tailieunhanh - Báo cáo khoa học: Insulin like growth factor-1-induced phosphorylation and altered distribution of tuberous sclerosis complex (TSC)1⁄TSC2 in C2C12 myotubes

Insulin like growth factor-1 (IGF-1) is established as an anabolic factor that can induce skeletal muscle growth by activating the phosphoinosi-tide 3-kinase⁄Akt⁄mammalian target of rapamycin (mTOR) pathway. Although this signaling pathway has been the subject of much study, the molecular mechanisms linking IGF-1 binding to mTOR activation remain poorly defined in muscle. | ễFEBS Journal Insulin like growth factor-1-induced phosphorylation and altered distribution of tuberous sclerosis complex TSC 1 TSC2 in C2C12 myotubes Mitsunori Miyazaki John J. McCarthy and Karyn A. Esser Center for Muscle Biology Department of Physiology College of Medicine University of Kentucky Lexington KY USA Keywords mTOR rapamycin TSC1 TSC2 wortmannin Correspondence K. A. Esser Department of Physiology College of Medicine University of Kentucky 800 Rose Street UKMC MS508 Lexington KY 40536 USA Fax 1 859 323 1070 Tel 1 859 323 8103 E-mail kaesse2@ Received 11 January 2010 revised 26 February 2010 accepted 2 March 2010 doi Insulin like growth factor-1 IGF-1 is established as an anabolic factor that can induce skeletal muscle growth by activating the phosphoinositide 3-kinase Akt mammalian target of rapamycin mTOR pathway. Although this signaling pathway has been the subject of much study the molecular mechanisms linking IGF-1 binding to mTOR activation remain poorly defined in muscle. The present study aimed to test the hypothesis that IGF-1 activation of mTOR in C2C12 myotubes requires a phosphorylation-dependent altered distribution of the tuberous sclerosis complex TSC 1 TSC2 complex from the membrane to the cytosol. We found that IGF-1 treatment does not affect complex formation between TSC1 and TSC2 but rather IGF-1 induces an altered distribution of the TSC1 TSC2 complex in C2C12 myotubes. In response to IGF-1 treatment there was a relative redistribution of the TSC1 TSC2 complex composed of TSC1 and phosphorylated TSC2 from the membrane to the cytosol. IGF-1-stimu-lated TSC1 TSC2 phosphorylation and redistribution were completely prevented by the phosphoinositide 3-kinase inhibitor wortmannin but were not with the downstream mTOR inhibitor rapamycin. When a nonphosph-orylatable form of TSC2 S939A was overexpressed phosphorylationdependent binding of the scaffold protein 14-3-3 to TSC2 was diminished and no .