A Role for the p 38 Mitogen-activated Protein Kinase Pathway in Myocardial Cell Growth , Sarcomeric Organization , and Cardiac-specific Gene Expression

Three hallmark features of the cardiac hypertrophic growth program are increases in cell size, sarcomeric organization, and the induction of certain cardiac-specific genes. All three features of hypertrophy are induced in cultured myocardial cells by a 1 adrenergic receptor agonists, such as phenylephrine (PE) and other growth factors that activate mitogenactivated protein kinases (MAPKs). In this study the MAPK family members extracellular signal–regulated kinase (ERK), c-jun NH 2 -terminal kinase (JNK), and p38 were activated by transfecting cultured cardiac myocytes with constructs encoding the appropriate kinases possessing gain-of-function mutations. Transfected cells were then analyzed for changes in cell size, sarcomeric organization, and induction of the genes for the Aand B-type natriuretic peptides (NPs), as well as the a -skeletal actin ( a -SkA) gene. While activation of JNK and/or ERK with MEKK1 COOH or Raf-1 BXB, respectively, augmented cell size and effected relatively modest increases in NP and a -SkA promoter activities, neither upstream kinase conferred sarcomeric organization. However, transfection with MKK6 (Glu), which specifically activated p38, augmented cell size, induced NP and a -Ska promoter activities by up to 130-fold, and elicited sarcomeric organization in a manner similar to PE. Moreover, all three growth features induced by MKK6 (Glu) or PE were blocked with the p38-specific inhibitor, SB 203580. These results demonstrate novel and potentially central roles for MKK6 and p38 in the regulation of myocardial cell hypertrophy. Address all correspondence to Christopher C. Glembotski, Department of Biology, San Diego State University, San Diego, CA 92182. Tel. : (619) 594-2959. Fax: (619) 594-6200. e-mail: cglembotski@sunstroke.sdsu. edu 1. Abbreviations used in this paper : a -SkA, a -skeletal actin; ANP and BNP, Aand B-type cardiac natriuretic peptides; ATF, activating transcription factor; CMV, cytomegalovirus; ERK, extracellular signal–regulated kinase; HA, hemagglutinin; hsp, heat-shock protein; JNK, NH 2 -terminal kinase; MAPK, mitogen-activated protein kinase; MAPKAP, MAPK-activated protein kinase; PE, phenylephrine. C ardiac myocytes, which are postmitotic, increase in size during postnatal development through a well-studied hypertrophic growth program. Myocardial cell hypertrophic growth is characterized by a number of phenotypic changes, including the activation of several immediate early genes (e.g., c-fos, c-jun, and egr-1), increased expression of genes encoding certain sarcomeric proteins (e.g., a -skeletal actin, b -myosin heavy chain, and myosin light chain-2), and the induction of the genes for the Aand B-type cardiac natriuretic peptides (ANP and BNP) 1 (Schneider et al., 1992; Van Bilsen and Chien, 1993; Lembo et al., 1995). Although myocardial mass in the fully developed adult does not generally undergo significant increases in size, in some pathological conditions, such as overload-induced hypertrophy, adult cardiac myocytes do reenter a hypertrophic growth program very similar to that observed in the developing neonatal heart (Schneider et al., 1992; Van Bilsen and Chien, 1993; Lembo et al., 1995; Van Heugten et al., 1995; Yamazaki et al., 1995). Cultured neonatal rat ventricular cardiac myocytes have served as a model system for studies aimed at gaining a better understanding of this interesting mechanism of cell growth. Primary myocardial cells respond to a variety of stimuli by undergoing a hypertrophic growth program virtually identical to that observed in the developing neonate and the pathologic adult myocardium (Van Bilsen and Chien, 1993). For example, cultured myocardial cells treated with the a 1 -adrenergic receptor agonist, phenylephrine (PE), various other growth factors, or mechanical loading or electrical pacing of contractions display marked increases in size, enhanced sarcomeric organization, and induction of the cardiac genes associated with the hypertrophic growth program (Simpson, 1983; Komuro et al., 1990; McDonough and Glembotski, 1992; LaMorte et al., 1994; Sadoshima et al., 1995; Bogoyevitch et al., 1995 b ; Karns et al., 1995; Sprenkle et al., 1995; LaPointe et al., 1996; Thuerauf and Glembotski, 1997). The convergence on A uust 5, 2017 jcb.rress. org D ow nladed fom