Associations between NBS1 Polymorphisms and Colorectal Cancer in Chinese Population

Abstract

As the central protein of the double strand breaks (DSB)-induced DNA repair pathway, NBS1 participates in detecting the DSBs and plays an essential role in maintaining genomic stability. Single nucleotide polymorphisms (SNPs) in NBS1 gene were commonly tested that associated with the susceptibility to multiple cancers, but the results remained controversial. Thus, we conducted two independent hospital-based case-control studies comprising 1,072 colorectal cancer patients and 1,263 controls to evaluate the association between four NBS1 SNPs and colorectal cancer risk. The result showed that rs2735383C/G polymorphism in the 3'-untranslated region (UTR) of NBS1 was significantly associated with risk of colorectal cancer using logistic regression (P<10(-4)). Furthermore, we observed that rs2735383CC genotype was associated with substantially increased risk of colorectal cancer (odds ratio=1.55, 95% confidence interval=1.27-1.94), compared with the rs2735383GC+GG genotypes. Further functional experiments demonstrated that the rs2735383C allele in the NBS1 disrupted the binding affinity of has-miR-509-5p to the NBS1 3'-UTR in colorectal cancer cells, affecting the NBS1 transcriptional activity and expression level. In conclusion, current evidence suggests that the rs2735383C/G polymorphism might contribute to the risk for colorectal cancer.

Fig 1. Schematic drawing of the luciferase reporter vectors (psi-CHECK2) contains NBS1 3’-UTR sequence with either the G or C at the rs2735383 locus.

The luciferase activity of the rs2735383 variant allele on luciferase reporter bearing NBS1 3’-UTR co-transfected with or without hsa-miR-509-5p mimics or hsa-miR-509-5p inhibitors in HCT116 cells (A) and HT-29 cells (B). Renilla luciferase activity was measured and normalized to firefly luciferase. Six replicates were carried out for each group, and the experiment was repeated at least three times. Data are mean±standard error of the mean; **P<0.01. (C) NBS1 mRNA expression level in tumor tissue samples from colorectal cancer individuals with different rs2735383 variant alleles genotype (11 rs2735383GG, 13 rs2735383GC and 5 rs2735383CC); data are mean±standard error of the mean, normalized to GAPDH, P = 0.027. (D) hsa-miR-509-5p mRNA expression in 29 colorectal cancer tissues grouped by rs2735383 C/G genotypes. The hsa-miR-509-5p mRNA expression was calculated relative to expression of U6 mRNA. Data are mean ± standard error of the mean, P = 0.345.