title: APE1 overexpression in XRCC1-deficient cells complements the defective repair of oxidative single strand breaks but increases genomic instability.
abstract: XRCC1 protein is essential for mammalian viability and is required for the efficient repair of single strand breaks (SSBs) and damaged bases in DNA. XRCC1-deficient cells are genetically unstable and sensitive to DNA damaging agents. XRCC1 has no known enzymatic activity and is thought to act as a scaffold protein for both SSB and base excision repair activities. To further define the defects leading to genetic instability in XRCC1-deficient cells, we overexpressed the AP endonuclease APE1, shown previously to interact with and be stimulated by XRCC1. Here, we report that the overexpression of APE1 can compensate for the impaired capability of XRCC1-deficient cells to repair SSBs induced by oxidative DNA damage, both in vivo and in whole-cell extracts. We show that, for this kind of damage, the repair of blocked DNA ends is rate limiting and can be performed by APE1. Conversely, APE1 overproduction resulted in a 3-fold increase in the sensitivity of XRCC1-deficient cells to an alkylating agent, most probably due to the accumulation of SSBs. Finally, the overproduction of APE1 results in increases of 40% in the frequency of micronuclei and 33% in sister chromatid exchanges of XRCC1- cells. These data suggest that the spontaneous generation of AP sites could be at the origin of the SSBs responsible for the spontaneous genetic instability characteristic of XRCC1-deficient cells.
authors.affiliation: Département de Radiobiologie et Radiopathologie, CEA UMR217 CNRS, Route du Panorama, F-92265 Fontenay aux Roses, France.
authors.forename: Marguerite
authors.initials: M
authors.lastname: Sossou
authors.forename: Claudia
authors.initials: C
authors.lastname: Flohr-Beckhaus
authors.forename: Ina
authors.initials: I
authors.lastname: Schulz
authors.forename: Fayza
authors.initials: F
authors.lastname: Daboussi
authors.forename: Bernd
authors.initials: B
authors.lastname: Epe
authors.forename: J Pablo
authors.initials: JP
authors.lastname: Radicella
mesh_terms: D000477:Alkylating Agents / Q000494:pharmacology; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D004249:DNA Damage; D004260:DNA Repair; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics*; D017353:Gene Deletion; D042822:Genomic Instability; D010084:Oxidation-Reduction; D000076105:X-ray Repair Cross Complementing Protein 1
chemical_list: D000477:Alkylating Agents; D004268:DNA-Binding Proteins; D000076105:X-ray Repair Cross Complementing Protein 1; C000619371:XRCC1 protein, human; C085108:APEX1 protein, human; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase