CDKN1A and neoplasm: Interestingly, several of these proteins are paradigmatic targets of the p53 tumor suppressor pathway.33, 34, 35, 36, 37, 38 Indeed, the G1/S cell cycle regulator cyclin-dependent kinase inhibitor 1A (CDKN1A), a major p53-regulated inhibitor of cyclin-dependent kinases,33, 34, 35, 36, 37, 38 was significantly induced by TIA expression.