title: XRCC1 and base excision repair balance in response to nitric oxide.
abstract: Inflammation associated reactive oxygen and nitrogen species (RONs), including peroxynitrite (ONOO(-)) and nitric oxide (NO), create base lesions that potentially play a role in the toxicity and large genomic rearrangements associated with many malignancies. Little is known about the role of base excision repair (BER) in removing these endogenous DNA lesions. Here, we explore the role of X-ray repair cross-complementing group 1 (XRCC1) in attenuating RONs-induced genotoxicity. XRCC1 is a scaffold protein critical for BER for which polymorphisms modulate the risk of cancer. We exploited CHO and human glioblastoma cell lines engineered to express varied levels of BER proteins to study XRCC1. Cytotoxicity and the levels of DNA repair intermediates (single-strand breaks; SSB) were evaluated following exposure of the cells to the ONOO(-) donor, SIN-1, and to gaseous NO. XRCC1 null cells were slightly more sensitive to SIN-1 than wild-type cells. We used small-scale bioreactors to expose cells to NO and found that XRCC1-deficient CHO cells were not sensitive. However, using a molecular beacon assay to test lesion removal in vitro, we found that XRCC1 facilitates AAG-initiated excision of two key NO-induced DNA lesions: 1,N(6)-ethenoadenine and hypoxanthine. Furthermore, overexpression of AAG rendered XRCC1-deficient cells sensitive to NO-induced DNA damage. These results show that AAG is a key glycosylase for BER of NO-induced DNA damage and that XRCC1's role in modulating sensitivity to RONs is dependent upon the cellular level of AAG. This demonstrates the importance of considering the expression of other components of the BER pathway when evaluating the impact of XRCC1 polymorphisms on cancer risk.
authors: Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA, United States.
authors: James T
authors: JT
authors: Mutamba
authors: David
authors: D
authors: Svilar
authors: Somsak
authors: S
authors: Prasongtanakij
authors: Xiao-Hong
authors: XH
authors: Wang
authors: Ying-Chih
authors: YC
authors: Lin
authors: Peter C
authors: PC
authors: Dedon
authors: Robert W
authors: RW
authors: Sobol
authors: Bevin P
authors: BP
authors: Engelward
mesh_terms: D000818:Animals; D016466:CHO Cells; D002457:Cell Extracts; D045744:Cell Line, Tumor; D006224:Cricetinae; D003412:Cricetulus; D004260:DNA Repair / Q000187:drug effects*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D042822:Genomic Instability / Q000187:drug effects; D006801:Humans; D008741:Methyl Methanesulfonate / Q000633:toxicity; D009699:N-Glycosyl Hydrolases / Q000378:metabolism; D009569:Nitric Oxide / Q000633:toxicity*; D030421:Peroxynitrous Acid / Q000633:toxicity; D000076105:X-ray Repair Cross Complementing Protein 1
chemical_list: D002457:Cell Extracts; D004268:DNA-Binding Proteins; D000076105:X-ray Repair Cross Complementing Protein 1; C000619371:XRCC1 protein, human; D030421:Peroxynitrous Acid; D009569:Nitric Oxide; D008741:Methyl Methanesulfonate; D009699:N-Glycosyl Hydrolases; C437225:adenine glycosylase