Hao B, Miao X, Li Y, Zhang X, Sun T, Liang G, Zhao Y, Zhou Y, Wang H, Chen X, Zhang L, Tan W, Wei Q, Lin D, He F
Department of Biology Sciences and Biotechnology, Tsinghua University, Beijing, China.
Oncogene. 2006 Jun 15;25(25):3613-20. doi: 10.1038/sj.onc.1209355. Epub 2006 May 1.
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' untranslated region (UTR) was significantly associated with the risk of developing esophageal squamous-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 increased 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=1.46, 95% CI=1.18-1.82; P=0.001) and the increased risk was more pronounced in smokers (OR=1.63, 95% CI=1.20-2.21) than in non-smokers (OR=1.28, 95% CI=0.94-1.76). Taken together, these results showed that the functional SNP -77T>C in XRCC1 5'UTR was associated with cancer development owing to the decreased transcriptional activity of C-allele-containing promoter with higher affinity to Sp1 binding.
X射线修复交叉互补蛋白1（XRCC1）在DNA碱基切除修复中起关键作用，缺乏其活性的细胞对DNA损伤高度敏感。最近，我们报道XRCC1基因5'非翻译区（UTR）中的一个单核苷酸多态性（SNP，rs3213245，-77T>C）与食管鳞状细胞癌的发生风险显著相关。计算机分析预测该SNP位于Sp1结合基序的核心区域，提示其具有功能意义。凝胶迁移和超迁移分析证实，XRCC1启动子中的-77T>C多态性位点位于Sp1结合基序内，T>C替换大大增强了Sp1与该区域的结合亲和力。荧光素酶分析表明，与Sp1具有高亲和力的C等位基因XRCC1启动子与转录活性降低有关。在1024例患者和1118例对照中检测了-77T>C与XRCC1中其他三个导致氨基酸替代的多态性与肺癌风险之间的关联，结果显示只有-77T>C多态性与肺癌发生风险增加显著相关。多因素逻辑回归分析发现，与TT基因型相比，携带变异型XRCC1 -77基因型（TC和CC）的肺癌发生风险增加（OR=1.46，95%CI=1.18-1.82；P=0.001），且吸烟者（OR=1.63，95%CI=1.20-2.21）的风险增加比非吸烟者（OR=1.28，95%CI=0.94-1.76）更明显。综上所述，这些结果表明，XRCC1 5'UTR中的功能性SNP -77T>C与癌症发生有关，这是由于含C等位基因的启动子对Sp1结合具有更高亲和力，导致转录活性降低。
