VCAM-1 activates endothelial cell–associated MMPs. (A,C,E) mHEVc cells and (B,D,F) HUVECs were incubated with isotype antibody-coated beads or anti–VCAM-1 antibody-coated beads. mHEVc cells were also incubated in the presence or absence of 10 μM GM6001. At the indicated time points, the cells were washed. Equal cell numbers were lysed, nuclei were removed by centrifugation, and supernatants were examined by zymography. (A-B) Representative zymograms of VCAM-1 activation of endothelial cell–associated MMPs. Arrows label the latent forms (pro-MMP) and smaller active forms of the MMPs. The activity of MMP-9 and MMP-2 were compared with migration by purified standards (data not shown). (C-D) Same as for panels A and B except with 0.01 M EDTA, indicating the cation dependence of MMP degradation of gelatin. (E-F) Densitometry analysis of the active forms of MMPs in zymograms from 3 experiments. Fold increase is the change in the active form of MMP activity as compared with the nonstimulated cultures. Presented are the mean ± SD. *P < .05 compared with mHEVc cells at 0 minutes. **P < .05 compared with anti–VCAM-1–bead-stimulated cells. (G) Western blots for 1 (MT1)–MMP, MMP-2, and MMP-9 expression using rabbit antihuman MT1-MMP (a kind gift from Qing-Xiang Amy Sang, Florida State University)²¹  (1:200), affinity-purified rabbit antihuman MMP-9 (no. SA-106; Biomol, Plymouth Meeting, PA) (1:200), or purified rabbit antirat MMP-2 (1:200) (no. AB19015; Chemicon) followed by a horseradish peroxidase (HRP)–conjugated donkey antirabbit secondary antibody (Amersham Pharmacia Biotech, Piscataway, NJ) (1:4000) and enhanced chemiluminescence (ECL) detection.