Functional analysis of an isolated fos promoter element with AP-1 site homology reveals cell type-specific transcriptional properties.

A DNA element located at positions -295 to -289 of the c-fos promoter (FAP site) is highly homologous to a consensus 12-O-tetradecanoyl phorbol-13-acetate-responsive element (TRE) and to a cyclic AMP (cAMP)-responsive element (CRE). We found that an oligonucleotide containing the FAP element was a transcription regulator which was distinct from both the TRE and CRE. When cloned in multiple copies in front of a reporter gene in HeLa cells, the FAP oligonucleotide was a powerful constitutive activator sequence. Conversely, in the same cells, reporter plasmids containing multiple copies of the TRE of the human metallothionein gene required phorbol esters for their induction. In PC12 cells, the FAP oligonucleotide was cAMP responsive. Its activity was mediated through a cAMP-dependent protein kinase II and did not rely on ongoing protein synthesis for activation. Adenovirus E1a proteins activated viral promoters through ATF (activation transcription factor) consensus binding sequences identical to the CRE. However, E1a repressed the FAP oligonucleotide-associated transcriptional activity in HeLa cells. In PC12 cells, E1a neither transactivated nor transrepressed the basal and cAMP-stimulated FAP activity. In contrast, the CRE of the human c-fos promoter located at -60 was weakly induced by cAMP and E1a in both HeLa and PC12 cells. We suggest that the FAP oligonucleotide acts through a factor(s) distinct from those employed by the TRE and CRE and that the FAP-associated protein factor(s) may differ in HeLa and PC12 cells in expression or posttranslational regulation.