A Role for the p38 Mitogen-activated Protein Kinase Pathway in Myocardial Cell Growth, Sarcomeric Organization, and Cardiac-specific Gene Expression

Abstract

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 α1- 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 α-skeletal actin (α-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 α-SkA promoter activities, neither upstream kinase conferred sarcomeric organization. However, transfection with MKK6 (Glu), which specifically activated p38, augmented cell size, induced NP and α-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.

Specific role of the extracellular signal-regulated kinase pathway in angiotensin II-induced cardiac hypertrophy in vitro

“…Phenylephrine seems to use signalling pathway(s) insensitive to PD98059 for ANF expression, although a minor contribution of ERK cannot be excluded. MEKK1-mediated cell signals and SB203580-sensitive pathways (presumably p38 and some JNK isoforms [46]) are potential candidates, as demonstrated in previous studies [25,31] as well as this study, although the SB203580-sensitive pathway has only a minor role, if any, in phenylephrine-induced endogenous ANF expression ( Figure 2B and Table 1). Although MEKK1 is able to activate both the JNK and ERK pathways, the JNK pathway might be more important for phenylephrine-induced ANF-Luc activation because inhibition of the ERK pathway by PD98059 or dominant-negative MEK1 did not show a significant effect on phenylephrineinduced ANF-Luc activation.…”

“…As shown in Figure 4(A), SB203580 (20 µM) significantly inhibited phenylephrineinduced ANF-Luc activation (4.8p1.0-fold, 65 % decrease ; P 0.05 compared with phenylephrine alone, n l 6), confirming previous observations [25]. In contrast, SB203580 failed to inhibit ANF-Luc activity significantly, both before (0.73p0.23, n l 6) and after (1.62p0.19, n l 6) stimulation with Ang II.…”

“…Although Ang II and phenylephrine activate ERKs with comparable magnitudes (Figure 1A), the activation of JNK and p38 by phenylephrine is more strong and sustained than that by Ang II (Figures 1B and 1C). Both our observation ( Figure 3B) and those by others suggest that activation of each member of the MAP kinases is sufficient, if not equally potent, to stimulate ANF transcription [19,25,30]. Thus the relative contribution of each MAP kinase on ANF expression might depend on the parallel activation of other members of the MAP kinases.…”

“…Although the role of ERKs in phenylephrineinduced cardiac hypertrophy has been studied by several investigators with different methods, reported roles of ERKs in cardiac hypertrophy vary substantially [19][20][21][22][23]. Furthermore, recent evidence indicates that agonists for the G q -coupled receptor activate not only ERKs but also other members of the MAP kinase family, namely JNK and p38 [17,[24][25][26][27][28], and that these MAP kinases are also important in cardiac hypertrophy [25,26,[29][30][31][32] (reviewed in [5]). However, it should be noted that relative levels of activation of each MAP kinase can differ depending on the type of stimulus ; therefore the role of ERKs in cardiac hypertrophy must be determined for each hypertrophic stimulus.…”

Signaling by dual specificity kinases

“…Cardiac hypertrophic growth can be characterized by three distinct features such as (1) increases in cell size; (2) sarcomeric organization; and (3) induction of cardiac-speci®c genes (for natriuretic Dual Specificity Kinases N Dhanasekaran and EP Reddy peptides A and B; alpha-skeletal actin). Coexpression of activated MKK6 along with p38MAPK in cultured myocardial cells resulted in inducing all the three characteristic features of cardiac hypertrophic growth suggesting a central role for MKK6-p38MAPK in myocardial cell hypertrophy (Zechner et al, 1997).…”