TY - JOUR
T1 - Insulin like growth factor-1-induced phosphorylation and altered distribution of tuberous sclerosis complex (TSC)1/TSC2 in C2C12 myotubes
AU - Miyazaki, Mitsunori
AU - McCarthy, John J.
AU - Esser, Karyn A.
PY - 2010/5
Y1 - 2010/5
N2 - 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-stimulated 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 nonphosphorylatable form of TSC2 (S939A) was overexpressed, phosphorylation-dependent binding of the scaffold protein 14-3-3 to TSC2 was diminished and no redistribution of the TSC1/TSC2 complex was observed after IGF-1 stimulation. These results indicate that TSC2 phosphorylation in response to IGF-1 treatment is necessary for the altered distribution of the TSC1/TSC2 complex to the cytosol. We suggest that this translocation is likely critical for mTOR activation by dissociating the interaction between the GTPase activating protein activity of the TSC1/TSC2 complex and its downstream target, Ras homolog enriched in brain.
AB - 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-stimulated 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 nonphosphorylatable form of TSC2 (S939A) was overexpressed, phosphorylation-dependent binding of the scaffold protein 14-3-3 to TSC2 was diminished and no redistribution of the TSC1/TSC2 complex was observed after IGF-1 stimulation. These results indicate that TSC2 phosphorylation in response to IGF-1 treatment is necessary for the altered distribution of the TSC1/TSC2 complex to the cytosol. We suggest that this translocation is likely critical for mTOR activation by dissociating the interaction between the GTPase activating protein activity of the TSC1/TSC2 complex and its downstream target, Ras homolog enriched in brain.
KW - MTOR
KW - Rapamycin
KW - TSC1
KW - TSC2
KW - Wortmannin
UR - http://www.scopus.com/inward/record.url?scp=77951213258&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=77951213258&partnerID=8YFLogxK
U2 - 10.1111/j.1742-4658.2010.07635.x
DO - 10.1111/j.1742-4658.2010.07635.x
M3 - Article
C2 - 20412061
AN - SCOPUS:77951213258
VL - 277
SP - 2180
EP - 2191
IS - 9
ER -