TRANSCRIPTIONAL REPRESSION OF THE C-FOS GENE BY YY1 IS MEDIATED BY A DIRECT INTERACTION WITH ATF CREB/

Transcriptional activation of the mouse c-fos gene by the adenovirus 2 43-amino-acid E1A protein requires a binding site for transcription fa ctor YY1 located at -54 of the c-fos promoter. YY1 normally represses transcription of c-fos, and this repression depends on the presence of a cyclic AMP (cAMP) response element located immediately upstream of the -54 YY1 DNA-binding site. This finding suggested that the mechanis m of transcriptional repression by YY1 might involve a direct interact ion with members of the ATF/CREB family of transcription factors. In v itro and in vivo binding assays were used to demonstrate that YY1 can interact with ATF/CREB proteins, including CREB, ATF-2, ATFa1, ATFa2, and ATFa3. Structure-function analyses of YY1 and ATFa2 revealed that the C-terminal zinc finger domain of YY1 is necessary and sufficient f or binding to ATFa2 and that the basic-leucine zipper region of ATFa2 is necessary and sufficient for binding to YY1. Overexpression of YY1 in HeLa cells resulted in repression of a mutant c-fos chloramphenicol acetyltransferase reporter that lacked binding sites for YY1, suggest ing that repression can be triggered through protein-protein interacti ons with ATF/CREB family members. Consistent with this finding, repres sion was relieved upon removal of the upstream cAMP response element. These data support a model in which YY1 binds simultaneously to its ow n DNA-binding site in the c-fos promoter and also to adjacent DNA-boun d ATF/CREB proteins in order to effect repression. They further sugges t that the ATF/CREB YY1 complex serves as a target for the adenovirus 243-amino-acid E1A protein.