Tumor suppressor protein p53 plays a central role in maintaining genomic integrity [1–3]. In unstimulated cells p53 is maintained at very low levels but in response to DNA damage or other stress stimuli, such as hypoxia or activation of oncogenes, p53 becomes stabilized and accumulates in the cell [4, 5]. p53 can exert its tumor suppressor function in different ways (Fig. ). It can function as a transcription factor that binds to the promoters of many target genes, such as p21, mdm2, puma and bax, thereby elevating or repressing their expression levels to induce cell cycle arrest and apoptosis. Nuclear and cytoplasmic p53 also physically interact with many.
