Germline miRNA DNA variants and the risk of colorectal cancer by subtype

Functions of the Bloom Syndrome Helicase N-terminal Intrinsically Disordered Region

Bloom Syndrome helicase (Blm) is a RecQ family helicase involved in DNA repair, cell-cycle progression, and development. Pathogenic variants in human BLM cause the autosomal recessive disorder Bloom Syndrome, characterized by predisposition to numerous types of cancer. Prior studies of Drosophila Blm mutants lacking helicase activity or protein have shown sensitivity to DNA damaging agents, defects in repairing DNA double-strand breaks (DSBs), female sterility, and improper segregation of chromosomes in meiosis. Blm orthologs have a well conserved and highly structured RecQ helicase domain, but more than half of the protein, particularly in the N-terminus, is predicted to be unstructured. Because this region is poorly conserved across multicellular organisms, we compared closely related species to identify regions of conservation, potentially indicating important functions. We deleted two of these Drosophila-conserved regions in D. melanogaster using CRISPR/Cas9 gene editing and assessed the effects on different Blm functions. Each deletion had distinct effects on different Blm activities. Deletion of either conserved region 1 (CR1) or conserved region 2 (CR2) compromised DSB repair through synthesis-dependent strand annealing and resulted in increased mitotic crossovers. In contrast, CR2 is critical for embryonic development but CR1 is not as important. CR1 deletion allows for proficient meiotic chromosome segregation but does lead to defects in meiotic crossover designation and patterning. Finally, deletion of CR2 does not lead to significant meiotic defects, indicating that while each region has overlapping functions, there are discreet roles facilitated by each. These results provide novel insights into functions of the N-terminal disordered region of Blm.

Impact of Mir196a-2 Genotypes on Colorectal Cancer Risk in Taiwan

We aimed to investigate the association between genotypes for mir146a and mir196a-2 and the risk of developing colorectal cancer (CRC). We used polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) to determine the mir146a rs2910164 and mir196a-2 rs11614913 genotypes in 362 CRC patients and 362 controls. We also assessed the interactions between these genotypes and age, gender, smoking, alcohol consumption, and BMI status on CRC risk. Additionally, the serum expression level of mir196a-2 was quantified using quantitative reverse transcription-PCR. Our findings demonstrated that among the controls, the proportions of TT, CT, and CC genotypes of mir196a-2 rs11614913 were 32.3%, 48.1%, and 19.6%, respectively. As for the cases, the proportions were 24.6%, 45.0%, and 30.4%, respectively. Logistic regression analysis revealed that the CC genotype carriers had a 2.04-fold increased risk (95% confidence interval [CI] = 1.36-3.06, p = 0.0008). Furthermore, carriers of the CT + CC genotypes also exhibited a significant association with CRC risk (odds ratio [OR] = 1.46, 95% CI = 1.06-2.03, p = 0.0261). Moreover, carriers of the CC genotype had significantly higher serum levels of mir196a-2 compared to those with the TT genotype (p < 0.0001), indicating a genotype-phenotype correlation. No association was found regarding mir146a rs2910164. In conclusion, mir196a-2 rs2910164 genotypes, along with their associated expression, can serve as predictive markers for CRC risk.

Single Nucleotide Polymorphisms in microRNA Genes and Colorectal Cancer Risk and Prognosis

There is growing interest in single nucleotide polymorphisms (SNPs) in the genes of microRNAs (miRNAs), which could be associated with susceptibility to colorectal cancer (CRC) and therefore for prognosis of the disease and/or treatment response. Moreover, these miRNAs-SNPs could serve as new, low-invasive biomarkers for early detection of CRC. In the present article, we performed a thorough review of different SNPs, which were investigated for a correlation with the CRC risk, prognosis, and treatment response. We also analyzed the results from different meta-analyses and the possible reasons for reported contradictory findings, especially when different research groups investigated the same SNP in a gene for a particular miRNA. This illustrates the need for more case-control studies involving participants with different ethnic backgrounds. According to our review, three miRNAs-SNPs-miR-146a rs2910164, miR-27a rs895819 and miR-608 rs4919510-appear as promising prognostic, diagnostic and predictive biomarkers for CRC, respectively.

Lack of association between miR-146a rs2910164 C/G locus and colorectal cancer: from a case-control study to a meta-analysis

Previous studies suggested that miR-146a rs2910164 (C/G) locus was predicted to influence the risk of cancer. However, the relationship of miR-146a rs2910164 locus with colorectal cancer (CRC) susceptibility was controversial. We recruited 1003 CRC patients and 1303 controls, and performed a case–control study to clarify the correlation of miR-146a rs2910164 locus with CRC risk. Subsequently, a comprehensive meta-analysis was conducted to verify our findings. In the case–control study, we suggested that miR-146a rs2910164 variants did not alter CRC risk (CG vs. CC: adjusted P=0.465; GG vs. CC: adjusted P=0.436, CG/GG vs. CC: adjusted P=0.387 and GG vs. CC/CG: adjusted P=0.589), even in subgroup analysis. Next, we conducted a pooled-analysis to identify the correlation of miR-146a rs2910164 locus with CRC risk. In this pooled-analysis, 7947 CRC cases and 12,168 controls were included. We found that miR-146a rs2910164 polymorphism did not influence the risk of CRC (G vs. C: P=0.537; GG vs. CC: P=0.517, CG/GG vs. CC: P=0.520 and GG vs. CC/CG: P=0.167). Our findings suggest that miR-146a rs2910164 C/G polymorphism is not correlated with the susceptibility of CRC. In the future, more case–control studies are needed to confirm our results.

MicroRNA-3191 promotes migration and invasion by downregulating TGFBR2 in colorectal cancer

Mutations in transforming growth factor beta receptor II (TGFBR2) are detected in up to 30% of overall colorectal cancer (CRC). Dysregulation of some microRNAs participated in the CRC pathogenesis. In this study, we used the gene ontology analyses, the Kyoto Encyclopedia of Genes and Genomes pathway analyses and gene set enrichment analysis to indicate that miR-3191 was involved in the regulation of transforming growth factor beta (TGF-BETA) signal pathway in CRC. These bioinformatics results were supported by data obtained from CRC samples and experiments in vitro. The luciferase reporter assay was used to confirm that miR-3191 modulates TGF-BETA signal pathway by targeting TGFBR2. By transwell migration and invasion assays, we showed that miR-3191 promoted CRC cell migration and invasion by downregulating TGFBR2. And it may serve as a novel therapeutic strategy for treating CRC patients.

Polymorphisms in non-coding RNAs and risk of colorectal cancer: A systematic review and meta-analysis

Colorectal cancer (CRC) has been regarded as a common cancer due to its prevailing incidence in both males and females. Recently, non-coding RNAs used as biomarkers for screening, diagnosis and prognosis of different cancers have been under the focus of attention. As a result of this, the aim of this study was to systematically review articles that investigated the SNPs in genes related to microRNAs and long non-coding RNAs to assess the genetic susceptibility of colorectal cancer risk. The outcome is presented as the results of a meta-analysis. We systematically searched PubMed, Web of Science, and Scopus to identify relevant studies published up to 20/5/2017. These included eligible studies consisting of 23,581 patients and 22,697 controls. The conferred risk was estimated and presented using odds ratios (ORs) and 95% confidence intervals (CI). The Hardy-Weinberg equilibrium (HWE) was assessed by the goodness-of-fit chi-square test in all studies. The power of each study was also calculated based on the available results. Out of 27 different microRNAs which had published results, although most of the studies were under powered, miR-146a and miR-196a were amongst the most studied microRNAs. For five miRNAs (miR-196a, miR-146a, miR-27a, miR-499 and miR-149) which we performed a meta-analysis, miR-27a and miR-149 gene polymorphisms were associated with susceptibility to CRC. Other miRNAs did not show any effect on the CRC risk. Overall, significant association between miR-149 rs2292832 and susceptibility to cancer was identified in a recessive genetic model, TT/ (TC + CC) (OR = 1.19, 95% CI = 1.02-1.39, P = 0.02). On the other hand, rs895819 (miR-27a) GG carriers were more susceptible to CRC (OR = 1.47, 95% CI = 1.21-1.78, P = <0.05) in a recessive genetic model. Analysis of the data based on race revealed that rs2910164 (miR-146a) polymorphism may decrease the risk of CRC among Europeans, in a co dominant model [OR = 0.81, 95% CI 0.66-0.99, p = 0.04], but not among Asians. In conclusion, certain miRNAs (miR-27a and miR-149) may affect the CRC risk and can be regarded as genetic markers amongst different populations. LncRNAs still have to be studied more to reach a conclusion for their association with CRC risk.