Direct and Indirect Interactions between Calcineurin-NFAT and MEK1-Extracellular Signal-Regulated Kinase 1/2 Signaling Pathways Regulate Cardiac Gene Expression and Cellular Growth

Abstract

MEK1, a member of the mitogen-activated protein kinase (MAPK) cascade that directly activates extracellular signal-regulated kinase (ERK), induces cardiac hypertrophy in transgenic mice. Calcineurin is a calciumregulated protein phosphatase that also functions as a positive regulator of cardiac hypertrophic growth through a direct mechanism involving activation of nuclear factor of activated T-cell (NFAT) transcription factors. Here we determined that calcineurin-NFAT and MEK1-ERK1/2 signaling pathways are interdependent in cardiomyocytes, where they directly coregulate the hypertrophic growth response. For example, genetic deletion of the calcineurin A␤ gene reduced the hypertrophic response elicited by an activated MEK1 transgene in the heart, while inhibition of calcineurin or NFAT in cultured neonatal cardiomyocytes also blunted the hypertrophic response driven by activated MEK1. Conversely, targeted inhibition of MEK1-ERK1/2 signaling in cultured cardiomyocytes attenuated the hypertrophic growth response directed by activated calcineurin. However, targeted inhibition of MEK1-ERK1/2 signaling did not directly affect calcineurin-NFAT activation, nor was MEK1-ERK1/2 activation altered by targeted inhibition of calcineurin-NFAT. Mechanistically, we show that MEK1-ERK1/2 signaling augments NFAT transcriptional activity independent of calcineurin, independent of changes in NFAT nuclear localization, and independent of alterations in NFAT transactivation potential. In contrast, MEK1-ERK1/2 signaling enhances NFAT-dependent gene expression through an indirect mechanism involving induction of cardiac AP-1 activity, which functions as a necessary NFAT-interacting partner. As a second mechanism, MEK1-ERK1/2 and calcineurin-NFAT proteins form a complex in cardiac myocytes, resulting in direct phosphorylation of NFATc3 within its C terminus. MEK1-ERK1/2-mediated phosphorylation of NFATc3 directly augmented its DNA binding activity, while inhibition of MEK1-ERK1/2 signaling reduced NFATc3 DNA binding activity. Collectively, these results indicate that calcineurin-NFAT and MEK1-ERK1/2 pathways constitute a codependent signaling module in cardiomyocytes that coordinately regulates the growth response through two distinct mechanisms.The physiologic and pathological growth of the myocardium is typically initiated by membrane-bound receptors that promote intracellular signaling through multiple GTPase proteins, kinases, and phosphatases. One such regulator is the calciumcalmodulin-activated protein phosphatase calcineurin (PP2B) and its downstream transcriptional target, nuclear factor of activated T cells (NFAT). Calcineurin is a serine/threoninespecific phosphatase that is uniquely activated by sustained elevations in intracellular calcium (12,16,26). Calcineurin is comprised of a 59-to 63-kDa catalytic A (CnA) subunit and a 19-kDa calcium binding B (CnB) subunit. Three mammalian CnA catalytic genes (␣, ␤, ␥) and two CnB regulatory genes (B1, B2) have been identified in vertebrates. The CnA␣, A␤, and B1 gene products are ea...

Could modifications of signalling pathways activated after ICSI induce a potential risk of epigenetic defects?

“…For example, PADI4 is a Ca idependent peptidylarginine deiminase enzyme that can function to antagonize arginine methylation levels by demethylimination (Hagiwara et al, 2005). Histone deacetylase also interacts with Ca i /calcineurin -mediated signalling pathways during T cell activation and proliferation (Im and Rao, 2004) and cardiac gene expression (Sanna et al, 2005). Moreover, stimulation of the integrin pathway could lead to histone epigenetic modifications after fertilization.…”

Myocardium defects and ventricular hypoplasia in mice homozygous null for the Forkhead Box m1 transcription factor

“…4). Since NFATc3 protein regulates genes essential for cardiac hypertrophy and cardiomyocyte proliferation (Wilkins et al, 2002;Sanna et al, 2005), diminished NFATc3 levels may contribute to the proliferation defects seen in Foxm1 Ϫ/Ϫ cardiomyocytes. Interestingly, we observed normal cardiac expression of calmodulin, H11 kinase, serotonin 5-HT 2B receptor, and FoxO3a transcription factor (Fig.…”

Pleiotropic Phenotype of a Genomic Knock-In of an RGS-Insensitive G184S Gnai2 Allele

“…It could be related to either systemic alterations, such as increased sympathetic tone, or to enhanced intrinsic cardiac signaling through ERK (29,61) or Akt (14) activation, which can both cause cardiac hypertrophy. If this were due to intrinsic cardiac signaling, it would probably be mediated by the ␤␥ subunit, which is the primary signaling molecule to ERK and Akt, since the G␣ i subunit generally does not activate those pathways.…”