Novel mode for neutrophil protease cathepsin G-mediated signaling: membrane shedding of epidermal growth factor is required for cardiomyocyte anoikis

S645C Point Mutation Suppresses Degradation of EGFR to Promote Progression of Glioblastoma

Background

The tightly controlled activity of EGFR is important for the homeostasis of self-renewal of human tissue. Mutations in the extracellular domain of EGFR are frequent and function as a novel mechanism for oncogenic EGFR activation in GBM, and impact the response of patients to small-molecule inhibitors.

Methods

We constructed glioblastoma cell lines stably expressing wild-type EGFR and the mutant of EGFR S645C. We detected cell growth in vitro and in vivo. We evaluated the anti-tumor activity and effectiveness of gefitinib and osimertinib in cells.

Results

In the present study, we identified an oncogenic substituted mutation of EGFR—S645C. The mutation can promote the proliferation and colony formation of glioblastoma in vitro and in vivo. Mechanistically, the EGFR S645C mutation potentially changes the formation of hydrogen bonds within dimerized EGFR and inhibits the degradation of EGFR to prolong downstream signaling. The mutation induces resistance to gefitinib but presents an opportunity for osimertinib treatment.

Conclusion

The study indicated a novel oncogenic mutation and advises on the precise treatment of individual patients with the EGFR S645C mutation.

Epidermal growth factor receptor association with β1-adrenergic receptor is mediated via its juxtamembrane domain

β1-adrenergic receptor (β1AR)-mediated transactivation of epidermal growth factor receptor (EGFR) engages downstream signaling events that impact numerous cellular processes including growth and survival. While association of these receptors has been shown to occur basally and be important for relaying transactivation-specific intracellular events, the mechanism by which they do so is unclear and elucidation of which would aid in understanding the consequence of disrupting their interaction. Using fluorescence resonance energy transfer (FRET) and immunoprecipitation (IP) analyses, we evaluated the impact of C-terminal truncations of EGFR on its ability to associate with β1AR. While loss of the last 230 amino acid C-terminal phosphotyrosine-rich domain did not disrupt the ability of EGFR to associate with β1AR, truncation of the entire intracellular domain of EGFR resulted in almost complete loss of its interaction with β1AR, suggesting that either the kinase domain or juxtamembrane domain (JMD) may be required for this association. Treatment with the EGFR antagonist gefitinib did not prevent β1AR-EGFR association, however, treatment with a palmitoylated peptide encoding the first 20 amino acids of the JMD domain (JMD-A) disrupted β1AR-EGFR association over time and prevented β1AR-mediated ERK1/2 phosphorylation, both in general and specifically in association with EGFR. Conversely, neither a mutated JMD-A peptide nor a palmitoylated peptide fragment consisting of the subsequent 18 amino acids of the JMD domain (JMD-B) were capable of doing so. Altogether, the proximal region of the JMD of EGFR is responsible for its association with β1AR, and its disruption prevents β1AR-mediated transactivation, thus providing a new tool to study the functional consequences of disrupting β1AR-EGFR downstream signaling.

Loss of Protease-Activated Receptor 4 Prevents Inflammation Resolution and Predisposes the Heart to Cardiac Rupture After Myocardial Infarction

BACKGROUND

Cardiac rupture is a major lethal complication of acute myocardial infarction (MI). Despite significant advances in reperfusion strategies, mortality from cardiac rupture remains high. Studies suggest that cardiac rupture can be accelerated by thrombolytic therapy, but the relevance of this risk factor remains controversial.

METHODS

We analyzed protease-activated receptor 4 (Par4) expression in mouse hearts with MI and investigated the effects of Par4 deletion on cardiac remodeling and function after MI by echocardiography, quantitative immunohistochemistry, and flow cytometry.

RESULTS

Par4 mRNA and protein levels were increased in mouse hearts after MI and in isolated cardiomyocytes in response to hypertrophic and inflammatory stimuli. Par4-deficient mice showed less myocyte apoptosis, reduced infarct size, and improved functional recovery after acute MI relative to wild-type (WT). Conversely, Par4^-/- mice showed impaired cardiac function, greater rates of myocardial rupture, and increased mortality after chronic MI relative to WT. Pathological evaluation of hearts from Par4^-/- mice demonstrated a greater infarct expansion, increased cardiac hemorrhage, and delayed neutrophil accumulation, which resulted in impaired post-MI healing compared with WT. Par4 deficiency also attenuated neutrophil apoptosis in vitro and after MI in vivo and impaired inflammation resolution in infarcted myocardium. Transfer of Par4^-/- neutrophils, but not of Par4^-/- platelets, in WT recipient mice delayed inflammation resolution, increased cardiac hemorrhage, and enhanced cardiac dysfunction. In parallel, adoptive transfer of WT neutrophils into Par4^-/- mice restored inflammation resolution, reduced cardiac rupture incidence, and improved cardiac function after MI.

CONCLUSIONS

These findings reveal essential roles of Par4 in neutrophil apoptosis and inflammation resolution during myocardial healing and point to Par4 inhibition as a potential therapy that should be limited to the acute phases of ischemic insult and avoided for long-term treatment after MI.

Inflammatory Serine Proteases Play a Critical Role in the Early Pathogenesis of Diabetic Cardiomyopathy

Background/Aims:

Diabetic cardiomyopathy (DCM) is characterized by structural and functional alterations that can lead to heart failure. Several mechanisms are known to be involved in the pathogenesis of DCM, however, the molecular mechanism that links inflammation to DCM is incompletely understood. To learn about this mechanism, we investigated the role of inflammatory serine proteases (ISPs) during the development of DCM.

Methods:

Eight weeks old mice with deletion of dipeptidyl peptidase I (DPPI), an enzyme involved in the maturation of major ISPs, and wild type (WT) mice controls were injected with streptozotocin (50 mg/kg for 5 days intraperitoneally) and studied after 4, 8, 16, and 20 week after induction of type 1 diabetes mellitus (T1DM). Induction of diabetes was followed by echocardiographic measurements, glycemic and hemoglobulin A1c profiling, immunoblot, qPCR, enzyme activity assays, and immunohistochemistry (IHC) analysis of DPPI, ISPs, and inflammatory markers. Fibrosis was determined from left ventricular heart by Serius Red staining and qPCR. Apoptosis was determined by TUNEL assay and immunoblot analysis.

Results:

In the diabetic WT mice, DPPI expression increased along with ISP activation, and DPPI accumulated abundantly in the left ventricle mainly from infiltrating neutrophils. In diabetic DPPI-knockout (DPPI-KO) mice, significantly decreased activation of ISPs, myocyte apoptosis, fibrosis, and cardiac function was improved compared to diabetic WT mice. In addition, DPPI-KO mice showed a decrease in overall inflammatory status mediated by diabetes induction which was manifested by decreased production of pro-inflammatory cytokines like TNF-α, IL-1β and IL-6.

Conclusion:

This study elucidates a novel role of ISPs in potentiating the immunological responses that lead to the pathogenesis of DCM in T1DM. To the best of our knowledge, this is the first study to report that DPPI expression and activation promotes the inflammation that enhances myocyte apoptosis and contributes to the adverse cardiac remodeling that subsequently leads to DCM.

Intracardiac administration of neutrophil protease cathepsin G activates noncanonical inflammasome pathway and promotes inflammation and pathological remodeling in non-injured heart

BACKGROUND

Inflammatory serine proteases (ISPs) play an important role in cardiac repair after injury through hydrolysis of dead cells and extracellular matrix (ECM) debris. Evidence also suggests an important role of ISPs in the coordination of the inflammatory response. However, the effect of ISPs on inflammation is obfuscated by the confounding factors associated with cell death and inflammatory cell infiltration induced after cardiac injury. This study investigated whether neutrophil-derived cathepsin G (Cat.G) influences inflammation and remodeling in the absence of prior cardiac injury and cell death.

METHODS AND RESULTS

Intracardiac catheter delivery of Cat.G (1 mg/kg) in rats induced significant left ventricular (LV) dilatation and cardiac contractile dysfunction at day 5, but not at day 2, post-delivery compared to vehicle-treated animals. Cat.G delivery also significantly increased matrix metalloprotease activity and collagen and fibronectin degradation at day 5 compared to vehicle-treated rats and these changes were associated with increased death signaling pathways and myocyte apoptosis. Mechanistic analysis shows that Cat.G-treatment induced potent chemotactic activity in hearts at day 2 and 5 post-delivery, characterized by processing and activation of interleukin (IL)-1β and IL-18, stimulation of inflammatory signaling pathways and accumulation of myeloid cells when compared to vehicle-treated rats. Cat.G-induced processing of IL-1β and IL-18 was independent of the canonical NLRP-3 inflammasome pathway and treatment of isolated cardiomyocytes with inhibitors of NLRP-3 or caspase-1 failed to reduce Cat.G-induced cardiomyocyte death. Notably, rats treated with IL-1 receptor antagonist (IL-1Ra) show reduced inflammation and improved cardiac remodeling and function following Cat.G delivery.

CONCLUSIONS

Cat.G exerts potent chemoattractant and pro-inflammatory effects in non-stressed or injured heart in part through processing and activation of IL-1 family cytokines, subsequently leading to adverse cardiac remodeling and function. Thus, targeting ISPs could be a novel therapeutic strategy to reduce cardiac inflammation and improve cardiac remodeling and function after injury or stress.

Molecular network, pathway, and functional analysis of time-dependent gene changes related to cathepsin G exposure in neonatal rat cardiomyocytes

The molecular pathways activated in response to acute cathepsin G (CG) exposure, as well as the mechanisms involved in activation of signaling pathways that culminate in myocyte detachment and apoptosis remain unclear. This study aimed to determine the changes in gene expression patterns associated with time dependent CG exposure to neonatal rat cardiomyocytes (NRCMs). Microarray analysis revealed a total of 451, 572 and 1127 differentially expressed genes after CG exposure at 1, 4 and 8 h respectively. A total of 54 overlapped genes at each time point were mapped by Ingenuity Pathway Analysis (IPA). The top up-regulated genes included Hamp, SMAD6, NR4A1, FOSL2, ID3 and SLAMF7, and down-regulated genes included CYR61, GDF6, Olr640, Vom2r36, DUSP6 and MMP20. Our data suggest that there are multiple deregulated pathways associated with cardiomyocyte death after CG exposure, including JAK/Stat signaling, IL-9 signaling and Nur77 signaling. In addition, we also generated the molecular network of expressed gene and found most of the molecules were connected to ERK1/2, caspase, BCR (complex) and Cyclins. Our study reveals the ability to assess time-dependent changes in gene expression patterns in NRCMs associated with CG exposure. The global gene expression profiles may provide insight into the cellular mechanism that regulates CG dependent myocyte apoptosis. In future, the pathways important in CG response, as well as the genes found to be differentially expressed might represent the therapeutic targets for myocyte survival in heart failure.

Dual inhibition of cathepsin G and chymase reduces myocyte death and improves cardiac remodeling after myocardial ischemia reperfusion injury

Early reperfusion of ischemic cardiac tissue increases inflammatory cell infiltration which contributes to cardiomyocyte death and loss of cardiac function, referred to as ischemia/reperfusion (IR) injury. Neutrophil- and mast cell-derived proteases, cathepsin G (Cat.G) and chymase, are released early after IR, but their function is complicated by potentially redundant actions and targets. This study investigated whether a dual inhibition of Cat.G and chymase influences cardiomyocyte injury and wound healing after experimental IR in mice. Treatment with a dual Cat.G and chymase inhibitor (DCCI) immediately after reperfusion blocked cardiac Cat.G and chymase activity induced after IR, which resulted in decreased immune response in the infarcted heart. Mice treated with DCCI had less myocardial collagen deposition and showed preserved ventricular function at 1 and 7 days post-IR compared with vehicle-treated mice. DCCI treatment also significantly attenuated focal adhesion (FA) complex disruption and myocyte degeneration after IR. Treatment of isolated cardiomyocytes with Cat.G or chymase significantly promoted FA signaling downregulation, myofibril degeneration and myocyte apoptosis. Conversely, treatment of cardiac fibroblasts with Cat.G or chymase induced FA signaling activation and increased their migration and differentiation to myofibroblasts. These opposite responses in cardiomyocytes and fibroblasts were blocked by treatment with DCCI. These findings show that Cat.G and chymase are key mediators of myocyte apoptosis and fibroblast migration and differentiation that play a role in adverse cardiac remodeling and function post-IR. Thus, dual targeting of neutrophil- and mast cell-derived proteases could be used as a novel therapeutic strategy to reduce post-IR inflammation and improve cardiac remodeling.

Insulin-like growth factor-1 signaling is responsible for cathepsin G-induced aggregation of breast cancer MCF-7 cells

Cathepsin G (CG), a neutrophil serine protease, induces cell migration and multicellular aggregation of human breast cancer MCF-7 cells in a process that is dependent on E-cadherin and CG enzymatic activity. While these tumor cell aggregates can cause tumor emboli that could represent intravascular growth and extravasation into the surrounding tissues, resulting in metastasis, the molecular mechanism underlying this process remains poorly characterized. In this study, we aimed to identify the signaling pathway that is triggered during CG-mediated stimulation of cell aggregation. Screening of a library of compounds containing approximately 90 molecular-targeting drugs revealed that this process was suppressed by the insulin-like growth factor-1 (IGF-1) receptor (IGF-1R)-specific kinase inhibitor OSI-906, as well as the multikinase inhibitors axitinib and sunitinib. Antibody array analysis, which is capable of detecting tyrosine phosphorylation of 49 distinct receptor tyrosine kinases, and the results of immunoprecipitation studies indicated that IGF-1R is phosphorylated in response to CG treatment. Notably, IGF-1R neutralization via treatment with a specific antibody or silencing of IGF-1R expression through siRNA transfection suppressed cell aggregation. Furthermore, CG treatment of MCF-7 cells resulted in increased release of IGF-1 into the medium for 24 h, while antibody-mediated IGF-1 neutralization partially prevented CG-induced cell aggregation. These results demonstrate that autocrine IGF-1 signaling is partly responsible for the cell aggregation induced by CG.

Protease-activated receptor 4 deficiency offers cardioprotection after acute ischemia reperfusion injury

Protease-activated receptor (PAR)4 is a low affinity thrombin receptor with less understood function relative to PAR1. PAR4 is involved in platelet activation and hemostasis, but its specific actions on myocyte growth and cardiac function remain unknown. This study examined the role of PAR4 deficiency on cardioprotection after myocardial ischemia-reperfusion (IR) injury in mice. When challenged by in vivo or ex vivo IR, PAR4 knockout (KO) mice exhibited increased tolerance to injury, which was manifest as reduced infarct size and a more robust functional recovery compared to wild-type mice. PAR4 KO mice also showed reduced cardiomyocyte apoptosis and putative signaling shifts in survival pathways in response to IR. Inhibition of PAR4 expression in isolated cardiomyocytes by shRNA offered protection against thrombin and PAR4-agonist peptide-induced apoptosis, while overexpression of wild-type PAR4 significantly enhanced the susceptibility of cardiomyocytes to apoptosis, even under low thrombin concentrations. Further studies implicate Src- and epidermal growth factor receptor-dependent activation of JNK on the proapoptotic effect of PAR4 in cardiomyocytes. These findings reveal a pivotal role for PAR4 as a regulator of cardiomyocyte survival and point to PAR4 inhibition as a therapeutic target offering cardioprotection after acute IR injury.

Up-regulation of Cathepsin G in the Development of Chronic Postsurgical Pain

Background:

Proteases have been shown to modulate pain signaling in the spinal cord and may contribute to the development of chronic postsurgical pain. By using peripheral inflammation in rats as a chronic pain model, the authors identified the deregulation of proteases and their inhibitors as a hallmark of chronic pain development using a genome-wide screening approach.

Methods:

A microarray analysis was performed and identified spinal cathepsin G (CTSG) as the most up-regulated gene in rats with persistent hyperalgesia after intraplantar injection of complete Freund’s adjuvant (n = 4). Further experiments were performed to elucidate the mechanisms of CTSG-induced hyperalgesia by intrathecally applying specific CTSG inhibitor (n = 10). The authors also evaluated the association between CTSG gene polymorphisms and the risk of chronic postsurgical pain in 1,152 surgical patients.

Results:

CTSG blockade reduced heat hyperalgesia, accompanied by a reduction in neutrophil infiltration and interleukin 1β levels in the dorsal horns. In the gene association study, 246 patients (21.4%) reported chronic postsurgical pain at 12-month follow-up. Patients with AA genotypes at polymorphisms rs2070697 (AA-15.3%, GA-24.1%, and GG-22.3%) or rs2236742 (AA-6.4%, GA-20.4%, and GG-22.6%) in the CTSG gene had lower risk for chronic postsurgical pain compared with wild-types. The adjusted odds ratios were 0.67 (95% CI, 0.26 to 0.99) and 0.34 (95% CI, 0.21 to 0.98), respectively.

Conclusions:

This study demonstrated that CTSG is a pronociceptive mediator in both animal model and human study. CTSG represents a new target for pain control and a potential marker to predict patients who are prone to develop chronic pain after surgery.

Granzyme B-expressing neutrophils correlate with bacterial load in granulomas from Mycobacterium tuberculosis-infected cynomolgus macaques

The role of neutrophils in tuberculosis (TB), and whether neutrophils express granzyme B (grzB), a pro-apoptotic enzyme associated with cytotoxic T cells, is controversial. We examined neutrophils in peripheral blood (PB) and lung granulomas of Mycobacterium tuberculosis-infected cynomolgus macaques and humans to determine whether mycobacterial products or pro-inflammatory factors induce neutrophil grzB expression. We found large numbers of grzB-expressing neutrophils in macaque and human granulomas and these cells contained more grzB+ granules than T cells. Higher neutrophil, but not T cell, grzB expression correlated with increased bacterial load. Although unstimulated PB neutrophils lacked grzB expression, grzB expression increased upon exposure to M.tuberculosis bacilli, M.tuberculosis culture filtrate protein or lipopolysaccharide from Escherichia coli. Perforin is required for granzyme-mediated cytotoxicity by T cells, but was not observed in PB or granuloma neutrophils. Nonetheless, stimulated PB neutrophils secreted grzB as determined by enzyme-linked immunospot assays. Purified grzB was not bactericidal or bacteriostatic, suggesting secreted neutrophil grzB acts on extracellular targets, potentially enhancing neutrophil migration through extracellular matrix and regulating apoptosis or activation in other cell types. These data indicate mycobacterial products and the pro-inflammatory environment of granulomas up-regulates neutrophil grzB expression and suggests a previously unappreciated aspect of neutrophil biology in TB.

Uncovering the cathepsin system in heart failure patients submitted to Left Ventricular Assist Device (LVAD) implantation

Background

In end-stage heart failure (HF), the implantation of a left ventricular assist device (LVAD) is able to induce reverse remodeling. Cellular proteases, such as cathepsins, are involved in the progression of HF. The aim of this study was to evaluate the role of cathepsin system in HF patients supported by LVAD, in order to determine their involvement in cardiac remodeling.

Methods

The expression of cysteine (CatB, CatK, CatL, CatS) and serine cathepsin (CatG), and relative inhibitors (Cystatin B, C and SerpinA3, respectively) was determined in cardiac biopsies of 22 patients submitted to LVAD (pre-LVAD) and compared with: 1) control stable chronic HF patients on medical therapy at the moment of heart transplantation without prior LVAD (HT, n = 7); 2) patients supported by LVAD at the moment of transplantation (post-LVAD, n = 6).

Results

The expression of cathepsins and their inhibitors was significantly higher in pre-LVAD compared to the HT group and LVAD induced a further increase in the cathepsin system. Significant positive correlations were observed between cardiac expression of cathepsins and their inhibitors as well as inflammatory cytokines. In the pre-LVAD group, a relationship of cathepsins with dilatative etiology and length of hospitalization was found.

Conclusions

A parallel activation of cathepsins and their inhibitors was observed after LVAD support. The possible clinical importance of these modifications is confirmed by their relation with patients’ outcome. A better discovery of these pathways could add more insights into the cardiac remodeling during HF.

Cathepsin G deficiency decreases complexity of atherosclerotic lesions in apolipoprotein E-deficient mice

Cathepsin G is a serine protease with a broad range of catalytic activities, including production of angiotensin II, degradation of extracellular matrix and cell-cell junctions, modulation of chemotactic responses, and induction of apoptosis. Cathepsin G mRNA expression is increased in human coronary atheroma vs. the normal vessel. To assess whether cathepsin G modulates atherosclerosis, cathepsin G knockout (Cstg(-/-)) mice were bred with apolipoprotein E knockout (Apoe(-/-)) mice to obtain Ctsg(+/-)Apoe(-/-) and Ctsg(+/+)Apoe(-/-) mice. Heterozygous cathepsin G deficiency led to a 70% decrease in cathepsin G activity in bone marrow cells, but this reduced activity did not impair generation of angiotensin II in bone marrow-derived macrophages (BMDM). Atherosclerotic lesions were compared in male Cstg(+/-)Apoe(-/-) and Cstg(+/+)Apoe(-/-) mice after 8 wk on a high-fat diet. Plasma cholesterol levels and cholesterol distribution within serum lipoprotein fractions did not differ between genotypes nor did the atherosclerotic lesion areas in either the aortic root or aortic arch. Cstg(+/-)Apoe(-/-) mice, however, showed a lower percentage of complex lesions within the aortic root and a smaller number of apoptotic cells compared with Cstg(+/+)Apoe(-/-) littermates. Furthermore, apoptotic Cstg(-/-) BMDM were more efficiently engulfed by phagocytic BMDM than were apoptotic Ctsg(+/+) BMDM. Thus cathepsin G activity may impair efferocytosis, which could lead to an accumulation of lesion-associated apoptotic cells and the accelerated progression of early atherosclerotic lesions to more complex lesions in Apoe(-/-) mice.

SerpinB1 is critical for neutrophil survival through cell-autonomous inhibition of cathepsin G

Bone marrow (BM) holds a large reserve of polymorphonuclear neutrophils (PMNs) that are rapidly mobilized to the circulation and tissues in response to danger signals. SerpinB1 is a potent inhibitor of neutrophil serine proteases neutrophil elastase (NE) and cathepsin G (CG). SerpinB1 deficiency (sB1(-/-)) results in a severe reduction of the BM PMN reserve and failure to clear bacterial infection. Using BM chimera, we found that serpinB1 deficiency in BM cells was necessary and sufficient to reproduce the BM neutropenia of sB1(-/-) mice. Moreover, we showed that genetic deletion of CG, but not NE, fully rescued the BM neutropenia in sB1(-/-) mice. In mixed BM chimera and in vitro survival studies, we showed that CG modulates sB1(-/-) PMN survival through a cell-intrinsic pathway. In addition, membrane permeabilization by lysosomotropic agent l-leucyl-l-leucine methyl ester that allows cytosolic release of granule contents was sufficient to induce rapid PMN death through a CG-dependent pathway. CG-mediated PMN cytotoxicity was only partly blocked by caspase inhibition, suggesting that CG cleaves a distinct set of targets during apoptosis. In conclusion, we have unveiled a new cytotoxic function for the serine protease CG and showed that serpinB1 is critical for maintaining PMN survival by antagonizing intracellular CG activity.

Cathepsin G-regulated release of formyl peptide receptor agonists modulate neutrophil effector functions

Neutrophil serine proteases play an important role in inflammation by modulating neutrophil effector functions. We have previously shown that neutrophils deficient in the serine proteases cathepsin G and neutrophil elastase (CG/NE neutrophils) exhibit severe defects in chemokine CXCL2 release and reactive oxygen species (ROS) production when activated on immobilized immune complex. Exogenously added active CG rescues these defects, but the mechanism remains undefined. Using a protease-based proteomic approach, we found that, in vitro, the addition of exogenous CG to immune complex-stimulated CG/NE neutrophils led to a decrease in the level of cell-associated annexin A1 (AnxA1) and cathelin-related antimicrobial peptide (CRAMP), both known inflammatory mediators. We further confirmed that, in vivo, CG was required for the extracellular release of AnxA1 and CRAMP in a subcutaneous air pouch model. In vitro, CG efficiently cleaved AnxA1, releasing the active N-terminal peptide Ac2-26, and processed CRAMP in limited fashion. Ac2-26 and CRAMP peptides enhanced the release of CXCL2 by CG/NE neutrophils in a dose-dependent manner via formyl peptide receptor (FPR) stimulation. Blockade of FPRs by an antagonist, Boc2 (t-Boc-Phe-d-Leu-Phe-d-Leu-Phe), abrogates CXCL2 release, whereas addition of FPR agonists, fMLF and F2L, relieves Boc2 inhibition. Furthermore, the addition of active CG, but not inactive CG, also relieves Boc2 inhibition. These findings suggest that CG modulates neutrophil effector functions partly by controlling the release (and proteolysis) of FPR agonists. Unexpectedly, we found that mature CRAMP, but not Ac2-26, induced ROS production through an FPR-independent pathway.

Protein targets of inflammatory serine proteases and cardiovascular disease

Serine proteases are a key component of the inflammatory response as they are discharged from activated leukocytes and mast cells or generated through the coagulation cascade. Their enzymatic activity plays a major role in the body's defense mechanisms but it has also an impact on vascular homeostasis and tissue remodeling. Here we focus on the biological role of serine proteases in the context of cardiovascular disease and their mechanism(s) of action in determining specific vascular and tissue phenotypes. Protease-activated receptors (PARs) mediate serine protease effects; however, these proteases also exert a number of biological activities independent of PARs as they target specific protein substrates implicated in vascular remodeling and the development of cardiovascular disease thus controlling their activities. In this review both PAR-dependent and -independent mechanisms of action of serine proteases are discussed for their relevance to vascular homeostasis and structural/functional alterations of the cardiovascular system. The elucidation of these mechanisms will lead to a better understanding of the molecular forces that control vascular and tissue homeostasis and to effective preventative and therapeutic approaches.

Activation of the epidermal growth factor receptor (EGFR) by a novel metalloprotease pathway

Neutrophil Elastase (NE) is a pro-inflammatory protease present at higher than normal levels in the lung during inflammatory disease. NE regulates IL-8 production from airway epithelial cells and can activate both EGFR and TLR4. TACE/ADAM17 has been reported to trans-activate EGFR in response to NE. Here, using 16HBE14o-human bronchial epithelial cells we demonstrate a new mechanism by which NE regulates both of these events. A high molecular weight soluble metalloprotease activity detectable only in supernatants from NE-treated cells by gelatin and casein zymography was confirmed to be meprin alpha by Western immunoblotting. In vitro studies demonstrated the ability of NE to activate meprin alpha, which in turn could release soluble TGFalpha and induce IL-8 production from 16HBE14o- cells. These effects were abrogated by actinonin, a specific meprin inhibitor. NE-induced IL-8 expression was also inhibited by meprin alpha siRNA. Immunoprecipitation studies detected EGFR/TLR4 complexes in NE-stimulated cells overexpressing these receptors. Confocal studies confirmed colocalization of EGFR and TLR4 in 16HBE14o- cells stimulated with meprin alpha. NFkappaB was also activated via MyD88 in these cells by meprin alpha. In bronchoalveolar lavage fluid from NE knock-out mice infected intra-tracheally with Pseudomonas aeruginosa meprin alpha was significantly decreased compared with control mice, and was significantly increased and correlated with NE activity, in bronchoalveolar lavage fluid from individuals with cystic fibrosis but not healthy controls. The data describe a previously unidentified lung metalloprotease meprin alpha, and its role in NE-induced EGFR and TLR4 activation and IL-8 production.