Proteinase-activated receptor 2 (PAR2) decreases apoptosis in colonic epithelial cells

Tissue Kallikrein-1 Suppresses Type I Interferon Responses and Reduces Depressive-Like Behavior in the MRL/lpr Lupus-Prone Mouse Model

Excessive production and response to Type I interferons (IFNs) is a hallmark of systemic lupus erythematosus (SLE). Neuropsychiatric lupus (NPSLE) is a common manifestation of human SLE, with major depression as the most common presentation. Clinical studies have demonstrated that IFNα can cause depressive symptoms. We have shown that the kallikrein-kinin system (KKS) [comprised of kallikreins (Klks) and bradykinins] and angiotensin-converting enzyme inhibitors suppressed Type I IFN responses in dendritic cells from lupus-prone mice and human peripheral blood mononuclear cells. Tissue Klk genes are decreased in patients with lupus, and giving exogenous Klk1 ameliorated kidney pathology in mice. We retro-orbitally administered mouse klk1 gene-carrying adenovirus in the Murphy Roths Large lymphoproliferative (MRL/lpr) lupus-prone mice at early disease onset and analyzed immune responses and depressive-like behavior. Klk1 improved depressive-like behavior, suppressed interferon-responsive genes and neuroinflammation, and reduced plasma IFNα levels and proinflammatory cytokines. Klk1 also reduced IFNAR1 and JAK1 protein expression, important upstream molecules in Type I IFN signaling. Klk1 reduced bradykinin B1 receptor expression, which is known to induce proinflammatory response. Together, these findings suggest that Klk1 may be a potential therapeutic candidate to control IFNα production/responses and other inflammatory responses in SLE and NPSLE.

Chymotrypsin activity signals to intestinal epithelium by protease-activated receptor-dependent mechanisms

BACKGROUND AND PURPOSE

Chymotrypsin is a pancreatic protease secreted into the lumen of the small intestine to digest food proteins. We hypothesized that chymotrypsin activity may be found close to epithelial cells and that chymotrypsin signals to them via protease-activated receptors (PARs). We deciphered molecular pharmacological mechanisms and gene expression regulation for chymotrypsin signalling in intestinal epithelial cells.

EXPERIMENTAL APPROACH

The presence and activity of chymotrypsin were evaluated by Western blot and enzymatic activity tests in the luminal and mucosal compartments of murine and human gut samples. The ability of chymotrypsin to cleave the extracellular domain of PAR1 or PAR2 was assessed using cell lines expressing N-terminally tagged receptors. The cleavage site of chymotrypsin on PAR1 and PAR2 was determined by HPLC-MS analysis. The chymotrypsin signalling mechanism was investigated in CMT93 intestinal epithelial cells by calcium mobilization assays and Western blot analyses of (ERK1/2) phosphorylation. The transcriptional consequences of chymotrypsin signalling were analysed on colonic organoids.

KEY RESULTS

We found that chymotrypsin was present and active in the vicinity of the colonic epithelium. Molecular pharmacological studies have shown that chymotrypsin cleaves both PAR1 and PAR2 receptors. Chymotrypsin activated calcium and ERK1/2 signalling pathways through PAR2, and this pathway promoted interleukin-10 (IL-10) up-regulation in colonic organoids. In contrast, chymotrypsin disarmed PAR1, preventing further activation by its canonical agonist, thrombin.

CONCLUSION AND IMPLICATIONS

Our results highlight the ability of chymotrypsin to signal to intestinal epithelial cells via PARs, which may have important physiological consequences in gut homeostasis.

Protease-activated receptor 2 drives migration in a colon cancer cell line but not in noncancerous human epithelial cells

The inflamed mucosa contains a complex assortment of proteases that may participate in wound healing or the development of inflammation-associated colon cancer. We sought to determine the role of protease-activated receptor 2 (PAR2) in epithelial wound healing in both untransformed and transformed colonic epithelial cells. Monolayers of primary epithelial cells derived from organoids cultivated from patient colonic biopsies and of the T84 colon cancer cell line were grown to confluence, wounded in the presence of a selective PAR2-activating peptide, and healing was visualized by live cell microscopy. Inhibitors of various signaling molecules were used to assess the relevant pathways responsible for wound healing. Activation of PAR2 induced an enhanced wound-healing response in T84 cells but not primary cells. The PAR2-enhanced wound-healing response was associated with the development of lamellipodia in cells at the wound edge, consistent with sheet migration. The response to PAR2 activation in T84 cells was completely dependent on Src kinase activity and partially dependent on Rac1 activity. The Src-associated signaling molecules, focal adhesion kinase, and epidermal growth factor receptor, which typically mediate wound-healing responses, were not involved in the PAR2 response. Experiments repeated in the presence of the inflammatory cytokines TNF and IFNγ revealed a synergistically enhanced PAR2 wound-healing response in T84s but not primary cells. The epithelial response to proteases may be different between primary and cancer cells and is accentuated in the presence of inflammatory cytokines. Our findings have implications for understanding epithelial restitution in the context of inflammatory bowel disease (IBD) and inflammation-associated colon cancer.NEW & NOTEWORTHY Protease-activated receptor 2 enhances wound healing in the T84 colon cancer cell line, but not in primary cells derived from patient biopsies, an effect that is synergistically enhanced in the presence of the inflammatory cytokines TNF and IFNγ.

The proteolytic activity in inflammatory bowel disease: insight from gut microbiota

Inflammatory bowel disease (IBD) is a chronic, recurrent inflammatory disease caused by the destruction of the intestinal mucosal epithelium that affects a growing number of people worldwide. Although the etiology of IBD is complex and still elucidated, the role of dysbiosis and dysregulated proteolysis is well recognized. Various studies observed altered composition and diversity of gut microbiota, as well as increased proteolytic activity (PA) in serum, plasma, colonic mucosa, and fecal supernatant of IBD compared to healthy individuals. The imbalance of intestinal microecology and intestinal protein hydrolysis were gradually considered to be closely related to IBD. Notably, the pivotal role of intestinal microbiota in maintaining proteolytic balance received increasing attention. In summary, we have speculated a mesmerizing story, regarding the hidden role of PA and microbiota-derived PA hidden in IBD. Most importantly, we provided the diagnosis and therapeutic targets for IBD as well as the formulation of new treatment strategies for other digestive diseases and protease-related diseases.

Protease-activated receptor 2 attenuates doxorubicin-induced apoptosis in colon cancer cells

Drug resistance represents a major problem in cancer treatment. Doxorubicin (adriamycin) is an injectable DNA intercalating drug that halts cancer cell growth by inhibiting topoisomerase 2, but its long-term effectiveness is compromised by onset of resistance. This study demonstrates that expression of the PAR2 gene in human colon adenocarcinoma tissue samples was the highest among 32 different cancer types (n = 10,989), and higher in colon adenocarcinoma tissues (n = 331) than normal colon tissues (n = 308), revealing an association between PAR2 expression and human colon cancer. HT29 cells are a human colorectal adenocarcinoma cell line that is sensitive to the chemotherapeutic drug doxorubicin and also expresses PAR2. We find that PAR2 activation in HT29 cells, either by an endogenous protease agonist (trypsin) or an exogenous peptide agonist (2f-LIGRL-NH2), significantly reduces doxorubicin-induced cell death, reactive oxygen species production, caspase 3/7 activity and cleavage of caspase-8 and caspase-3. Moreover, PAR2-mediated MEK1/2-ERK1/2 pathway induced by 2f-LIGRL-NH2 leads to upregulated anti-apoptotic MCL-1 and Bcl-xL proteins that promote cellular survival. These findings suggest that activation of PAR2 compromises efficacy of doxorubicin in colon cancer. Further support for this conclusion came from experiments with human colon cancer HT29 cells, either with the PAR2 gene deleted or in the presence of a pharmacological antagonist of PAR2, which showed full restoration of all doxorubicin-mediated effects. Together, these findings reveal a strong link between PAR2 activation and signalling in human colon cancer cells and increased survival against doxorubicin-induced cell death. They support PAR2 antagonism as a possible new strategy for enhancing doxorubicin therapy.

Edoxaban, a Factor Xa-Specific Direct Oral Anticoagulant, Significantly Suppresses Tumor Growth in Colorectal Cancer Colon26-Inoculated BALB/c Mice

Introduction  Certain low-molecular-weight heparins have been reported to reduce tumor growth and metastasis in tumor cell-inoculated mouse models and cancer patients. Recently, direct oral anticoagulants (DOACs) have been widely used in patients with thromboembolism. This study was aimed at investigating the effect of DOACs, which target thrombin or factor Xa, on tumor growth in a syngeneic mouse model comprising BALB/c mice inoculated with colon cancer Colon26 cells. Materials and Methods  DOACs targeting thrombin (dabigatran etexilate [DABE]) or factor Xa (rivaroxaban [RVX] and edoxaban [EDX]) were orally administered daily to male BALB/c mice inoculated with Colon26 cells, followed by analyses of tumor growth and plasma levels of coagulation- and tumor-related factors such as tissue factor (TF), plasminogen activator inhibitor-1 (PAI-1), interleukin-6 (IL-6), and matrix metalloproteinase-2 (MMP-2). Results  Colon26 cells expressed significant amounts of functionally active TF. Tumor growth in Colon26-inoculated mice was significantly suppressed in DABE- or RVX-treated mice ( p <0.05) and was suppressed more significantly in EDX-treated mice ( p <0.01). Therefore, the antitumor mechanism of action of EDX was investigated next. Plasma levels of TF, PAI-1, IL-6, and MMP-2 were elevated in Colon26-inoculated mice but were significantly reduced in EDX-treated mice ( p <0.01). The expression of protease-activated receptor (PAR)1, PAR2, signal transducer and activator of transcription-3 (STAT3), cyclin D1, and Ki67 was increased in tumor tissue of Colon26-inoculated mice but (except for PAR1) was significantly decreased in tumor tissues of EDX-treated mice ( p <0.01). In addition, apoptotic cells and p53 protein levels were significantly increased in tumor tissues of EDX-treated mice. Conclusion  The data suggest that among the tested DOACs, EDX significantly suppresses tumor cell proliferation via the factor Xa-PAR2 pathway, which is activated by coagulation and inflammation in Colon26-inoculated mice and induces tumor cell apoptosis.

Protease-activated receptors in health and disease

Proteases are signaling molecules that specifically control cellular functions by cleaving protease-activated receptors (PARs). The four known PARs are members of the large family of G protein-coupled receptors. These transmembrane receptors control most physiological and pathological processes and are the target of a large proportion of therapeutic drugs. Signaling proteases include enzymes from the circulation; from immune, inflammatory epithelial, and cancer cells; as well as from commensal and pathogenic bacteria. Advances in our understanding of the structure and function of PARs provide insights into how diverse proteases activate these receptors to regulate physiological and pathological processes in most tissues and organ systems. The realization that proteases and PARs are key mediators of disease, coupled with advances in understanding the atomic level structure of PARs and their mechanisms of signaling in subcellular microdomains, has spurred the development of antagonists, some of which have advanced to the clinic. Herein we review the discovery, structure, and function of this receptor system, highlight the contribution of PARs to homeostatic control, and discuss the potential of PAR antagonists for the treatment of major diseases.

PARs in the inflammation-cancer transformation of CRC

Colorectal cancer (CRC) is one of the common malignancies with a global trend of increasing incidence and mortality. There is an urgent need to identify new predictive markers and therapeutic targets for the treatment of CRC. Protease-activated receptors (PARs) are a class of G-protein-coupled receptors, with currently identified subtypes including PAR1, PAR2, PAR3 and PAR4. Increasingly, studies suggest that PARs play an important role in the growth and metastasis of CRC. By targeting multiple signaling pathways may contribute to the pathogenesis of CRC. In this review, we first describe recent studies on the role of PARs in CRC inflammation-cancer transformation, focusing on the important role of PARs in signaling pathways associated with inflammation-cancer transformation, and summarize the progress of research on PARs-targeted drugs.

Critical roles of G protein-coupled receptors in regulating intestinal homeostasis and inflammatory bowel disease

G protein-coupled receptors (GPCRs) are a group of membrane proteins that mediate most of the physiological responses to various signaling molecules such as hormones, neurotransmitters, and environmental stimulants. Inflammatory bowel disease (IBD) is a chronic relapsing disorder of the gastrointestinal tract and presents a spectrum of heterogeneous disorders falling under two main clinical subtypes including Crohn's disease (CD) and ulcerative colitis (UC). The pathogenesis of IBD is multifactorial and is related to a genetically dysregulated mucosal immune response to environmental drivers, mainly microbiotas. Although many drugs, such as 5-aminosalicylic acid, glucocorticoids, immunosuppressants, and biological agents, have been approved for IBD treatment, none can cure IBD permanently. Emerging evidence indicates significant associations between GPCRs and the pathogenesis of IBD. Here, we provide an overview of the essential physiological functions and signaling pathways of GPCRs and their roles in mucosal immunity and IBD regulation.

Protease-Activated Receptors - Key Regulators of Inflammatory Bowel Diseases Progression

The pathogenesis and course of inflammatory bowel diseases are related to both immune system disorders and dysfunction of colon permeability. Moreover, co-existing diseases in patients with Crohn's disease and ulcerative colitis are identified. Currently, there are some therapeutic strategies that affect the function of cytokine/s causing inflammation in the intestinal wall. However, additional approaches which target other components of inflammatory bowel diseases pathogenesis are still needed. Accumulating evidence suggests that proteases and protease-activated receptors seem to be responsible for colitis progression. Experimental and observational studies showed alteration of protease-activated receptors expression in the colon of patients with Crohn's disease and ulcerative colitis. Furthermore, it was suggested that the expression of protease-activated receptors correlated with inflammatory bowel diseases activity. Moreover, regulation of protease-activated receptors seems to be responsible for the modulation of colitis and clinical manifestation of inflammatory bowel diseases. In this review, we present the current state of knowledge about the contribution of protease-activated receptors to Crohn's disease and ulcerative colitis and its implications for diagnosis and treatment.

Cells and mediators of inflammation as effectors of epithelial repair in the inflamed intestine

Mucosal and histological healing have become the gold standards for assessing the efficacy of therapy in patients living with inflammatory bowel diseases (IBD). Despite these being the accepted goals in therapy, the mechanisms that underlie the healing of the mucosa after an inflammatory insult are not well understood, and many patients fail to meet this therapeutic endpoint. Here we review the emerging evidence that mediators (e.g., prostaglandins, cytokines, proteases, reactive oxygen, and nitrogen species) and innate immune cells (e.g., neutrophils and monocytes/macrophages), that are involved in the initiation of the inflammatory response, are also key players in the mechanisms underlying mucosal healing to resolve chronic inflammation in the colon. The dual function mediators comprise an inflammation/repair program that returns damaged tissue to homeostasis. Understanding details of the dual mechanisms of these mediators and cells may provide the basis for the development of drugs that can help to stimulate epithelial repair in patients affected by IBD.

Protease-activated receptor 2 stabilizes Bcl-xL and regulates EGFR-targeted therapy response in colorectal cancer

The Bcl-2 homolog Bcl-xL is emerging as a key factor in tumorigenesis due to its prominent pro-survival and cell death-independent functions. However, the regulation of Bcl-xL by microenvironment and its implication in cancer therapy of colorectal carcinoma (CRC) are unclear. Here, we demonstrated that Bcl-xL expression was positively associated with protease-activated receptor 2 (PAR2) in CRC. Activation of PAR2 stabilized Bcl-xL protein in a proteasome-dependent manner, whereas E3 ligase RING finger protein 152 (RNF152) accelerated the ubiquitination and degradation of Bcl-xL. RNF152 silencing by specific siRNAs rescued the expression of Bcl-xL in PAR2-deficient cells. Moreover, RNF152 physically interacted with Bcl-xL, which was disturbed by PAR2 activation. Further studies with serial mutation of Bcl-xL revealed that phosphorylation of Bcl-xL at S145 reduced its binding affinity for RNF152 and stabilized Bcl-xL. Importantly, inhibition of PAR2 signaling by its gene silencing or specific chemical inhibitors increased apoptosis induced by different EGFR-targeted therapies. In patient-derived xenograft model, inhibition of PAR2 increased the response of CRC to different EGFR-targeted therapies. These results indicate that PAR2 stabilizes Bcl-xL by altering RNF152 signaling and that PAR2 inhibition sensitizes CRC to EGFR-targeted therapies in vivo.

PAR2 Deficiency Induces Mitochondrial ROS Generation and Dysfunctions, Leading to the Inhibition of Adipocyte Differentiation

Protease-activated receptor 2 (PAR2) is a member of G-protein-coupled receptors and affects ligand-modulated calcium signaling. Although PAR2 signaling promotes obesity and adipose tissue inflammation in high fat- (HF-) fed conditions, its role in adipocyte differentiation under nonobesogenic conditions needs to be elucidated. Here, we used several tissues and primary-cultured adipocytes of mice lacking PAR2 to study its role in the development of adipose tissues. C57BL/6J mice with PAR2 deficiency exhibited a mild lipodystrophy-like phenotype in a chow diet-fed condition. When adipocyte differentiation was examined using primary-cultured preadipocytes, PAR2 deficiency led to a notable decrease in adipocyte differentiation and related protein expression, and PAR2 agonist treatment elevated adipocyte differentiation. Regarding the mechanism, PAR2-deficient preadipocytes exhibited impaired mitochondrial energy consumption. Further studies indicated that calcium-related signaling pathways for mitochondrial biogenesis are disrupted in the adipose tissues of PAR2-deficient mice and PAR2-deficient preadipocytes. Also, a PAR2 antagonist elevated mitochondrial reactive oxygen species and reduced the MitoTracker fluorescent signal in preadipocytes. Our studies revealed that PAR2 is important for the development of adipose tissue under basal conditions through the regulation of mitochondrial biogenesis and adipocyte differentiation.

Blockage of protease-activated receptor 2 exacerbates inflammation in high-fat environment partly through autophagy inhibition

Protease-activated receptor 2 (PAR2) regulates inflammatory responses and lipid metabolism. However, its precise role in colitis remains unclear. In this study, we aimed to investigate the function of PAR2 in high-fat diet-fed mice with colitis and its potential role in autophagy. PAR2^+/+ and PAR2^-/- mice were fed a high-fat diet (HFD) for 7 days before colitis induction with dextran sodium sulfate. Deletion of PAR2 and an HFD significantly exacerbated colitis, as shown by increased mortality, body weight loss, diarrhea or bloody stools, colon length shortening, and mucosal damage. Proinflammatory cytokine levels were elevated in HFD-fed PAR2^-/- mice and in cells treated with the PAR2 antagonist GB83, palmitic acid (PA), and a cytokine cocktail (CC). Damaging effects of PAR2 blockage were associated with autophagy regulation by reducing the levels of YAP1, SIRT1, PGC-1α, Atg5, and LC3A/B-I/II. In addition, mitochondrial dysfunction was demonstrated only in cells treated with GB83, PA, and CC. Reduced cell viability and greater induction of apoptosis, as shown by increased levels of cleaved caspase-9, cleaved caspase-3, and cleaved poly(ADP-ribose) polymerase (PARP), were observed in cells treated with GB83, PA, and CC but not in those treated with only PA and CC. Collectively, protective effects of PAR2 were elucidated during inflammation accompanied by a high-fat environment by promoting autophagy and inhibiting apoptosis, suggesting PAR2 as a therapeutic target for inflammatory bowel disease co-occurring with metabolic syndrome.NEW & NOTEWORTHY Deletion of PAR2 with high-fat diet feeding exacerbates colitis in a murine colitis model. Proinflammatory effects of PAR2 blockage in a high-fat environment were associated with an altered balance between autophagy and apoptosis. Increased colonic levels of PAR2 represent as a therapeutic strategy for IBD co-occurring with metabolic syndrome.

Expression of Proteinase-Activated Receptor 2 During Colon Volvulus in the Horse

Large colon volvulus in horses is associated with a poor prognosis, especially when ischemic-reperfusion injury of the affected intestinal tract develops. Proteinase-activated receptor 2 (PAR₂) plays an important role in the pathogenesis of inflammation in the gastrointestinal tract. The aim of this study was to evaluate the distribution and expression of PAR₂ in colonic pelvic flexure of horses spontaneously affected by large colon volvulus (CVH group). Eight horses admitted for severe abdominal colon volvolus and which underwent surgery were included. Colon samples were collected after enterotomy. Data previously obtained from healthy horses were used as a control group. Histologic evaluation was carried out to grade the severity of the colon lesions. Immunofluorescence, western blot and quantitative polymerase chain reaction (RT-qPCR) were carried out on colon samples to evaluate PAR₂ expression. In addition, the transcriptional profile of cytokines and chemokines was evaluated using RT² Profiler™ PCR Array Horse Cytokines & Chemokines. Three out of the eight patients were euthanised due to clinical deterioration. Immunostaining for PAR² was observed in the enterocytes, intestinal glands and neurons of the submucosal and myenteric plexi. In the CVH horses, the expression of PAR₂ mesenger RNA (mRNA) did not differ significantly from that of the healthy animals; western blots of the mucosa of the colon tracts showed a clear band of the expected molecular weight for PAR₂ (~44 kDa) and a band smaller than the expected molecular weight for PAR₂ (25kDa), suggesting its activation. The gene expressions for C-X-C motif ligand 1 (CXCL1); interleukin 8 (IL8), macrophage inflammatory protein 2 beta (MIP-2BETA) were upregulated in the colic horses as compared with the colons of the healthy horses. Therefore, in the present study, the expression and activation of PAR₂ in the colons of horses in the presence of an inflammatory reaction like that occurring in those with spontaneous colon volvulus was confirmed.

Treatment of Pulpectomized Teeth With Trypsin Prior to Transplantation of Mobilized Dental Pulp Stem Cells Enhances Pulp Regeneration in Aged Dogs

There is an age-dependent decline of pulp regeneration, due to the decline of migration, proliferation, and cell survival of resident stem cells. Trypsin is a proteolytic enzyme clinically used for tissue repair. Here, we investigated the effects of trypsin pretreatment of pulpectomized teeth prior to cell transplantation on pulp regeneration in aged dogs. The amount of regenerated pulp was significantly higher in trypsin-pretreated teeth compared to untreated teeth. Trypsin pretreatment increased the number of cells attached to the dentinal wall that differentiated into odontoblast-like cells. The trypsin receptor, PAR2, was higher in vitro expression in the periodontal ligament cells (PDLCs) from aged dogs compared to those from young. The direct effects of trypsin on aged PDLCs were increased expression of genes related to immunomodulation, cell survival, and extracellular matrix degradation. To examine the indirect effects on microenvironment, highly extracted proteins from aged cementum were identified by proteomic analyses. Western blotting demonstrated that significantly increased fibronectin was released by the trypsin treatment of aged cementum compared to young cementum. The aged cementum extract (CE) and dentin extract (DE) by trypsin treatment increased angiogenesis, neurite extension and migration activities as elicited by fibronectin. Furthermore, the DE significantly increased the mRNA expression of immunomodulatory factors and pulp markers in the aged DPSCs. These results demonstrated the effects of trypsin on the microenvironment in addition to the resident cells including PDLCs in the aged teeth. In conclusion, the potential utility of trypsin pretreatment to stimulate pulp regeneration in aged teeth and the underlying mechanisms were demonstrated.

Faecal Proteases from Pouchitis Patients Activate Protease Activating Receptor-2 to Disrupt the Epithelial Barrier

BACKGROUND AND AIMS

The pathogenesis of pouch inflammation may involve epithelial barrier disruption. We investigated whether faecal proteolytic activity is increased during pouchitis and results in epithelial barrier dysfunction through protease activating receptor [PAR] activation, and assessed whether the intestinal microbiome may be the source of the proteases.

METHODS

Faecal samples were measured for protease activity using a fluorescein isothiocyanate [FITC]-casein florescence assay. Caco-2 cell monolayers were exposed to faecal supernatants to assess permeability to FITC-dextran. Tight junction protein integrity and PAR activation were assessed by immunoblot and immunofluorescence. A truncated PAR2 protein in Caco-2 cells was achieved by stable transfection using CRISPR/Cas9 plasmid. PAR2 activation in pouch biopsies was examined using antibodies directed to the N-terminus of the protein. Microbial composition was analysed based on 16S rRNA gene sequence analysis.

RESULTS

Ten pouchitis patients, six normal pouch [NP] patients and nine healthy controls [HC] were recruited. The pouchitis patients exhibited a 5.19- and 5.35-fold higher faecal protease [FP] activity [p ≤ 0.05] compared to the NP and HC participants, respectively. The genus Haemophilus was positively associated with FP activity [R = 0.718, false discovery rate < 0.1]. Faecal supernatants from pouchitis patients activated PAR2 on Caco-2 monolayers, disrupted tight junction proteins and increased epithelial permeability. PAR2 truncation in Caco-2 abrogated faecal protease-mediated permeability. Pouch biopsies obtained from pouchitis patients, but not from NP patients, displayed PAR2 activation.

CONCLUSIONS

Protease-producing bacteria may increase faecal proteolytic activity that results in pouch inflammation through disruption of tight junction proteins and increased epithelial permeability in a PAR2-dependent manner. This mechanism may initiate or propagate pouch inflammation.

Protease activated receptors (PAR)-1 and -2 mediate cellular effects of factor VII activating protease (FSAP)

Factor VII activating protease (FSAP) is a circulating serine protease implicated in thrombosis, atherosclerosis, stroke, and cancer. Using an overexpression strategy, we have systematically investigated the role of protease activated receptors (PAR)-1, -2, -3, and -4 on FSAP-mediated signaling in HEK293T and A549 cells. Cleavage of PAR-reporter constructs and MAPK phosphorylation was used to monitor receptor activation. FSAP cleaved PAR-2 and to a lesser degree PAR-1, but not PAR-3 or PAR-4 in both cell types. Robust MAPK activation in response to FSAP was observed after PAR-2, but not PAR-1 overexpression in HEK293T. Recombinant serine protease domain of wild type FSAP, but not the Marburg I isoform of FSAP, could reproduce the effects of plasma purified FSAP. Canonical cleavage of both PARs was suggested by mass spectrometric analysis of synthetic peptide substrates from the N-terminus of PARs and site directed mutagenesis studies. Surprisingly, knockdown of endogenous PAR-1, but not PAR-2, prevented the apoptosis-inhibitory effect of FSAP, suggesting that PAR1 is nevertheless a direct or indirect target in some cell types. This molecular characterization of PAR-1 and -2 as cellular receptors of FSAP will help to define the actions of FSAP in the context of cancer and vascular biology.

Clematichinenoside AR ameliorated spontaneous colitis in Il-10-/- mice associated with improving the intestinal barrier function and abnormal immune responses

OBJECTIVES

Clematichinenoside AR (AR) is a saponin extracted for traditional Chinese medicine with the effects of improving the expression of tight junction (TJ) proteins and mediating anti-inflammatory activities. However, its effect on Crohn's disease (CD) is still unknown. We aimed to investigate the impact of AR on CD-like colitis and determine the mechanism underlying its effects.

METHODS

Interleukin-10 gene knockout (Il-10^-/-) mice (male, fifteen weeks old) with spontaneous colitis were allocated to the positive control and AR-treated (32 mg/kg AR administered every other day by gavage for 4 weeks) groups. Wild-type (WT) mice (male, fifteen weeks old) composed the negative control group. The effects of AR on intestinal barrier function and structure and T cell responses as well as the potential mechanisms underlying these effects were investigated.

RESULTS

AR treatment significantly improved spontaneous colitis in Il-10^-/- mice as demonstrated by reductions in the inflammatory score, disease activity index (DAI) and levels of inflammatory factors. The effects of AR on colitis in Il-10^-/- mice were related to protecting intestinal barrier function and maintaining immune system homeostasis (regulatory T cell (Treg)/T helper 17 (Th17) cell balance). The anticolitis effect of AR may partly act by downregulating PI3K/Akt signaling.

CONCLUSIONS

AR may have therapeutic potential for treating CD in humans.

Proteinase‑activated receptor 2 deficiency is a protective factor against cardiomyocyte apoptosis during myocardial ischemia/reperfusion injury

Previous studies have established that proteinase‑​activated receptor 2 (PAR2) activation protects against myocardial ischemia/reperfusion injury (MI/RI). However, the role of PAR2 deficiency in MI/RI remains unclear. The aim of the present study was to examine the effect of PAR2 deficiency on cardiomyocyte apoptosis and to clarify the potential molecular mechanisms for its protective effect against MI/RI. Using a mouse model of MI/RI, cardiac function was evaluated by echocardiography, infarct size was assessed by triphenyltetrazolium chloride staining, and myocardial cell apoptosis was measured by terminal deoxynucleotide transferase‑mediated dUTP nick end‑labeling staining. Annexin V/propidium iodide staining, and expression of Bcl‑2 and cleaved PARP were determined to assess apoptosis in myocardial H9c2 cells exposed to hypoxia/reoxygenation (H/R) injury‑simulating MI/RI. Phosphorylated ERK1/2, JNK, and p38 MAPK protein expression levels were analyzed by western blotting. The findings indicated that PAR2 deficiency markedly reduced cardiomyocyte apoptosis in the MI/RI mouse model, as well as in myocardial H9c2 cells exposed to H/R. Furthermore, PAR2 knockdown clearly prevented phosphorylation of ERK1/2 and JNK in myocardial H9c2 cells. The results revealed that PAR2 deficiency alleviated MI/RI‑associated apoptosis by inhibiting phosphorylation of ERK1/2 and JNK. Therefore, targeted PAR2 silencing may be a potential therapeutic approach for alleviation of MI/RI.

Triple-negative breast cancer-derived microvesicles transfer microRNA221 to the recipient cells and thereby promote epithelial-to-mesenchymal transition

The triple-negative phenotype is the most prevalent form of human breast cancer worldwide and is characterized by poor survival, high aggressiveness, and recurrence. Microvesicles (MV) are shredded plasma membrane components and critically mediate cell-cell communication, but can also induce cancer proliferation and metastasis. Previous studies have revealed that protease-activated receptor 2 (PAR2) contributes significantly to human triple-negative breast cancer (TNBC) progression by releasing nano-size MV and promoting cell proliferation, migration, and invasion. MV isolated from highly aggressive human TNBC cells impart metastatic potential to nonmetastatic cells. Over-expression of microRNA221 (miR221) has also been reported to enhance the metastatic potential of human TNBC, but miR221's relationship to PAR2-induced MV is unclear. Here, using isolated MV, immunoblotting, quantitative RT-PCR, FACS analysis, and enzymatic assays, we show that miR221 is translocated via human TNBC-derived MV, which upon fusion with recipient cells, enhance their proliferation, survival, and metastasis both in vitro and in vivo by inducing the epithelial-to-mesenchymal transition (EMT). Administration of anti-miR221 significantly impaired MV-induced expression of the mesenchymal markers Snail, Slug, N-cadherin, and vimentin in the recipient cells, whereas restoring expression of the epithelial marker E-cadherin. We also demonstrate that MV-associated miR221 targets phosphatase and tensin homolog (PTEN) in the recipient cells, followed by AKT Ser/Thr kinase (AKT)/NF-κB activation, which promotes EMT. Moreover, elevated miR221 levels in MV derived from human TNBC patients' blood could induce cell proliferation and metastasis in recipient cells. In summary, miR221 transfer from TNBC cells via PAR2-derived MV induces EMT and enhances the malignant potential of recipient cells.

Store-operated calcium entry (SOCE) contributes to phosphorylation of p38 MAPK and suppression of TNF-α signalling in the intestinal epithelial cells

Calcium influx via store-operated calcium entry (SOCE) has an important role for regulation of vast majority of cellular physiological events. MAPK signalling is also another pivotal modulator of many cellular functions. However, the relationship between SOCE and MAPK is not well understood. In this study, we elucidated the involvement of SOCE in Gα_q/11 protein-mediated activation of p38 MAPK in an intestinal epithelial cell line HT-29/B6. In this cell line, we previously showed that the stimulation of M3 muscarinic acetylcholine receptor (M3-mAChR) but not histamine H1 receptor (H1R) led to phosphorylation of p38 MAPK which suppressed tumor necrosis factor-α (TNF-α)-induced NF-κB signalling through ADAM17 protease-mediated shedding of TNF receptor-1 (TNFR1). First, we found that stimulation of M3-mAChR and protease-activated receptor-2 (PAR-2) but not H1R induced persistent upregulation of cytosolic Ca²⁺ concentration through SOCE. Activation of M3-mAChR or PAR-2 also suppressed TNF-α-induced NF-κB phosphorylation, which was dependent on the p38 MAPK activity. Time course experiments revealed that M3-mAChR stimulation evoked intracellular Ca²⁺-dependent early phase p38 MAPK phosphorylation and extracellular Ca²⁺-dependent later phase p38 MAPK phosphorylation. This later phase p38 MAPK phosphorylation, evoked by M3-mAChRs or PAR-2, was abolished by inhibition of SOCE. Thapsigargin or ionomycin also phosphorylate p38 MAPK by Ca²⁺ influx through SOCE, leading to suppression of TNF-α-induced NF-κB phosphorylation. Finally, we showed that p38 MAPK was essential for thapsigargin-induced cleavage of TNFR1 and suppression of TNF-α-induced NF-κB phosphorylation. In conclusion, SOCE is important for p38 MAPK phosphorylation and is involved in TNF-α signalling suppression.

Embryonic Stem Cells Modulate the Cancer-Permissive Microenvironment of Human Uveal Melanoma

The currently used anti-cancer therapies work by killing cancer cells but result in adverse effects and resistance to treatment, which accelerates aging and causes damage to normal somatic cells. On one hand, chicken and zebrafish embryos can reprogram cancer cells towards a non-tumorigenic phenotype; however, they cannot be used in the clinical practice. On the other hand, embryonic stem cells (ESCs) mimic the early embryonic microenvironment and are easily available. We investigated the therapeutic efficacy of the ESC microenvironment (ESCMe) in human uveal melanoma in vitro and in vivo.

Methods: Human uveal melanoma C918 cells co-cultured with ESCs were used to measure the levels of mRNA and protein of the phosphoinositide 3-kinase (PI3K) pathway. Cell proliferation, invasiveness, and tumorigenicity of C918 cells were also analyzed. To mimic the tumor microenvironment in vivo, we co-cultured C918 cells and normal somatic cells with ESCs in a co-culture system and evaluated the therapeutic potential of ESCMe in both cell types. For an in vivo study, a mouse tumor model was used to test the safety and efficacy of the transplanted ESC. Elimination of the transplanted ESCs in mice was carried out by using the ESC-transfected with a thymidine kinase suicidal gene followed by administration of ganciclovir to prevent the formation of teratomas by ESCs.

Results: In vitro studies confirmed that ESCMe inhibits the proliferation, invasiveness, and tumorigenicity of C918 cells, and the PI3K agonist abolished these effects. ESCMe suppressed the various malignant behaviors of uveal melanoma cells but enhanced the proliferation of normal somatic cells both in vitro and in vivo. Further, we demonstrated that ESCMe suppressed the PI3K pathway in tumor cells but activated in somatic cells.

Conclusions: The ESCMe can effectively suppress the malignant phenotype of uveal melanoma cells and modulate the tumor-promoting aging environment by preventing the senescence of normal cells through the bidirectional regulation of the PI3K signaling. Our results suggest that ESC transplantation can serve as an effective and safe approach for treating cancer without killing cells.

PRSS21/testisin inhibits ovarian tumor metastasis and antagonizes proangiogenic angiopoietins ANG2 and ANGPTL4

Ovarian cancer is the leading cause of death among all the gynecological cancers in the USA. Ovarian cancer employs a unique mode of metastasis, as exfoliated tumor cells disseminate within the peritoneal cavity, colonizing in several sites as well as accumulating ascites. Tumor recurrence and widespread metastasis are significant factors contributing to poor prognosis. PRSS21 is a metastasis-associated ovarian cancer gene that encodes the glycosyl-phosphatidylinositol-linked serine protease, testisin. Testisin expression is increased in multiple ovarian tumor types, with relatively little expression in normal tissues, but is differentially decreased in metastatic ovarian serous carcinomas compared to primary tumors. Here we explored the function of testisin in late-stage ovarian cancer progression using a murine xenograft model of ovarian intraperitoneal tumor metastasis. Increased tumor testisin expression inhibited intra-peritoneal tumor seeding and colonization, ascites accumulation, and metastatic tumor burden that was dependent on catalytically active testisin. The known testisin substrate, protease-activated receptor-2 (PAR-2), is a target of testisin activity. Gene profiling and mechanistic studies demonstrate that testisin activity suppresses the synthesis and secretion of pro-angiogenic angiopoietins, ANG2 and ANGPTL4, which normally promote vascular leak and edema. These observations support a model wherein testisin activates PAR-2 to antagonize proangiogenic angiopoietins that modulate vascular permeability and ascites accumulation associated with ovarian tumor metastasis. KEY MESSAGES: Testisin inhibits metastatic ovarian tumor burden and ascites production. Testisin activity antagonizes ANG2 and ANGPTL4 synthesis and secretion. PAR-2 is a proteolytic target of testisin on the surface of ovarian cancer cells.

Overexpressed Hsp70 alleviated formaldehyde-induced apoptosis partly via PI3K/Akt signaling pathway in human bronchial epithelial cells

Formaldehyde (FA) is a ubiquitous environmental pollutant, which can induce apoptosis in lung cell and is related to the pathogenesis of asthma, pneumonia, and chronic obstructive pulmonary disease. Heat shock protein 70 (Hsp70) is an ATP-dependent molecular chaperone and exhibits an anti-apoptosis ability in a variety of cells. Previous studies reported that the expression of Hsp70 was induced when organisms were exposed to FA. Whether Hsp70 plays a role in the FA-induced apoptosis and the involved cell signaling pathway remain largely unknown. In this study, human bronchial epithelial cells with overexpressed Hsp70 and the control were exposed to different concentrations of FA (0, 40, 80, and 160 μmol/L) for 24 hours. Apoptosis and the expression levels of PI3K, Akt, p-Akt, MEK, p-MEK, and GLI2 were detected by Annexin-APC/7AAD double-labeled flow cytometry and western blot. The results showed that overexpression of Hsp70 decreased the apoptosis induced by FA and alleviated the decline of PI3k and p-Akt significantly. Inhibitor (LY 294002, a specific inhibitor of PI3K-Akt) test result indicated that PI3K-Akt signaling pathway was involved in the inhibition of FA-induced apoptosis by Hsp70 overexpression and also active in the maintenance of GLI2 level. However, it also suggested that other signaling pathways activated by overexpressed Hsp70 participated in this process, which was needed to be elucidated in further research.

Protease-activated receptors (PARs): mechanisms of action and potential therapeutic modulators in PAR-driven inflammatory diseases

Inflammatory diseases have become increasingly prevalent with industrialization. To address this, numerous anti-inflammatory agents and molecular targets have been considered in clinical trials. Among molecular targets, protease-activated receptors (PARs) are abundantly recognized for their roles in the development of chronic inflammatory diseases. In particular, several inflammatory effects are directly mediated by the sensing of proteolytic activity by PARs.

PARs belong to the seven transmembrane domain G protein-coupled receptor family, but are unique in their lack of physiologically soluble ligands. In contrast with classical receptors, PARs are activated by N-terminal proteolytic cleavage. Upon removal of specific N-terminal peptides, the resulting N-termini serve as tethered activation ligands that interact with the extracellular loop 2 domain and initiate receptor signaling. In the classical pathway, activated receptors mediate signaling by recruiting G proteins. However, activation of PARs alternatively lead to the transactivation of and signaling through receptors such as co-localized PARs, ion channels, and toll-like receptors.

In this review we consider PARs and their modulators as potential therapeutic agents, and summarize the current understanding of PAR functions from clinical and in vitro studies of PAR-related inflammation.

PAR2 Inhibition Enhanced the Sensitivity of Colorectal Cancer Cells to 5-FU and Reduced EMT Signaling

The aim of this study was to investigate the underlying mechanisms that transforming growth factor-β (TGF-β)-mediated epithelial-to-mesenchymal transition (EMT) in tumor cells contributes to 5-FU resistance. A series of experiments involving cell viability and caspase activity analyses, siRNA transfection, RNA isolation, and quantitative-PCR (qPCR) assay, cell migration analysis, Western blotting analysis of total protein and membrane protein were performed in this study. Mouse xenograft model was used to determine the effect of the PAR2 inhibitor in vivo. In this study, we found that protease-activated receptor 2 (PAR2) induction in 5-FU therapy is correlated with TGF-β-mediated EMT and apoptosis resistance. PAR2 and TGF-β were both activated in response to 5-FU treatment in vivo and in vitro, and whereas TGF-β inhibition sensitized CRC cells to 5-FU and suppressed cell migration, PAR2 activation eliminated the effect of TGF-β inhibition. Conversely, siRNA-mediated PAR2 depletion or PAR2 inhibition with a specific inhibitor produced a similar phenotype as TGF-β signal inhibition: 5-FU sensitization and cell migration suppression. Moreover, the results of xenograft experiments indicated that the PAR2 inhibitor can enhance cell killing by 5-FU in vivo and suppress EMT signaling. Our results reveal that the TGF-β effects require the coordinating action of PAR2, suggesting that PAR2 inhibition could be a new therapeutic strategy to combat 5-FU resistance in CRC.

Protease-activated receptor 2 exacerbates cisplatin-induced nephrotoxicity

Acute kidney injury (AKI) is associated with hypercoagulability. Tissue factor/factor VIIa complex and factor Xa in the coagulation cascade activate protease-activated receptor 2 (PAR2). Previously, we have shown that PAR2-mediated inflammation aggravates kidney injury in models of diabetic kidney disease and adenine-induced renal fibrosis. However, the role of PAR2 in AKI remains unclear. To clarify the role of PAR2, we administered cisplatin, one of the most common causal factors of AKI, to wild-type and PAR2-deficient mice. The expression levels of tissue factor and PAR2 were significantly increased in the kidneys of mice that were administered cisplatin. A lack of PAR2 corrected the levels of plasma blood urea nitrogen and creatinine as well as ameliorated the acute tubular injury score in the kidney. A lack of PAR2 corrected the infiltration of neutrophils and the gene expression levels of proinflammatory cytokines/chemokines in these mouse kidneys. Similarly, apoptotic markers, such as cleaved caspase-3-positive area and Bax/Bcl2 ratio, were attenuated via PAR2 deletion. Thus, elevated PAR2 exacerbates cisplatin nephrotoxicity, and targeting PAR2 is a novel therapeutic option that aids in the treatment of patients with cisplatin-induced AKI.

Protease-Activated Receptors in the Intestine: Focus on Inflammation and Cancer

Protease-activated receptors (PARs) belong to the G protein-coupled receptor (GPCR) family. Compared to other GPCRs, the specificity of the four PARs is the lack of physiologically soluble ligands able to induce their activation. Indeed, PARs are physiologically activated after proteolytic cleavage of their N-terminal domain by proteases. The resulting N-terminal end becomes a tethered activation ligand that interact with the extracellular loop 2 domain and thus induce PAR signal. PARs expression is ubiquitous and these receptors have been largely described in chronic inflammatory diseases and cancer. In this review, after describing their discovery, structure, mechanisms of activation, we then focus on the roles of PARs in the intestine and the two main diseases affecting the organ, namely inflammatory bowel diseases and cancer.

Cathepsin S Alters the Expression of Pro-Inflammatory Cytokines and MMP-9, Partially through Protease-Activated Receptor-2, in Human Corneal Epithelial Cells

Cathepsin S (CTSS) activity is increased in tears of Sjögren's syndrome (SS) patients. This elevated CTSS may contribute to ocular surface inflammation. Human corneal epithelial cells (HCE-T cells) were treated with recombinant human CTSS at activity comparable to that in SS patient tears for 2, 4, 8, and 24 h. Acute CTSS significantly increased HCE-T cell gene and protein expression of interleukin 6 (IL-6), interleukin 8 (IL-8), tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β) from 2 to 4 h, while matrix metalloproteinase 9 (MMP-9), CTSS, and protease-activated receptor-2 (PAR-2) were increased by chronic CTSS (24 h). To investigate whether the increased pro-inflammatory cytokines and proteases were induced by CTSS activation of PAR-2, HCE-T cells were transfected with PAR-2 siRNA, reducing cellular PAR-2 by 45%. Cells with reduced PAR-2 expression showed significantly reduced release of IL-6, TNF-α, IL-1β, and MMP-9 into culture medium in response to acute CTSS, while IL-6, TNF-α, and MMP-9 were reduced in culture medium, and IL-6 and MMP-9 in cell lysates, after chronic CTSS. Moreover, cells with reduced PAR-2 expression showed reduced ability of chronic CTSS to induce gene expression of pro-inflammatory cytokines and proteases. CTSS activation of PAR-2 may represent a potential therapeutic target for amelioration of ocular surface inflammation in SS patients.

Positive crosstalk between EGFR and the TF-PAR2 pathway mediates resistance to cisplatin and poor survival in cervical cancer

Cisplatin-based chemoradiation is the standard treatment for cervical cancer, but chemosensitizing strategies are needed to improve patient survival. EGFR (Epidermal Growth Factor Receptor) is an oncogene overexpressed in cervical cancer that is involved in chemoresistance. Recent studies showed that EGFR upregulates multiple elements of the coagulation cascade, including tissue factor (TF) and the protease-activated receptors (PAR) 1 and 2. Moreover, many G protein-coupled receptors, including PARs, have been implicated in EGFR transactivation. However, the role of coagulation proteins in the progression of cervical cancer has been poorly investigated. Herein we employed cervical cancer cell lines and The Cancer Genome Atlas (TCGA) database to evaluate the role of EGFR, TF and PAR2 in chemoresistance. The SLIGKL-NH2 peptide (PAR2-AP) and coagulation factor VIIa (FVIIa) were used as PAR2 agonists, while cetuximab was used to inhibit EGFR. The more aggressive cell line CASKI showed higher expression levels of EGFR, TF and PAR2 than that of C33A. PAR2 transactivated EGFR, which further upregulated cyclooxygenase-2 (COX2) expression. PAR2-AP decreased cisplatin-induced apoptosis through an EGFR- and COX2-dependent mechanism. Furthermore, treatment of CASKI cells with EGF upregulated TF expression, while treatment with cetuximab decreased the TF protein levels. The RNA-seq data from 309 TCGA samples showed a strong positive correlation between EGFR and TF expression (P = 0.0003). In addition, the increased expression of EGFR, PAR2 or COX2 in cervical cancer patients was significantly correlated with poor overall survival. Taken together, our results suggest that EGFR and COX2 are effectors of the TF/FVIIa/PAR2 signaling pathway, promoting chemoresistance.

The Protease Activated Receptor2 Promotes Rab5a Mediated Generation of Pro-metastatic Microvesicles

Metastasis, the hallmark of cancer propagation is attributed by the modification of phenotypic/functional behavior of cells to break attachment and migrate to distant body parts. Cancer cell-secreted microvesicles (MVs) contribute immensely in disease propagation. These nano-vesicles, generated from plasma membrane outward budding are taken up by nearby healthy cells thereby inducing phenotypic alterations in those recipient cells. Protease activated receptor 2 (PAR2), activated by trypsin, also contributes to cancer progression by increasing metastasis, angiogenesis etc. Here, we report that PAR2 activation promotes pro-metastatic MVs generation from human breast cancer cell line, MDA-MB-231. Rab5a, located at the plasma membrane plays vital roles in MVs biogenesis. We show that PAR2 stimulation promotes AKT phosphorylation which activates Rab5a by converting inactive Rab5a-GDP to active Rab5a-GTP. Active Rab5a polymerizes actin which critically regulates MVs shedding. Not only MVs generation, has this Rab5a activation also promoted cell migration and invasion. We reveal that Rab5a is over-expressed in human breast tumor specimen and contributes MVs generation in those patients. The involvement of p38 MAPK in MVs-induced cell metastasis has also been highlighted in the present study. Blockade of Rab5a activation can be a potential therapeutic approach to restrict MVs shedding and associated breast cancer metastasis.

A Potent Antagonist of Protease-Activated Receptor 2 That Inhibits Multiple Signaling Functions in Human Cancer Cells

Protease-activated receptor 2 (PAR2) is a cell surface protein linked to G-protein dependent and independent intracellular signaling pathways that produce a wide range of physiological responses, including those related to metabolism, inflammation, pain, and cancer. Certain proteases, peptides, and nonpeptides are known to potently activate PAR2. However, no effective potent PAR2 antagonists have been reported yet despite their anticipated therapeutic potential. This study investigates antagonism of key PAR2-dependent signaling properties and functions by the imidazopyridazine compound I-191 (4-(8-(tert-butyl)-6-(4-fluorophenyl)imidazo[1,2-b]pyridazine-2-carbonyl)-3,3-dimethylpiperazin-2-one) in cancer cells. At nanomolar concentrations, I-191 inhibited PAR2 binding of and activation by structurally distinct PAR2 agonists (trypsin, peptide, nonpeptide) in a concentration-dependent manner in cells of the human colon adenocarcinoma grade II cell line (HT29). I-191 potently attenuated multiple PAR2-mediated intracellular signaling pathways leading to Ca²⁺ release, extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation, Ras homologue gene family, member A (RhoA) activation, and inhibition of forskolin-induced cAMP accumulation. The mechanism of action of I-191 was investigated using binding and calcium mobilization studies in HT29 cells where I-191 was shown to be noncompetitive and a negative allosteric modulator of the agonist 2f-LIGRL-NH₂ The compound alone did not activate these PAR2-mediated pathways, even at high micromolar concentrations, indicating no bias in these signaling properties. I-191 also potently inhibited PAR2-mediated downstream functional responses, including expression and secretion of inflammatory cytokines and cell apoptosis and migration, in human colon adenocarcinoma grade II cell line (HT29) and human breast adenocarcinoma cells (MDA-MB-231). These findings indicate that I-191 is a potent PAR2 antagonist that inhibits multiple PAR2-induced signaling pathways and functional responses. I-191 may be a valuable tool for characterizing PAR2 functions in cancer and in other cellular, physiological, and disease settings.

Tumor necrosis factor α decreases aquaporin 3 expression in intestinal epithelial cells through inhibition of constitutive transcription

Inflammatory diseases of the gut are associated with altered electrolyte and water transport, leading to the development of diarrhea. Epithelially expressed aquaporins (AQPs) are downregulated in inflammation, although the mechanisms involved are not known. We hypothesized that AQP3 expression in intestinal epithelial cells is altered in intestinal inflammation and that these changes are driven by tumor necrosis factor (TNF) α. Human colonic adenocarcinoma (HT‐29) cells were treated with TNFα to investigate signaling mechanisms in vitro. AQP3 expression was assessed by real‐time PCR and radiolabeled glycerol uptake, with select inhibitors and a luciferase reporter construct used to further elucidate intracellular signaling. AQP3 expression was downregulated in HT‐29 cells treated with TNFα. Luciferase reporter construct experiments revealed that TNFα downregulated constitutive transcriptional activity of the AQP3 promoter, and inhibition of MEK/ERK and nuclear factor κB (NF‐κB) signaling prevented the decrease in AQP3 mRNA expression. Constitutive AQP3 expression was suppressed by specificity protein (Sp) 3, and knockdown of this transcription factor bound to the AQP3 promoter was able to partially prevent the TNFα‐induced downregulation of AQP3. TNFα signals through MEK/ERK and NF‐κB to enhance the negative transcriptional control of AQP3 expression exerted by Sp3. Similar mechanisms regulate numerous ion channels, suggesting a common mechanism by which both ion and water transport are altered in inflammation.

Biased Signaling by Agonists of Protease Activated Receptor 2

Protease activated receptor 2 (PAR2) is associated with metabolism, obesity, inflammatory, respiratory and gastrointestinal disorders, pain, cancer, and other diseases. The extracellular N-terminus of PAR2 is a common target for multiple proteases, which cleave it at different sites to generate different N-termini that activate different PAR2-mediated intracellular signaling pathways. There are no synthetic PAR2 ligands that reproduce the same signaling profiles and potencies as proteases. Structure-activity relationships here for 26 compounds spanned a signaling bias over 3 log units, culminating in three small ligands as biased agonist tools for interrogating PAR2 functions. DF253 (2f-LAAAAI-NH₂) triggered PAR2-mediated calcium release (EC₅₀ 2 μM) but not ERK1/2 phosphorylation (EC₅₀ > 100 μM) in CHO cells transfected with hPAR2. AY77 (Isox-Cha-Chg-NH₂) was a more potent calcium-biased agonist (EC₅₀ 40 nM, Ca²⁺; EC₅₀ 2 μM, ERK1/2), while its analogue AY254 (Isox-Cha-Chg-A-R-NH₂) was an ERK-biased agonist (EC₅₀ 2 nM, ERK1/2; EC₅₀ 80 nM, Ca²⁺). Signaling bias led to different functional responses in human colorectal carcinoma cells (HT29). AY254, but not AY77 or DF253, attenuated cytokine-induced caspase 3/8 activation, promoted scratch-wound healing, and induced IL-8 secretion, all via PAR2-ERK1/2 signaling. Different ligand components were responsible for different PAR2 signaling and functions, clues that can potentially lead to drugs that modulate different pathway-selective cellular and physiological responses.

Functional inhibition of PAR2 alleviates allergen-induced airway hyperresponsiveness and inflammation

BACKGROUND

Proteinase-activated receptor 2 (PAR2 ) is a G protein-coupled receptor activated by trypsin-like serine proteinases. PAR2 activation has been associated with inflammation including allergic airway inflammation. We have also shown that PAR2 activation in the airways leads to allergic sensitization. The exact contribution of PAR2 in the development of eosinophilic inflammation and airway hyperresponsiveness (AHR) in sensitized individuals is not clear.

OBJECTIVE

To investigate whether functional inhibition of PAR2 during allergen challenge of allergic mice would inhibit allergen-induced AHR and inflammation in mouse models of asthma.

METHODS

Mice were sensitized and challenged with ovalbumin (OVA) or cockroach extract (CE). To investigate the role of PAR2 in the development of AHR and airway inflammation, we administered blocking anti-PAR2 antibodies, or a cell permeable peptide inhibitor of PAR2 signalling, pepducin, i.n. before allergen challenges and then assessed AHR and airway inflammation.

RESULTS

Administration of anti-PAR2 antibodies significantly inhibited OVA- and CE-induced AHR and airway inflammation. In particular, two anti-PAR2 antibodies, the monoclonal SAM-11 and polyclonal B5, inhibited AHR, airway eosinophilia, the increase of cytokines in the lung tissue and antigen-specific T cell proliferation, but had no effect on antigen-specific IgG and IgE levels. Pepducin was also effective in inhibiting AHR and airway inflammation in an OVA model of allergic airway inflammation.

CONCLUSIONS AND CLINICAL RELEVANCE

Functional blockade of PAR2 in the airways during allergen challenge improves allergen-induced AHR and inflammation in mice. Therefore, topical PAR2 blockade in the airways, through anti-PAR2 antibodies or molecules that interrupt PAR2 signalling, has the potential to be used as a therapeutic option in allergic asthma.

The serine protease-mediated increase in intestinal epithelial barrier function is dependent on occludin and requires an intact tight junction

Barrier dysfunction is a characteristic of the inflammatory bowel diseases (IBD), Crohn's disease and ulcerative colitis. Understanding how the tight junction is modified to maintain barrier function may provide avenues for treatment of IBD. We have previously shown that the apical addition of serine proteases to intestinal epithelial cell lines causes a rapid and sustained increase in transepithelial electrical resistance (TER), but the mechanisms are unknown. We hypothesized that serine proteases increase barrier function through trafficking and insertion of tight junction proteins into the membrane, and this could enhance recovery of a disrupted monolayer after calcium switch or cytokine treatment. In the canine epithelial cell line, SCBN, we showed that matriptase, an endogenous serine protease, could potently increase TER. Using detergent solubility-based cell fractionation, we found that neither trypsin nor matriptase treatment changed levels of tight junction proteins at the membrane. In a fast calcium switch assay, serine proteases did not enhance the rate of recovery of the junction. In addition, serine proteases could not reverse barrier disruption induced by IFNγ and TNFα. We knocked down occludin in our cells using siRNA and found this prevented the serine protease-induced increase in TER. Using fluorescence recovery after photobleaching (FRAP), we found serine proteases induce a greater mobile fraction of occludin in the membrane. These data suggest that a functional tight junction is needed for serine proteases to have an effect on TER, and that occludin is a crucial tight junction protein in this mechanism.

PAR2-dependent activation of GSK3β regulates the survival of colon stem/progenitor cells

Protease-activated receptors PAR1 and PAR2 play an important role in the control of epithelial cell proliferation and migration. However, the survival of normal and tumor intestinal stem/progenitor cells promoted by proinflammatory mediators may be critical in oncogenesis. The glycogen synthase kinase-3β (GSK3β) pathway is overactivated in colon cancer cells and promotes their survival and drug resistance. We thus aimed to determine PAR1 and PAR2 effects on normal and tumor intestinal stem/progenitor cells and whether they involved GSK3β. First, PAR1 and PAR2 were identified in colon stem/progenitor cells by immunofluorescence. In three-dimensional cultures of murine crypt units or single tumor Caco-2 cells, PAR2 activation decreased numbers and size of normal or cancerous spheroids, and PAR2-deficient spheroids showed increased proliferation, indicating that PAR2 represses proliferation. PAR2-stimulated normal cells were more resistant to stress (serum starvation or spheroid passaging), suggesting prosurvival effects of PAR2 Accordingly, active caspase-3 was strongly increased in PAR2-deficient normal spheroids. PAR2 but not PAR1 triggered GSK3β activation through serine-9 dephosphorylation in normal and tumor cells. The PAR2-triggered GSK3β activation implicates an arrestin/PP2A/GSK3β complex that is dependent on the Rho kinase activity. Loss of PAR2 was associated with high levels of GSK3β nonactive form, strengthening the role of PAR2 in GSK3β activation. GSK3 pharmacological inhibition impaired the survival of PAR2-stimulated spheroids and serum-starved cells. Altogether our data identify PAR2/GSK3β as a novel pathway that plays a critical role in the regulation of stem/progenitor cell survival and proliferation in normal colon crypts and colon cancer.

Protease activated receptor 2 (PAR2) modulators: a patent review (2010-2015)

INTRODUCTION

Protease activated receptor 2 (PAR2) is a self-activated G protein-coupled receptor that has been implicated in several diseases, including inflammatory, gastrointestinal, respiratory, metabolic diseases, cancers and others, making it an important prospective drug target. No known endogenous ligands are available for PAR2, so having potent exogenous agonists and antagonists can be helpful for studying physiological functions of PAR2.

AREAS COVERED

This review covers agonist-, antagonist-, antibody- and pepducin-based modulators of PAR2 reported in patent applications between 2010-2015, along with their available structure-activity relationships, biological activities and potential uses for studying PAR2.

EXPERT OPINION

In the last six years, substantial efforts were made towards developing PAR2 modulators, but most lack potency or selectivity or have poor pharmacokinetic profiles. Many PAR2 modulators were assessed by measuring Gαq protein-mediated calcium release in cells. This may be insufficient to fully characterize ligand function, since different ligands signal through PAR2 via multiple signaling pathways. It may be feasible to develop biased ligands as drugs that can selectively modulate one or more specific signaling pathways linking PAR2 to a specific diseased state. Accordingly, potent, orally bioavailable, pathway- and receptor-selective PAR2 modulators may be an achievable goal to realizing effective drugs that can treat PAR2-mediated diseases.

Effect of knockdown or overexpression of heat shock transcription factor 2 on apoptosis and migration of human colonic epithelial cells

AIM: To explore the role of heat shock transcription factor 2 (HSF2) in cell apoptosis and migration in human colonic epithelial cell line HT-29 by means of interference and overexpression.

METHODS: Apoptosis of HT-29 cells was induced by incubation with sodium butyrate (SB) for different durations. Cytotoxicity was estimated by MTT assay, and the cell cycle and apoptosis were observed by flow cytometry to choose the optimal time and concentration of SB. HT-29 cells were then transfected with HSF2 siRNA or a lentiviral vector (Ubi-MCS-3FLAG-SV40-EGFP). The overexpression or knockdown of HSF2 was detected by Leica DMIRB and Western blot. After transfection, cell migration ability was measured by wound healing assay and Transwell assay. Apoptosis of HT-29 cells was induced with SB after transfection, cell proliferation was studied by MTT assay, and cell cycle and apoptosis were observed by flow cytometry.

RESULTS: Compared with the negative control (NC) group, SB at 2.5, 5.0, or 10 mmol/L could significantly cause growth inhibition after 48 h of incubation (P < 0.01), and the effect was time- and dose-dependent. The apoptosis rate was significantly higher in the SB treated groups (1.25, 2.5, 5.0, or 10 mmol/L for 48 h) than in the NC group (51.588% ± 5.110%, 77.732% ± 2.746%, 90.115% ± 1.438%, 94.247% ± 1.243% vs 0.548% ± 0.113%, P < 0.01). When the SB concentration was>2.5 mmol/L, the apoptosis rate increased significantly (P < 0.01). When treated with 1.25 mmol/L SB for 48 h, the percentage of cells in G₀/G₁ phase cell did not show a significant difference compared with the NC group; when the concentration was > 2.5 mmol/L (5.0 or 10.0 mmol/L), SB could induce G₁/G₀ arrest (P < 0.01). After lentiviral transfection, a large number of HT-29 cells with green fluorescence was observed by Leica DMIRB (transfection efficiency>80%). Lentiviral transfection of siRNA could effectively inhibit expression of HSF2, while lentiviral transfection of Ubi-MCS-3FLAG-SV40-EGFP induced overexpression of HSF2. HSF2 overexpression significantly increased cell proliferation and migration compared with the empty vector treated group (P < 0.05), while HSF2 knockdown significantly inhibited the proliferation and migration of HT-29 cells compared with the negative siRNA group (P < 0.05). HSF2 overexpression or knockdown had no significant impact on cell cycle distribution. HSF2 overexpression significantly decreased cell apoptosis rate (P < 0.05), while HSF2 knockdown significantly increased cell apoptosis rate (P < 0.05).

CONCLUSION: HSF2 might be a protective factor for epithelial cell apoptosis. HSF2 achieves the effects of cell protection possibly through the cell cycle regulation.

Hesperidin from Citrus seed induces human hepatocellular carcinoma HepG2 cell apoptosis via both mitochondrial and death receptor pathways

Citrus seeds are full of phenolic compounds, such as flavonoids. The aims of this study were to identify the types of flavonoids in Citrus seed extracts, the cytotoxic effect, mode of cell death, and signaling pathway in human hepatic cancer HepG2 cells. The flavonoids contain anticancer, free radical scavenging, and antioxidant activities. Neohesperidin, hesperidin, and naringin, active flavanone glycosides, were identified in Citrus seed extract. The cytotoxic effect of three compounds was in a dose-dependent manner, and IC50 levels were determined. The sensitivity of human HepG2 cells was as follows: hesperidin > naringin > neohesperidin > naringenin. Hesperidin induced HepG2 cells to undergo apoptosis in a dose-dependent manner as evidenced by the externalization of phosphatidylserine and determined by annexin V-fluorescein isothiocyanate and propidium iodide staining using flow cytometry. Hesperidin did not induce the generation of reactive oxygen species, which was determined by using 2',7'-dichlorohydrofluorescein diacetate and flow cytometry method. The number of hesperidin-treated HepG2 cells with the loss of mitochondrial transmembrane potential increased concentration dependently, using 3,3'-dihexyloxacarbocyanine iodide employing flow cytometry. Caspase-9, -8, and -3 activities were activated and increased in hesperidin-treated HepG2 cells. Bcl-xL protein was downregulated whereas Bax, Bak, and tBid protein levels were upregulated after treatment with hesperidin in a dose-dependent manner. In conclusion, the bioflavanone from Citrus seeds, hesperidin, induced human HepG2 cell apoptosis via mitochondrial pathway and death receptor pathway. Citrus seed flavonoids are beneficial and can be developed as anticancer drug or food supplement, which still needs further in vivo investigation in animals and human beings.

Protease-activated receptors and their biological role - focused on skin inflammation

OBJECTIVES

For several years, protease-activated receptors (PARs) are targets of science regarding to various diseases and platelet aggregation. In the past, a number of publications related to PARs have been published, which refer to a variety of aspects. An important point of view is the inflammation of the skin, which has not been reported in detail yet. This review will provide an overview of the current knowledge on PARs, and in particular, on the involvement of PARs in terms of skin inflammation.

KEY FINDINGS

Wound healing is an important step after skin injury and is connected with involvement of PARs and inflammation. An important point in skin inflammation is the coagulation-dependent skin inflammation.

SUMMARY

PARs are a special kind of receptors, being activated by proteolytic cleavage or chemical agonists. They may play an important role in various physiological processes. It is shown that the proteases are involved in many diseases for example Parkinson's disease and Alzheimer's disease. The fact, that proteases regulate the coagulation, and are involved in interleukin and cytokine release leads to the conclusion that they are involved in inflammation processes.