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.

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Key Points A calcineurin-like phosphatase dephosphorylates annexin A2 in the course of cAMP-induced Weibel-Palade body exocytosis. Dephosphorylation at serine 11 of annexin A2 triggers complex formation with S100A10 that is required for von Willebrand factor secretion.

The tissue factor (TF) pathway serves both hemostasis and cell signaling, but how cells control these divergent functions of TF remains incompletely understood. TF is the receptor and scaffold of coagulation proteases cleaving protease-activated receptor 2 (PAR2) that plays pivotal roles in angiogenesis and tumor development. Here we demonstrate that coagulation factor VIIa (FVIIa) elicits TF cytoplasmic domain-dependent proangiogenic cell signaling independent of the alternative PAR2 activator matriptase. We identify a Lys-Gly-Glu (KGE) integrin-binding motif in the FVIIa protease domain that is required for association of the TF-FVIIa complex with the active conformer of integrin β1. A point mutation in this motif markedly reduces TF-FVIIa association with integrins, attenuates integrin translocation into early endosomes, and reduces delayed mitogen-activated protein kinase phosphorylation required for the induction of proangiogenic cytokines. Pharmacologic or genetic blockade of the small GTPase ADP-ribosylation factor 6 (arf6) that regulates integrin trafficking increases availability of TF-FVIIa with procoagulant activity on the cell surface, while inhibiting TF-FVIIa signaling that leads to proangiogenic cytokine expression and tumor cell migration. These experiments delineate the structural basis for the crosstalk of the TF-FVIIa complex with integrin trafficking and suggest a crucial role for endosomal PAR2 signaling in pathways of tissue repair and tumor biology.

Endothelial cells regulate thrombosis, hemostasis, and inflammatory responses by supplying the vasculature with several factors that include procoagulant von Willebrand factor (VWF) and fibrinolytic tissue-type plasminogen activator (tPA). Both proteins can be secreted in a Ca 2؉ -regulated manner after endothelial activation but exhibit opposing physiologic effects. In search for factors that could modulate endothelial responses by selectively affecting the secretion of procoagulant or anticoagulant proteins, we identify here phospholipase D1 (PLD1) as a specific regulator of VWF secretion. PLD1 is translocated to the plasma membrane upon stimulation of endothelial secretion, and this process correlates with the generation of phosphatidic acid (PA) in the plasma membrane. Histamine-evoked secretion of VWF, but not tPA, is inhibited by blocking PLD-mediated production of PA, and this effect can be attributed to PLD1 and not PLD2. IntroductionVascular endothelial cells (ECs) secrete a variety of procoagulant, anticoagulant, and inflammatory factors that regulate blood clotting and local immune responses. The tight regulation of these events permits endothelial cells to present an anticoagulant surface under normal conditions and to help promoting thrombus formation at sites of vessel injury. Secreted factors mediating these responses are procoagulant and proinflammatory proteins like von Willebrand factor (VWF) and P-selectin and anticoagulant proteins like tissue-type plasminogen activator (tPA) and protein S. 1,2 VWF and P-selectin are stored in Weibel-Palade bodies (WPbs), large, elongated secretory granules that constitute a unique morphologic hallmark of endothelial cells. 3,4 Their exocytosis generally requires an intraendothelial rise in Ca 2ϩ or cAMP and can be induced by several agonists, such as thrombin, histamine, and other mediators of thrombosis or inflammation. 5,6 The anticoagulant tPA has been localized to small vesicular structures, which differ from WPbs in size and morphology but are also released after intraendothelial Ca 2ϩ elevation. 7,8 Furthermore, it has been reported that the acute secretion of WPbs and smaller granules, possibly those containing tPA, occurs with different kinetics. 9 Storage of VWF and tPA in different granules and their selective release after cell stimulation would enable the endothelium to specifically respond to a given (patho)physiologic situation by locally elevating the levels of either procoagulant (VWF) or anticoagulant factors (tPA). Thus, specific release machineries and specific signaling pathways triggering the acute secretion of either WPbs or tPA granules are likely to exist. However, very little, if any, is known about the underlying mechanisms.Phospholipase D (PLD) enzymes have emerged recently as major players in a varied set of secretory events. In mammals, 2 phosphatidylcholine (PC)-selective PLDs, termed PLD1 and PLD2, catalyze the hydrolysis of PC to release choline and yield phosphatidic acid (PA). PLD2 exhibits relatively high basal activity, b...

The tethering factor Munc13-4 is recruited to Weibel–Palade body (WPB) fusion sites after secretagogue stimulation to promote WPB exocytosis. Annexin A2-S100A10 is a novel Munc13-4 interaction partner assisting Munc13-4 tethering at the plasma membrane.

Summary Background Tissue factor (TF) is frequently overexpressed in cancer cells and correlated with more aggressive tumor phenotypes and poor prognosis. In addition to promoting coagulation-dependent metastasis and cancer-associated thrombosis, tumor cell-expressed TF mediates direct cell signaling involving the protease activated receptor (PAR) 2. Ixolaris is a tick-derived inhibitor of the TF-FVIIa-Xa coagulation initiation complex which blocks primary tumor growth and angiogenesis in glioblastoma and melanoma models. Methods Here we address the anti-tumor effects of Ixolaris in TF-VIIa-PAR2 signaling-dependent breast cancer models, a xenograft model of highly aggressive human MDA-MB-231mfp cells and a syngeneic model of PAR2-deficient and replete PyMT mouse mammary carcinoma cells. Results Ixolaris potently inhibited the procoagulant activity of human MDA-MB-231mfp or murine PyMT breast cancer cells. Ixolaris blocked signaling by the ternary TF-FVIIa-FXa complex, and, surprisingly, at higher concentrations also the binary TF-FVIIa complex on MDA-MB-231 cells. We show that Ixolaris interacts with certain residues in the human VIIa protease domain that are involved in PAR2 cleavage. In contrast to human VIIa, Ixolaris was a poor inhibitor of murine TF-FVIIa signaling and did not attenuate PAR2-dependent tumor growth in a syngeneic mouse model of breast cancer progression. Conclusion These data show that Ixolaris inhibits PAR2 cleavage specifically by human TF signaling complexes and suggest that Ixolaris may block tumor growth of human cell models with ectopic FVIIa expression through inhibition of direct TF-FVIIa-PAR2 signaling as well as its anticoagulant activity.

Human XT-I (xylosyltransferase I; EC 2.4.2.26) initiates the biosynthesis of the glycosaminoglycan linkage region and is a diagnostic marker of an enhanced proteoglycan biosynthesis. In the present study, we have investigated mutant enzymes of human XT-I and assessed the impact of the N-terminal region on the enzymatic activity. Soluble mutant enzymes of human XT-I with deletions at the N-terminal domain were expressed in insect cells and analysed for catalytic activity. As many as 260 amino acids could be truncated at the N-terminal region of the enzyme without affecting its catalytic activity. However, truncation of 266, 272 and 273 amino acids resulted in a 70, 90 and >98% loss in catalytic activity. Interestingly, deletion of the single 12 amino acid motif G261KEAISALSRAK272 leads to a loss-of-function XT-I mutant. This is in agreement with our findings analysing the importance of the Cys residues where we have shown that C276A mutation resulted in a nearly inactive XT-I enzyme. Moreover, we investigated the location of the heparin-binding site of human XT-I using the truncated mutants. Heparin binding was observed to be slightly altered in mutants lacking 289 or 568 amino acids, but deletion of the potential heparin-binding motif P721KKVFKI727 did not lead to a loss of heparin binding capacity. The effect of heparin or UDP on the XT-I activity of all mutants was not significantly different from that of the wild-type. Our study demonstrates that over 80% of the nucleotide sequence of the XT-I-cDNA is necessary for expressing a recombinant enzyme with full catalytic activity.