Activation of the Mammalian Target of Rapamycin Pathway Acutely Inhibits Insulin Signaling to Akt and Glucose Transport in 3T3-L1 and Human Adipocytes

• Published in: Endocrinology (Philadelphia) 2005-03, Vol.146 (3), p.1328-1337
• Main Authors: Tremblay, Frédéric, Gagnon, AnneMarie, Veilleux, Alain, Sorisky, Alexander, Marette, André
• Format: Article
• Language: English
• Subjects: 3-O-Methylglucose - metabolism; 3T3-L1 Cells - metabolism; Adipocytes; Adipocytes - cytology; Adipocytes - metabolism; AKT protein; Animals; Biological and medical sciences; Cell Differentiation; Cell Membrane - metabolism; Cytosol; Density; Deoxyglucose - metabolism; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation; Glucose; Glucose - metabolism; Glucose transport; Glucose Transporter Type 1; Glucose Transporter Type 4; Humans; Immunoblotting; Immunoprecipitation; Insulin; Insulin - metabolism; Insulin receptor substrate 1; Insulin Receptor Substrate Proteins; Kinases; Kinetics; Mammals; Membranes; Mice; Modulators; Monosaccharide Transport Proteins - metabolism; Muscle Proteins - metabolism; Phosphatidylinositol 3-Kinases - metabolism; Phosphoproteins - metabolism; Phosphorylation; Protein Kinases - metabolism; Protein Kinases - physiology; Protein Transport; Protein-Serine-Threonine Kinases - metabolism; Proto-Oncogene Proteins - metabolism; Proto-Oncogene Proteins c-akt; Rapamycin; Ribosomal protein S6 kinase; Ribosomal Protein S6 Kinases, 70-kDa - metabolism; Serine - chemistry; Signal Transduction; Sirolimus - pharmacology; Subcellular Fractions; Time Factors; TOR protein; TOR Serine-Threonine Kinases; Translocation; Vertebrates: endocrinology
• ISSN: 0013-7227; 1945-7170
• DOI: 10.1210/en.2004-0777

The mammalian target of rapamycin (mTOR) pathway has recently emerged as a chronic modulator of insulin-mediated glucose metabolism. In this study, we evaluated the involvement of this pathway in the acute regulation of insulin action in both 3T3-L1 and human adipocytes. Insulin rapidly (t1/2 = 5 min) stimulated the mTOR pathway, as reflected by a 10-fold stimulation of 70-kDa ribosomal S6 kinase 1 (S6K1) activity in 3T3-L1 adipocytes. Inhibition of mTOR/S6K1 by rapamycin increased insulin-stimulated glucose transport by as much as 45% in 3T3-L1 adipocytes. Activation of mTOR/S6K1 by insulin was associated with a rapamycin-sensitive increase in Ser636/639 phosphorylation of insulin receptor substrate (IRS)-1 but, surprisingly, did not result in impaired IRS-1-associated phosphatidylinositol (PI) 3-kinase activity. However, insulin-induced activation of Akt was increased by rapamycin. Insulin also activated S6K1 and increased phosphorylation of IRS-1 on Ser636/639 in human adipocytes. As in murine cells, rapamycin treatment of human adipocytes inhibited S6K1, blunted Ser636/639 phosphorylation of IRS-1, leading to increased Akt activation and glucose uptake by insulin. Further studies in 3T3-L1 adipocytes revealed that rapamycin prevented the relocalization of IRS-1 from the low-density membranes to the cytosol in response to insulin. Furthermore, inhibition of mTOR markedly potentiated the ability of insulin to increase PI 3,4,5-triphosphate levels concomitantly with an increased phosphorylation of Akt at the plasma membrane, low-density membranes, and cytosol. However, neither GLUT4 nor GLUT1 translocation induced by insulin were increased by rapamycin treatment. Taken together, these results indicate that the mTOR pathway is an important modulator of the signals involved in the acute regulation of insulin-stimulated glucose transport in 3T3-L1 and human adipocytes.