Adipocytes from Munc18c-null mice show increased sensitivity to insulin-stimulated GLUT4 externalization
Hajime Kanda, Yoshikazu Tamori, Hiroaki Shinoda, Mari Yoshikawa, Motoyoshi Sakaue, Jun Udagawa, Hiroki Otani, Fumi Tashiro, Jun-ichi Miyazaki, Masato Kasuga
Hajime Kanda, Yoshikazu Tamori, Hiroaki Shinoda, Mari Yoshikawa, Motoyoshi Sakaue, Jun Udagawa, Hiroki Otani, Fumi Tashiro, Jun-ichi Miyazaki, Masato Kasuga
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Article Metabolism

Adipocytes from Munc18c-null mice show increased sensitivity to insulin-stimulated GLUT4 externalization

Abstract

Insulin-stimulated glucose uptake in adipocytes is mediated by translocation of vesicles containing the glucose transporter GLUT4 from intracellular storage sites to the cell periphery and the subsequent fusion of these vesicles with the plasma membrane, resulting in the externalization of GLUT4. Fusion of the GLUT4-containing vesicles with the plasma membrane is mediated by a soluble N-ethylmaleimide–sensitive factor attachment protein receptor (SNARE) complex consisting of vesicle-associated membrane protein 2 (VAMP2), 23-kDa synaptosomal-associated protein (SNAP23), and syntaxin4. We have now generated mouse embryos deficient in the syntaxin4 binding protein Munc18c and show that the insulin-induced appearance of GLUT4 at the cell surface is enhanced in adipocytes derived from these Munc18c−/− mice compared with that in Munc18c+/+ cells. Wortmannin, an inhibitor of PI3K, inhibited insulin-stimulated GLUT4 externalization, without affecting GLUT4 translocation to the cell periphery, in Munc18c+/+ adipocytes, but it did not affect GLUT4 externalization in Munc18c−/− cells. Phosphatidylinositol 3-phosphate, which induced GLUT4 translocation to the cell periphery without externalization in Munc18c+/+ cells, elicited GLUT4 externalization in Munc18c−/− cells. These findings demonstrate that Munc18c inhibits insulin-stimulated externalization of GLUT4 in a wortmannin-sensitive manner, and they suggest that disruption of the interaction between syntaxin4 and Munc18c in adipocytes might result in enhancement of insulin-stimulated GLUT4 externalization.

Authors

Hajime Kanda, Yoshikazu Tamori, Hiroaki Shinoda, Mari Yoshikawa, Motoyoshi Sakaue, Jun Udagawa, Hiroki Otani, Fumi Tashiro, Jun-ichi Miyazaki, Masato Kasuga

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PI3P-induced externalization of GLUT4 in Munc18c−/− adipocytes. (A) Mun...
PI3P-induced externalization of GLUT4 in Munc18c−/− adipocytes. (A) Munc18c+/+ or Munc18c−/− adipocytes expressing GLUT4-myc7-GFP were exposed for 7 minutes to a mixture of PI3P and polyamine carrier or to the carrier alone and were then analyzed as described in Figure 8A. Scale bar: 10 &––––m. (B–D) Quantitation of GLUT4 movement to the cell periphery (B), of GLUT4 externalization (C), and of the proportion of GLUT4 molecules translocated to the cell periphery that undergo externalization (the percentage of cells with peripheral GFP fluorescence that also show surface PE fluorescence) (D) in experiments similar to that shown in A. Data are mean ± SE of values from 3 independent experiments. *P < 0.01, **P < 0.001 versus the corresponding values for Munc18c+/+ cells.