MiR-137 and miR-34a directly target Snail and inhibit EMT, invasion and sphere-forming ability of ovarian cancer cells

Abstract

BackgroundIn ovarian cancer (OC) cells, Snail was reported to induce the epithelial-to-mesenchymal transition (EMT), which is a critical step in OC metastasis. At present little is known about controlling Snail expression in OC cells by using specific microRNAs (miRNAs).MethodsWe first used a computational target prediction analysis to identify 6 candidate miRNAs that bind to the 3′-untranslated region (3′-UTR) region of the Snail mRNA. Among these miRNAs, two miRNAs (miR-137 and miR-34a) with a potential to regulate Snail were validated by quantitative real-time PCR, Western blot analysis, and Snail 3′-UTR reporter assays. We assessed the effects of miR-137 and miR-34a on EMT, invasion and sphere formation in OC cells. We also evaluated the expression of miR-137 and miR-34a in OC tissues and adjacent normal tissues and analyzed the relationship between their expression and patient survival.ResultsWe report that OC tissues possess significantly decreased levels of miR-137 and miR-34a and increased expression of Snail when compared to their adjacent normal tissues, and lower miR-137 and miR-34a expression correlates with worse patient survival. Using luciferase constructs containing the 3′-UTR region of Snail mRNA combined with miRNA overexpression and mutagenesis, we identified miR-137 and miR-34a as direct suppressors of Snail in OC cells. The introduction of miR-137 and miR-34a resulted in the suppression of Snail at both the transcript and protein levels, and effectively suppressed the EMT phenotype and sphere formation of OC cells. However, the inhibition of miR-137 and miR-34a with antisense oligonucleotides promoted EMT and OC cell invasion. Moreover, ectopic expression of Snail significantly reversed the inhibitory effects of miR-137 and miR-34a on OC cell invasion and sphere formation.ConclusionsThese findings suggest that both miR-137 and miR-34a act as Snail suppressors to negatively regulate EMT, invasive and sphere-forming properties of OC cells.

Epithelial-mesenchymal transition in cancer: Role of the IL-8/IL-8R axis

“…Induction of EMT is closely associated with distant metastasis and cell invasion in tumor progression, and indicates a poor prognosis. A number of studies have reported that multiple factors can affect EMT in cancer, including IL-6, IL-8, VEGF, TGFβ, SNAIL, MMP, TNFα and TWIST (30,110,111), which can enhance cell motility and promote tumor metastasis. EMT in cancer cells involves loss of cell-cell junctions and the acquisition of cell motility and invasion factors.…”

Interplay among SNAIL Transcription Factor, MicroRNAs, Long Non-Coding RNAs, and Circular RNAs in the Regulation of Tumor Growth and Metastasis

“…SNAIL-dependent EMT in cancer has also been demonstrated to be regulated by p53 and miR-34 axis. In the absence of wild-type p53 function, SNAIL-dependent EMT is activated in colon, breast, lung carcinoma cells [71], and ovarian cancer [72] as a consequence of a decrease in miR-34 levels. A conserved miR-34a/b/c seed-matching sequence was detected in the SNAIL 3 -UTR.…”

MicroRNAs in gynecological cancers: Small molecules with big implications

“…Wnt signaling is also targeted by miR-1207, a miRNA that promotes stemness in OC cells [171]. In another study on OC [172], miR-34a and miR-137 were observed to be important for stemness, as determined by their role in sphere formation and invasion. These suppressor miRNAs were down-regulated in OC, resulting in de-repression of their target Snail.…”

“…Snail promoted invasion and sphere formation by inducing EMT. Low levels of miR-34a and miR-137 correlated with poor survival of OC patients [172]. …”

“…EMT is also regulated by several other miRNAs, with implications on migration and invasion, in CC, EC and OC cells [172, 208–220]. miR-181a mediates TGF-β-mediated EMT in a smad7-dependent manner and its expression correlates with poor outcome and shorter time to recurrence in patients with epithelial OC [221].…”