Consequences of cathepsin C inactivation for membrane exposure of proteinase 3, the target antigen in autoimmune vasculitis

Membrane-bound proteinase 3 (PR3^m) is the main target antigen of anti-neutrophil cytoplasmic autoantibodies (ANCA) in granulomatosis with polyangiitis, a systemic small-vessel vasculitis. Binding of ANCA to PR3^m triggers neutrophil activation with the secretion of enzymatically active PR3 and related neutrophil serine proteases, thereby contributing to vascular damage. PR3 and related proteases are activated from pro-forms by the lysosomal cysteine protease cathepsin C (CatC) during neutrophil maturation. We hypothesized that pharmacological inhibition of CatC provides an effective measure to reduce PR3^m and therefore has implications as a novel therapeutic approach in granulomatosis with polyangiitis. We first studied neutrophilic PR3 from 24 patients with Papillon-Lefèvre syndrome (PLS), a genetic form of CatC deficiency. PLS neutrophil lysates showed a largely reduced but still detectable (0.5-4%) PR3 activity when compared with healthy control cells. Despite extremely low levels of cellular PR3, the amount of constitutive PR3^m expressed on the surface of quiescent neutrophils and the typical bimodal membrane distribution pattern were similar to what was observed in healthy neutrophils. However, following cell activation, there was no significant increase in the total amount of PR3^m on PLS neutrophils, whereas the total amount of PR3^m on healthy neutrophils was significantly increased. We then explored the effect of pharmacological CatC inhibition on PR3 stability in normal neutrophils using a potent cell-permeable CatC inhibitor and a CD34⁺ hematopoietic stem cell model. Human CD34⁺ hematopoietic stem cells were treated with the inhibitor during neutrophil differentiation over 10 days. We observed strong reductions in PR3^m, cellular PR3 protein, and proteolytic PR3 activity, whereas neutrophil differentiation was not compromised.

Exploiting the S4-S5 Specificity of Human Neutrophil Proteinase 3 to Improve the Potency of Peptidyl Di(chlorophenyl)-phosphonate Ester Inhibitors: A Kinetic and Molecular Modeling Analysis

The neutrophilic serine protease proteinase 3 (PR3) is involved in inflammation and immune response and thus appears as a therapeutic target for a variety of infectious and inflammatory diseases. Here we combined kinetic and molecular docking studies to increase the potency of peptidyl-diphenyl phosphonate PR3 inhibitors. Occupancy of the S1 subsite of PR3 by a nVal residue and of the S4-S5 subsites by a biotinylated Val residue as obtained in biotin-VYDnV^P(O-C₆H₄-4-Cl)₂ enhanced the second-order inhibition constant k_obs/[I] toward PR3 by more than 10 times ( k_obs/[I] = 73000 ± 5000 M^-1 s^-1) as compared to the best phosphonate PR3 inhibitor previously reported. This inhibitor shows no significant inhibitory activity toward human neutrophil elastase and resists proteolytic degradation in sputa from cystic fibrosis patients. It also inhibits macaque PR3 but not the PR3 from rodents and can thus be used for in vivo assays in a primate model of inflammation.

Prolonged pharmacological inhibition of cathepsin C results in elimination of neutrophil serine proteases

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.

Neutrophilic Cathepsin C Is Maturated by a Multistep Proteolytic Process and Secreted by Activated Cells during Inflammatory Lung Diseases

The cysteine protease cathepsin C (CatC) activates granule-associated proinflammatory serine proteases in hematopoietic precursor cells. Its early inhibition in the bone marrow is regarded as a new therapeutic strategy for treating proteolysis-driven chronic inflammatory diseases, but its complete inhibition is elusive in vivo Controlling the activity of CatC may be achieved by directly inhibiting its activity with a specific inhibitor or/and by preventing its maturation. We have investigated immunochemically and kinetically the occurrence of CatC and its proform in human hematopoietic precursor cells and in differentiated mature immune cells in lung secretions. The maturation of proCatC obeys a multistep mechanism that can be entirely managed by CatS in neutrophilic precursor cells. CatS inhibition by a cell-permeable inhibitor abrogated the release of the heavy and light chains from proCatC and blocked ∼80% of CatC activity. Under these conditions the activity of neutrophil serine proteases, however, was not abolished in precursor cell cultures. In patients with neutrophilic lung inflammation, mature CatC is found in large amounts in sputa. It is secreted by activated neutrophils as confirmed through lipopolysaccharide administration in a nonhuman primate model. CatS inhibitors currently in clinical trials are expected to decrease the activity of neutrophilic CatC without affecting those of elastase-like serine proteases.

New selective peptidyl di(chlorophenyl) phosphonate esters for visualizing and blocking neutrophil proteinase 3 in human diseases

The function of neutrophil protease 3 (PR3) is poorly understood despite of its role in autoimmune vasculitides and its possible involvement in cell apoptosis. This makes it different from its structural homologue neutrophil elastase (HNE). Endogenous inhibitors of human neutrophil serine proteases preferentially inhibit HNE and to a lesser extent, PR3. We constructed a single-residue mutant PR3 (I217R) to investigate the S4 subsite preferences of PR3 and HNE and used the best peptide substrate sequences to develop selective phosphonate inhibitors with the structure Ac-peptidyl(P)(O-C6H4-4-Cl)2. The combination of a prolyl residue at P4 and an aspartyl residue at P2 was totally selective for PR3. We then synthesized N-terminally biotinylated peptidyl phosphonates to identify the PR3 in complex biological samples. These inhibitors resisted proteolytic degradation and rapidly inactivated PR3 in biological fluids such as inflammatory lung secretions and the urine of patients with bladder cancer. One of these inhibitors revealed intracellular PR3 in permeabilized neutrophils and on the surface of activated cells. They hardly inhibited PR3 bound to the surface of stimulated neutrophils despite their low molecular mass, suggesting that the conformation and reactivity of membrane-bound PR3 is altered. This finding is relevant for autoantibody binding and the subsequent activation of neutrophils in granulomatosis with polyangiitis (formerly Wegener disease). These are the first inhibitors that can be used as probes to monitor, detect, and control PR3 activity in a variety of inflammatory diseases.

A functional variant of elafin with improved anti-inflammatory activity for pulmonary inflammation

Elafin is a serine protease inhibitor produced by epithelial and immune cells with anti-inflammatory properties. Research has shown that dysregulated protease activity may elicit proteolytic cleavage of elafin, thereby impairing the innate immune function of the protein. The aim of this study was to generate variants of elafin (GG- and QQ-elafin) that exhibit increased protease resistance while retaining the biological properties of wild-type (WT) elafin. Similar to WT-elafin, GG- and QQ-elafin variants retained antiprotease activity and susceptibility to transglutaminase-mediated fibronectin cross-linking. However, in contrast to WT-elafin, GG- and QQ-elafin displayed significantly enhanced resistance to degradation when incubated with bronchoalveolar lavage fluid from patients with cystic fibrosis. Intriguingly, both variants, particularly GG-elafin, demonstrated improved lipopolysaccharide (LPS) neutralization properties in vitro. In addition, GG-elafin showed improved anti-inflammatory activity in a mouse model of LPS-induced acute lung inflammation. Inflammatory cell infiltration into the lung was reduced in lungs of mice treated with GG-elafin, predominantly neutrophilic infiltration. A reduction in MCP-1 levels in GG-elafin treated mice compared to the LPS alone treatment group was also demonstrated. GG-elafin showed increased functionality when compared to WT-elafin and may be of future therapeutic relevance in the treatment of lung diseases characterized by a protease burden.

Secretory leukocyte protease inhibitor (SLPI) is, like its homologue trappin-2 (pre-elafin), a transglutaminase substrate

Human lungs contain secretory leukocyte protease inhibitor (SLPI), elafin and its biologically active precursor trappin-2 (pre-elafin). These important low-molecular weight inhibitors are involved in controlling the potentially deleterious proteolytic activities of neutrophil serine proteases including elastase, proteinase 3 and cathepsin G. We have shown previously that trappin-2, and to a lesser extent, elafin can be linked covalently to various extracellular matrix proteins by tissue transglutaminases and remain potent protease inhibitors. SLPI is composed of two distinct domains, each of which is about 40% identical to elafin, but it lacks consensus transglutaminase sequence(s), unlike trappin-2 and elafin. We investigated the actions of type 2 tissue transglutaminase and plasma transglutaminase activated factor XIII on SLPI. It was readily covalently bound to fibronectin or elastin by both transglutaminases but did not compete with trappin-2 cross-linking. Cross-linked SLPI still inhibited its target proteases, elastase and cathepsin G. We have also identified the transglutamination sites within SLPI, elafin and trappin-2 by mass spectrometry analysis of tryptic digests of inhibitors cross-linked to mono-dansyl cadaverin or to a fibronectin-derived glutamine-rich peptide. Most of the reactive lysine and glutamine residues in SLPI are located in its first N-terminal elafin-like domain, while in trappin-2, they are located in both the N-terminal cementoin domain and the elafin moiety. We have also demonstrated that the transglutamination substrate status of the cementoin domain of trappin-2 can be transferred from one protein to another, suggesting that it may provide transglutaminase-dependent attachment properties for engineered proteins. We have thus added to the corpus of knowledge on the biology of these potential therapeutic inhibitors of airway proteases.

Protease inhibitors derived from elafin and SLPI and engineered to have enhanced specificity towards neutrophil serine proteases

The secretory leukocyte protease inhibitor (SLPI), elafin, and its biologically active precursor trappin-2 are endogeneous low-molecular weight inhibitors of the chelonianin family that control the enzymatic activity of neutrophil serine proteases (NSPs) like elastase, proteinase 3, and cathepsin G. These inhibitors may be of therapeutic value, since unregulated NSP activities are linked to inflammatory lung diseases. However SLPI inhibits elastase and cathepsin G but not proteinase 3, while elafin targets elastase and proteinase 3 but not cathepsin G. We have used two strategies to design polyvalent inhibitors of NSPs that target all three NSPs and may be used in the aerosol-based treatment of inflammatory lung diseases. First, we fused the elafin domain with the second inhibitory domain of SLPI to produce recombinant chimeras that had the inhibitory properties of both parent molecules. Second, we generated the trappin-2 variant, trappin-2 A62L, in which the P1 residue Ala is replaced by Leu, as in the corresponding position in SLPI domain 2. The chimera inhibitors and trappin-2 A62L are tight-binding inhibitors of all three NSPs with subnanomolar K(i)s, similar to those of the parent molecules for their respective target proteases. We have also shown that these molecules inhibit the neutrophil membrane-bound forms of all three NSPs. The trappin-2 A62L and elafin-SLPI chimeras, like wild-type elafin and trappin-2, can be covalently cross-linked to fibronectin or elastin by a tissue transglutaminase, while retaining their polypotent inhibition of NSPs. Therefore, the inhibitors described herein have the appropriate properties to be further evaluated as therapeutic anti-inflammatory agents.

The antibacterial and antifungal properties of trappin-2 (pre-elafin) do not depend on its protease inhibitory function

Trappin-2 (also known as pre-elafin) is an endogenous inhibitor of neutrophil serine proteases and is involved in the control of excess proteolysis, especially in inflammatory events, along with the structurally related secretory leucocyte proteinase inhibitor. Secretory leucocyte proteinase inhibitor has been shown to have antibacterial and antifungal properties, whereas recent data indicate that trappin-2 has antimicrobial activity against Pseudomonas aeruginosa and Staphylococcus aureus. In the present study, we tested the antibacterial properties of trappin-2 towards other respiratory pathogens. We found that trappin-2, at concentrations of 5-20 microm, has significant activity against Klebsiella pneumoniae, Haemophilus influenzae, Streptococcus pneumoniae, Branhamella catarrhalis and the pathogenic fungi Aspergillus fumigatus and Candida albicans, in addition to P. aeruginosa and S. aureus. A similar antimicrobial activity was observed with trappin-2 A62D/M63L, a trappin-2 variant that has lost its antiprotease properties, indicating that trappin-2 exerts its antibacterial effects through mechanisms independent from its intrinsic antiprotease capacity. Furthermore, the antibacterial and antifungal activities of trappin-2 were sensitive to NaCl and heparin, demonstrating that its mechanism of action is most probably dependent on its cationic nature. This enables trappin-2 to interact with the membranes of target organisms and disrupt them, as shown by our scanning electron microscopy analyses. Thus, trappin-2 not only provides an antiprotease shield, but also may play an important role in the innate defense of the human lungs and mucosae against pathogenic microorganisms.

Multifaceted roles of human elafin and secretory leukocyte proteinase inhibitor (SLPI), two serine protease inhibitors of the chelonianin family

Elafin and SLPI are low-molecular weight proteins that were first identified as protease inhibitors in mucous fluids including lung secretions, where they help control excessive proteolysis due to neutrophil serine proteases (elastase, proteinase 3 and cathepsin G). Elafin and SLPI are structurally related in that both have a fold with a four-disulfide core or whey acidic protein (WAP) domain responsible for inhibiting proteases. Elafin is derived from a precursor, trappin-2 or pre-elafin, by proteolysis. Trappin-2, which is itself a protease inhibitor, has a unique N-terminal domain that enables it to become cross-linked to extracellular matrix proteins by transglutaminase(s). SLPI and elafin/trappin-2 are attractive candidates as therapeutic molecules for inhibiting neutrophil serine proteases in inflammatory lung diseases. Hence, they have become the WAP proteins most studied over the last decade. This review focuses on recent findings revealing that SLPI and elafin/trappin-2 have many biological functions as diverse as anti-bacterial, anti-fungal, anti-viral, anti-inflammatory and immuno-modulatory functions, in addition to their well-recognized role as protease inhibitors.

Elafin and its precursor trappin-2 still inhibit neutrophil serine proteinases when they are covalently bound to extracellular matrix proteins by tissue transglutaminase

Elafin and its precursor trappin-2 (also called pre-elafin) are potent protein inhibitors of neutrophil serine proteases such as leukocyte elastase and proteinase 3. Trappin-2 has unique conserved sequence motifs rich in Gln and Lys residues. These motifs are substrates for transglutaminases that may enable trappin-2 to be cross-linked to extracellular matrix proteins, thus anchoring the inhibitor at its site of action. We have used Western blotting and ELISA-based assays to demonstrate that both elafin and trappin-2 can be conjugated to various extracellular matrix proteins in vitro by a type 2 transglutaminase. Cross-linked elafin and trappin-2 still inhibited their target proteases. Surface plasmon resonance studies allowed the determination of the kinetic constants governing the interaction of fibronectin-bound elafin and trappin-2 with neutrophil elastase and proteinase 3. Both inhibitors were potent inhibitors when cross-linked to fibronectin by transglutamination, with equilibrium dissociation constants K(i) for their interaction with target proteases of 0.3 nM (elastase-elafin), 20 nM (proteinase 3-elafin), 0.3 nM (elastase-trappin-2), and 12 nM (proteinase 3-trappin-2). The conjugated inhibitors reacted more slowly with their target enzymes than did the soluble inhibitors, perhaps due to their immobilization, with association rate constants of 2-7 x 10(5) M(-)(1) s(-)(1) for elastase and 1-4 x 10(4) M(-)(1) s(-)(1) for proteinase 3. We believe this is the first demonstration that transglutaminase-mediated cross-linking of serine protease inhibitors to proteins preserves their inhibitory capacities.

Proteolytic susceptibility of the serine protease inhibitor trappin-2 (pre-elafin): evidence for tryptase-mediated generation of elafin

A number of serine, cysteine, metallo- and acid proteases were evaluated for their ability to proteolytically cleave the serine protease inhibitor trappin-2, also known as pre-elafin, and to release elafin from its precursor. None of the metalloproteases or acid proteases examined cleaved trappin-2, while serine and cysteine proteases preferentially cleaved trappin-2 within its non-inhibitory N-terminal moiety. Cathepsin L, cathepsin K, plasmin, trypsin and tryptase were able to release elafin by cleaving the Lys 38 -Ala 39 peptide bond in trappin-2. However, purified tryptase appeared to be efficient at releasing elafin. Incubation of trappin-2 with purified mast cells first challenged with anti-immunoglobulin E or calcium ionophore A23187 resulted in the rapid generation of elafin. This proteolytic release of elafin from trappin-2 was inhibited in the presence of a tryptase inhibitor, suggesting that this mast cell enzyme was involved in the process. Finally, ex vivo incubation of trappin-2 with sputum from cystic fibrosis patients indicated the production of a proteolytic immunoreactive fragment with the same mass as that of native elafin. This cleavage did not occur when preincubating the sputum with polyclonal antibodies directed against tryptase. Taken together, these findings indicate that tryptase could likely be involved in the maturation of trappin-2 into elafin under physiological conditions.

Effects of hydrostatic pressure on horse liver alcohol dehydrogenase (HLADH): a new way of analyzing kinetic study

Oxidation of ethanol by horse liver alcohol dehydrogenase (HLADH) is monitored under pressure (0.1 MPa - 225 MPa). The pressure-induced modifications of catalytic activity are followed by plotting reaction velocities as a function of substrates concentrations in the traditional double reciprocal form: then, pressure is treated as an activator (p < 100 MPa) or an inhibitor (p<225 MPa). Surprising typical patterns of Lineweaver-Burk curves are observed and interpreted. These results suggest that this approach could be a powerful tool to study enzyme's structure-activity relationship.

Fluorescence and FTIR study of pressure-induced structural modifications of horse liver alcohol dehydrogenase (HLADH)

The process of pressure-induced modification of horse liver alcohol dehydrogenase (HLADH) was followed by measuring in situ catalytic activity (up to 250 MPa), intrinsic fluorescence (0.1-600 MPa) and modifications of FTIR spectra (up to 1000 MPa). The tryptophan fluorescence measurements and the kinetic data indicated that the pressure-induced denaturation of HLADH was a process involving several transitions and that the observed transient states have characteristic properties of molten globules. Low pressure (< 100 MPa) induced no important modification in the catalytic efficiency of the enzyme and slight conformational changes, characterized by a small decrease in the centre of spectral mass of the enzyme's intrinsic fluorescence: a native-like state was assumed. Higher pressures (100-400 MPa) induced a strong decrease of HLADH catalytic efficiency and further conformational changes. At 400 MPa, a dimeric molten globule-like state was proposed. Further increase of pressure (400-600 MPa) seemed to induce the dissociation of the dimer leading to a transition from the first dimeric molten globule state to a second monomeric molten globule. The existence of two independent structural domains in HLADH was assumed to explain this transition: these domains were supposed to have different stabilities against high pressure-induced denaturation. FTIR spectroscopy was used to follow the changes in HLADH secondary structures. This technique confirmed that the intermediate states have a low degree of unfolding and that no completely denatured form seemed to be reached, even up to 1000 MPa.