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Abstract: Proteinase 3 (PR3) is one of the four elastase-related serine proteinases stored in the azurophilic granules of neutrophils. Although it participates in the pro- and anti-inflammatory responses to infection and inflammation it also retains specific functions that make it different from neutrophil elastase in spite of their close structural resemblance. PR3 is involved in the immune response to infection and is the major autoantigen in granulomatosis with polyangiitis (GPA, formerly Wegener disease), an autoimmune systemic vasculitis with granulomas. Thus, PR3 appears to be a relevant therapeutic target in a variety of inflammatory human diseases. Animal models are required for the testing of new drugs that target PR3 specifically but differences between human and rodent neutrophil PR3 expression and substrate specificity have greatly impaired progress in this direction. This may explain that, to date, there is no spontaneous model of vasculitis associated with anti-PR3 antibodies. In this review, we will focus on the structural and functional differences between human and murine PR3, and how these differences may be by-passed in order to develop a relevant animal model. [Copyright &y& Elsevier]

[Display omitted] Epidemiological studies established an association between chronic inflammation and higher risk of cancer. Inhibition of proteolytic enzymes represents a potential treatment strategy for cancer and prevention of cancer metastasis. Cathepsin C (CatC) is a highly conserved lysosomal cysteine dipeptidyl aminopeptidase required for the activation of pro-inflammatory neutrophil serine proteases (NSPs, elastase, proteinase 3, cathepsin G and NSP-4). NSPs are locally released by activated neutrophils in response to pathogens and non-infectious danger signals. Activated neutrophils also release neutrophil extracellular traps (NETs) that are decorated with several neutrophil proteins, including NSPs. NSPs are not only NETs constituents but also play a role in NET formation and release. Although immune cells harbor large amounts of CatC, additional cell sources for this protease exists. Upregulation of CatC expression was observed in different tissues during carcinogenesis and correlated with metastasis and poor patient survival. Recent mechanistic studies indicated an important interaction of tumor-associated CatC, NSPs, and NETs in cancer development and metastasis and suggested CatC as a therapeutic target in a several cancer types. Cancer cell-derived CatC promotes neutrophil recruitment in the inflammatory tumor microenvironment. Because the clinical consequences of genetic CatC deficiency in humans resulting in the elimination of NSPs are mild, small molecule inhibitors of CatC are assumed as safe drugs to reduce the NSP burden. Brensocatib, a nitrile CatC inhibitor is currently tested in a phase 3 clinical trial as a novel anti-inflammatory therapy for patients with bronchiectasis. However, recently developed CatC inhibitors possibly have protective effects beyond inflammation. In this review, we describe the pathophysiological function of CatC and discuss molecular mechanisms substantiating pharmacological CatC inhibition as a potential strategy for cancer treatment. [ABSTRACT FROM AUTHOR]

Neutrophils are among the first cells implicated in acute inflammation. Leaving the blood circulation, they quickly migrate through the interstitial space of tissues and liberate oxidants and other antimicrobial proteins together with serine proteinases. Neutrophil elastase, cathepsin G, proteinase 3 (PR3), and neutrophil serine protease 4 are four hematopoietic serine proteases activated by dipeptidyl peptidase I during neutrophil maturation and are mainly stored in cytoplasmic azurophilic granules. They regulate inflammatory and immune responses after their release from activated neutrophils at inflammatory sites. Membrane-bound PR3 (mbPR3) at the neutrophil surface is the prime antigenic target of antineutrophil cytoplasmic autoantibodies (ANCA) in granulomatosis with polyangiitis (GPA), a vasculitis of small blood vessels and granulomatous inflammation of the upper and/or lower respiratory tracts. The interaction of ANCA with mbPR3 results in excessive activation of neutrophils to produce reactive oxygen species and liberation of granular proteinases to the pericellular environment. In this review, we focus on PR3 and dipeptidyl peptidase I as attractive pharmacological targets whose inhibition is expected to attenuate autoimmune activation of neutrophils in GPA. [ABSTRACT FROM AUTHOR]

The physiological and pathological functions of proteinase 3 (PR3) are not well understood due to its close similarity to human neutrophil elastase (HNE) and the lack of a specific inhibitor. Based on structural analysis of the active sites of PR3 and HNE, we generated mutants derived from the polyvalent inhibitor SerpinB1 (monocyte/neutrophil elastase inhibitor) that specifically inhibit PR3 and that differ from wt-SerpinB1 by only 3 or 4 residues in the reactive center loop. The rate constant of association between the best SerpinB1 mutant and PR3 is 1.4 x 107 M-1 ⋅ s-1, which is ~100-fold higher than that observed with wt-SerpinB1 and compares with that of al-protease inhibitor (α1-PI) toward HNE. SerpinB1 (S/ DAR) is cleaved by HNE, but due to differences in rate, inhibition of PR3 by SerpinB1 (S/DAR) is only minimally affected by the presence of HNE even when the latter is in excess. SerpinB1 (S/DAR) inhibits soluble PR3 and also membrane-bound PR3 at the surface of activated neutrophils. Moreover, SerpinB1 (S/DAR) clears induced PR3 from the surface of activated neutrophils. Overall, these specific inhibitors of PR3 will be valuable for defining biological functions of the protease and may prove useful as therapeutics for PR3-related inflammatory diseases, such as Wegener's granulomatosis. [ABSTRACT FROM AUTHOR]

Cathepsin C (CatC) is a tetrameric cysteine dipeptidyl aminopeptidase that plays a key role in activation of pro-inflammatory serine protease zymogens by removal of a N-terminal pro-dipeptide sequence. Loss of function mutations in the CatC gene is associated with lack of immune cell serine protease activities and cause Papillon-Lefèvre syndrome (PLS). Also, only very low levels of elastase-like protease zymogens are detected by proteome analysis of neutrophils from PLS patients. Thus, CatC inhibitors represent new alternatives for the treatment of neutrophil protease-driven inflammatory or autoimmune diseases. We aimed to experimentally inactivate and lower neutrophil elastase-like proteases by pharmacological blocking of CatC-dependent maturation in cell-based assays and in vivo . Isolated, immature bone marrow cells from healthy donors pulse-chased in the presence of a new cell permeable cyclopropyl nitrile CatC inhibitor almost totally lack elastase. We confirmed the elimination of neutrophil elastase-like proteases by prolonged inhibition of CatC in a non-human primate. We also showed that neutrophils lacking elastase-like protease activities were still recruited to inflammatory sites. These preclinical results demonstrate that the disappearance of neutrophil elastase-like proteases as observed in PLS patients can be achieved by pharmacological inhibition of bone marrow CatC. Such a transitory inhibition of CatC might thus help to rebalance the protease load during chronic inflammatory diseases, which opens new perspectives for therapeutic applications in humans. [ABSTRACT FROM AUTHOR]