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Originally published In Press as doi:10.1074/jbc.M704896200 on September 20, 2007
J. Biol. Chem., Vol. 282, Issue 47, 34139-34147, November 23, 2007
Resistin Is a Key Mediator of Glucose-dependent Insulinotropic Polypeptide (GIP) Stimulation of Lipoprotein Lipase (LPL) Activity in Adipocytes*
Su-Jin Kim,
Cuilan Nian, and
Christopher H. S. McIntosh1
From the
Department of Cellular and Physiological Sciences and the Diabetes Research Group, Life Sciences Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada
Studies on the physiological roles of the incretin hormone, glucose-dependent insulinotropic polypeptide (GIP) have largely focused on its insulinotropic action and ability to regulate -cell mass. In previous studies on the stimulatory effect of GIP on adipocyte lipoprotein lipase (LPL), a pathway was identified involving increased phosphorylation of protein kinase B (PKB) and reduced phosphorylation of LKB1 and AMP-activated protein kinase (AMPK). The slow time of onset of the responses suggested that GIP may have induced release of an intermediary molecule, and the current studies focused on the possible contribution of the adipokine resistin. In differentiated 3T3-L1 adipocytes, GIP, in the presence of insulin, increased resistin secretion through a pathway involving p38 mitogen-activated protein kinase (p38 MAPK) and the stress-activated protein kinase/Jun amino-terminal kinase (SAPK/JNK). The other major incretin hormone, glucagon-like peptide-1 (GLP-1), exhibited no significant effects. Chronic elevation of circulating GIP levels in the Vancouver Diabetic Fatty (VDF) Zucker rat resulted in increases in circulating resistin levels and activation of p38 MAPK or SAPK/JNK in epididymal fat tissue, suggesting the existence of identical pathways in vivo as well as in vitro. Administration of resistin to 3T3-L1 adipocytes mimicked the effects of GIP on the PKB/LKB1/AMPK/LPL pathway: increasing phosphorylation of PKB, reducing levels of phosphorylated LKB1 and AMPK, and increasing LPL activity. Knockdown of resistin using RNA interference attenuated the effect of GIP on the PKB/LKB1/AMPK/LPL pathway in 3T3-L1 adipocytes, supporting a role for resistin as a mediator.
Received for publication, June 13, 2007
, and in revised form, September 10, 2007.
* This work was supported by grants to C.H.S.M. from the Canadian Institutes of Health Research and the Canadian Foundation for Innovation. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. S1–S4.
1 To whom correspondence should be addressed: 2350 Health Sciences Mall, Vancouver, British Columbia V6T 1Z3, Canada. Tel.: 604-822-3088; Fax: 604-822-6048; E-mail: mcintoch{at}interchange.ubc.ca.

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Copyright © 2007 by the American Society for Biochemistry and Molecular Biology.
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