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

The effect of transforming growth factor-beta(1) (TGF-beta(1)) and interfer on-gamma (IFN-gamma) was studied on urokinase receptor (uPAR) expression of cultured human retinal pigment epithelial (RPE) cells. Human RPE cells wer e incubated with 1, 5 or 10 ng/ml of TGF-beta(1) or with 10, 100 or 1,000 I U/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-beta(1) paralleled enhanced uPAR level at the cell sur face and in conditioned medium. TGF-beta appeared to induce also membrane-b ound uPA activity and the release of active plasminogen activator inhibitor -1, indicating that TGF-beta has the potential to regulate plasminogen acti vation 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 T GF-beta regulates the pericellular proteolysis in RPE cells by increasing u PAR expression.