IGF-1 induces IP sub(3)-dependent calcium signal involved in the regulation of myostatin gene expression mediated by NFAT during myoblast differentiation

• Published in: Journal of cellular physiology 2013-07, Vol.228 (7), p.1452-1463
• Main Authors: Valdes, Juan A, Flores, Sylvia, Fuentes, Eduardo N, Osorio-Fuentealba, Cesar, Jaimovich, Enrique, Molina, Alfredo
• Format: Article
• Language: English
• Subjects: 1-Phosphatidylinositol 3-kinase
• ISSN: 0021-9541; 1097-4652
• DOI: 10.1002/jcp.24298

Skeletal muscle differentiation is a complex and highly regulated process characterized by cell cycle arrest, which is associated with morphological changes including myoblast alignment, elongation, and fusion into multinucleated myotubes. This is a balanced process dynamically coordinated by positive and negative signals such as the insulin-like growth factor I (IGF-1) and myostatin (MSTN), respectively. In this study, we report that the stimulation of skeletal myoblasts during differentiation with IGF-1 induces a rapid and transient calcium increase from intracellular stores, which are principally mediated through the phospholipase C gamma (PLC [gamma])/inositol 1,4,5-triphosphate (IP sub(3))-dependent signaling pathways. This response was completely blocked when myoblasts were incubated with LY294002 or transfected with the dominant-negative p110 gamma, suggesting a fundamental role of phosphatidylinositol 3-kinase (PI3K) in PLC[gamma] activation. Additionally, we show that calcium released via IP sub(3) and induced by IGF-1 stimulates NFAT-dependent gene transcription and nuclear translocation of the GFP-labeled NFATc3 isoform. This activation was independent of extracellular calcium influx and calcium release mediated by ryanodine receptor (RyR). Finally, we examined mstn mRNA levels and mstn promoter activity in myoblasts stimulated with IGF-1. We found a significant increase in mRNA contents and in reporter activity, which was inhibited by cyclosporin A, 11R-VIVIT, and by inhibitors of the PI3K[gamma], PLC[gamma], and IP sub(3) receptor. Our results strongly suggest that IGF-1 regulates myostatin transcription through the activation of the NFAT transcription factor in an IP sub(3)/calcium-dependent manner. This is the first study to demonstrate a role of calcium-dependent signaling pathways in the mRNA expression of myostatin. J. Cell. Physiol. 228: 1452-1463, 2013. copyright 2012 Wiley Periodicals, Inc.