Epithelial Membrane Protein 2 (EMP2) Controls Collagen Gel Contraction in ARPE-19 Cells by Modulating FAK Activation

¹ Department of Pathology and Laboratory Medicine, University of California, Los Angeles , 650 Charles E. Young Dr. South, Los Angeles, California, 90095, United States; Department of Ophthalmology, University of California, Los Angeles , Los Angeles, California, United States
² Department of Ophthalmology, University of California, Los Angeles, Los Angeles, California, United States
³ Department of Pathology and Laboratory Medicine, University of California, Los Angeles, Los Angeles, California, United States
⁴ Department of Ophthalmology, Jules Stein Eye Institute / UCLA, 100 Stein Plaza, Los Angeles, California, 90095, United States; Department of Surgery, Greater Los Angeles Veterans Affairs Healthcare System, Los Angeles, California, United States

^* To whom correspondence should be addressed. E-mail: shawnmor{at}ucla.edu.

	Abstract

Purpose: Proliferative vitreoretinopathy (PVR) occurs in approximately 10% of patients following retinal detachment. PVR results from a multi-phase process that leads to an aberrant wound-healing strategy with contractile cellular forces and retinal detachment (TRD). Epithelial membrane protein 2 (EMP2) controls cell surface expression and function of integrin isoforms associated with cellular contraction in many cell types. Since EMP2 is highly expressed in retinal pigment epithelium, this study investigates the role of EMP2 in collagen gel contraction. Methods: EMP2 expression was recombinantly modified in the ARPE-19 cell line. Cell surface integrin expression was assessed by flow cytometry. Collagen gel contraction was assessed using an in vitro assay and percent contraction quantified using NIH Image software. Proliferation and migration was measured by BrdU incorporation and a wound healing assay respectively. Cellular invasion was investigated using polycarbonate membranes coated with collagen. Results: EMP2 expression levels correlate positively with the ability to contract collagen gels. As compared to wildtype ARPE-19, cells with increased EMP2 expression exhibited enhanced contraction (p=0.02) and decreased EMP2 expression concomitantly resulted in decreased contraction (p=0.002). EMP2 over expression resulted in reduced proliferation, migration, and integrin 1 and 2 integrin expression. EMP2 overexpression was associated with a 70% increase in FAK activation (p=0.0003) and relative resistance of gel contraction to inhibitors of FAK/Src activation. Conclusions: ARPE-19-mediated collagen gel contraction is a multi-step process which requires integrin ligation and activation of the FAK/Src complex. EMP2 positively modulates collagen gel contraction by ARPE-19 cells through increased FAK activation.

Key Words: cell-matrix interactions, retinal detachment, retinal pigment epithelium