RNA interference-based silencing reveals the regulatory role of fatty acid-binding protein 4 in the production of IL-6 and vascular endothelial growth factor in 3T3-L1 adipocytes

The fatty acid-binding protein 4 (FABP4) is believed to play an important role in maintaining glucose and lipid homeostasis. However, the physiological functions of FABP4 in adipocytes have not been fully elucidated because of difficulties associated with the effective transfection of small interfering RNA (siRNA) to differentiated adipocytes. The aim of this study was to clarify the physiological roles of FABP4 in adipocytes by establishing an efficient, universal technique for endogenous gene silencing in fully differentiated 3T3-L1 cells. Confocal-based three-dimensional observations demonstrated that, in traditionally cultured 3T3-L1 cells, multilayers of undifferentiated cells were formed. As a result, small interfering RNA failed to reach many of the differentiated cells. To solve this problem, we developed a reliable method, denoted as density-based separation followed by replating of enriched adipocytes in a monolayer (DREAM) and, using the developed method, succeeded in a significant knockdown of FABP4. Loss-of-function analyses revealed that FABP4 regulates the expression of IL-6 and vascular endothelial growth factor (VEGF) mediated by the protease-activated receptor 1 (PAR1), a thrombin receptor, in adipocytes. In addition, the basal IL-6 production was partially suppressed by PAR1 knockdown. Moreover, we also demonstrated that IL-6 stimulates the proliferation of primary endothelial cells isolated from murine adipose tissue. These findings indicate that FABP4 may have a crucial role in modulating IL-6 and vascular endothelial growth factor as angiogenesis inducers stimulated by the cellular action of thrombin on adipocytes via PAR1. These findings promise to be helpful for developing an understanding of physiological counterparts with respect to the inflammatory and angiogenic properties of adipose tissue.

PAR-1 polymorphisms and risk of Helicobacter pylori-related gastric cancer in a Chinese population

BACKGROUND

PAR-1 has been involved in inflammation of the gastrointestinal tract, tumour cell growth and invasion of gastric carcinoma cells. Thus, we aimed at determining, for the first time, the association between PAR-1 - 506 ins/del and -IVSn-14 A/T and risk of Helicobacter pylori-related gastric cancer (GC) in an ethnic Chinese population.

MATERIALS AND METHODS

A case-control study comprising of 225 ethnic Chinese individuals (77 non-cardia GC cases and 148 controls with functional dyspepsia) was conducted. PAR-1 IVSn-14 A/T and 506 ins/del were genotyped by means of real-time PCR and MALDI-TOF mass spectrometry, respectively.

RESULTS

H. pylori infection, male gender and the PAR-1 IVSn-14 TT genotype increased GC risk (OR:3.15, 95% CI:1.54-6.45, OR:2.44, 95% CI:1.35-4.42 and OR:2.58, 95% CI:1.09-6.13, respectively). PAR-1 -506 ins/del did not provide significant results.

CONCLUSION

PAR-1 IVSn-14 T allele is a risk factor for H. pylori-related GC in ethnic Chinese subjects. PAR-1 -506 ins/del polymorphism is not involved in gastric carcinogenesis.

Progesterone promotes focal adhesion formation and migration in breast cancer cells through induction of protease-activated receptor-1

Progesterone and progestins have been demonstrated to enhance breast cancer cell migration, although the mechanisms are still not fully understood. The protease-activated receptors (PARs) are a family of membrane receptors that are activated by serine proteases in the blood coagulation cascade. PAR1 (F2R) has been reported to be involved in cancer cell migration and overexpressed in breast cancer. We herein demonstrate that PAR1 mRNA and protein are upregulated by progesterone treatment of the breast cancer cell lines ZR-75 and T47D. This regulation is dependent on the progesterone receptor (PR) but does not require PR phosphorylation at serine 294 or the PR proline-rich region mPRO. The increase in PAR1 mRNA was transient, being present at 3  h and returning to basal levels at 18  h. The addition of a PAR1-activating peptide (aPAR1) to cells treated with progesterone resulted in an increase in focal adhesion (FA) formation as measured by the cellular levels of phosphorylated FA kinase. The combined but not individual treatment of progesterone and aPAR1 also markedly increased stress fiber formation and the migratory capacity of breast cancer cells. In agreement with in vitro findings, data mining from the Oncomine platform revealed that PAR1 expression was significantly upregulated in PR-positive breast tumors. Our observation that PAR1 expression and signal transduction are modulated by progesterone provides new insight into how the progestin component in hormone therapies increases the risk of breast cancer in postmenopausal women.

Protease-activated receptor-1 cleaved at R46 mediates cytoprotective effects

BACKGROUND

Activated protein C (aPC) mediates powerful cytoprotective effects through the protease-activated receptor-1 (PAR1) that translate into reduced harm in mouse injury models. However, it remains elusive how aPC-activated PAR1 can mediate cytoprotective effects whereas thrombin activation does the opposite.

OBJECTIVES

We hypothesized that aPC and thrombin might induce distinct active conformations in PAR1 causing opposing effects.

METHODS

We analyzed antibody binding to, and cleavage and signalling of PAR1 in either endogenously expressing endothelial or overexpressing 293T cells.

RESULTS

In thrombin-cleaved PAR1 neither the tethered ligand nor the hirudin-like domain were available for anti-PAR1 ATAP2 and WEDE15 binding unless the tethered ligand was quenched. In contrast, aPC irreversibly prevented ATAP2 binding while not affecting WEDE15 binding. Reporter constructs with selective glutamine substitutions confirmed R41 as the only thrombin cleavage site in PAR1, whereas aPC preferentially cleaved at R46. Similarly, we report distinct cleavage sites on PAR3, K38 for thrombin and R41 for aPC. A soluble peptide corresponding to R46-cleaved PAR1 enhanced the endothelial barrier function and reduced staurosporine toxicity in endothelial as well as in 293T cells if PAR1 was expressed. Overexpression of PAR1 variants demonstrated that cleavage at R46 but not R41 is required for cytoprotective aPC signaling.

CONCLUSIONS

We provide a novel concept on how aPC and thrombin mediate distinct effects. We propose that the enzyme-specific cleavage sites induce specific conformations which mediate divergent downstream effects. This unexpected model of PAR1 signaling might lead to novel therapeutic options for the treatment of inflammatory diseases.

Developmental role of zebrafish protease-activated receptor 1 (PAR1) in the cardio-vascular system

Thrombin receptor, F2R or PAR1 is a G-protein coupled receptor, located in the membrane of endothelial cells. It has been initially found to transduce signals in hemostasis, but recently also known to act in cancer and in vascular development. Mouse embryos lacking PAR1 function die from hemorrhages with varying frequency at midgestation. We have performed a survey of potential PAR1 homologs in the zebrafish genome and identified a teleost ortholog of mammalian PAR1. Knockdown of par1 function in zebrafish embryos demonstrates a requirement for Par1 in cardio-vascular development. Furthermore, we show that function of Par1 requires the presence of a phylogenetically conserved proteolytic cleavage site and a second intracellular domain. Altogether our results demonstrate a high degree of conservation of PAR1 proteins in the vertebrate lineage in respect to amino acid sequence as well as protein function.

PAR-1 and thrombin: the ties that bind the microenvironment to melanoma metastasis

Progression of melanoma is dependent on cross-talk between tumor cells and the adjacent microenvironment. The thrombin receptor, protease-activated receptor-1 (PAR-1), plays a key role in exerting this function during melanoma progression. PAR-1 and its activating factors, which are expressed on tumor cells and the surrounding stroma, induce not only coagulation but also cell signaling, which promotes the metastatic phenotype. Several adhesion molecules, cytokines, growth factors, and proteases have recently been identified as downstream targets of PAR-1 and have been shown to modulate interactions between tumor cells and the microenvironment in the process of melanoma growth and metastasis. Inhibiting such interactions by targeting PAR-1 could potentially be a useful therapeutic modality for melanoma patients.

Activation of protease-activated receptor (PAR) 1 by frog trefoil factor (TFF) 2 and PAR4 by human TFF2

Trefoil factors (TFFs) promote epithelial cell migration to reseal superficial wounds after mucosal injury, but their receptors and the molecular mechanisms underlying this process are poorly understood. In this study, we showed that frog TFF2 activates protease-activated receptor (PAR) 1 to induce human platelet aggregation. Based on this result, we further tested the involvement of PARs in human TFF2 (hTFF2)-promoted mucosal healing. hTFF2-stimulated migration of epithelial HT-29 cells was largely inhibited by PAR4 depletion with small interfering RNAs but not by PAR1 or PAR2 depletion. The PAR4-negative epithelial cell lines AGS and LoVo were highly responsive to hTFF2 as assessed by phosphorylation of ERK1/2 and cell migration upon PAR4 expression. Our findings suggest that hTFF2 promotes cell migration via PAR4. These findings will be helpful in further investigations into the functions and molecular mechanisms of TFFs and PARs in physiology and disease.

Galectin-3 facilitates cell motility in gastric cancer by up-regulating protease-activated receptor-1 (PAR-1) and matrix metalloproteinase-1 (MMP-1)

BACKGROUND

Galectin-3 is known to regulate cancer metastasis. However, the underlying mechanism has not been defined. Through the DNA microarray studies after galectin-3 silencing, we demonstrated here that galectin-3 plays a key role in up-regulating the expressions of protease-activated receptor-1 (PAR-1) and matrix metalloproteinase-1 (MMP-1) PAR-1 thereby promoting gastric cancer metastasis.

METHODOLOGY/PRINCIPAL FINDINGS

We examined the expression levels of Galectin-3, PAR-1, and MMP-1 in gastric cancer patient tissues and also the effects of silencing these proteins with specific siRNAs and of over-expressing them using specific lenti-viral constructs. We also employed zebrafish embryo model for analysis of in vivo gastric cancer cell invasion. These studies demonstrated that: a) galectin-3 silencing decreases the expression of PAR-1. b) galectin-3 over-expression increases cell migration and invasion and this increase can be reversed by PAR-1 silencing, indicating that galectin-3 increases cell migration and invasion via PAR-1 up-regulation. c) galectin-3 directly interacts with AP-1 transcriptional factor, and this complex binds to PAR-1 promoter and drives PAR-1 transcription. d) galectin-3 also amplifies phospho-paxillin, a PAR-1 downstream target, by increasing MMP-1 expression. MMP-1 silencing blocks phospho-paxillin amplification and cell invasion caused by galectin-3 over-expression. e) Silencing of either galectin-3, PAR-1 or MMP-1 significantly reduced cell migration into the vessels in zebrafish embryo model. f) Galectin-3, PAR-1, and MMP-1 are highly expressed and co-localized in malignant tissues from gastric cancer patients.

CONCLUSIONS/SIGNIFICANCE

Galectin-3 plays the key role of activating cell surface receptor through production of protease and boosts gastric cancer metastasis. Galectin-3 has the potential to serve as a useful pharmacological target for prevention of gastric cancer metastasis.

Inhibiting metastasis of breast cancer cells in vitro using gold nanorod-siRNA delivery system

Breast cancer is the most common malignant disease in women, and it is not the primary tumor but its metastasis kills most patients with breast cancer. Anti-metastasis therapy based on RNA interference (RNAi) is emerging as one of promising strategies in tumor therapy. However, construction of an efficient delivery system for siRNA is still one of the major challenges. In this work, siRNA against protease-activated receptor-1 (PAR-1) which is a pivotal gene involved in tumor metastasis was conjugated to gold nanorods (AuNRs) via electrostatic interaction and delivered to highly metastatic human breast cancer cells. It was demonstrated that the siRNA oligos were successfully delivered into the cancer cells and mainly located in vesicle-like structures including lysosome. After transfected with the complex of AuNRs and PAR-1 siRNA (AuNRs@PAR-1 siRNA), expression of PAR-1 at both mRNA and protein levels were efficiently down regulated, as evidenced by quantitative real time PCR and flow cytometry analysis, respectively. Transwell migration assay confirmed the decrease in metastatic ability of the cancer cells. The silencing efficiency of the complex was in-between that of TurboFect and Lipofectamine, however, the cytotoxicity of the AuNRs was lower than that of the latter two. Taken together, AuNRs with PAR-1 siRNA are suited for RNAi based anti-metastasis therapy.

Statins prevent tissue factor induction by protease-activated receptors 1 and 2 in human umbilical vein endothelial cells in vitro

BACKGROUND

Protease-activated receptors (PARs) are G-protein-coupled receptors that function in hemostasis and thrombosis, as well as in the inflammatory and proliferative responses triggered by tissue injury. We have previously shown that PAR1 or PAR2 occupancy by specific PAR-agonist peptides (PAR-APs) induces tissue factor (TF) expression in human umbilical vein endothelial cells (HUVECs), where TF regulation by PAR1 (but not by PAR2) requires intact endothelial caveolin-enriched membrane microdomains in which PAR1 and caveolin-1 associate.

OBJECTIVES

The aim of this study was to determine the effects of cholesterol-lowering agents (statins) and cholesterol-loading lipoprotein on PAR1-AP-mediated and PAR2-AP-mediated TF induction in HUVECs.

RESULTS

Statins completely prevented TF induction by PAR-APs in an isoprenoid-independent manner, induced the delocalization of PAR1 from caveolin-enriched membrane microdomains without affecting PAR1 mRNA, and decreased PAR2 mRNA and protein levels. Statins also prevented PAR-AP-mediated extracellular signal-related kinase 1/2 activation, which is crucial for TF induction. The redistribution of PAR1 is accompanied by the relocation of the membrane microdomain-associated G-protein α, caveolin-1, and Src, which we previously showed to play a key role in signal transduction and TF induction. Conversely, cholesterol loading potently amplified PAR1-AP-induced TF, probably as a result of the increased abundance of PAR1 and the Src and G-protein α signaling molecules in the caveolin-1-enriched fraction, without affecting PAR1 mRNA.

CONCLUSIONS

As PARs have important functions in hemostasis, cancer, thrombosis, and inflammatory processes, our findings that statins prevent TF induction by PAR-APs altering the membrane localization of PAR1 and the expression of PAR2 suggest that they may provide health benefits other than reducing atherosclerosis.

X-ray imaging of differential vascular density in MMP-9-/-, PAR-1-/+, hyperhomocysteinemic (CBS-/+) and diabetic (Ins2-/+) mice

Although protease activated receptor-1 (PAR-1) and matrix metalloproteinase-9 (MMP-9) play significant role in vascular remodelling in hyperhomocysteinemia (HHcy due to cystathionine beta synthase deficiency, CBS-/+) and diabetes, mechanism remains nebulous. We hypothesized that differential vascular density and remodelling in different vascular beds in HHcy and diabetes were responsible for an adaptive metabolic homeostasis during the pathogenesis. To test this hypothesis, vascular density in mice lacking PAR-1, MMP-9, CBS and Insulin-2 gene mutant (Ins2-/+, Akita) was measured and compared with wild type (WT, C57BL/6J) mice. The vascular density was detected by x-ray angiography using KODAK 4000 MM image station, using barium sulphate as contrasting agent. The % vascular density in the hearts of WT, CBS-/+ (HHcy), MMP-9-/-, PAR-1-/+ and Ins2-/+ (type-1 diabetes) was 100 ± 2.8, 85 ± 3.3, 90 ± 3.3, 95 ± 3.8 and 73 ± 1.7, respectively. The vascular density in CBS-/+ and Akita hearts decreased while it was increased in lungs of CBS-/+ and MMP-9-/-.There was decreased vascular density in liver and kidney of Akita mice. Vascular density in brain, kidney and mesentery was decreased in CBS-/+ mice. These findings support the notation that metabolic derangement in diabetes and HHcy causes the chronic decline and/or rarefaction in vascular density.

Expression of thrombin and its associated protein in cerebellum of human and rat after intracerebral hemorrhage

BACKGROUND

Intracerebral hemorrhage (ICH) can cause brain damage through a number of pathways. The purpose of the study was to explore the effect of thrombin, protease nexin-1 (PN-1) and protease activated receptor-1 (PAR-1) in rat and human cerebellum after ICH.

METHODS

A model of ICH was produced in adult Sprague-Dawley rats by direct injection of autologous blood (50 microl) into caudate nucleus. Patients with injured hemorrhage were also enrolled in this study. Different expressions of thrombin, PAR-1, PN-1 were detected in rat and human cerebellum by immunohistochemistry and in situ hybridization.

RESULTS

In rat cerebellum, thrombin protein significantly increased at 6 hours and reached the maximum 2 days after ICH. The expression of PAR-1 protein reached the maximum at 24 - 48 hours, and then began to decrease. The expression of PN-1 protein reached the maximum at 3 hours, decreased somewhat after that and increased a little at 5 days after ICH. While in human cerebellum, the changing tendency of thrombin, PAR-1 and PN-1 was almost conform to the rat.

CONCLUSION

In cerebellum, thrombin can activate PAR-1 expression after ICH, and PN-1 appears quickly after ICH in order to control the deleterious effect of thrombin.

Interplay of protease-activated receptors and NOD pattern recognition receptors in epithelial innate immune responses to bacteria

Protease-activated receptors (PARs), nucleotide-binding oligomerization domain (NOD) receptors and Toll-like receptors (TLRs) play a role in innate immunity, but little is known about interaction between these receptors. The goal of this study was to investigate how silencing one receptor affects the expression of other receptors and downstream innate immune markers in response to bacteria. Human gingival epithelial cells (GECs) were transfected with siRNA specific for PAR1 or PAR2, then stimulated with periopathogen Porphyromonas gingivalis, bridging organism between pathogens and non-pathogens Fusobacterium nucleatum, or non-pathogen Streptococcus gordonii. PAR1 or PAR2 knock-down resulted in up-regulated NOD1 and NOD2 expression with P. gingivalis or F. nucleatum stimulation (p<0.01), as well as enhanced TLR2 and TLR4 expression when cells were stimulated by bacteria that utilize TLR2 or TLR4, respectively. Involvement of PARs for induction of CC chemokine ligand 20 (CCL20), a cytokine with antimicrobial properties, was observed following stimulation of the three bacterial species. Furthermore, results from multiple cytokine ELISA array showed receptors utilized in the induction of various innate immune markers are tailored to individual bacterium tested. Our data suggest complex interplay of several receptors is required for appropriate innate immune responses to the different types of bacteria present within the oral cavity and that receptor expression itself is altered depending on which organism the cell encounters.

Thrombin regulates the metastatic potential of human rhabdomyosarcoma cells: distinct role of PAR1 and PAR3 signaling

We observed that human rhabdomyosarcoma (RMS) cells highly express a tissue factor that promotes thrombin formation, which indirectly and directly affects RMS progression. First, we found that thrombin activates platelets to generate microvesicles (PMV), which transfer to RMS cells' alpha2beta3 integrin and increase their adhesiveness to endothelial cells. Accordingly, RMS cells covered with PMVs showed higher metastatic potential after i.v. injection into immunodeficient mice. Furthermore, PMVs activate mitogen-activated protein kinase (MAPK)p42/44 and AKT to chemoattract RMS cells. We also found that RMS cells express functional protease-activated receptor-1 (PAR1) and PAR3 and respond to thrombin stimulation by MAPKp42/44 and MAPKp38 phosphorylation. To our surprise, thrombin did not affect RMS proliferation or survival; it inhibited the chemotactic and adhesive properties of RMS cells. However, when PAR1-specific agonist thrombin receptor-activating peptide 6 was used, which does not activate PAR3, selective PAR1 stimulation enhanced RMS proliferation. To learn more on the role of PAR1 and PAR3 antagonism in RMS proliferation and metastasis, we knocked down both receptors by using a short hairpin RNA strategy. We found that although thrombin does not affect growth of PAR1(-/-) cells, it stimulated the proliferation of PAR3(-/-) cells. More importantly, PAR3(-/-) cells, in contrast to PAR1(-/-) ones, formed larger tumors in immunodeficient mice. We conclude that thrombin is a novel underappreciated modulator of RMS metastasis and that we have identified a novel role for PAR3 in thrombin signaling.

[PAR-1 regulation of intracellular Ca²(+) mobilization in pulmonary giant cell carcinoma cell line PLA801D/PLA801C]

OBJECTIVES

To investigate molecular mechanisms of PAR-1 regulation on intracellular Ca²(+) mobilization in lung giant cell carcinoma cells in vitro and its involvement in tumor metastasis.

METHODS

Free intracellular Ca²(+) ([Ca²(+)]i) was measured in lung giant cell carcinoma PLA801C and PLA801D cells by confocal microscopy. Sense and anti-sense PAR-1 expression vectors were transfected into PLA801C (C+)and PLA801D(D-) cells, respectively. The effects of PAR-1 expression were investigated by thrombin and TRAP-induced mobilization of [Ca²(+)]i in the C+ and D-cells.

RESULTS

There were significant differences of the mean values of [Ca²(+)]i between PLA801D (59.55) and PLA801C cells (35.46, P < 0.01). The mean [Ca²(+)]i of C+ cells (45.77) was significantly higher than that of its control CV cells (35.46, P < 0.05), and the mean [Ca²(+)]i of D-cells (48.42) was significantly lower than that of its control DV cells (59.55, P < 0.05). The peaks of [Ca²(+)]i of C+ and CV cells were 48.19 ± 9.84 and 45.64 ± 9.87 (P < 0.05) respectively at 80 s and 100 s after thrombin treatment, but were 111.31 ± 25.00 and 52.93 ± 11.21 (P < 0.05) respectively at 60 s after TRAP treatment. The peaks of [Ca²(+)]i of D- and DV cells were 40.71 ± 5.89 and 61.07 ± 21.36 (P < 0.05) respectively at 60 s after thrombin treatment, but were 84.98 ± 11.23 and 102.58 ± 21.48 (P < 0.05) respectively at 40 s after TRAP treatment.

CONCLUSIONS

The high metastatic potential of PLA801D and PLA801C may be related to [Ca²(+)]i of the tumor cells. PAR-1 may play an important role in the metastasis of lung giant cell carcinoma cells by up-regulating the intracellular Ca²(+).

Coagulation factor Xa cleaves protease-activated receptor-1 and mediates signaling dependent on binding to the endothelial protein C receptor

BACKGROUND AND OBJECTIVE

Coagulation is intrinsically tied to inflammation, and both proinflammatory and anti-inflammatory responses are modulated by coagulation protease signaling through protease-activated receptor-1 (PAR1). Activated factor X (FXa) can elicit cellular signaling through PAR1, but little is known about the role of cofactors in this pathway. Endothelial protein C receptor (EPCR) supports PAR1 signaling by the protein C pathway, and in the present study we tested whether EPCR mediates surface recruitment and signaling of FXa.

METHODS AND RESULTS

Here, we show that FXa binds to overexpressed as well as native endothelial EPCR. PAR1 cleavage by FXa as analyzed with conformation-sensitive antibodies and a tagged PAR1 reporter construct was strongly enhanced if EPCR was available. Anti-EPCR failed to affect the tissue factor-dependent activation of FX, but high concentrations of FXa decreased EPCR-dependent protein C activation. Most importantly, the FXa-mediated induction of Erk1/2 activation, expression of the transcript for connective tissue growth factor and barrier protection in endothelial cells required binding to EPCR.

CONCLUSIONS

Our results demonstrate that EPCR plays an unexpected role in supporting cell surface recruitment, PAR1 activation, and signaling by FXa.

PAR-1 genotype influences platelet aggregation and procoagulant responses in patients with coronary artery disease prior to and during clopidogrel therapy

Genetic variations of the protease-activated receptor-1 (PAR-1) have been associated with platelet receptor density and linked to thrombin receptor-activating peptide (TRAP)-induced phenotypes of platelet aggregation and P-selectin expression. We investigated whether the PAR-1 intervening sequence-14 A>T dimorphism influences platelet procoagulant activity. We also determined whether the P2Y12 antagonist clopidogrel could offset any observed functional polymorphism of the PAR-1 receptor by inhibiting P2Y12-mediated amplification of TRAP-induced responses. We studied 54 patients listed for elective percutaneous coronary intervention assessing TRAP-induced platelet aggregation and markers of procoagulant activity. Platelet responses were measured at baseline, 4 h post clopidogrel 300 mg, and 10 and 28 days following clopidogrel 75 mg daily. Each patient was genotyped for the PAR-1 intervening sequence-14 A/T dimorphism. Increased platelet aggregation and procoagulant responses were observed with PAR-1 A allele homozygotes. Clopidogrel significantly inhibited these platelet responses regardless of PAR-1 genotype, but did not offset the hyper-reactivity associated with the A/A homozygotes. We conclude that a common sequence variation within the PAR-1 gene influences TRAP-induced platelet procoagulant activity as well as aggregation. Higher platelet reactivity associated with PAR-1 IVSn-14 A allele homozygotes persists despite clopidogrel therapy. These individuals may be at higher risk of thromboembolic events and may require additional anti-platelet medication.

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.

Up-regulation of protease-activated receptor-1 in diabetic glomerulosclerosis

Patients with diabetes are under a hypercoagulable state leading to generation of thrombin. It is not known whether thrombin plays a role in the progression of diabetic nephropathy. We analyzed gene expression of two thrombin receptors, protease-activated receptor-1 (PAR-1) and PAR-4 in the kidney of diabetic db/db mice. Mice developed hyperglycemia from 7 to 10 weeks of age and showed renal abnormalities such as mesangial expansion and urinary albumin excretion at 10 weeks of age. PAR-1 mRNA was up-regulated in isolated glomeruli in db/db mice compared with age-matched db/m littermates, but PAR-4 mRNA was not. In situ hybridization studies showed that PAR-1 mRNA was detected mainly at the glomerulus, and that intensive signals were observed in mesangial cells and podocytes. The up-regulation of PAR-1 in glomeruli in diabetic mice may play a role in the progression of glomerulosclerosis and abnormal urinary albumin excretion in diabetic nephropathy.

Thrombin-stimulated growth factor and cytokine expression in osteoblasts is mediated by protease-activated receptor-1 and prostanoids

Thrombin exerts multiple effects upon osteoblasts including stimulating proliferation, and inhibiting osteoblast differentiation and apoptosis. Some of these effects are believed to be mediated by the synthesis and secretion of autocrine factors such as growth factors and cytokines. Many but not all cellular responses to thrombin are mediated by members of the protease-activated receptor (PAR) family of G protein-coupled receptors. The current study was undertaken to investigate the nature of thrombin's induction of autocrine factors by analysing the expression of twelve candidate genes in thrombin-stimulated primary mouse osteoblasts. Analysis by quantitative reverse transcription polymerase chain reaction (qRT-PCR) demonstrated that thrombin induced transforming growth factor beta, cyclooxygenase-2, tenascin C, fibroblast growth factor-1 and -2, connective tissue growth factor and interleukin-6 expression in wild type osteoblasts, but not PAR-1 null mouse osteoblasts. Induction of all the thrombin-responsive genes was blocked by the presence of the non-selective cyclooxygenase inhibitor indomethacin. Further studies were conducted on interleukin-6, which was the gene that showed the greatest increase in expression following stimulation of osteoblast-like cells with thrombin. A PAR-1-specific activating peptide, but neither a PAR-4-activating peptide nor catalytically inactive thrombin induced release of interleukin-6 by osteoblasts. Furthermore, in the presence of the selective cyclooxygenase-1 and -2 inhibitors SC-560 and NS-398 thrombin-induced interleukin-6 release was prevented. Levels of both prostaglandin E(2) and interleukin-6 in medium conditioned by thrombin-stimulated osteoblast-like cells were found to be significantly increased compared to medium conditioned by non-stimulated cells, however release of prostaglandin E(2) was found to precede release of interleukin-6. Treatment of isolated osteoblast-like cells with a number of synthetic prostanoids stimulated secretion of interleukin-6 with differing potencies. These studies suggest that activation of PAR-1 on osteoblasts by thrombin induces cyclooxygenase activity, which in turn results in the increased expression of multiple secreted factors. The induction of these secreted factors may act in an autocrine fashion to alter osteoblast function, allowing these cells to participate in the earliest stages of bone healing by both autocrine and paracrine mechanisms.

Variants in the coagulation factor 2 receptor (F2R) gene influence the risk of myocardial infarction in men through an interaction with interleukin 6 serum levels

Thrombin-activated factor 2 receptor (F2R) links thrombosis to inflammation modulating interleukin (IL)6 synthesis. We have investigated the role of F2R genetic variants and their interaction with IL6 serum levels in the occurrence of myocardial infarction (MI) in the Stockholm Heart Epidemiology Program (SHEEP). Seven SNPs -1738 G/A, -506-/GGCCGCGGGAAGC (D/I), 2860 G/A, 2930 T/C, 9113 C/A, 9333 C/T and 120813 T/C within F2R locus were genotyped in the SHEEP (n=2,774). The C allele at position 2930 was associated with a slight reduction in MI risk in men. IL6 serum levels were higher in male cases carrying genotypes AA at the -1738 (p= 0.01) and GG at the 2860 loci (p= 0.03) and both alleles were found to differentially modulate IL6 serum levels in the context of selective haplotypes. High IL6 serum levels (>75(th) percentile), were independently associated with an increased risk of MI in men with an odds ratio (OR) (95% confidence interval [CI]) of 2.44 (1.72-3.46), (p=0.0016), but not in women ( OR 0.83 [95%CI 0.50-1.36], p=0.64). In the presence of high IL6 serum levels, the -1738A allele increased and the 2860A allele reduced the risk of MI (all p < or = 0.02). Consistently, the AG diplotype increased MI risk (OR 1.71 [95%CI 1.17-2.51], p=0.005). The -1738 and 2860 loci association with IL6 serum levels was replicated in men in the Stockholm Coronary Artery Risk Factor (SCARF) study (both p < or = 0.04). In the pooled data from the two populations, the A and G allele modulated the risk of MI in men with high IL6 serum levels (p < or = 0.03). Our results demonstrate that in men F2R genetic variants influence the risk of MI mainly through an interaction with IL6 serum levels.

Relative importance of proteinase-activated receptor-1 versus matrix metalloproteinases in intracerebral hemorrhage-mediated neurotoxicity in mice

BACKGROUND AND PURPOSE

To reduce bleeding and damage to central nervous system tissue in intracerebral hemorrhage, the coagulant effect of thrombin is essential. However, thrombin itself can kill neurons in intracerebral hemorrhage as can the matrix metalloproteinases (MMPs), which are also elevated in this condition, in part due to thrombin-mediated activation of MMPs. It is thus important to understand and block the neurotoxic effects of thrombin without inhibiting its therapeutic outcomes. In this study, we have investigated the relative roles of proteinase activated receptor-1, a thrombin receptor, and MMPs in brain injury induced by thrombin or blood.

METHODS

Mice were subjected to stereotactic intracerebral injections of saline, thrombin, and autologous blood, with or without hirudin, a thrombin inhibitor, or GM6001, an MMP inhibitor. Twenty-four hours later, tissue sections were obtained to evaluate the area of brain damage and extent of dying neurons. Data from wild-type mice were compared with results obtained with proteinase activated receptor-1 null mice.

RESULTS

In blood-induced damage to the brain parenchyma, both hirudin and GM6001 significantly reduced injury to a comparable extent (>40%) implicating both thrombin and MMPs in neurotoxicity. In proteinase activated receptor-1 null mice, blood-induced brain damage was reduced by 22.6% relative to wild-type animals; by comparison, the blood-induced brain damage was reduced by 48.3% using GM6001.

CONCLUSIONS

The neurotoxicity of blood in intracerebral hemorrhage involves both proteinase activated receptor-1 and MMP activation, with the latter appearing more prominent in causing death.

Protection of vascular barrier integrity by activated protein C in murine models depends on protease-activated receptor-1

Protease activated receptor-1 (PAR1) mediates barrier protective signalling of activated protein C (APC) in human endothelial cells in vitro and may contribute to APC's beneficial effects in patients with severe sepsis. Mouse models are of key importance for translational research but species differences may limit conclusions for the human system. We analysed whether mouse APC can cleave, activate and induce signalling through murine PAR1 and tested in newly established mouse models if long-term infusion of APC prevents from vascular leakage. Cell surface immunoassays demonstrated efficient cleavage of endogenous murine endothelial PAR1 by either murine or human APC. Pharmacological concentrations of APC of either species had powerful barrier protective effects on cultured murine endothelial cells that required PAR1 cleavage. Vascular endothelial growth factor-mediated hyperpermeability in the skin was reduced by either endogenously generated as well as directly infused recombinant mouse APC in wild-type mice. However APC did not significantly alter the vascular barrier function in PAR1-deficient mice. In endotoxin-challenged mice, infused APC significantly prevented from pulmonary fluid accumulation in the wild-type mice but not in mice lacking PAR1. Our results directly show that murine APC cleaves and signals through PAR1 in mouse endothelial cells. APC reduces vascular permeability in mouse models and PAR1 plays a major role in mediating these effects. Our data in vitro and in vivo support the paradigm that PAR1 contributes to protective effects of APC on vascular barrier integrity in sepsis.

[Effect of Xuebijing injection on expression of endothelial protein C receptor and protease activated receptor 1 mRNA and protein in endothelial cells induced by lipopolysaccharide]

OBJECTIVE

To investigate the effect of Xuebijing injection on expression of endothelial protein C receptor (EPCR) and protease activated receptor 1 (PAR1) mRNA and protein in rat aortic endothelial cells (RAECs) after lipopolysaccharide (LPS) challenge.

METHODS

RAECs were cultured for one week, and the purity was determined with flow cytometry. ARECs were randomly divided into four groups: control group, LPS stimulation group (1 mg/L LPS), Xuebijing injection treatment group (LPS: 1 mg/L, Xuebijing injection ; 10 g/L) and activated protein C (APC) treatment group (LPS: 1 mg/L, APC: 0.1 mg/L). The RAECs were collected at 12, 24, 48, and 72 hours after being stimulated by LPS. EPCR and PAR1 mRNA of RAECs were assessed by reverse transcription-polymerase chain reaction (RT-PCR). EPCR and PAR1 protein were assessed by flow cytometry.

RESULTS

At 12 hours, EPCR and PAR1 protein expressions were not significantly different among groups (all P>0.05). The level of EPCR and PAR1 mRNA were decreased in LPS stimulation group, but they were elevated in both APC and Xuebijing injection treatment groups (P<0.05 or P<0.01). From 24 to 72 hours, compared to control group, the levels of EPCR mRNA and protein expression were significantly decreased after LPS stimulation (P<0.05 or P<0.01). The levels of EPCR expression were decreased and negatively correlated with the time of LPS treatment. Also, compared to LPS stimulation group, treatment with Xuebijing markedly elevated the levels of EPCR (P<0.01). The levels of PAR1 expression were significantly decreased by LPS stimulation compared with those of control group (P<0.05 or P<0.01). After the treatment with Xuebijng, the expression of PAR1 was gradually increased (all P<0.01). Compared with APC treatment group, Xuebijing could increase the PAR1 expression better.

CONCLUSION

Xuebijing could raise EPCR and PAR1 mRNA and protein expression of RAECs after LPS challenge, and it may be related to its protection of endothelial cell from undergoing apoptosis.