Recruitment of CREB binding protein is sufficient for CREB-mediated gene activation

Phosphorylation of the transcription factor CREB leads to the recruitment o f the coactivator, CREB binding protein (CBP), Recent studies have suggeste d that CBP recruitment is not sufficient for CREB function, however, We hav e identified a conserved protein-protein interaction motif within the CBP-b inding domains of CREB and another transcription factor, SREBP (sterol-resp onsive element binding protein). In contrast to CREB, SREBP interacts with CBP in the absence of phosphorylation, We have exploited the conservation o f this interaction motif to test whether CBP recruitment to CREB is suffici ent for transcriptional activation. Substitution of six nonconserved amino acids from SREBP into the activation domain of CREB confers high-affinity, phosphorylation-independent CBP binding. The mutated CREB molecule, CREBDIE DML, activates transcription in F9 teratocarcinoma and PC12 cells even in t he absence of protein kinase A (PKA), Addition of exogenous CBP augments th e level of transcription mediated by CREBDIEDML, and adenovirus 12S E1A blo cks transcription, implicating CBP in the activation process. Thus, recruit ment of CBP to CREB is sufficient for transcriptional activation, Addition of PKA stimulates transcription induced by CREBDIEDML further, suggesting t hat a phosphorylation event downstream from CBP recruitment augments CREB s ignaling.