Divergent Regulation of the Human Atrial Natriuretic Peptide Gene by c-jun and c-fos

Employing transient transfection analysis in neonatal rat cardiocytes, we have demonstrated that overexpression of c-jun results in a dose-dependent induction of the human atrial natriuretic peptide (hANP) gene promoter. Studies using a series of mutations in the hANP gene promoter identified a TRE-like, cis-acting regulatory sequence which conferred c-jun sensitivity. This same region was shown to interact with the c-jun/c-fos complex in an in vitro gel mobility shift assay. Selective mutation of this site suppressed basal activity of the hANP promoter and significantly reduced c-jun-dependent activation. Overexpression of c-fos had a biphasic effect on hANP gene promoter activity. At low levels, in concert with c-jun, it activated, while at higher levels it suppressed, transcription from the hANP gene promoter. This inhibition was both cell and promoter specific. hANP gene promoter sequences which mediate c-fos-dependent inhibition appear to be separable from those responsible for the induction. In addition, the protein domains on c-fos responsible for transcriptional activation and repression can be segregated topographically, with the inhibitory activity being localized to the carboxy-terminal domain. Thus, c-fos can activate or repress hANP gene expression through two separate functional domains that act on distinct regulatory elements in the hANP gene promoter. These data imply that the ANP gene may be a physiological target for c-fos- and c-jun-dependent activity in the heart and suggest a potential mechanism linking environmental stimuli to its expression.