We investigated whether thrombin, the final activator of coagulation cascade, regulates expression of matrix metalloproteinases (MMP)-9 in human monocytes. We show that thrombin stimulation induced MMP-9 secretion of monocytes dose- and time-dependently as revealed by gelatin zymography. Real-time RT-PCR and Western blot analysis demonstrated that thrombin up-regulated mRNA and protein levels of MMP-9. Pre-incubation with anti-protease-activated receptor (PAR)-1 or anti-PAR-3 antibody partially inhibited the thrombin-induced MMP-9 secretion. Simultaneous incubation with both showed synergistic effect, indicating the involvement of both receptors in this thrombin effect. BAPTA, a Ca2+ chelator, abolished the thrombin-induced MMP-9 secretion, indicating the requirement of Ca2+ mobilization in this process. Inhibition of thrombin-induced MMP-9 secretion by either MEK inhibitor or p38 kinase inhibitor revealed that the thrombin effect was mediated by both ERK1/2 and p38 pathways. The activation of NF kappa B by thrombin as demonstrated by electromobility shift assay was also shown to be critical to the thrombin-induced MMP-9 up-regulation. (C) 2009 Elsevier Inc. All rights reserved.