Plasmin-independent gelatinase B (matrix metalloproteinase-9) release by monocytes under the influence of urokinase

It is shown that the release of matrix metalloproteinase-9 (gelatinase B) b y THP-1 and U937 cells into conditioned media is increased under the action of recombinant single-chain Urokinase. This effect is not accompanied by p roteolytic activation of gelatinase B and is related to release of a pro-fo rm of the enzyme. The action of urokinase on monocytes is time-dependent an d becomes significant 12-24 h after the beginning of cell incubation. The d ependence of the effect on the concentration of urokinase is characterized by half-maximum at about 20 nM and saturation at about 200 nM. The urokinas e-induced gelatinase B release is not dependent on the action of plasmin be cause plasmin inhibitors aprotinin and alpha (2)-antiplasmin do not abolish this action. Additionally, tissue type plasminogen activator does not indu ce gelatinase B release by monocytes as observed under the action of urokin ase. Nevertheless, the catalytic activity of urokinase participates in the development of the observed effect because it is significantly depressed by the natural urokinase inhibitor PAI- 1. The effect of urokinase is complet ely abolished by actinomycin D and cycloheximide, indicating the participat ion of transcription and translation processes in its development.