RESUMO
Reports that ataxia telangiectasia mutated (ATM) is required for full activation of Akt raise the hypothesis that ATM plays a role in insulin-like growth factor 1 (IGF-1) signalling through the Akt/mammalian target of rapamycin (mTOR) pathway. Differentiated C2C12 cells harbouring either ATM-targeting short hairpin RNA (shRNA) or non-targeting shRNA and myotubes from a C2C12 lineage previously exposed to empty vector lentivirus were incubated in the presence or absence of 10 nm IGF-1 followed by Western blot analysis. Parallel experiments were performed in isolated soleus muscles from mice expressing only one functional ATM allele (ATM(+/-)) compared with muscles from wild-type (ATM(+/+)) mice. Insulin-like growth factor 1 increased phosphorylation of Akt S473, Akt T308 and p70 S6 kinase (S6K) in myotubes expressing non-targeting shRNA and in empty vector controls, but the IGF-1 effects were significantly reduced in myotubes with shRNA-mediated ATM knockdown. Likewise, IGF-1-stimulated phosphorylation of Akt S473, Akt T308, mTOR and S6K was lower in isolated soleus muscles from ATM(+/-) mice compared with muscles from ATM(+/+) mice. The ATM inhibitor KU55933 prevented stimulation of S6K phosphorylation in C2C12 myotubes exposed to IGF-1, suggesting that decreased IGF-1 action is not limited to chronic conditions of decreased ATM function. Stimulation of insulin receptor substrate 1 tyrosine 612 phosphorylation by IGF-1 was unaffected by ATM deficiency, though IGF-1 phosphatidylinositol 3-kinase activity tended to be lower in muscle from ATM haploinsufficient mice compared with wild-type muscle. The data suggest that ATM is a modulator of IGF-1 signalling downstream of insulin receptor substrate 1 in skeletal muscle.
Assuntos
Proteínas de Ciclo Celular/metabolismo , Proteínas de Ligação a DNA/metabolismo , Fator de Crescimento Insulin-Like I/metabolismo , Músculo Esquelético/enzimologia , Mioblastos Esqueléticos/enzimologia , Proteínas Serina-Treonina Quinases/metabolismo , Transdução de Sinais , Proteínas Supressoras de Tumor/metabolismo , Animais , Proteínas Mutadas de Ataxia Telangiectasia , Western Blotting , Proteínas de Ciclo Celular/antagonistas & inibidores , Proteínas de Ciclo Celular/deficiência , Proteínas de Ciclo Celular/genética , Linhagem Celular , Proteínas de Ligação a DNA/antagonistas & inibidores , Proteínas de Ligação a DNA/deficiência , Proteínas de Ligação a DNA/genética , Ativação Enzimática , Vetores Genéticos , Genótipo , Haploinsuficiência , Proteínas Substratos do Receptor de Insulina/metabolismo , Lentivirus/genética , Camundongos , Camundongos Knockout , Morfolinas/farmacologia , Músculo Esquelético/efeitos dos fármacos , Mioblastos Esqueléticos/efeitos dos fármacos , Fenótipo , Fosfatidilinositol 3-Quinase/metabolismo , Fosforilação , Inibidores de Proteínas Quinases/farmacologia , Proteínas Serina-Treonina Quinases/antagonistas & inibidores , Proteínas Serina-Treonina Quinases/deficiência , Proteínas Serina-Treonina Quinases/genética , Proteínas Proto-Oncogênicas c-akt/metabolismo , Pironas/farmacologia , Interferência de RNA , Proteínas Quinases S6 Ribossômicas 70-kDa/metabolismo , Transdução de Sinais/efeitos dos fármacos , Serina-Treonina Quinases TOR/metabolismo , Transfecção , Proteínas Supressoras de Tumor/antagonistas & inibidores , Proteínas Supressoras de Tumor/deficiência , Proteínas Supressoras de Tumor/genéticaRESUMO
There are reports that ataxia telangiectasia mutated (ATM) plays a role in insulin-stimulated Akt phosphorylation, although this is not the case in some cell types. Because Akt plays a key role in insulin signaling, which leads to glucose transport in skeletal muscle, the predominant tissue in insulin-stimulated glucose disposal, we examined whether insulin-stimulated Akt phosphorylation and (or) glucose transport would be decreased in skeletal muscle of mice lacking functional ATM, compared with muscle from wild-type mice. We found that in vitro insulin-stimulated Akt phosphorylation was normal in soleus muscle from mice with 1 nonfunctional allele of ATM (ATM+/-) and from mice with 2 nonfunctional alleles (ATM-/-). However, insulin did not stimulate glucose transport or the phosphorylation of AS160 in ATM-/- soleus. ATM protein level was markedly higher in wild-type extensor digitorum longus (EDL) than in wild-type soleus. In EDL from ATM-/- mice, insulin did not stimulate glucose transport. However, in contrast to findings for soleus, insulin-stimulated Akt phosphorylation was blunted in ATM-/- EDL, concomitant with a tendency for insulin-stimulated phosphatidylinositol 3-kinase activity to be decreased. Together, the findings suggest that ATM plays a role in insulin-stimulated glucose transport at the level of AS160 in muscle comprised of slow and fast oxidative-glycolytic fibers (soleus) and at the level of Akt in muscle containing fast glycolytic fibers (EDL).