylphorbol-13-acetate. Possible involvement of mitogen activated protein kinase

The role of cyclic AMP as a second messenger in the stimulation of protein synthesis and the potential involvement of mitogen activated protein (MAP) kinase in this response was studied in L6 myoblasts. Dibutyryl-cAMP (dbt-cAMP) increased protein synthesis at 90 min and 6 h in a concentration-dependent manner. The responses at 90 min were probably mediated by increased translation as they were not blocked by actinomycin D; effects at 6 h were accompanied by increases in RNA content implying a transcriptional component. 100 nM 12-O-tetradecanoylphorbol-13-acetate (TPA), 1 nM Insulin (90 min incubations) and 100 nM vasopressin (6 h incubation) also increased protein synthesis and these responses were additive with those of 500 mu M dbt-cAMP. Responses to forskolin were similar to dbt-cAMP whilst 1,9-dideoxyforskolin had no effect. Cell extracts immunoblotted with MAP kinase antibody showed bands corresponding to approx. 42, 44, 54 and 83 kDa. 500 mu M dbt-cAMP elicited an increase in activity of both the 42 and 44 kDa bands when assayed by the 'in gel' method and a similar response was also observed with forskolin. TPA and vasopressin also stimulated the activity of these two isoforms, but had no significant additive or inhibitory effects when added in combination with 500 mu M dbt-cAMP, In contrast, although 1 nM insulin alone had no effect, a synergistic response in terms of MAP kinase activation was observed in the presence of dbt-cAMP. The data demonstrate that cAMP stimulates protein synthesis in L6 cells and suggest a role for MAP kinase in this event.