The ability of human mast cell chymase and tryptase to process procollagen was examined. Purified human intestinal smooth muscle cell procollagen was incubated with human mast cell tryptase or human mast cell chymase. Purified chymase, but not tryptase, exhibited procollagen proteinase activity in the presence of EDTA. Addition of purified porcine heparin over a range of 0.1-100 g/ml did not affect either the rate or the products of procollagen chymase cleavage. The cleavage site of chymase on the pro-␣1(I) collagen carboxyl terminus was found to be in the propeptide region at Leu-1248-Ser-1249. Cleavage at this site suggested that the collagen products would form fibrils and confirmed the production of a unique carboxyl-terminal propeptide. Turbidometric fibril formation assay demonstrated de novo formation of chymase-generated collagen fibrils with characteristic lag, growth, and plateau phases. When observed by dark field microscopy, these fibrils were similar to fibrils formed by the action of procollagen proteinases. Thus, mast cell chymase, but not tryptase, exhibits procollagen peptidase-like activity as evidenced by its ability to process procollagen to fibrilforming collagen with concurrent formation of a unique carboxyl-terminal propeptide. These data demonstrate that mast cell chymase has a potential role in the regulation of collagen biosynthesis and in the pathogenesis of fibrosis.Mast cells are abundant in connective tissues of skin, lung, and intestine (1, 2). Increased numbers (or increased activity) of mast cells are associated with fibrotic disorders such as scleroderma, pulmonary fibrosis, and Crohn's disease (3-5). The precise role for mast cells in connective tissue biology and fibrosis is not known. One potential mechanism for mast cell involvement in these processes is through the production of unique proteolytic enzymes that may act on matrix proteins. Mast cell enzymes include the neutral proteases tryptase, chymase, cathepsin G, and a zinc-dependent carboxypeptidase (6). Although chymase and tryptase cleave fibronectin (7-9) and chymase cleaves vitronectin (10), no direct effect of these enzymes on procollagen or collagen has been demonstrated.Because procollagen (the precursor of collagen) requires proteolytic cleavage in the extracellular space prior to normal collagen fibril formation, we have speculated that newly secreted procollagen may be a substrate for mast cell proteolytic enzymes. The smooth muscle cells of the intestinal muscularis are a major contributor of collagen to the extracellular matrix in normal and fibrotic human intestine (11). Therefore, in vitro studies were performed to test the above hypothesis utilizing procollagen secreted by human intestinal smooth muscle cells.
MATERIALS AND METHODSPurification of Procollagen-Human intestinal smooth muscle cells (12) were grown to confluence in Dulbecco's modified Eagle's medium containing 200 units/ml penicillin, 0.2 mg/ml streptomycin, 50 units/ml Nystatin, and 10% fetal bovine serum. Cell monolayers were then rinsed wit...