Involvement of Oct-1 in the regulation of CDKN1A in response to clinically relevant doses of ionizing radiation

CDKN1A is a cyclin-dependent kinase inhibitor that plays a critical role in cell cycle checkpoint regulation.It is transcriptionally induced by TP53 (p53)following exposure to ionizing radiation (IR).Induction of CDKN1A after irradiation is closely related to IR-sensitivity of tumor cells but the UNDERLYING mechanisms remain obscure because conventional reporter gene systems respond poorly to IR unless hyperlethal doses are used.Here we performed a promoter analysis of the CDKN1A gene following irradiation withclinically relevant doses of IR using the adeno-associated virus-mediated reporter system which we have recently shown to be highly responsive to IR.We demonstrate that there are regulatory elements at –1.1 kb,–1.4 kb,and –1.8 kb,and deletion of these elements attenuated induction of the CDKN1A gene promoter in response to 0.2-2.0 Gy of IR.EMSA and ChIP assays showed that Oct-1 binds constitutively to the elements at –1.1 kb and –1.8 kb.Functional involvement of Oct-1 was confirmed by RNA interference targeting the Oct-1 gene which suppressed both the basal and IR-inducible components of CDKN1A expression. Thus our results reveal that Oct-1 is crucial to the TP53-mediated regulation of the CDKN1A gene promoter following exposure to clinically relevant doses of IR