FXa-mediated PAR-2 promotes the efficacy of immunotherapy for hepatocellular carcinoma through immune escape and anoikis resistance by inducing PD-L1 transcription.

BACKGROUND: The high metastasis rate is one of the main reasons for the poor prognosis of patients with hepatocellular carcinoma (HCC). Coagulation factor Xa (FXa) and its receptor proteinase-activated receptor-2 (PAR-2) proven to promote tumor metastasis in other forms of cancer. Here, we explore the role and mechanism of FXa in the regulation of resistance of anoikis and immune escape of HCC. METHODS: In vitro and in vivo experiments were conducted to explore the role of FXa in HCC metastasis and its potential mechanism. The effects of FXa inhibitor rivaroxaban on HCC immunotherapy were evaluated using intrahepatic metastasis animal models and clinical trial (No. ChiCTR20000040540). We investigated the potential of FXa inhibition as a treatment for HCC. RESULTS: FXa was highly expressed in HCC and promoted metastasis by activating PAR-2. Mechanistically, FXa-activated PAR-2 endows HCC cells with the ability of anoikis resistance to survive in the circulating blood by inhibiting the extrinsic apoptosis pathway. Furthermore, suspension stimulation-induced phosphorylation of STAT2, which promotes programmed death-ligand 1 (PD-L1) transcription and inhibits the antitumor effects of immune cells by inhibiting the infiltration of CD8+T cells in tumors and the levels of secreted cytokines. In vivo inhibition of FXa with rivaroxaban reduced HCC metastasis by decreasing PD-L1 expression and exhausting tumor-infiltrating lymphocytes. Notably, the combination of rivaroxaban and anti-programmed death-1 monoclonal antibody (anti-PD-1) programmed Death-1 monoclonal antibody (anti-PD-1) induced synergistic antitumor effects in animal models. Most importantly, rivaroxaban improved the objective response rate of patients with HCC to immune checkpoint inhibitors and prolonged overall survival time. CONCLUSIONS: FXa-activated PAR-2 promotes anoikis resistance and immune escape in HCC, suggesting the potential for combining coagulation inhibitors and PD-1/PD-L1 immune checkpoint blockade to enhance the therapeutic efficacy of HCC.

Andexanet Alfa: What We Have Learned from Clinical Trials and Real-World Data.

Andexanet alfa is a specific reversal agent for factor Xa inhibitors with immediate reversal of their anticoagulant effect. Andexanet alfa is currently approved for use in patients treated with rivaroxaban and apixaban who have life-threatening or uncontrolled bleeding. New data from both controlled clinical trials and real-world experience are continuously being published, providing greater insight into the clinical characteristics of the drug, such as efficacy and safety. It is worth considering that andexanet alfa could be of benefit in a variety of different clinical scenarios where patients receiving treatment with apixaban and rivaroxaban (and endoxaban) have life-threatening conditions. These different clinical scenarios, which range from pre-treatment of urgent surgery, especially neurosurgical interventions, and concomitant use of andexanet alfa and prothrombin complex concentrate to onset of bleeding more than 6 h prior to admission, should be clarified as well as the issue of "low/high" dose of andexanet alfa and the need for baseline anti-Xa inhibitor levels measured by point-of-care testing. Finally, management of patients at high risk of thrombosis or recent arterial/venous thrombotic events needs to be further explored. In this current opinion, we address these urgent questions in the light of recent literature and clinical trial data.

Thrombin Generation Profile in Various Lymphoma Sub-Groups and Its Augmentation by Andexanet Alfa.

The prevalence of thrombosis in lymphoma patients is reportedly high and ranges from 3-10%. Vascular malfunction and inflammatory processes further contribute to the thrombotic activation process in these patients. Andexanet alfa (AA) is an antidote for factor Xa inhibitors and its usage has been reported with thrombotic complications. This study was designed to compare the effect of AA on the thrombin generation (TG) potential. Blood samples from 78 patients with confirmed diagnosis of non-Hodgkin lymphoma (NHL), Hodgkin lymphoma (HL) and Chronic lymphocytic leukemia (CLL) were collected from the University of Belgrade Clinic, Serbia. Normal human plasma (NHP) was used for referencing purposes. Individual samples were supplemented with AA at 100 ug/ml. TG studies were carried out using a commercially available fluorogenic substrate method. TG parameters such as peak thrombin (PT), lag time (LT) and area under the curve (AUC) were compiled. Cumulatively, lymphoma patients showed an increase in LT compared to NHP which decreases with AA. The PT and AUC levels were decreased compared to NHP and increases with AA. Upon sub-grouping of lymphoma patients, PT levels for all sub-groups were increased with AA. The AUC values increased for HL and NHL and decreased for CLL with AA. Variations in lag time were noted in all 3 sub-groups. Lymphoma represents a heterogenous group of patients where both the hypercoagulable state and inflammatory responses simultaneously occur. Increased thrombin generation in post AA supplemented samples suggest that the use of this agent may potentially be associated with thrombotic complications.

Strategies of neutralization of the direct oral anticoagulants effect: review of the literature.

Many neutralizing agents of anticoagulant effect of factor Xa or thrombin inhibitors (xabans and dabigatran, respectively) have been developed since the commercialization of direct oral anticoagulants (DOAC) in 2008. Idarucizumab is a specific antidote of dabigatran commercialised since 2016. An antidote of xabans, andexanet-α, was very recently approved by the Food and Drug Administration (FDA). Other antidotes of DOAC are under pre-clinical or clinical development; the most advanced being the aripazine in addition to γ-thrombine S195A and GDFXa-α2M complex. Prothrombin complex concentrates activated or not, are part of the pro-hemostatic agents suggested for DOAC handling in case of haemorrhage or preceeding urgent surgery or invasive procedures. Other pro-hemostatic agents (FXaI16L, FX (a)-C, superFVa) are in pre-clinical stage. The efficacy of these different agents in DOAC reversal and mortality reduction is still controversal in the light of the sparse results of in vitro, ex vivo, pre-clinical and clinical studies.

Andexanet alfa for the treatment of hemorrhage.

INTRODUCTION: While associated life-threatening and fatal bleeding events are less frequent with the direct factor Xa inhibitors compared to vitamin K antagonists, significant concern surrounding management of major bleeds and urgent periprocedural interruption of these agents exists among clinicians. Andexanet alfa is a recombinant human factor Xa decoy protein developed in response to this clinical gap in the care of patients receiving anticoagulation with factor Xa inhibitors. Areas covered: This paper reviews results from preclinical and healthy-volunteer studies demonstrating the ability of andexanet to rapidly and reliably normalize coagulation indices in patients treated with both direct and indirect factor Xa inhibitors. An interim analysis from an ongoing phase 3/4b clinical study assessing the efficacy and safety of andexanet in patients experiencing life-threatening hemorrhage in association with factor Xa inhibitors is discussed. It also provides an overview of the major safety concerns reported in these trials which include allergic and infusion reactions, development of anti-andexanet antibodies and, importantly, thrombosis. Expert commentary: While initial reports on restoration of hemostasis and safety are promising, further study of andexanet is required to gauge its efficacy and toxicity, including a potential prothrombotic effect. Further, its use in patients requiring urgent surgery should be studied.

Andexanet alfa effectively reverses edoxaban anticoagulation effects and associated bleeding in a rabbit acute hemorrhage model.

INTRODUCTION: Increasing use of factor Xa (FXa) inhibitors necessitates effective reversal agents to manage bleeding. Andexanet alfa, a novel modified recombinant human FXa, rapidly reverses the anticoagulation effects of direct and indirect FXa inhibitors. OBJECTIVE: To evaluate the ability of andexanet to reverse anticoagulation in vitro and reduce bleeding in rabbits administered edoxaban. MATERIALS AND METHODS: In vitro studies characterized the interaction of andexanet with edoxaban and its ability to reverse edoxaban-mediated anti-FXa activity. In a rabbit model of surgically induced, acute hemorrhage, animals received edoxaban vehicle+andexanet vehicle (control), edoxaban (1 mg/kg)+andexanet vehicle, edoxaban+andexanet (75 mg, 5-minute infusion, 20 minutes after edoxaban), or edoxaban vehicle+andexanet prior to injury. RESULTS: Andexanet bound edoxaban with high affinity similar to FXa. Andexanet rapidly and dose-dependently reversed the effects of edoxaban on FXa activity and coagulation pharmacodynamic parameters in vitro. In edoxaban-anticoagulated rabbits, andexanet reduced anti-FXa activity by 82% (from 548±87 to 100±41 ng/ml; P<0.0001), mean unbound edoxaban plasma concentration by ~80% (from 100±10 to 21±6 ng/ml; P<0.0001), and blood loss by 80% vs. vehicle (adjusted for control, 2.6 vs. 12.9 g; P = 0.003). The reduction in blood loss correlated with the decrease in anti-FXa activity (r = 0.6993, P<0.0001) and unbound edoxaban (r = 0.5951, P = 0.0035). CONCLUSION: These data demonstrate that andexanet rapidly reversed the anticoagulant effects of edoxaban, suggesting it could be clinically valuable for the management of acute and surgery-related bleeding. Correlation of blood loss with anti-FXa activity supports the use of anti-FXa activity as a biomarker for assessing anticoagulation reversal in clinical trials.

Activated Factor X Induces Endothelial Cell Senescence Through IGFBP-5.

Uncontrolled coagulation contributes to the pathophysiology of several chronic inflammatory diseases. In these conditions, senescent cells are often observed and is involved in the generation of inflammation. The coincidence of hyper-coagulation, cell senescence, and inflammation suggests the existence of a common underlying mechanism. Recent evidence indicates that activated coagulation factor X (FXa) plays a role in the processes beyond blood coagulation. This non-hematologic function entails the mediation of inflammation and tissue remodeling. We therefore tested the hypothesis that FXa induces cell senescence resulting in tissue inflammation and impaired tissue regeneration. Human umbilical vein endothelial cells were stimulated with FXa for 14 days. The proliferation of cells treated with FXa was significantly smaller, and the fraction of senescence-associated ß-galactosidase-positive cells was increased as compared to the control group. RT-qPCR array revealed that FXa increased the expression of IGFBP-5, EGR-1, p53, and p16INK4a. Inhibition of FXa by a direct FXa inhibitor, rivaroxaban, or IGFBP-5 by siRNA decreased FXa-induced cell senescence, restoring cell proliferation. Moreover, in an ischemic hind limb mouse model, FXa inhibited neovascularization by endothelial progenitor cell. However, rivaroxaban significantly restored FXa-induced impaired angiogenesis. In summary, FXa induced endothelial cell senescence through IGFBP-5, resulting in impaired angiogenesis.

[Factor Xa Promotes Differentiation of Meg-01 Cell Line].

OBJECTIVE: To investigate the effect and mechanism of Factor Xa on the differentiation of Meg-01 cells into platelet-like particles. METHODS: The Meg-01 cells were used as experimental object, Factor Xa was used as agonist. Cell proliferation was detected by CCK-8 assay. The viability of platelet-like particles was analyzed by AlamaBlue kit. MAPK/ERK pathway and PI3K/AKT pathway were assayed by Western blot. The expression of CD41b was analyzed by Western blot and flow cytometry. Cell cycle and apoptosis were detected by flow cytometry. RESULTS: The Factor Xa (1 µg/ml) inhibited cell viability, induced apoptosis. Factor Xa triggered cell arrest at the G(2)/M stage and down-regulated the expression of SKP2. After Meg-01 cells were stimulated by Factor Xa, the expression of CD41b was up-regulated and the MAPK/ERK pathway and PI3K/AKT pathway were activated. The platelets-like particles stimulated by FXa activation were viable. CONCLUSION: The Factor Xa maybe display some effect on the differentiation of megakaryocytes into platelets.

The Coagulant Factor Xa Induces Protease-Activated Receptor-1 and Annexin A2-Dependent Airway Smooth Muscle Cytokine Production and Cell Proliferation.

During asthma exacerbation, plasma circulating coagulant factor X (FX) enters the inflamed airways and is activated (FXa). FXa may have an important role in asthma, being involved in thrombin activation and an agonist of protease-activated receptor-1 (PAR-1). Extracellular annexin A2 and integrins are also implicated in PAR-1 signaling. In this study, the potential role of PAR-1 in mediating the effects of FXa on human airway smooth muscle (ASM) cell cytokine production and proliferation was investigated. FXa (5-50 nM), but not FX, stimulated increases in ASM IL-6 production and cell number after 24- and 48-hour incubation, respectively (P < 0.05; n = 5). FXa (15 nM) also stimulated increases in the levels of mRNA for cytokines (IL-6), cell cycle-related protein (cyclin D1), and proremodeling proteins (FGF-2, PDGF-B, CTGF, SM22, and PAI-1) after 3-hour incubation (P < 0.05; n = 4). The actions of FXa were insensitive to inhibition by hirudin (1 U/ml), a selective thrombin inhibitor, but were attenuated by SCH79797 (100 nM), a PAR-1 antagonist, or Cpd 22 (1 µM), an inhibitor of integrin-linked kinase. The selective targeting of PAR-1, annexin A2, or ß1-integrin by small interfering RNA and/or by functional blocking antibodies also attenuated FXa-evoked responses. In contrast, the targeting of annexin A2 did not inhibit thrombin-stimulated ASM function. In airway biopsies of patients with asthma, FXa and annexin A2 were detected in the ASM bundle by immunohistochemistry. These findings establish FXa as a potentially important asthma mediator, stimulating ASM function through actions requiring PAR-1 and annexin A2 and involving integrin coactivation.

Independent anti-angiogenic capacities of coagulation factors X and Xa.

Knockout models have shown that the coagulation system has a role in vascular development and angiogenesis. Herein, we report for the first time that zymogen FX and its active form (FXa) possess anti-angiogenic properties. Both the recombinant FX and FXa inhibit angiogenesis in vitro using endothelial EA.hy926 and human umbilical cord vascular endothelial cells (HUVEC). This effect is dependent on the Gla domain of FX. We demonstrate that FX and FXa use different mechanisms: the use of Rivaroxaban (RX) a specific inhibitor of FXa attenuated its anti-angiogenic properties but did not modify the anti-angiogenic effect of FX. Furthermore, only the anti-angiogenic activity of FXa is PAR-1dependent. Using in vivo models, we show that FX and FXa are anti-angiogenic in the zebrafish intersegmental vasculature (ISV) formation and in the chick embryo chorioallantoic membrane (CAM) assays. Our results provide further evidence for the non-hemostatic functions of FX and FXa and demonstrate for the first time a biological role for the zymogen FX.

Thrombin induces epithelial-mesenchymal transition and collagen production by retinal pigment epithelial cells via autocrine PDGF-receptor signaling.

PURPOSE: De-differentiation of RPE cells into mesenchymal cells (epithelial-mesenchymal transition; EMT) and associated collagen production contributes to development of proliferative vitreoretinopathy (PVR). In patients with PVR, intraocular coagulation cascade activation occurs and may play an important initiating role. Therefore, we examined the effect of the coagulation proteins factor Xa and thrombin on EMT and collagen production by RPE cells. METHODS: Retinal pigment epithelial cells were stimulated with factor Xa or thrombin and the effect on zonula occludens (ZO)-1, α-smooth muscle actin (α-SMA), collagen, and platelet-derived growth factor (PDGF)-B were determined by real-time quantitative-polymerase chain reaction (RQ-PCR), immunofluorescence microscopy, and HPLC and ELISA for collagen and PDGF-BB in culture supernatants, respectively. PDGF-receptor activation was determined by phosphorylation analysis and inhibition studies using the PDGF-receptor tyrosine kinase inhibitor AG1296. RESULTS: Thrombin reduced ZO-1 gene expression (P < 0.05) and enhanced expression of the genes encoding α-SMA and the pro-alpha1 chain of collagen type-1 (P < 0.05), indicating EMT. Also, ZO-1 protein expression declined on thrombin stimulation, whereas production of α-SMA and collagen increased. In contrast to thrombin, factor Xa hardly stimulated EMT by RPE. Thrombin clearly induced PDGF-BB production and PDGF-Rß chain phosphorylation in RPE. Moreover, AG1296 significantly blocked the effect of thrombin on EMT and collagen production. CONCLUSIONS: Our findings demonstrate that thrombin is a potent inducer of EMT by RPE via autocrine activation of PDGF-receptor signaling. Coagulation cascade-induced EMT of RPE may thus contribute to the formation of fibrotic retinal membranes in PVR and should be considered as treatment target in PVR.

Drug development from Australian elapid snake venoms and the Venomics pipeline of candidates for haemostasis: Textilinin-1 (Q8008), Haempatch™ (Q8009) and CoVase™ (V0801).

Snake venoms are attractive for drug discovery and development, with a number of therapeutics derived from snake venom either in clinical use or in development. Recognising this opportunity, Australian biopharmaceutical company QRxPharma Ltd and its subsidiary Venomics Pty Ltd (VPL) has partnered with the University of Queensland (UQ) to screen and develop drug candidates from Australian elapid snake venoms. VPL has three haemostasis candidates in early preclinical development. Textilinin-1 (Q8008) is a 7 kDa potent and selective plasmin inhibitor that has application as an anti-fibrinolytic agent to reduce blood loss associated with complex surgeries. Haempatch™ (Q8009) is a Factor Xa-like protein that displays potent procoagulant effects and is being developed as a topical haemostatic agent to reduce blood loss resulting from surgery or trauma. CoVase™ (V0801) is a procoagulant cofactor that may have application as a systemic anti-bleeding agent in the treatment of internal bleeding and non-compressible haemorrhage. This review focuses on drug discovery from Australian elapid snake venoms, with emphasis on the QRxPharma/VPL drug discovery project undertaken in collaboration with UQ and candidates at further stages of development.

The molecular charge and size of heparins determine their impact on the decidualization of human endometrial stromal cells.

Heparin modulates the decidualization of human endometrial stromal cells (ESCs), but the molecular mechanisms behind these effects are still unknown. In the present study, we further specified this biological effect of heparin in human ESCs in vitro. ESCs were isolated from hysterectomy specimens, decidualized over 12 days using progesterone and 17ß-estradiol and incubated with thrombin, factor Xa (FXa), unfractionated heparin, dextran sulfate, danaparoid or different low-molecular-weight heparins (LMWHs). Production of insulin-like growth factor (IGF)-I, prolactin (PRL) and IGF-binding protein (IGFBP)-1 by ESCs was measured using ELISAs. Like heparin, thrombin and FXa cause an increase in IGF-I in ESCs, suggesting an action of heparin independent from its anticoagulatory effects. This was supported by demonstrating the induction of the same effects on IGF-I, PRL and IGFBP-1 as heparin by dextran sulfate, a polysaccharide of similar size and charge as heparin, but without anticoagulatory properties. LMWHs with the same anti-FXa activity as heparin showed less pronounced effects on ESCs than heparin, whereas the very short pentasaccharide fondaparinux (17 kDa) had barely any effect, further supporting the primary role of molecular size and charge mediating these biological effects of heparin on ESCs. In conclusion, the effects of heparin on the decidualization of human ESCs seem to be independent of its anticoagulatory function, but rather depend on the charge and the size of this polysulfated glycosaminoglycan. Therefore, highly sulfated polysaccharides with a molecular weight >17 kDa might be an interesting pharmacological approach for the therapy of endometrial pathologies, e.g. the treatment of women suffering from recurrent miscarriage or repeated implantation failure.

Tissue Factor/ FVIIa prevents the extrinsic pathway of apoptosis by regulation of the tumor suppressor Death-Associated Protein Kinase 1 (DAPK1).

INTRODUCTION: This study determines the impact of tissue factor (TF)-signaling on the extrinsic pathway of apoptosis in cancer cells and propose death associated protein kinase-1 (DAPK1) as a novel key regulator. MATERIALS AND METHODS: In MDA-MB-231 breast and PC3 prostate cancer cells, mRNA levels were analyzed by real-time PCR and protein expressions were assessed by flow cytometry or western blot. Caspase-8 and -3 levels, cell size, and changes in nuclear morphology were recorded using the ArrayScan microscope and 84 apoptosis-related genes were screened with the RT2 Profiler™ PCR Array. RESULTS: In serum starved MDA-MB-231 cells, a TF/FVIIa-sensitive upregulation of apoptosis markers was recorded. Similarly, TRAIL-induced apoptosis was negatively regulated by TF/FVIIa (10 and 100 nM) and TF/FVIIa/FXa but not by active-site inhibited FVIIa. FVIIa, moreover, decreased the transcription of DAPK1 and thereby diminished the association between DAPK1 and FADD in the caspase-8 activating death-inducing signaling complex (DISC). TF/FVIIa regulation of caspase-8 and DAPK1 was dependent on PI3-kinase/AKT and independent of the protease activated receptors (PAR) 1 and 2. Despite of receptor expression and functional signaling, both PAR-agonist treatment and PAR-blocking antibodies in combination with FVIIa failed to influence the anti-apoptotic signal. CONCLUSIONS: We hereby report that TF/FVIIa-induced signaling governs the extrinsic pathway of apoptosis by reducing the levels of DAPK1 in the DISC independently of PAR1 and PAR2. This implies the conceivable involvement of cell surface components other than the PARs and entails the search for TF-dependent regulators of DAPK1 transcription.

Coagulation Factor Xa inhibits cancer cell migration via LIMK1-mediated cofilin inactivation.

Previously, we showed that activated coagulation factor X (FXa) inhibits migration of breast, lung and colon cancer cells. We showed that the effect of FXa on migration was protease-activated receptor (PAR)-1-dependent, but the subsequent cellular signaling routes remained elusive. In the current manuscript, we show that both the Rho/ROCK and Src/FAK/paxillin pathways are required for FXa-mediated inhibition of breast cancer cell migration. FXa induced pronounced stress fiber formation that was partially inhibited by pre-treatment with specific ROCK or Src inhibitors. Downstream of Rho/ROCK and Src/FAK/paxillin, FXa induced myosin light chain phosphorylation and LIMK1 activation resulting in cofilin inactivation. Knocking-down LIMK1 expression abolished FXa-induced inhibition of cell invasion. Our results reveal that FXa-mediated sustained cofilin inactivation leads to stabilization of actin filaments incompatible with migration. Overall we confirm that, beyond its role in blood coagulation, FXa plays a key role in cell migration and we unravel a new mechanism of PAR-1-mediated inhibition of migration via Rho and Src dependent pathways.

The role of protease-activated receptors PAR-1 and PAR-2 in the repair of 16HBE 14o(-) epithelial cell monolayers in vitro.

BACKGROUND: We recently reported that repair following mechanical wounding of epithelial cell layers in vitro is dependent on fibrin formation and the activity of locally expressed coagulation cascade proteins. Serine proteases of the coagulation cascade are an important group of protease-activated receptor (PAR) activators and PAR-1 to 4 are expressed by the normal bronchial epithelium. OBJECTIVE: We tested the hypothesis that activation of PAR-1 and PAR-2 by coagulation cascade proteases stimulates epithelial repair via effects on fibrin formation. METHODS: Using mechanically wounded 16HBE 14o(-) epithelial cell layers in culture, we investigated the effect of PAR-1 and PAR-2 agonist peptides, control partially scrambled peptides and PAR-neutralizing antibodies on the rate of repair and fibrin formation. Coagulation factors in culture supernatants were measured by immunoblot. RT-PCR was used to investigate PAR-1, PAR-2 and PGE2 receptor (EP-1 to EP-4) expression in this model and qRT-PCR to quantify responses to wounding. Additionally, we investigated the effect of exogenously added factor Xa (FXa) and neutrophil elastase and the influence of PGE2 and indomethacin on the repair response. RESULTS: PAR-1 and PAR-2 peptide agonists stimulated the rate of repair and enhanced the formation of a fibrin provisional matrix to support the repair process. Conversely, PAR-neutralizing antibodies inhibited repair. Under serum-free culture conditions, 16HBE 14o(-) cells expressed EP-2 and EP-3, but not EP-1 or EP-4, receptors. Wounding induced an increased expression of EP-3 but did not alter EP-2, PAR-1 or PAR-2 expression. In the absence of PAR agonists, there was no evidence for a role for PGE2 in fibrin formation or the repair process. Indomethacin attenuated fibrin formation in wounded cultures only in the presence of the PAR-2 peptide. FXa stimulated epithelial repair while neutrophil elastase reduced the levels of coagulation factors and inhibited repair. CONCLUSION: Locally expressed serine proteases of the coagulation cascade activate PAR-1 and PAR-2 to enhance fibrin formation and bronchial epithelial repair.

Inhibitory properties of the P1 Tyr variant of antithrombin.

Antithrombin (AT) and protein Z-dependent protease inhibitor (ZPI) are among two physiological serpin inhibitors in plasma that are involved in the regulation of the clotting cascade. Unlike AT, which can inhibit the proteolytic activity of all coagulation proteases, ZPI has narrower protease specificity, inhibiting only factors Xa (fXa) and XIa. Unlike an Arg at the P1 site of the AT reactive center loop (RCL), this residue is a Tyr in ZPI. To investigate the contribution of P1 Tyr in restricting the specificity of ZPI, we engineered an AT mutant in which the P1 Arg of the RCL was replaced with the P1 Tyr of ZPI (AT-R393Y). The reactivity of AT-R393Y with fXa and thrombin was decreased 155- and 970-fold, respectively. However, the serpin mutant inhibited chymotrypsin with an efficiency higher by >4 orders of magnitude. By contrast, chymotrypsin did not exhibit any reactivity with ZPI. The substitution of Asp-189 of fXa with the corresponding residue of chymotrypsin (Ser) did not improve the reactivity of the protease mutant with AT-R393Y; however, the fXa mutant reacted normally with ZPI. These results suggest that the contribution of P1 Tyr to restricting the protease specificity of ZPI is RCL context-dependent and that in addition to P1 Tyr, other structural features within and/or outside the ZPI RCL are involved in determining the protease specificity of the serpin. The results further suggest that thrombin is less tolerant than fXa in accommodating the nonoptimal P1 Tyr of the AT mutant in its active-site pocket.

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.