Induction of protein synthesis in cardiac fibroblasts by cardiotrophin-1: integration of multiple signaling pathways

OBJECTIVE: Cardiotrophin-1 (CT-1) is a member of the IL-6 family of cytokines and is expressed in various cardiovascular disease states. CT-1 induces cardiomyocyte hypertrophy, and protects myocytes from ischemia reperfusion injury. We sought to elucidate CT-1 signaling in cardiac fibroblasts with respect to initiation of protein synthesis. METHODS: Cardiac fibroblasts were isolated from the ventricles of 200-g Sprague-Dawley rats and stimulated with CT-1 at specified concentrations with or without inhibitors of cell signaling pathways. Activation of intracellular signaling pathways was determined by Western analysis and immunocytochemistry. Protein synthesis was measured by incorporation of [3H]leucine. RESULTS: CT-1 treatment resulted in activation of the Jak/STAT, MAPK, and Akt pathways in addition to protein synthesis regulatory proteins with resultant increase in overall protein synthesis. Analysis with phospho-specific antibodies revealed that AG490 (Jak inhibitor), PD98059 (MEK1/2 inhibitor), SB203580 (p38 MAPK inhibitor), LY294002 (PI3-K inhibitor) and rapamycin (mTOR inhibitor) act at different levels in the signaling cascade to inhibit CT-1 induced protein synthesis. CONCLUSION: Cardiotrophin-1 activates the Jak/STAT, PI3K/Akt, p38 and p42/44 MAPK pathways in cardiac fibroblasts. Use of pharmacologic inhibitors reveals that each of these pathways play a role in CT-1 induced protein synthesis.