The tetraspan protein EMP2 modulates the surface expression of caveolins and glycosylphosphatidyl inositol-linked proteins.
The tetraspan protein EMP2 modulates the surface expression of caveolins and glycosylphosphatidyl inositol-linked proteins.
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DOI：
10.1091/mbc.e03-07-0488
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发表时间：
2004-05
影响因子：
3.3
通讯作者：
M. Wadehra;L. Goodglick;J. Braun
中科院分区：
文献类型：
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作者：
M. Wadehra;L. Goodglick;J. Braun
小凹是脂筏的一个子集，富含鞘糖脂和富含胆固醇的结构域，但选择性地缺乏糖基磷脂酰肌醇锚定蛋白 (GPI-AP)。小窝蛋白是小窝的组织成分，但其他类别脂筏的相应蛋白质尚不清楚。上皮膜蛋白 2 (EMP2) 是四次跨膜超家族的成员，可促进某些整合素的质膜递送。在这项研究中，我们通过激光共聚焦显微镜发现 EMP2 与 GPI-AP 相关（通过 GPI-AP 结合细菌毒素溶血素原检测到）。生化膜分级分离和甲基-β-环糊精处理证明这种关联发生在脂筏内。 EMP2 与含有小窝蛋白的膜结构无关，NIH3T3 细胞中 EMP2 的重组过表达会降低小窝蛋白 1 和小窝蛋白 2 蛋白水平，同时增加 GPI-AP 的表面表达。相反，特异性切割 EMP2 转录物的核酶构建体会减少表面 GPI-AP 并增加小窝蛋白的表达。这些发现表明，EMP2 促进携带 GPI-AP 的脂筏的形成和表面运输，并减少小窝蛋白表达，导致小窝形成受损。
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 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.