The signal transduction pathway leading from the insulin receptor to stimulate the fusion of vesicles containing the glucose transporter GLUT4 with the plasma membrane in adipocytes and muscle cells is not completely understood. Current evidence suggests that in addition to the Rab GTPase-activating protein AS160, at least one other substrate of Akt (also called protein kinase B), which is as yet unidentified, is required. Sec8 is a component of the exocyst complex that has been previously implicated in GLUT4 trafficking. In the present study, we report that insulin stimulates the phosphorylation of Sec8 on Ser-32 in 3T3-L1 adipocytes. On the basis of the sequence around Ser-32 and the finding that phosphorylation is inhibited by the PI3K (phosphoinositide 3-kinase) inhibitor wortmannin, it is likely that Akt is the kinase for Ser-32. We examined the possible role of Ser-32 phosphorylation in the insulin-stimulated trafficking of GLUT4, as well as the TfR (transferrin receptor), to the plasma membrane by determining the effects of overexpression of the non-phosphorylatable S32A mutant of Sec8 and the phosphomimetic S32E mutant of Sec8. Substantial overexpression of both mutants had no effect on the amount of GLUT4 or TfR at the cell surface in either the untreated or insulin-treated states. These results indicate that insulin-stimulated phosphorylation of Sec8 is not part of the mechanism by which insulin enhances the fusion of vesicles with the plasma membrane.
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Research Article|
May 07 2009
Insulin stimulates the phosphorylation of the exocyst protein Sec8 in adipocytes
Patrick D. Lyons;
Patrick D. Lyons
*Department of Biochemistry, Dartmouth Medical School, Hanover, NH 03755 U.S.A.
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Grantley R. Peck;
Grantley R. Peck
*Department of Biochemistry, Dartmouth Medical School, Hanover, NH 03755 U.S.A.
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Arminja N. Kettenbach;
Arminja N. Kettenbach
†Department of Genetics and Norris Cotton Cancer Center, Dartmouth Medical School, Lebanon, NH 03756, U.S.A.
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Scott A. Gerber;
Scott A. Gerber
†Department of Genetics and Norris Cotton Cancer Center, Dartmouth Medical School, Lebanon, NH 03756, U.S.A.
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Liya Roudaia;
Liya Roudaia
*Department of Biochemistry, Dartmouth Medical School, Hanover, NH 03755 U.S.A.
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Gustav E. Lienhard
Gustav E. Lienhard
1
*Department of Biochemistry, Dartmouth Medical School, Hanover, NH 03755 U.S.A.
1To whom any correspondence should be addressed (email gustav.e.lienhard@dartmouth.edu).
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Publisher: Portland Press Ltd
Received:
November 10 2008
Accepted:
November 13 2008
Accepted Manuscript online:
November 13 2008
Online ISSN: 1573-4935
Print ISSN: 0144-8463
© The Authors Journal compilation © 2009 Biochemical Society
2009
Biosci Rep (2009) 29 (4): 229–235.
Article history
Received:
November 10 2008
Accepted:
November 13 2008
Accepted Manuscript online:
November 13 2008
Citation
Patrick D. Lyons, Grantley R. Peck, Arminja N. Kettenbach, Scott A. Gerber, Liya Roudaia, Gustav E. Lienhard; Insulin stimulates the phosphorylation of the exocyst protein Sec8 in adipocytes. Biosci Rep 1 August 2009; 29 (4): 229–235. doi: https://doi.org/10.1042/BSR20080162
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