Protease-activated receptors: contribution to physiology and disease

Activity of recombinant trypsin isoforms on human proteinase-activated receptors (PAR): mesotrypsin cannot activate epithelial PAR-1, -2, but weakly activates brain PAR-1

Trypsin-like serine proteinases trigger signal transduction pathways through proteolytic cleavage of proteinase-activated receptors (PARs) in many tissues. Three members, PAR-1, PAR-2 and PAR-4, are trypsin substrates, as trypsinolytic cleavage of the extracellular N terminus produces receptor activation. Here, the ability of the three human pancreatic trypsin isoforms (cationic trypsin, anionic trypsin and mesotrypsin (trypsin IV)) as recombinant proteins was tested on PARs. Using fura 2 [Ca(2+)](i) measurements, we analyzed three human epithelial cell lines, HBE (human bronchial epithelial), A549 (human pulmonary epithelial) and HEK (human embryonic kidney)-293 cells, which express functional PAR-1 and PAR-2. Human mesotrypsin failed to induce a PAR-mediated Ca(2+) response in human epithelial cells even at high concentrations. In addition, mesotrypsin did not affect the magnitude of PAR activation by subsequently added bovine trypsin. In HBE cells, which like A549 cells express high PAR-2 levels with negligible PAR-1 levels (<11%), half-maximal responses were seen for both cationic and anionic trypsins at about 5 nM. In the epithelial cells, mesotrypsin did not activate PAR-2 or PAR-1, whereas both anionic and cationic trypsins were comparable activators. We also investigated human astrocytoma 1321N1cells, which express PAR-1 and some PAR-3, but no PAR-2. High concentrations (>100 nM) of mesotrypsin produced a relatively weak Ca(2+) signal, apparently through PAR-1 activation. Half-maximal responses were observed at 60 nM mesotrypsin, and at 10-20 nM cationic and anionic trypsins. Using a desensitization assay with PAR-2-AP, we confirmed that both cationic and anionic trypsin isoforms cause [Ca(2+)](i) elevation in HBE cells mainly through PAR-2 activation. Desensitization of PAR-1 with thrombin receptor agonist peptide in 1321N1 cells demonstrated that all three recombinant trypsin isoforms act through PAR-1.Thus, the activity of human cationic and anionic trypsins on PARs was comparable to that of bovine pancreatic trypsin. Mesotrypsin (trypsin IV), in contrast to cationic and anionic trypsin, cannot activate or disable PARs in human epithelial cells, demonstrating that the receptors are no substrates for this isoenzyme. On the other hand, mesotrypsin activates PAR-1 in human astrocytoma cells. This might play a role in protection/degeneration or plasticity processes in the human brain.

Jab1, a novel protease-activated receptor-2 (PAR-2)-interacting protein, is involved in PAR-2-induced activation of activator protein-1

Protease-activated receptor-2 (PAR-2), a G protein-coupled receptor for trypsin and tryptase, exerts important physiological and pathological functions in multiple systems. However, unlike PAR-1, the PAR-2-mediated intracellular signal transductions are hardly known. Here, using yeast two-hybrid screening with a human brain cDNA library, we identified an interacting partner of human PAR-2, the Jun activation domain-binding protein 1 (Jab1). The interaction was confirmed by glutathione S-transferase pull-down assays in vitro, and by co-immunoprecipitation assays in vivo. Jab1 was also shown to be colocalized with PAR-2 in both transfected HEK293 cells and in normal primary human astrocytes by double immunofluorescence staining. Further experiments demonstrated that multiple intracellular domains of PAR-2 are required for the interaction with Jab1. We then showed that agonist stimulation of PAR-2 disrupted the interaction, which could be prevented by the inhibitor of receptor endocytosis phenylarsine oxide, but not by the lysosomal protease inhibitor ZPAD. Importantly, we found that activation of PAR-2 induced the redistribution of Jab1 from the plasma membrane to the cytosol, but did not influence expression of Jab1. Furthermore, Jab1 mediated PAR-2-induced c-Jun activation, which was followed by increased activation of activator protein-1. Loss-of-function studies, using Jab1 small interfering RNA, demonstrated that Jab1 knockdown blocked PAR-2-induced activator protein-1 activation. Taken together, our data demonstrate that Jab1 is an important effector that mediates a novel signal transduction pathway for PAR-2-dependent gene expression.

Extracellular granzymes: current perspectives

Granzyme A (GrA) and granzyme B (GrB) play key roles in the induction of target cell death induced by cytotoxic lymphocytes. Whilst these roles have been extensively studied, it is becoming apparent that both granzymes also possess extracellular activities. Soluble granzymes are found extracellularly in normal plasma and are elevated in a number of diseases, ranging from viral and bacterial infections to autoimmune diseases. Here, we discuss the current knowledge of extracellular granzyme substrates, inhibitors and functions; and the pathological consequences of extracellular granzymes in disease. In addition, we provide new evidence for the role of glycosaminoglycan-binding sites of granzymes in extracellular matrix remodeling.

Scratching behavior in mice induced by the proteinase-activated receptor-2 agonist, SLIGRL-NH2

We examined whether the proteinase-activated receptor-2 (PAR2) agonist, H-Ser-Leu-Ile-Gly-Arg-Leu-NH2 (SLIGRL-NH2), could induce scratching behavior in mice. Intradermal injections of SLIGRL-NH2 (10-50 microg) evoked dose dependent scratching. This behavior peaked near 5 min and returned to preinjection levels within 30 min. Pretreatment of animals with a histamine H1 receptor antagonist, pyrilamine, blocked histamine induced scratching, but it had little effect on SLIGRL scratching. Our study suggests that PAR2 mediates histamine independent itch.

Mechanisms for modulation of mouse gastrointestinal motility by proteinase-activated receptor (PAR)-1 and -2 in vitro

Proteinase-activated receptor (PAR)-1 or -2 modulates gastrointestinal transit in vivo. To clarify the underlying mechanisms, we characterized contraction/relaxation caused by TFLLR-NH2 and SLIGRL-NH2, PAR-1- and -2-activating peptides, respectively, in gastric and small intestinal (duodenal, jejunal and ileal) smooth muscle isolated from wild-type and PAR-2-knockout mice. Either SLIGRL-NH2 or TFLLR-NH2 caused both relaxation and contraction in the gastrointestinal preparations from wild-type animals. Apamin, a K+ channel inhibitor, tended to enhance the peptide-evoked contraction in some of the gastrointestinal preparations, whereas it inhibited relaxation responses to either peptide completely in the stomach, but only partially in the small intestine. Indomethacin reduced the contraction caused by SLIGRL-NH2 or TFLLR-NH2 in both gastric and ileal preparations, but unaffected apamin-insensitive relaxant effect of either peptide in ileal preparations. Repeated treatment with capsaicin suppressed the contractile effect of either peptide in the stomach, but not clearly in the ileum, whereas it enhanced the apamin-insensitive relaxant effect in ileal preparations. In any gastrointestinal preparations from PAR-2-knockout mice, SLIGRL-NH2 produced no responses. Thus, the inhibitory component in tension modulation by PAR-1 and -2 involves both apamin-sensitive and -insensitive mechanisms in the small intestine, but is predominantly attributable to the former mechanism in the stomach. The excitatory component in the PAR-1 and -2 modulation may be mediated, in part, by activation of capsaicin-sensitive sensory nerves and/or endogenous prostaglandin formation. Our study thus clarifies the multiple mechanisms for gastrointestinal motility modulation by PAR-1 and -2, and also provides ultimate evidence for involvement of PAR-2.

PAR-2 activating peptide-induced stimulation of pregnant rat myometrium contractile activity partly involves the other membrane receptors

OBJECTIVE

To study if spontaneous contractions augmented by proteinase-activated receptor-2 (PAR-2)-activating peptide serine-leucine-isoleucine-glycine-arginine-leucine (SLIGRL) involve coactivation of membrane chemoceptors and are associated with expression of PAR-2 mRNA in non-pregnant and pregnant rat myometrium.

MATERIALS AND METHODS

Non-pregnant, mid-pregnant, and late pregnant rat uterine horn and small intestine segments were snap-frozen in liquid nitrogen to determine PAR-2 mRNA levels by real time polymerase chain reaction (PCR). Uterine rings were used for isometric tension recording. Effect of SLIGRL (0.1 mM) on spontaneous contractions before and after exposure to ibuprofen (cyclooxygenase inhibitor, 1.0 microM), SQ-29548 (thromboxane A(2) receptor inhibitor, 1.0 microM), ketotifen (histamine 1 receptor inhibitor, 10 microM), WEB-2170BS (platelet-activating factor (PAF) receptor inhibitor, 10 microM), atropine (muscarinic receptor inhibitor, 0.1 microM), or ketanserin (serotonin receptor inhibitor, 10 microM) were compared. Paired t-test and one-way ANOVA followed by Dunnett's or Newman-Keuls post hoc tests were used for statistical analysis when appropriate.

SIGNIFICANCE

P<0.05.

RESULTS

The agents did not significantly affect time-associated decay in spontaneous contractile activity in any group of the tissues. Activation of spontaneous contractions induced by SLIGRL in non-pregnant rat myometrium did not involve coactivation of membrane chemoceptors, while in mid-pregnant rat myometrium coactivation of prostanoid, histamine, and serotonin receptors and in late pregnant rat myometrium coactivation of thromboxane receptors was noted. Expression of PAR-2 mRNA was similar in non-pregnant, mid-pregnant, and late pregnant rat myometrium.

CONCLUSIONS

Expression of PAR-2 in rat myometrium is not dependent on gestational age. Stimulation of PAR-2 is associated with production/release of cyclooxygenase pathway product(s) activating thromboxane/prostaglandin H2 receptors, partial involvement of histamine H1 receptors and serotonin receptors in midpregnancy and thromboxane A2/prostaglandin H2 receptors in late pregnancy.

Protease-activated receptors-1 and -2 can mediate endothelial barrier protection: role in factor Xa signaling

Coagulation and inflammation are intimately linked and cellular signaling by coagulation proteases through protease-activated receptors (PARs) may affect pro- and anti-inflammatory responses. Permeability of the endothelial cell barrier at the blood-tissue interface plays a key role in inflammatory disorders such as sepsis. We have recently shown that PAR1 signaling by activated protein C or low concentrations of thrombin can enhance endothelial barrier integrity. In the present study, we analyzed effects of coagulation factor Xa (FXa), which is known to activate both endothelial cell PAR1 and PAR2, on monolayer integrity using a transformed human umbilical vein endothelial cell (HUVEC) line in a dual-chamber system. Preincubation with FXa potently reduced high-dose thrombin-mediated hyperpermeability and basal permeability. FXa was protective at concentrations of 5 nm or higher and proteolytic activity was required. Barrier protective FXa signaling was not affected by cleavage-blocking anti-PAR1 antibodies or by a PAR1 antagonist. Similarly, cleavage-blocking anti-PAR2 alone had no effect, but blocking both PAR1 and PAR2 inhibited barrier protection by FXa. Incubation of the cell layer with a PAR2-specific agonist peptide reduced thrombin-mediated hyperpermeability and basal permeability similar to FXa. In conclusion, not only PAR1, but also PAR2 can mediate barrier protection in endothelial cells and FXa can use either receptor to enhance barrier integrity. Although it is currently unknown whether PAR signaling by FXa has a physiological role, the results suggest a potential protective effect of FXa and other agonists of endothelial PAR2, which should be explored in models of local and systemic inflammation in vivo.

Immune regulation of protease-activated receptor-1 expression in murine small intestine during Nippostrongylus brasiliensis infection

Infection with gastrointestinal nematodes exerts profound effects on both immune and physiological responses of the host. Helminth infection induces a hypercontractility of intestinal smooth muscle that is dependent on the Th2 cytokines, IL-4 and IL-13, and may contribute to worm expulsion. Protease-activated receptors (PARs) are expressed throughout the gut, and activation of PAR-1 was observed in asthma, a Th2-driven pathology. In the current study we investigated the physiologic and immunologic regulation of PAR-1 in the murine small intestine, specifically 1) the effect of PAR-1 agonists on small intestinal smooth muscle contractility, 2) the effects of Nippostrongylus brasiliensis infection on PAR-1 responses, 3) the roles of IL-13 and IL-4 in N. brasiliensis infection-induced alterations in PAR-1 responses, and 4) the STAT6 dependence of these responses. We demonstrate that PAR-1 activation induces contraction of murine intestinal smooth muscle that is enhanced during helminth infection. This hypercontractility is associated with an elevated expression of PAR-1 mRNA and protein. N. brasiliensis-induced changes in PAR-1 function and expression were seen in IL-4-deficient mice, but not in IL-13- or STAT6-deficient mice, indicating the dependence of IL-13 on the STAT6 signaling pathway independent of IL-4.

Involvement of neutrophil recruitment and protease-activated receptor 2 activation in the induction of IL-18 in mice

Activated neutrophils produce serine proteases, which activate cells through protease-activated receptor 2 (PAR2). As proteinase 3 (PR3) induces the secretion of interleukin (IL)-18 from epithelial cells in combination with lipopolysaccharide (LPS) in vitro, we examined whether neutrophils, serine proteases, and PAR2 are involved in the induction of serum IL-18 and IL-18-dependent liver injury in mice treated with heat-killed Propionibacterium acnes and LPS. LPS-induced serum IL-18 levels in P. acnes-primed mice were reduced significantly by anti-Gr-1 injection (depletion of neutrophils and macrophages) but not by a macrophage "suicide" technique, using liposomes encapsulating clodronate. The IL-18 induction was decreased significantly by coadministration of a serine protease inhibitor [Nafamostat mesilate (FUT-175)] with LPS. Serum levels of tumor necrosis factor alpha and liver enzymes induced by P. acnes and LPS were abolished by anti-Gr-1 treatment, and concomitantly, liver injury (necrotic change and granuloma formation) and Gr-1(+) cell infiltration into the liver were prevented by the treatment. A deficiency of PAR2 in mice significantly impaired IL-18 induction by treatment with P. acnes and LPS, and only slight pathological changes in hepatic tissues occurred in the PAR2-deficient mice treated with P. acnes and LPS. Furthermore, coadministration of exogenous murine PR3 or a synthetic PAR2 agonist (ASKH95) with LPS in the anti-Gr-1-treated mice restored the serum IL-18 levels to those in control mice treated with P. acnes and LPS. These results indicate that neutrophil recruitment and PAR2 activation by neutrophil serine proteases are critically involved in the induction of IL-18 and IL-18-dependent liver injury in vivo.

Therapeutic promise of proteinase-activated receptor-2 antagonism in joint inflammation

Biological therapies such as tumor necrosis factor-alpha inhibitors have advanced the treatment of rheumatoid arthritis, but one-third of patients do not respond to such therapy. Furthermore, these inhibitors are now usually administered in combination with conventional disease-modifying antirheumatic drugs, suggesting they have not achieved their early promise. This study investigates a novel therapeutic target, proteinase-activated receptor (PAR)-2, in joint inflammation. Intra-articular carrageenan/kaolin (C/K) injection in mice resulted in joint swelling that was associated with synovial PAR2 up-regulation. Inhibiting receptor up-regulation using small interfering RNA technology, as confirmed by immunoblotting, substantially reduced the inflammatory response in the joint. Serine proteinase-induced joint swelling was mediated primarily via PAR2 activation, since the response to exogenous application of trypsin and tryptase was absent in PAR2 knockout mice. Furthermore, serine proteinase inhibitors were effective anti-inflammatory agents in this model. Disrupting proteolytic activation of PAR2 using antiserum (B5) directed to the receptor cleavage/activation site also attenuated C/K-induced inflammation, as did the similarly targeted PAR2 monoclonal antibody SAM-11. Finally, we report the activity of a novel small molecule PAR2 antagonist, N1-3-methylbutyryl-N4-6-aminohexanoyl-piperazine (ENMD-1068), that dose dependently attenuated joint inflammation. Our findings represent a major advance in collectively identifying PAR2 as a novel target for the future treatment of arthritis.

RNA interference decreases PAR-2 expression and function in human airway smooth muscle cells

Asthma is characterized by bronchial inflammation and hyperresponsiveness that involves mast cell tryptase and potentially its specific receptor protease activated receptor 2 (PAR-2). Tryptase increases free intracellular calcium concentration ([Ca2+]i), a key step in activation of human airway smooth muscle cells (HASMC). The aim of this study was to analyze the effect of PAR-2 gene silencing on HASMC, in terms of calcium response, since no antagonist is available for this receptor. Five siRNA against PAR-2 were synthesized and transfected in HASMC using lipid agents, and PAR-2 expression was examined using Western blot, fluorescence-activated cell sorter, immunocytochemistry and RT-PCR. [Ca2+]i was measured using microspectrofluorimetry in response to tryptase, the activating peptide SLIGKV, trypsin, or caffeine. Two siRNA significantly inhibited PAR-2 expression in terms of both total and surface protein expression, as well as mRNA levels. Tryptase- and SLIGKV-induced transient increase in [Ca2+]i was significantly inhibited after transfection with the most appropriate siRNA, whereas neither trypsin nor caffeine response was altered. Two control siRNA had no effect in terms of both PAR-2 expression and calcium response. Transfection efficiency was maximal after 24 h and disappeared after 48 h. Gene silencing using siRNA can thus be used in vitro to assess the function of PAR-2 in HASMC.

Thrombin stimulates proinflammatory and proliferative responses in primary cultures of human proximal tubule cells

BACKGROUND

Fibrin deposition is frequently observed within the tubulointerstitium in various forms of chronic renal disease. This suggests the presence of active components of the coagulation pathway, which may contribute to the progressive deterioration in renal function. The aim of this study was to investigate the proinflammatory and fibroproliferative effects of the coagulation protease thrombin on human proximal tubular cells (PTC) in culture.

METHODS

Primary cultures of PTC were established from normal kidney tissue and grown under serum-free conditions with or without thrombin or the protease-activated receptor (PAR) activating peptides TFLLRN-NH(2), SLIGKV-NH(2), and SFLLRN-NH(2) (100 to 400 micromol/L). DNA synthesis (thymidine incorporation), intracellular Ca(2+) mobilization (fura-2 fluorimetry), fibronectin secretion [enzyme-linked immunosorbent assay (ELISA), immunoblotting], monocyte chemoattractant protein-1 (MCP-1) secretion (ELISA), and transforming growth factor-beta1 (TGF-beta1) secretion (ELISA) were measured. Reverse transcription-polymerase chain reaction (RT-PCR) was used to assess PAR mRNA expression in these cells.

RESULTS

Thrombin enhanced DNA synthesis, fibronectin secretion, MCP-1 secretion, and TGF-beta1 secretion in a concentration-dependent manner. Cell injury [lactate dehydrogenase (LDH) release] and cellular protein levels were unaffected. RT-PCR showed that cultures of PTC expressed mRNA transcripts for the thrombin receptors PAR-1 and PAR-3, but not PAR-4. Thrombin and each of the PAR activating peptides enhanced intracellular calcium mobilization. However, the other effects of thrombin were only fully reproduced by the PAR-2-specific peptide, SLIGKV-NH(2), only partially by SFLLRN-NH(2), (a PAR-1 peptide that can activate PAR-2), and not at all by the PAR-1-specific peptide, TFLLRN-NH(2). Thrombin-induced DNA synthesis, fibronectin, and MCP-1 secretion were unaffected by a TGF-beta neutralizing antibody, the matrix metalloproteinase (MMP) inhibitor, GM6001 and the epidermal growth factor (EGF) receptor kinase inhibitor AG1478.

CONCLUSION

Thrombin initiates both proinflammatory and fibroproliferative responses in human PTC. These responses which are dependent on its protease activity appear not to be mediated by PAR-1 activation, the autocrine action of thrombin-induced TGF-beta1 secretion, MMP activation, or EGF receptor transactivation. The proinflammatory and fibroproliferative actions of thrombin on human PTC may help explain the extent of tubulointerstitial fibrosis observed in kidney diseases where fibrin deposition is evident.

[Development of agonists/antagonists for protease-activated receptors (PARs) and the possible therapeutic application to gastrointestinal diseases]

Protease-activated receptors (PARs), a family of G-protein-coupled seven-transmembrane-domain receptors, are activated by proteolytic unmasking of the N-terminal cryptic tethered ligand by certain serine proteases. Among four PAR family members cloned to date, PAR-1, PAR-2, and PAR-4 can also be activated through a non-enzymatic mechanism, which is achieved by direct binding of exogenously applied synthetic peptides based on the tethered ligand sequence, known as PARs-activating peptides, to the body of the receptor. Various peptide mimetics have been synthesized as agonists for PARs with improved potency, selectivity, and stability. Some peptide mimetics and/or nonpeptide compounds have also been developed as antagonists for PAR-1 and PAR-4. PARs are widely distributed in the mammalian body, especially throughout the alimentary systems, and play various roles in physiological/pathophysiological conditions, i.e., modulation of salivary, gastric, or pancreatic glandular exocrine secretion, gastrointestinal smooth muscle motility, gastric mucosal cytoprotection, suppression/facilitation of visceral pain and inflammation, etc. Thus PARs are now considered novel therapeutic targets, and development of selective agonists and/or antagonists for PARs might provide a novel strategy for the treatment of various diseases that are resistant to current therapeutics.

Proteinase-activated receptor-2 mediates arterial vasodilation in diabetes

OBJECTIVE

Proteinase-activated receptor-2 is widely expressed in vascular tissue and in highly vascularized organs in humans and other species. Its activation mainly causes endothelium-dependent vasorelaxation in vitro and hypotension in vivo. Here, using nonobese diabetic (NOD) mice at different disease stages, we have evaluated the role of PAR2 in the arterial vascular response during diabetes progression.

METHODS AND RESULTS

High (NOD-II; 20 to 500 mg/dL) or severe glycosuria (NOD-III; 500 to 1000 mg/dL) provokes a progressive reduction in the response to acetylcholine paralleled by an increase in the vasodilatory response to PAR2 stimulation. Western blot and quantitative real-time polymerase chain reaction (RT-PCR) studies showed that this effect is tied to an increased expression of PAR2 coupled to cyclooxygenase-2 expression. Pharmacological dissection performed with specific inhibitors confirmed the functional involvement of cyclooxygenase-2 in PAR2 vasodilatory effect. This vasodilatory response was confirmed to be dependent on expression of PAR2 in the smooth muscle component by immunohistochemistry studies performed on aorta isolated by both NOD-III and transgenic PAR2 mice.

CONCLUSIONS

Our data demonstrate an important role for PAR2 in modulating vascular arterial response in diabetes and suggest that this receptor could represent an useful therapeutic target.

Distinct defensin profiles in Neisseria gonorrhoeae and Chlamydia trachomatis urethritis reveal novel epithelial cell-neutrophil interactions

Defensins are key participants in mucosal innate defense. The varied antimicrobial activity and differential distribution of defensins at mucosal sites indicate that peptide repertoires are tailored to site-specific innate defense requirements. Nonetheless, few studies have investigated changes in peptide profiles and function after in vivo pathogen challenge. Here, we determined defensin profiles in urethral secretions of healthy men and men with Chlamydia trachomatis- and Neisseria gonorrhoeae-mediated urethritis by immunoblotting for the epithelial defensins HBD1, HBD2, and HD5 and the neutrophil defensins HNP1 to -3 (HNP1-3). HBD1 was not detectable in secretions, and HBD2 was only induced in a small proportion of the urethritis patients; however, HD5 and HNP1-3 were increased in C. trachomatis infection and significantly elevated in N. gonorrhoeae infection. When HNP1-3 levels were low, HD5 appeared mostly as the propeptide; however, when HNP1-3 levels were >10 microg/ml, HD5 was proteolytically processed, suggesting neutrophil proteases might contribute to HD5 processing. HD5 and HNP1-3 were bactericidal against C. trachomatis and N. gonorrhoeae, but HD5 activity was dependent upon N-terminal processing of the peptide. In vitro proteolysis of proHD5 by neutrophil proteases and analysis of urethral secretions by surface-enhanced laser desorption ionization substantiated that neutrophils contribute the key convertases for proHD5 in the urethra during these infections. This contrasts with the small intestine, where Paneth cells secrete both proHD5 and its processing enzyme, trypsin. In conclusion, we describe a unique defensin expression repertoire in response to inflammatory sexually transmitted infections and a novel host defense mechanism wherein epithelial cells collaborate with neutrophils to establish an antimicrobial barrier during infection.

Go G-proteins mediate rapid heterologous desensitization of G-protein coupled receptors in Xenopus oocytes

We have shown previously that responses to lysophosphatidic acid (LPA) in Xenopus oocytes exhibit pronounced rapid homologous desensitization mediated by Go family of G-proteins (Itzhaki-Van Ham et al., 2004, J Cell Physiol, 200: 125-133). The present study was aimed at examining the involvement of Go G-proteins in rapid heterologous desensitization of native and expressed G-protein-coupled receptors in Xenopus oocytes. Threshold stimulation of the native lysophosphatidic acid receptors (LPA-Rs) induced about 50% rapid desensitization of responses evoked by stimulation of either native trypsin or expressed M1-muscarinic cholinergic receptors (M1-Rs). Similarly, threshold stimulation of expressed M1-Rs or thyrotropin-releasing hormone receptors induced 40% rapid desensitization of responses to LPA. Inactivation of all Gi/o G-proteins with pertussis toxin (PTX) completely abolished rapid heterologous desensitization in all protocols. Depletion of either Galphao or Galphao1 by antisense oligodeoxynucleotides targeted at either member of the Galphao family decreased or completely abolished rapid heterologous desensitization. Expression of two dominant negative mutants of the human Galphao family, highly homologous to oocyte Galphao species, either decreased or virtually abolished rapid desensitization. Homologous and heterologous desensitizations of the LPA response were non-additive and proceeded, apparently, via the same pathway. We conclude that Go G-proteins mediate both homologous and heterologous rapid desensitization of responses mediated by G-protein-coupled receptors (GPCRs) coupled to the phosphoinositide phospholipase C-inositol 1,4,5-trisphosphate-Ca(2+) (PI-PLC-InsP(3)-Ca(2+)) pathway in Xenopus oocytes.

Signal transduction for proteinase-activated receptor-2-triggered prostaglandin E2 formation in human lung epithelial cells

We investigated proteinase-activated receptor-2 (PAR(2))-triggered signal transduction pathways causing increased prostaglandin E(2) (PGE(2)) formation in human lung-derived A549 epithelial cells. The PAR(2) agonist, SLIGRL-NH(2) (Ser-Leu-Ile-Gly-Arg-Leu-amide), evoked immediate cytosolic Ca(2+) mobilization and delayed (0.5-3 h) PGE(2) formation. The PAR(2)-triggered PGE(2) formation was attenuated by inhibition of the following signal pathway enzymes: cyclooxygenases 1 and 2 (COX-1 and COX-2, respectively), cytosolic Ca(2+)-dependent phospholipase A(2) (cPLA(2)), the mitogen-activated protein kinases (MAPKs), mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK)-extracellular signal-regulated kinase (ERK) and p38 MAPK, Src family tyrosine kinase, epidermal growth factor (EGF) receptor tyrosine kinase (EGFRK), and protein kinase C (PKC), but not by inhibition of matrix metalloproteinases. SLIGRL-NH(2) caused prompt (5 min) and transient ERK phosphorylation, blocked in part by inhibitors of PKC and tyrosine kinases but not by an EGFRK inhibitor. SLIGRL-NH(2) also evoked a relatively delayed (15 min) and persistent (30 min) phosphorylation of p38 MAPK, blocked by inhibitors of Src and EGFRK but not by inhibitors of COX-1 or COX-2. SLIGRL-NH(2) elicited a Src inhibitor-blocked prompt (5 min) and transient phosphorylation of the EGFRK. SLIGRL-NH(2) up-regulated COX-2 protein and/or mRNA levels that were blocked by inhibition of p38 MAPK, EGFRK, Src, and COX-2 but not MEK-ERK. SLIGRL-NH(2) also caused COX-1-dependent up-regulation of microsomal PGE synthase-1 (mPGES-1). We conclude that PAR(2)-triggered PGE(2) formation in A549 cells involves a coordinated up-regulation of COX-2 and mPGES-1 involving cPLA(2), increased cytosolic Ca(2+), PKC, Src, MEK-ERK, p38 MAPK, Src-mediated EGF receptor trans-activation, and also metabolic products of both COX-1 and COX-2.

Synergistic induction of tissue factor by coagulation factor Xa and TNF: evidence for involvement of negative regulatory signaling cascades

Enzymes of the blood coagulation pathway enhance the inflammatory response leading to endothelial dysfunction, accounting, in part, for the vascular complications occurring in sepsis and cardiovascular disease. The responses of endothelial cell activation include induction of the expression of tissue factor (TF), a membrane glycoprotein that promotes thrombosis, and of E-selectin, a cell adhesion molecule that promotes inflammation. In this report, we demonstrate synergistic interactions between the coagulation factor Xa (fXa) and the proinflammatory cytokines TNF, IL-1beta, and CD40L, leading to enhanced expression of TF and E-selectin in endothelial cells. A detailed analysis of the molecular pathways that could account for this activity of fXa showed that fXa inhibited the cytokine-induced expression of dual specificity phosphatases, MAP kinase phosphatase-L, -4, -5, and -7, blocking a negative regulatory effect on c-Jun N-terminal kinase. The synergistic interaction between fXa and TNF was also involved in the inhibition of A20 and IkappaBalpha expression in the IkappaB kinase-NF-kappaB pathway. The data indicate that inhibition of negative regulatory signaling accounts for the amplification of cytokine-induced endothelial cell activation by fXa.

Pancreatic trypsin activates human promatrix metalloproteinase-2

In contrast to the prevalent view in the literature hitherto, the present study shows that pancreatic trypsin can activate human promatrix metalloproteinase-2 (proMMP-2). It is shown that trypsin's ability to activate proMMP-2 is dependent on various environmental factors such as the level of exogenously added Ca(2+) and Brij-35, temperature, as well as trypsin concentration. The activation occurred as a sequential processing of the proenzyme, initially generating an active 62kDa species. This was followed by successive truncation of the C-terminal domain, giving rise to active species of 56kDa, 52kDa and 50kDa. Tissue inhibitor of matrix metalloproteinases-2 (TIMP-2) prevented the trypsin-mediated C-terminal truncation, without affecting the generation of the 62kDa species, while the presence of EDTA increased the rate of the trypsin-mediated activation of proMMP-2. MALDI-TOF MS analysis of the 50kDa form indicated that trypsin generated active forms with either Lys87 or Trp90 as the N-terminal residue and Arg538 as a C-terminal residue. The trypsin-activated MMP-2 was active in solution against both synthetic and physiologic substrates, and the steady-state kinetic coefficients k(cat), K(m) and k(cat)/K(m) were determined for the enzyme activated either by APMA, membrane-type 1 matrix metalloproteinase (MT1-MMP) or trypsin. The trypsin-activated MMP-2 exhibited slightly lower k(cat) and k(cat)/K(m) values as well as a slightly higher K(i) value against TIMP-1 compared to the enzyme activated by APMA or MT1-MMP. Docking studies of TIMP-1 revealed that the slightly weaker binding of the inhibitor to the trypsin-activated MMP-2 could be attributed to its shorter N terminus (Lys87/Trp90 versus Tyr81), as Phe83 and Arg86 interacted directly with the inhibitor. Our results suggest that the trypsin-activated MMP-2 possesses the catalytic and regulatory potential to be of significance in vivo.

Mast cell tryptase stimulates DLD-1 carcinoma through prostaglandin- and MAP kinase-dependent manners

We found that striptease-positive mast cells were abundant in the invasive front of human colon adenocarcinoma by examining 30 cases. Because tryptase has been suggested to be the agonist proteinase for protease-activated receptor-2 (PAR-2), we investigated the effects of stimulation of PAR-2 by tryptase on the cell signaling and proliferation of DLD-1, a human colon carcinoma cell line. PAR-2 stimulation by tryptase induced the increase in [Ca(2+)](i), which was desensitized by the prior application of PAR-2 activating peptide (AP). The proliferative responses of DLD-1 to tryptase and PAR-2 AP were associated with the phosphorylation of MEK and MAP kinase. Inhibition of MEK by PD98059 completely inhibited the proliferation-enhancing effects of tryptase and PAR-2 AP as well as phosphorylation of MAP kinase. Moreover, tryptase and PAR-2 AP stimulated the production of prostaglandin E2 and the inhibition of prostaglandin synthesis by indomethacin or NS398 resulted in the complete inhibition of the proliferative responses to tryptase and PAR-2 AP. Furthermore, the tryptase-stimulated proliferation of DLD-1 was concentration-dependently inhibited by nafamostat mesilate, a specific inhibitor of tryptase. These results as a whole indicated that tryptase has proliferative effects on DLD-1 through cyclooxygenase- and MAP kinase-dependent manners acting on PAR-2 by its proteolytic activity.

Role of coagulation factor Xa and protease-activated receptor 2 in human mesangial cell proliferation

BACKGROUND

Fibrin deposition and mesangial cell proliferation are frequently observed in the active type of mesangioproliferative glomerulonephritis. Coagulation factors, such as factor V and factor Xa are colocalized with fibrin in the mesangial areas in active type of IgA nephropathy with mesangial cell proliferation. In this study, therefore, we studied the role of factor Xa and its receptor, protease-activated receptor 2 (PAR2) in mesangial cell proliferation and fibrin deposition, and examined ant-proliferative effects of a specific factor Xa inhibitor, DX-9065a, in cultured human mesangial cells.

METHODS

To examine the effect of DX-9065a on the factor Xa-induced proliferation of cultured human mesangial cells, we measured thymidine incorporation and cell numbers. We also examined the effect of DX-9065a on extracellular regulated kinase (ERK) activation and fibrin production induced by factor Xa in human mesangial cells.

RESULTS

Factor Xa increased [(3)H]-thymidine incorporation and cell numbers in a dose-dependent manner in mesangial cells, which was inhibited by DX-9065a. DX-9065a also suppressed factor Xa-triggered fibrin deposition on mesangial cell surface. Factor Xa induced the activation of ERK in mesangial cells and this activation was also completely inhibited by DX-9065a, but not inhibited by PAR1 antagonist. Factor Xa-induced cell proliferation and ERK activation were inhibited by PD98059.

CONCLUSION

There results suggest that factor Xa can induce mesangial cell proliferation through the activation of ERK via PAR2 in mesangial cells and that PAR2 may play a crucial role in the cell proliferation induced by factor Xa. Our results implicate that DX-9065a may be a promising agent to regulate proliferation of mesangial cellss and inhibit the coagulation process in mesangium.

Proteinase-activated receptor-2 induction by neuroinflammation prevents neuronal death during HIV infection

Proteinase-activated receptors (PARs), a newly discovered subgroup of G-protein coupled receptors, are widely expressed by neural cells, but their roles in the nervous system remain uncertain. In this study, we report that PAR-2 was up-regulated on neurons in conjunction with neuroinflammation in brain tissue from patients with HIV-1-associated dementia. The inflammatory cytokines TNF-alpha and IL-1beta were also increased in HIV-1-associated dementia brains compared with patients without dementia (p < 0.05), but these same cytokines induced PAR-2 expression on neurons. Enhanced PAR-2 expression and subsequent activation prevented neuronal cell death and induction of the tumor suppressor, p53, caused by the HIV-encoded protein, Tat (p < 0.01). Intrastriatal implantation of a PAR-2 peptide agonist also inhibited Tat-induced neurotoxicity in a mouse model of HIV neuropathogenesis (p < 0.05). Moreover, PAR-2 null animals showed more severe neuroinflammation and neuronal loss caused by Tat neurotoxicity (p < 0.05). TNF-alpha protected wild-type neurons from Tat-related neurotoxicity, but in PAR-2-deficient neurons, the same concentrations of TNF-alpha were cytotoxic (p < 0.001). Thus, neuroinflammation can exert protective effects by which it induces PAR-2 expression with the ensuing abrogation of neuronal death.

Multiple tissue kallikrein mRNA and protein expression in normal skin and skin diseases

BACKGROUND

Human tissue kallikreins are a gene family (KLK1-KLK15) encoding for 15 secretory serine proteases (hK1-hK15). Two tissue kallikrein proteins, hK5 and hK7, were previously found in the stratum corneum (SC), stratum granulosum (SG) and appendages. hK8 was also shown to be secreted via lamellar granules and numerous KLK mRNAs were previously identified. KLKs are believed to be responsible for desquamation of corneocytes and sebum, sweat and hair maturation.

OBJECTIVES

To demonstrate immunohistochemically the expression of hK6, hK8 and hK13 in normal skin tissue and to show an increased cell number expressing kallikrein mRNAs and proteins in psoriasis vulgaris (PV) and atopic dermatitis (AD).

METHODS

Samples of normal, PV and AD skin were obtained. hK6-, hK8- and hK13-specific antibodies were produced and used for immunohistochemical analysis. Multiple KLK mRNAs were synthesized and used for in situ hybridization study.

RESULTS

Three other hKs, namely hK6, hK8 and hK13, were immunohistochemically identified as new skin serine proteases in the whole SC, SG, sebaceous glands, eccrine sweat glands, hair follicles and nerves. We also demonstrated an increased number of cells expressing KLK mRNAs and hKs in PV and AD. In PV, KLK mRNAs/hKs were predominantly expressed in the upper epidermis. In AD, hK distribution was rather diffuse and expanded into the lower epidermis.

CONCLUSIONS

The colocalization of various hKs seems to be essential for the regulation of serine protease activity in skin and for steady desquamation and skin barrier function. Moreover, the increased number of cells expressing multiple KLK mRNA and hK in PV and AD could be a clue to elucidate their pathogenesis.

Subnanomolar concentrations of thrombin enhance the volume-sensitive efflux of taurine from human 1321N1 astrocytoma cells

The ability of subnanomolar concentrations of thrombin to protect both neurons and glia from ischemia and other metabolic insults has recently been reported. In this study, we demonstrate an additional neuroprotective property of thrombin; its ability to promote the release of the organic osmolyte, taurine, in response to hypoosmotic stress. Incubation of human 1321N1 astrocytoma cells with hypo-osmolar buffers (320-227 mOsM) resulted in a time-dependent release of taurine. Inclusion of thrombin (EC(50) = 60 pM) resulted in a marked increase in taurine efflux that, although evident under isotonic conditions (340 mOsM), was maximal at an osmolarity of 270 mOsM (3-4-fold stimulation). Thrombin-stimulated taurine efflux was dependent upon its protease activity and could be mimicked by addition of the peptide SFLLRN, a proteinase activated receptor-1 (PAR-1) subtype-specific ligand. Inclusion of anion channel blockers known to inhibit the volume-sensitive organic osmolyte anion channel attenuated thrombin-stimulated taurine release. Depletion of intracellular Ca(2+) with either 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) or thapsigargin, or alternatively, inhibition of protein kinase C (PKC) with bisindolylmaleimide or chelerythrine resulted in a 30 to 50% inhibition of thrombin-stimulated taurine efflux. Under conditions in which intracellular Ca(2+) was depleted and PKC activity inhibited, thrombin-stimulated taurine efflux was reduced by >85%. The results indicate that activation of PAR-1 receptors by thrombin facilitates the ability of 1321N1 astrocytoma cells to release osmolytes in response to a reduction in osmolarity via a mechanism that is dependent on intracellular Ca(2+) and PKC activity.

Mast cell tryptase controls paracellular permeability of the intestine. Role of protease-activated receptor 2 and beta-arrestins

Tight junctions between intestinal epithelial cells prevent ingress of luminal macromolecules and bacteria and protect against inflammation and infection. During stress and inflammation, mast cells mediate increased mucosal permeability by unknown mechanisms. We hypothesized that mast cell tryptase cleaves protease-activated receptor 2 (PAR2) on colonocytes to increase paracellular permeability. Colonocytes expressed PAR2 mRNA and responded to PAR2 agonists with increased [Ca2+]i. Supernatant from degranulated mast cells increased [Ca2+]i in colonocytes, which was prevented by a tryptase inhibitor, and desensitized responses to PAR2 agonist, suggesting PAR2 cleavage. When applied to the basolateral surface of colonocytes, PAR2 agonists and mast cell supernatant decreased transepithelial resistance, increased transepithelial flux of macromolecules, and induced redistribution of tight junction ZO-1 and occludin and perijunctional F-actin. When mast cells were co-cultured with colonocytes, mast cell degranulation increased paracellular permeability of colonocytes. This was prevented by a tryptase inhibitor. We determined the role of ERK1/2 and of beta-arrestins, which recruit ERK1/2 to PAR2 in endosomes and retain ERK1/2 in the cytosol, on PAR2-mediated alterations in permeability. An ERK1/2 inhibitor abolished the effects of PAR2 agonist on permeability and redistribution of F-actin. Down-regulation of beta-arrestins with small interfering RNA inhibited PAR2-induced activation of ERK1/2 and suppressed PAR2-induced changes in permeability. Thus, mast cells signal to colonocytes in a paracrine manner by release of tryptase and activation of PAR2. PAR2 couples to beta-arrestin-dependent activation of ERK1/2, which regulates reorganization of perijunctional F-actin to increase epithelial permeability. These mechanisms may explain the increased epithelial permeability of the intestine during stress and inflammation.

Trypsin stimulates the phosphorylation of p42,44 mitogen-activated protein kinases via the proteinase-activated receptor-2 and protein kinase C epsilon in human cultured prostate stromal cells

BACKGROUND

The pathogenesis of benign prostatic hyperplasia (BPH) is not well understood. It involves the proliferation of prostate stromal cells. The proteinase-activated receptor subtype 2 (PAR-2) receptor is expressed by human prostate tissue and can be stimulated by serine proteases. Prostate epithelial cells secrete serine proteases such as trypsin, prostate specific antigen (PSA), and human glandular kallikrein (hK2). The p42,44 mitogen activated protein kinase (MAP kinase) pathway regulates cell proliferation. Trypsin can stimulate this pathway via the PAR-2 receptor and protein kinase C (PKC) in other tissues. Serine proteases secreted by prostate epithelial cells may interact with PAR-2 receptors expressed by prostate stromal cells causing them to proliferate. The aim of the present study was to establish whether functional PAR-2 receptors are expressed by human prostate stromal cells (HPSCs) and to determine whether PAR-2 stimulation can activate p42,44 MAP kinase via a pathway involving PKC.

METHODS

HPSCs were cultured from patients undergoing trans urethral resection of the prostate (TURP). HPSCs were stimulated with PAR agonists. Immunoblotting of HPSC lysate with anti-p42,44 MAP kinase and -PKC isoforms. Data were analyzed with densitometry.

RESULTS

Trypsin and the PAR-2 synthetic peptide SLIGKV caused significant increases in MAP kinase phosphorylation and calcium mobilization in HPSCs. The MAP kinase response was attenuated by pertussis toxin (PTX), phorbol 12,13 dibutyrate, Go6983, and Ro 318220. The PKC isoforms alpha, delta, epsilon, and zeta were detected in HPSCs. Trypsin caused the translocation of PKC(epsilon) from the cytosol to the membrane in HPSCs and was able to stimulate cellular proliferation.

CONCLUSIONS

The PAR-2 selective serine protease trypsin activates p42,44 MAP kinase phosphorylation via PKC(epsilon). This may be an important mechanism of BPH pathophysiology.

The future: critical knowledge about anti-itch therapy

Itch is an extremely frequent and enervating symptom of many diseases. Current anti-itch therapy, which is based almost exclusively on an "immunocentric" viewpoint, is often unsatisfactory. Recent studies show that this symptom is in fact the result of a complex interplay among skin, nervous system, endocrine system, and immune system. This explains the frequent failure of therapeutic strategies focused only on a single factor and suggests the usefulness of a polypharmacologic symptomatic treatment, designed on a case-by-case basis as a result of a multidisciplinary approach. We discuss the perspectives of anti-itch therapy in light of the new pathogenetic and pharmacologic acquisitions.

Absence of proteinase-activated receptor-1 signaling affords protection from bleomycin-induced lung inflammation and fibrosis

Activation of the coagulation cascade is commonly observed in the lungs of patients with both acute and chronic inflammatory and fibrotic lung disorders, as well as in animal models of these disorders. The aim of this study was to examine the contribution of the major thrombin receptor, proteinase-activated receptor-1 (PAR-1), during the acute inflammatory and chronic fibrotic phases of lung injury induced by intratracheal instillation of bleomycin in mice. Inflammatory cell recruitment and increases in bronchoalveolar lavage fluid (BALF) protein were attenuated by 56 +/- 10% (P < 0.05) and 53 +/- 12% (P < 0.05), respectively, in PAR-1-deficient (PAR-1-/-) mice compared with wild-type (WT) mice. PAR-1-/- mice were also protected from bleomycin-induced pulmonary fibrosis with total lung collagen accumulation reduced by 59 +/- 5% (P < 0.05). The protection afforded by PAR-1 deficiency was accompanied by significant reductions in pulmonary levels of the potent PAR-1-inducible proinflammatory and profibrotic mediators, monocyte chemoattractant protein-1 (MCP-1), transforming growth factor-beta-1 (TGF-beta1), and connective tissue growth factor/fibroblast-inducible secreted protein-12 (CTGF/FISP12). In addition, PAR-1 was highly expressed in inflammatory and fibroproliferative lesions in lung sections obtained from patients with fibrotic lung disease. These data show for the first time that PAR-1 signaling plays a key role in experimentally induced lung injury, and they further identify PAR-1 as one of the critical receptors involved in orchestrating the interplay between coagulation, inflammation, and remodeling in response to tissue injury.

Epithelial effects of proteinase-activated receptors in the gastrointestinal tract

The intestinal epithelium plays a crucial role in providing a barrier between the external environment and the internal milieu of the body. A compromised mucosal barrier is characteristic of mucosal inflammation and is a key determinant of the development of intestinal diseases such as Crohn's disease and ulcerative colitis. The intestinal epithelium is regularly exposed to serine proteinases and this exposure is enhanced in numerous disease states. Thus, it is important to understand how proteinase-activated receptors (PARs), which are activated by serine proteinases, can affect intestinal epithelial function. This review surveys the data which demonstrate the wide distribution of PARs, particularly PAR-1 and PAR-2, in the gastrointestinal tract and accessory organs, focusing on the epithelium and those cells which communicate with the epithelium to affect its function. PARs have a role in regulating secretion by epithelia of the salivary glands, stomach, pancreas and intestine. In addition, PARs located on subepithelial nerves, fibroblasts and mast cells have important implications for epithelial function. Recent data outline the importance of the cellular site of PAR expression, as PARs expressed on epithelia may have effects that are countered by PARs expressed on other cell types. Finally, PARs and their ability to promote epithelial cell proliferation are discussed in terms of colon cancer.

Inhibitors of Prostaglandin Transport and Metabolism Augment Protease-Activated Receptor-2-Mediated Increases in Prostaglandin E2 Levels and Smooth Muscle Relaxation in Mouse Isolated Trachea

Stimulants of protease-activated receptor-2 (PAR(2)), such as Ser-Leu-Ile-Gly-Arg-Leu-NH(2) (SLIGRL), cause airway smooth muscle relaxation via the release of the bronchodilatory prostanoid prostaglandin E(2) (PGE(2)). The principal aim of the current study was to determine whether compounds that inhibit PGE(2) reuptake by the prostaglandin transporter [bromocresol green and U46619 (9,11-dideoxy-9alpha,11alpha-methanoepoxy PGF2alpha) and PGE(2) metabolism by 15-hydroxyprostaglandin dehydrogenase (thiazolidenedione compounds rosiglitazone and ciglitazone) significantly enhanced the capacity of SLIGRL to elevate PGE(2) levels and produce relaxation in isolated segments of upper and lower mouse trachea. SLIGRL produced concentration-dependent increases in PGE(2) levels and smooth muscle relaxation, although both effects were significantly greater in lower tracheal segments than in upper tracheal segments. SLIGRL-induced increases in PGE(2) levels were significantly enhanced in the presence of ciglitazone and rosiglitazone, and these effects were not inhibited by GW9662 (2-chloro-5-nitrobenzanilide), a peroxisome proliferator-activated receptor-gamma antagonist. SLI-GRL-induced relaxation responses were also significantly enhanced by ciglitazone and rosiglitazone, whereas responses to isoprenaline, a PGE(2)-independent smooth muscle relaxant, were unaltered. Ciglitazone and rosiglitazone alone produced concentration-dependent increases in PGE(2) levels and smooth muscle relaxation, and these responses were inhibited by indomethacin, a cyclooxygenase inhibitor. Bromocresol green, an inhibitor of prostaglandin transport, significantly enhanced SLIGRL-induced increases in PGE(2) levels and relaxation. Immunohistochemical staining for 15-hydroxyprostaglandin dehydrogenase was relatively intense over airway smooth muscle, as was staining for the prostaglandin transporter over both airway smooth muscle and epithelium. In summary, inhibitors of PGE(2) reuptake and metabolism significantly potentiate PAR(2)-mediated increases in PGE(2) levels and smooth muscle relaxation in murine-isolated airways.

Effect of E. coli Nissle 1917 on post-inflammatory visceral sensory function in a rat model

OBJECTIVE

Visceral hyperalgesia (VH) plays a key role for the manifestation of functional gastrointestinal (GI) disorders. In a subgroup of patients, the initial manifestation is preceded by GI inflammation. Recent studies have demonstrated an improvement of inflammation and symptoms during treatment with Escherichia coli Nissle 1917 (EcN).

AIM

We aimed to characterize the effects of EcN on visceral sensitivity in a rat model of post-inflammatory VH.

METHODS

Male Lewis rats underwent colorectal instillation of trinitrobenzenesulphonic acid (TNBS) plus an equal amount of ethanol (test group) or physiological saline solution (control group). After 28, 35 and 42 days, standardized colorectal distensions were performed and the visceromotor reflex (VMR) of abdominal wall muscles was quantified by electromyographic recording. From day 28 onwards, EcN was administered in drinking water.

RESULTS

After TNBS, a significant increase of VMR was observed compared with saline controls over all study days. Administration of EcN reduced the TNBS-induced hyperalgesia [EcN: 863+/-125 microV vs placebo: 1258+/-157 microV (P<0.05)] at day 35, while there were no significant alterations at any other study day.

CONCLUSION

The EcN administration caused a significant reduction of VH. Whether EcN might play a role in the treatment of post-infectious functional bowel disorders remains to be investigated in further studies.

Expression of protease-activated receptors 1 and 2 in melanocytic nevi and malignant melanoma

Protease-activated receptors (PARs) are members of the G protein-coupled receptor superfamily that are activated by the proteolytic cleavage of their amino terminal domain. PAR-1 activation by thrombin results in several biologic effects, including platelet adhesion to other cells or extracellular matrix, fibroblast, and endothelial cell growth, whereas PAR-2, activated by trypsin, has mainly a proinflammmatory and angiogenetic role. PAR-1 and PAR-2 modulate cell proliferation in physiopathologic cell invasion processes, suggesting that they may play a role in the setting of cancer growth and metastasis. Here, we have investigated the expression of PAR-1 and PAR-2 proteins by immunohistochemistry in a series of benign and malignant melanocytic lesions: 20 melanocytic lesions (10 common melanocytic nevi and 10 atypical or "dysplastic" melanocytic nevi) and 50 melanomas (10 in situ melanomas, 10 melanomas T1, 10 melanomas T2, 10 melanomas T3 to T4, and 10 metastatic melanomas). PAR-1 was significantly overexpressed in atypical nevi and melanomas in comparison with common melanocytic nevi. PAR-2 was strongly and diffusely expressed by immunohistochemistry in all melanocytic lesions, with no statistically significant differences between nevi and melanomas. Because we found a differential expression in PAR-1 protein, but not in PAR-2, we next investigated the expression of PAR-1 messenger RNA (mRNA) by ribonuclease protection assay in paraffin-embedded tissues using a paraffin block RNA isolation procedure. Similarly to immunohistochemical results, PAR-1 mRNA expression was significantly higher in atypical nevi and melanomas in comparison with common nevi and controls. Overexpression of PAR-1 in atypical nevi and melanomas supports a role for PAR-1 in the initial phases of melanoma development as well as in tumor progression and metastasis. Conversely, the significance of PAR-2 up-regulation in both benign and malignant melanocytic lesions requires further research.

2-Furoyl-LIGRL-NH2, a potent agonist for proteinase-activated receptor-2, as a gastric mucosal cytoprotective agent in mice

1. Proteinase-activated receptor-2 (PAR(2)), expressed in capsaicin-sensitive sensory neurons, plays a protective role in gastric mucosa. The present study evaluated gastric mucosal cytoprotective effect of 2-furoyl-LIGRL-NH(2), a novel highly potent PAR(2) agonist, in ddY mice and in wild-type and PAR(2)-knockout mice of C57BL/6 background. 2. Gastric mucosal injury was created by oral administration of HCl/ethanol solution in the mice. The native PAR(2)-activating peptide SLIGRL-NH(2), administered intraperitoneally (i.p.) at 0.3-1 micromol kg(-1) in combination with amastatin, an aminopeptidase inhibitor, but not alone, revealed gastric mucosal protection in ddY mice, which was abolished by ablation of capsaicin-sensitive sensory neurons. 3. I.p. administration of 2-furoyl-LIGRL-NH(2) at 0.1 micromol kg(-1), without combined treatment with amastatin, exhibited gastric mucosal cytoprotective activity in ddY mice, the potency being much greater than SLIGRL-NH(2) in combination with amastatin. This effect was also inhibited by capsaicin pretreatment. 4. Oral administration of 2-furoyl-LIGRL-NH(2) at 0.003-0.03 micromol kg(-1) also protected against gastric mucosal lesion in a capsaicin-reversible manner in ddY mice. 5. I.p. 2-furoyl-LIGRL-NH(2) at 0.1-0.3 micromol kg(-1) caused prompt salivation in anesthetized mice, whereas its oral administration at 0.003-1 micromol kg(-1) was incapable of eliciting salivation. 6. In wild-type, but not PAR(2)-knockout, mice of C57BL/6 background, i.p. administration of 2-furoyl-LIGRL-NH(2) caused gastric mucosal protection. 7. Thus, 2-furoyl-LIGRL-NH(2) is considered a potent and orally available gastric mucosal protective agent. Our data also substantiate a role for PAR(2) in gastric mucosal protection and the selective nature of 2-furoyl-LIGRL-NH(2).

Teaching resources. Proteases and signaling

This teaching resource provides lecture notes and slides for a class covering proteases and signaling and is part of the course "Cell signaling systems: a course for graduate students." The lecture begins with a discussion of protease-activated receptors and the ubiquitin-proteasome system and then proceeds to describe some of the ways that proteolysis can function in signal transduction.

Rac1 regulation of surface expression of protease-activated receptor-1 and responsiveness to thrombin in vascular smooth muscle cells

OBJECTIVE

Protease-activated receptor-1 (PAR1) mediates the thrombin-induced proliferation and hypertrophy of vascular smooth muscle cells. A role of Rac1 in the regulation of PAR1 expression was investigated.

METHODS AND RESULTS

Treatment with simvastatin, a hydroxy-3-methyl-glutaryl coenzyme A reductase inhibitor, for 24 hours attenuated the transient [Ca2+]i elevation induced by thrombin. Immunofluorescence staining revealed that simvastatin decreased the surface expression of PAR1 in a manner dependent on protein geranylgeranylation. Introduction of a Rac1/Cdc42 inhibitory fragment but not a RhoA inhibitory fragment using a cell-penetrating peptide also attenuated the response to thrombin and decreased the surface expression of PAR1. Finally, downregulation of Rac1, but not RhoA, using an RNA interference technique attenuated the thrombin-induced [Ca2+]i elevation. However, the level of PAR1 mRNA and the total amount of PAR1 protein remained unchanged.

CONCLUSIONS

Here, we provide for the first time 3 lines of evidence that Rac1 plays a critical role in maintaining the surface expression of PAR1 and the responsiveness to thrombin in vascular smooth muscle cells. Rac1 is suggested to regulate the constitutive trafficking of PAR1 and thereby regulate the surface expression of PAR1.

Neutrophil serine proteases: potential key regulators of cell signalling during inflammation

The serine proteases cathepsin G, human leucocyte elastase and proteinase 3 are major contents of neutrophils and are released at sites of inflammation. The common picture of their function was that they do not degrade extracellular proteins specifically. Recent studies provided evidence that these proteases are able to activate specifically pro-inflammatory cytokines and lead to the activation of different receptors. Neutrophil serine proteases might therefore be important regulators of inflammatory processes and are interesting targets for new therapeutic approaches against inflammatory disorders. This review summarizes the current knowledge on the regulation of cell signalling by neutrophil serine proteases.

Double transfection improves small interfering RNA-induced thrombin receptor (PAR-1) gene silencing in DU 145 prostate cancer cells

The efficiency of small interfering RNA (siRNA)-induced gene knockdown is hampered by low transfection efficiency. We established a novel and simple double transfection method using specific siRNA duplexes targeted against human thrombin receptor PAR-1 in DU 145 prostate cancer cells. The initial siRNA transfection of cell suspensions followed by re-transfection of adherent cells on the following day resulted in undetectable PAR-1 mRNA and absent receptor protein. PAR-1 mRNA expression was silenced for up to five days. Functional studies showed that PAR-1 gene silencing in DU 145 cells abolished the modulating effects of thrombin on cell adhesion to the extracellular matrix proteins, fibronectin and laminin, thus demonstrating the essential role of PAR-1 in mediating thrombin effects on DU 145 cell adhesion.

Role of protease-activated receptor-2 in inflammation, and its possible implications as a putative mediator of periodontitis

Proteinase-activated receptor-2 (PAR2) belongs to a novel subfamily of G-protein-coupled receptors with seven-transmembrane domains. This receptor is widely distributed throughout the body and seems to be importantly involved in inflammatory processes. PAR2 can be activated by serine proteases such as trypsin, mast cell tryptase, and bacterial proteases, such as gingipain produced by Porphyromonas gingivalis. This review describes the current stage of knowledge of the possible mechanisms that link PAR2 activation with periodontal disease, and proposes future therapeutic strategies to modulate the host response in the treatment of periodontitis.

Matrix metalloproteinases target protease-activated receptors on the tumor cell surface

Matrix metalloproteinases, or MMPs, have been implicated in tumor invasion and metastasis by virtue of their ability to degrade the extracellular matrix (ECM) barrier. However, MMPs are also capable of cleaving non-ECM molecules. The protease-activated receptors (PARs) are the latest MMP targets. The thrombin receptor PAR1 has now been shown to be cleaved and activated on the tumor cell surface by stromal-derived MMP1. The resulting PAR1 activates intracellular G proteins to turn on the migratory and invasive program in tumor cells. This MMP-PAR axis may represent a novel signaling pathway communicating between tumor and stromal cells during tumor progression.

c-Cbl mediates ubiquitination, degradation, and down-regulation of human protease-activated receptor 2

Mechanisms that arrest G-protein-coupled receptor (GPCR) signaling prevent uncontrolled stimulation that could cause disease. Although uncoupling from heterotrimeric G-proteins, which transiently arrests signaling, is well described, little is known about the mechanisms that permanently arrest signaling. Here we reported on the mechanisms that terminate signaling by protease-activated receptor 2 (PAR(2)), which mediated the proinflammatory and nociceptive actions of proteases. Given its irreversible mechanism of proteolytic activation, PAR(2) is a model to study the permanent arrest of GPCR signaling. By immunoprecipitation and immunoblotting, we observed that activated PAR(2) was mono-ubiquitinated. Immunofluorescence indicated that activated PAR(2) translocated from the plasma membrane to early endosomes and lysosomes where it was degraded, as determined by immunoblotting. Mutant PAR(2) lacking intracellular lysine residues (PAR(2)Delta14K/R) was expressed at the plasma membrane and signaled normally but was not ubiquitinated. Activated PAR(2) Delta14K/R internalized but was retained in early endosomes and avoided lysosomal degradation. Activation of wild type PAR(2) stimulated tyrosine phosphorylation of the ubiquitin-protein isopeptide ligase c-Cbl and promoted its interaction with PAR(2) at the plasma membrane and in endosomes in an Src-dependent manner. Dominant negative c-Cbl lacking the ring finger domain inhibited PAR(2) ubiquitination and induced retention in early endosomes, thereby impeding lysosomal degradation. Although wild type PAR(2) was degraded, and recovery of agonist responses required synthesis of new receptors, lysine mutation and dominant negative c-Cbl impeded receptor ubiquitination and degradation and allowed PAR(2) to recycle and continue to signal. Thus, c-Cbl mediated ubiquitination and lysosomal degradation of PAR(2) to irrevocably terminate signaling by this and perhaps other GPCRs.

Pseudomonas aeruginosa elastase disables proteinase-activated receptor 2 in respiratory epithelial cells

Pseudomonas aeruginosa, a major lung pathogen in cystic fibrosis (CF) patients, secretes an elastolytic metalloproteinase (EPa) contributing to bacterial pathogenicity. Proteinase-activated receptor 2 (PAR2), implicated in the pulmonary innate defense, is activated by the cleavage of its extracellular N-terminal domain, unmasking a new N-terminal sequence starting with SLIGKV, which binds intramolecularly and activates PAR2. We show that EPa cleaves the N-terminal domain of PAR2 from the cell surface without triggering receptor endocytosis as trypsin does. As evaluated by measurements of cytosolic calcium as well as prostaglandin E(2) and interleukin-8 production, this cleavage does not activate PAR2, but rather disarms the receptor for subsequent activation by trypsin, but not by the synthetic receptor-activating peptide, SLIGKV-NH(2). Proteolysis by EPa of synthetic peptides representing the N-terminal cleavage/activation sequences of either human or rat PAR2 indicates that cleavages resulting from EPa activity would not produce receptor-activating tethered ligands, but would disarm PAR2 in regard to any further activating proteolysis by activating proteinases. Our data indicate that a pathogen-derived proteinase like EPa can potentially silence the function of PAR2 in the respiratory tract, thereby altering the host innate defense mechanisms and respiratory functions, and thus contributing to pathogenesis in the setting of a disease like CF.

Protection against acute pancreatitis by activation of protease-activated receptor-2

Protease-activated receptor-2 (PAR-2) is a widely expressed tethered ligand receptor that can be activated by trypsin and other trypsin-like serine proteases. In the exocrine pancreas, PAR-2 activation modulates acinar cell secretion of digestive enzymes and duct cell ion channel function. During acute pancreatitis, digestive enzyme zymogens, including trypsinogen, are activated within the pancreas. We hypothesized that trypsin, acting via PAR-2, might regulate the severity of that disease, and to test this hypothesis, we examined the effect of either genetically deleting or pharmacologically activating PAR-2 on the severity of secretagogue-induced experimental pancreatitis. We found that experimental acute pancreatitis is more severe in PAR-2(-/-) than in wild-type mice and that in vivo activation of PAR-2, achieved by parenteral administration of the PAR-2-activating peptide SLIGRL-NH2, reduces the severity of pancreatitis. In the pancreas during the early stages of pancreatitis, the MAPK ERK1/2 is activated and translocated to the nucleus, but nuclear translocation is reduced by activation of PAR-2. Our findings indicate that PAR-2 exerts a protective effect on pancreatitis and that activation of PAR-2 ameliorates pancreatitis, possibly by inhibiting ERK1/2 translocation to the nucleus. Our observations suggest that PAR-2 activation may be of therapeutic value in the treatment and/or prevention of severe clinical pancreatitis, and they lead us to speculate that, from a teleological standpoint, PAR-2 may have evolved in the pancreas as a protective mechanism designed to dampen the injurious effects of intrapancreatic trypsinogen activation.

Physiology and pathophysiology of proteinase-activated receptors (PARs): PAR-2-mediated proliferation of colon cancer cell

Proteinase-activated receptor-2 (PAR-2) has been demonstrated to be highly expressed in the gastrointestinal tract. In the present minireview, we summarize the effects of PAR-1 and PAR-2 stimulation using their activating peptides and agonist proteinases on the calcium signaling and the cell proliferation in DLD-1 cell, a human colon cancer cell line. PAR-2 but not PAR-1 stimulation induced the enhancement of cell proliferation, whereas both PAR-1 and PAR-2 stimulation induced the transient increase in [Ca(2+)](i). PAR-2 stimulation induced the phosphorylation of MEK1/2 and ERK1/2, but PAR-1 stimulation did not. The inhibition of MEK1/2 by PD98059 completely abolished the proliferative response to PAR-2 stimulation. Thus, MEK-ERK activation plays major role in the PAR-2-mediated proliferative response. The coupling of PARs to calcium signaling and MEK-ERK activation may be independent, and varied dependent on cell types.

Physiology and pathophysiology of proteinase-activated receptors (PARs): PARs in the respiratory system: cellular signaling and physiological/pathological roles

Proteinase-activated receptors (PARs), a family of G protein-coupled receptors, are widely distributed in the mammalian body, playing a variety of physiological/pathophysiological roles. In the respiratory systems, PARs, particularly PAR-2 and PAR-1, are expressed in the epithelial and smooth muscle cells. In addition to the G(q/11)-mediated activation of the phospholipase C beta pathway, epithelial PAR activation causes prompt and/or delayed prostanoid formation, leading to airway smooth muscle relaxation and/or modulation of an inflammatory process. PAR-2 present in the epithelium and smooth muscle is considered primarily pro-inflammatory in the respiratory system, although PAR-2 may also be anti-inflammatory under certain conditions. In the lung epithelial cells, PAR-2 can also be activated by exogenous proteinases including house dust mite allergens, in addition to various possible endogenous agonist proteinases. Clinical evidence also suggests possible involvement of PARs, particularly PAR-2, in respiratory diseases. PARs thus appear to play critical roles in the respiratory systems, and the agonists/antagonists for PARs may serve as the novel therapeutic strategy for treatment of certain respiratory diseases including asthma.

Physiology and Pathophysiology of Proteinase-Activated Receptors (PARs): Proteinases as Hormone-Like Signal Messengers: PARs and More

Proteinases like thrombin and trypsin, long known for their ability to activate the coagulation cascade or to act as digestive enzymes for many protein targets, are now recognized as hormone-like regulators of cell function. These serine proteinases activate cell signaling by triggering a novel family of G-protein-coupled receptors, termed proteinase-activated receptors (PARs). This article summarizes the unique mechanisms involved in PAR activation and outlines the many different settings in which the PARs act to regulate tissue function. The PARs can be seen to play a role in inflammatory processes in large part via a neurogenic mechanism. Apart from activating PARs to cause their physiological effects in tissues, proteinases can also mediate cell signaling via a number of other mechanisms, including the activation of growth factor receptors, like the one for insulin. Thus, this article also points out the non-PAR mechanisms whereby proteinases can have hormone-like actions in cells and tissues.

Assembly and regulation of prothrombinase complex on B16F10 melanoma cells

A number of studies indicate that coagulation proteases play significant roles in cancer biology. Melanoma is a highly metastatic cancer, and there is evidence that thrombin contributes to this aggressive pattern. However, few studies correlate this type of cancer with formation of the prothrombinase complex, which is responsible for conversion of prothrombin into thrombin in the coagulation system. The aim of this study was to investigate the assembly and regulation of prothrombinase complex on the murine melanoma cell line, B16F10. B16F10 cells were unable to activate prothrombin except when previously incubated with factor Xa. This effect was dependent on factor Xa binding to cell membranes, since no activation was detected with Gla-domainless factor Xa. The thrombin formation by B16F10-bound factor Xa was enhanced approximately 10 fold in the presence of factor Va, indicating the assembly of prothrombinase complex. Differently from platelets, B16F10-assembled prothrombinase complex was inhibited by prothrombin fragment 1 but not by fragment 2. In addition, bothrojaracin, a specific ligand of proexosite I on prothrombin, caused a significant decrease in the zymogen activation. Our data demonstrate that B16F10 melanoma cells generate thrombin by promoting assembly of the prothrombinase complex. This ability might be correlated with the increased metastatic potential of this cell line. Moreover, B16F10-assembled prothrombinase complex seems to be modulated in a different way from that found for the physiological complex assembled on platelets.

Protease-activated receptors: regulation of neuronal function

Certain serine proteases from the circulation (e.g., coagulation factors), inflammatory cells (e.g., mast-cell tryptase, neutrophil proteinase 3), and from many other cell types (e.g., trypsins) can specifically signal to cells by cleaving protease-activated receptors (PARs), a family of four G protein-coupled receptors. Proteases cleave PARs at specific sites within the extracellular amino-terminus to expose amino-terminal tethered ligand domains that bind to and activate the cleaved receptors. The proteases that activate PARs are often generated and released during injury and inflammation, and activated PARs orchestrate tissue responses to injury, including hemostasis, inflammation, pain, and repair. This review concerns protease and PAR signaling in the nervous system. Neurons of the central and peripheral nervous systems express all four PARs. Proteases that may derive from the circulation, inflammatory cells, or neural tissues can cleave PARs on neurons and thereby activate diverse signaling pathways that control survival, morphology, release of neurotransmitters, and activity of ion channels. In this manner proteases and PARs regulate neurodegeneration, neurogenic inflammation, and pain transmission. Thus, PARs may participate in disease states and PAR antagonists or agonists may be useful therapies for certain disorders.

Redundant signaling mechanisms contribute to the vasodilatory response of the afferent arteriole to proteinase-activated receptor-2

We previously demonstrated that stimulation of proteinase-activated receptor-2 (PAR-2) by SLIGRL-NH2elicits afferent arteriolar vasodilation, in part, by elaborating nitric oxide (NO), suggesting an endothelium-dependent mechanism (Trottier G, Hollenberg M, Wang X, Gui Y, Loutzenhiser K, and Loutzenhiser R. Am J Physiol Renal Physiol 282: F891–F897, 2002). In the present study, we characterized the NO-independent component of this response, using the in vitro perfused hydronephrotic rat kidney. SLIGRL-NH2(10 μmol/l) dilated afferent arterioles preconstricted with ANG II, and the initial transient component of this response was resistant to NO synthase (NOS) and cyclooxygenase inhibition. This NO-independent response was not prevented by treatment with 10 nmol/l charybdotoxin and 1 μmol/l apamin, a manipulation that prevents the endothelium-derived hyperpolarizing factor (EDHF)-like response of the afferent arteriole to acetylcholine, nor was it blocked by the addition of 1 mmol/l tetraethylammonium (TEA) or 50 μmol/l 17-octadecynoic acid, treatments that block the EDHF-like response to bradykinin. To determine whether the PAR-2 response additionally involves the electrogenic Na+-K+-ATPase, responses were evaluated in the presence of 3 mmol/l ouabain. In this setting, SLIGRL-NH2induced a biphasic dilation in control and a transient response after NOS inhibition. The latter was not prevented by charybdotoxin plus apamin or by TEA alone but was abolished by combined treatment with charybdotoxin, apamin, and TEA. This treatment did not prevent the NO-dependent dilation evoked in the absence of NOS inhibition. Our findings indicate a remarkable redundancy in the signaling cascade mediating PAR-2 -induced afferent arteriolar vasodilation, suggesting an importance in settings such as inflamation or ischemia, in which vascular mechanisms might be impaired and the PAR system is thought to be activated.