TP53 and neoplasm: 24 p14ARF is a tumor suppressor that activates p53 and whose expression is impaired in most tumor cell lines retaining wild-type p53 including MCF7 and HCT116 cells.25 Overall, the effect of TSA on HDM2 mRNA was either very low or imperceptible and TSA-induced variations on endogenous hdm2 protein levels were negligible in comparison with the effects of TSA on p21 and pig3, as discussed below.