Isolation of a human cDNA of urokinase and its expression in COS-1 cells.

The cDNA encoding human urokinase (UK) has been isolated from a cDNA library prepared from human normal fibroblast (WI38) cells, which had been stimulated by endothelial cell growth factor and heparin. This cDNA was sequenced and found to contain a few silent substitutions, thus encoding the same amino acids as deduced from the published genomic sequence of UK. After modification, the cDNA of UK was inserted into a transient expression vector and used to transfect COS-1 cells. The recombinant UK protein (rUK) in the serum-free medium of transfected COS-1 cells was characterized by biochemical and functional assays. These studies indicated that rUK from COS-1 cells is glycosylated, enzymatically active, and very similar to native single-chain plasminogen activator (scuPA). Therefore, such rUK can be a convenient source of scuPA for any further studies.