CYTOKINE EFFECT ON FIBRONECTIN RELEASE BY RETINAL-PIGMENT EPITHELIAL-CELLS

Because fibronectin (FN) is known to be present in membranes in prolif erative vitreoretinopathy, we sought to identify cytokines that regula te the release of FN by retinal pigment epithelial cells (RPE). Levels of FN in the supernatant of cultured human RPE cells were quantified with an ELISA, after which the cells were stimulated with human recomb inant cytokines, interleukin-1 beta (IL-1 beta), tumor necrosis factor alpha (TNF alpha), interleukin-6 (IL-6), interferon gamma (INF-gamma) , transforming growth factor beta 1 and 2 (TGF-beta), and phorbol myri state acetate (PMA). Protein kinase C (PKC) was blocked by 2 nM calpho stin C or 1 mM staurosporine. RPE cells released FN into the supernata nt constitutively. TGF-beta(1) and TGF-beta(2) upregulated the FN rele ase in a dose- and time-dependent manner. The other cytokines tested w ere without effect. In combination, INF-gamma and IL-1 beta reduced th e effect of TGF-beta. PMA, which is a PKC activator, also increased th e release of FN in a dose-dependent manner. Blocking of PKC with speci fic inhibitors abolished the effects of TGF-beta and PMA. The results show that TGF-beta is a potent stimulator of FN release by RPE cells, and exerts its effects via signal transduction involving PKC. Its effe ct is reduced by INF-gamma.