Cyclic AMP stimulates the phosphorylation and activation of p42 and p44 mitogen-activated protein kinases in 3T3-F442A preadipocytes.

The effects of cyclic AMP on mitogen-activated protein (MAP) kinase activation were investigated in 3T3-F442A preadipocytes. Several agents, which raise intracellular cyclic AMP levels by distinct mechanisms, induced a transient activation of the p42 and p44 isoforms of MAP kinase and of a MAP kinase kinase. Activation of MAP kinase by cyclic AMP was prevented by two distinct inhibitors of cyclic AMP-dependent protein kinase and by PD 098059, a specific inhibitor of the activation of the MAP kinase kinase MEK 1. Therefore, in contrast to most cell types studied, cyclic AMP exerts a positive influence on the MAP kinase pathway in 3T3-F442A preadipocytes at a level upstream of the activation of MAP kinase kinase.