A question of life or death: the p53 tumor suppressor gene.

The tumor suppressor gene p53 plays a major role in the protection of cell from DNA damage. Activation of the protein in response to irradiation or genotoxic agents, and possibly by other signals, results in growth arrest at the G1 phase of the cell cycle or in apoptosis. While it has been shown that the ability of p53 to function as a sequence-specific transcriptional activator is necessary for the induction of growth arrest, the mechanism of p53-mediated apoptosis is not clear yet. It appears that under some conditions activation of the G1 checkpoint will prevent apoptosis, but cellular environment may alter the result of p53 activation towards cell death. p53 may also directly induce apoptosis through several pathways, which may be transcriptionally dependent or independent. The outcome--a G1 arrest or apoptosis--will depend on a complex network of regulatory signals.