TP53 is activated in response to
The tumor-suppressor protein p53 is kept at low levels in unstressed cells by continuous MDM2-mediated ubiquitination and degradation. DNA damage or oncogenic stress leads to phosphorylation of p53 or induction of ARF, both of which block the p53–MDM2 interaction. Stabilized p53 then transcriptionally activates genes that induce cell-cycle arrest, DNA repair or apoptosis, thereby preventing propagation of damaged genomes.
Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)