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Insulin like growth factor‐1‐induced phosphorylation and altered distribution of tuberous sclerosis complex (TSC)1/TSC2 in C2C12 myotubes
Author(s) -
Miyazaki Mitsunori,
McCarthy John J.,
Esser Karyn A.
Publication year - 2010
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2010.07635.x
Subject(s) - pi3k/akt/mtor pathway , tsc2 , wortmannin , phosphorylation , microbiology and biotechnology , protein kinase b , tsc1 , mechanistic target of rapamycin , myogenesis , rheb , c2c12 , chemistry , mtorc1 , biology , signal transduction , myocyte
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. Structured digital abstract• MINT‐7712277 , MINT‐7712399 : Tsc2 (uniprotkb: Q61037 ), S6K1 (uniprotkb: Q8BSK8 ) and Tsc1 (uniprotkb: Q9EP53 ) colocalize ( MI:0403 ) by cosedimentation through density gradient ( MI:0029 ) • MINT‐7712211 , MINT‐7712236 , MINT‐7712313 , MINT‐7712323 : Tsc1 (uniprotkb: Q9EP53 ) physically interacts ( MI:0915 ) with Tsc2 (uniprotkb: Q61037 ) by anti bait coimmunoprecipitation ( MI:0006 ) • MINT‐7712377 : 14‐3‐3 beta (uniprotkb: Q9CQV8 ) physically interacts ( MI:0914 ) with Tsc1 (uniprotkb: Q9EP53 ) and Tsc2 (uniprotkb: Q61037 ) by pull down ( MI:0096 ) • MINT‐7712483 : Tsc1 (uniprotkb: Q9EP53 ) and Tsc2 (uniprotkb: Q61037 ) colocalize ( MI:0403 ) by cosedimentation through density gradient ( MI:0029 ) • MINT‐7712436 : TSC2 (uniprotkb: P49815 ) physically interacts ( MI:0915 ) with TSC1 (uniprotkb: Q92574 ) by anti bait coimmunoprecipitation ( MI:0006 ) • MINT‐7712451 : Tsc1 (uniprotkb: Q9EP53 ), Rheb (uniprotkb: Q921J2 ) and Tsc2 (uniprotkb: Q61037 ) colocalize ( MI:0403 ) by cosedimentation through density gradient ( MI:0029 )