| Breast cancer is the most frequent malignancy of women in the world. Although the breast cancer incidence rate in China is about one-third of that in the United States, it shows a significantly increasing trend in the last two decades especially in the developed city such as Shanghai and Beijing. However, the exact molecular mechanisms to breast cancer are still unclear. It is well accepted that interaction of environmental factors and genetic factors may contribute to the etiology of breast cancer. The individuals with different genetic background have different risk of breast cancer. So the most critical thing is the identification of the breast cancer susceptibility genes in a high-risk population for breast cancer. Although mutations in human family breast cancer susceptibility genes, BRCA1and BRCA2, are regarded as the strong risk factors to breast cancer, but it only account for less than 5% of all breast cancer cases. Thus, it is crucial to investigate other genetic risk factors of breast cancer in general population.RecQ helicases belong to the superfamily II group of DNA helicases and play ritical roles in DNA replication, repair and recombination, telomere maintenance and genomic stability. Deficiencies in the human RecQ helicases genes,WRN and BLM, lead to high levels of genomic instability and increased susceptibility to several types of cancer. WRN and BLM have several protein interacting partners, such as BRCA1. Different interactions might contribute to the different roles of WRN and BLM in specific DNA metabolic pathways involve in cancer development. Besides the protein coding genes, such as WRN, BLM and BRCA1, recent evidence shows that small, non-coding RNA molecules, called microRNAs (miRNAs), function as tumor suppressors or oncogenes. MiRNAs are a family of endogenous 21-24nt long small noncoding RNA gene products, that regulate gene expression by base pairing with target mRNAs at the 3'-terminal untranslated regions (3'-UTRs), leading to mRNAs cleavage or translational repression. Mutation, mis-expression or altered mature miRNA processing are implicated in carcinogenesis and tumor progression. Thus, we conducted a case-control study to investigate the association of low-penetrance WRN, BLM, BRCA1 and miRNA genes polymorphisms with breast cancer susceptibility in Chinese populations.Part I: WRN, BLM and BRCA1 Gene Polymorphism and the Susceptibility of Breast CancerRecQ helicases, which belong to the superfamily II group of DNA helicases, participate in numerous nucleic acid transactions, including replication, repair and recombination and have been demonstrated to play important roles in the DNA damage response. Mutations of the human RecQ helicases genes, WRN and BLM, have been linked to rare autosomal recessive genomic instability disorders, referred to as Werner syndrome and Bloom syndrome, which are associated with premature ageing and cancer predisposition. These disorders are characterized by genetic instability, implicating a central role of these DNA helicases in one or more DNA repair pathways. Studies have shown that WRN and BLM have a highly conserved multifunctional RecQ C-terminal region (RQC) that involves in the interactions with some important cancer-related proteins, such as the tumor suppressor protein BRCA1. In vitro studies show that WRN and BLM interact with BRCA1 and play important roles in DNA repair and genomic stability.The aim of this case-control study including 1025 breast cancer cases and 1025 controls is to investigate the associations of WRN leu1074Phe (rs2725362), Cys1367Arg(rs1346044),BLM Met298Thr (rs28384991) and BRCA1 Pro871Leu(rs799917) with breast cancer risk in Chinese populations.We genotyped the four polymorphisms by PCR-RFLP (PCR-Restriction Fragment Length Polymorphism) and PCR-PIRA (PCR-Primer Introduced Restriction Analysis) method. In addition, genotyping was performed blindly and 10% of the samples were randomly selected for repeated assays. Finally, a total of 1004 (98.0%) breast cancer cases and 1008 (98.3%) controls were successfully genotyped.In the present case-control study, the variant genotype of WRN Leu1074Phe was associated with a significantly increased risk of breast cancer (adjusted OR=1.36, 95% CI=1.06-1.74 for 1074Phe/Phe genotype), compared with the wild-type 1074Leu/Leu genotype. We also found a remarkable locus-environment interaction effect between WRN Leu1074Phe and age at menarche on breast cancer risk (Pint =0.02).We did not find overall significant associations between the three variants, BLM Met298Thr, WRN Cys1367Arg and BRCA1 Pro871Leu, and breast cancer risk in this study population.These findings suggested that WRN Leu1074Phe variant may contribute to breast risk susceptibility in Chinese women.Part II: Common Genetic Variants of miRNAs and Breast Cancer SusceptibilityMicroRNAs (miRNAs) are an abundant class of small non-cong, single-stranded RNAs of 21-24 nucleotides that form base-pairs with target mRNAs and negatively regulate their translational efficiency and stability. miRNAs participate in the regulation of almost each of biological processes and are involved in the pathogenesis of human diseases, including embryonic development, chromosome architecture, cell proliferation, apoptosis, stress resistance, fat metabolism and stem cell maintenance. Study showed that about 50% of annotated human miRNAs are located in areas of the genome, known as fragile sites, which are associated with cancer. This indicates that miRNAs might have a crucial function in cancer progression. Single nucleotide polymorphisms (SNPs) or mutations may change the property of miRNAs through altering miRNA expression and/or maturation. We genotyped four selected SNPs (rs2910164, rs2292832, rs11614913 and rs3746444), which are located at the pre-miRNA regions of hsa-mir-146a, hsa-mir-149, hsa-mir-196a2 and hsa-mir-499 by PCR-RFLP (PCR-Restriction Fragment Length Polymorphism) and PCR-PIRA (PCR-Primer Introduced Restriction Analysis) method and evaluated their associations with breast cancer risk in a case-control study of 1009 breast cancer cases and 1093 cancer-free controls of Chinese women. In addition,genotyping was performed blindly and 10% of the samples were randomly selected for repeated assays. Finally, a total of 1009 (98.1%) breast cancer cases and 1093 (98.7%) controls were successfully genotyped.In this case-control study, we found subjects carrying variant homozygous genotypes of hsa-mir-196a2 rs11614913:T>C and hsa-mir-499 rs3746444:A>G had significantly increased risks of breast cancer (OR = 1.37, 95% CI = 1.08-1.74 for rs11614913 CC and OR = 1.75, 95% CI = 1.07-2.85 for rs3746444 GG) compared with their wild-type homozygotes, respectively. And we also found that the increased risk associated with rs11614913 variant genotypes (CC/CT) was more pronounced in younger subjects (OR = 1.32, 95% CI = 1.03-1.70), those with an early age at menarche(OR = 1.30, 95% CI = 1.04-1.63), premenopause(OR = 1.33, 95% CI = 1.01-1.75), and positive ER(OR= 1.42, 95% CI = 1.10-1.83) and PR (OR = 1.39, 95% CI = 1.08-1.80)status, whereas the increased risk associated with rs3746444 variant genotypes (GG/AG) was more notable in younger subjects(OR = 1.34, 95% CI = 1.04-1.73), those at late age at menarche (OR = 1.61, 95% CI = 1.13-2.27) and premenopause (OR = 1.51, 95% CI = 1.14-2.00). |
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