ONCOGENOMICS A novel T-77C polymorphism in DNA repair gene XRCC1 contributes to diminished promoter activity and increased risk of non-small cell lung cancer B Hao 1,3,5 , X Miao 2,5 ,YLi 3 , X Zhang 2 , T Sun 2 , G Liang 2 , Y Zhao 3 , Y Zhou 2 , H Wang 3 , X Chen 3 , L Zhang 3 , W Tan 2 , Q Wei 4 , D Lin 2 and F He 1,3 1 Department of Biology Sciences and Biotechnology, Tsinghua University, Beijing, China; 2 Department of Etiology and Carcinogenesis, Cancer Institute & Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China; 3 Laboratory of Systems Biology, Beijing Institute of Radiation Medicine, Beijing, China and 4 Department of Epidemiology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA X-ray repair cross-complementing 1 (XRCC1) plays a key role in DNA base excision repair and cells lacking its activity are hypersensitive to DNA damage. Recently, we reported a SNP (rs3213245, 77T>C) in the XRCC1 gene 5 0 untranslated region (UTR) was significantly associated with the risk of developing esophageal squa- mous-cell carcinoma. Computer analysis predicted that this SNP was in the core of Sp1-binding motif, which suggested its functional significance. Gel shift and super shift assays confirmed that 77T>C polymorphic site in the XRCC1 promoter was within the Sp1-binding motif and the T>C substitution greatly enhanced the binding affinity of Sp1 to this region. Luciferase assays indicated that the Sp1-high-affinity C-allelic XRCC1 promoter was associated with a reduced transcriptional activity. The association between 77T>C and three other amino-acid substitution-causing polymorphisms in XRCC1 and risk of lung cancer was examined in 1024 patients and 1118 controls and the results showed that only the 77T>C polymorphism was significantly associated with an in- creased risk of developing lung cancer. Multivariate logistic regression analysis found that an increased risk of lung cancer was associated with the variant XRCC1 77 genotypes (TC and CC) compared with the TT genotype (OR ¼ 1.46, 95% CI ¼ 1.18–1.82; P ¼ 0.001) and the increased risk was more pronounced in smokers (OR ¼ 1.63, 95% CI ¼ 1.20–2.21) than in non-smokers (OR ¼ 1.28, 95% CI ¼ 0.94–1.76). Taken together, these results showed that the functional SNP 77T>C in XRCC1 5 0 UTR was associated with cancer development owing to the decreased transcriptional activity of C-allele- containing promoter with higher affinity to Sp1 binding. Oncogene (2006) 25, 3613–3620. doi:10.1038/sj.onc.1209355; published online 1 May 2006 Keywords: base excision repair; non-small cell lung cancer; single nucleotide polymorphism; transcription regulation Introduction A wide diversity of DNA damage in human cells could be induced by endogenous sources such as various metabolites including radical oxygen species and exo- genous sources such as exposure to ultraviolet, ionizing radiation, and genotoxic chemicals. If not repaired, such DNA damage can cause mutations and genomic instability, leading to cellular malignant transformation. Nevertheless, cells have evolved a set of complex DNA repair systems that safeguard the integrity of genome to minimize the consequences of detrimental mutations (Hoeijmakers, 2001). The normal expression and func- tion of DNA repair proteins are therefore critical for cells to remove damage and thus prevent carcinogenesis. Among DNA repair systems, the base excision repair (BER) pathway is one important mechanism that repairs DNA base damage and single-strand breaks (Hoeijmakers, 2001; Wood et al., 2001). BER includes two major processes, that is, excision of damaged base residues and core BER reaction including strand incision at the abasic site, one-nucleotide gap-filling reaction, and sealing of the remaining nick (Wood etal., 2001). As a scaffold protein in BER, the X-ray repair cross-complementing 1 (XRCC1) assembles a DNA- protein complex at the damage site with poly(ADP- ribose) polymerase, DNA polymerase-b and DNA ligase IIIa to complete the repair process (Weinfeld et al., 2001; Caldecott, 2003). The importance of XRCC1 in maintaining genomic stability is indicated by an increased frequency of spontaneous chromosome aberrations and deletions in XRCC1 mutant cells and by embryonic lethality in XRCC1 knockout mice (Thomp- son et al., 1990; Tebbs et al., 1999). The XRCC1 gene is polymorphic (Shen et al., 1998; Mohrenweiser etal., 2002; Hao etal., 2004) and, to date, there are dozens of variants that have been identified, Received 18 April 2005; revised 28 November 2005; accepted 28 November 2005; published online 1 May 2006 Correspondence: Professor D Lin, Department of Etiology and Carcinogenesis, Cancer Institute, Chinese Academy of Medical Sciences, Beijing 100021, China; and Professor F He, Laboratory of Systems Biology, Beijing Institute of Radiation Medicine, Beijing 100850, China. E-mail: dlin@public.bta.net.cn; hefc@nic.bmi.ac.cn 5 These authors contributed equally to this work. Oncogene (2006) 25, 3613–3620 & 2006 Nature Publishing Group All rights reserved 0950-9232/06 $30.00 www.nature.com/onc ONCOGENOMICS