TUMOR CELL-CONDITIONED MEDIUM STIMULATES EXPRESSION OF THE UROKINASE RECEPTOR IN VASCULAR ENDOTHELIAL-CELLS

We have previously reported that culture medium conditioned by human S K-Hep1 hepatoma cells or mouse S180 sarcoma cells induces in vitro ang iogenesis and stimulates production of urokinase plasminogen activator (uPA) in vascular endothelial cells. These activities are mediated by a 3.5-10 kDa, heparin-binding peptide that upregulates endothelial ce ll expression of basic fibroblast growth factor (bFGF; Peverali et al. , 1994, J. Cell. Physiol. 161:1-14.) We now report that SK-Hep1 or S18 0 cell-conditioned medium rapidly induces a 4- to 5-fold increase in c ell-bound uPA activity and in the high-affinity binding of I-125-prouP A to vascular endothelial cells. Ligand blotting and purification expe riments show an equivalent increase in the synthesis of a cell surface protein corresponding to the endothelial cell uPA receptor (uPAR) on the basis of M(r) (45-50 kDa) and sensitivity to phosphatidylinositol- specific phospholipase C (PI-PLC). The tumor cell-conditioned media al so upregulate uPAR mRNA levels in endothelial cells. Thus, the increas e in uPA binding capacity of endothelial cells is mediated by an incre ased expression of uPAR. The uPAR-inducing activity of SK-Hep1 or S180 cell-conditioned medium is not neutralized by antibodies to bFGF, and is associated with a peptide that has a M(r) higher than 10 kDa and n o affinity for heparin. Therefore, it appears to be distinct from the bFGF/uPA-inducing factor secreted by the same cells, and from other he parin-binding cytokines that upregulate uPAR expression in endothelial cells. (C) 1996 Wiley-Liss, Inc.