Wadehra Madhuri, Iyer Ramaswamy, Goodglick Lee, Braun Jonathan
Molecular Biology Institute, The David Geffen School of Medicine at UCLA and Jonsson Comprehensive Cancer Center, 108ee Le Conte Avenue, Los Angeles, CA 90095, USA.
J Biol Chem. 2002 Oct 25;277(43):41094-100. doi: 10.1074/jbc.M206868200. Epub 2002 Aug 19.
The growth arrest-specific-3 (GAS3)/PMP22 proteins are members of the four-transmembrane (tetraspan) superfamily. Although the function of these proteins is poorly understood, GAS3/PMP22 proteins have been implicated in the control of growth and progression of certain cancers. Epithelial membrane protein-2 (EMP2), a GAS3/PMP22 family member, was recently identified as a putative tumor suppressor gene. Here, we addressed the normal function of EMP2 by testing the prediction that it influences integrin-related cell functions. We observed that EMP2 associates with the beta(1) integrin subunit. Co-immunoprecipitation and immunodepletion experiments indicated that approximately 60% of beta(1) integrins and EMP2 can be isolated in common protein complexes. Whereas this association between EMP2 and beta(1) integrin may be direct or indirect, it has features of integrin heterodimer selectivity. Thus, by laser confocal microscopy, EMP2 colocalized with alpha(6)beta(1) but not alpha(5)beta(1) integrin. Increased expression of EMP2 also influenced the integrin heterodimer repertoire present on the plasma membrane. EMP2 specifically increased the surface expression of the alpha(6)beta(1) integrin while decreasing that of the alpha(5)beta(1) protein. Reciprocally, reduction in EMP2 expression using a specific ribozyme decreased surface expression of alpha(6)beta(1) integrin. Accordingly, these EMP2-mediated changes resulted in a dramatic alteration in cellular adhesion to extracellular matrix proteins. This study demonstrates for the first time the interaction of a GAS3/PMP22 family member with an integrin protein and suggests that such interactions and their functional consequences are a physiologic role of GAS3/PMP22 proteins.
生长停滞特异性蛋白3（GAS3）/外周髓鞘蛋白22（PMP22）属于四次跨膜（四跨膜）超家族。尽管对这些蛋白的功能了解甚少，但GAS3/PMP22蛋白与某些癌症的生长和进展调控有关。上皮膜蛋白2（EMP2）是GAS3/PMP22家族成员，最近被鉴定为一种假定的肿瘤抑制基因。在此，我们通过测试其影响整合素相关细胞功能的预测来研究EMP2的正常功能。我们观察到EMP2与β1整合素亚基相关联。免疫共沉淀和免疫耗竭实验表明，约60%的β1整合素和EMP2可在共同的蛋白复合物中分离出来。虽然EMP2与β1整合素之间的这种关联可能是直接的或间接的，但它具有整合素异二聚体选择性的特征。因此，通过激光共聚焦显微镜观察，EMP2与α6β1整合素共定位，但不与α5β1整合素共定位。EMP2表达的增加也影响了质膜上存在的整合素异二聚体组成。EMP2特异性增加了α6β1整合素的表面表达，同时降低了α5β1蛋白的表面表达。相反，使用特异性核酶降低EMP2表达会降低α6β1整合素的表面表达。因此，这些由EMP2介导的变化导致细胞与细胞外基质蛋白的黏附发生显著改变。本研究首次证明了GAS3/PMP22家族成员与整合素蛋白之间的相互作用，并表明这种相互作用及其功能后果是GAS3/PMP22蛋白的生理作用。
