Mechanisms involved in the coordinate regulation of mTORC1 by insulin and amino acids.
In this study, we explored the coordinate regulation of mTORC1 by insulin and amino acids. Rat livers were perfused with medium containing various concentrations of insulin and/or amino acids. At fasting (1×) or 2× (2×AA) concentrations of amino acids, insulin maximally stimulated Akt phosphorylation but had no effect on global rates of protein synthesis. In the absence of insulin, 4×AA produced a moderate stimulation of protein synthesis and activation of mTORC1. The combination of 4×AA and insulin produced a maximal stimulation of protein synthesis and activation of mTORC1. These effects were accompanied by decreases in raptor and PRAS40 and an increase in RagC associated with mTOR (mammalian target of rapamycin). The studies were extended to a cell culture model in which mTORC1 activity was repressed by deprivation of leucine and serum, and resupplementation with the amino acid and insulin acted in an additive manner to restore mTORC1 activation. In deprived cells, mTORC1 was activated by expressing either constitutively active (ca) Rheb or a caRagB·caRagC complex, and coexpression of the constructs had an additive effect. Notably, resupplementation with leucine in cells expressing caRheb or with insulin in cells expressing the caRagB·caRagC complex was as effective as resupplementation with both leucine and insulin in non-transfected cells. Moreover, changes in mTORC1 activity correlated directly with altered association of mTOR with RagB/RagC, Rheb, raptor, and PRAS40. Overall, the results suggest that amino acids signal through the Rag complex and insulin through Rheb to achieve coordinate activation of mTORC1.
From the Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033.
Michael D
MD
Dennis
From the Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033.
Jamie I
JI
Baum
From the Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033. Electronic address: skimball@psu.edu.
Scot R
SR
Kimball
From the Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033.
Leonard S
LS
Jefferson
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D000596:Amino Acids / Q000494:pharmacology*; D000818:Animals; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism*; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D014176:Protein Biosynthesis / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; C516104:Akt1s1 protein, rat; D000596:Amino Acids; D007004:Hypoglycemic Agents; D007328:Insulin; D046912:Multiprotein Complexes; D010750:Phosphoproteins; D014157:Transcription Factors; C546845:mTOR protein, rat; D058570:TOR Serine-Threonine Kinases; D020559:Monomeric GTP-Binding Proteins
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