Removing all obstacles A critical role for p53 in promoting tissue renewal

Defects in DNA repair pathways or exposure to high levels of DNA damaging agents limit the renewal potential of adult tissues and accelerate the development of age-related degenerative pathologies. 1-3 Many studies suggest these tissue homeostatic defects can result from the accumulation of DNA damage in tissue-specific stem cells. 4,5 Although maintenance of genome integrity in progenitor cells is required for the renewal of adult tissues, recent studies have highlighted the importance of additional mechanisms that facilitate and direct the process of tissue regeneration. These reports indicate that the p53 tumor suppressor gene maintains adult tissue homeostasis and promotes tissue renewal by suppressing the accumulation of DNA-damaged cells.(6-8) Without p53, tissue deterioration caused by the elimination of genome maintenance regulators (ATR, Hus1 or Terc) is exacerbated and, in some cases, leads to synthetic lethality at the organismal level. Importantly, the accumulation of highly damaged cells in multiple tissues appears to severely impede regeneration from undamaged progenitors, suggesting that p53-mediated removal of damaged cells is a prerequisite for efficient progenitor driven renewal. These findings argue that tissue homeostasis is governed not only by the intrinsic repopulating potential of competent progenitors, but also by mechanisms that limit the accumulation of defective cells and, thereby, promote compensatory regeneration. As discussed in this review, these findings advance our understanding of processes that counter the effects of DNA damage at the tissue level and have important implications for the development of therapeutic approaches to combating age-related pathologies and p53-deficient malignancies.