Inhibition of rat mast cell protease 1 by vitronectin

Mast cell chymase in complex with heparin proteoglycan is regulated by protamine

Protamines are polycationic proteins that are widely used for neutralisation of the anticoagulant action of heparin. However, several reports have shown adverse, mast cell-dependent reactions to protamine. The exact mechanism by which protamine causes these adverse effects is not clear. In the present study, the possibility that protamine may influence mast cell chymase function was investigated. Mast cell chymase is in vivo recovered in a macromolecular complex with heparin proteoglycan, and this interaction is essential for expression of optimal enzymatic activity. Protamine was shown to strongly reduce the activity of mast cell chymase by a mechanism that involved displacement of the chymase from heparin proteoglycan.

Regulation of rat mast cell protease 1 activity. Protease inhibition is prevented by heparin proteoglycan

Rat mast cell protease 1 (RMCP-1) is a chymotrypsin-like serine protease (chymase) that is specifically expressed by connective-tissue-type mast cells. It is stored in the secretory granules of the cells in a complex with heparin proteoglycan, and the chymase/heparin proteoglycan complexes are released following mast cell activation. The present study was undertaken to examine if the association with heparin proteoglycan influenced the regulation of RMCP-1 by various macromolecular protease inhibitors. Endogenous mast cell heparin proteoglycan was shown to significantly block the inhibition of RMCP-1 by the serpins alpha 1-protease inhibitor and alpha 1-antichymotrypsin, as well as the inhibition by alpha 2-macroglobulin, soybean trypsin inhibitor and plasma. The blocking of protease inhibition showed an optimum at a RMCP-1/proteoglycan ratio of 5:1 (by mass), corresponding to approximately 80 RMCP-1 molecules bound/proteoglycan molecule. Chymase activity present on intact peritoneal mast cells, i.e. present in its native complex with heparin proteoglycan, was also shown to be largely resistant to inhibition by alpha 1-antichymotrypsin and alpha 1-protease inhibitor. Heparin 10-saccharides and 20-saccharides were inefficient in preventing the interaction of RMCP-1 with alpha 1-antichymotrypsin, whereas pig mucosal heparin (approximately 50 monosaccharide units) blocked protease inhibition. We have previously shown that heparin potentiates the catalytic activity of RMCP-1 and, in the present study, we show that the mechanism for chymase activation involves a sixfold reduction of the Km,app value of RMCP-1 for the chromogenic substrate S-2586. Thus, the association of mast cell chymase with heparin proteoglycan may serve both to potentiate the catalytic activity of the enzyme and to increase the life-span of the chymases by preventing their inhibition after exocytosis.