title: The actions of exogenous leucine on mTOR signalling and amino acid transporters in human myotubes.
abstract: BACKGROUND
  The branched-chain amino acid (BCAA) leucine has been identified to be a key regulator of skeletal muscle anabolism. Activation of anabolic signalling occurs via the mammalian target of rapamycin (mTOR) through an undefined mechanism. System A and L solute carriers transport essential amino acids across plasma membranes; however it remains unknown whether an exogenous supply of leucine regulates their gene expression. The aim of the present study was to investigate the effects of acute and chronic leucine stimulation of anabolic signalling and specific amino acid transporters, using cultured primary human skeletal muscle cells.
  
  
  RESULTS
  Human myotubes were treated with leucine, insulin or co-treated with leucine and insulin for 30 min, 3 h or 24 h. Activation of mTOR signalling kinases were examined, together with putative nutrient sensor human vacuolar protein sorting 34 (hVps34) and gene expression of selected amino acid transporters. Phosphorylation of mTOR and p70S6K was transiently increased following leucine exposure, independently to insulin. hVps34 protein expression was also significantly increased. However, genes encoding amino acid transporters were differentially regulated by insulin and not leucine.
  
  
  CONCLUSIONS
  mTOR signalling is transiently activated by leucine within human myotubes independently of insulin stimulation. While this occurred in the absence of changes in gene expression of amino acid transporters, protein expression of hVps34 increased.
authors.affiliation: Molecular Nutrition Unit, School of Exercise and Nutrition Sciences, Deakin University, Burwood, Victoria, Australia.
authors.forename: Petra
authors.initials: P
authors.lastname: Gran
authors.forename: David
authors.initials: D
authors.lastname: Cameron-Smith
mesh_terms: D000328:Adult; D026905:Amino Acid Transport Systems / Q000187:drug effects* / Q000378:metabolism; D058546:Class III Phosphatidylinositol 3-Kinases / Q000096:biosynthesis* / Q000235:genetics; D039603:Eukaryotic Initiation Factor-4G / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D007930:Leucine / Q000494:pharmacology*; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000187:drug effects* / Q000378:metabolism; D009924:Organ Culture Techniques; D010766:Phosphorylation; D039665:Prokaryotic Initiation Factor-3 / Q000187:drug effects; D011499:Protein Processing, Post-Translational; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D058570:TOR Serine-Threonine Kinases / Q000096:biosynthesis / Q000187:drug effects*; D055815:Young Adult
chemical_list: D026905:Amino Acid Transport Systems; C113920:EIF4G1 protein, human; D039603:Eukaryotic Initiation Factor-4G; D007328:Insulin; D039665:Prokaryotic Initiation Factor-3; C546842:MTOR protein, human; D058546:Class III Phosphatidylinositol 3-Kinases; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; D007930:Leucine