BACKGROUND-MicroRNAs (miRNAs/miRs) are small conserved RNA molecules of 22 nucleotides that negatively modulate gene expression primarily through base paring to the 3′ untranslated region of target messenger RNAs. The muscle-specific miR-1 has been implicated in cardiac hypertrophy, heart development, cardiac stem cell differentiation, and arrhythmias through targeting of regulatory proteins. In this study, we investigated the molecular mechanisms through which miR-1 intervenes in regulation of muscle cell growth and differentiation. METHODS AND RESULTS-On the basis of bioinformatics tools, biochemical assays, and in vivo models, we demonstrate that (1) insulin-like growth factor-1 (IGF-1) and IGF-1 receptor are targets of miR-1; (2) miR-1 and IGF-1 protein levels are correlated inversely in models of cardiac hypertrophy and failure as well as in the C2C12 skeletal muscle cell model of differentiation; (3) the activation state of the IGF-1 signal transduction cascade reciprocally regulates miR-1 expression through the Foxo3a transcription factor; and (4) miR-1 expression correlates inversely with cardiac mass and thickness in myocardial biopsies of acromegalic patients, in which IGF-1 is overproduced after aberrant synthesis of growth hormone. CONCLUSIONS-Our results reveal a critical role of miR-1 in mediating the effects of the IGF-1 pathway and demonstrate a feedback loop between miR-1 expression and the IGF-1 signal transduction cascade. © 2009 American Heart Association, Inc.
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