Keeping an old friend under control: regulation of p53 stability.

The tumor suppressor protein p53 plays a pivotal role in protection against the development of cancer and is inactivated in many human malignancies. p53 is thought to prevent accumulation of genomic alterations by hindering cell proliferation in response to genotoxic stress, and two of the principal functions of p53 are the induction of cell-cycle arrest and the activation of apoptotic cell death. Because p53 is an extremely efficient inhibitor of cell growth, keeping p53 function under control in normal cells is critical. One of the principal mechanisms by which cells achieve this is by regulating the p53 protein level, although the ability of the protein to adopt active and latent forms and its cellular localization also contribute to the regulation of its function. Here, we summarize recently identified mechanisms that regulate the stability of the p53 protein and discuss the potentially immense clinical relevance of these observations in developing therapeutical approaches that aim to restore p53 function in human tumors.