The C-terminal lysines fine-tune P53 stress responses in a mouse model but are not required for stability control or transactivation

摘要

P53 is an unstable transcription factor that is mutated in a majority of human cancers. With a significant role in initiating cell elimination programs, a network has evolved to fine-tune P53 transcrip-tional output and prevent errant activation. Modifications of the C terminus have long been viewed as critical binary determinants of P53 stability or activation. However, these conclusions are based on in vitro transfection or biochemical analyses where the stoi-chiometries between P53 and its regulators are perturbed. Therefore, we tested the importance of the C-terminal regulatory region for P53 control in mice where the seven C-terminal lysines were changed to arginine (Trp-53~(7KR)). Surprisingly, the homozygous mutant mice are viable and phenotypically normal. We have functionally characterized the mutant protein in both MEFs and thymocytes, revealing the unexpected result that Trp-53~(7KR) exhibits a normal half-life and functions like WT P53 in cell cycle arrest and apoptosis, and in an E1A-ras xenograft tumor suppression assay. However, a significant difference is that P53~(7KR) is activated more easily by DNA damage in thymus than WT P53. Importantly, although MEFs encoding WT P53 spontaneously emerge from crisis to become immortal in a 3T3 growth protocol, we do not observe any such escape with the P53~(7KR) cells. We propose that the C-terminal modifications believed to be critical for proper P53 regulation are not essential, but contribute to a fine-tuning mechanism of homeostatic control in vivo.