Proteolytic cleavage of p53 mutants in response to mismatched DNA

Interaction of p53 with mismatched DNA induces proteolytic cleavage with re lease of a 35-kDa protein fragment from the p53-DNA complexes. The 35-kDa c leavage product is activated for specific biochemical function(s) and may p lay a role in the cellular response to DNA damage (Molinari et al (1996) On cogene 13: 2077-2086; Okorokov et al (1997) EMBO J16: 6008-6017). In the pr esent study we have asked ii mutants of p53 retain the ability to undergo s imilar proteolytic cleavage, and compared sequence-specific 'DNA contact' w ith 'structural' mutants commonly found in human cancer. In addition, a ser ies of phosphorylation site mutants were generated to investigate the possi ble effects of phosphorylation/dephosphorylation on the proteolytic cleavag e of p53. All mutants tested bound to a mismatched DNA target in vitro. Mor eover, studies in vitro and in vivo indicate that p53 mutants with intact c onformational structure (as determined by immunoreactivity with PAb246 and PAb1620) retain the ability to undergo proteolytic cleavage similar, if not identical, to the wild-type p53 protein. Our results suggest that the capa city for p53 to bind mismatched DNA is independent of structural conformati on of the central core domain. Proteolytic cleavage, however, is crucially dependent upon a wild-type conformation of the protein. (C) 1999 Cancer Res earch Campaign.