Stimulation of p53 DNA binding by c-Abl requires the p53 c terminus and tetramerization

The carboxyl terminus of p53 is a target of a variety of signals for regula tion of p53 DNA binding. Growth suppressor c-Abl interacts with p53 in resp onse to DNA damage and overexpression of c-Abl leads to G(1) growth arrest in a p53-dependent manner. Here, we show that c-Abl binds directly to the c arboxyl-terminal regulatory domain of p53 and that this interaction require s tetramerization of p53. Importantly, we demonstrate that c-Abl stimulates the DNA-binding activity of wild-type p53 but not of a carboxyl-terminally truncated p53 (p53363C). A deletion mutant of c-Abl that does not bind to p53 is also incapable of activating p53 DNA binding. These data suggest tha t the binding to the p53 carboxyl terminus is necessary for c-Abl stimulati on. To investigate the mechanism for this activation, we have also shown th at c-Abl stabilizes the p53-DNA complex. These results led us to hypothesiz e that the interaction of c-Abl with the C terminus of p53 may stabilize th e p53 tetrameric conformation, resulting in a more stable p53-DNA complex. Interestingly, the stimulation of p53 DNA-binding by c-Abl does not require its tyrosine kinase activity, indicating a kinase-independent function for c-Abl. Together, these results suggest a detailed mechanism by which c-Abl activates p53 DNA-binding via the carboxyl-terminal regulatory domain and tetramerization.