Protease-activated receptors: contribution to physiology and disease

The roles of proteinase-activated receptors in the vascular physiology and pathophysiology

Proteinase-activated receptors (PARs) belong to a family of G protein-coupled receptors, thus mediating the cellular effects of proteinases. In the vascular system, thrombin and other proteinases in the coagulation-fibrinolysis system are considered to be the physiologically relevant agonists, whereas PARs are among the most important mechanisms mediating the interaction between the coagulation-fibrinolysis system and the vascular wall. Under physiological conditions, PARs are mainly expressed in endothelial cells, and participate in the regulation of vascular tone, mostly by inducing endothelium-dependent relaxation. PARs in endothelial cells are also suggested to contribute to a proinflammatory phenotypic conversion and an increase in the permeability of vascular lesions. In smooth muscle cells, PARs mediate contraction, migration, proliferation, hypertrophy, and production of the extracellular matrix, thereby contributing to the development of vascular lesions and the pathophysiology of such vascular diseases as atherosclerosis. However, the expression of PARs in the smooth muscle of normal arteries is limited. The upregulation of PARs in the smooth muscle is thus considered to be a key step for PARs to participate in the pathogenesis of vascular lesions. Elucidating the molecular mechanism regulating the PARs expression is therefore important to develop new strategies for the prevention and treatment of vascular diseases.

Coagulation factor Xa modulates airway remodeling in a murine model of asthma

RATIONALE

Previous studies have demonstrated that dysregulated coagulation and fibrinolysis contribute to the pathogenesis of asthma.

OBJECTIVE

The role of procoagulant factor X in a murine model of ovalbumin (OVA)-induced asthma was investigated.

METHODS

Biochemical, cellular, and physiologic in vivo and in vitro approaches were used to determine effects of factor X on the asthmatic response in mice.

MEASUREMENTS AND MAIN RESULTS

Factor X transcript levels and factor Xa activity were increased in lungs of asthmatic mice challenged with OVA, compared with controls treated with phosphate-buffered saline. Factor X was highly expressed in bronchoalveolar lavage fluid macrophages from asthmatic mice. Treatment of mice with the factor Xa inhibitor fondaparinux during the last 4 wk of OVA challenge resulted in the attenuation of airway hyperresponsiveness but did not alter infiltration of inflammatory cells into the lung. There was a significant decrease in the thickness of the mucosal layer and in lung collagen deposition in fondaparinux-treated mice. In vitro investigations using human mucus-producing NCI-H292 cells indicated that exogenous factor Xa enhanced mucin production in a dose-dependent manner. Levels of amphiregulin, a protein that induces mucin production, were also increased in cells stimulated by factor Xa.

CONCLUSIONS

The results of this study introduce a novel participant in the asthmatic response and indicate that factor Xa functions in airway remodeling in asthma by stimulating mucin production, through regulation of amphiregulin expression and collagen deposition.

Expression of proteinase-activated receptors (PAR)-2 in articular chondrocytes is modulated by IL-1beta, TNF-alpha and TGF-beta

OBJECTIVE

To investigate the modulation of expression of proteinase-activated receptor-2 (PAR-2) in articular chondrocytes by inflammatory cytokines.

DESIGN

Articular synovium and cartilage tissues were collected from eight patients with osteoarthritis (OA), and three patients without arthropathy ("normal"). Chondrocytes were stimulated with interleukin (IL)-1beta, tumor necrosis factor (TNF)-alpha or transforming growth factor (TGF)-beta1. The expression of PAR-2 was detected using reverse transcriptase-polymerase chain reaction (PCR), Western blotting and immunofluorescence. Quantitative PCR was performed to assess the expression levels of PAR-2 messenger RNA (mRNA).

RESULTS

The expression of PAR-2 mRNA was demonstrated in both OA and normal chondrocytes as well as in synovial fibroblasts. However, the level of PAR-2 in OA chondrocytes was much higher than in normal chondrocytes. Long-term culture revealed that PAR-2 mRNA expression was maintained up to three passages in OA but not in normal chondrocytes. IL-1beta and TNF-alpha both upregulated PAR-2 expression in normal and OA chondrocytes. In contrast, TGF-beta1 significantly decreased expression of PAR-2 in OA chondrocytes but increased PAR-2 in normal chondrocytes.

CONCLUSIONS

Overexpression of PAR-2 in OA chondrocytes is upregulated by proinflammatory cytokines IL-1beta and TNF-alpha, and down-regulated by regulatory cytokine TGF-beta1. PAR-2 may be involved in the pathogenesis of OA.

Protease-activated receptors in cardiovascular diseases

Thrombosis associated with the pathophysiological activation of platelets and vascular cells has brought thrombin and its receptors to the forefront of cardiovascular medicine. Thrombin signaling through the protease-activated receptors (PARs) has been shown to influence a wide range of physiological responses including platelet activation, intimal hyperplasia, inflammation, and maintenance of vascular tone and barrier function. The thrombin receptors PAR1 and PAR4 can be effectively targeted in animals in which acute or prolonged exposure to thrombin leads to thrombosis and/or restenosis. In the present study, we describe the molecular and pharmacological basis of small-molecule inhibitors that target PAR1. In addition, we discuss a new class of cell-penetrating inhibitors, termed pepducins, that provide insight into previously unidentified roles of PAR1 and PAR4 in protease signaling.

Serratia marcescens serralysin induces inflammatory responses through protease-activated receptor 2

The Serratia marcescens-derived protease serralysin is considered to play an important role in the pathogenesis of infection. Protease-activated receptor 2 (PAR-2) is activated by trypsin and also several other trypsin-like serine proteases, leading to the modulation of inflammatory and immune responses. However, little is known about the activation of PAR-2 by bacterial proteases and its roles in bacterial infection. In this study, we investigated whether S. marcescens serralysin activates host inflammatory responses through PAR-2. Our results demonstrated that serralysin induces interleukin-6 (IL-6) and IL-8 mRNA expression in a human lung squamous cell carcinoma, EBC-l cells. In addition, serralysin activated activator protein 1 (AP-1)-, CCAAT/enhancer-binding protein (C/EBP)-, and nuclear factor-kappaB (NF-kappaB)-driven promoters in EBC-1 cells. An electrophoretic mobility shift assay showed that serralysin activates the binding of AP-1, C/EBPbeta, and NF-kappaB in the cells. Inactivation of serralysin resulted in the failure of transactivation of AP-1-, C/EBP-, and NF-kappaB-driven promoters in the cells. Furthermore, serralysin activated AP-1-, C/EBP-, and NF-kappaB-driven promoters via PAR-2 in HeLa cells. PAR-2 antagonist peptides decreased serralysin-induced transactivation of AP-1-, C/EBP-, and NF-kappaB-driven promoters in EBC-1 cells. Considered together, these results suggest that serralysin requires PAR-2 to activate the critical transcription factors AP-1, C/EBPbeta, and NF-kappaB for host inflammatory responses.

[Roles of protease-activated receptor-2 (PAR-2), a G protein-coupled receptor, in modulation of exocrine gland functions]

Protease-activated receptor-2 (PAR-2), a G protein-coupled receptor, is activated by proteolytic unmasking of the N-terminal extracellular tethered ligand that presumably binds to the extracellular loop 2 of the receptor itself. PAR-2 is widely distributed in the mammalian body and plays various roles in biological events in the cardiovascular, respiratory, alimentary, and central neurons systems. PAR-2-activating peptides administered systemically to mice and rats trigger prompt salivation in vivo. In an in vitro study, PAR-2 agonists including the endogenous PAR-2 activator trypsin induce secretion of amylase and mucin from isolated rat parotid glands and sublingual glands, respectively. PAR-2-activating peptides administered systemically also modulate pancreatic exocrine secretion in vivo as well as in vitro. In the gastric mucosa, PAR-2 stimulation enhances secretion of mucus and pepsinogen and suppresses acid secretion. Tear secretion can also be caused by PAR-2-related peptides in PAR-2-dependent and -independent manners. PAR-2 thus plays a general or key role in the regulation of exocrine secretion. This review focuses on the physiologic and/or pathophysiologic roles of PAR-2 in glandular exocrine secretion. The possibility of PAR-2 as a target for drug development is also discussed.

Induction of IL-6 release from human T cells by PAR-1 and PAR-2 agonists

Proteinase-activated receptors (PAR) have been recognized as playing an important role in inflammation and immune response. However, little is known of the expression and function of PAR on human T cells. In this study, the expression of PAR on highly purified human T cells was determined and the secretion of IL-6 from cultured T cells in response to serine proteinases and agonist peptides of PAR was examined. The results showed that T cells express PAR-1, PAR-2 and PAR-3 proteins and genes. Thrombin, trypsin and tryptase, but not elastase, were able to stimulate concentration-dependent secretion of IL-6 from T cells following a 16 h incubation period. The specific inhibitors of thrombin, trypsin and tryptase inhibited the actions of these proteinases on T cells, indicating that the enzymatic activity is essential for their actions. Agonist peptides of PAR SFLLR-NH2, TFLLRN-NH2 and SLIGKV-NH2, but not TFRGAP-NH2, GYPGQV-NH2 and AYPGKF-NH2, are also capable of inducing IL-6 release from T cells. In conclusion, induction of IL-6 secretion from T cells by thrombin, trypsin and tryptase is probably through the activation of PAR, suggesting that serine proteinases are involved in the regulation of immune response of the body.

Proteinase-activated Receptors, Targets for Kallikrein Signaling

Serine proteinases like thrombin can signal to cells by the cleavage/activation of proteinase-activated receptors (PARs). Although thrombin is a recognized physiological activator of PAR(1) and PAR(4), the endogenous enzymes responsible for activating PAR(2) in settings other than the gastrointestinal system, where trypsin can activate PAR(2), are unknown. We tested the hypothesis that the human tissue kallikrein (hK) family of proteinases regulates PAR signaling by using the following: 1) a high pressure liquid chromatography (HPLC)-mass spectral analysis of the cleavage products yielded upon incubation of hK5, -6, and -14 with synthetic PAR N-terminal peptide sequences representing the cleavage/activation motifs of PAR(1), PAR(2), and PAR(4); 2) PAR-dependent calcium signaling responses in cells expressing PAR(1), PAR(2), and PAR(4) and in human platelets; 3) a vascular ring vasorelaxation assay; and 4) a PAR(4)-dependent rat and human platelet aggregation assay. We found that hK5, -6, and -14 all yielded PAR peptide cleavage sequences consistent with either receptor activation or inactivation/disarming. Furthermore, hK14 was able to activate PAR(1), PAR(2), and PAR(4) and to disarm/inhibit PAR(1). Although hK5 and -6 were also able to activate PAR(2), they failed to cause PAR(4)-dependent aggregation of rat and human platelets, although hK14 did. Furthermore, the relative potencies and maximum effects of hK14 and -6 to activate PAR(2)-mediated calcium signaling differed. Our data indicate that in physiological settings, hKs may represent important endogenous regulators of the PARs and that different hKs can have differential actions on PAR(1), PAR(2), and PAR(4).

Neuronal Control of Skin Function: The Skin as a Neuroimmunoendocrine Organ

This review focuses on the role of the peripheral nervous system in cutaneous biology and disease. During the last few years, a modern concept of an interactive network between cutaneous nerves, the neuroendocrine axis, and the immune system has been established. We learned that neurocutaneous interactions influence a variety of physiological and pathophysiological functions, including cell growth, immunity, inflammation, pruritus, and wound healing. This interaction is mediated by primary afferent as well as autonomic nerves, which release neuromediators and activate specific receptors on many target cells in the skin. A dense network of sensory nerves releases neuropeptides, thereby modulating inflammation, cell growth, and the immune responses in the skin. Neurotrophic factors, in addition to regulating nerve growth, participate in many properties of skin function. The skin expresses a variety of neurohormone receptors coupled to heterotrimeric G proteins that are tightly involved in skin homeostasis and inflammation. This neurohormone-receptor interaction is modulated by endopeptidases, which are able to terminate neuropeptide-induced inflammatory or immune responses. Neuronal proteinase-activated receptors or transient receptor potential ion channels are recently described receptors that may have been important in regulating neurogenic inflammation, pain, and pruritus. Together, a close multidirectional interaction between neuromediators, high-affinity receptors, and regulatory proteases is critically involved to maintain tissue integrity and regulate inflammatory responses in the skin. A deeper understanding of cutaneous neuroimmunoendocrinology may help to develop new strategies for the treatment of several skin diseases.

Modulation of hippocampal neuron survival by thrombin and factor Xa

Effects of thrombin, factor Xa (FXa), and protease-activated receptor 1 and 2 agonist peptides (PAR1-AP and PAR2-AP) on survival and intracellular Ca2+ homeostasis in hippocampal neuron cultures treated with cytotoxic doses of glutamate were investigated. It is shown that at low concentrations (<or=10 nM) thrombin and FXa protect neurons from glutamate-induced excitotoxicity. Inactivation of the proteases blocked the neuroprotective effect. Using PAR1-AP, PAR2-AP, and PAR1 antagonist, we have demonstrated that the neuroprotective effect of thrombin is mediated through activation of PAR1, whereas the effect of FXa may involve novel subtype(s) of PARs. Unlike FXa, thrombin induced transient intracellular calcium signal in hippocampal neurons, which was mainly mediated via IP(3) receptors of the endoplasmic reticulum. Both of the serine proteases improved the recovery of neuronal Ca2+ homeostasis after glutamate treatment.

Tumor-derived matrix metalloproteinase-1 targets endothelial proteinase-activated receptor 1 promoting endothelial cell activation

In the vascular system, circulating tumor cells interact with endothelial cells. Tumor-endothelial cross-talk transforms the intravascular milieu to a prothrombotic, proinflammatory, and cell-adhesive state called endothelial cell activation (ECA). In the present study, we analyze the potential of metastatic tumor-derived soluble factors to transform the vascular endothelium into a prothrombotic and proinflammatory activated state. Supernatant from cultured melanoma and colon cancer cells (A375, WM9, A7, and HT-29) induced an acute activation of macrovascular and microvascular endothelial cells (human umbilical vein endothelial cells and human dermal microvascular endothelial cells) as shown by intracellular calcium flux and secretion of von Willebrand factor and interleukin-8, all markers of acute ECA. This process was inhibited using specific proteinase-activated receptor 1 (PAR1) inhibitors (RWJ-58259 and SCH-79797), indicating a mediating role for endothelial thrombin receptors. Immunofluorescence, Western blot analysis, and collagenase activity assay of tumor cells and culture supernatant revealed the presence of matrix metalloproteinase-1 (MMP-1), a recently described activator of PAR1. Inhibition of MMP-1 in supernatant from cultured tumor cells significantly attenuated ECA. Additional studies using isolated human MMP-1 (5 nmol/L) proved the presence of a functional MMP-1/PAR1 axis in tumor-endothelial communication. These findings show a new pathway of tumor-endothelial cross-talk via an intravascular MMP1/PAR1 axis in microvascular and macrovascular endothelium. Inhibition of this cross-talk may be a powerful means to prevent tumor-induced ECA and thus thrombotic and inflammatory cell adhesion.

Mechanisms for prostaglandin E2 formation caused by proteinase-activated receptor-1 activation in rat gastric mucosal epithelial cells

Proteinase-activated receptor-1 (PAR1), a thrombin receptor, plays a protective role in gastric mucosa via prostanoid formation. Thus, we studied effects of PAR1 stimulation on prostaglandin E(2) (PGE(2)) formation in rat normal gastric mucosal epithelial RGM1 cells and analyzed the underlying signal transduction mechanisms. The PAR1-activating peptide (PAR1-AP) and thrombin increased PGE(2) release from RGM1 cells for 18h, an effect being suppressed by inhibitors of COX-1, COX-2, MEK, p38 MAP kinase (p38 MAPK), protein kinase C (PKC), Src and EGF receptor-tyrosine kinase (EGFR-TK), but not JNK and matrix metalloproteinase (MMP)/a disintegrin and metalloproteinases (ADAMs). PAR1-AP caused persistent (6h or more) and transient (5min) phosphorylation of ERK and p38 MAPK, respectively, followed by delayed reinforcement at 18h. PAR1-AP up-regulated COX-2 in a manner dependent on MEK and EGFR-TK, but not p38 MAPK. The PAR1-mediated persistent ERK phosphorylation was reduced by inhibitors of Src and EGFR-TK. PAR1-AP actually phosphorylated EGF receptors and up-regulated mRNA for heparin-binding-EGF (HB-EGF), the latter effect being blocked by inhibitors of Src, EGFR-TK and MEK. Heparin, an inhibitor for HB-EGF, suppressed PAR1-mediated PGE(2) formation and persistent ERK phosphorylation. These results suggest that PAR1 up-regulates COX-2 via persistent activation of MEK/ERK that is dependent on EGFR-TK activation following induction of HB-EGF, leading to PGE(2) formation. In addition, our data also indicate involvement of COX-1, PKC and p38 MAPK in PAR1-triggered PGE(2) formation. PAR1, thus stimulates complex multiple signaling pathways responsible for PGE(2) formation in RGM1 cells.

Constitutive expression of functionally active protease-activated receptors 1 and 2 in human conjunctival epithelial cells

Protease-activated receptors (PARs) are G-protein-coupled receptors which initiate inflammatory responses when activated by specific serine proteases. This study was conducted to examine whether human conjunctival epithelial cells (HCECs) express functionally active PAR1 and PAR2 using Chang conjunctival epithelial cells as in vitro model. We performed RT-PCR and immunofluorescence analyses to determine the expression of PAR1 and PAR2, and monitored the production of IL-6 after activating HCECs with PAR1 activating agents (thrombin or TFLLRN) or PAR2 activating agents (tryptase, trypsin, or SLIGKV). The results show that HCECs constitutively express PAR1 and PAR2 mRNA and proteins, and produce significant amounts of IL-6 when incubated with specific PAR-activating enzymes or agonist peptides. Thrombin- and tryptase-induced HCEC activation was blocked by PAR1 and PAR2 neutralizing antibodies, respectively, and by specific enzyme inhibitors. The constitutive expression of PAR1 and PAR2, and their activation by thrombin and tryptase, respectively, may have important implications in ocular inflammation.

The C-terminus of murine S100A9 protein inhibits hyperalgesia induced by the agonist peptide of protease-activated receptor 2 (PAR2)

BACKGROUND AND PURPOSE

S100A9 protein induces anti-nociception in rodents, in different experimental models of inflammatory pain. Herein, we investigated the effects of a fragment of the C-terminus of S100A9 (mS100A9p), on the hyperalgesia induced by serine proteases, through the activation of protease-activated receptor-2 (PAR2).

EXPERIMENTAL APPROACH

Mechanical and thermal hyperalgesia induced by PAR2 agonists (SLIGRL-NH2 and trypsin) was measured in rats submitted to the paw pressure or plantar tests, and Egr-1 expression was determined by immunohistochemistry in rat spinal cord dorsal horn. Calcium flux in human embryonic kidney cells (HEK), which naturally express PAR2, in Kirsten virus-transformed kidney cells, transfected (KNRK-PAR2) or not (KNRK) with PAR2, and in mouse dorsal root ganglia neurons (DRG) was measured by fluorimetric methods.

KEY RESULTS

mS100A9p inhibited mechanical hyperalgesia induced by trypsin, without modifying its enzymatic activity. Mechanical and thermal hyperalgesia induced by SLIGRL-NH2 were inhibited by mS100A9p. SLIGRL-NH2 enhanced Egr-1 expression, a marker of nociceptor activation, and this effect was inhibited by concomitant treatment with mS100A9p. mS100A9p inhibited calcium mobilization in DRG neurons in response to the PAR2 agonists trypsin and SLIGRL-NH2, but also in response to capsaicin and bradykinin, suggesting a direct effect of mS100A9 on sensory neurons. No effect on the calcium flux induced by trypsin or SLIGRL in HEK cells or KNRK-PAR2 cells was observed.

CONCLUSIONS AND IMPLICATIONS

These data demonstrate that mS100A9p interferes with mechanisms involved in nociception and hyperalgesia and modulates, possibly directly on sensory neurons, the PAR2-induced nociceptive signal.

PAR4, but not PAR1, signals human platelet aggregation via Ca2+ mobilization and synergistic P2Y12 receptor activation

Regulation of platelet activation plays a central role in hemostasis and pathophysiological processes such as coronary artery disease. Thrombin is the most potent activator of platelets. Human platelets express two thrombin receptors, PAR1 and PAR4, both of which signal platelet activation. Evidence is lacking on the mechanism by which PAR1 and PAR4 may differentially signal platelet aggregation. Here we show that at the relatively high concentration of agonist most likely found at the site of a local thrombus, dual inhibition of the P2Y12 receptor and calcium mobilization result in a complete inhibition of PAR4-induced aggregation, while having no effect on either thrombin or PAR1-mediated platelet aggregation. Both PAR1- and PAR4mediated aggregation are independent of calcium mobilization. Furthermore, we show that P2Y12 receptor activation is not required for protease-activated receptor-mediated aggregation at higher agonist concentrations and is only partially required for Rap1 as well as GPIIbIIIa activation. P2Y12 receptor inhibitors clinically in use such as clopidogrel are postulated to decrease platelet aggregation through partial inhibition of PAR1 signaling. Our data, however, indicate that at high local concentrations of thrombin, it is the signaling through PAR4 rather than PAR1 that may be regulated through purinergic feedback. Thus, our data identify an intra-platelet mechanism that may function as a future site for therapeutic intervention.

Disulfide isomerization switches tissue factor from coagulation to cell signaling

Cell-surface tissue factor (TF) binds the serine protease factor VIIa to activate coagulation or, alternatively, to trigger signaling through the G protein-coupled, protease-activated receptor 2 (PAR2) relevant to inflammation and angiogenesis. Here we demonstrate that TF.VIIa-mediated coagulation and cell signaling involve distinct cellular pools of TF. The surface-accessible, extracellular Cys186-Cys209 disulfide bond of TF is critical for coagulation, and protein disulfide isomerase (PDI) disables coagulation by targeting this disulfide. A TF mutant (TF C209A) with an unpaired Cys186 retains TF.VIIa signaling activity, and it has reduced affinity for VIIa, a characteristic of signaling TF on cells with constitutive TF expression. We further show that PDI suppresses TF coagulant activity in a nitric oxide-dependent pathway, linking the regulation of TF thrombogenicity to oxidative stress in the vasculature. Furthermore, a unique monoclonal antibody recognizes only the noncoagulant, cryptic conformation of TF. This antibody inhibits formation of the TF.PAR2 complex and TF.VIIa signaling, but it does not prevent coagulation activation. These experiments delineate an upstream regulatory mechanism that controls TF function, and they provide initial evidence that TF.VIIa signaling can be specifically inhibited with minimal effects on coagulation.

Protease-activated receptor 2 sensitizes TRPV1 by protein kinase Cepsilon- and A-dependent mechanisms in rats and mice

Proteases that are released during inflammation and injury cleave protease-activated receptor 2 (PAR2) on primary afferent neurons to cause neurogenic inflammation and hyperalgesia. PAR2-induced thermal hyperalgesia depends on sensitization of transient receptor potential vanilloid receptor 1 (TRPV1), which is gated by capsaicin, protons and noxious heat. However, the signalling mechanisms by which PAR2 sensitizes TRPV1 are not fully characterized. Using immunofluorescence and confocal microscopy, we observed that PAR2 was colocalized with protein kinase (PK) Cepsilon and PKA in a subset of dorsal root ganglia neurons in rats, and that PAR2 agonists promoted translocation of PKCepsilon and PKA catalytic subunits from the cytosol to the plasma membrane of cultured neurons and HEK 293 cells. Subcellular fractionation and Western blotting confirmed this redistribution of kinases, which is indicative of activation. Although PAR2 couples to phospholipase Cbeta, leading to stimulation of PKC, we also observed that PAR2 agonists increased cAMP generation in neurons and HEK 293 cells, which would activate PKA. PAR2 agonists enhanced capsaicin-stimulated increases in [Ca2+]i and whole-cell currents in HEK 293 cells, indicating TRPV1 sensitization. The combined intraplantar injection of non-algesic doses of PAR2 agonist and capsaicin decreased the latency of paw withdrawal to radiant heat in mice, indicative of thermal hyperalgesia. Antagonists of PKCepsilon and PKA prevented sensitization of TRPV1 Ca2+ signals and currents in HEK 293 cells, and suppressed thermal hyperalgesia in mice. Thus, PAR2 activates PKCepsilon and PKA in sensory neurons, and thereby sensitizes TRPV1 to cause thermal hyperalgesia. These mechanisms may underlie inflammatory pain, where multiple proteases are generated and released.

Protective effect of proteinase-activated receptor 2 activation on motility impairment and tissue damage induced by intestinal ischemia/reperfusion in rodents

We hypothesized that proteinase-activated receptor-2 (PAR(2)) modulates intestinal injuries induced by ischemia/reperfusion. Ischemia (1 hour) plus reperfusion (6 hours) significantly delayed gastrointestinal transit (GIT) compared with sham operation. Intraduodenal injection of PAR(2)-activating peptide SLIGRL-NH(2) significantly accelerated transit in ischemia/reperfusion but not in sham-operated rats. GIT was significantly delayed in ischemia/reperfusion and sham-operated PAR(2)(-/-) mice compared with PAR(2)(+/+). SLIGRL-NH(2) significantly accelerated transit in ischemia/reperfusion in PAR(2)(+/+) but not in PAR(2)(-/-) mice. Prevention of mast cell degranulation with cromolyn, ablation of visceral afferents with capsaicin, and antagonism of calcitonin gene-related peptide (CGRP) and neurokinin-1 receptors with CGRP(8-37) and RP67580, respectively, abolished the SLIGRL-NH(2)-induced stimulatory effect on transit in ischemia/reperfusion. Tissue damage was significantly reduced by SLIGRL-NH(2); this effect was not observed in cromolyn-, capsaicin-, or RP67580-treated rats but was detected following CGRP(8-37). Intestinal PAR(2) mRNA levels were not affected by SLIGRL-NH(2) in ischemia/reperfusion. We propose that PAR(2) modulates GIT and tissue damage in intestinal ischemia/reperfusion by a mechanism dependent on mast cells and visceral afferents. PAR(2) effect on transit might be mediated by CGRP and substance P, whereas the effect on tissue damage appears to involve substance P but not CGRP. PAR(2) might be a signaling system in the neuroimmune communication in intestinal ischemia/reperfusion.

Kallikrein-mediated cell signalling: targeting proteinase-activated receptors (PARs)

We tested the hypothesis that human tissue kallikreins (hKs) may regulate signal transduction by cleaving and activating proteinase-activated receptors (PARs). We found that hK5, 6 and 14 cleaved PAR N-terminal peptide sequences representing the cleavage/activation motifs of human PAR1 and PAR2 to yield receptor-activating peptides. hK5, 6 and 14 activated calcium signalling in rat PAR2-expressing (but not background) KNRK cells. Calcium signalling in HEK cells co-expressing human PAR1 and PAR2 was also triggered by hK14 (via PAR1 and PAR2) and hK6 (via PAR2). In isolated rat platelets that do not express PAR1, but signal via PAR4, hK14 also activated PAR-dependent calcium signalling responses and triggered aggregation. The aggregation response elicited by hK14 was in contrast to the lack of aggregation triggered by hK5 and 6. hK14 also caused vasorelaxation in a phenylephrine-preconstricted rat aorta ring assay and triggered oedema in an in vivo model of murine paw inflammation. We propose that, like thrombin and trypsin, the kallikreins must now be considered as important 'hormonal' regulators of tissue function, very likely acting in part via PARs.

Transducing the signals: a G protein takes a new identity

The prevailing dogma is that heterotrimeric G proteins exclusively transduce signals from the seven-transmembrane motif-containing cell surface receptors, also known as G protein-coupled receptors (GPCRs). New evidence indicates that Galpha(13), the alpha subunit of the G protein G(13), breaks away from this traditional exclusive signaling alliance with GPCRs to transmit signals from receptor tyrosine kinases (RTKs), such as platelet-derived growth factor receptor (PDGFR), epidermal growth factor receptor (EGFR), and vascular endothelial growth factor receptor (VEGFR). Galpha(13) is involved in cell migration in response to GPCRs activated by lysophosphatidic acid (LPA) or thrombin. A new report indicates that Galpha(13) is also required for cell migration induced by the growth factors, such as PDGF, EGF, or VEGF. GPCR coupling is not required for such RTK-to-Galpha(13) signaling. This new identity for Galpha(13) as a signal transducer for both GPCRs and RTKs may be a forerunner for similar findings involving other Galpha subunits. This expanding role of G proteins in both GPCR signaling and RTK signaling is likely to have a great impact not only on our understanding of cell signaling in general, but also more specifically where the dysregulation of signaling by GPCRs, RTKs, and G proteins cause pathophysiological changes such as in the case of tumorigenesis, tumor progression and/or metastasis.

Up-regulation of protease-activated receptor-2 by bFGF in cultured human synovial fibroblasts

Protease-activated receptors (PARs) have been implicated in the development of acute and chronic inflammatory responses. We have examined the expression of mRNA for PARs and their regulation by growth factors and cytokines in synovial fibroblasts derived from patients with rheumatoid arthritis (RA). Messenger RNA for PAR-1, -2 and -3 was detected in these cells, but not that for PAR-4. Expression of mRNA for PAR-2 was up-regulated by bFGF in a concentration-dependent manner, whereas expression of mRNA for PAR-1 and PAR-3 was not affected. Levels of mRNA encoding PAR-1, PAR-2 and PAR-3 did not increase in response to IL-1beta and TNF-alpha. Expression of mRNA for PAR-2 was maximal 12 h after addition of bFGF, and maximal levels of immunoreactive PAR-2 were reached after 24 h. Furthermore, PAR-2 agonist peptide (SLIGKV-NH(2)), but not the inactive reverse peptide (VKGILS-NH(2)), induced transitory cytosolic Ca(2+) mobilization in cells, and its response was increased by pretreatment with bFGF. An important role could be played by bFGF in the regulation of functional PAR-2 expression in cultured RA synovial fibroblasts.

Induction of interleukin-6 release from monocytes by serine proteinases and its potential mechanisms

Serine proteinases have been recognized playing an important role in inflammation via proteinase-activated receptors (PAR). However, little is known of the influence of serine proteinases and PAR on interleukin-6 (IL-6) secretion from highly purified monocytes. We challenged monocytes from human peripheral blood with serine proteinases and agonist peptides of PAR and measured the levels of IL-6, IL-1beta and IL-12 in culture supernatants by enzyme-linked immunosorbent assay. The results showed that thrombin, trypsin, tryptase and elastase stimulated approximately up to 2.9-, 2.0-, 1.8- and 2.1-fold increase in IL-6 release from monocytes following 16 h of incubation, respectively. Proteinase inhibitors inhibited the actions of proteinases on monocytes. Agonist peptides of PAR-1 (SFLLR-NH(3)) and PAR-4 (GYPGQV-NH(2)), but not PAR-3 (TFRGAP-NH(2)), also induced IL-6 release from monocytes. The proteinases and agonists of PAR failed to stimulate IL-1beta and IL-12 secretion. In conclusion, the induction of IL-6 secretion by serine proteinases may be through the activation of PAR.

Biology of mast cell tryptase. An inflammatory mediator

In 1960, a trypsin-like activity was found in mast cells [Glenner GG & Cohen LA (1960) Nature 185, 846-847] and this activity is now commonly referred to as 'tryptase'. Over the years, much knowledge about mast cell tryptase has been gathered, and a recent (18 January 2006) PubMed search for the keywords 'tryptase + mast cell*' retrieved 1661 articles. However, still very little is known about its true biological function. For example, the true physiological substrate(s) for mast cell tryptase has not been identified, and the potential role of tryptase in mast cell-related disease is not understood. Mast cell tryptase has several unique features, with perhaps the most remarkable being its organization into a tetrameric state with all of the active sites oriented towards a narrow central pore and its consequent complete resistance towards endogenous macromolecular protease inhibitors. Much effort has been invested to elucidate these properties of tryptase. In this review we summarize the current knowledge of mast cell tryptase, including novel insights into its possible biological functions and mechanisms of regulation.

Frontiers in pruritus research: scratching the brain for more effective itch therapy

This Review highlights selected frontiers in pruritus research and focuses on recently attained insights into the neurophysiological, neuroimmunological, and neuroendocrine mechanisms underlying skin-derived itch (pruritogenic pruritus), which may affect future antipruritic strategies. Special attention is paid to newly identified itch-specific neuronal pathways in the spinothalamic tract that are distinct from pain pathways and to CNS regions that process peripheral pruritogenic stimuli. In addition, the relation between itch and pain is discussed, with emphasis on how the intimate contacts between these closely related yet distinct sensory phenomena may be exploited therapeutically. Furthermore, newly identified or unduly neglected intracutaneous itch mediators (e.g., endovanilloids, proteases, cannabinoids, opioids, neurotrophins, and cytokines) and relevant receptors (e.g., vanilloid receptor channels and proteinase-activated, cannabinoid, opioid, cytokine, and new histamine receptors) are discussed. In summarizing promising new avenues for managing itch more effectively, we advocate therapeutic approaches that strive for the combination of peripherally active antiinflammatory agents with drugs that counteract chronic central itch sensitization.

Neutrophil and pathogen proteinases versus proteinase-activated receptor-2 lung epithelial cells: more terminators than activators

The proteinase-activated receptor-2 (PAR-2) is expressed by different lung cells, including bronchial and alveolar epithelial cells. Since its discovery in 1995, numerous in vivo and in vitro studies have demonstrated its involvement in lung inflammation, whether from infectious or allergic causes. However, its role is controversial because there is evidence of both pro- and anti-inflammatory activities. PARs, including PAR-2, display a unique activation process. Specific proteinases cleave the N-terminal extracellular domain at a particular site. The new N-terminal sequence functions as a tethered ligand and binds intramolecularly to activate the receptor. Recently, other specific proteinases have been shown to cleave the N-terminal exodomain at other sites, resulting in a disarming of the receptor. Some of these activating and disabling proteinases are produced by host cells and others by pathogens, and may be present in the airspaces under diverse pathophysiologic settings.

Protease-activated receptor regulation of Cl- secretion in Calu-3 cells requires prostaglandin release and CFTR activation

Human lung epithelial (Calu-3) cells were used to investigate the effects of protease-activated receptor (PAR) stimulation on Cl(-) secretion. Quantitative RT-PCR (QRT-PCR) showed that Calu-3 cells express PAR-1, -2, and -3 receptor mRNAs, with PAR-2 mRNA in greatest abundance. Addition of either thrombin or the PAR-2 agonist peptide SLIGRL to the basolateral solution of monolayers mounted in Ussing chambers produced a rapid increase in short-circuit current (I(sc): thrombin, 21 +/- 2 microA; SLIGRL, 83 +/- 22 microA), which returned to baseline within 5 min after stimulation. Pretreatment of monolayers with the cell-permeant Ca(2+)-chelating agent BAPTA-AM (50 microM) abolished the increase in I(sc) produced by SLIGRL. When monolayers were treated with the cyclooxygenase inhibitor indomethacin (10 microM), nearly complete inhibition of both the thrombin- and SLIGRL-stimulated I(sc) was observed. In addition, basolateral treatment with the PGE(2) receptor antagonist AH-6809 (25 microM) significantly inhibited the effects of SLIGRL on I(sc). QRT-PCR revealed that Calu-3 cells express mRNAs for CFTR, the Ca(2+)-activated KCNN4 K(+) channel, and the KCNQ1 K(+) channel subunit, which, in association with KCNE3, is known to be regulated by cAMP. Stimulation with SLIGRL produced an increase in apical Cl(-) conductance that was blocked in cells expressing short hairpin RNAs designed to target CFTR. These results support the conclusion that PAR stimulation of Cl(-) secretion occurs by an indirect mechanism involving the synthesis and release of prostaglandins. In addition, PAR-stimulated Cl(-) secretion requires activation of CFTR and at least two distinct K(+) channels located in the basolateral membrane.

The Dose of Nafamostat Mesilate During Plasma Exchange With Continuous Hemodiafiltration in the Series-Parallel Circuit

We studied nafamostat mesilate (NM) and interleukin (IL)-18 levels to determine whether the dose of NM is reduced during plasma exchange (PE) with continuous hemodiafiltration (CHDF) when the series-parallel circuit is used. The subjects of the current study included four patients with acute hepatic failure who underwent PE with CHDF. The four patients underwent a total 15 PE + CHDF procedures, and for each procedure, they were randomized to receive either a half-dose of NM or no NM in the CHDF circuit. Eight procedures were carried out with NM administration, and seven were carried out without NM administration. The dose of NM in the NM group was significantly higher than that in the non-NM group (P = 0.040). No significant differences were observed between the two groups in the inlet NM concentration, the outlet NM concentration, or the rate of IL-18 removal. No statistical correlation was observed between the IL-18 level and the NM dose, the inlet NM concentration, or the outlet NM concentration. There was no blood access difficulty such as catheter failure or clotting of the filter. Thus, it might be possible to carry out PE and CHDF with the series-parallel method without administration of NM in the CHDF circuit.

Proteinase-mediated cell signalling: targeting proteinase-activated receptors (PARs) by kallikreins and more

Serine proteinases, like trypsin, can play a hormone-like role by triggering signal transduction pathways in target cells. In many respects these hormone-like actions of proteinases can now be understood in terms of the pharmacodynamics of the G protein-coupled ‘receptor’ responsible for the cellular actions of thrombin (proteinase-activated receptor-1, or PAR1). PAR1, like the other three members of this receptor family (PAR2, PAR3and PAR4), has a unique mechanism of activation involving the proteolytic unmasking of an N-terminally tethered sequence that can activate the receptor. The selective activation of each PAR by short synthetic peptides representing these sequences has demonstrated that PAR1, PAR2and PAR4play important roles in regulating physiological responses ranging from vasoregulation and cell growth to inflammation and nociception. We hypothesise that the tissue kallikreins may regulate signal transduction via the PARs. Although PARs can account for many of their biological actions, kallikreins may also cause effects by mechanisms not involving the PARs. For instance, trypsin activates the insulin receptor and thrombin can act via a mechanism involving its non-catalytic domains. Based on the data we summarise, we propose that the kallikreins, like thrombin and trypsin, must now be considered as important ‘hormonal’ regulators of tissue function.

Development of activity-based probes for trypsin-family serine proteases

A series of diphenylphosphonate-based probes were developed for the trypsin-like serine proteases. These probes selectively target serine proteases rather than general serine hydrolases that are targets for fluorophosphonate-based probes. This increased selectivity allows detection of low abundance serine proteases in complex proteomes using simple SDS-PAGE methods. We present here the application of multiple probes in enzyme activity profiling of intact mast cells, a type of inflammatory cell implicated in allergy and autoimmune diseases.

Protease-activated receptor-2 activation: a major role in the pathogenesis of Porphyromonas gingivalis infection

We have investigated the specific contribution of protease-activated receptor-2 (PAR(2)) to host defense during Porphyromonas gingivalis infection. Culture supernatants from P. gingivalis strains 33277 and W50 provoked Ca(2+) mobilization in cells transfected with PAR(2) (PAR(2)-KNRK) and desensitized the subsequent responses to PAR(2)-selective agonist. In addition, culture supernatants of P. gingivalis E8 (RgpA/RgpB double knockout) did not cause calcium response in PAR(2)-KNRK cells, evidencing the involvement of the arginine-specific cysteine proteases RgpA and RgpB in PAR(2) activation by P. gingivalis. Injection of P. gingivalis into mouse subcutaneous chambers provoked an increased proteolytic activity, which was inhibited by serine protease inhibitors. Fluids collected from chambers of P. gingivalis-injected mice were able to activate PAR(2) and this activation was inhibited by serine protease inhibitors. P. gingivalis inoculation into subcutaneous chambers of wild-type mice induced an inflammatory response that was inhibited by a serine protease inhibitor and was significantly reduced in PAR(2)-deficient mice. Finally, mice orally challenged with P. gingivalis developed alveolar bone loss, which was significantly reduced in PAR(2)-deficient mice at 42 and 60 days after P. gingivalis infection. We conclude that PAR(2) is activated on P. gingivalis infection, in which it plays an important role in the host inflammatory response.

The role of protease-activated receptors on the intracellular calcium ion dynamics of vascular smooth muscles, with special reference to cerebral arterioles

Protease-activated receptors (PARs) mediate cellular responses to various proteases in numerous cell types, including smooth muscles and the endothelium of blood vessels. To clarify whether the stimulation of PARs induces responses in smooth muscle cells of cerebral arterioles, intracellular Ca2+([Ca2+]i) dynamics and nitric oxide (NO) production during PARs stimulation were investigated in the rat cerebral arterioles by real-time confocal microscopy, since [Ca2+]i and NO are both key factors in the maintenance of strain in blood vessels. Testicular arterioles were also investigated for comparison. In smooth muscle cells of small cerebral arterioles (< 50 microm in diameter), thrombin and PAR1-activating peptide (AP) induced an increase in [Ca2+]i and contraction. The response to PAR1 activation was caused by Ca2+ mobilization from intracellular Ca2+ stores. Trypsin and PAR2-AP induced a decrease in [Ca2+]i in the cells which was considered to be mediated by endothelium-derived NO and/or by promoting a Ca2+ sequestration mechanism. PAR3- and 4-AP had little effect. In contrast to small cerebral arterioles, [Ca2+]i dynamics in smooth muscle cells of large cerebral arterioles (< 150 microm in diameter) or testicular arterioles remained unchanged during PARs activation. The effects of PARs activation on the [Ca2+]i dynamics and the contraction/relaxation of cerebral arterioles are also discussed in relation to the role of proteases in the regional tissue circulation of the brain.

Hypersensitivity of pulmonary chemosensitive neurons induced by activation of protease-activated receptor-2 in rats

This study was carried out to determine the effect of protease-activated receptor-2 (PAR2) activation on the pulmonary chemoreflex responses and on the sensitivity of isolated rat vagal pulmonary chemosensitive neurons. In anaesthetized, spontaneously breathing rats, intratracheal instillation of trypsin (0.8 mg ml(-1), 0.1 ml), an endogenous agonist of PAR2, significantly amplified the capsaicin-induced pulmonary chemoreflex responses. The enhanced responses were completely abolished by perineural capsaicin treatment of both cervical vagi, suggesting the involvement of pulmonary C-fibre afferents. In patch-clamp recording experiments, pretreatment with trypsin (0.1 microM, 2 min) potentiated the capsaicin-induced whole-cell inward current in isolated pulmonary sensory neurons. The potentiating effect of trypsin was mimicked by PAR2-activating peptide (PAR2-AP) in a concentration-dependent manner. PAR2-AP pretreatment (100 microM, 2 min) also markedly enhanced the acid-evoked inward currents in these sensory neurons. Furthermore, the sensitizing effect of PAR2 was completely abolished by pretreatment with either U73122 (1 microM, 4 min), a phospholipase C inhibitor, or chelerythrine (10 microM, 4 min), a protein kinase C (PKC) inhibitor. In summary, our results have demonstrated that activation of PAR2 upregulates the pulmonary chemoreflex sensitivity in vivo and the excitability of isolated pulmonary chemosensitive neurons in vitro, and this effect of PAR2 activation was mediated through the PKC-dependent transduction pathway. These results further suggest that the hypersensitivity of these neurons may play a part in the development of airway hyper-responsiveness resulting from PAR2 activation.

Trypsin increases pseudorabies virus production through activation of the ERK signalling pathway

Extracellular proteases that are expressed in primary and secondary foci of viral infection are potentially important mediators of infectious inflammatory processes. For some viruses, such as influenza virus and rotaviruses, proteases such as trypsin enhance infectivity by a direct proteolytic effect on some virion proteins. By using an in vitro model of herpesvirus infection, the possibility that proteases modulate the viral cycle through signalling delivered to the infected cell was investigated. It is reported that exposure of pseudorabies virus-infected cells to trypsin increased virus production. Moreover, this treatment induced synergistic and sustained activation of the extracellular signal-regulated kinase (ERK) 1/2 signalling pathway, which appeared to be necessary for this increased viral production. These results suggest that herpesviruses could take advantage of the inflammatory context and particularly of the presence of proteases to increase their replication. Thus, these data point to a potentially important role of extracellular proteases in herpesvirus infection.

Induction of release and up-regulated gene expression of interleukin (IL)-8 in A549 cells by serine proteinases

BACKGROUND

Hypersecretion of cytokines and serine proteinases has been observed in asthma. Since protease-activated receptors (PARs) are receptors of several serine proteinases and airway epithelial cells are a major source of cytokines, the influence of serine proteinases and PARs on interleukin (IL)-8 secretion and gene expression in cultured A549 cells was examined.

RESULTS

A549 cells express all four PARs at both protein and mRNA levels as assessed by flow cytometry, immunofluorescence microscopy and reverse transcription polymerase chain reaction (PCR). Thrombin, tryptase, elastase and trypsin induce a up to 8, 4.3, 4.4 and 5.1 fold increase in IL-8 release from A549 cells, respectively following 16 h incubation period. The thrombin, elastase and trypsin induced secretion of IL-8 can be abolished by their specific inhibitors. Agonist peptides of PAR-1, PAR-2 and PAR-4 stimulate up to 15.6, 6.6 and 3.5 fold increase in IL-8 secretion, respectively. Real time PCR shows that IL-8 mRNA is up-regulated by the serine proteinases tested and by agonist peptides of PAR-1 and PAR-2.

CONCLUSION

The proteinases, possibly through activation of PARs can stimulate IL-8 release from A549 cells, suggesting that they are likely to contribute to IL-8 related airway inflammatory disorders in man.

Prognostic Role of Protease-Activated Receptors 1 and 4 in Resected Stage IB Non-Small-Cell Lung Cancer

BACKGROUND

Protease-activated receptor (PAR)-1 and PAR-4 are involved in extracellular matrix invasion and angiogenesis.

PATIENTS AND METHODS

A series of 60 resected stage IB non-small-cell lung cancers (NSCLCs), including 30 adenocarcinomas (ADCs) and 30 squamous cell carcinomas (SCCs), were processed by immunohistochemistry with antibodies to PAR-1, PAR-4, vascular endothelial growth factor (VEGF), and CD34.

RESULTS

Protease-activated receptor-1 was expressed in 37 cases (62%) and PAR-4 in 39 (65%). Adenocarcinomas were significantly more positive than SCC for PAR-1 (17 vs. 8 cases) and PAR-4 (10 vs. 5 cases). Vascular endothelial growth factor was expressed in 42 cases (70%): 22 ADC and 20 SCC. A significant correlation emerged between PAR-1 and/or PAR-4 expression and VEGF but not with microvessel density. Median follow-up was 38 months; actuarial 5-year survival was 43%. At univariate analysis, 3-year survival was shorter in patients expressing PAR-4 versus negative cases (29% vs. 60%; P = 0.002). In 46 patients expressing PAR-1 and/or PAR-4, 3-year survival was 30% versus 68% in 14 patients with no PAR expression (P = 0.002). A trend toward shorter 3-year survival was seen in PAR-1-positive versus PAR-1-negative cases (34% vs. 46%; P = 0.06). Multivariate analysis identified expression of PAR-1 and/or PAR-4 as an independent prognostic factor for reduced survival in resected stage IB NSCLC.

CONCLUSION

Expression of PAR-1 and PAR-4 in early-stage NSCLC could be included in a molecular algorithm for the selection of patients eligible for adjuvant studies.

Protease-activated receptor-2 activation exaggerates TRPV1-mediated cough in guinea pigs

A lowered threshold to the cough response frequently accompanies chronic airway inflammatory conditions. However, the mechanism(s) that from chronic inflammation results in a lowered cough threshold is poorly understood. Irritant agents, including capsaicin, resiniferatoxin, and citric acid, elicit cough in humans and in experimental animals through the activation of the transient receptor potential vanilloid 1 (TRPV1). Protease-activated receptor-2 (PAR2) activation plays a role in inflammation and sensitizes TRPV1 in cultured sensory neurons by a PKC-dependent pathway. Here, we have investigated whether PAR2 activation exaggerates TRPV1-dependent cough in guinea pigs and whether protein kinases are involved in the PAR2-induced cough modulation. Aerosolized PAR2 agonists (PAR2-activating peptide and trypsin) did not produce any cough per se. However, they potentiated citric acid- and resiniferatoxin-induced cough, an effect that was completely prevented by the TRPV1 receptor antagonist capsazepine. In contrast, cough induced by hypertonic saline, a stimulus that provokes cough in a TRPV1-independent manner, was not modified by aerosolized PAR2 agonists. The PKC inhibitor GF-109203X, the PKA inhibitor H-89, and the cyclooxygenase inhibitor indomethacin did not affect cough induced by TRPV1 agonists, but abated the exaggeration of this response produced by PAR2 agonists. In conclusion, PAR2 stimulation exaggerates TRPV1-dependent cough by activation of diverse mechanism(s), including PKC, PKA, and prostanoid release. PAR2 activation, by sensitizing TRPV1 in primary sensory neurons, may play a role in the exaggerated cough observed in certain airways inflammatory diseases such as asthma and chronic obstructive pulmonary disease.

Protease-activated receptor-2 regulates vascular endothelial growth factor expression in MDA-MB-231 cells via MAPK pathways

Protease-activated receptor 2 (PAR2) is a G-protein coupled receptor that is cleaved and activated by serine proteases including the coagulation protease factor VIIa (FVIIa). There is evidence that PAR2 function contributes to angiogenesis, but the mechanisms involved are poorly defined. Here we show that PAR2 activation in human breast cancer cells leads to the upregulation of vascular endothelial growth factor (VEGF). Activation of PAR2 with agonist peptide (AP), trypsin or FVIIa results in a robust increase of VEGF message and protein. Incubation of cells with PAR1-AP, PAR3-AP, PAR4-AP, or thrombin has only a modest effect on VEGF production. Cleavage blocking antibodies show that FVIIa-mediated VEGF production is PAR2 mediated. Mitogen-activated protein kinase (MAPK) pathway inhibitors U0126 and SB203580 inhibit PAR2-mediated VEGF production. Incubation of cells with PAR2-AP leads to significant extracellular regulated kinase1/2 (ERK1/2) and p38 MAPK phosphorylation and activation. Collectively, these data suggest that PAR2 signaling through MAPK pathways leads to the production of proangiogenic VEGF in breast cancer cells.

Blockade of Angiogenesis by Small Molecule Antagonists to Protease-Activated Receptor-1: Association with Endothelial Cell Growth Suppression and Induction of Apoptosis

Many studies support the notion that protease-activated receptor (PAR)-1 plays a pivotal role in angiogenesis. However, direct evidence and understanding the molecular mechanisms involved were limited because PAR-1-specific antagonists have been developed only recently. In the present study, we evaluated the effects of two well characterized PAR-1 antagonists, SCH79797 ((N-3-cyclopropyl-7-{[4-(1-methylethyl)phenyl]-methyl}-7H-pyrrolo[3,2-f]quinazoline-1,3-diamine)) and RWJ56110 [(alphaS)-N-[(1S)-3-amino-1-[[(phenylmethyl)amino]carbonyl]propyl]-alpha-[[[[[1-(2,6-dichlorophenyl)methyl]-3-(1-pyrrolidinylmethyl)-1H-indol-6-yl]amino]carbonyl]amino]-3,4-difluorobenzenepropanamide], in the angiogenic cascade. These antagonists suppressed both the basic angiogenesis and that stimulated by thrombin in the chick chorioallantoic membrane model in vivo. PAR-1 antagonists also abrogated tube formation in the in vitro Matrigel system. These inhibitory effects were dose-dependent and well correlated with the inhibitory effects of SCH79797 and RWJ56110 on primary endothelial cell proliferation and on the initiation of apoptosis. PAR-1 blockage resulted in inhibition of endothelial cell growth by increasing the sub-G0/G1 fraction and reducing the percentage of cells in the S phase. Consistent with this, PAR-1 antagonists reduced incorporation of [3H]thymidine in endothelial cells and blocked the phosphorylation of extracellular signal-regulated kinases in a fashion depending specifically on PAR-1 activation. Analysis by annexin V/propidium iodide staining and poly(ADP-ribose) polymerase cleavage revealed that PAR-1 blockage increased apoptotic cell death by a mechanism involving caspases. These results provide further evidence that PAR-1 is a key receptor that mediates angiogenesis and suggest PAR-1 as target for developing antiangiogenic agents with potential therapeutic application in cancer and other angiogenesis-related diseases.

Proinflammatory gene expression in mouse ST2 cell line in response to infection by Porphyromonas gingivalis

Porphyromonas gingivalis is a predominant periodontal pathogen, whose infection causes inflammatory responses in periodontal tissue and alveolar bone resorption. Various virulence factors of this pathogen modulate host innate immune responses. It has been reported that gingipains degrade a wide variety of host cell proteins, and fimbriae are involved in bacterial adhesion to and invasion of host cells. In the present study, we profiled ST2 stromal cell gene expression following infection with the viable P. gingivalis strain ATCC33277 as well as with its gingipain- and fimbriae-deficient mutants, using microarray technology and quantitative real-time polymerase chain reaction. Using a mouse array of about 20,000 genes, we found that infection with the wild strain elicited a significant upregulation (greater than 2-fold) of expression of about 360 genes in ST2 cells, which included the chemokines CCL2, CCL5, and CXCL10, and other proinflammatory proteins such as interleukin-6 (IL-6) and matrix metalloproteinase-13 (MMP-13). Further, infection with the gingipain-deficient mutant elicited a reduced expression of the CXCL10, IL-6 and MMP-13 genes, suggesting that gingipains play an important role in inducing the expression of those genes following P. gingivalis infection. On the other hand, the pattern of global gene expression induced by the fimbriae-deficient mutant was similar to that by the wild strain. These results suggest that P. gingivalis infection induces gene expression of a wide variety of proinflammatory proteins in stromal cells/osteoblasts, and gingipains may be involved in inducing several of the proinflammatory factors.

Proangiogenic Effects of Protease-Activated Receptor 2 Are Tumor Necrosis Factor-α and Consecutively Tie2 Dependent

Objective— Angiogenesis is essential physiologically in growth and pathologically in tumor development, chronic inflammatory disorders, and proliferative retinopathies. Activation of protease-activated receptor 2 (PAR2) leads to a proangiogenic response, but its mechanisms have yet to be specifically described. Here, we investigated the mode of action of PAR2 in retinal angiogenesis.

Methods and Results— PAR2-activating peptide, SLIGRL, increased retinal angiogenesis associated with an induction of vascular endothelial growth factor and angiopoetin-2 and most notably tie2 in the retina in vivo as well as in cultured neuroretinal endothelial cells. SLIGRL also induced release of the proinflammatory and angiogenic mediator tumor necrosis factor-α (TNF-α) via the MEK/extracellular signal-regulated kinase (ERK) (MEK/ERK) pathway in these endothelial cells. TNF-α, in turn, elicited tie2 expression by activating the MEK/ERK pathway. PAR2-evoked tie2 expression, endothelium proliferation (in vitro), and retinal neovascularization (in vivo) were abrogated by selective TNF-α blockers (neutralizing antibody infliximab and soluble TNF-α receptor-Fc fusion protein etanercept) as well as the MEK inhibitor PD98059.

Conclusion— The proangiogenic properties of PAR2 are intertwined with its proinflammatory effects, such that in retinal vasculature, they depend on TNF-α and subsequent induction of tie2 via the MEK/ERK pathway.

Effects of a reversible beta-tryptase and trypsin inhibitor (RWJ-58643) on nasal allergic responses

BACKGROUND

beta-Tryptase is a multifunctional mast cell serine protease released during mast cell degranulation and tryptase/trypsin inhibitors are a novel potential therapeutic approach for allergic inflammatory diseases.

OBJECTIVES

This study was performed to assess the effects of RWJ-58643 on nasal symptoms, eosinophil influx, and cytokine and chemokine release following nasal allergen challenge (NAC).

METHODS

Male patients with grass pollen allergic rhinitis (n=16) out of season received single doses of RWJ-58643 (100, 300, 600 microg) or matched placebo given 30 min before NAC in a double-blind, randomized crossover design. A single dose of 200 microg budesonide was studied in an open-label extension phase. NAC was performed with Timothy grass pollen (ALK) via a nasal device, and nasal lavage was performed at times 0 (pre-drug, pre-allergen), 0.5 (30 min post-drug, pre-NAC) 1.5, 2.5, 4.5, 6.5, 8.5, and 24 h after drug administration. Nasal lavage mediators were analysed using a sensitive multiplexed bead immunoassay system.

RESULTS

Low-dose RWJ-58643 (100 microg) and budesonide (200 microg) significantly reduced symptoms, eosinophils and levels of IL-5 following NAC. However, higher doses of RWJ-58643 (300 and 600 microg) caused a late eosinophilia and preceding increases in IL-5 compared with placebo.

CONCLUSIONS

This study suggests that combined beta-tryptase and trypsin inhibition has therapeutic potential in allergic inflammation, however, this property is dose responsive and higher doses are ineffective and may cause eosinophilia.

Functional Characterization and Expression Analysis of the Proteinase-Activated Receptor-2 in Human Cutaneous Mast Cells

Proteinase-activated receptor-2 (PAR2) belongs to a new G protein-coupled receptor subfamily activated by serine proteinases. PAR2 has been demonstrated to play a role during inflammation and immune response in different tissues including the skin. We examined whether PAR2 is functionally expressed by cutaneous human primary skin mast cells (HPMC) and the human mast cell line 1 (HMC-1). Reverse transcription-polymerase chain reaction and FACS analysis show expression of PAR2 both at the RNA and protein level. HPMCs and HMC-1 also express PAR1, PAR3, and PAR4. Ca-mobilization studies demonstrate functional PAR2 expressed by human skin mast cells, as shown by natural and synthetic PAR2 agonists. PAR2 agonists induced histamine release from HPMC indicating a role of PAR2 in regulating inflammatory and immune responses by skin mast cells. Double-immunofluorescence staining reveals colocalization of PAR2 with tryptase in the majority of human skin mast cells. In conclusion, trypsin and tryptase as well as specific agonists for PAR2 were able to induce Ca2+ mobilization in HPMCs, and agonists of PAR2 induce the release of histamine from these cells. Thus, PAR2 may be an important regulator of skin mast cell function during cutaneous inflammation and hypersensitivity.

Trypsin and thrombin accelerate aggregation of human endocrine pancreas precursor cells

Human islet-derived precursor cells (hIPCs) and human pancreatic ductal carcinoma (PANC-1) cells can be induced to form aggregates that subsequently differentiate into hormone-expressing islet-like cell aggregates (ICAs). We show that challenge of hIPCs or PANC-1 cells with thrombin or trypsin resulted in stimulation of signaling via the inositol-tris-phosphate second messenger pathway leading to rapid, transient increases in cytosolic calcium ion concentration in the majority of the cells. Because we found that hIPCs, PANC-1 cells, human fetal pancreas, and human adult islets express two protease-activated receptors (PARs), PAR-1 and PAR-2, we tested whether the effects of thrombin and trypsin were mediated, at least in part, by these receptors. Peptide agonists that are relatively specific for PAR-1 (SFLLRN-amide) or PAR-2 (SLIGRL-amide) stimulated increases in inositol phosphates and cytosolic calcium ion concentration, and increased the phosphorylation of Rho, a small G-protein associated with cytoskeletal changes affecting cellular morphology and migration. Most importantly, we show that these agonists increased the rate of hIPC aggregation leading to the formation of more viable, smaller ICAs. Our data show that thrombin and trypsin accelerate aggregation, an early stage of hIPC differentiation in vitro, and imply that pancreatic trypsin and thrombin may be involved in islet development in vivo.

Thrombin/thrombin receptor (PAR-1)-mediated induction of IL-8 and VEGF expression in prostate cancer cells

Interleukin 8 (IL-8) and vascular endothelial growth factor (VEGF) are two cytokines promoting prostate tumor growth and angiogenesis. The main coagulation protease thrombin may modulate the malignant phenotype of prostate cancer cells via its cellular receptor(s). We aimed to investigate the effects of thrombin on IL-8 and VEGF expression in DU 145 prostate cancer cells. Thrombin induced the expression and secretion of IL-8 and VEGF, with more pronounced effects on IL-8. Target-specific siRNA-induced protease-activated receptor 1 (PAR-1) knockdown completely neutralized thrombin-enhanced cytokine secretion, demonstrating the essential role of PAR-1. Inhibitors of either extracellular signal-regulating kinase (ERK) or phosphatidylinositol 3-kinase (PI3K) partly reversed the thrombin-induced cytokine expression, suggesting that both ERK and PI3K kinase pathways may be involved in IL-8 and VEGF expression. The results suggest that the thrombin/PAR-1 system upregulates cytokines in prostate cancer cells which in turn may contribute to the progression of prostate cancer.

Neutrophils and the kallikrein-kinin system in proteinase-activated receptor 4-mediated inflammation in rodents

1 We evaluated a potential role for proteinase-activated receptor 4 (PAR(4)) in a rodent paw inflammation model, with a focus on two main features of inflammation: (1) oedema and (2) granulocyte recruitment. 2 A PAR(4) antagonist (Pepducin P4pal-10; palmitoyl-SGRRYGHALR-NH(2)) reduced both the oedema and granulocyte recruitment induced by a localized administration of carrageenan in the rat hind paw, pointing to a key role for PAR(4) in this inflammation model. 3 Further, intraplantar injection in the mouse hind paw of a PAR(4) agonist (AYPGKF-NH(2)), but not its standard PAR(4)-inactive peptide control (YAPGKF-NH(2)), caused an inflammatory reaction characterized by oedema (increased paw thickness) and granulocyte recruitment (increased paw myeloperoxidase activity). The PAR(4) agonist-induced effects were inhibited in mice pretreated with pepducin P4pal10. 4 These PAR(4) agonist-mediated effects were not affected by pretreatment with inhibitors of either NO production or prostaglandin release (L-NAME and indomethacin, respectively). 5 However, selective immuno-depletion of neutrophils significantly reduced PAR(4) agonist-induced oedema formation. 6 Moreover, AYPGKF-NH(2)-induced oedema was also reduced by pretreatment with either a kinin B(2) receptor antagonist (icatibant) or a tissue or plasma kallikrein inhibitor (FE999024 and FE999026, respectively), but not with a kinin B(1) receptor antagonist (SSR240612). 7 We conclude: (1) that PAR(4) plays an important role in the inflammatory response as it mediates some of the hallmarks of inflammation and (2) that PAR(4)-mediated oedema is dependent on the recruitment of neutrophils and components of the kallikrein-kinin system.

The protease-activated receptor2 (PAR2)-prostaglandin E2-prostanoid EP receptor axis: a potential bronchoprotective unit in the respiratory tract?

Protease-activated receptor2 (PAR2) is a subtype of G protein-coupled receptor that is widely expressed within the respiratory tract. Stimulation of PAR2 by proteases such as trypsin and tryptase, or by small peptidic activators induces a complex array of effects within the airways. One such PAR2-mediated effect by basal airway epithelial cells is the generation of prostaglandin E2. Prostaglandin E2 produces a raft of anti-inflammatory effects within the airways, principally through the activation of the prostanoid EP2 and EP3 receptor subtypes. This article reviews the PAR2-prostaglandin E2-prostanoid EP receptor axis and discusses approaches through which its activation may provide beneficial effects in respiratory disease.

Proteinase-activated receptor 2 modulates neuroinflammation in experimental autoimmune encephalomyelitis and multiple sclerosis

The proteinase-activated receptors (PARs) are widely recognized for their modulatory properties of inflammation and neurodegeneration. We investigated the role of PAR2 in the pathogenesis of multiple sclerosis (MS) in humans and experimental autoimmune encephalomyelitis (EAE) in mice. PAR2 expression was increased on astrocytes and infiltrating macrophages in human MS and murine EAE central nervous system (CNS) white matter (P < 0.05). Macrophages and astrocytes from PAR2 wild-type (WT) and knockout (KO) mice exhibited differential immune gene expression with PAR2 KO macrophages showing significantly higher interleukin 10 production after lipopolysaccharide stimulation (P < 0.001). PAR2 activation in macrophages resulted in the release of soluble oligodendrocyte cytotoxins (P < 0.01). Myelin oligodendrocyte glycoprotein-induced EAE caused more severe inflammatory gene expression in the CNS of PAR2 WT animals (P < 0.05), together with enhanced T cell proliferation and interferon gamma production (P < 0.05), compared with KO littermates. Indeed, PAR2 WT animals showed markedly greater microglial activation and T lymphocyte infiltration accompanied by worsened demyelination and axonal injury in the CNS compared with their PAR2 KO littermates. Enhanced neuropathological changes were associated with a more severe progressive relapsing disease phenotype (P < 0.001) in WT animals. These findings reveal previously unreported pathogenic interactions between CNS PAR2 expression and neuroinflammation with ensuing demyelination and axonal injury.

Substrate specificity of human kallikrein 6: salt and glycosaminoglycan activation effects

Human kallikrein 6 (hK6) is abundantly expressed in the central nervous system and is implicated in demyelinating disease. This study provided biochemical data about the substrate specificity and activation of hK6 by glycosaminoglycans and by kosmotropic salts, which followed the Hofmeister series. The screening of fluorescence resonance energy transfer (FRET) peptide families derived from Abz-KLRSSKQ-EDDnp resulted in the finding that Abz-AFRFSQ-EDDnp (where Abz is ortho-aminobenzoic acid and EDDnp is N-[2,4-dinitrophenyl]ethylenediamine)) is the best synthetic substrate described so far for hK6 (kcat/Km 38,667 s(-1) mm(-1)). It is noteworthy that the AFRFS sequence was found as a motif in the amino-terminal domain of seven human ionotropic glutamate receptor subunits. We also examined the hK6 hydrolytic activity on FRET peptides derived from human myelin basic protein, precursor of the Abeta amyloid peptide, reactive center loop of alpha1-antichymotrypsin, plasminogen, and maturation and inactivation cleavage sites of hK6, which were described earlier as natural substrates for hK6. The best substrates were derived from myelin basic protein. The hK6 maturation cleavage site was poorly hydrolyzed, and no evidence was found to support a two-step self-activation process reported previously. Finally, we assayed FRET peptides derived from sequences that span the cleavage sites for activation of protease-activated receptors (PAR) 1-4, and only the substrate with the PAR 2 sequence was hydrolyzed. These results further supported the hypothesis that hK6 expressed in the central nervous system is involved in normal myelin turnover/demyelination processes, but it is unlikely to self-activate. This report also suggested the possible modulation of ionotropic glutamate receptors and activation of PAR 2 by hK6.