CREB-BINDING PROTEIN ACTIVATES TRANSCRIPTION THROUGH MULTIPLE DOMAINS

CREB-binding protein (CBP) functions as a coactivator molecule for a n umber of transcription factors including CREB, c-Fos, c-Jun, c-Myb, an d several nuclear receptors. Although binding sites for these factors within CBP have been identified, the regions of CBP responsible for tr anscriptional activation are unknown. In this report, we show that the N-terminal half of CBP is sufficient for activation of CREB-mediated transcription and that this region contains a strong transcriptional a ctivation domain (TAD). Both deletion of this TAD or sequestering of f actors that the TAD binds using a squelching assay were found to great ly decrease the ability of CBP to activate CREB-mediated transcription , In vivo studies by others have shown that p300/CBP associates with T BP; using an in vitro approach, we show the N-terminal TAD binds TBP. We also examined the ability of the C terminus of CBP to activate tran scription using GAL-CBP chimeras, With this approach, we identified tw o C-terminal TADs located adjacent to the c-Fos binding site, In previ ous studies, cAMP-dependent protein kinase A (PKA) increased the trans criptional activity of a GAL full-length CBP chimera in F9 cells, and of the C terminus in PC-12 cells. Here, we demonstrate that PKA also i ncreased the ability of the N-terminal TADs of CBP to activate transcr iption in PC-12 but not F9 or COS-7 cells, suggesting that this PKA-re sponsiveness is cell type-specific.