CDKN2A and cancer: p16INK4a is one of the crucial factors for senescence in human tumors.30 However, like many other cancer cell lines, the p16INK4A gene is silenced in HCT116 cells owing to a frameshift mutation and the hypermethylated promoter.22 In contrast, TRA2β4 knockdown, but not Tra2β knockdown, induced p21 without changing p53 expression.