SIRT1 and neoplasm: In cells retaining wildtypep53, SIRT1 regulates and maintains p53 in an inactive state by deacetylatingthe transcription factor and promoting cellular senescence over apoptosis.However, in cells lacking p53, such as p53 null tumor cells, SIRT1 may loserepression from tumor suppressors such as p53 and HIC1 allowing for theoverexpression of SIRT1.