Inhibition of insulin-induced GLUT4 translocation by Munc18c through interaction with syntaxin4 in 3T3-L1 adipocytes.
Insulin induces the translocation of vesicles containing the glucose transporter GLUT4 from an intracellular compartment to the plasma membrane in adipocytes. SNARE proteins have been implicated in the docking and fusion of these vesicles with the cell membrane. The role of Munc18c, previously identified as an n-Sec1/Munc18 homolog in 3T3-L1 adipocytes, in insulin-regulated GLUT4 trafficking has now been investigated in 3T3-L1 adipocytes. In these cells, Munc18c was predominantly associated with syntaxin4, although it bound both syntaxin2 and syntaxin4 to similar extents in vitro. In addition, SNAP-23, an adipocyte homolog of SNAP-25, associated with both syntaxins 2 and 4 in 3T3-L1 adipocytes. Overexpression of Munc18c in 3T3-L1 adipocytes by adenovirus-mediated gene transfer resulted in inhibition of insulin-stimulated glucose transport in a virus dose-dependent manner (maximal effect, approximately 50%) as well as in inhibition of sorbitol-induced glucose transport (by approximately 35%), which is mediated by a pathway different from that used by insulin. In contrast, Munc18b, which is also expressed in adipocytes but which did not bind to syntaxin4, had no effect on glucose transport. Furthermore, overexpression of Munc18c resulted in inhibition of insulin-induced translocation of GLUT4, but not of that of GLUT1, to the plasma membrane. These results suggest that Munc18c is involved in the insulin-dependent trafficking of GLUT4 from the intracellular storage compartment to the plasma membrane in 3T3-L1 adipocytes by modulating the formation of a SNARE complex that includes syntaxin4.
Tamori
Y
Y
Second Department of Internal Medicine, Kobe University School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650, Japan.
Kawanishi
M
M
Niki
T
T
Shinoda
H
H
Araki
S
S
Okazawa
H
H
Kasuga
M
M
D016475:3T3 Cells; D000256:Adenoviridae / Q000235:genetics; D017667:Adipocytes / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002352:Carrier Proteins / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D015870:Gene Expression / Q000235:genetics; D018014:Gene Transfer Techniques; D005947:Glucose / Q000378:metabolism; D051275:Glucose Transporter Type 4; D007328:Insulin / Q000494:pharmacology*; D007329:Insulin Antagonists / Q000494:pharmacology*; D008565:Membrane Proteins / Q000378:metabolism / Q000502:physiology; D051379:Mice; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D051938:Munc18 Proteins; D009124:Muscle Proteins; D009419:Nerve Tissue Proteins; D011485:Protein Binding / Q000502:physiology; D011506:Proteins / Q000502:physiology*; D050765:Qa-SNARE Proteins; D050766:Qb-SNARE Proteins; D050767:Qc-SNARE Proteins; D050600:SNARE Proteins; D013012:Sorbitol / Q000494:pharmacology; D033921:Vesicular Transport Proteins
D002352:Carrier Proteins; D051275:Glucose Transporter Type 4; D007328:Insulin; D007329:Insulin Antagonists; D008565:Membrane Proteins; D009004:Monosaccharide Transport Proteins; D051938:Munc18 Proteins; D009124:Muscle Proteins; D009419:Nerve Tissue Proteins; D011506:Proteins; D050765:Qa-SNARE Proteins; D050766:Qb-SNARE Proteins; D050767:Qc-SNARE Proteins; C100493:SNAP23 protein, human; D050600:SNARE Proteins; C495693:Slc2a4 protein, mouse; C107017:Snap23 protein, mouse; C497941:Stxbp2 protein, mouse; C497943:Stxbp3 protein, mouse; D033921:Vesicular Transport Proteins; D013012:Sorbitol; D005947:Glucose