Tyrosine Phosphorylation-Dependent and -Independent Role of Shc in the Regulation of IGF-1-Induced Mitogenesis and Glycogen Synthesis

• Published in: Endocrinology (Philadelphia) 2001-12, Vol.142 (12), p.5226-5235
• Main Authors: Sasaoka, Toshiyasu, Ishiki, Manabu, Wada, Tsutomu, Hori, Hiroyuki, Hirai, Hiroki, Haruta, Tetsuro, Ishihara, Hajime, Kobayashi, Masashi
• Format: Article
• Language: English
• Subjects: 1-Phosphatidylinositol 3-kinase; AKT protein; Cell activation; Glycogen; Glycogens; Grb2 protein; Insulin receptor substrate 1; Insulin-like growth factor I; Insulin-like growth factors; MAP kinase; Myoblasts; Phosphorylation; Phosphotyrosine; Receptors; Stimulation; Synthesis; Thymidine; Tyrosine
• ISSN: 0013-7227; 1945-7170
• DOI: 10.1210/endo.142.12.8543

To examine the functional role of Shc tyrosine phosphorylation in IGF-1 signaling, wild-type (WT)-Shc and Y239,240,317F (3F)-Shc were transiently transfected into L6 myoblasts. IGF-1 signaling was compared among the transfected cells. IGF-1-induced tyrosine phosphorylation of Shc and its subsequent association with Grb2 were increased in WT-Shc cells, whereas they were decreased in 3F-Shc cells compared with those in parental L6 cells. Consistent with their changes, IGF-1-induced MAPK activation and thymidine incorporation were enhanced in WT-Shc cells, whereas they were again decreased in 3F-Shc cells. It is possible that Shc and insulin receptor substrate (IRS)-1 can interact competitively, via their phosphotyrosine binding (PTB) domains, with the activated IGF-1 receptor. In this regard, IGF-1-induced tyrosine phosphorylation of IRS-1 was decreased by overexpressing both WT-Shc and 3F-Shc cells. Consistent with the decrease, IGF-1-induced IRS-1 association with the p85 subunit of PI3K and activation of PI3K and Akt were reduced in both WT-Shc and 3F-Shc cells. As a result, IGF-1-induced glycogen synthesis was also decreased in both cells. Furthermore, expression of Shc PTB domain alone inhibited IGF-1 stimulation of Akt and glycogen synthesis. These results indicate that tyrosine phosphorylation of Shc is important for IGF-1 stimulation of MAPK leading to mitogenesis and that Shc, via its PTB domain, negatively regulates IGF-1-induced glycogen synthesis by competing with IRS-1, which is not relevant to Shc tyrosine phosphorylation.