Role Of Protease-activated Receptor-2 Research Articles

Novel Role for Proteinase-activated Receptor 2 (PAR2) in Membrane Trafficking of Proteinase-activated Receptor 4 (PAR4)

Proteinase-activated receptors 4 (PAR(4)) is a class A G protein-coupled receptor (GPCR) recognized through the ability of serine proteases such as thrombin and trypsin to mediate receptor activation. Due to the irreversible nature of activation, a fresh supply of receptor is required to be mobilized to the cell surface for responsiveness to agonist to be sustained. Unlike other PAR subtypes, the mechanisms regulating receptor trafficking of PAR(4) remain unknown. Here, we report novel features of the intracellular trafficking of PAR(4) to the plasma membrane. PAR(4) was poorly expressed at the plasma membrane and largely retained in the endoplasmic reticulum (ER) in a complex with the COPI protein subunit β-COP1. Analysis of the PAR(4) protein sequence identified an arginine-based (RXR) ER retention sequence located within intracellular loop-2 (R(183)AR → A(183)AA), mutation of which allowed efficient membrane delivery of PAR(4). Interestingly, co-expression with PAR(2) facilitated plasma membrane delivery of PAR(4), an effect produced through disruption of β-COP1 binding and facilitation of interaction with the chaperone protein 14-3-3ζ. Intermolecular FRET studies confirmed heterodimerization between PAR(2) and PAR(4). PAR(2) also enhanced glycosylation of PAR(4) and activation of PAR(4) signaling. Our results identify a novel regulatory role for PAR(2) in the anterograde traffic of PAR(4). PAR(2) was shown to both facilitate and abrogate protein interactions with PAR(4), impacting upon receptor localization and cell signal transduction. This work is likely to impact markedly upon the understanding of the receptor pharmacology of PAR(4) in normal physiology and disease.

The Role of Proteinase-activated Receptor-2 in Idiopathic Pulmonary Fibrosis: Is There Really Novel Therapeutic Potential Here?

The Role of Proteinase-activated Receptor-2 in Idiopathic Pulmonary Fibrosis: Is There Really Novel Therapeutic Potential Here?

The Role of Proteinase-activated Receptor-2 in Idiopathic Pulmonary Fibrosis: Is There Really Novel Therapeutic Potential Here?

The Role of Proteinase-activated Receptor-2 in Idiopathic Pulmonary Fibrosis: Is There Really Novel Therapeutic Potential Here?

Protease-Activated Receptors in Hemostasis, Thrombosis and Beyond

Protease-activated receptors (PARs) provide a mechanism by which thrombin and related proteases can regulate the behavior of platelets and other cells. Overall, the coagulation cascade and PARs together provide an elegant system that links mechanical information in the form of disruption of vascular integrity to appropriate cellular responses involved in hemostasis, inflammation, repair, and even pain perception. This talk will focus on lessons from animal models regarding the roles of PARs in hemostasis and thrombosis and how these lessons might and might not relate to the pathophysiology of myocardial infarction in humans and ongoing trials of PAR1 antagonists for secondary prevention of the same. Recent work that reveals unexpected roles for PARs outside the context of response to injury –– specifically in vascular and neural development in vertebrate embryos –– will be also be briefly summarized.

Role of proteinase-activated receptor-2 in allergic sensitization to house dust mite allergens

Background A number of common aeroallergens have serine proteinase activity, which is important for allergic sensitization. House dust mite (HDM), and other allergens with serine proteinase activity activate Protease-Activated Receptor-2 (PAR-2). We have shown that PAR-2 activation in the airways leads to allergic sensitization to concomitantly inhaled antigens, implicating PAR-2 in the pathogenesis of asthma. We hypothesized that PAR-2 activation in the airways by HDM allergens is important for the development of allergic sensitization. Methods HDM extract was administered to mice intranasally for 5 consecutive days to induce allergic sensitization. One group of mice received a blocking anti-PAR-2 antibody intranasally before each HDM administration. Results Administration of the PAR-2 blocking antibody decreased IL-4, IL13 and IL-33 mRNA as well as IL-4, IL-5 and MIP1A protein levels in the lung tissue, suggesting decreased allergic airway sensitization. Mice sensitized in the presence of the PAR-2 blocking antibody or isotype control were then challenged intranasally with HDM extract for 4 consecutive days. Mucosal exposure to HDM extract induced AHR and airway eosinophilic inflammation. Administration of the anti-PAR-2 blocking antibody during the sensitization phase completely inhibited the development of AHR and airway inflammation in response to HDM challenge. Conclusions These results indicate that HDM extract induces PAR-2dependent allergic sensitization in mice and lead to PAR-2-dependet allergic airway inflammation. These results will allow us to better define the mechanisms of allergic sensitization to allergens with serine proteinase activity.

Role of Protease-activated Receptor-2 in Idiopathic Pulmonary Fibrosis

Activation of the coagulation cascade has been demonstrated in pulmonary fibrosis. In addition to its procoagulant function, various coagulation proteases exhibit cellular effects that may also contribute to fibrotic processes in the lung. To investigate the importance of protease-activated receptor (PAR)-2 and its activators, coagulation factor VIIa (FVIIa)/tissue factor (TF), in the development of idiopathic pulmonary fibrosis (IPF). Expression and localization of PAR-2 and its activators were examined in IPF lung tissue. The ability of PAR-2 to mediate various cellular processes was studied in vitro. Expression of PAR-2 was strongly elevated in IPF lungs and was attributable to alveolar type II cells and fibroblasts/myofibroblasts. Transforming growth factor-β(1), a key profibrotic cytokine, considerably enhanced PAR-2 expression in human lung fibroblasts. FVIIa stimulated proliferation of human lung fibroblasts and extracellular matrix production in a PAR-2-dependent manner, but did not initiate differentiation of fibroblasts into myofibroblasts. PAR-2/FVIIa-driven mitogenic activities were mediated via the p44/42 mitogen-activated protein kinase pathway and were independent of factor Xa and thrombin production. Proproliferative properties of FVIIa were markedly potentiated in the presence of TF and abrogated by TF antisense oligonucleotides. Hyperplastic alveolar type II cells overlying fibroblastic foci were found to be the source of FVII in IPF lungs. Moreover, TF colocalized with PAR-2 on fibroblasts/myofibroblasts in IPF lungs. The PAR-2/TF/FVIIa axis may contribute to the development of pulmonary fibrosis; thus, interference with this pathway confers novel therapeutic potential for the treatment of IPF.

Role of protease-activated receptors in human skin fibrosis and scleroderma

Proteases and their receptors have poorly understood roles in skin fibrosis and systemic scleroderma (SSc). We examined the role of protease-activated receptors (PAR(1) and PAR(2) ) in the pathophysiology of human SSc and skin fibrosis. Immunohistochemistry showed that PAR(1) immunoreactivity was positive in fibroblasts of SSc skin and healthy skin. PAR(2) immunoreactivity was positive in SSc skin, but negative in endothelial cells and fibroblasts of healthy skin. Double immunofluorescence using an antibody against smooth muscle actin (α-SMA) as a marker for myofibroblasts verified a certain percentage of myofibroblasts positive for PAR(1) and PAR(2) in SSc skin. In human dermal cultured fibroblasts (HDF), PAR(1) stimulation with or without bleomycin pretreatment mobilized intracellular calcium, indicating that the expressed PARs are functional and have effects on downstream signalling by calcium release. PAR(2) -induced intracellular calcium mobilization was only measurable in HDF after bleomycin pretreatment. Thus, PAR(1) - and PAR(2) -positive fibroblasts are increased in SSc, indicating a regulatory role. Intriguingly, bleomycin activated PAR(2) in HDF indicating that fibrosis-promoting factors have a direct effect on PAR(2) expression and functionality.

Role of protease-activated receptor-2 on cell death and DNA fragmentation in Helicobacter pylori-infected gastric epithelial cells

BackgroundHelicobacter pylori (H. pylori) infection is associated with chronic gastritis, peptic ulceration and gastric carcinoma. Protease-activated receptor-2 (PAR-2), which is activated by trypsin, induced the activation of mitogen-activated protein kinases (MAPK), cell proliferation and apoptosis in several cells. Previously, we found that H. pylori induces the expression of PAR-2, which mediates the expression of adhesion molecules integrins in gastric epithelial cells. In the present study, the role of PAR-2 on H. pylori-induced cell death was investigated by determining cell viability, DNA fragmentation, and the activation of MAPK in gastric epithelial AGS cells.MethodsAGS cells were cultured in the presence of H. pylori transfected with PAR-2 antisense (AS) oligonucleotide (ODN) or treated with a soybean trypsin inhibitor (SBTI). Viable cells and DNA fragmentation were determined by trypan blue exclusion assay and the amount of oligonucleosome-bound DNA, respectively. The activation of MAPK such as extracellular signal-regulated kinases (ERK), p38, and c-Jun N-terminal kinases (JNK), was assessed by Western blotting for phospho-specific forms of MAPK.ResultsH. pylori-induced cell death and DNA fragmentation augmented in the cells transfected with PAR-2 AS ODN or treated with SBTI. The activation of MAPK, induced by H. pylori, were suppressed by transfection with PAR-2 AS ODN or treatment with SBTI.ConclusionPAR-2, whose expression is induced by H. pylori, may prevent cell death and DNA fragmentation with the activation of MAPK in gastric epithelial cells.

Pulmonary hypertension in smoking mice over-expressing protease-activated receptor-2

The mechanism(s) involved in the development of pulmonary hypertension (PH) in COPD is still the object of investigation. Cigarette smoke (CS) may lead to remodelling of intrapulmonary vessels and dynamic changes in vascular function, at least in some smokers. A role for proteases in PH has been recently put forward. We investigated, in smoking mice, the role of protease-activated receptor (PAR)-2 in the pathogenesis of PH associated with emphysema. We demonstrated that CS exposure can modulate PAR-2 expression in mouse lung. Acute CS exposure induces in wildtype (WT) and in transgenic mice over-expressing PAR-2 (FVB(PAR-2-TgN)) a similar degree of neutrophil influx in bronchoalveolar lavage fluids. After chronic CS exposure WT and FVB(PAR-2-TgN) mice show emphysema, but only transgenic mice develop muscularisation of small intrapulmonary vessels that precedes the development of PH (~45% increase) and right ventricular hypertrophy. Smoking in FVB(PAR-2-TgN) mice results in an imbalance between vasoconstrictors (especially endothelin-1) and vasodilators (i.e. vascular endothelial growth factor, endothelial nitric oxide synthase and inducible nitric oxide synthase) and enhanced production of growth factors involved both in fibroblast-smooth muscle cell transaction (i.e. platelet-derived growth factor (PDGF) and transforming growth factor β) and vascular cell proliferation (PDGF). PAR-2 signalling can influence the production and release of many factors, which may play a role in the development of PH in smokers.

Activation of PAR‐2 Elicits NO‐Dependent and CGRP‐Independent Dilation of the Dural Artery

The goal of this study was to determine the vascular effects of protease-activated receptor-2 (PAR-2) activation in the rat cranial vasculature. The role of PAR-2 in pain and inflammatory conditions has been established but the information available on its effects and receptor distribution in the trigeminal vascular axis is limited. We studied the dilatory function and expression of PAR-2 in the neuro-vascular circuit, critical in migraine pathogenesis. We also investigated the interaction of PAR-2 with calcitonin gene-related peptide (CGRP) and dural mast cells. We used an improved model of intravital microscopy on the closed cranial window in rats to study the vascular effects of PAR-2 activating peptides (PAR-2 APs; SLIGRL-NH(2), 2-Furoyl-LIGRLO-NH(2)) in the dural vasculature. Measurement of immunoreactive CGRP in skull halves and in trigeminal nucleus caudalis was done by using an enzyme-linked immunosorbent assay. We also analyzed the presence of PAR-2 in different migraine relevant tissues by quantitative real-time PCR and Western blot analysis. PAR-2 APs and trypsin induced a dose-dependent increase in dural artery diameter. The topical application of a nonspecific nitric oxide synthase (NOS) inhibitor, L-N(G)-Nitroarginine methyl ester, attenuated SLIGRL-NH(2) responses. Olcegepant, a CGRP receptor antagonist, did not a have significant effect on the SLIGRL-NH(2) responses, though exogenous CGRP responses were completely blocked. There was no significant release of CGRP from skull halves incubated with SLIGRL-NH(2) as compared with those incubated with the corresponding negative peptide. Chronic mast cell degranulation did not change the vascular effects of PAR-2 APs. mRNA and protein expression of PAR-2 were found throughout trigeminovasuclar axis. PAR-2 activation leads to vasodilation of dural arteries and these responses are partially mediated by nitric oxide. As PAR-2 is present throughout trigeminovasuclar axis, it may have a role in migraine pathogenesis, independent of CGRP and mast cell mediated mechanism.

Investigation of Possible Role of the PAR-2 Receptor in Intestinal Inflammation

The present study was undertaken to study the role of PAR-2 receptor activation in pathophysiology of intestinal inflammation. Inflammatory bowel disease was induced in Wistar albino rats by intrarectal administration of 2, 4, 6 trinitrobenzenesulfonic acid (TNBS, 0.25 ml 120 mg/ml in 50% ethanol intrarectally, on 1st day only). Trypsin (500 μg/kg, 1 mg/kg, 5 mg/kg, intrarectal) was given from the same day up to 20 days. Various physical parameters including body weight, food and water intake were measured on 1st and 20th days. At end of the experiment, colon weight and various histopathological indexes were assessed. The colon homogenate malondialdehyde (MDA), myeloperoxidase (MPO), and superoxide dismutase (SOD) and % mast cell protection in mesentery were also measured. Trypsin at higher dose (5 mg/kg) showed the higher level of oxidative enzymes and lower level of protective enzymes as compared to the animals treated with only TNBS. Trypsin treatment produced significantly more mast cell degranulation. Finally in the histopathology, there was increased in severity of the disease in trypsin-treated animals. The role of PAR-2 (protease activated receptor-2) receptor in gut is pro-inflammatory and thus appears as a new potential therapeutic target for inflammatory bowel disease treatments.

Activation of microglial cells via protease-activated receptor 2 mediates neuronal cell death in cultured rat primary neuron

The role of protease-activated receptor (PARs) in the regulation of microglial activation process is increasingly evident. In the present study, we have investigated the role of PAR-2, which can be activated by trypsin-like proteases, in microglial activation and neuronal cell death. In cultured rat primary microglia, activation of PAR-2 induced nitrite production by PKC- and MAPKs-dependent mechanism. Among the three members of MAPK pathway, ERK and JNK but not p38 mediated PAR-2-induced microglial activation. The down-stream regulator of PAR-2–PKC–MAPK pathway-induced microglial activation was NF-κB pathway. Besides nitrite, PAR-2 activation increased production of a variety of inflammatory mediators such as ROS and pro-inflammatory cytokines including TNF-α and IL-1β. The addition of culture spent media from PAR-2 activated microglia induced neuronal cell death in primary rat cortical neuron cultures with apoptotic features such as increased number of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive neurons, dissipation of mitochondrial membrane potential, increased expression of pro-apoptotic Bax, decreased expression of anti-apoptotic Bcl-2, Bcl-X L, and activation of caspase-3 in neurons. Interestingly, the increased production of cytoactive molecules as well as the neuronal cell death was normalized by PAR-2 or trypsin inhibitor or an NO synthase inhibitor, N G -nitro- l-arginine-methyl ester. Taken together, these results suggest that overt PAR-2 activation may induce microglial activation, which contributes to neuronal cell death.

The role of protease-activated receptor-2 in skeletal growth and bone repair

The role of protease-activated receptor-2 in skeletal growth and bone repair

Differential Effects of Serine Proteases on the Migration of Normal and Tumor Cells: Implications for Tumor Microenvironment

The supporting role of proteases in tumor progression and invasion is well known; however, the use of proteases as therapeutic agents has also been demonstrated. In this article, the authors report on the differential effects of exogenous serine proteases on the motility of tumor and normal cells. The treatment of normal and tumor cells with a single dose of pancreatic serine proteases, trypsin (TR) and chymotrypsin (CH), leads to a concentration-dependent response by cells, first accelerating and then slowing mobility. Tumor cells are 10 to 20 times more sensitive to exogenous TR/CH, suggesting that a single dose of proteases may cause discordant movements of normal and tumor cells within the tumor environment. The inhibitory effects of TR on cell motility are contradicted by thrombin (TH), particularly in the regulation of normal cells' migration. The purpose of this investigation was to ascertain the role of protease-activated receptors (PARs) in terms of normal and tumor cell motility. Duplicate treatments with proteases resulted in diminished mobility of both normal and tumor cells. Repeated application of TR and TH in 1-hour treatment intervals initially desensitizes cell surface PARs. However, cell surface PARs reappear regardless of subsequent protease treatments in both normal and tumor cells. The resensitization process is retarded in tumor cells when compared with normal cells. This is evidenced by lower expression of PARs as well as by their relocalization at the tumor cell surfaces. Under these conditions, normal cells remain responsive to exogenous proteases in terms of cell motility. Exogenous proteases do not modulate motility of repeatedly stimulated tumor cells, and consequently, the migration of tumor cells appears disconnected from the PAR signaling pathways. The use of activating peptides in lieu of the cognate proteases for a given PAR system indicated that proteases may act through additional targets not regulated by PAR signaling. We hypothesize that the divergent migration patterns of normal and tumor cells due to exposure to proteases is in part mediated by PARs. Thus, treatment with exogenous proteases may cause rearrangement of the tumor and stromal cells within the tumor microenvironment. Such topographical effects may lead to the inhibition of tumor progression and metastasis development.

Protease-activated receptor-2 activation: a major actor in intestinal inflammation

Background and aims:The role of protease-activated receptor-2 (PAR2) during intestinal inflammation is still unclear due to the fact that PAR2-activating peptide has both pro- and anti-inflammatory properties. The aim of...

Role of protease-activated receptors in inflammatory responses, innate and adaptive immunity

Serine proteases are well known as enzymes involved in digestion of dietary proteins, blood coagulation, and homeostasis. Only recent groundbreaking studies revealed a novel role of serine proteases as signaling molecules acting via protease-activated receptors (PARs). Important effects of PAR activation on leukocyte motility, cytokine production, adhesion molecule expression, and a variety of other physiological or pathophysiological functions have been described in vitro and in vivo. The crucial role of PAR activation during disease progression was revealed in animal models of different gastrointestinal pathologies, neuroinflammatory and neurodegenerative processes, skin, joint and airway inflammation, or allergic responses. This review focuses on the findings related to the impact of PAR deficiency in animal models of inflammatory and allergic diseases. Additionally, we observe the role of PAR activation in the regulation of functional responses of innate and adaptive immune cells in vitro. Understanding the mechanisms by which PARs exert the effects of serine proteases on immune cells may lead to new therapeutic strategies in inflammation, immune defense, and allergy.

Salmon trypsin stimulates the expression of interleukin-8 via protease-activated receptor-2

In this study, we focus on salmon trypsin as an activator of inflammatory responses in airway cells in vitro. The rationale behind the investigation is that salmon industry workers are exposed to aerosols containing enzymes, which are generated during industrial processing of the fish. Knowing that serine proteases such as trypsin are highly active mediators with diverse biological activities, the stimulation of nuclear factor-kappa B (NF-κB) and interleukin (IL)-8 and the role of protease-activated receptors (PAR) in inflammatory signal mediation were investigated. Protease-activated receptors are considered important under pathological situations in the human airways, and a thorough understanding of PAR-induced cellular events and their consequences in airway inflammation is necessary. Human airway epithelial cells (A549) were exposed to trypsin isolated from fish ( Salmo salar), and we observed that purified salmon trypsin could generate secretion of IL-8 in a concentration-dependent manner. Furthermore, we demonstrate that PAR-2 activation by salmon trypsin is coupled to an induction of NF-κB-mediated transcription using a PAR-2 transfected HeLa cell model. Finally, we show that the release of IL-8 from A549 following stimulation with purified salmon trypsin is mediated through activation of PAR-2 using specific small interfering RNAs (siRNAs). The results presented suggest that salmon trypsin, via activation of PAR-2, might influence inflammation processes in the airways if inhaled in sufficient amounts.

Role of coagulation and fibrinolysis in lung and renal fibrosis

Elevated procoagulant and suppressed fibrinolytic activities are regularly encountered in different forms of clinical and experimental fibrosis of the lungs and the kidneys. Although primarily serving to provide a provisional matrix of repair largely consisting of fibrin and fibronectin, the involved procoagulant serine proteases and protease inhibitors may also exert distinct cellular downstream signaling events modifying the fibrotic response. In this review, evidence for an impaired regulation of coagulation and fibrinolysis factors in clinical and experimental lung and renal fibrosis is provided and the role of PAR (protease activated receptor) induced profibrotic and HGF (hepatocyte growth factor) elicited antifibrotic cellular events is worked out. In view of experiments obtained in animal models of lung and renal fibrosis, the potential therapeutic usefulness of anticoagulant or profibrinolytic strategies is discussed.

Basic and Translational Research on Proteinase-Activated Receptors: Implication of Proteinase/Proteinase-Activated Receptor in Gastrointestinal Inflammation

Recently, the role of serine proteinases in the pathogenesis of inflammation and autoimmune diseases via interaction with the proteinase-activated receptor (PAR) has attracted attention. Activation of PAR has a pro-inflammatory effect through the overproduction of inflammatory cytokines such as interleukin (IL)-6 and IL-8. PAR2 activation in human esophageal epithelial cells by trypsin induces NFκB– and AP-1–dependent IL-8 production in association with activation of p38 MAPK and ERK1/2, suggesting that esophageal inflammation may be induced by PAR2 activation via reflux of trypsin. It has been also proposed that Helicobacter pylori (H. pylori) induces PAR expression in the gastric epithelial cells and H. pylori–derived serine proteinase promotes IL-8 production via PAR in the epithelial cells. In addition, an increase of PAR-dependent IL-8 production has been observed in H. pylori–infected human gastric mucosa, suggesting an important role for PAR2 in the modulation of gastric inflammation associated with H. pylori. Recent studies have strongly indicated that tryptase and PAR are implicated in the pathogenesis of inflammatory bowel disease and experimental colitis. We demonstrated that anti-tryptase therapy may become a new therapeutic strategy in human ulcerative colitis. Thus, the role of PAR in the gastrointestinal tract has been gradually clarified, but further investigations are needed because the receptor has a variety of functions.

Over-expression of the thrombin receptor (PAR-1) in the placenta in preeclampsia: A mechanism for the intersection of coagulation and inflammation

Objective. Preeclampsia (PE) is characterized by excessive thrombin generation, which has been implicated in the multiple organ damage associated with the disease. The biological effects of thrombin on coagulation and inflammation are mediated by protease-activated receptor-1 (PAR-1), a G protein-coupled receptor. The aim of this study was to determine whether preterm PE is associated with changes in placental expression of PAR-1.Study design. This cross-sectional study included two groups matched for gestational age at delivery: (1) patients with preterm PE (<37 weeks of gestation; n = 26) and (2) a control group of patients with preterm labor without intra-amniotic infection (n = 26). Placental tissue microarrays were immunostained for PAR-1. Immunoreactivity of PAR-1 in the villous trophoblasts was graded as negative, weak-positive, or strong-positive.Results. (1) The proportion of cases with strong PAR-1 immunoreactivity was significantly higher in placentas of patients with PE than in placentas from the control group (37.5% (9/24) vs. 8.7% (2/23); p = 0.036, respectively). (2) PAR-1 immunoreactivity was found in the cellular compartments of the placental villous tree, mainly in villous trophoblasts and stromal endothelial cells. (3) PAR-1 was detected in 92.3% (24/26) of the placentas of women with PE and in 88.5% (23/26) of the placentas from the control group.Conclusion. Placentas from pregnancies complicated by preterm PE had a significantly higher frequency of strong PAR-1 expression than placentas from women with spontaneous preterm labor. This observation is consistent with a role for PAR-1 as a mediator of the effect of thrombin on coagulation and inflammation in PE. We propose that the effects of thrombin in PE are due to increased thrombin generation and higher expression of PAR-1, the major receptor for this enzyme.