Chymases, serine proteases exclusively expressed by mast cells, have been implicated in
various pathological conditions. However, the basis for these activities is not known, ie the in
vivo substrate (s) for mast cell chymase has not been identified. In this study we show that
mice lacking the chymase mouse mast cell protease 4 (mMCP-4) fail to process pro-matrix
metalloprotease 9 (pro-MMP-9) to its active form in vivo, whereas both the pro and active
form of MMP-9 was found in tissues of wild type mice. Moreover, the processing of pro-MMP …