Amino acids and leucine allow insulin activation of the PKB/mTOR pathway in normal adipocytes treated with wortmannin and in adipocytes from db/db mice.
Amino acids are nutrients responsible for mammalian target of rapamycin (mTOR) regulation in mammalian cells. The mTOR protein is mainly known for its role in regulating cell growth, notably via protein synthesis. In addition to amino acids, mTOR is regulated by insulin via a phosphatidylinositol 3-kinase (PI 3-kinase)-dependent pathway. mTOR mediates crosstalk between amino acids and insulin signaling. We show that in freshly isolated rat adipocytes, insulin stimulates the phosphorylation of mTOR on serine 2448, a protein kinase B (PKB) consensus phosphorylation site. This site is also phosphorylated by amino acids, which in contrast to insulin do not activate PKB. Moreover, insulin and amino acids have an additive effect on mTOR phosphorylation, indicating that they act via two independent pathways. Importantly, amino acids, notably leucine, permit insulin to stimulate PKB when PI 3-kinase is inhibited. They also rescue glucose transport and the mTOR pathway. Further, leucine alone can improve insulin activation of PKB in db/db mice. Our results define the importance of amino acids in insulin signaling and reveal leucine as a key amino acid in disease situations associated with insulin-resistance in adipocytes.
INSERM, Unité 145, Institut Fédératif de Recherche, Nice, Cédex 02, France.
Charlotte
C
Hinault
Isabelle
I
Mothe-Satney
Nadine
N
Gautier
John C
JC
Lawrence
Emmanuel
E
Van Obberghen
D017667:Adipocytes / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D000596:Amino Acids / Q000494:pharmacology* / Q000502:physiology; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology*; D007930:Leucine / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008817:Mice, Mutant Strains; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases; D000077191:Wortmannin
D000596:Amino Acids; D000730:Androstadienes; D004791:Enzyme Inhibitors; D007328:Insulin; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D011494:Protein Kinases; C546843:mTOR protein, mouse; C546845:mTOR protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D007930:Leucine; D005947:Glucose; D000077191:Wortmannin