Thrombin, a critical enzyme in the coagulation cascade, has also been associated with angiogenesis and activation of the zymogen form of matrix metalloproteinase-2 (MMP-2 or gelatinase-A). We show that thrombin activated pro-MMP-2 in a dose- and time-dependent manner in cultured human umbilical-vein endothelial cells (HUVECs) to generate a catalytically active 63kDa protein that accumulated as the predominant form in the conditioned medium. This 63kDa thrombin-activated MMP-2 is distinct from the 62kDa species found following concanavalin A or PMA stimulated pro-MMP-2 activation. Hirudin and leupeptin blocked thrombin-induced pro-MMP-2 activation, demonstrating that the proteolytic activity of thrombin is essential. However, activation was also dependent upon membrane-type-MMP (MT-MMP) action, since it was blocked by EDTA, o-phenanthroline, hydroxamate metalloproteinase inhibitors, tissue inhibitor of metalloproteinase-2 (TIMP-2) and TIMP-4, but not TIMP-1. Thrombin inefficiently cleaved recombinant 72kDa pro-MMP-2, but efficiently cleaved the 64kDa MT-MMP-processed intermediate form in the presence of cells. Thrombin also rapidly (within 1h) increased cellular MT-MMP activity, and at longer time points (>6h) it increased expression of MT1-MMP mRNA and protein. Thus signalling via proteinase-activated receptors (PARs) may play a role in thrombin-induced MMP-2 activation, though this does not appear to involve PAR1, PAR2, or PAR4 in HUVECs. These results indicate that in HUVECs the activation of pro-MMP-2 by thrombin involves increased MT-MMP activity and preferential cleavage of the MT-MMP-processed 64kDa MMP-2 form in the presence of cells. The integration of these proteinase systems in the vascular endothelium may be important during thrombogenesis and tissue remodelling associated with neovascularization.

Abbreviations used: BCA, bicinchronic acid; con A, concanavalin A; E64, trans-epoxysuccinyl-l-leucylamido-(4-guanidino)butane; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; HUVEC, human umbilical-vein endothelial cell; MMP, matrix metalloproteinase; MT-MMP, membrane-type matrix metalloproteinase; PAR, proteinase-activated receptor; RT, reverse transcriptase; TIMP, tissue inhibitor of metalloproteinase.

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