title: Mechanical stretch activates mammalian target of rapamycin and AMP-activated protein kinase pathways in skeletal muscle cells.
abstract: Cellular protein synthesis is believed to be antagonistically regulated by mammalian target of rapamycin (mTOR) and AMP-activated protein kinase (AMPK) signaling pathways. In the present study, we examined the relationship between mTOR/p70 S6 kinase (p70S6K) and AMPK in response to mechanical stretch. C2C12 myoblasts were grown on a silicone elastomer chamber to confluence and further cultured in differentiation medium for 4 days to form multinucleated myotubes. Cells were subjected to 15% cyclic uniaxial stretch for 4 h at a frequency of 1 Hz. Phosphorylation of p70S6K at threonine 389 and AMPK at threonine 172 of the catalytic α subunit were concomitantly increased by mechanical stretch. Stimulation of the mTOR pathway by adding leucine and insulin increased the phosphorylation of p70S6K without inactivation of AMPK. In contrast, addition of compound C, a pharmacological inhibitor of AMPK, increased the phosphorylation of p70S6K in stretched cells. Activation of AMPK by the addition of 5-amino-4-imidazolecarboxamide ribonucleoside reduced the phosphorylation of p70S6K in response to mechanical stretch. In conclusion, crosstalk between mTOR and AMPK signaling was not tightly regulated in response to physiological stimuli, such as mechanical stress and/or nutrients. However, pharmacological modulation of AMPK influenced the mTOR/p70S6K signaling pathway.
authors.affiliation: Department of Health and Sports Sciences, Graduate School of Medicine, Osaka University, 1-17 Machikaneyama-cho, Toyonaka, Osaka, 560-0043, Japan, nakai@hss.osaka-u.ac.jp.
authors.forename: Naoya
authors.initials: N
authors.lastname: Nakai
authors.forename: Fuminori
authors.initials: F
authors.lastname: Kawano
authors.forename: Ken
authors.initials: K
authors.lastname: Nakata
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001696:Biomechanical Phenomena; D002460:Cell Line; D004789:Enzyme Activation; D007328:Insulin / Q000502:physiology; D007930:Leucine / Q000502:physiology; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000201:enzymology*; D018482:Muscle, Skeletal / Q000166:cytology; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D012265:Ribonucleotides / Q000494:pharmacology; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*
chemical_list: D007328:Insulin; D012265:Ribonucleotides; D000620:Aminoimidazole Carboxamide; C546843:mTOR protein, mouse; C548179:Prkaa1 protein, mouse; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; C031143:AICA ribonucleotide; D007930:Leucine