MiR-137 Targets the 3′ Untranslated Region of MSH2: Potential Implications in Lynch Syndrome-Related Colorectal Cancer

SIMPLE SUMMARY: In a previous study, we identified a patient carrying the variant c.*226A>G in the MSH2 3′ untranslated region that showed overexpression of MSH2 protein. In this study, we hypothesized that the MSH2 3′UTR contained a seed region for miR-137, indicating MSH2 was indeed targeted by miR-137. Our in vitro studies showed an inverse correlation between miR-137 and MSH2; this functional interaction was also confirmed in normal and tumoral tissue samples from the patient carrying the c.*226A>G variant in the MSH2 3′UTR. ABSTRACT: Mismatch Repair (MMR) gene dysregulation plays a fundamental role in Lynch Syndrome (LS) pathogenesis, a form of hereditary colorectal cancer. Loss or overexpression of key MMR genes leads to genome instability and tumorigenesis; however, the mechanisms controlling MMR gene expression are unknown. One such gene, MSH2, exerts an important role, not only in MMR, but also in cell proliferation, apoptosis, and cell cycle control. In this study, we explored the functions and underlying molecular mechanisms of increased MSH2 expression related to a c.*226A>G variant in the 3′untranslated (UTR) region of MSH2 that had been previously identified in a subject clinically suspected of LS. Bioinformatics identified a putative binding site for miR-137 in this region. To verify miRNA targeting specificity, we performed luciferase gene reporter assays using a MSH2 3′UTR psiCHECK-2 vector in human SW480 cells over-expressing miR-137, which showed a drastic reduction in luciferase activity (p > 0.0001). This effect was abolished by site-directed mutagenesis of the putative miR-137 seed site. Moreover, in these cells we observed that miR-137 levels were inversely correlated with MSH2 expression levels. These results were confirmed by results in normal and tumoral tissues from the patient carrying the 3′UTR c.*226A>G variant in MSH2. Finally, miR-137 overexpression in SW480 cells significantly suppressed cell proliferation in a time- and dose-dependent manner (p < 0.0001), supporting a role for MSH2 in apoptosis and cell proliferation processes. Our findings suggest miR-137 helps control MSH2 expression via its 3′UTR and that dysregulation of this mechanism appears to promote tumorigenesis in colon cells.