A cultured myocardial cell model was used to examine the role ofprotein kinase C-dependent pathways in the transcriptional activation of two cardiac muscle genes [myosin light chain 2 (MLC-2) and atrial natriuretic factor (ANF)] during a-adrenergic receptor-mediated hypertrophy. Phorbol ester (phorbol 12-myristate 13-acetate) and the a-adrenergic agonist phenylephrine both activate protein kinase C (PKC) and induce 4-to 5-fold increases in the expression of MLC-2 and ANF promoter/luciferase reporter genes with little effect on Rous sarcoma virus/luciferase or minimal prolactin promoter/luciferase genes. To further assess the role of PKC in cardiac gene regulation, PKC expression vectors encoding constitutively activated PKC-a or PKC-fi, or a catalytically inactive PKC, were transiently cotransfected with the cardiac promoter/luciferase constructs. Cotransfection of either activated PKC-a or PKC-fi cDNA induces the expression of MLC-2 and ANF promoter/luciferase genes and of a reporter gene responsive to the transcription factor AP-1. The Rous sarcoma virus/luciferase and minimal prolactin promoter/ luciferase genes are not concomitantly induced by cotransfectin with the PKC genes, indicating specificity of the transcriptional effect. The finding that activated PKC increases cardiac gene transcription suggests that activation of this enzyme may be a proximal signal for coregulation of two cardiac genes, MLC-2 and ANF, during the course of myocardial cell hypertrophy.

A recombinant cDNA clone, pCRABP-

Positive hemodynamic effects of the antidiabetic agent rosiglitazone on perfused whole hearts have recently been described, but the mechanisms regulating these effects are not well understood. This study reports the effects of rosiglitazone on calcium regulation in isolated neonatal rat ventricular myocytes by measurement of Ca²⁺ transient decay rates and SERCA2 gene expression, and shows that rosiglitazone enhances known cardioprotective signaling pathways. Myocyte treatment with 10 μmol/L rosiglitazone accelerated Ca²⁺ transient decay rates by ñ30%, enhanced SERCA2 mRNA levels by ñ1.5-fold and SERCA2 production by ñ3-fold. Rosiglitazone treatment (1, 5, and 10 μmol/L) also led to a dose-dependent increase (ñ1.2-1.5-fold) in SERCA2 promoter activity. Comparable levels of cardiac SERCA overexpression have been associated with physiologically relevant and compensatory effects in vivo. These data link thiazolidinedione-induced improvement in cardiac myocyte function to an upregulation of SERCA2 gene expression. Since NF-κB-dependent pathways, including the upregulation of IL-6 secretion, were shown to protect neonatal rat ventricular myocytes from apoptosis upon TNFα stimulation, additional experiments were designed to determine whether rosiglitazone enhances TNFα-induced NF-κB-dependent transcription and IL-6 secretion. Because the endotoxin stress response in ventricular myocytes involves the upregulation of TNFα, and the activation of NF-κB, the effects of rosiglitazone on lipopolysaccharide-induced NF-κB-dependent transcription were also investigated. Treatment of neonatal rat ventricular myocytes with 10 μmol/L rosiglitazone enhanced TNF-α- and lipopolysaccharide-induced NF-κB-dependent transcription by ñ1.8- and ñ1.4-fold respectively, and TNF-α-induced IL-6 secretion by ñ1.5-fold. Rosiglitazone had no significant effects on basal levels of NF-κB-dependent transcription and IL-6 secretion. Thus, cardioprotective effects of rosiglitazone may be partly mediated by NF-κB.

No abstract