Angiotensin II (AngII), potassium ion, and ACTH are the main factors controlling aldosterone biosynthesis in adrenal glomerulosa cells. AP-1 response elements for the immediate early gene products, c-Fos and c-Jun, have been identified, among others, in the promoter of the steroidogenic acute regulatory (StAR) protein gene, whose expression is acutely regulated by activators of aldosterone production. In bovine glomerulosa cells, AngII treatment led to a rapid and transient increase in c-fos mRNA expression, c-Fos protein expression, and c-Fos phosphorylation. Inhibition of the ERK1/2 MAPK pathway abolished the effect of AngII on c-fos mRNA, protein, and phosphorylation. EMSA and chromatin immunoprecipitation experiments demonstrated that c-Fos binds with c-Jun to the proximal StAR promoter and that AngII treatment increases the amount of c-Fos bound to the promoter. Overexpression of a dominant-negative form of c-Fos with adenoviral vectors inhibited StAR mRNA and StAR protein expression as well as aldosterone biosynthesis in response to AngII. The dominant-negative c-Fos also prevented the increase in protein synthesis induced by AngII in glomerulosa cells, as assessed by [(3)H]leucine incorporation. These results indicate that AngII rapidly induces c-Fos expression and posttranslational modifications. Furthermore, a heterodimeric c-Fos/c-Jun complex binds to the proximal StAR promoter in glomerulosa cells, thus activating StAR gene expression and acute aldosterone biosynthesis. Finally, c-Fos also contributes to other functional responses to the hormone, such as protein synthesis.