p53 (Guardian of the Genome)
The transcription factor that decides whether to repair, senesce, or eliminate damaged cells
Definition
The p53 gene (TP53) encodes a 393-amino-acid protein called 'the guardian of the genome' by David Lane (1992). Activated upon DNA damage, oxidative stress, hypoxia, or oncogenic activation, p53 functions as a transcription factor that decides cellular fate: DNA repair (temporary cell cycle arrest), senescence (permanent arrest if damage is severe), or apoptosis (suicide, if damage is irreparable). It is the most frequently mutated gene in human cancer: ~50% of all tumours present TP53 mutations that inactivate it or confer oncogenic functions.
Detailed explanation
Specific functions activated by p53:
DNA repair: induces GADD45, BAX, p21 that arrest cell cycle in G1 allowing repair. Senescence: activates p21^WAF1/CIP1, inducing permanent cell cycle arrest in non-repairable damages. Apoptosis: induces PUMA, NOXA, BAX that activate the mitochondrial pathway of programmed cell death. Metabolism: regulates glycolysis (TIGAR), oxidative phosphorylation (SCO2), autophagy. Immunity: modulates antigen presentation and anti-tumour immune response.
The p53 paradox in longevity: although its loss is highly oncogenic, its chronic hyperactivation accelerates ageing. Mice with constitutively hyperactive p53 (Donehower models) have lower cancer incidence but shortened lifespan due to stem cell exhaustion. The optimal balance between tumour suppression and stem cell maintenance is one of the great unsolved problems of ageing biology.
Interventions to optimise p53 activity without hyperactivation: caloric restriction (induces pulsatile p53), exercise (protective moderate activation), polyphenols (resveratrol, quercetin, EGCG favourably modulate p53), reduction of chronic oxidative stress that 'wears down' the p53 response. Direct clinical measurement of functional p53 is unavailable; it is inferred indirectly from DNA damage/repair biomarkers.
Scientific sources
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