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Department of Biology and Molecular Biology Institute, San Diego State University, San Diego, California 92182
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
1- adrenergic receptor agonists, such as phenylephrine
(PE) and other growth factors that activate mitogen-
activated protein kinases (MAPKs). In this study the
MAPK family members extracellular signal-regulated kinase (ERK), c-jun NH2-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
A- and B-type natriuretic peptides (NPs), as well as the
-skeletal actin (
-SkA) gene. While activation of JNK
and/or ERK with MEKK1COOH or Raf-1 BXB, respectively, augmented cell size and effected relatively modest increases in NP and
-SkA promoter activities,
neither upstream kinase conferred sarcomeric organization. However, transfection with MKK6 (Glu), which
specifically activated p38, augmented cell size, induced
NP and
-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.
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