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J. Biol. Chem., Vol. 280, Issue 39, 33536-33540, September 30, 2005

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Insulin and Angiotensin II Induce the Translocation of Scavenger Receptor Class B, Type I from Intracellular Sites to the Plasma Membrane of Adipocytes^*

From the INSERM U671, Université Pierre et Marie Curie, Institut Biomédical des Cordeliers, 15 Rue de l'École de Médecine, 75006 Paris, France

Scavenger receptor class B, type I (SR-BI) mediates the selective uptake of lipids from high density lipoproteins and is expressed in several types of tissues. However, to date little is known about its role in adipocytes. In this study, we investigated the cellular distribution of SR-BI in 3T3-L1 adipocytes and its regulation by hormones known to increase lipid storage such as angiotensin II (Ang II) and insulin. SR-BI was mainly distributed in the cytoplasm as determined by laser-scanning confocal analysis of the immunofluorescence labeling of SR-BI or the study of an enhanced green fluorescent protein-tagged SR-BI fusion protein. Exposure of cells to either insulin or Ang II (1-2 h) induced the mobilization of SR-BI from intracellular pools to the plasma membrane. This was further confirmed by Western blotting on purified plasma membrane and by fluorescence-activated cell sorter analysis of the SR-BI receptor. Similar results were also observed in primary adipocytes. We also demonstrated that, in the presence of either insulin or Ang II, SR-BI translocation to the cell membrane is functional, because insulin and Ang II induced a significant increase in the high density lipoprotein-delivered 22-(N-7-nitrobenz-2-oxa-1,3-diazo-4-yl)-amino-23,24-bisnor-5-cholen-3-ol uptake and in total cholesterol content. These data demonstrate that SR-BI can be acutely mobilized from intracellular stores to the cell surface by insulin or Ang II, two hormones that exert lipogenic effects in adipocytes. This suggests that SR-BI might participate in the storage of lipids in the adipose tissue.

Received for publication, March 3, 2005 , and in revised form, July 19, 2005.

^* 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 data in the form of a video presentation of EGFP-SR-BI traffic in living 3T3-L1 adipocytes.

¹ To whom correspondence should be addressed. Tel.: 33-1-42346923; Fax: 33-1-40518586; E-mail: dagher{at}ccr.jussieu.fr.

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