Abstract
Purpose: :
The retinal pigment epithelium (RPE) plays an important role in proliferative vitreoretinopathy (PVR), an aberrant wound-healing process caused in part by RPE cell migration, membrane formation, and contractile cellular forces leading to tractional retinal detachment. An in vitro model of PVR, collagen gel contraction by RPE, requires integrin engagement followed by FAK activation which can be modulated by epithelial membrane protein 2 (EMP2). This study explored the relationship between EMP2 and FAK activation.
Methods: :
FAK, p-FAK, and alpha-smooth muscle actin expression was assessed in ARPE-19 cells by Western blot. Co-immunoprecipitation (co-IP) and confocal microscopy were used to evaluate the physical association of EMP2 and FAK. Confocal microscopy also was used to visualize FAK protein expression, focal adhesion distribution, and F-actin expression. Cellular adhesion was evaluated using a collagen substrate.
Results: :
EMP2 and FAK are physically associated, evidenced by co-immunoprecipitation and immunofluorescent co-localization. Increased EMP2 expression led to greater and more sustained FAK activation (P=.0003), and enhanced FAK phosphorylation at all measured sites. Increased EMP2 was also associated with altered distribution of focal adhesions, changes in actin organization, and increased α-sma expression. Adherence to a collagen coated surface was increased in EMP2-overexpressing cells (P=.0001).
Conclusions: :
EMP2 supports greater contractile cellular capacity by regulating FAK activity through a physical association with FAK. Altering EMP2 levels has a direct affect on FAK regulated cellular functions such as actin organization, actin composition, focal adhesion distribution, and cellular adhesive capacity. Understanding the mechanism that EMP2 regulates collagen gel contraction through FAK in the RPE may provide new targets for therapeutic intervention in PVR.
Keywords: signal transduction • proliferative vitreoretinopathy • retinal pigment epithelium