Characterization of single chain urokinase-type plasminogen activator with a novel amino-acid substitution in the kringle structure.

ECV304 is a cell line established by a spontaneous transformation of endothelial cells of a human umbilical vein. It was shown that ECV304 secretes single chain urokinase-type plasminogen activator (scu-PA). A subclone, ECV304 clone 15, was obtained by acclimatization of the parental clone to serum-free medium followed by limiting dilution. The clone was found to produce approximately five times as much scu-PA (≈ 20 IU/106 cells per day) as the parental clone after a 40 days' culture. Though the biochemical characteristics of the purified scu-PA were indistinguishable from those of the native scu-PA, it had a lower affinity for fibrin clots under the employed conditions. Molecular cloning of a cDNA encoding the scu-PA has identified a novel substitution from C to T in the nucleotide sequence encoding the kringle structure. The substitution resulted in an alteration from Pro (CCG) to Len (CTG) at amino-acid position 121, which may be directly or indirectly involved in the decrease in the apparent affinity.