title: Ataxia telangiectasia mutated impacts insulin-like growth factor 1 signalling in skeletal muscle.
abstract: 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.
authors.affiliation: Department of Biology, Saint Louis University, St Louis, MO 63103, USA.
authors.forename: James Kain
authors.initials: JK
authors.lastname: Ching
authors.forename: Stephen H
authors.initials: SH
authors.lastname: Luebbert
authors.forename: Roy L
authors.initials: RL
authors.lastname: Collins
authors.forename: Zhihong
authors.initials: Z
authors.lastname: Zhang
authors.forename: Nandhini
authors.initials: N
authors.lastname: Marupudi
authors.forename: Sankha
authors.initials: S
authors.lastname: Banerjee
authors.forename: Robin D
authors.initials: RD
authors.lastname: Hurd
authors.forename: Lyle
authors.initials: L
authors.lastname: Ralston
authors.forename: Jonathan S
authors.initials: JS
authors.lastname: Fisher
mesh_terms: D000818:Animals; D064007:Ataxia Telangiectasia Mutated Proteins; D015153:Blotting, Western; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation; D005822:Genetic Vectors; D005838:Genotype; D057895:Haploinsufficiency; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D016086:Lentivirus / Q000235:genetics; D051379:Mice; D018345:Mice, Knockout; D009025:Morpholines / Q000494:pharmacology; D018482:Muscle, Skeletal / Q000187:drug effects / Q000201:enzymology*; D032448:Myoblasts, Skeletal / Q000187:drug effects / Q000201:enzymology*; D010641:Phenotype; D058539:Phosphatidylinositol 3-Kinase / Q000378:metabolism; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011753:Pyrones / Q000494:pharmacology; D034622:RNA Interference; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D014162:Transfection; D025521:Tumor Suppressor Proteins / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*
chemical_list: C495818:2-morpholin-4-yl-6-thianthren-1-yl-pyran-4-one; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; D009025:Morpholines; D047428:Protein Kinase Inhibitors; D011753:Pyrones; D025521:Tumor Suppressor Proteins; C519530:insulin-like growth factor-1, mouse; D007334:Insulin-Like Growth Factor I; C546843:mTOR protein, mouse; D058539:Phosphatidylinositol 3-Kinase; D064007:Ataxia Telangiectasia Mutated Proteins; C576325:Atm protein, mouse; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases