Comparison of integrin expression between the rat Retinal Pigment Epithelium (RPE) and the RPE-J cell line

Purpose. To determine if RPE-J cells can serve as a model system to study interactions of RPE apical domains with the interphotoreceptor matrix, the pattern of integrin expression in the rat RPE in vivo and in cultured RPE-J cells were analyzed. Methods. Integrin subunit expression was studied by western blot detection. Laser scanning confocal microscopy was used to show subcellular protein distributions. These data were confirmed by biotin polarity assays. Results. We show that integrin subunits alpha 3, alpha 6, alpha v, and alpha 9 as well as beta 1 and beta 3 of predicted molecular weights can be detected under non-reducing conditions in immunoblots of whole cell lysates of RPE-J cells. Alpha 4, alpha 5 and beta 4 integrins were not found in western blots of these lysates. In the adult rat RPE, all subunits expressed in RPE-J cells were detected as well. Steady-state polarity of integrin receptors has been determined in RPE-J cells and the adult rat RPE. Conclusions. We have compared the distribution of integrin receptors in RPE cells and the adult rat RPE. The presence of integrin receptors in distinct membrane domains of epithelial cells suggests that they, there, establish cell-substrate interactions. In the eye, the apical surface of the RPE interacts with photoreceptors through the interphotoreceptor matrix. Thus, identification of specific integrin receptors in the apical plasma membrane of RPE is a prerequisite to characterize retinal adhesion. Here, we show that RPE-J cells provide a valuable tool to initiate these studies.