Abstract 15253: Microrna 26b Family Encoded by the Introns of Small CTD Phosphatases (SCPs) 1 to 3 Suppresses Phenylephrine-Induced Cardiomyocyte Hypertrophy by Targeting TRPC3/6 and GATA4
Tissue-specific gene expression pattern plays an important role in metazoan biology and represents fundamental aspects of many complex diseases including heart failure. Neuronal gene transcription is repressed in non-neuronal cells by the repressor element 1 (RE-1)-silencing transcription factor/neuron-restrictive silencer factor (REST/NRSF) complex. Expression of a family of class-C RNA polymerase II (RNAPII) carboxyl-terminal domain (CTD) phosphatases [small CTD phosphatases (SCPs) 1 to 3] is restricted to non-neuronal tissues. SCPs 1 to 3 are recruited by REST/NRSF to neuronal genes that contain RE-1 elements, leading to neuronal gene silencing in non-neuronal cells. SCPs are highly expressed in the heart and contain microRNA (miR)-26b, 26a-2, and 26a-1 in their introns, implying their important functions in cardiomyocytes. Therefore, we have investigated roles of these miRs in rat neonatal cardiomyocytes in culture. Overexpression of miR-26b by lentivirus suppressed the mRNA expressions of ANF and βMHC and reduced cell surface area in cardiomyocytes. Through the bioinformatics approach, we identified as potential targets of miR-26 family several important molecules involved in hypertrophic responses. These include a zinc finger transcription factor GATA4 and canonical transient receptor potential channel (TRPC) 3 and TRPC6, mediators of Ca2+-dependent signal transduction activated by stretch or membrane-bound receptors. We confirmed that miR-26 family targets the 3'UTR of these genes by luciferase assay. Overexpression of miR-26b in cardiomyocytes reduced the expressions of TRPC3/6 and GATA4. Conversely, silencing of endogenous miR-26b family by transduction of ‘decoy’ gene, which has 6-tandem repeats of antisense sequence of miR-26b downstream of luciferase gene, enhanced the expressions of TRPC3/6 and GATA4. Moreover, transduction of miR-26b into cardiomocytes reduced phosphorylation of Akt and ERK after stimulation with phenylephrine. Thus, SCPs 1 to 3 not only repress neuron-specific genes but also inhibit hypertrophic responses thorough their intronic miR-26b, 26a-2, and 26a-1 in cardiomyocytes. The results also suggest that this inhibition is mediated, at least in part, by targeting TRPC3/6 and GATA4.
- © 2010 by American Heart Association, Inc.