title: Spatial and temporal regulation of GLUT4 translocation by flotillin-1 and caveolin-3 in skeletal muscle cells.
abstract: Skeletal muscle tissue is one of the main sites where glucose uptake occurs in response to insulin. The glucose transporter type-4 (GLUT4) is primarily responsible for the insulin-stimulated increase in glucose uptake. Upon insulin stimulation, GLUT4 is recruited from intracellular reserves to the plasma membrane. The molecular mechanisms that regulate the translocation of GLUT4 to the sarcolemma remain to be fully identified. Here, we demonstrate that GLUT4 is localized to perinuclear stores that contain flotillin-1, a marker of lipid rafts, in skeletal muscle cells. Stimulation with insulin for 10 min results in the translocation of flotillin-1/GLUT4-containing domains to the plasma membrane in a PI3K- and PKCzeta-dependent manner. We also demonstrate that caveolin-3, a marker of caveolae, is required for the insulin receptor-mediated activation of the PI3K-dependent pathway, which occurs 2 min after insulin stimulation. In fact, we demonstrate that lack of caveolin-3 significantly reduces insulin-stimulated glucose uptake in caveolin-3 null myotubes by inhibiting both PI3K and Akt, as well as the movement of GLUT4 to the plasma membrane. Interestingly, caveolin-3 moves away from the plasma membrane toward the cytoplasm 5 min after insulin stimulation and temporarily interacts with flotillin-1/GLUT4-containing domains before they reach the sarcolemma, with the consequent movement of the insulin receptor from caveolin-3-containing domains to flotillin-1-containing domains. Such translocation temporally matches the insulin-stimulated movement of Cbl and CrkII in flotillin-1/GLUT4-containing domains, as well as the activation of the GDP-GTP exchange factor C3G. Disruption of flotillin-1-based domains prevents the activation of C3G, movement of GLUT4 to the sarcolemma, and glucose uptake in response to insulin. Thus, the activation of the Cbl/C3G/TC10-dependent pathway, which occurs before flotillin-1/GLUT4-containing domains reach the plasma membrane, is flotillin-1 mediated and follows the activation of the PI3K-mediated signaling. Taken together, these results indicate that flotillin-1 and caveolin-3 may regulate muscle energy metabolism through the spatial and temporal segregation of key components of the insulin signaling.
authors.affiliation: Department of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA.
authors.forename: Katia
authors.initials: K
authors.lastname: Fecchi
authors.forename: Daniela
authors.initials: D
authors.lastname: Volonte
authors.forename: Michael P
authors.initials: MP
authors.lastname: Hezel
authors.forename: Kevin
authors.initials: K
authors.lastname: Schmeck
authors.forename: Ferruccio
authors.initials: F
authors.lastname: Galbiati
mesh_terms: D000818:Animals; D002292:Carcinoma, Renal Cell; D051244:Caveolin 3 / Q000378:metabolism*; D002462:Cell Membrane; D002478:Cells, Cultured; D005786:Gene Expression Regulation; D051275:Glucose Transporter Type 4 / Q000378:metabolism*; D007328:Insulin; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D018482:Muscle, Skeletal / Q000166:cytology* / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D021381:Protein Transport; D050721:Proto-Oncogene Proteins c-cbl / Q000378:metabolism; D050737:Proto-Oncogene Proteins c-crk / Q000378:metabolism; D013997:Time Factors; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism; D000099221:Protein Kinase C zeta
chemical_list: D051244:Caveolin 3; D051275:Glucose Transporter Type 4; D007328:Insulin; D008565:Membrane Proteins; D019869:Phosphatidylinositol 3-Kinases; D011493:Protein Kinase C; D050721:Proto-Oncogene Proteins c-cbl; D050737:Proto-Oncogene Proteins c-crk; D048051:p38 Mitogen-Activated Protein Kinases; D000099221:Protein Kinase C zeta; C495548:Cav3 protein, mouse; C495693:Slc2a4 protein, mouse; C106354:flotillins; C493849:Cbl protein, mouse