| Co-Investigator(Kenkyū-buntansha) |
YUASA Tomoyuki The University of Tokushima, Institute for Enzyme Research, Research Associate, 分子酵素学研究センター, 助手 (50304556)
KISHI Kazuhiro The University of Tokushima, Institute for Enzyme Research, Associate Professor, 分子酵素学研究センター, 助教授 (70284320)
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| Research Abstract |
One of the down stream effectors of P13-kinase is serine-threonine kinase Akt (protein kinase B, RAK-PK), but the involvement of Akt in insulin-stimulated GLUT4 translocation is controversial. To investigate whether Akt 1 regulates insulin-stimulated GLUT4 translocation and glucose uptake in L6 myotubes, we established L6 myotubes stably expressing c-myc epitope-tagged GLUT4 (GLUT4myc) and mouse wild type (WT) Akt 1 . We found that overexpression of WT Akt 1 promoted insulin-stimulated p70S6 kinase (p70S6K) activity and increased the basal activity of GSK3β, but did not promote insulin-stimulated GLUT4 translocation or glucose uptake. These data supported the result that Akt is not a main signaling molecule to transmit the signal of insulin-stimulated GLUT4 translocation or glucose uptake from insulin-activated P13-kinase. To define the effect of platelet-derived growth factor (PDGF) on glucose transport in 3T3-L1 adipocytes, we investigated the PDGF- and insulin-induced glucose uptake
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, translocation of glucose transporters and PI 3-kinase activity in 3T3-L1, 3T3-L1GLUT4myc and 3T3-L1GLUT1myc adipocytes. Insulin and PDGF stimulated glucose uptake by 9-10 and 5.5-6.5-fold, respectively, in both 3T3-L1 and 3T3-L1GLUT4myc adipocytes. Exogenous GLUT4myc expression led to enhanced PDGF-induced glucose transport. In 3T3-L1GLUT4myc adipocytes, insulin and PDGF induced an 8-fold and 5-fold increase in GLUT4myc translocation, respectively, determined in a cell surface anti-c-myc antibody binding assay. This PDGF-induced GLUT4myc translocation was further demonstrated with fluorescent detection. In contrast, PDGF stimulated a 2-fold increase of GLUT1myc translocation and 2.5-fold increase of glucose uptake in 3T3-L1GLUT1myc adipocytes. The PDGF-induced GLUT4myc translocation, glucose uptake and PI 3-kinase activity were maximal(100%) at 5-10 mm, and thereafter rapidly declined to 40, , and 12%, respectively, within 60 mm, a time when effects of insulin were maximal. Wortmannin (0.1 μM) abolished PDGF-induced GLUT4myc translocation and glucose uptake in 3T3-L1GLUT4myc adipocytes. These results suggest that PDGF can transiently trigger the translocation of GLUT4 and stimulates glucose uptake by translocation of both GLUT4 and GLUT 1 in a phosphatidylinositol 3-kinase-dependent signaling pathway in 3T3-L1 adipocytes. Less
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