Identification of a cathepsin G-like proteinase in the MCTC type of human mast cell.

Abstract

Human mast cells can be divided into two subsets based on serine proteinase composition: a subset that contains the serine proteinases tryptase and chymase (MCTC), and a subset that contains only tryptase (MCT). In this study we examined both types of mast cells for two additional proteinases, cathepsin G and elastase, which are the major serine proteinases of neutrophils. Because human mast cell chymase and cathepsin G are both chymotrypsin-like proteinases, the properties of these enzymes were further defined to confirm their distinctiveness. Comparison of their N-terminal sequences showed 30% nonidentity over the first 35 amino acids, and comparison of their amino acid compositions demonstrated a marked difference in their Arg/Lys ratios, which was approximately 1 for chymase and 10 for cathepsin G. Endoglycosidase F treatment increased the electrophoretic mobility of chymase on SDS gels, indicating significant N-linked carbohydrate on chymase; no effect was observed on cathepsin G. Immunoprecipitation and immunoblotting with specific antisera to each proteinase revealed little, if any, detectable cross-reactivity. Immunocytochemical studies showed selective labelling of MCTC type mast cells by cathepsin G antiserum in sections of human skin, lung, and bowel. No labeling of mast cells by elastase antiserum was detected in the same tissues, or in dispersed mast cells from lung and skin. A protein cross-reactive with cathepsin G was identified in extracts of human skin mast cells by immunoblot analysis. This protein had a slightly higher Mr (30,000) than the predominant form of neutrophil cathepsin G (Mr 28,000), and could not be separated from chymase (Mr 30,000) by SDS gel electrophoresis because of the size similarity. Using casein, a protein substrate hydrolyzed at comparable rates by chymase and cathepsin G, it was shown that about 30% of the caseinolytic activity in mast cell extracts was sensitive to inhibitors of cathepsin G that had no effect on chymase. Hydrolytic activity characteristic of elastase was not detected in these extracts. These studies indicate that human MCTC mast cells may contain two different chymotrypsin-like proteinases: chymase and a proteinase more closely related to cathepsin G, both of which are undetectable in MCT mast cells. Neutrophil elastase, on the other hand, was not detected in human mast cells by our procedures.

The mast cell: A Janus in kidney transplants

“…In the human setting, there are two main types of MCs: those that contain tryptase granules (MC T ), and those containing both tryptase and chymase granules (MC TC ) ( 40 ). MC TC also contain cathepsin G, a serine protease similar to chymase ( 41 ). In lung tissue, MC subtype occurrence depends on its surrounding tissue; MCs around smooth muscle tissue are mostly MC TCs while MCs in alveoli are more often MC Ts ( 42 ).…”

Analysis of human lung mast cells by single cell RNA sequencing

“…Human mast cells have been shown to be heterogeneous when it comes to the presence of proteases and thus divided into MC T and MC TC depending on their expression of chymase ( CMA1 ). The MC TC subset has in addition also been shown to contain CPA3 and cathepsin G ( 44 , 45 ). Human lung mast cells are predominantly of the MC T subtype, and consistent with this CMA1 was only detectable in a small proportion of the cells ( Figures 3 , 5 ).…”

An optimized method for IgE-mediated degranulation of human lung mast cells

“…Mast cells have been shown to be heterogeneous, and human mast cells are divided into the MC T and MC TC subtypes, depending on their expression of mast cell proteases. MC T expresses tryptase and MC TC , in addition to tryptase, also express chymase, carboxypeptidase A3, and cathepsin G (2)(3)(4). The prevalence of these subtypes varies in various tissues, where, for example, mast cells in the skin are predominantly of the MC TC type, and in the lung, they are predominantly of the MC T type (2).…”