CaM kinase signaling induces cardiac hypertrophy and activates the MEF2 transcription factor in vivo
Robert Passier, … , Stephen R. Grant, Eric N. Olson
Robert Passier, … , Stephen R. Grant, Eric N. Olson
Published May 15, 2000
Citation Information: J Clin Invest. 2000;105(10):1395-1406. https://doi.org/10.1172/JCI8551.
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Article

CaM kinase signaling induces cardiac hypertrophy and activates the MEF2 transcription factor in vivo

Abstract

Hypertrophic growth is an adaptive response of the heart to diverse pathological stimuli and is characterized by cardiomyocyte enlargement, sarcomere assembly, and activation of a fetal program of cardiac gene expression. A variety of Ca2+-dependent signal transduction pathways have been implicated in cardiac hypertrophy, but whether these pathways are independent or interdependent and whether there is specificity among them are unclear. Previously, we showed that activation of the Ca2+/calmodulin-dependent protein phosphatase calcineurin or its target transcription factor NFAT3 was sufficient to evoke myocardial hypertrophy in vivo. Here, we show that activated Ca2+/calmodulin-dependent protein kinases-I and -IV (CaMKI and CaMKIV) also induce hypertrophic responses in cardiomyocytes in vitro and that CaMKIV overexpressing mice develop cardiac hypertrophy with increased left ventricular end-diastolic diameter and decreased fractional shortening. Crossing this transgenic line with mice expressing a constitutively activated form of NFAT3 revealed synergy between these signaling pathways. We further show that CaMKIV activates the transcription factor MEF2 through a posttranslational mechanism in the hypertrophic heart in vivo. Activated calcineurin is a less efficient activator of MEF2-dependent transcription, suggesting that the calcineurin/NFAT and CaMK/MEF2 pathways act in parallel. These findings identify MEF2 as a downstream target for CaMK signaling in the hypertrophic heart and suggest that the CaMK and calcineurin pathways preferentially target different transcription factors to induce cardiac hypertrophy.

Authors

Robert Passier, Hong Zeng, Norbert Frey, Francisco J. Naya, Rebekka L. Nicol, Timothy A. McKinsey, Paul Overbeek, James A. Richardson, Stephen R. Grant, Eric N. Olson

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CaM kinase-dependent activation of MEF2 in vivo. (a) Induction of MEF2 a...
CaM kinase-dependent activation of MEF2 in vivo. (a) Induction of MEF2 activity by CaMKIV in the intact heart. MEF2 indicator mice were bred with mice harboring an αMHC-CaMKIV or αMHC-calcineurin (CN) transgenes, as described in the text. Littermates positive for the lacZ transgene and lacking (left) or containing the CaMKIV or calcineurin transgene were sacrificed at 8 weeks of age, and hearts were stained for lacZ expression. LacZ expression was not detected above background levels in control hearts, whereas lacZ expression was detected throughout the CaMKIV transgenic heart. In αMHC-calcineurin transgenics, lacZ staining was observed sporadically in subsets of hypertrophic cardiomyocytes. This was revealed more clearly in histological cross section (lower panels). (b) β-Galactosidase assays were performed on cardiac extracts from wild-type, αMHC-CaMKIV, and αMHC-calcineurin transgenic mice harboring the MEF2-lacZ transgene, as described in Methods. (c) Extracts were prepared from hearts of wild-type, αMHC-CaMKIV, and αMHC-calcineurin transgenic littermates and used for gel mobility shift assays with a 32P-labeled MEF2 site as probe. Anti-MEF2A antibody was added to assays as indicated. Comparable amounts of MEF2 DNA binding activity were detected in both extracts, and all activity was supershifted with anti-MEF2A antibody. Nonimmune serum had no effect on the MEF2-DNA protein complex (data not shown). Only the region of the gel containing the shifted probe is shown.