Partial characterization of novel serine proteinase inhibitors from human umbilical vein endothelial cells.

Serine proteinase inhibitors play major roles in physiological and pathophysiological processes such as angiogenesis, intravascular fibrinolysis, wound healing, and tumor invasion, and metastasis. Here, we report that human umbilical vein endothelial cells (HUVEC) synthesize three inhibitors (33,000, 31,000, and 27,000 Da) which inhibit degradation of gelatin or casein by trypsin, elastase, plasmin, and alpha-chymotrypsin. The 33- and 31-kDa inhibitors were constitutively found in the cell lysate and extracellular matrix, but not in the conditioned medium of HUVEC. Following treatment with phorbol 12-myristate-13-acetate (PMA), all the three inhibitors were expressed in the CM and increased activity was found in cell lysates and extracellular matrix. The inhibitors were not detected in PMA-treated cells in the presence of cycloheximide or actinomycin D. The inhibitors specifically bound to trypsin and were recovered from trypsin affinity column as smaller-sized inhibitors without loss of antitrypsin activity. Polyclonal antibodies to inter-alpha-trypsin inhibitor did not cross-react with the 33-, 31-, and 27-kDa inhibitors. These results suggest that HUVEC synthesize and secrete novel 33-, 31-, and 27-kDa serine proteinase inhibitors.