Involvement of common and cell type-specific pathways in c-fos gene control: stable induction of cAMP in macrophages.

The c-fos proto-oncogene is rapidly and transiently induced by PDGF in fibroblast and by CSF-1 in macrophages. In both cells, the breakdown of phospholipids with the ensuing activation of protein kinase C (PKC) and intracellular release of Ca2+ seems to play a role in the induction of c-fos. The transient induction of c-fos mRNA and protein by PDGF is both increased and prolonged by inhibitors of calmodulin, apparently by inhibiting the degradation of c-fos mRNA. While no response to cyclic nucleotides is observed in fibroblasts, cAMP is a strong inducer of c-fos in macrophages. In contrast to the transient induction by PKC/Ca2+, cAMP induces stable transcription of the c-fos gene for many hours, suggesting the existence of different mechanisms regulating c-fos transcription in the same cell.