Background Enhanced sarcoplasmic reticulum (SR) Ca2+-leak via ryanodine receptor type-2 (RyR2) contributes to the pathogenesis of atrial fibrillation (AF). Recent studies have shown that the level of RyR2 protein is elevated in atria of paroxysmal AF (pAF) patients, suggesting that microRNA-mediated post-transcriptional regulation of RyR2 might be an underlying mechanism. Bioinformatic analysis suggests that miR-106b and miR-93, members of the miR-106b-25 cluster, could bind to RYR2-3′UTR and suppress its translation. Thus, we tested the hypothesis that loss of the miR-106b-25 cluster promotes AF via enhanced RyR2-mediated SR Ca2+-leak. Methods and Results Quantitative real-time PCR showed that the levels of mature miR-106b, miR-93 and miR-25 were lower in atria of pAF patients compared with patients with sinus rhythm. In vitro assay showed that miR-93 reduced RYR2-3′UTR luciferase activity. Total RyR2 protein in atrial tissue of miR-106b-25−/− mice was increased by 42% compared to wild-type (WT) littermates, but still maintained a normal subcellular distribution. Ca2+-spark frequency and total SR Ca2+-leak were increased in atrial myocytes of miR-106b-25−/− mice. Telemetry ECG recordings revealed that miR-106b-25−/− mice exhibited more frequent atrial ectopy and were also more susceptible to pacing-induced AF than WT littermates. Increased SR Ca2+-release and AF susceptibility in miR-106b-25−/− mice were abolished by the RyR2-blocker K201. Conclusions These results suggest that miR-106b-25 cluster mediated post-transcriptional regulation of RyR2 is a potential molecular mechanism involved in pAF pathogenesis. As such, the miR-106b-25 cluster could be a novel gene-therapy target in AF associated with enhanced RyR2 expression.

The importance of translational regulation in tumour biology is increasingly appreciated. Here, we leverage polyribosomal profiling to prospectively define translational regulatory programs underlying epithelial-to-mesenchymal transition (EMT) in breast epithelial cells. We identify a group of ten translationally regulated drivers of EMT sharing a common GU-rich cis-element within the 3′-untranslated region (3′-UTR) of their mRNA. These cis-elements, necessary for the regulatory activity imparted by these 3′-UTRs, are directly bound by the CELF1 protein, which itself is regulated post-translationally during the EMT program. CELF1 is necessary and sufficient for both mesenchymal transition and metastatic colonization, and CELF1 protein, but not mRNA, is significantly overexpressed in human breast cancer tissues. Our data present an 11-component genetic pathway, invisible to transcriptional profiling approaches, in which the CELF1 protein functions as a central node controlling translational activation of genes driving EMT and ultimately tumour progression.

Scope The uptake of dietary plant small RNAs (sRNAs) in consumers remains controversial, which is mainly due to low dietary content in combination with poor fractional absorption. MIR2911, among all the plant sRNAs including microRNAs, has been shown to be one of the most robustly absorbed sRNAs. Here we analyze the unusual abundance and unique genesis of MIR2911 during vegetable processing. Methods and Results Using qRT-PCR, the abundance of MIR2911 increased dramatically in macerated tissues while other microRNAs degraded. The accumulation of MIR2911 correlated with the degradation of the rRNAs, consistent with MIR2911 being derived from the 26S rRNA. Bioinformatic analysis predicts a microRNA-like precursor structure for MIR2911; however, no reciprocal increase in the putative star-strand was noted, and using an Arabidopsis mutation deficient in miRNA processing the accumulation of MIR2911 appeared Dicer independent. MIR2911 was incorporated into the mammalian RNA-induced silencing complex as demonstrated in HEK293T cells, where transfected synthetic MIR2911 modestly suppressed the activity of a cognate luciferase reporter. Conclusion The genesis and increase of MIR2911 post-harvest is atypical, as traditional plant bioactives are less plentiful as vegetables lose freshness. These findings explain the disparity in sera detection between MIR2911 and canonical plant-based miRNAs.

Myoblasts are mononucleated precursors of myofibers; they persist in mature skeletal muscles for growth and regeneration post injury. During myotonic dystrophy type 1 (DM1), a complex autosomal-dominant neuromuscular disease, the differentiation of skeletal myoblasts into functional myotubes is impaired, resulting in muscle wasting and weakness. The mechanisms leading to this altered differentiation are not fully understood. Here, we demonstrate that the calcium- and voltage-dependent potassium channel, KCa1.1 (BK, Slo1, KCNMA1), regulates myoblast proliferation, migration, and fusion. We also show a loss of plasma membrane expression of the pore-forming α subunit of KCa1.1 in DM1 myoblasts. Inhibiting the function of KCa1.1 in healthy myoblasts induced an increase in cytosolic calcium levels and altered nuclear factor kappa B (NFκB) levels without affecting cell survival. In these normal cells, KCa1.1 block resulted in enhanced proliferation and decreased matrix metalloproteinase secretion, migration, and myotube fusion, phenotypes all observed in DM1 myoblasts and associated with disease pathogenesis. In contrast, introducing functional KCa1.1 α-subunits into DM1 myoblasts normalized their proliferation and rescued expression of the late myogenic marker Mef2. Our results identify KCa1.1 channels as crucial regulators of skeletal myogenesis and suggest these channels as novel therapeutic targets in DM1.