Highly Selective Cleavage of Cytokines and Chemokines by the Human Mast Cell Chymase and Neutrophil Cathepsin G

Abstract

Human mast cell chymase (HC) and human neutrophil cathepsin G (hCG) show relatively similar cleavage specificities: they both have chymotryptic activity but can also cleave efficiently after leucine. Their relatively broad specificity suggests that they may cleave almost any substrate if present in high enough concentrations or for a sufficiently long time. A number of potential substrates have been identified for these enzymes and, recently, these enzymes have also been implicated in regulating cytokine activity by cleaving numerous cytokines and chemokines. To obtain a better understanding of their selectivity for various potential in vivo substrates, we analyzed the cleavage of a panel of 51 active recombinant cytokines and chemokines. Surprisingly, our results showed a high selectivity of HC; only 4 of 51 of these proteins were substantially cleaved. hCG cleaved a few additional proteins, although this occurred after adding almost equimolar amounts of enzyme to target. The explanation for this wide difference in activity against peptides or other linear substrates compared with native proteins is most likely related to the reduced accessibility of the enzymes to potential cleavage sites in folded proteins. In this article, we present evidence that sites not exposed on the surface of the protein are not cleaved by the enzyme. Interestingly, both enzymes readily cleaved IL-18 and IL-33, two IL-1-related alarmins, as well as the cytokine IL-15, which is important for T cell and NK cell homeostasis. Cleavage of the alarmins by HC and hCG suggests a function in regulating excessive inflammation.

The Chymase Mouse Mast Cell Protease-4 Regulates Intestinal Cytokine Expression in Mature Adult Mice Infected with Giardia intestinalis

“…Alternatively, the lack of mMCP-4 may result in less numbers of intestinal Tuft cells, since epithelial cell migration is reduced in the mMCP-4 −/− mice [34]. We and others have shown that mMCP-4 can activate the pro-cytokine IL-33 and that human and mouse chymase then degrades active IL-33, which is likely to reduce excessive inflammation in the stressed tissue [70][71][72]. The observed increased IL-25 expression and determination of intestinal protein levels of IL-25 and IL-33 during infection with G. intestinalis warrants further investigation.…”

Non‐IgE mediated mast cell activation

“…On the other hand, activated MCs can modulate IL‐33 activity via the secretion of serine proteases. Human MC chymase and tryptase selectively cleave full‐length human IL‐33 (IL‐33 1‐270 ) and generate the active forms: IL‐33 95‐270 , IL‐33 107‐270 , and IL‐33 109‐270 , which were 30‐fold more potent than full‐length protein for activation of group‐2 innate lymphoid cells (ILC2s) ex vivo . It was also shown that cleavage of full‐length IL‐33 by tryptase contributes to the allergic airway inflammation in vivo .…”

“…It exacerbates allergic bronchoconstriction by increasing secretion of serotonin from MCs and IL‐33 has also been reported to induce Th17‐mediated airway inflammation via MCs. Vice versa, MCs release IL‐33 under IgE/antigen stimulation and the generation of potent forms by the cleavage of proteases, thus leading to a positive feedback of IL‐33 activity.…”

“…Human MC chymase and tryptase selectively cleave full-length human IL-33 (IL-33 ) and generate the active forms: IL-33 , IL-33 , and IL-33 , which were 30-fold more potent than full-length protein for activation of group-2 innate lymphoid cells (ILC2s) ex vivo. 269,270 It was also shown that cleavage of full-length IL-33 by tryptase contributes to the allergic airway inflammation in vivo. 269 In contrast, mouse MC chymase (MCPT4) has been reported to degrade IL-33, dampening inflammatory responses.…”

Quantitative In-Depth Analysis of the Mouse Mast Cell Transcriptome Reveals Organ-Specific Mast Cell Heterogeneity

“…Connective tissue mast cells also express an MC-specific carboxypeptidasecarboxypeptidase A3 (Cpa3). These proteases have been shown to inactivate snake, bee, and scorpion toxins; regulate blood pressure by angiotensin II generation; and control inflammation by cleaving a selective panel of cytokines [1,12,[16][17][18][19][20]. Mast cell proteases likely have several other important physiological functions, including connective tissue turnover and regulating coagulation [21,22].…”