Transforming growth factor beta induces urokinase receptor expression in cultured retinal pigment epithelial cells

The effect of transforming growth factor-beta1 (TGF-beta1) and interferon-gamma (IFN-gamma) was studied on urokinase receptor (uPAR) expression of cultured human retinal pigment epithelial (RPE) cells. Human RPE cells were incubated with 1, 5 or 10 ng/ml of TGF-beta1 or with 10, 100 or 1,000 IU/ml of IFN-gamma to measure total cellular uPAR protein and released uPAR by enzyme immunoassay. uPAR at cell surface was measured by flow cytometric analysis at 8, 12, 24 and 48 h. uPAR mRNA levels were assayed by Northern blotting at 2, 6, 12 and 24 h. The increase in uPAR gene expression in RPE cells exposed to TGF-beta1 paralleled enhanced uPAR level at the cell surface and in conditioned medium. TGF-beta appeared to induce also membrane-bound uPA activity and the release of active plasminogen activator inhibitor-1, indicating that TGF-beta has the potential to regulate plasminogen activation at the RPE cell surface. The increase in uPAR gene expression by IFN-gamma did not seem to translate into the protein level. We conclude that TGF-beta regulates the pericellular proteolysis in RPE cells by increasing uPAR expression.