Matrix metalloproteinases (MMPs) are zinc-containing proteinases that participate in tissue remodeling under physiological and pathological conditions. To test the involvement of bacterial proteinases in tissue injury during bacterial infections, we investigated the activation potential of various bacterial proteinases against precursors of MMPs (proMMPs) purified from human neutrophils (proMMP-8 and -9) and from human fibrosarcoma cells (proMMP-1). Each proMMP was subjected to treatment with a series of bacterial proteinases at molar ratios of 0.01-0.1 (bacterial proteinase to proMMP), and activities of MMPs generated were determined. Among six different bacterial proteinases, thermolysin family enzymes (family M4) such as Pseudomonas aeruginosa elastase, Vibrio cholerae proteinase, and thermolysin strongly activated all three proMMPs via limited proteolysis to generate active forms of the MMPs. N-terminal sequence analysis of the active MMPs revealed that cleavage occurred at the Val 82 -Leu 83 and Thr 90 -Phe 91 bonds of proMMP-1 and proMMP-9, respectively, which are located near the N terminus of the catalytic domain of MMPs. In contrast, Serratia 56-kDa proteinase and Pseudomonas alkaline proteinase, both of which are classified as members of the serralysin subfamily of zinc metalloproteinases (family M10), and Serratia 73-kDa thiol proteinase did not evidence proteolytic processing or activation of proMMP-1, -8, and -9 under these experimental conditions. These results indicate that bacterial proteinases may play an important role in tissue destruction and disintegration of extracellular matrix at the site of infections.Collagen, one of the major structural components of the extracellular matrix, has a triple-helical structure and exhibits resistance to proteolytic cleavage by endogenous and exogenous proteinases (1) except for matrix metalloproteinases (MMPs) 1 such as human neutrophil collagenase (MMP-8). Bacterial proteinases have been suggested to mediate direct tissue destruction, resulting in impairment of host defense mechanisms in septic foci (2-4). Most bacterial proteinases, however, have weak degradative activity against collagen (1, 5). Thus, the mechanism of extracellular matrix destruction at the site of bacterial infection is poorly understood.MMPs, a family of zinc neutral endopeptidases, are secreted by a variety of cells as inactive precursors (proMMPs) and degrade a series of collagens (6). Two distinct proMMPs (proMMP-8 and neutrophil progelatinase, proMMP-9) are synthesized and secreted extracellularly from specific granules of human neutrophils after membrane stimulation (7, 8). Macrophages and fibroblasts produce interstitial procollagenase (proMMP-1) (6, 9) and 92-kDa progelatinase (proMMP-9), whose expressions vary constitutively or inducibly after stimulation with proinflammatory cytokines and lipopolysaccharide (10 -12). MMP-8 and -1 specifically cleave native triplehelical type I collagen into two major fragments, one-fourth and three-fourths the size of native collagen, respect...