In the corticotroph cell line AtT20, Ca2+ stimulates c-fos mRNA and nuclear c-fos protein accumulation. We show that Ca2+ stimulates transcription of a chloramphenicol-acetyl-transferase reporter gene driven by the c-fos promoter. This effect is mimicked by both constitutively active Ca2+/calmodulin-dependent protein kinase types II (CamK II) and IV (CamK IV). The effects of CamK IV are synergistic with those obtained by cAMP stimulation, whereas CamK II-dependent transcription is not further stimulated. Deletion of the distal promoter sequence revealed that CamK IV, and to a lesser extent CamK II, activate a cis-acting element(s) located between -99 and -53 bp prior to the transcription initiation site. Moreover, CamK II further stimulates transcription through the fos AP1-like element. CamK IV has a lower effect on this element but represses the serum response element. The latter observation might account for the lower transcriptional effects of CamK IV on the full length c-fos promoter.