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Abstract: gp130-dependent signaling is known to play a critical role in the onset of heart failure. In that regard, cardiotrophin-1 (CT-1) activates several signaling pathways via gp130, and induces hypertrophy in neonatal rat cardiomyocytes. Among the mediators activated by CT-1, STAT3 is thought to be important for induction of cell hypertrophy, though its precise function in the CT-1 signaling pathway is not fully understood. In the present study, therefore, to better understand the significance of STAT3 activity in CT-1 signaling, we infected cultured cardiomyocytes with adenoviral vectors harboring a dominant-negative STAT3 mutant or one of two endogenous negative regulators of cytokine signaling via the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathways [suppressor of cytokine signaling (SOCS) 1 and 3] and then examined their effects on three indexes of CT-1-induced cell hypertrophy: protein synthesis, secretion of brain natriuretic peptide and changes in cell surface area. In control cells, CT-1-induced both STAT3 phosphorylation and cell hypertrophy. Overexpression of dominant-negative STAT3 mutant suppressed CT-1-induced STAT3 phosphorylation, but did not affect cell hypertrophy. On the other hand overexpression of SOCS1 or SOCS3 inhibited both CT-1-induced STAT3 phosphorylation and cell hypertrophy. CT-1 also induced phosphorylations of ERK1/2 and ERK5 in cardiomyocytes, and those, too, were suppressed by overexpression of SOCSs. CT-1-induced cell hypertrophy was suppressed by overexpression of a dominant-negative MEK5 mutant, and not by overexpression of a dominant-negative MEK1 mutant. These findings indicate that the major pathway responsible for the hypertrophic responses to CT-1 is not JAK-STAT3 pathway nor MEK1-ERK1/2 pathway, but MEK5-ERK5 pathway. [Copyright &y& Elsevier]

Abstract: We recently reported that a transcriptional repressor, neuron-restrictive silencer factor (NRSF), represses expression of fetal cardiac genes, including atrial and brain natriuretic peptide (ANP and BNP), by recruiting class I histone deacetylase (HDAC) and that attenuation of NRSF-mediated repression contributes to the reactivation of fetal gene expression during cardiac hypertrophy. The molecular mechanism by which the activity of the NRSF–HDAC complex is inhibited in cardiac hypertrophy remains unresolved, however. In the present study, we show that class II HDACs (HDAC4 and 5), which are Ca/calmodulin-dependent kinase (CaMK)-responsive repressors of hypertrophic signaling, associate with NRSF and participate in NRSF-mediated repression. Blockade of the CaMK-class II HDAC signaling pathway using a CaMK-resistant HDAC5 mutant, a CaMK inhibitor (KN62) or a dominant-negative CaMK mutant inhibited ET-1-inducible ANP and BNP promoter activity, but that inhibitory effect was abolished by mutation of the neuron-restrictive silencer element (NRSE) within the ANP and BNP promoter. In addition, adenovirus-mediated expression of a dominant-negative NRSF mutant abolished the inhibitory effect of KN62 on ET-1-inducible endogenous ANP gene expression in ventricular myocytes. Finally, the interaction between NRSF and class II HDACs was decreased in both in vitro and in vivo models of cardiac hypertrophy. These findings show that ET-1-induced CaMK signaling disrupts class II HDAC–NRSF repressor complexes, thereby enabling activation of ANP and BNP gene transcription in ventricular myocytes, and shed light on a novel mechanism by which the fetal cardiac gene program is reactivated. [Copyright &y& Elsevier]