Protease-activated receptor-2 activation in gastric cancer cells promotes epidermal growth factor receptor trans-activation and proliferation

Proteinase-activated receptor 2 expression in breast cancer and its role in breast cancer cell migration

Proteinase-activated receptor 2 (PAR2) is a G protein-coupled receptor that is activated by trypsin-like proteinases. PAR2 is detected in breast tumor specimens; however, it is not clear how PAR2 level in breast cancer cell/tissues compares with normal cell/tissues. Here, we show the elevation of PAR2 protein level in 76 of 105 breast tumor specimens but only 5 of 24 normal breast tissues. PAR2 level is also higher in breast cancer cell lines than that in normal breast cells and non-cancerous breast cell lines. To determine the role of PAR2 in breast carcinogenesis, we examined the effect of PAR2 agonists on cell proliferation and migration. Our studies show that PAR2 agonists (PAR2-activating peptide and trypsin) are neither potent growth enhancers nor chemoattractants to breast cancer cells. Instead, PAR2 agonists induce significant chemokinesis. PAR2-mediated chemokinesis is G(alphai)-dependent, and inhibiting Src kinase activity or silencing c-Src expression blocks PAR2-mediated chemokinesis. These results suggest that c-Src works downstream of G(alphai) to mediate this PAR2 agonist-induced event. To characterize c-Src effector, we reveal that PAR2 agonists activate JNKs in a Src-dependent manner and that JNK activity is essential for PAR2-mediated chemokinesis. Moreover, PAR2 agonist stimulation leads to paxillin Ser(178) phosphorylation and paxillin(S178A) mutant inhibits PAR2-mediated chemokinesis. In conclusion, our studies show that PAR2 agonists facilitate breast cancer cell chemokinesis through the G(alphai)-c-Src-JNK-paxillin signaling pathway.

Protease-activated receptor-1 is upregulated in reactive stroma of primary prostate cancer and bone metastasis

BACKGROUND

Prostate cancer progression is partly facilitated by tumor-stroma interactions. We recently reported that protease-activated receptors (PAR-1 and PAR-2) are overexpressed in prostate cancer, and PAR-1 expression in peritumoral stroma is associated with biochemical recurrence. However, the nature of PAR expression in prostate tumor microenvironment is not fully understood. We therefore evaluated PAR-1 and PAR-2 expression in primary prostate cancer and bone metastasis.

METHODS

PAR-1 and PAR-2 expression in normal, primary prostate cancer and the corresponding bone metastatic tissues were examined by immunohistochemistry, and double-label immunohistochemistry with the use of additional markers.

RESULTS

PAR-1 was expressed in peritumoral stroma in the majority of primary cancer tissues (83%). Serial sections and double-label immunohistochemistry determined that these PAR-1 expressing stromal cells were predominantly myofibroblasts, the primary cell type in reactive stroma. Analysis of cancer glands revealed that PAR-1 expression was significantly increased in the reactive stroma around higher Gleason grade cancers. PAR-2 was predominantly expressed in the primary cancer cells as well as smooth muscle cells but not in reactive stroma. In bone metastasis, PAR-1 expression in cancer cells was elevated compared to the primary site from the same patient. In the bone reactive stroma, PAR-1 was present in vascular endothelial cells and fibroblasts, while both PAR-1 and PAR-2 were expressed in osteoblasts and osteoclasts.

CONCLUSIONS

In primary prostate cancer and bone metastasis, PAR-1 is upregulated in reactive stroma and PAR-2 is uniformly overexpressed in carcinoma cells, suggesting these receptors may play potentially different roles in prostate cancer development and metastasis.

Role of protease activated receptor-2 in lymph node metastasis of uterine cervical cancers

BACKGROUND

Protease activated receptor-2 (PAR-2) has been implicated in cellular proliferation, invasion and metastasis in various tumors. Lymph node metastasis is an important patient prognostic factor for uterine cervical cancers. This prompted us to study the role of PAR-2 in lymph node metastasis of uterine cervical cancers.

METHODS

Thirty patients underwent surgery for uterine cervical cancers. PAR-2 histoscores and mRNA levels were determined by immunohistochemistry and real-time reverse transcription-polymerase chain reaction, respectively. Patient prognosis was analyzed with a 48-month survival rate.

RESULTS

PAR-2 histoscores and mRNA levels significantly (P < 0.05) increased in 12 of 30 metastatic lymph node lesions from the corresponding primary tumor. The 48-month survival rate of the 12 patients with increased PAR-2 levels in metastatic lymph nodes was 42%, while the rate of the other 18 patients with no change in PAR-2 levels was 82%, regardless of histopathological type.

CONCLUSION

PAR-2 might work on lymph node metastasis of uterine cervical cancers, and is considered to be a novel prognostic indicator for uterine cervical cancers.

Helicobacter pylori protein HP0175 transactivates epidermal growth factor receptor through TLR4 in gastric epithelial cells

The pathophysiology of Helicobacter pylori-associated gastroduodenal diseases, ulcerogenesis, and carcinogenesis is intimately linked to activation of epidermal growth factor receptor (EGFR) and production of vascular endothelial growth factor (VEGF). Extracellular virulence factors, such as CagA and VacA, have been proposed to regulate EGFR activation and VEGF production in gastric epithelial cells. We demonstrate that the H. pylori secretory protein, HP0175, by virtue of its ability to bind TLR4, transactivates EGFR and stimulates EGFR-dependent VEGF production in the gastric cancer cell line AGS. Knock-out of the hp0175 gene attenuates the ability of the resultant H. pylori strain to activate EGFR or to induce VEGF production. HP0175-induced activation of EGFR is preceded by translocation of TLR4 into lipid rafts. In lipid rafts, the Src kinase family member Lyn interacts with TLR4, leading to tyrosine phosphorylation of TLR4. Knockdown of Lyn prevents HP0175-induced activation of EGFR and VEGF production. Tyrosine-phosphorylated TLR4 interacts with EGFR. This interaction is necessary for the activation of EGFR. Disruption of lipid rafts with methyl beta-cyclodextrin prevents HP0175-induced tyrosine phosphorylation of TLR4 and activation of EGFR. This mechanism of transactivation of EGFR is novel and distinct from that of metalloprotease-dependent shedding of EGF-like ligands, leading to autocrine activation of EGFR. It provides new insight into our understanding of the receptor cross-talk network.

Proteinase-activated receptor 2 (PAR-2) in gastrointestinal and pancreatic pathophysiology, inflammation and neoplasia

Of all the body systems, the gastrointestinal (GI) tract is the most exposed to proteinases. Proteolytic activity must thus be tightly regulated in the face of diverse environmental challenges, because unrestrained or excessive proteolysis leads to pathological GI conditions. The protease-activated receptor-2 (PAR-2) is expressed in numerous cell types within the GI tract, suggesting both multiple functions and numerous modes of receptor activation. Although best known as a pancreatic digestive enzyme, trypsin has also been found in other tissues and various cancers. Of interest, trypsin and PAR-2 act together in an autocrine loop that promotes proliferation, invasion and metastasis in neoplasia through various mechanisms. Trypsin and PAR-2 seem to act both directly and indirectly through activation of other proteinase cascades, including metalloproteinases. PAR-2 activation can participate in inflammatory reactions, be protective to mucosal surfaces, send or inhibit nociceptive messages, modify gut motility or secretory functions, and stimulate cell proliferation and motility. Several studies point to a role for the PARs in disease processes of the GI tract and pancreas ranging from inflammatory bowel disease, symptoms associated with irritable bowel syndrome, pain in pancreatitis, development of colon and other GI cancers, and even infectious colitis. Proteinases should not only be considered from the traditional view as digestive or degradative enzymes in the gut, but additionally as signalling molecules that actively participate in the spectrum of physiology and diseased states of the GI tract.

Protease-activated receptor-1 upregulates fibroblast growth factor 7 in stroma of benign prostatic hyperplasia

BACKGROUND

Benign prostatic hyperplasia (BPH) is characterized by abnormal epithelial and stromal proliferation causing urinary obstruction. Prostate growth is regulated by a variety of growth factors secreted from the stroma, including fibroblast growth factor 7 (FGF-7), a potent epithelial-specific growth factor which is increased in hyperplastic prostate. However, the mediator(s) of FGF-7 over-expression is unclear. Protease-activated receptor-1 (PAR-1) is a G-protein coupled receptor known to induce multiple biological processes, but its effect on BPH pathogenesis is mostly unknown. The aim of this study was to investigate the role of PAR-1 as a mediator of BPH development.

METHODS

PAR-1 expression was investigated in BPH and normal prostate tissues by immunohistochemistry. Prostate stromal cells were isolated from BPH specimens, cultured and immunohistochemically characterized. Cultured stromal cells were stimulated with PAR-1 agonists, and extracellular-signal regulated kinase (ERK1/2) activation and cell proliferation were examined. PAR-1 mediated FGF-7 production by cultured stromal cells was assessed by RT-PCR and immunoassays, and verified by small interfering RNA (siRNA).

RESULTS

PAR-1 expression was increased in BPH stroma. In stromal cells isolated from BPH tissues, PAR-1 agonists activated ERK1/2 in a time- and concentration-dependent manner and with resultant enhanced cell proliferation. Pertussis toxin-sensitive G protein/(betagamma-subunits)-phosphatidylinositol 3-kinase and protein kinase C pathways were involved in ERK1/2 phosphorylation. PAR-1 activation strikingly induced FGF-7 production from cultured stromal cells mediated predominantly via ERK1/2 signaling pathway, and PAR-1 siRNA decreased the elicited FGF-7 upregulation.

CONCLUSIONS

The expression and function of PAR-1 in BPH stroma indicate PAR-1 may play important roles in BPH pathogenesis.

TF/FVIIa Transactivate PDGFRβ to Regulate PDGF-BB–Induced Chemotaxis in Different Cell Types

Background— We have previously reported the potentiation of PDGF-BB–induced chemotaxis of fibroblasts, vascular smooth muscle cells, and endothelial cells by FVIIa. Here we studied the role of TF/FVIIa and the induced signaling pathways in regulation of chemotaxis of human monocytes, fibroblasts, and porcine aorta endothelial cells.

Methods and Results— Human monocytes were obtained by using Ficoll-Paque gradient and the MACS system (for highly purified population), fibroblasts and PAE cells have been characterized previously. Inhibitors of selected signaling intermediates were used, and the effect of TF/FVIIa on the migratory response of all cells to chemotactic agents was analyzed. The induced signaling was studied by immunoprecipitation and Western blotting. TF/FVIIa complex selectively enhanced PDGF-BB–induced chemotaxis in a Src-family, PLC, and PAR-2–dependent manner. Using PAE cells we identified c-Src and c-Yes as the Src-family members activated by TF/FVIIa. We report for the first time the PAR-2 and Src family-dependent transactivation of PDGFRβ by TF/FVIIa involving phosphorylation of a subset of PDGFRβ tyrosines.

Conclusions— The described transactivation is a likely mechanism of TF/FVIIa-mediated regulation of PDGF-BB–induced chemotaxis. Similar behavior of 3 principally different cell types in our experimental setup may reflect a general function of TF in regulation of cell migration.

Role of protease activated receptor-2 in tumor advancement of ovarian cancers

BACKGROUND

Protease activated receptor-2 (PAR-2) has been implicated in cellular proliferation, invasion and metastasis with angiogenesis in various tumors. This prompted us to study the role of PAR-2 in tumor advancement of ovarian cancers.

MATERIALS AND METHODS

Forty-eight patients underwent surgery for ovarian cancers. In ovarian cancers, PAR-2 histoscores and mRNA levels were determined by immunohistochemistry and real-time reverse transcription-polymerase chain reaction, respectively. Patient prognosis was analysed with a 36-month survival rate. Microvessel counts were determined by immunohistochemistry for CD31 and factor VIII-related antigen and the rate of cell proliferation was determined by immunohistochemistry for Ki67.

RESULTS

Immunohistochemical staining revealed distribution of PAR-2, dominantly in cancer cells and faintly in stromal cells of the tumor. PAR-2 histoscores in cancer cells and mRNA levels both significantly increased in ovarian cancers with clinical stages (I < II < III < IV, P < 0.05), regardless of histopathological type. The 36-month survival rate of 24 patients with high PAR-2 was poor (58%), while that of the other 24 patients with low PAR-2 was significantly higher (83%). There were significant correlations between PAR-2 histoscores in cancer cells and mRNA levels with microvessel counts and with the rate of cell proliferation in ovarian cancers.

CONCLUSIONS

PAR-2 was up-regulated during ovarian cancer progression. Therefore, PAR-2 might work on tumor advancement of ovarian cancers via angiogenic activity and is considered to be a novel prognostic indicator in ovarian cancers.

Protease-activated receptor signalling, endocytic sorting and dysregulation in cancer

Protease-activated receptors (PARs) are G-protein-coupled receptors (GPCRs) that are activated by a unique proteolytic mechanism. PARs play crucial roles in hemostasis and thrombosis, as well as in inflammation and vascular development. Coagulant proteases, which are generated at sites of vascular injury, act mainly through PARs to elicit signalling in a variety of cell types. Since PARs are irreversibly activated signalling must be tightly regulated. Desensitization and trafficking of proteolytically activated PARs control the magnitude, duration and spatial aspects of receptor signalling. Recent studies have revealed novel endocytic sorting mechanisms that regulate PAR signalling. PARs have also been implicated in tumor progression. PARs are overexpressed in several types of malignant cancer, transmit signals in response to tumor-generated proteases and promote tumor growth, invasion and metastasis. Recent work also indicates that matrix metalloprotease 1 (MMP-1) signals through PAR1 to promote tumor growth and invasion. In addition to PAR overexpression, tumor cells display aberrant PAR1 trafficking, which causes persistent signalling and cellular invasion. Thus, a novel type of gain-of-function in GPCR signalling in cancer can be acquired through dysregulation of receptor trafficking.

Gastrointestinal roles for proteinase-activated receptors in health and disease

It has been almost a decade since the molecular cloning of all four members of the proteinase-activated receptor (PAR) family was completed. This unique family of G protein-coupled receptors (GPCRs) mediates specific cellular actions of various endogenous proteinases including thrombin, trypsin, tryptase, etc. and also certain exogenous enzymes. Increasing evidence has been clarifying the emerging roles played by PARs in health and disease. PARs, particularly PAR1 and PAR2, are distributed throughout the gastrointestinal (GI) tract, modulating various GI functions. One of the most important GI functions of PARs is regulation of exocrine secretion in the salivary glands, pancreas and GI mucosal epithelium. PARs also modulate motility of GI smooth muscle, involving multiple mechanisms. PAR2 appears to play dual roles in pancreatitis and related pain, being pro-inflammatory/pro-nociceptive and anti-inflammatory/anti-nociceptive. Similarly, dual roles for PAR1 and PAR2 have been demonstrated in mucosal inflammation/damage throughout the GI tract. There is also fundamental and clinical evidence for involvement of PAR2 in colonic pain. PARs are thus considered key molecules in regulation of GI functions and targets for development of drugs for treatment of various GI diseases.

Proteinase-activated receptor-2 induces cyclooxygenase-2 expression through beta-catenin and cyclic AMP-response element-binding protein

Chronic inflammation of mucosae is associated with an increased cancer risk. Tumorigenesis in these tissues is associated with the activity of some proteinases, cyclooxygenase-2 (COX-2), and beta-catenin. Serine proteinases participate in both inflammation and tumorigenesis through the activation of proteinase-activated receptor-2 (PAR(2)), which up-regulates COX-2 by an unknown mechanism. We sought to determine whether beta-catenin participated in PAR(2)-induced COX-2 expression and through what cellular mechanism. In A549 epithelial cells, we showed that PAR(2) activation increased COX-2 expression through the beta-catenin/T cell factor transcription pathway. This effect was dependent upon ERK1/2 MAPK, which inhibited the beta-catenin-regulating protein, glycogen synthase kinase-3beta, and induced the activity of the cAMP-response element-binding protein (CREB). Knockdown of CREB by small interfering RNA revealed that PAR(2)-induced beta-catenin transcriptional activity and COX-2 expression were CREB-dependent. A co-immunoprecipitation assay revealed a physical interaction between CREB and beta-catenin. Thus, PAR(2) up-regulated COX-2 expression via an ERK1/2-mediated activation of the beta-catenin/Tcf-4 and CREB pathways. These findings reveal new cellular mechanisms by which serine proteinases may participate in tumor development and are particularly relevant to cancers associated with chronic mucosal inflammation, where serine proteinases are abundant and COX-2 overexpression is a common feature.

Protease-activated receptor-2 (PAR-2) in cervical cancer proliferation

OBJECTIVE

Protease-activated receptor-2 (PAR-2) is a G-protein-coupled receptor that is cleaved and activated by trypsin and tryptase. There is evidence that PAR-2 contributes to tumor progression in stomach, colon, pancreas, prostate and breast cancer patients. However, the role of PAR-2 in cervical cancer is still unknown. The aim of this work was to study the PAR-2 expression in cervical cancer tissues and the effect of PAR-2 activation on cervical cancer proliferation.

METHODS

Immunohistochemistry was used to analyze PAR-2 expression in fixed paraffin-embedded tumor tissue from 16 patients with invasive cervical cancer. HPV types were identified by PCR. PAR-2 expression in UISO-SQC-1, HeLa, SiHa, CasKi and C-33 A cervical cancer cell lines was evaluated by flow cytometry. Trypsin was detected by Western blot. Tumor proliferation in response to trypsin or agonist peptide was evaluated by the MTT method.

RESULTS

A strong correlation between trypsin and PAR-2 expression in five cervical cancer cell lines, in association with proliferative growth in the presence of trypsin or agonist peptide, was found. All tumors from cervical cancer patients expressed PAR-2 (immunoreactive score was higher in poorly differentiated tumors).

CONCLUSIONS

Results suggest that trypsin and PAR-2 are involved in cervical cancer cell proliferation.

A refined agonist pharmacophore for protease activated receptor 2

Protease activated receptor 2 (PAR(2)) is a G protein-coupled receptor implicated in inflammation and cancer. Only a few peptide agonists are known with greater potency than the native agonist SLIGRL-NH(2). Here we report 52 peptide agonists of PAR(2), 26 with activity at sub-micromolar concentrations, and one being iodinated for radioligand experiments. Potency was highest when the N- or C-termini of SLIGRL-NH(2) were modified, pointing to a new ligand pharmacophore model that may aid development of drug-like PAR(2) modulators.

A novel therapeutic target in various lung diseases: Airway proteases and protease-activated receptors

Protease-activated receptors (PAR), which are G protein-coupled receptors, have 4 members, PAR-1 to PAR-4. PARs are activated by proteolysis of a peptide bond at the N-terminal domain of the receptor. PARs are widely distributed throughout the airways. Their activity is modulated by airway proteases of endogenous and exogenous origin, which can either activate or disable the receptors. The regulation of PAR activity by proteases is important under pathological conditions when the activity of proteases is increased. Moreover, various inflammatory mediators, such as cytokines, growth factors, or prostanoids, alter the PAR expression level. Elevated PAR levels are observed in various lung disorders, and their significance in the development of pathological situations in the lung is currently intensively investigated. Consequences of PAR activation can be either beneficial or deleterious, depending on the PAR subtype. PAR-1 has been shown to be an important player in the development of pulmonary fibrosis. Thus, PAR-1 represents an exciting target for clinical intervention in fibrotic diseases. PAR-2 contributes to allergic airway inflammation. However, the question whether the impact of PAR-2 is beneficial or deleterious is still under intensive discussion. Therefore, precise information concerning the participation of PAR-2 in various lesions is required. Moreover, it is necessary to generate selective PAR- and organ-targeted approaches for treating the diseases. A thorough understanding of PAR-induced cellular events and the consequences of receptor blockade may help in the development of novel therapeutic strategies targeted to prevent lung destruction and to avoid deterioration of conditions of patients with inflammatory or fibrotic lung diseases.

Histamine stimulation of MMP-1(collagenase-1) secretion and gene expression in gastric epithelial cells: role of EGFR transactivation and the MAP kinase pathway

BACKGROUND AND AIMS

GPCR stimulation by various ligands including histamine has been shown to transactivate the epidermal growth factor receptor (EGFR). This study examines the functional interactions between the H2 receptor and the EGFR in the regulation of matrix metalloproteinase-1 (MMP-1) secretion and gene expressions in cultured gastric epithelial cells.

METHODS

AGS cells were incubated for up to 24 h with either histamine or heparin binding-epidermal growth factor (HB-EGF) and MMP-1 release was determined by immunoassay. MMP-1 responses to histamine and HB-EGF were further tested by the use of H2 receptor antagonist, EGFR inhibitor and mitogen activator protein kinase (MAPK) inhibitor. The role of EGFR in MMP-1 release was further tested in cells transfected with specific EGFR siRNA. EGFR and ERK1/2 phosphorylation was determined by Western blot analysis. MMP-1 gene expression was determined by RNase protection assay (RPA).

RESULTS

Histamine and HB-EGF caused a dose-dependent release of MMP-1 with maximal responses that were 2.7- and 4.5-fold greater, respectively, than control, P<0.001. Famotidine prevented histamine-mediated MMP-1 release and AG1478 and EGFR siRNA completely inhibited MMP-1 secretion stimulated by both histamine and HB-EGF. Both histamine and HB-EGF stimulation of MMP-1 release was associated with activation of ERK1/2. MAPK inhibition also prevented histamine-and HB-EGF-induced MMP-1 secretion. Results of MMP-1 gene expression, either stimulatory or inhibitory, paralleled responses to MMP-1 secretion.

CONCLUSION

Histamine stimulation of the H2 receptor on AGS cells evoked MMP-1 secretion and gene up regulation that was dependent on transactivation of the EGFR and downstream activation of MAPK.

Proteinase-activated receptor 4 stimulation-induced epithelial-mesenchymal transition in alveolar epithelial cells

BACKGROUND

Proteinase-activated receptors (PARs; PAR1-4) that can be activated by serine proteinases such as thrombin and neutrophil catepsin G are known to contribute to the pathogenesis of various pulmonary diseases including fibrosis. Among these PARs, especially PAR4, a newly identified subtype, is highly expressed in the lung. Here, we examined whether PAR4 stimulation plays a role in the formation of fibrotic response in the lung, through alveolar epithelial-mesenchymal transition (EMT) which contributes to the increase in myofibroblast population.

METHODS

EMT was assessed by measuring the changes in each specific cell markers, E-cadherin for epithelial cell, alpha-smooth muscle actin (alpha-SMA) for myofibroblast, using primary cultured mouse alveolar epithelial cells and human lung carcinoma-derived alveolar epithelial cell line (A549 cells).

RESULTS

Stimulation of PAR with thrombin (1 U/ml) or a synthetic PAR4 agonist peptide (AYPGKF-NH2, 100 muM) for 72 h induced morphological changes from cobblestone-like structure to elongated shape in primary cultured alveolar epithelial cells and A549 cells. In immunocytochemical analyses of these cells, such PAR4 stimulation decreased E-cadherin-like immunoreactivity and increased alpha-SMA-like immunoreactivity, as observed with a typical EMT-inducer, tumor growth factor-beta (TGF-beta). Western blot analyses of PAR4-stimulated A549 cells also showed similar changes in expression of these EMT-related marker proteins. Such PAR4-mediated changes were attenuated by inhibitors of epidermal growth factor receptor (EGFR) kinase and Src. PAR4-mediated morphological changes in primary cultured alveolar epithelial cells were reduced in the presence of these inhibitors. PAR4 stimulation increased tyrosine phosphorylated EGFR or tyrosine phosphorylated Src level in A549 cells, and the former response being inhibited by Src inhibitor.

CONCLUSION

PAR4 stimulation of alveolar epithelial cells induced epithelial-mesenchymal transition (EMT) as monitored by cell shapes, and epithelial or myofibroblast marker at least partly through EGFR transactivation via receptor-linked Src activation.

New developments in the relationship between protease activated recerptor-2 and alimentary system diseases

Protease-activated receptor-2 (PAR-2) is a G-protein-coupled receptor, and its special molecule structure and activation way are similar to other protease-activated receptors. PAR-2 is widely distributed in alimentary system and series of effects are produced when it is activated by certain proteases. For example, PAR-2 exerts gastric mucosal cytoprotective effect, influences the secretion of digestive glands and movement of gastrointestinal tract, participates in the development of pancreatitis, and associates closely with malignant tumors in alimentary system. More and more researches are now focusing on the relationship between PAR-2 and alimentary system diseases.