Reassessing the role of p53 in cancer and ageing from an evolutionary perspective.

The gene p53 has been fashioned as the guardian of the genome and as prototype of the tumour suppressor gene (TSG) whose function must be inactivated in order for tumours to develop. The ubiquitous expression of truncated p53 protein isoforms, results in "premature ageing" of laboratory mouse strains engineered for expressing such isoforms. These facts have been construed in the argument that p53 evolved in order to protect organisms with renewable tissues from developing cancer yet, because p53 is also an inducer of cellular senescence or apoptosis after extensive DNA damage, it becomes a limiting factor for tissue renewal by depleting tissues from stem/precursor cells thus leading to whole-organism ageing. From that point of view p53 displays antagonist pleiotropy contributing to the establishment of degenerative diseases and ageing. Therefore, tumour suppression becomes a balancing act between cancer prevention and ageing. Nevertheless, here we present current evidence showing that the aforementioned argument is rather inconsistent and unwarranted on evolutionary grounds. The evolutionary perspective indicates that p53 evolved so as to play a subtle but very important role during development while its role as a TSG is only important in animals that are protected from most sources of extrinsic mortality, thus suggesting that p53 was primarily selected for its developmental role and not as a TSG. Therefore no real antagonist pleiotropy can be attached to p53 functions and their relationship with whole-organism ageing might be a laboratory artefact.