Rewiring integrin-mediated signaling and cellular response with the peripheral myelin protein 22 and epithelial membrane protein 2 components of the tetraspan web.

Purpose: Integrin-mediated collagen gel contraction by ARPE-19 is an in vitro model for proliferative vitreoretinopathy (PVR), an aberrant wound healing response after retinal detachment or ocular trauma. Expression of the tetraspan protein epithelial membrane protein 2 (EMP2) controls gel contraction through FAK activation. Peripheral myelin protein 22 (PMP22), another member of the tetraspan web, is closely related to EMP2. The purpose of this study was to determine whether PMP22 also controls the contractile phase associated with PVR.

Methods: Integrin expression, adhesion, and protein expression were assessed, respectively, through flow cytometry, binding to collagen types I and IV, and Western blot analysis. Collagen gel contraction was assessed using an in vitro assay.

Results: Overexpression of PMP22 in ARPE-19 cells (ARPE-19/PMP22) resulted in increased collagen adhesion. Gel contraction, however, was reduced by greater than 50% in ARPE-19/PMP22 cells (P < 0.001). In contrast to the FAK activation observed by increasing EMP2 expression, PMP22 overexpression led to increased AKT activation. The decrease in gel contraction by the ARPE-19/PMP22 cells was partially reversed through either PMP22 siRNA or by blockade of AKT.

Conclusions: Relative expression of EMP2 or PMP22 within the tetraspan web drives a cellular response toward a FAK- or AKT-dependent pathway, respectively. EMP2 and PMP22 differentially regulate collagen gel contraction in the ARPE-19 cell line. The implication of this finding adds a new dimension to the concept of the tetraspan web, in which the abundance of individual tetraspan family members differentially regulates signal transduction and the downstream cellular response.