Retinal Pigment Epithelial Cells Secrete Urokinase-Type Plasminogen Activator and Its Inhibitor PAI-1

Abstract

Secretion of plasminogen activators and their inhibitors was examined in cultures of human retinal pigment epithelial (RPE) cells. The methods employed were zymography and reverse zymography, solid-phase immunocapture assay, metabolic labeling followed by immunoprecipitation, and immunofluorescence. The results showed that these cells produce urokinase-type plasminogen activator (u-PA) and a plasminogen activator inhibitor (PAI) which is immunologically and biochemically similar to PAI-1. Tissue-type plasminogen activator activity (t-PA) was not detected, but we detected small amounts of t-PA in an inactive complex with inhibitor in RPE cell-conditioned media. We conclude that RPE cells have the potential to utilize u-PA-catalyzed plasminogen activation which is subject to regulation by PAI-1. These results may have a bearing on the pathogenesis of proliferative retinal diseases.

Alpha- and Gamma-lnterferon Inhibit Plasminogen Activator Inhibitor-1 Gene Expression in Human Retinal Pigment Epithelial Cells

“…Although not documented here, the pre dominant type of PAI produced by human RPE cells is PAI-1, identified with monoclon al antibody which neutralizes the inhibitory activity of PAI-1 [17].…”

“…Plasminogen-activation-mediated proteo lysis in human RPE cells seems to be affected by various factors, including the number of cell passages [17], phagocytosis of microbeads [37], certain growth factors [38], and retinoids [39], Our results indicate that both IFN-a and IFN-y have a potent stimulatory effect on u-PA-mediated plasminogen activation by human RPE cells in culture.…”

“…It does not interact with single-chain u-PA, which has lit tle or no enzymatic activity [13]. Human RPE cells in culture have been shown to produce active u-PA and its inhibitor PAI-1 [16,17], As proteolytic degradation of the extracel lular matrix is a prerequisite for cellular pro liferation and migration in tissues, we wanted to study the effect of IFNs on the plasmino gen-mediated proteolytic cascade of RPE cells in culture. We now report that both IFN-a and IFN-y inhibit PAI-1 gene expression by human RPE cells in culture.…”

Transforming Growth Factor Beta Induces Urokinase Receptor Expression in Cultured Retinal Pigment Epithelial Cells

“…ProuPA can be converted to active enzyme by traces of plasmin initiating the plasminogen activation cascade. We have recently demonstrated that uPA staining in cultured human RPE cells was localized to focal contact sites at the leading edges of cultured subconfluent RPE cells [12], a distribution typical of migrating cells [18]. TGF-ß is produced by most cultured cells in a latent form which can be converted to the biologically active molecule by plasmin [19].…”

“…Regulation of uPA and uPAR activity is involved in proliferation, migration and invasive growth of many cell types [8][9][10]. We and others have shown that human RPE cells in culture secrete uPA and its inhibitor PAI-1 [11,12]. We have also reported that interferon-Á (IFN-Á) enhanced uPA activity in RPE cells due to the suppressed PAI-1 mRNA expression [13].…”