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MBC in Press, published online ahead of print February 20, 2004
Mol. Biol. Cell 10.1091/mbc.E03-07-0488

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Submitted on July 11, 2003
Revised on November 14, 2003
Accepted on December 9, 2003

The Tetraspan Protein EMP2 Modulates the Surface Expression of Caveolins and GPI Linked Proteins

Madhuri Wadehra1, Lee Goodglick2, and Jonathan Braun3*

1 Molecular Biology Institute, University of California at Los Angeles, Los Angeles, California 90095
2 Department of Pathology and Laboratory Medicine, and Jonsson Comprehensive Cancer Center, University of California at Los Angeles, Los Angeles, California 90095
3 Molecular Biology Institute; Department of Pathology and Laboratory Medicine, and Jonsson Comprehensive Cancer Center, University of California at Los Angeles, Los Angeles, California 90095

* Corresponding author. E-mail address: jbraun{at}mednet.ucla.edu.

Caveolae are a subset of lipid rafts enriched in glycosphingolipids and cholesterol rich domains, but selectively lacking glycosylphosphatidyl inositol-anchored proteins (GPI-APs). Caveolin proteins are the organizing component of caveolae, but the corresponding proteins for other classes of lipid rafts are poorly defined. Epithelial membrane protein-2 (EMP2), a member of the four transmembrane superfamily, facilitates plasma membrane delivery of certain integrins. In this study, we found by laser confocal microscopy that EMP2 was associated with GPI-APs (detected by the GPI-AP binding bacterial toxin proaerolysin). Biochemical membrane fractionation and methyl-{beta}-cyclodextrin (M{beta}CD) treatment demonstrated that this association occurred within lipid rafts. EMP2 did not associate with caveolin-bearing membrane structures, and recombinant overexpression of EMP2 in NIH3T3 cells decreased caveolin-1 and caveolin-2 protein levels while increasing the surface expression of GPI-APs. Conversely, a ribozyme construct that specifically cleaves the EMP2 transcript reduced surface GPI-APs and increased caveolin protein expression. These findings suggest that EMP2 facilitates the formation and surface trafficking of lipid rafts bearing GPI-APs, and reduces caveolin expression, resulting in impaired formation of caveolae.




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