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J. Biol. Chem., Vol. 282, Issue 36, 26542-26551, September 7, 2007

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The Tetraspan Protein EMP2 Regulates Expression of Caveolin-1^*

Ashley Forbes¹, Madhuri Wadehra¹, Sergei Mareninov, Shawn Morales, Kaori Shimazaki, Lynn K. Gordon^¶||, and Jonathan Braun²

From the Molecular Biology Institute, Department of Pathology and Laboratory Medicine, David Geffen School of Medicine, and ^¶Department of Ophthalmology, UCLA, Los Angeles, California 90095 and the ^||Department of Surgery, Greater Los Angeles Veterans Affairs Healthcare System, Los Angeles, California 90099

Caveolin-1 is the primary component of caveolae and functions in a variety of intracellular activities, including membrane trafficking and signal transduction. EMP2 (epithelial membrane protein 2) is a tetraspan protein recently identified as a novel regulator of caveolin-1 expression. In this study, we analyzed the mechanism of EMP2-mediated caveolin-1 regulation. In NIH 3T3 cells and in the human retinal pigment epithelium cell line (ARPE-19), EMP2 regulates caveolin-1 transcription and more substantially its protein levels. EMP2-mediated down-regulation of caveolin-1 does not affect caveolin-1 translational efficiency, phosphorylation, or proteasome-mediated degradation. Analysis of caveolin-1 protein half-life indicates the EMP2-mediated loss of caveolin-1 occurs rapidly. Protease inhibition and laser confocal microscopy associates this fate with specific intracellular compartmentalization, including early lysosomal delivery. These findings elucidate a new mechanism of caveolin-1 regulation and define an additional role for EMP2 as a key regulator of cell membrane composition.

Received for publication, March 12, 2007 , and in revised form, June 8, 2007.

^* This work was supported by National Institutes of Health Grants GM7185 (to A. F.), AI52031 (to S. M.), HD48540 (to J. B.), and CA9120 (to M. W.), the Lalor Foundation (to M. W.), the Giannini Family Foundation (to M. W.), and the Ruzic Foundation (to J. B.). 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.

¹ Both authors contributed equally to this work.

² To whom correspondence should be addressed: Pathology and Laboratory Medicine, 13-222 Center for Health Sciences, Geffen School of Medicine, UCLA, Los Angeles, CA 90095. Tel.: 310-794-7953; Fax: 310-825-5674; E-mail: jbraun{at}mednet.ucla.edu.

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