Protease-activated receptor-1 (hPar1), a survival factor eliciting tumor progression

Osteoblasts Promote Prostate Cancer Cell Proliferation Through Androgen Receptor Independent Mechanisms

Patients with metastatic prostate cancer frequently develop bone metastases that elicit significant skeletal morbidity and increased mortality. The high tropism of prostate cancer cells for bone and their tendency to induce the osteoblastic-like phenotype are a result of a complex interplay between tumor cells and osteoblasts. Although the role of osteoblasts in supporting prostate cancer cell proliferation has been reported by previous studies, their precise contribution in tumor growth remains to be fully elucidated. Here, we tried to dissect the molecular signaling underlining the interactions between castration-resistant prostate cancer (CRPC) cells and osteoblasts using in vitro co-culture models. Transcriptomic analysis showed that osteoblast-conditioned media (OCM) induced the overexpression of genes related to cell cycle in the CRPC cell line C4-2B but, surprisingly, reduced androgen receptor (AR) transcript levels. In-depth analysis of AR expression in C4-2B cells after OCM treatment showed an AR reduction at the mRNA (p = 0.0047), protein (p = 0.0247), and functional level (p = 0.0029) and, concomitantly, an increase of C4-2B cells in S-G2-M cell cycle phases (p = 0.0185). An extensive proteomic analysis revealed in OCM the presence of some molecules that reduced AR activation, and among these, Matrix metalloproteinase-1 (MMP-1) was the only one able to block AR function (0.1 ng/ml p = 0.006; 1 ng/ml p = 0.002; 10 ng/ml p = 0.0001) and, at the same time, enhance CRPC proliferation (1 ng/ml p = 0.009; 10 ng/ml p = 0.033). Although the increase of C4-2B cell growth induced by MMP-1 did not reach the proliferation levels observed after OCM treatment, the addition of Vorapaxar, an MMP-1 receptor inhibitor (Protease-activated receptor-1, PAR-1), significantly reduced C4-2B cell cycle (0.1 μM p = 0.014; 1 μM p = 0.0087). Overall, our results provide a novel AR-independent mechanism of CRPC proliferation and suggest that MMP-1/PAR-1 could be one of the potential pathways involved in this process.

Targeting G protein-coupled receptors in cancer therapy

As basic research into GPCR signaling and its association with disease has come into fruition, greater clarity has emerged with regards to how these receptors may be amenable to therapeutic intervention. As a diverse group of receptor proteins, which regulate a variety of intracellular signaling pathways, research in this area has been slow to yield tangible therapeutic agents for the treatment of a number of diseases including cancer. However, recently such research has gained momentum based on a series of studies that have sought to define GPCR proteins dynamics through the elucidation of their crystal structures. In this chapter, we define the approaches that have been adopted in developing better therapeutics directed against the specific parts of the receptor proteins, such as the extracellular and the intracellular domains, including the ligands and auxiliary proteins that bind them. Finally, we also briefly outline how GPCR-derived signaling transduction pathways hold great potential as additional targets.

Crosstalk between BCR-ABL and protease-activated receptor 1 (PAR1) suggests a novel target in chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm characterized by the presence of the Philadelphia chromosome, which generates the oncogene BCR-ABL1. Protease-activated receptor 1 (PAR1) is involved in tumor progression and angiogenesis. We have previously reported that PAR1 expression is elevated in human leukemias that display a more aggressive clinical behavior, including the blast crisis of CML. In this study, we analyzed the crosstalk between the oncoprotein BCR-ABL and PAR1 in CML. Leukemic cell lines transfected with the BCR-ABL1 oncogene showed significantly higher expression levels of PAR1 compared with that of wild-type counterparts. This phenomenon was reversed by treatment with tyrosine kinase inhibitors (TKIs). Conversely, treatment with the PAR1 antagonist SCH79797 inhibited BCR-ABL expression. The PAR1 antagonist induced apoptosis in a dose- and time-dependent manner. Higher vascular endothelial growth factor (VEGF) levels were observed in cells transfected with BCR-ABL1 than in their wild-type counterparts. VEGF expression was strongly inhibited after treatment with either TKIs or the PAR1 antagonist. Finally, we evaluated PAR1 expression in CML patients who were either in the blast or chronic phases and had either received TKI treatment or no treatment. A significant decrease in PAR1 expression was observed in treatment-responsive patients, as opposed to a significant increase in PAR1 expression levels in treatment-resistant patients. Patients classified as high risk according to the Sokal index showed higher PAR1 expression levels. Our results demonstrate the crosstalk between BCR-ABL and PAR1. These data may offer important insight into the development of new therapeutic strategies for CML.

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.

Clinical significance of serum Protease-Activated Receptor-1 (PAR-1) levels in patients with cutaneous melanoma

Background

Protease-Activated Receptor-1 (PAR-1) plays an important role in the pathogenesis of multiple malignancies and its expression strongly also affects the outcomes of cancer patients. The objective of this study was to determine the clinical significance of the serum levels of PAR-1in cutaneous melanoma patients.

Methods

A total of 60 patients with a pathologically confirmed diagnosis of cutaneous melanoma were enrolled into this study. Serum PAR-1concentrations were determined by the solid-phase sandwich ELISA method.

Results

No significant difference in serum PAR-1 levels between melanoma patients and healthy controls was found (p = 0.07). The known clinical variables including age of patient, gender, site of lesion, histology, stage of disease, serum LDH levels and chemotherapy responsiveness were not correlated with serum PAR-1 concentrations (p > 0.05). Likewise, serum PAR-1 concentration had also no prognostic role on survival (p = 0.41).

Conclusion

Serum levels of PAR-1 have no diagnostic, predictive and prognostic roles in cutaneous melanoma patients.

General significance

Measurement of PAR-1 in serum is not a clinical significance in cutaneous melanoma patients.

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PAR-1 plays an important role in the pathogenesis of multiple malignancies.

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Its expression strongly also affects the outcomes of cancer patients.

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Serum levels of PAR-1 have no diagnostic, predictive and prognostic roles in cutaneous melanoma patients.

Prognostic value of protease activated receptor-1 in children with acute lymphoblastic leukemia

BACKGROUND

Acute Lymphoblastic leukemia (ALL) is a malignant disorder of lymphoid progenitor cells that proliferate and replace the normal hematopoietic cells of the bone marrow. Protease-activated receptors (PARs) comprise a family of trans-membrane G-protein coupled receptors. Protease-activated receptor 1 (PAR-1) is a typical member of this family of receptors that mediate cellular responses to thrombin and related proteases. PAR1 is expressed by a wide range of tumor cells and can promote tumor growth, invasion and metastasis. The aim of this work was to study the role of PAR-1 expression in newly diagnosed ALL patients.

PATIENTS AND METHODS

This study was conducted on 44 children with newly diagnosed ALL who were admitted to Hematology Unit, Pediatric department, Tanta University Hospital including 24 males and 20 females with their age ranged from 4-17 years and their mean age value of 9.06±3.26. All patients were subjected to complete history taking, thorough clinical examination, bone marrow aspiration and flow cytometric analysis for detection of PAR-1 expression by malignant cells.

RESULTS

PAR-1 was positive in 18 cases (41%) and negative in 26 cases (59%) of studied patients. This study showed no significant relation between PAR-1 expression and age, sex and most of the clinical data including hepatomegaly, splenomegaly and purpura while generalized lymphadenopathy was significantly higher in PAR-1 positive group. PAR-1 positive expression was associated with some bad prognostic laboratory parameters including higher hemoglobin, higher white blood cells, higher peripheral blood and bone marrow blast cells, higher serum LDH and lower platelets count. No significant association was detected between PAR-1 expression and immunophenotyping. There were significantly higher remission rates in PAR-1 negative group and significantly higher relapse and death rates in PAR-1 positive group.

CONCLUSION

From this study, it could be concluded that PAR-1 expression on ALL cells represents an important adverse prognostic factor.

RECOMMENDATIONS

PAR-1 expression should be routinely investigated for better prognostic assessment of ALL patients at diagnosis and should be taken in consideration in designing future therapeutic strategies based on patients- specific risk factors.

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.

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.

Identification of thrombin-like activity in ovarian cancer associated ascites and modulation of multiple cytokine networks

Blood coagulation cascades can be activated by different mechanisms and to different levels in cancer patients. In a study conducted on the transcriptional profile of epithelial ovarian cancer patients a number of possible links between coagulation and inflammation have been suggested and we and others have reported that, in addition to its central role in blood coagulation and haemostasis, thrombin is a powerful regulator of inflammatory responses. Here, we report that thrombin- like activities were present in the malignant ascites of patients with ovarian carcinoma. Malignant ascites significantly enhanced the release of cytokines/chemokines, which have been previously shown to support tumour progression, such as interleukin (IL)-6, IL-1β, CCL2 and CXCL8, in human peripheral blood mononuclear cells of healthy volunteers. Interestingly, ascites enhanced the release of the anti-inflammatory cytokine IL-10 and inhibited the production of interferon-γ and IL-12. The presence of the anticoagulant antithrombin reversed IL-12 inhibition induced by ascites in human monocytes. Finally, the use of thrombin and of the specific thrombin receptor (PAR) agonist peptides, TFLLRN and AYGPK, suggests that IL-12 inhibition is thrombin-specific and related to PAR-1, but not to PAR-4. These findings underline the tight relationship between the coagulation pathway, where thrombin is the key enzyme, and cytokine modulation, including IL-12 inhibition, which is a critical feature of the tumour microenvironment, and may represent a powerful strategy used by tumours to escape immune surveillance.

The association of protease activated receptor 1 gene -506 I/D polymorphism with disease-free survival in breast cancer patients

BACKGROUND

Recent data have shown that tumor development and dissemination may be regulated by procoagulant/anticoagulant axis. The aim of the present study was to search for an association of the protease activated receptor (PAR)1 gene -506 insertion/deletion (I/D), factor V Leiden (FVL), prothrombin (PT) G20210A, and methylenetetrahydrofolate reductase (MTHFR) C677T polymorphisms with disease-free survival (DFS) in breast cancer.

METHODS

Genotyping of -506 I/D in the promoter region of PAR1 gene was performed by single-strand conformation polymorphism analysis and sequencing. FVL, PT G20210A, and MTHFR C677T were also determined by the method of polymerase chain reaction-based DNA analysis. Data regarding patient's age, menopausal status, tumor size, lymph node status, disease stage, tumor grade, estrogen and progesterone receptor, c-erb B2 expression, PAR1 -506 I/D, MTHFR C677T, FVL, and PT G20210A polymorphisms were examined by the univariate and multivariate analyses.

RESULTS

Recurrent disease occurred in 29 patients (19.6 %) within a median of 20 months. It was found that tumor size, lymph node status, tumor stage, tumor grade, c-erbB2 expression, and PAR1 -506 I/D polymorphism were associated with DFS when Kaplan-Meier method was applied (P<.05). By Cox proportional hazards model, the presence of allele D at -506 locus (P=.0249) and small tumor size (P=.0001) were significant favorable prognostic factor, but c-erbB2 expression was an adverse prognostic factor (P=.0049).

CONCLUSION

Our study suggested the protective effect of the allele D at -506 locus of PAR1 gene on the recurrence of breast cancer.

Tissue factor and cell signalling in cancer progression and thrombosis

The close link between coagulation activation and clinical cancer is well established and recent progress has defined underlying molecular pathways by which tumour cells interact with the haemostatic system to promote cancer progression. Tumour type-specific oncogenic transformations cause constitutive and hypoxia-dependent upregulation of tissue factor (TF) in cancer cells, but TF expressed by vascular, stromal and inflammatory cells also contributes to the procoagulant character of the tumour microenvironment. A growing body of genetic and pharmacological evidence implicates signalling by protease activated receptors (PARs) and specifically by tumour cell-expressed TF-VIIa-PAR2 in the induction of an array of proangiogenic and immune modulating cytokines, chemokines and growth factors. Specific inhibition of this pathway results in attenuated tumour growth and angiogenesis. PARs are increasingly recognised as targets for proteases outside the coagulation system and emerging evidence indicates that alternative protease signalling pathways synergise with the coagulation system to promote tumour growth, angiogenesis and metastasis. The elucidation of new therapeutic targets in tumour-promoting protease signalling pathways requires new diagnostic approaches to identify patients that will benefit from tailored therapy targeting procoagulant or signalling aspects of the TF pathway.

PAR1 plays a role in epithelial malignancies: transcriptional regulation and novel signaling pathway

Protease-activated receptor 1 (PAR(1)) is the first and prototype member of an established PAR family comprising four members. The role of PAR(1) in tumor biology has been established, and is characterized by a consistent direct correlation between overexpression of its levels and epithelial tumor aggressiveness. We have found that high expression of the human Par(1) (hPar(1)) gene in epithelial tumors is controlled largely at the transcriptional level. This led us to assign Egr-1, a transcription activator, as an inducer of hPar(1), and p53, a tumor suppressor gene, as an inhibitor, both acting to achieve fine tuning of hPar(1) in prostate carcinoma. High PAR(1) levels maintain prosurvival signals in tumor cells while silencing or ablation of the gene induce apoptosis. Studies of our hPar(1) transgenic mice, which overexpress hPar(1) in the mammary glands, revealed a novel PAR(1)-induced β-catenin stabilization function. The components connecting PAR(1) to β-catenin stabilization have been determined, assigning at first G(α)(13) as a selective immediate component. The PAR(1)-G(α) (13) axis recruits disheveled (DVL), an upstream signaling partner of the canonical Wnt signaling pathway. Silencing of DVL by siRNA-DVL potently abrogates PAR(1)-induced β-catenin stabilization, demonstrating its critical role in the process. We, thus, propose that transcriptional regulation of hPar(1) gene over expression in epithelia malignancies initiates a novel signaling pathway, directly connecting to β-catenin stabilization, a core event in both tumorigenesis and developmental processes.

Reversible protease-activated receptor 1 downregulation mediated by Ankaferd blood stopper inducible with lipopolysaccharides inside the human umbilical vein endothelial cells

Ankaferd Blood Stopper (ABS) is a novel topical hemostatic agent with pleiotropic actions indicated in clinical hemorrhages. Protease-activated receptor 1 (PAR-1) is located in the crossroads of hemostasis, inflammation, infection, apoptosis and tumorigenesis. ABS-induced formation of the protein network with vital erythroid aggregation covers the entire physiological hemostatic process. The aim of this study is to assess the effects of ABS on PAR-1 in the Human Umbilical Vein Endothelial Cells (HUVEC) model, in relation to the "ipopolysaccharides (LPS)-challenge" to endothelium. For this purpose, ABS 10 μL and 100 μL, had been applied to HUVEC within the time periods of 5 minutes (min), 25 min, 50 min, 6 hours (h) and 24 h. The cells have lifted from the plastic surface and adhered to each other during theABSapplication to the HUVECs. After 24 hours the cells returned to normal baseline level. We observed dose-dependent reversible PAR-1 down-regulation mediated by ABS inside the human umbilical vein endothelial cells. ABS-induced sustained PAR-1 down-regulation in the presence of LPS. Those findings indicated that ABS hemostatic agent may act as a topical biological response modifier by acting on PAR-1 at the vascular endothelial and cellular level.

Structure, function and pathophysiology of protease activated receptors

Discovered in the 1990s, protease activated receptors(1) (PARs) are membrane-spanning cell surface proteins that belong to the G protein coupled receptor (GPCR) family. A defining feature of these receptors is their irreversible activation by proteases; mainly serine. Proteolytic agonists remove the PAR extracellular amino terminal pro-domain to expose a new amino terminus, or tethered ligand, that binds intramolecularly to induce intracellular signal transduction via a number of molecular pathways that regulate a variety of cellular responses. By these mechanisms PARs function as cell surface sensors of extracellular and cell surface associated proteases, contributing extensively to regulation of homeostasis, as well as to dysfunctional responses required for progression of a number of diseases. This review examines common and distinguishing structural features of PARs, mechanisms of receptor activation, trafficking and signal termination, and discusses the physiological and pathological roles of these receptors and emerging approaches for modulating PAR-mediated signaling in disease.

Interleukin-1β regulates the migratory potential of MDAMB231 breast cancer cells through the hypoxia-inducible factor-1α

The casual relationship between inflammation and tumour progression has been widely accepted and the etiology of breast cancer has been associated with inflammatory processes. Interleukin (IL)-1β, besides its central role in inflammation, has also been recognised as a powerful player in tumour progression, angiogenesis and invasiveness. Recently, there has been considerable interest in understanding the non-hypoxic upregulation of the hypoxia-inducible factor (HIF)-1α by IL-1 in neoplastic cells since aberrant expression of HIF-1α correlates with tumour progression. Here, using the highly invasive human breast cancer cell line MDAMB231, we studied the effect of IL-1β on tumour cell migration along with HIF-1α accumulation. We observed that non-hypoxic induction of HIF-1α by IL-1β in MDAMB231 was associated with increased cell migration, paralleled by upregulation of p38 MAPK phosphorylation and CXCL8/CXCR1 expression. Inhibition of HIF-1α by siRNA resulted in a significant reduction of CXCR1 expression and IL-1β-induced cell migration in MDAMB231 cells, thus confirming a role of HIF-1α in the non-hypoxic-IL-1β-dependent induction of migratory potentials. Our observation that IL-1 induces HIF-1α accumulation in MDAMB231 cells was confirmed in tumour cells growing in vivo using an experimental approach, mimicking the endogenous release of IL-1 in mice bearing MDAMB231 xenografts. Our in vivo data, along with the fact that inhibition of HIF-1α resulted in the decrease of IL-1β-promoted cell migration, further support the link between inflammation and cancer. The overall results may have important implications in those therapeutic approaches aimed to inhibit IL-1-mediated activities in tumour cells, specifically in breast cancer.

Etk/Bmx regulates proteinase-activated-receptor1 (PAR1) in breast cancer invasion: signaling partners, hierarchy and physiological significance

BACKGROUND

While protease-activated-receptor 1 (PAR(1)) plays a central role in tumor progression, little is known about the cell signaling involved.

METHODOLOGY/PRINCIPAL FINDINGS

We show here the impact of PAR(1) cellular activities using both an orthotopic mouse mammary xenograft and a colorectal-liver metastasis model in vivo, with biochemical analyses in vitro. Large and highly vascularized tumors were generated by cells over-expressing wt hPar1, Y397Z hPar1, with persistent signaling, or Y381A hPar1 mutant constructs. In contrast, cells over-expressing the truncated form of hPar1, which lacks the cytoplasmic tail, developed small or no tumors, similar to cells expressing empty vector or control untreated cells. Antibody array membranes revealed essential hPar1 partners including Etk/Bmx and Shc. PAR(1) activation induces Etk/Bmx and Shc binding to the receptor C-tail to form a complex. Y/A mutations in the PAR(1) C-tail did not prevent Shc-PAR(1) association, but enhanced the number of liver metastases compared with the already increased metastases obtained with wt hPar1. We found that Etk/Bmx first binds via the PH domain to a region of seven residues, located between C378-S384 in PAR(1) C-tail, enabling subsequent Shc association. Importantly, expression of the hPar1-7A mutant form (substituted A, residues 378-384), which is incapable of binding Etk/Bmx, resulted in inhibition of invasion through Matrigel-coated membranes. Similarly, knocking down Etk/Bmx inhibited PAR(1)-induced MDA-MB-435 cell migration. In addition, intact spheroid morphogenesis of MCF10A cells is markedly disrupted by the ectopic expression of wt hPar1. In contrast, the forced expression of the hPar1-7A mutant results in normal ball-shaped spheroids. Thus, by preventing binding of Etk/Bmx to PAR(1) -C-tail, hPar1 oncogenic properties are abrogated.

CONCLUSIONS/SIGNIFICANCE

This is the first demonstration that a cytoplasmic portion of the PAR(1) C-tail functions as a scaffold site. We identify here essential signaling partners, determine the hierarchy of binding and provide a platform for therapeutic vehicles via definition of the critical PAR(1)-associating region in the breast cancer signaling niche.

A matrix metalloproteinase-1/protease activated receptor-1 signaling axis promotes melanoma invasion and metastasis

Hallmarks of malignant melanoma are its propensity to metastasize and its resistance to treatment, giving patients with advanced disease a poor prognosis. The transition of melanoma from non-invasive radial growth phase (RGP) to invasive and metastatically competent vertical growth phase (VGP) is a major step in tumor progression, yet the mechanisms governing this transformation are unknown. Matrix Metalloproteinase-1 (MMP-1) is highly expressed by VGP melanomas, and is thought to contribute to melanoma progression by degrading type I collagen within the skin to facilitate melanoma invasion. Protease activated receptor-1 (PAR-1) is activated by MMP-1, and is also expressed by VGP melanomas. However, the effects MMP-1 signaling through PAR-1 have not been examined in melanoma. Here, we demonstrate that an MMP-1/PAR-1 signaling axis exists in VGP melanoma, and is necessary for melanoma invasion. Introduction of MMP-1 into RGP melanoma cells induced gene expression associated with tumor progression and promoted invasion in vitro, and enhanced tumor growth and conferred metastatic capability in vivo. This study demonstrates that both the type I collagenase and PAR-1 activating functions of MMP-1 are required for melanoma progression, and suggests that MMP-1 may be a major contributor to the transformation of melanoma from non-invasive to malignant disease.

Blockade of PAR1 signaling with cell-penetrating pepducins inhibits Akt survival pathways in breast cancer cells and suppresses tumor survival and metastasis

Protease-activated receptor 1 (PAR1) is a G protein-coupled receptor that is not expressed in normal breast epithelia but is up-regulated in invasive breast carcinomas. In the present study, we found that matrix metalloprotease-1 (MMP-1) robustly activates the PAR1-Akt survival pathway in breast carcinoma cells. This process is blocked by a cell-penetrating lipopeptide "pepducin," P1pal-7, which is a potent inhibitor of cell viability in breast carcinoma cells expressing PAR1. Both a MMP-1 inhibitor and P1pal-7 significantly promote apoptosis in breast tumor xenografts and inhibit metastasis to the lungs by up to 88%. Dual therapy with P1pal-7 and Taxotere inhibits the growth of MDA-MB-231 xenografts by 95%. Consistently, biochemical analysis of xenograft tumors treated with P1pal-7 or MMP-1 inhibitor showed attenuated Akt activity. Ectopic expression of constitutively active Akt rescues breast cancer cells from the synergistic cytotoxicity of P1pal-7 and Taxotere, suggesting that Akt is a critical component of PAR1-dependent cancer cell viability. Together, these findings indicate that blockade of MMP1-PAR1 signaling may provide a benefit beyond treatment with Taxotere alone in advanced, metastatic breast cancer.

Coagulation factor Xa inhibits cancer cell migration via protease-activated receptor-1 activation

Cell migration is critically important in (patho)physiological processes. The metastatic potential of cancer cells partly depends on activation of the coagulation cascade. The aim of the present study was to determine whether coagulation factor X (FXa) can regulate the migration and invasion of cancer cells. Quite unexpectedly, we found that FXa markedly diminished the migration of different cancer cell lines of various origins (breast, lung and colon cancer cells). We showed that FXa mediated inhibition of cancer cell migration was specific, as it was inhibited by TAP (a specific FXa inhibitor) but not by Hirudin (a specific thrombin inhibitor). Moreover, the FXa effect was dose dependent, with a maximal inhibitory effect reached at 0.75 U/ml FXa (corresponding to 130.5 nM). Next, we determined that FXa acted via protease-activated receptor (PAR)-1-dependent signaling, and PAR-1 desensitization, as well as knocking-down PAR-1 expression, abolished the FXa effects. Finally, we showed that Gialpha was not involved in FXa mediated inhibition of cell migration as its effects were not reverted by pertussis toxin. These results suggest that, beyond its role in blood coagulation, FXa plays a key role in cancer cell migration. They also shed light on an unexpected role of PAR-1, which appears to be a Janus-like receptor in cancer cell biology.

Identification of a functional role for the protease-activated receptor-1 in hypoxic breast cancer cells

Aberrant expression of the protease-activated receptor (PAR)-1 has been associated with tumour progression. Indeed, PAR-1 expression correlates with tumour invasiveness, as well as with cancer cell survival. As the tumour microenvironment is characterised by a low oxygen tension, we decided to investigate the role of PAR-1 in cancer cells exposed to a hypoxic microenvironment. In this study we show that hypoxia enhances PAR-1 expression in MDAMB231 breast cancer cells. We next provided evidence for a novel role of PAR-1 in protecting hypoxic breast cancer against cell death, since inhibition of PAR-1 by RNA interference resulted in a decreased cell survival. Finally, we found that treatment of hypoxic MDAMB231 cells with the specific PAR-1 agonist peptide (TRAP) resulted in a significant increase of cell survival and migration. The overall results identify for the first time a functional role for PAR-1 in the cellular responses of breast cancer to a hypoxic microenvironment.

Persistent transactivation of EGFR and ErbB2/HER2 by protease-activated receptor-1 promotes breast carcinoma cell invasion

Hyperactivation of ErbB signaling is implicated in metastatic breast cancer. However, the mechanisms that cause dysregulated ErbB signaling and promote breast carcinoma cell invasion remain poorly understood. One pathway leading to ErbB activation that remains unexplored in breast carcinoma cell invasion involves transactivation by G-protein-coupled receptors (GPCRs). Protease-activated receptor-1 (PAR1), a GPCR activated by extracellular proteases, is overexpressed in invasive breast cancer. PAR1 is also proposed to function in breast cancer invasion and metastasis, but how PAR1 contributes to these processes is not known. In this study, we report that proteolytic activation of PAR1 by thrombin induces persistent transactivation of EGFR and ErbB2/HER2 in invasive breast carcinoma, but not in normal mammary epithelial cells. PAR1-stimulated EGFR and ErbB2 transactivation leads to prolonged extracellular signal-regulated kinase-1 and -2 signaling and promotes breast carcinoma cell invasion. We also show that PAR1 signaling through Galpha(i/o) and metalloprotease activity is critical for ErbB transactivation and cellular invasion. Finally, we demonstrate that PAR1 expression in invasive breast carcinoma is essential for tumor growth in vivo assessed by mammary fat pad xenografts. These studies reveal a critical role for PAR1, a receptor activated by tumor-generated proteases, in hyperactivation of ErbB signaling that promotes breast carcinoma cell invasion.