Coculture of FaDu tumor cells and wild-type (WT) fibroblasts induces MMP-dependent tumor cell invasion. WT fibroblasts were cultured in a 2:1 ratio with FaDU HNSCC tumor cells atop Type I collagen for 6 days. EMMPRIN immunoreactivity identified invading tumor cells (A). Protease inhibitors were added to assess the role of MMPs in the invasive program (B). FaDu-WT fibroblast invasion was sensitive to synthetic (GM6001, 20 uM) and endogenous (TIMP2, 10 nM) broad spectrum MMP inhibitors and to furin inhibition (synthetic peptidyl chloromethyl ketones, CMK, 50 uM), but not TIMP-1 (10 nM), serine protease inhibitors (leupeptin, 10 uM; epsilon-amino-caproic acid (EACA), 10 mM) or cysteine protease inhibitors (E64, 10 ug/ml). Bar, 100 μm.