Regulation of the activity of secreted human lung mast cell tryptase by mast cell proteoglycans

Abstract

When mast cells from human lungs were stimulated in vitro to degranulate, all of the tryptase secreted was found to be complexed with proteoglycans, three quarters with heparin proteoglycans and one quarter with chondroitin sulphate proteoglycans. Isolation of the tryptase–proteoglycan complexes by fibronectin affinity chromatography and gel filtration on a Sephacryl S-200 column gave the complexes an apparent M r of 200 000, suggesting the presence of heparin and chondroitin sulphate proteoglycans ( M rs=60 000) and tryptase ( M r=134 000) in a molar ratio of 1:1, equivalent to a mass ratio of about 0.45:1. However, analysis of the total mast cell releasate showed that it contained more proteoglycans (mass ratio of about 2:1) than was needed to complex tryptase. We could demonstrate that the releasate contained two proteoglycan fractions, one complexed (20%) with tryptase and the other not (80%). Incubation of the isolated tryptase–proteoglycan complexes led to rapid monomerisation and inactivation of tryptase, whereas the releasate, containing both complexed and free proteoglycans, retained its tryptase activity for up to at least 18 h. The results indicate that the majority of the proteoglycans secreted by stimulated lung mast cells, although not complexed with the secreted tryptase, are critical for the preservation of its activity.