The tetraspan protein epithelial membrane protein-2 interacts with β1 integrins and regulates adhesion

Abstract

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 β1 integrin subunit. Co-immunoprecipitation and immunodepletion experiments indicated that ∼60% of β1 integrins and EMP2 can be isolated in common protein complexes. Whereas this association between EMP2 and β1 integrin may be direct or indirect, it has features of integrin heterodimer selectivity. Thus, by laser confocal microscopy, EMP2 colocalized with α6β1 but not α5β1 integrin. Increased expression of EMP2 also influenced the integrin heterodimer repertoire present on the plasma membrane. EMP2 specifically increased the surface expression of the α6β1 integrin while decreasing that of the α5β1 protein. Reciprocally, reduction in EMP2 expression using a specific ribozyme decreased surface expression of α6β1 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.