The N-terminal domain of p73 interacts with the CH1 domain of p300/CREB binding protein and mediates transcriptional activation and apoptosis

The newly identified p53 homolog p73 mimics the transcriptional function of p53. We have investigated the regulation of p73's transcriptional activity by p300/CREB binding protein (CBP). p73-p300 complexes were identified in HeLa cell extracts by cofractionation and coimmunoprecipitation assays. The p73-p300 interaction was confirmed in vitro by glutathione S-transferase-p rotein association assays and in vivo by coimmunoprecipitating the overexpr essed p300 and p73 in human p53-free small-cell lung carcinoma H1299 or ost eosarcoma Saos-2 cells. The N terminus but not the N-terminal truncation of p73 bound to the CH1 domain (amino acids [aa] 350 to 450) of p300/CBP. Acc ordingly, this p73 N-terminal deletion was unable to activate transcription or to induce apoptosis. Overexpression of either p300 or CBP stimulated tr anscription mediated by p73 but not its N-terminally deleted mutant in vivo . The N-terminal fragment from aa 19 to 597, but not the truncated fragment from aa 242 to 1700 of p300, reduced p73 mediated transcription markedly. p73-dependent transcription or apoptosis was partially impaired in either p 300- or CBP-deficient human breast carcinoma MCF-7 or H1299 cells, suggesti ng that both coactivators mediate transcription by p73 in cells. These resu lts demonstrate that the N terminus of p73 directly interacts with the N-te rminal CH1 domain of p300/CBP to activate transcription.