Association Study Of Polymorphisms In MiRNAs Genes With The Susceptibility Of Hepatocellular Carcinoma

Liver cancer is the sixth most common malignancy and the third leading cause of cancer-related death worldwide. The distribution of liver cancer is imbalance throughout the world, and 82% of the cases (and the deaths) are estimated in developing countries (55% in China alone). Hepatocellular carcinoma (HCC) accounts for between 85%-90% of liver cancers.The major risk factors for HCC are chronic infections with the hepatitis B or C viruses, exposure to dietary aflatoxin B1, and alcohol consumption, with the hepatitis B virus (HBV) infection of particular interest, because of its coherent distribution with the HCC prevalence. However, the exact molecular mechanisms to HCC are still unclear. It is well accepted that interaction of environmental factors and genetic factors may contribute to the etiology of HCC. The individuals with different genetic background have different risk of HCC. So the most critical thing is the identification of the HCC susceptibility genes in a high-risk population for HCC.Mutations in the p53 tumor suppressor gene are found in nearly all types of cancers including hepatocellular carcinoma. Recently, studies have reported that p53 can regulate the expression of microRNAs (miRNAs), especially the miR-34 family members, which is the first time revealing an inter play between proteins and non-coding RNAs in this crucial tumor suppressor pathway. Transcription of miR-34 is directly induced by p53 in response to genotoxic stress and acts downstream to promote cell cycle arrest or apoptosis. Therefore, the miR-34 family acts as potential tumor suppressor genes.MicroRNAs (miRNAs) are 21- to 24-nucleotide-long small noncoding RNA gene products that regulate gene expression by base pairing with target mRNAs at the 3'-untranslated region (UTR), leading to mRNAs cleavage or translational repression. In cell nucleus, miRNAs are initiall made as large RNA precursors that are called pri-miRNAs, then the pri-miRNAs are processed by Drosha into ~100-nuclrotide pre-miRNAs, and exported into the cytoplasm by Exportin 5.The pre-miRNAs are finally excised into mature miRNAs by RNAseâ…¢enzyme Dicer. It has been suggested that miRNAs are involved in various biological processes. Moreover, several recent reports show that miRNAs participate in human tumorigenesis as tumor suppressors or oncogenes. A recent study demonstrated that more than 50% of miRNA genes are located in cancerassociated genomic regions or in fragile sites, suggesting that miRNAs may play an important role in the pathogenesis of a limited range of human cancers. SNPs in miRNA sequence may involve in hepatocellular carcinoma susceptibilityby altering miRNA expression, and influencing hundreds of target genes.Thus, we conducted a case-control study to investigate the association of a polymorphism rs4938723 T>C in the promoter regionof miR-34b/c and two common functional pre-miRNAs SNPs rs2910164 and rs11614913 with hepatocellular carcinoma susceptibility in Chinese populations. The miR-34 family members are direct transcriptional targets of tumor suppressor p53, and loss of miR-34 function can impair p53-mediated cell-cycle arrest and apoptosis. Besides loss of miR-34 in cancer due to the inactivating mutations of p53 or the expression of viral inhibitors of p53, the miR-34-encoding genes themselves may be targets for the mutational or the epigenetic inactivations in cancer. Therefore, the miR-34 family acts as potential tumor suppressor genes, and may serve as candidate biomarkers of cancer susceptibility, including HCC.The miR-34 family comprises three processed miRNAs that are encoded by two different primary miRNAs: miR-34a is encoded by its own transcript, whereas miR-34b and miR-34c shared a common primary transcript (pri-miR?34b/c). In the present study, we hypothesized that SNPs miR-34b/c rs4938723 and p53 Arg72Pro may independently or jointly contribute to primary hepatocellular carcinoma (HCC) susceptibility. We genotyped the two SNPs in a case-control study of 501 patients with primary HCC and 548 cancer-free controls in a Chinese population.We observed that the variant genotypes of miR-34b/c rs4938723 were associated with significantly increased HCC risks compared with the wild-type TT genotype (adjusted OR= 1.37, 95% CI =1.06-1.78 for TC; OR =1.53, 95% CI = 1.02-2.31 for CC and OR = 1.40, 95% CI = 1.10-1.80 for TC/CC). Furthermore, we found a significant interaction between alcohol drinking and SNP rs4938723 on HCC risk (P=0.05 for multiplicative and P=0.01 for additive interaction). However, we did not find any main effect of p53 Arg72Pro on HCC risk in this population. These findings indicate that the potentially functional SNP rs4938723 in the promoter region of pri-miR-34b/c may contribute to the susceptibility of HCC in this Chinese population. Partâ…¡Two common functional polymorphisms in pre-microRNAs and the susceptibility of hepatocellular carcinomaThe high conservational sequences of pre-miRNAs region suggest that SNP in the pre-miRNAs may have important functions. Two common functional polymorphisms in pre-miRNAs (pre-mir-146a rs2910164 and pre-mir-196a2 rs11614913) may change the processing of the miRNA as well as alter the target binding affinity and specificity, and thus play important roles in carcinogenesis.In the present study, we conducted a case-control study aiming to investigate the association between two common functional polymorphisms in two pre-microRNAs and hepatocellular carcinoma susceptibility. We genotyped this two SNPs (rs2910164 and rs11614913), which are located at the pre-miRNA regions of hsa-mir-146a and hsa-mir-196a2 by PCR-RFLP (PCR-Restriction Fragment Length Polymorphism) and PCR-PIRA (PCR-Primer Introduced Restriction Analysis) method and evaluated their associations with primary hepatocellular carcinoma (HCC) risk in the same samples of the study.We didn't observe that two SNPs rs2910164 and rs11614913 were associated with significantly increased HCC risks compared with the wild-type genotype ( rs2910164 GC/GG vs CC: OR=1.12,95%CI=0.86-1.45,rs11614913 CC vs TT/CT: OR=1.19,95%CI=0.88-1.62 ).However, we found that the risk effect of the variant genotypes of rs2910164 GC/GG was more evident in HBsAg/anti-HCV positive subjects (adjusted OR=1.78, 95%CI=1.07-2.97). Since pre-mir-146a rs2910164 and pre-mir-196a2 rs11614913 have been identificated two functional polymorphisms and chronic infections with the hepatitis B viruses are the major risk factors for HCC, it is necessary to investigate the role of these two genetic polymorphisms in hepatocarcinogenesis in the further case-control study with the positive HBV infection.