Urokinase-type plasminogen activator-induced monocyte adhesion is modulated by kininogen, kallikrein, factor XII, and plasminogen.

Urokinase-type plasminogen activator (u-PA) was found to induce monocyte adhesion through a u-PA receptor (u-PAR)-mediated cAMP-dependent signal transduction pathway (J. Biol. Chem. 270, 30282-30285, 1995). In the present study, the effects of kininogen, kallikrein, factor XII, and plasminogen on u-PA-induced monocyte adhesion were examined since these proteins are abundant in plasma and closely related to u-PA in fibrinolysis and inflammation. Monocyte adhesion to a standard plastic surface by u-PA was shown to be inhibited by the activated, two-chain forms of kininogen (HKa) and kallikrein. The latter occurred only at higher, though physiological, concentrations and was dependent on its catalytic activity. Monocyte adhesion was promoted by factor XII and plasminogen via a noncatalytic mechanism. The findings indicated that u-PA-induced monocyte adhesion was downregulated by HKa and kallikrein and upregulated by factor XII and plasminogen at physiological concentrations. Therefore, these contact system proteins may be important modulators of u-PA-induced monocyte adhesion, a process which is involved in many pathophysiological events.