First-in-Class Humanized Antibody against Alternatively Spliced Tissue Factor Augments Anti-Metastatic Efficacy of Chemotherapy in a Preclinical Model of Pancreatic Ductal Adenocarcinoma.

Alternatively spliced tissue factor (asTF) promotes the progression of pancreatic ductal adenocarcinoma (PDAC) by activating ß1-integrins on PDAC cell surfaces. hRabMab1, a first-in-class humanized inhibitory anti-asTF antibody we recently developed, can suppress PDAC primary tumor growth as a single agent. Whether hRabMab1 has the potential to suppress metastases in PDAC is unknown. Following in vivo screening of three asTF-proficient human PDAC cell lines, we chose to make use of KRAS G12V-mutant human PDAC cell line PaCa-44, which yields aggressive primary orthotopic tumors with spontaneous spread to PDAC-relevant anatomical sites, along with concomitant severe leukocytosis. The experimental design featured orthotopic tumors formed by luciferase labeled PaCa-44 cells; administration of hRabMab1 alone or in combination with gemcitabine/paclitaxel (gem/PTX); and the assessment of the treatment outcomes on the primary tumor tissue as well as systemic spread. When administered alone, hRabMab1 exhibited poor penetration of tumor tissue; however, hRabMab1 was abundant in tumor tissue when co-administered with gem/PTX, which resulted in a significant decrease in tumor cell proliferation; leukocyte infiltration; and neovascularization. Gem/PTX alone reduced primary tumor volume, but not metastatic spread; only the combination of hRabMab1 and gem/PTX significantly reduced metastatic spread. RNA-seq analysis of primary tumors showed that the addition of hRabMab1 to gem/PTX enhanced the downregulation of tubulin binding and microtubule motor activity. In the liver, hRabMab1 reduced liver metastasis as a single agent. Only the combination of hRabMab1 and gem/PTX eliminated tumor cell-induced leukocytosis. We here demonstrate for the first time that hRabMab1 may help suppress metastasis in PDAC. hRabMab1's ability to improve the efficacy of chemotherapy is significant and warrants further investigation.

Potential utility of a multi-component coagulation factor panel to calculate MELD scores and assess the risk of portal vein thrombosis in chronic liver disease.

BACKGROUND: Current quantitative approaches to assess chronic liver disease (CLD) severity have limitations. Further, portal vein thrombosis (PVT) pre-liver transplant (LT) is a major contributor to morbidity in CLD; the means of detecting and/or predicting PVT are limited. We sought to explore whether plasma coagulation factor activity levels can serve as a substitute for prothrombin time/international normalized ratio (PT/INR) in the Model for End-stage Liver Disease (MELD), and/or help assess the risk of PVT. METHODS: Plasma activity levels of Factor V (FV), Factor VIII (FVIII), Protein C (PC), and Protein S (PS) and the concentrations of D-dimer, sP-selectin, and asTF were assessed in two cohorts of CLD patients (ambulatory, n = 42; LT, n = 43). RESULTS: FV and PC activity levels strongly correlated with MELD scores, which enabled the development of a novel scoring system based on multiple linear regressions of the correlations of FV and PC activity with MELD-Na that substitutes PT/INR. Six-month and 1-year follow-up revealed that our novel approach was non-inferior to MELD-Na at predicting mortality. A significant inverse correlation between FVIII activity levels and PVT was found in the LT cohort (p = 0.010); FV and PS activity levels were in-trend (p = 0.069, p = 0.064). We developed a logistic regression-based compensation score to identify patients at risk of PVT. CONCLUSIONS: We demonstrate that FV and PC activity levels may be used to replace PT/INR in MELD scoring. We also show the potential of using the combination of FV, FVIII, and PS activity levels to assess the risk of PVT in CLD.

Enhanced Efficacy of Combination of Gemcitabine and Phosphatidylserine-Targeted Nanovesicles against Pancreatic Cancer.

Phosphatidylserine (PS) is often externalized in viable pancreatic cancer cells and is therapeutically targetable using PS-selective drugs. One of the first-line treatments for advanced pancreatic cancer disease, gemcitabine (GEM), provides only marginal benefit to patients. We therefore investigated the therapeutic benefits of combining GEM and the PS-targeting drug, saposin C-dioleoylphosphatidylserine (SapC-DOPS), for treating pancreatic ductal adenocarcinoma (PDAC). Using cell-cycle analyses and a cell surface PS-based sorting method in vitro, we observed an increase in surface PS as cells progress through the cell cycle from G1 to G2/M. We also observed that GEM treatment preferentially targets G1 phase cells that have low surface PS, resulting in an increased median surface PS level of PDAC cells. Inversely, SapC-DOPS preferentially targets high surface PS cells that are predominantly in the G2/M phase. Finally, combination therapy in subcutaneous and orthotopic PDAC tumors in vivo with SapC-DOPS and GEM or Abraxane (Abr)/GEM (one of the current standards of care) significantly inhibits tumor growth and increases survival compared with individual treatments. Our studies confirm a surface PS and cell cycle-based enhancement of cancer cytotoxicity following SapC-DOPS treatment in combination with GEM or Abr/GEM. Thus, PDAC patients treated with Abr/GEM may benefit from concurrent administration of SapC-DOPS.

A single high-fat meal provokes pathological erythrocyte remodeling and increases myeloperoxidase levels: implications for acute coronary syndrome.

High-fat meal (HFM) consumption can produce acute lipemia and trigger myocardial infarction in patients with atherosclerosis, but the mechanisms are poorly understood. Erythrocytes (red blood cells, RBCs) intimately interact with inflammatory cells and blood vessels and play a complex role in regulating vascular function. Chronic high-fat feeding in mice induces pathological RBC remodeling, suggesting a novel link between HFM, RBCs, and vascular dysfunction. However, whether acute HFM can induce RBC remodeling in humans is unknown. Ten healthy individuals were subjected to biochemical testing and assessment of endothelial-dependent flow-mediated dilation (FMD) before and after a single HFM or iso-caloric meal (ICM). Following the HFM, triglyceride, cholesterol, and free fatty acid levels were all significantly increased, in conjunction with impaired post-prandial FMD. Additionally, peripheral blood smears demonstrated microcytes, remodeled RBCs, and fatty monocytes. Increased intracellular ROS and nitration of protein band 3 was detected in RBCs following the HFM. The HFM elevated plasma and RBC-bound myeloperoxidase (MPO), which was associated with impaired FMD and oxidation of HDL. Monocytic cells exposed to lipid in vitro released MPO, while porcine coronary arteries exposed to fatty acids ex vivo took up MPO. We demonstrate in humans that a single HFM induces pathological RBC remodeling and concurrently elevates MPO, which can potentially enter the blood vessel wall to trigger oxidative stress and destabilize vulnerable plaques. These novel findings may have implications for the short-term risk of HFM consumption and alimentary lipemia in patients with atherosclerosis.

Red Blood Cell Dysfunction Induced by High-Fat Diet: Potential Implications for Obesity-Related Atherosclerosis.

BACKGROUND: High-fat diet (HFD) promotes endothelial dysfunction and proinflammatory monocyte activation, which contribute to atherosclerosis in obesity. We investigated whether HFD also induces the dysfunction of red blood cells (RBCs), which serve as a reservoir for chemokines via binding to Duffy antigen receptor for chemokines (DARC). METHODS AND RESULTS: A 60% HFD for 12 weeks, which produced only minor changes in lipid profile in C57/BL6 mice, markedly augmented the levels of monocyte chemoattractant protein-1 bound to RBCs, which in turn stimulated macrophage migration through an endothelial monolayer. Levels of RBC-bound KC were also increased by HFD. These effects of HFD were abolished in DARC(-/-) mice. In RBCs from HFD-fed wild-type and DARC(-/-) mice, levels of membrane cholesterol and phosphatidylserine externalization were increased, fostering RBC-macrophage inflammatory interactions and promoting macrophage phagocytosis in vitro. When labeled ex vivo and injected into wild-type mice, RBCs from HFD-fed mice exhibited ≈3-fold increase in splenic uptake. Finally, RBCs from HFD-fed mice induced increased macrophage adhesion to the endothelium when they were incubated with isolated aortic segments, indicating endothelial activation. CONCLUSIONS: RBC dysfunction, analogous to endothelial dysfunction, occurs early during diet-induced obesity and may serve as a mediator of atherosclerosis. These findings may have implications for the pathogenesis of atherosclerosis in obesity, a worldwide epidemic.

Activation of carbonic anhydrase IX by alternatively spliced tissue factor under late-stage tumor conditions.

Molecules of the coagulation pathway predispose patients to cancer-associated thrombosis and also trigger intracellular signaling pathways that promote cancer progression. The primary transcript of tissue factor, the main physiologic trigger of blood clotting, can undergo alternative splicing yielding a secreted variant, termed asTF (alternatively spliced tissue factor). asTF is not required for normal hemostasis, but its expression levels positively correlate with advanced tumor stages in several cancers, including pancreatic adenocarcinoma. The asTF-overexpressing pancreatic ductal adenocarcinoma cell line Pt45.P1/asTF+ and its parent cell line Pt45.P1 were tested for growth and mobility under normoxic conditions that model early-stage tumors, and in the hypoxic environment of late-stage cancers. asTF overexpression in Pt45.P1 cells conveys increased proliferative ability. According to cell cycle analysis, the major fraction of Pt45.P1/asTF+ cells reside in the dividing G2/M phase of the cell cycle, whereas the parental Pt45.P1 cells are mostly confined to the quiescent G0/G1 phase. asTF overexpression is also associated with significantly higher mobility in cells plated under either normoxia or hypoxia. A hypoxic environment leads to upregulation of carbonic anhydrase IX (CAIX), which is more pronounced in Pt45.P1/asTF+ cells. Inhibition of CAIX by the compound U-104 significantly decreases cell growth and mobility of Pt45.P1/asTF+ cells in hypoxia, but not in normoxia. U-104 also reduces the growth of Pt45.P1/asTF+ orthotopic tumors in nude mice. CAIX is a novel downstream mediator of asTF in pancreatic cancer, particularly under hypoxic conditions that model late-stage tumor microenvironment.

Alternatively spliced tissue factor promotes breast cancer growth in a ß1 integrin-dependent manner.

Full-length tissue factor (flTF), the coagulation initiator, is overexpressed in breast cancer (BrCa), but associations between flTF expression and clinical outcome remain controversial. It is currently not known whether the soluble alternatively spliced TF form (asTF) is expressed in BrCa or impacts BrCa progression. We are unique in reporting that asTF, but not flTF, strongly associates with both tumor size and grade, and induces BrCa cell proliferation by binding to ß1 integrins. asTF promotes oncogenic gene expression, anchorage-independent growth, and strongly up-regulates tumor expansion in a luminal BrCa model. In basal BrCa cells that constitutively express both TF isoforms, asTF blockade reduces tumor growth and proliferation in vivo. We propose that asTF plays a major role in BrCa progression acting as an autocrine factor that promotes tumor progression. Targeting asTF may comprise a previously unexplored therapeutic strategy in BrCa that stems tumor growth, yet does not impair normal hemostasis.

"Soluble Tissue Factor" in the 21st Century: Definitions, Biochemistry, and Pathophysiological Role in Thrombus Formation.

Tissue factor (TF), the main trigger of blood coagulation, is essential for normal hemostasis. Over the past 20 years, heightened intravascular levels and activity of TF have been increasingly perceived as an entity that significantly contributes to venous as well as arterial thrombosis. Various forms of the TF protein in the circulation have been described and proposed to be thrombogenic. Aside from cell and vessel wall-associated TF, several forms of non-cell-associated TF circulate in plasma and may serve as a causative factor in thrombosis. At the present time, no firm consensus exists regarding the extent, the vascular setting(s), and/or the mechanisms by which such TF forms contribute to thrombus initiation and propagation. Here, we summarize the existing paradigms and recent, sometimes paradigm-shifting findings elucidating the structural, mechanistic, and pathophysiological characteristics of plasma-borne TF.

Levels of Alternatively Spliced Tissue Factor in the Plasma of Patients with Pancreatic Cancer May Help Predict Aggressive Tumor Phenotype.

BACKGROUND: Circulating ('blood-borne') tissue factor (TF) is implicated in the pathogenesis of several chronic conditions, most notably cardiovascular disease, diabetes, and cancer. Full-length TF is an integral membrane protein, while alternatively spliced TF (asTF) can be secreted and, owing to its unique C-terminus, selectively detected in bio-specimens. The predictive and/or prognostic value of asTF in the circulation is unknown. In a retrospective study, we measured levels of circulating asTF in healthy subjects and individuals with acute coronary syndrome (ACS), diabetes mellitus (DM), ongoing ACS + DM, and pancreatic ductal adenocarcinoma (PDAC). METHODS: The prototype-tailored procedure (Diagnostica Stago) was used to measure asTF in plasma from 205 subjects. RESULTS: There was no significant difference between the proportion of healthy subjects with asTF ≥200 pg/mL and those with ACS, DM, or ACS + DM. The proportion of pancreatic cancer patients (n = 43; PDAC: 42; pancreatic neuroendocrine tumor: 1) with asTF levels ≥200 pg/mL was significantly higher than in healthy subjects; asTF levels ≥200 pg/mL were detected more often in patients with unresectable disease irrespective of initial evaluation and/or preoperative carbohydrate antigen 19-9 (CA19-9) levels. CONCLUSIONS: While asTF levels ≥200 pg/mL are not observed with increased frequency in patients with ACS and/or DM, they do occur more frequently in the plasma of patients with pancreatic cancer and are associated with lower likelihood of tumor resectability, irrespective of the preoperative diagnosis. asTF may thus have utility as a novel marker of aggressive pancreatic tumor phenotype.

Transplanted perivascular adipose tissue accelerates injury-induced neointimal hyperplasia: role of monocyte chemoattractant protein-1.

OBJECTIVE: Perivascular adipose tissue (PVAT) expands during obesity, is highly inflamed, and correlates with coronary plaque burden and increased cardiovascular risk. We tested the hypothesis that PVAT contributes to the vascular response to wire injury and investigated the underlying mechanisms. APPROACH AND RESULTS: We transplanted thoracic aortic PVAT from donor mice fed a high-fat diet to the carotid arteries of recipient high-fat diet-fed low-density lipoprotein receptor knockout mice. Two weeks after transplantation, wire injury was performed, and animals were euthanized 2 weeks later. Immunohistochemistry was performed to quantify adventitial macrophage infiltration and neovascularization and neointimal lesion composition and size. Transplanted PVAT accelerated neointimal hyperplasia, adventitial macrophage infiltration, and adventitial angiogenesis. The majority of neointimal cells in PVAT-transplanted animals expressed α-smooth muscle actin, consistent with smooth muscle phenotype. Deletion of monocyte chemoattractant protein-1 in PVAT substantially attenuated the effects of fat transplantation on neointimal hyperplasia and adventitial angiogenesis, but not adventitial macrophage infiltration. Conditioned medium from perivascular adipocytes induced potent monocyte chemotaxis in vitro and angiogenic responses in cultured endothelial cells. CONCLUSIONS: These findings indicate that PVAT contributes to the vascular response to wire injury, in part through monocyte chemoattractant protein-1-dependent mechanisms.

Alternatively spliced tissue factor contributes to tumor spread and activation of coagulation in pancreatic ductal adenocarcinoma.

Alternatively spliced tissue factor (asTF) promotes neovascularization and monocyte recruitment via integrin ligation. While asTF mRNA has been detected in some pancreatic ductal adenocarcinoma (PDAC) cell lines and increased asTF expression can promote PDAC growth in a subcutaneous model, the expression of asTF protein in bona fide PDAC lesions and/or its role in metastatic spread are yet to be ascertained. We here report that asTF protein is abundant in lesional and stromal compartments of the five studied types of carcinoma including PDAC. Analysis of 29 specimens of PDAC revealed detectable asTF in >90% of the lesions with a range of staining intensities. asTF levels in PDAC lesions positively correlated with the degree of monocyte infiltration. In an orthotopic model, asTF-overexpressing high-grade PDAC cell line Pt45P1/asTF+ produced metastases to distal lymph nodes, which stained positive for asTF. PDAC cells stimulated with and/or overexpressing asTF exhibited upregulation of genes implicated in PDAC progression and metastatic spread. Pt45P1/asTF+ cells displayed higher coagulant activity compared to Pt45P1 cells; the same effect was observed for cell-derived microparticles (MPs). Our findings demonstrate that asTF is expressed in PDAC and lymph node metastases and potentiates PDAC spread in vivo. asTF elicits global changes in gene expression likely involved in tumor progression and metastatic dissemination, and it also enhances the procoagulant potential of PDAC cells and cell-derived MPs. Thus, asTF may comprise a novel therapeutic target to treat PDAC and, possibly, its thrombotic complications.

Tumor-derived tissue factor activates coagulation and enhances thrombosis in a mouse xenograft model of human pancreatic cancer.

Cancer patients often have an activated clotting system and are at increased risk for venous thrombosis. In the present study, we analyzed tissue factor (TF) expression in 4 different human pancreatic tumor cell lines for the purpose of producing derivative tumors in vivo. We found that 2 of the lines expressed TF and released TF-positive microparticles (MPs) into the culture medium. The majority of TF protein in the culture medium was associated with MPs. Only TF-positive cell lines activated coagulation in nude mice, and this activation was abolished by an anti-human TF Ab. Of the 2 TF-positive lines, only one produced detectable levels of human MP TF activity in the plasma when grown orthotopically in nude mice. Surprisingly, < 5% of human TF protein in plasma from tumor-bearing mice was associated with MPs. Mice with TF-positive tumors and elevated levels of circulating TF-positive MPs had increased thrombosis in a saphenous vein model. In contrast, we observed no difference in thrombus weight between tumor-bearing and control mice in an inferior vena cava stenosis model. The results of the present study using a xenograft mouse model suggest that tumor TF activates coagulation, whereas TF on circulating MPs may trigger venous thrombosis.

Myeloid-specific Krüppel-like factor 2 inactivation increases macrophage and neutrophil adhesion and promotes atherosclerosis.

RATIONALE: Hemizygous deficiency of the transcription factor Krüppel-like factor 2 (KLF2) has been shown previously to augment atherosclerosis in hypercholesterolemic mice. However, the cell type responsible for the increased atherosclerosis due to KLF2 deficiency has not been identified. This study examined the consequence of myeloid cell-specific KLF2 inactivation in atherosclerosis. METHODS AND RESULTS: Cell-specific knockout mice were generated by Cre/loxP recombination. Macrophages isolated from myeloid-specific Klf2 knockout (myeKlf2(-/-)) mice were similar to myeKlf2(+/+) macrophages in response to activation, polarization, and lipid accumulation. However, in comparison to myeKlf2(+/+) macrophages, myeKlf2(-/-) macrophages adhered more robustly to endothelial cells. Neutrophils from myeKlf2(-/-) mice also adhered more robustly to endothelial cells, and fewer myeKlf2(-/-) neutrophils survived in culture over a 24-hour period in comparison with myeKlf2(+/+) neutrophils. When myeKlf2(-/-) mice were mated to Ldlr(-/-) mice and then fed a high fat and high cholesterol diet, significant increase in atherosclerosis was observed in the myeKlf2(-/-)Ldlr(-/-) mice compared with myeKlf2(+/+)Ldlr(-/-) littermates. The increased atherosclerosis in myeKlf2(-/-)Ldlr(-/-) mice was associated with elevated presence of neutrophils and macrophages, with corresponding increase of myeloperoxidase as well as chlorinated and nitrosylated tyrosine epitopes in their lesion areas compared with myeKlf2(+/+)Ldlr(-/-) mice. CONCLUSIONS: This study documents a role for myeloid KLF2 expression in modulating atherosclerosis. The increased neutrophil accumulation and atherosclerosis progression with myeloid-specific KLF2 deficiency also underscores the importance of neutrophils in promoting vascular oxidative stress and atherosclerosis. Collectively, these results suggest that elevating KLF2 expression may be a novel strategy for prevention and treatment of atherosclerosis.

Human coronary artery perivascular adipocytes overexpress genes responsible for regulating vascular morphology, inflammation, and hemostasis.

Inflammatory cross talk between perivascular adipose tissue and the blood vessel wall has been proposed to contribute to the pathogenesis of atherosclerosis. We previously reported that human perivascular (PV) adipocytes exhibit a proinflammatory phenotype and less adipogenic differentiation than do subcutaneous (SQ) adipocytes. To gain a global view of the genomic basis of biologic differences between PV and SQ adipocytes, we performed genome-wide expression analyses to identify differentially expressed genes between adipocytes derived from human SQ vs. PV adipose tissues. Although >90% of well-expressed genes were similarly regulated, we identified a signature of 307 differentially expressed genes that were highly enriched for functions associated with the regulation of angiogenesis, vascular morphology, inflammation, and blood clotting. Of the 156 PV upregulated genes, 59 associate with angiogenesis, vascular biology, or inflammation, noteworthy of which include TNFRSF11B (osteoprotegerin), PLAT, TGFB1, THBS2, HIF1A, GATA6, and SERPINE1. Of 166 PV downregulated genes, 21 associated with vascular biology and inflammation, including ANGPT1, ANGPTL1, and VEGFC. Consistent with the emergent hypothesis that PV adipocytes differentially regulate angiogenesis and inflammation, cell culture-derived adipocyte-conditioned media from PV adipocytes strongly enhanced endothelial cell tubulogenesis and monocyte migration compared with media from SQ adipocytes. These findings demonstrate that PV adipocytes have the potential to significantly modulate vascular inflammatory crosstalk in the setting of atherosclerosis by their ability to signal to both endothelial and inflammatory cells.

Nonproteolytic properties of murine alternatively spliced tissue factor: implications for integrin-mediated signaling in murine models.

This study was performed to determine whether murine alternatively spliced tissue factor (masTF) acts analogously to human alternatively spliced tissue factor (hasTF) in promoting neovascularization via integrin ligation. Immunohistochemical evaluation of a spontaneous murine pancreatic ductal adenocarcinoma model revealed increased levels of masTF and murine full-length tissue factor (mflTF) in tumor lesions compared with benign pancreas; furthermore, masTF colocalized with mflTF in spontaneous aortic plaques of Ldlr(-/-) mice, indicating that masTF is likely involved in atherogenesis and tumorigenesis. Recombinant masTF was used to perform in vitro and ex vivo studies examining its integrin-mediated biologic activity. Murine endothelial cells (ECs) rapidly adhered to masTF in a ß3-dependent fashion. Using adult and embryonic murine ECs, masTF potentiated cell migration in transwell assays. Scratch assays were performed using murine and primary human ECs; the effects of masTF and hasTF were comparable in murine ECs, but in human ECs, the effects of hasTF were more pronounced. In aortic sprouting assays, the potency of masTF-triggered vessel growth was undistinguishable from that observed with hasTF. The proangiogenic effects of masTF were found to be Ccl2-mediated, yet independent of vascular endothelial growth factor. In murine ECs, masTF and hasTF upregulated genes involved in inflammatory responses; murine and human ECs stimulated with masTF and hasTF exhibited increased interaction with murine monocytic cells under orbital shear. We propose that masTF is a functional homolog of hasTF, exerting some of its key effects via ß3 integrins. Our findings have implications for the development of murine models to examine the interplay between blood coagulation, atherosclerosis and cancer.

Potential factors influencing the development of thrombocytopenia and consumptive coagulopathy after genetically modified pig liver xenotransplantation.

Upregulation of tissue factor (TF) expression on activated donor endothelial cells (ECs) triggered by the immune response (IR) has been considered the main initiator of consumptive coagulopathy (CC). In this study, we aimed to identify potential factors in the development of thrombocytopenia and CC after genetically engineered pig liver transplantation in baboons. Baboons received a liver from either an α1,3-galactosyltransferase gene-knockout (GTKO) pig (n = 1) or a GTKO pig transgenic for CD46 (n = 5) with immunosuppressive therapy. TF exposure on recipient platelets and peripheral blood mononuclear cell (PBMCs), activation of donor ECs, platelet and EC microparticles, and the IR were monitored. Profound thrombocytopenia and thrombin formation occurred within minutes of liver reperfusion. Within 2 h, circulating platelets and PBMCs expressed functional TF, with evidence of aggregation in the graft. Porcine ECs were negative for expression of P- and E-selectin, CD106, and TF. The measurable IR was minimal, and the severity and rapidity of thrombocytopenia were not alleviated by prior manipulation of the IR. We suggest that the development of thrombocytopenia/CC may be associated with TF exposure on recipient platelets and PBMCs (but possibly not with activation of donor ECs). Recipient TF appears to initiate thrombocytopenia/CC by a mechanism that may be independent of the IR.

SARS-CoV-2, platelets, and endothelium: coexistence in space and time, or a pernicious ménage à trois?

As we enter year 3 of SARS-CoV-2 pandemic, long-term consequences of COVID-19 have become a major public health issue worldwide; however, the molecular and cellular underpinnings of 'long COVID' remain very poorly understood. A paradigm has recently emerged that thrombo-inflammatory consequences of SARS-CoV-2's impact on endothelial cells and platelets likely play a significant role in the development of chronic symptomatology associated with COVID-19. In this brief overview, we discuss the recent findings pertaining to the detection of SARS-CoV-2 virions in vascular cell subtypes, the contribution of the coagulation system to the development of 'long COVID', and the potential role of stem/progenitor cells in the viral and thrombotic dissemination in this disorder.

Integrin regulation by tissue factor promotes cancer stemness and metastatic dissemination in breast cancer.

Tissue Factor (TF) is the initiator of blood coagulation but also functions as a signal transduction receptor. TF expression in breast cancer is associated with higher tumor grade, metastasis and poor survival. The role of TF signaling on the early phases of metastasis has never been addressed. Here, we show an association between TF expression and metastasis as well as cancer stemness in 574 breast cancer patients. In preclinical models, blockade of TF signaling inhibited metastasis tenfold independent of primary tumor growth. TF blockade caused a reduction in epithelial-to-mesenchymal-transition, cancer stemness and expression of the pro-metastatic markers Slug and SOX9 in several breast cancer cell lines and in ex vivo cultured tumor cells. Mechanistically, TF forms a complex with ß1-integrin leading to inactivation of ß1-integrin. Inhibition of TF signaling induces a shift in TF-binding from α3ß1-integrin to α6ß4 and dictates FAK recruitment, leading to reduced epithelial-to-mesenchymal-transition and tumor cell differentiation. In conclusion, TF signaling inhibition leads to reduced pro-metastatic transcriptional programs, and a subsequent integrin ß1 and ß4-dependent reduction in metastasic dissemination.

Cdc2-like kinases and DNA topoisomerase I regulate alternative splicing of tissue factor in human endothelial cells.

Tumor necrosis factor (TNF)-alpha-stimulated human umbilical vein endothelial cells express 2 naturally occurring forms of tissue factor (TF), the primary initiator of blood coagulation: the soluble alternatively spliced isoform and the full-length TF isoform. The regulatory pathways enabling this phenomenon are completely unknown. Cdc2-like kinases and DNA topoisomerase I regulate alternative splicing via phosphorylation of serine/arginine-rich proteins. In this study, we examined effects of serine/arginine-rich protein kinases on TF splicing following stimulation with TNF-alpha. Human endothelial cells were pretreated with specific inhibitors or small interfering RNAs against Cdc2-like kinases and DNA topoisomerase I before stimulation with TNF-alpha. TF levels were determined by semiquantitative RT-PCR, real-time PCR, and Western blotting. Cellular procoagulant activity was analyzed in a chromogenic TF activity assay. All 4 known Cdc2-like kinases forms were expressed in human endothelial cells. Selective inhibition of Cdc2-like kinases and DNA topoisomerase I elicited distinct changes in TF biosynthesis in TNF-alpha-stimulated endothelial cells, which impacted endothelial procoagulant activity. This study is the first to demonstrate that serine/arginine-rich protein kinases modulate splicing of TF pre-mRNA in human endothelial cells and, consequently, endothelial procoagulant activity under inflammatory conditions.