The coactivators p300 and CBP have different functions during the differentiation of F9 cells.

We have characterized an element (differentiation response element, DRE) in the promoter region of the c-jun gene that is both necessary and sufficient for retinoic acid (RA) and adenovirus early region (E1A) mediated up-regulation of c-jun gene expression during the differentiation of F9 cells. The DRF complex, which binds specifically to DRE, is composed of the E1A-associated protein p300 and the activation transcription factor-2 (ATF-2) as a DNA-binding subunit of the DRF. The molecular association of p300 and ATF-2 enhances the transcription of the c-jun gene, which requires protein kinase C alpha mediated phosphorylation of Ser-121 of ATF-2 within its p300 interaction domain. We used antisense oligodeoxynucleotides (AS-ODNs) capable of binding specifically to the mRNA for either p300 or CBP to examine the individual roles of p300 and CBP during the RA-induced differentiation, exit from the cell cycle, and apoptosis of F9 cells. F9 cells treated with AS-ODNs specific for p300 mRNA became resistant to RA-induced differentiation, while cells incubated with AS-ODNs specific for CBP mRNA were still able to differentiate. Despite their similarities p300 and CBP appear to have distinct functions during the differentiation of F9 cells. These results suggest that ATF-2 and p300 cooperate in the control of transcription by forming a protein complex in response to RA or E1A, and that the phosphorylation of ATF-2 and p300 is probably a signaling event in the pathway that leads to the transactivation of the c-jun gene in F9 cell differentiation.