J Mol Cell Cardiol 32, 1447–1457 (2000) doi:10.1006/jmcc.2000.1185, available online at http://www.idealibrary.com on Phosphorylation of Elk-1 by MEK/ERK Pathway is Necessary for c-fos Gene Activation During Cardiac Myocyte Hypertrophy Gopal J. Babu 1 , M. Jane Lalli 1 , Mark A. Sussman 2 , Jun-ichi Sadoshima 3 and Muthu Periasamy 1 * 1 Laboratory of Molecular Cardiology, Division of Cardiology, Department of Internal Medicine, University of Cincinnati College of Medicine, 2 Division of Molecular Cardiovascular Biology, Children’s Hospital Medical Center, Cincinnati, OH 45267, 3 Weis Center for Research, Pennsylvania State University College of Medicine, Danville, Pennsylvania 17822-2601, USA (Received 31 March 2000, accepted in revised form 28 April 2000) G. J. B, M. J. L, M. A. S, J.-.S  M. P . Phosphorylation of Elk-1 by MEK/ ERK Pathway is Necessary for c-fos Gene Activation During Cardiac Myocyte Hypertrophy. Journal of Molecular and Cellular Cardiology (2000) 32, 1447–1457. Cardiac hypertrophy is associated with specific alterations in myocardial gene expression; however, the exact mechanisms responsible for altered gene expression are poorly defined. The goal of this study was to investigate whether signaling kinases that are activated during cardiac hypertrophy directly modulate transcription factor activity and regulate gene expression. In an effort to understand this process, we focused our studies on the transcriptional activation of c-fos gene through the serum response element (SRE)/ternary complex factor (TCF) element, during phenylephrine-induced myocyte hypertrophy. In this study, we show that phosphorylated Elk-1, a TCF, binds to c-fos SRE and its binding to SRE is increased upon phenylephrine stimulation. Phenylephrine treatment activates phosphorylation of Elk-1 in the nucleus within five minutes and Elk-1-dependent transcriptional activation is abolished by inhibitors selective for MEK/ ERK kinases. These studies implicate that phosphorylation of Elk-1 by ERK kinase pathway is important for early gene activation during phenylephrine-induced myocyte hypertrophy.  2000 Academic Press K W: Cardiac hypertrophy; c-fos; Elk-1; MEK; ERK; Phenylephrine; SRE. myosin, skeletal -actin and heat-shock pro- Introduction teins]. 1,2 During the past decade, significant progress has been made in identifying key intracellular sig- Myocardial hypertrophy is characterized by an in- crease in the mass and volume of individual myo- naling mechanisms that contribute to hypertrophic growth. These include protein kinase C, extra- cytes, resulting in an overall increase in heart weight and alterations in systolic and diastolic func- cellular signal-regulated protein kinase (ERK), c- jun N-terminal kinases (JNK) and p38 mitogen- tion. At the molecular level, cardiac hypertrophy is associated with specific alterations in gene ex- activated protein kinase pathways, and Ca 2+ /CaM- dependent calcineurin pathway. 3,4 Activation of one pression that includes activation of immediate early genes (c-myc, c-fos, c-jun and junB), fetal cardiac or more of these kinase pathways was shown to induce cardiac-specific gene promoters such as ANF, genes [atrial natruretic factor (ANF), SR Ca 2+ ATP- ase, -myosin heavy chain (-MHC), -tropo- -MHC, skeletal -actin, and myosin light chain 2 * Please address all correspondence to: Muthu Periasamy. E-mail: muthu.periasamy@uc.edu 0022–2828/00/081447+11 $35.00/0  2000 Academic Press