Regulation of Plasminogen Activator Activity in Human Fibroblastic Cells by Fibrosarcoma Cell-derived Factors1

Low-molecular-weight protein factors (Mr 8,000 to 18,000) from serum-free conditioned medium of human fibrosarcoma (8387) cells reversibly enhanced the secretion of proteinaseinhibitory activity by cultured normal human skin fibroblasts. This inhibitory activity could be absorbed by immobilized plasminogen activator (PA) of urokinase type but not by heparin, and it was sensitive to treatment with sodium dodecyl sulfate. The secretion of a heparin-binding Mr 60,000 proteinase inhibitor, resembling protease nexin, was also detected. Early passages of adult skin fibroblasts do not contain or secrete PA. When cell types se creting this enzyme were tested, the fibrosarcoma-derived fac tors decreased the PA secretion detectable after sodium dodecyl sulfate treatment in all conditioned media of normal and malignant fibroblastic cells examined, including the 8387 cell line itself. However, no effects on the secretion of PA by normal or malig nant cells of epithelioid origin or by melanoma cells were seen. A similar preparation from human epidermoid carcinoma (A431)conditioned medium did not affect the PA activity or secretion of proteinase inhibitors from fibroblastic cells. The ability of sarcoma cells to modulate the production of PA inhibitors is a novel characteristic in the regulation of cellular proteolysis. between different types of cells seem to affect the synthesis rate of PAs (23, 27), and cells secrete factors modulating the release of PA by other cells (7, 11, 14, 25, 30). Inhibitors secreted by several cell types are capable of inhibiting directly the PA reac tion. So far, the best characterized are protease nexins, heparinbinding components released by several types of human and other mammalian cells (20). PA inhibitors, obviously unrelated to protease nexin, have been described in human macrophages (41, 47), in rat hepatoma cells (12), and in human endothelial cells (26). The last one is obviously present also in circulation (22, 48). The regulation of these PA inhibitors in poorly known. The secretion rate of the hepatoma cell inhibitor is modulated by glucocorticoids (12), and the secretion of protease nexin can be increased by treatment of the cultures with phorbol esters, epidermal growth factor, and thrombin (9). In the present study, we report that cultured human 8387 fibrosarcoma cells produce factors that are able to modulate the secretion of PA activity in cultures of fibroblastic cells, by both decreasing the secretion of PA activator and increasing the production of an inhibitory sub stance obviously unrelated to protease nexin. This inhibitor af fects the PA activity in both the sarcoma cells themselves and normal human fibroblasts derived from embryonic tissues.