A QUESTION OF LIFE OR DEATH - THE P53 TUMOR-SUPPRESSOR GENE

The tumor suppressor gene p53 plays a major role in the protection of cells from DNA damage. Activation of the protein in response to irradi ation or genotoxic agents, and possibly by other signals, results in g rowth 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-sp ecific transcriptional activator is necessary for the induction of gro wth 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 apo ptosis through several pathways, which may be transcriptionally depend ent or independent. The outcome -a G1 arrest or apoptosis -will depend on a complex network of regulatory signals.