CYTOKINES AND SERUM CAUSE ALPHA(2)BETA(1) INTEGRIN-MEDIATED CONTRACTION OF COLLAGEN GELS BY CULTURED RETINAL-PIGMENT EPITHELIAL-CELLS

Purpose. Integrins, heterodimeric cell surface glycoproteins, are involved in cell-substratum and cell-cell interactions. The role of these molecules in cytokine-mediated contraction of extracellular matrix by retinal pigment epithelial cells has been investigated in a model system that may mimic epiretinal membrane contraction during retinal detachment in proliferative vitreoretinopathy. Methods. Retinal pigment epithelial cells were cultured on three-dimensional collagen gels that they cause to contract. The involvement of new protein synthesis and C-kinase-mediated signal transduction were studied using specific inhibitors. Cell surface integrins synthesized by pigment epithelial cells were identified using immunofluorescence, and the same antibodies were used in gel contraction assays to identify the integrin species responsible for force transduction. Results. Contraction of collagen type I gels was small without cytokines but was greatly enhanced in the presence of serum or IL1 plus TGF beta. It was dependent on new protein synthesis. Contraction induced by the combination of cytokines was dependent on active protein kinases, whereas that induced by serum was not because only the former was inhibited by staurosporine, a C-kinase inhibitor. Pigment epithelial cells were found to produce beta(1), alpha(2), and alpha, integrins, but only alpha(2) and beta(1) appeared to participate in the contraction process because only antibodies against these integrins inhibited contraction. Conclusions. Retinal pigment epithelial cells contract an extracellular matrix in vitro in a manner similar to epiretinal membrane contraction in vivo. This contraction is mediated via cell surface glycoproteins of the integrin family that bind directly to extracellular matrix molecules.