title: Regulation of the human AP-endonuclease (APE1/Ref-1) expression by the tumor suppressor p53 in response to DNA damage.
abstract: The human AP-endonuclease (APE1/Ref-1), an essential multifunctional protein, plays a central role in the repair of oxidative base damage via the DNA base excision repair (BER) pathway. The mammalian AP-endonuclease (APE1) overexpression is often observed in tumor cells, and confers resistance to various anticancer drugs; its downregulation sensitizes tumor cells to those agents via induction of apoptosis. Here we show that wild type (WT) but not mutant p53 negatively regulates APE1 expression. Time-dependent decrease was observed in APE1 mRNA and protein levels in the human colorectal cancer line HCT116 p53(+/+), but not in the isogenic p53 null mutant after treatment with camptothecin, a DNA topoisomerase I inhibitor. Furthermore, ectopic expression of WTp53 in the p53 null cells significantly reduced both endogenous APE1 and APE1 promoter-dependent luciferase expression in a dose-dependent fashion. Chromatin immunoprecipitation assays revealed that endogenous p53 is bound to the APE1 promoter region that includes a Sp1 site. We show here that WTp53 interferes with Sp1 binding to the APE1 promoter, which provides a mechanism for the downregulation of APE1. Taken together, our results demonstrate that WTp53 is a negative regulator of APE1 expression, so that repression of APE1 by p53 could provide an additional pathway for p53-dependent induction of apoptosis in response to DNA damage.
authors.affiliation: Department of Biochemistry and Molecular Biology, Sealy Center for Molecular Medicine, University of Texas Medical Branch, TX-77555, Galveston, USA.
authors.forename: Amira
authors.initials: A
authors.lastname: Zaky
authors.forename: Carlos
authors.initials: C
authors.lastname: Busso
authors.forename: Tadahide
authors.initials: T
authors.lastname: Izumi
authors.forename: Ranajoy
authors.initials: R
authors.lastname: Chattopadhyay
authors.forename: Ahmad
authors.initials: A
authors.lastname: Bassiouny
authors.forename: Sankar
authors.initials: S
authors.lastname: Mitra
authors.forename: Kishor K
authors.initials: KK
authors.lastname: Bhakat
mesh_terms: D045744:Cell Line, Tumor; D004249:DNA Damage; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000235:genetics* / Q000378:metabolism; D015536:Down-Regulation; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D009154:Mutation; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D020218:Response Elements; D016329:Sp1 Transcription Factor / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*
chemical_list: D012333:RNA, Messenger; D016329:Sp1 Transcription Factor; D016159:Tumor Suppressor Protein p53; C085108:APEX1 protein, human; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase