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(Circulation Research. 2004;95:867.)
© 2004 American Heart Association, Inc.

Reviews

Cyclin-Dependent Kinase-9

An RNAPII Kinase at the Nexus of Cardiac Growth and Death Cascades

Motoaki Sano, Michael D. Schneider

From the Center for Cardiovascular Development (M.S., M.D.S.), Departments of Medicine (M.S., M.D.S.), Molecular and Cellular Biology (M.D.S.), and Molecular Physiology and Biophysics (M.D.S.), Baylor College of Medicine, Houston, Tex.

Correspondence to Dr Michael D. Schneider, Center for Cardiovascular Development, Baylor College of Medicine, One Baylor Plaza, Rm 506D, Houston, TX 77030. E-mail michaels{at}bcm.tmc.edu

This Review is part of a thematic series on Gene Expression in Hypertrophy and Stress, which includes the following articles:

Gene Expression in Fibroblasts and Fibrosis: Involvement in Cardiac Hypertrophy

Roles of Cardiac Transcription Factors in Cardiac Hypertrophy

Ras, Akt, and Mechanotransduction in the Cardiac Myocyte

Cyclin-Dependent Kinase-9: An RNAPII Kinase at the Nexus of Cardiac Growth and Death Cascades
Ryozo Nagai Guest Editor

Over the past decade and a half, the paradigm has emerged of cardiac hypertrophy and ensuing heart failure as fundamentally a problem in signal transduction, impinging on the altered expression or function of gene-specific transcription factors and their partners, which then execute the hypertrophic phenotype. Strikingly, RNA polymerase II (RNAPII) is itself a substrate for two protein kinases—the cyclin-dependent kinases Cdk7 and Cdk9—that are activated by hypertrophic cues. Phosphorylation of RNAPII in the carboxyl terminal domain (CTD) of its largest subunit controls a number of critical steps subsequent to transcription initiation, among them enabling RNAPII to overcome its stalling in the promoter-proximal region and to engage in efficient transcription elongation. Here, we summarize our current understanding of the RNAPII-directed protein kinases in cardiac hypertrophy. Cdk9 activation is essential in tissue culture for myocyte enlargement and sufficient in transgenic mice for hypertrophy to occur and yet is unrelated to the "fetal" gene program that is typical of pathophysiological heart growth. Although this trophic effect of Cdk9 appears benign superficially, pathophysiological levels of Cdk9 activity render myocardium remarkably susceptible to apoptotic stress. Cdk9 interacts adversely with Gq-dependent pathways for hypertrophy, impairing the expression of numerous genes for mitochondrial proteins, and, in particular, suppressing master regulators of mitochondrial biogenesis and function, perioxisome proliferator-activated receptor- coactivator-1 (PGC-1), and nuclear respiratory factor-1 (NRF-1). Given the dual transcriptional roles of Cdk9 in hypertrophic growth and mitochondrial dysfunction, we suggest the potential usefulness of Cdk9 as a target in heart failure drug discovery.

Key Words: apoptosis • cyclin-dependent kinases • hypertrophy • mitochondria • perioxisome proliferator-activated receptor- coactivator-1

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