Identification of a novel human tissue factor splice variant that is upregulated in tumor cells

The Role of Tissue Factor In Signaling Pathways of Pathological Conditions and Angiogenesis

Tissue factor (TF) is an integral transmembrane protein associated with the extrinsic coagulation pathway. TF gene expression is regulated in response to inflammatory cytokines, bacterial lipopolysaccharides, and mechanical injuries. TF activity may be affected by phosphorylation of its cytoplasmic domain and alternative splicing. TF acts as the primary initiator of physiological hemostasis, which prevents local bleeding at the injury site. However, aberrant expression of TF, accompanied by the severity of diseases and infections under various pathological conditions, triggers multiple signaling pathways that support thrombosis, angiogenesis, inflammation, and metastasis. Protease-activated receptors (PARs) are central in the downstream signaling pathways of TF. In this study, we have reviewed the TF signaling pathways in different pathological conditions, such as wound injury, asthma, cardiovascular diseases (CVDs), viral infections, cancer and pathological angiogenesis. Angiogenic activities of TF are critical in the repair of wound injuries and aggressive behavior of tumors, which are mainly performed by the actions of vascular endothelial growth factor (VEGF) and hypoxia-inducible factor-1 (HIF1-α). Pro-inflammatory effects of TF have been reported in asthma, CVDs and viral infections, including COVID-19, which result in tissue hypertrophy, inflammation, and thrombosis. TF-FVII induces angiogenesis via clotting-dependent and -independent mechanisms. Clottingdependent angiogenesis is induced via the generation of thrombin and cross-linked fibrin network, which facilitate vessel infiltration and also act as a reservoir for endothelial cells (ECs) growth factors. Expression of TF in tumor cells and ECs triggers clotting-independent angiogenesis through induction of VEGF, urokinase-type plasminogen activator (uPAR), early growth response 1 (EGR1), IL8, and cysteine-rich angiogenic inducer 61 (Cyr61).

Tissue factor (coagulation factor III): a potential double-edge molecule to be targeted and re-targeted toward cancer

Tissue factor (TF) is a protein that plays a critical role in blood clotting, but recent research has also shown its involvement in cancer development and progression. Herein, we provide an overview of the structure of TF and its involvement in signaling pathways that promote cancer cell proliferation and survival, such as the PI3K/AKT and MAPK pathways. TF overexpression is associated with increased tumor aggressiveness and poor prognosis in various cancers. The review also explores TF's role in promoting cancer cell metastasis, angiogenesis, and venous thromboembolism (VTE). Of note, various TF-targeted therapies, including monoclonal antibodies, small molecule inhibitors, and immunotherapies have been developed, and preclinical and clinical studies demonstrating the efficacy of these therapies in various cancer types are now being evaluated. The potential for re-targeting TF toward cancer cells using TF-conjugated nanoparticles, which have shown promising results in preclinical studies is another intriguing approach in the path of cancer treatment. Although there are still many challenges, TF could possibly be a potential molecule to be used for further cancer therapy as some TF-targeted therapies like Seagen and Genmab's tisotumab vedotin have gained FDA approval for treatment of cervical cancer. Overall, based on the overviewed studies, this review article provides an in-depth overview of the crucial role that TF plays in cancer development and progression, and emphasizes the potential of TF-targeted and re-targeted therapies as potential approaches for the treatment of cancer.

The Tissue Factor Pathway in Cancer: Overview and Role of Heparan Sulfate Proteoglycans

Historically, the only focus on tissue factor (TF) in clinical pathophysiology has been on its function as the initiation of the extrinsic coagulation cascade. This obsolete vessel-wall TF dogma is now being challenged by the findings that TF circulates throughout the body as a soluble form, a cell-associated protein, and a binding microparticle. Furthermore, it has been observed that TF is expressed by various cell types, including T-lymphocytes and platelets, and that certain pathological situations, such as chronic and acute inflammatory states, and cancer, may increase its expression and activity. Transmembrane G protein-coupled protease-activated receptors can be proteolytically cleaved by the TF:FVIIa complex that develops when TF binds to Factor VII (PARs). The TF:FVIIa complex can activate integrins, receptor tyrosine kinases (RTKs), and PARs in addition to PARs. Cancer cells use these signaling pathways to promote cell division, angiogenesis, metastasis, and the maintenance of cancer stem-like cells. Proteoglycans play a crucial role in the biochemical and mechanical properties of the cellular extracellular matrix, where they control cellular behavior via interacting with transmembrane receptors. For TFPI.fXa complexes, heparan sulfate proteoglycans (HSPGs) may serve as the primary receptor for uptake and degradation. The regulation of TF expression, TF signaling mechanisms, their pathogenic effects, and their therapeutic targeting in cancer are all covered in detail here.

Expression of flTF and asTF splice variants in various cell strains and tissues

Tissue factor (TF) expressed at the protein level includes two isoforms: The membrane-bound full-length TF (flTF) and the soluble alternatively spliced TF (asTF). flTF is the major thrombogenic form of TF, whereas asTF is more closely associated with tumor growth, angiogenesis, metastasis and cell growth. In order to further investigate the different expression and functions of TF splice variants, the expression of these two splice variants were detected in numerous cell strains and tissues in the present study. Quantitative polymerase chain reaction was used to measure the transcript levels of the TF variants in 11 human cell lines, including cervical cancer, breast cancer, hepatoblastoma, colorectal cancer and umbilical vein cells, and five types of tissue specimen, including placenta, esophageal cancer, breast cancer, cervical cancer (alongside normal cervical tissues) and non-small cell lung cancer (alongside adjacent and normal tissues). Furthermore, the effects of chenodeoxycholic acid (CDCA) and apolipoprotein M (apoM) on the two variants were investigated. The results demonstrated that flTF was the major form of TF, and the mRNA expression levels of flTF were higher than those of asTF in all specimens tested. CDCA significantly upregulated the mRNA expression levels of the two variants. Furthermore, overexpression of apoM promoted the expression levels of asTF in Caco-2 cells. The mRNA expression levels of asTF in cervical cancer tissues were significantly higher than in the corresponding normal tissues. To the best of our knowledge, the present study is the first to compare the expression of flTF and asTF in various samples. The results demonstrated that CDCA and apoM may modulate TF isoforms in different cell lines, and suggested that asTF may serve a role in the pathophysiological mechanism underlying cervical cancer development. In conclusion, the TF isoforms serve important and distinct roles in pathophysiological processes.

Novel Splicing of Immune System Thyroid Stimulating Hormone β-Subunit-Genetic Regulation and Biological Importance

Thyroid stimulating hormone (TSH), a glycoprotein hormone produced by the anterior pituitary, controls the production of thyroxine (T₄) and triiodothyronine (T₃) in the thyroid. TSH is also known to be produced by the cells of the immune system; however, the physiological importance of that to the organism is unclear. We identified an alternatively-spliced form of TSHβ that is present in both humans and mice. The TSHβ splice variant (TSHβv), although produced at low levels by the pituitary, is the primary form made by hematopoietic cells in the bone marrow, and by peripheral leukocytes. Recent studies have linked TSHβv functionally to a number of health-related conditions, including enhanced host responses to infection and protection against osteoporosis. However, TSHβv also has been associated with autoimmune thyroiditis in humans. Yet to be identified is the process by which the TSHβv isoform is produced. Here, a set of genetic steps is laid out through which human TSHβv is generated using splicing events that result in a novel transcript in which exon 2 is deleted, exon 3 is retained, and the 3' end of intron 2 codes for a signal peptide of the TSHβv polypeptide.

Co-expression of tissue factor and IL-6 in immature endothelial cells of cerebral cavernous malformations

Cerebral cavernous malformations (CCMs) are congenital abnormal clusters of capillaries that are prone to leaking and thought to result from a disorder of endothelial cells. The underlying pathology of CCM is not fully understood. We analyzed the expression of tissue factor (TF) and interleukin-6 (IL-6) in CCMs to determine the association of TF and IL-6 with clinical and pathological findings. Thirteen cases of operative specimens of sporadic CCMs were included in this study. The expression of messenger RNA of TF and IL-6 was assayed and the association with clinical factors was investigated. Then, the distribution of TF and IL-6 was examined with immunofluorescence. The mRNA expression of TF of CCMs was significantly higher than that of the control (p=0.017), and was correlated with the number of hemorrhage appearances (p=0.190, ρ=0.62). The mRNA expression level of IL-6 was significantly correlated with the mRNA expression level of TF (p=0.034, ρ=0.58). Examination of immunostained sections indicated that TF⁺ cells were also positive for IL-6, and distributed around normal endothelial cells. Moreover, the TF⁺/IL-6⁺ cells expressed CD31 and VEGFR2. The expressions of IL-6 and TF were correlated, and both were present in the same immature endothelial cells. TF is elevated in CCM and might mediate progressive events. These factors may play a prognostic role in CCM.

Evaluation of procoagulant tissue factor expression in canine hemangiosarcoma cell lines

OBJECTIVE To evaluate expression of procoagulant tissue factor (TF) by canine hemangiosarcoma cells in vitro. SAMPLES 4 canine hemangiosarcoma cell lines (SB-HSA [mouse-passaged cutaneous tumor], Emma [primary metastatic brain tumor], and Frog and Dal-1 [primary splenic tumors]) and 1 nonneoplastic canine endothelial cell line (CnAoEC). PROCEDURES TF mRNA and TF antigen expression were evaluated by quantitative real-time PCR assay and flow cytometry, respectively. Thrombin generation was measured in canine plasma and in coagulation factor-replete or specific coagulation factor-deficient human plasma by calibrated automated thrombography. Corn trypsin inhibitor and annexin V were used to examine contributions of contact activation and membrane-bound phosphatidylserine, respectively, to thrombin generation. RESULTS All cell lines expressed TF mRNA and antigen, with significantly greater expression of both products in SB-HSA and Emma cells than in CnAoEC. A greater percentage of SB-HSA cells expressed TF antigen, compared with other hemangiosarcoma cell lines. All hemangiosarcoma cell lines generated significantly more thrombin than did CnAoEC in canine or factor-replete human plasma. Thrombin generation induced by SB-HSA cells was significantly lower in factor VII-deficient plasma than in factor-replete plasma and was abolished in factor X-deficient plasma; residual thrombin generation in factor VII-deficient plasma was abolished by incubation of cells with annexin V. Thrombin generation by SB-HSA cells was unaffected by the addition of corn trypsin inhibitor. CONCLUSIONS AND CLINICAL RELEVANCE Hemangiosarcoma cell lines expressed procoagulant TF in vitro. Further research is needed to determine whether TF can be used as a biomarker for hemostatic dysfunction in dogs with hemangiosarcoma.

Biological relevance of tissue factor and IL-6 in arteriovenous malformations

Arteriovenous malformations (AVMs) are congenital abnormal vessels that shunt blood directly from the arterial to the venous system without a capillary bed. The underlying pathology of AVMs is not fully understood. The objective of the study was to determine the association between the expression patterns of tissue factor (TF) and interleukin-6 (IL-6) in AVMs with clinical and pathological findings. Eighteen cases of sporadic AVM with operative specimens were included in this study. The expression of messenger RNA (mRNA) of TF and IL-6 was assayed, and association with clinical factors was investigated. The distribution of TF and IL-6 was examined with immunofluorescence. The mRNA expression of TF was significantly higher in AVM specimens than in control tissues (P = 0.002) and significantly higher in the symptomatic group than in the asymptomatic group (P = 0.037). The mRNA expression of IL-6 was likewise significantly higher in AVM specimens than in control tissues (P = 0.038). Examination of immunostained sections indicated that TF⁺ cells were also positive for IL-6 and were distributed around normal endothelial cells and pericytes. Moreover, TF⁺/IL-6⁺ cells also expressed CD31, vascular endothelial growth factor receptor 2 (VEGFR2), and platelet-derived growth factor receptor beta (PDGFR-beta). These results suggest that TF is elevated in AVMs and that it mediates symptomatic events. IL-6 is associated with the angiogenic activity of TF, and both are present in the same abnormal endothelial cells and pericytes. These factors may have interactive effects and may serve in a prognostic role for AVMs.

Tissue Factor: A Conventional or Alternative Target in Cancer Therapy

BACKGROUND

Tissue factor (TF) is an evolutionary conserved glycoprotein that plays an important role in the pathogenesis of cancer. TF is expressed in 2 naturally occurring protein isoforms, membrane-bound full-length (fl)TF and soluble alternatively spliced (as)TF. Both isoforms have been shown to affect a variety of pathophysiologically relevant functions, such as tumor-associated angiogenesis, thrombogenicity, tumor growth, and metastasis. Therefore, targeting TF either by direct inhibition or indirectly, i.e., on a posttranscriptional level, offers a novel therapeutic option for cancer treatment.

CONTENT

In this review we summarize the latest findings regarding the role of TF and its isoforms in cancer biology. Moreover, we briefly depict and discuss the therapeutic potential of direct and/or indirect inhibition of TF activity and expression for the treatment of cancer.

SUMMARY

asTF and flTF play important and often distinct roles in cancer biology, i.e., in thrombogenicity and angiogenesis, which is mediated by isoform-specific signal transduction pathways. Therefore, both TF isoforms and downstream signaling are promising novel therapeutic targets in malignant diseases.

Alternatively spliced tissue factor promotes plaque angiogenesis through the activation of hypoxia-inducible factor-1α and vascular endothelial growth factor signaling

BACKGROUND

Alternatively spliced tissue factor (asTF) is a novel isoform of full-length tissue factor, which exhibits angiogenic activity. Although asTF has been detected in human plaques, it is unknown whether its expression in atherosclerosis causes increased neovascularization and an advanced plaque phenotype.

METHODS AND RESULTS

Carotid (n=10) and coronary (n=8) specimens from patients with stable or unstable angina were classified as complicated or uncomplicated on the basis of plaque morphology. Analysis of asTF expression and cell type-specific expression revealed a strong expression and colocalization of asTF with macrophages and neovessels within complicated, but not uncomplicated, human plaques. Our results showed that the angiogenic activity of asTF is mediated via hypoxia-inducible factor-1α upregulation through integrins and activation of phosphatidylinositol-3-kinase/Akt and mitogen-activated protein kinase pathways. Hypoxia-inducible factor-1α upregulation by asTF also was associated with increased vascular endothelial growth factor expression in primary human endothelial cells, and vascular endothelial growth factor-Trap significantly reduced the angiogenic effect of asTF in vivo. Furthermore, asTF gene transfer significantly increased neointima formation and neovascularization after carotid wire injury in ApoE(-/-) mice.

CONCLUSIONS

The results of this study provide strong evidence that asTF promotes neointima formation and angiogenesis in an experimental model of accelerated atherosclerosis. Here, we demonstrate that the angiogenic effect of asTF is mediated via the activation of the hypoxia-inducible factor-1/vascular endothelial growth factor signaling. This mechanism may be relevant to neovascularization and the progression and associated complications of human atherosclerosis as suggested by the increased expression of asTF in complicated versus uncomplicated human carotid and coronary plaques.

The role of tissue factor isoforms in cancer biology

Tissue Factor (TF) is an evolutionary conserved glycoprotein, which is of immense importance for a variety of biologic processes. TF is expressed in two naturally occurring protein isoforms, membrane-bound "full-length" (fl)TF and soluble alternatively spliced (as)TF. The TF isoform expression is differentially modulated on post-transcriptional level via regulatory factors, such as serine/arginine-rich (SR) proteins, SR protein kinases and micro (mi)RNAs. Both isoforms mediate a variety of physiologic- and pathophysiologic-relevant functions, such as thrombogenicity, angiogenesis, cell signaling, tumor cell proliferation and metastasis. In this review, we will depict the main mechanisms regulating the TF isoform expression in cancer and under other pathophysiologic-relevant conditions. Moreover, we will summarize and discuss the latest findings regarding the role of TF and its isoforms in cancer biology.

Regulation of vascular function on posttranscriptional level

Posttranscriptional control of gene expression is crucial for regulating plurality of proteins and functional plasticity of the proteome under (patho)physiologic conditions. Alternative splicing as well as micro (mi)RNA-mediated mechanisms play an important role for the regulation of protein expression on posttranscriptional level. Both alternative splicing and miRNAs were shown to influence cardiovascular functions, such as endothelial thrombogenicity and the vascular tone, by regulating the expression of several vascular proteins and their isoforms, such as Tissue Factor (TF) or the endothelial nitric oxide synthase (eNOS). This review will summarize and discuss the latest findings on the (patho)physiologic role of alternative splicing processes as well as of miRNAs on modulation of vascular functions, such as coagulation, thrombosis, and regulation of the vascular tone.

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.

Tissue factor as a novel marker for detection of circulating cancer cells

Tissue factor (TF) is a molecular marker that is up-regulated in cancer cells and aids tumoral dissemination. Our purpose was to develop a nested RT-PCR strategy against TF for detecting blood-borne tumour cells. Our method detected TF expression in a minimum of 1.5 pg total RNA from MCF7 cells. A preliminary study in blood samples from 16 advanced breast carcinoma patients showed that 80% of patients with high TF load progressed and died, while only 18% with low TF load showed the same behaviour. Kaplan-Meier analysis confirmed worse overall survival in patients with high TF load.

Tissue factor in cancer progression and angiogenesis

Constitutive expression of tissue factor (TF) by cancer cells triggers local and systemic activation of the coagulation cascade and is a major cause of cancer-associated thrombosis. Primary breast cancer biopsies show a marked upregulation of TF and protease activated receptor (PAR) 2, as well as increased TF cytoplasmic domain phosphorylation that is correlated with cancer relapse. TF signaling involving PAR2 and integrins has multiple effects on angiogenesis and tumor progression. The non-coagulant, alternatively spliced form of TF retains an integrin-binding site and, upon deposition into the tumor stroma, stimulates angiogenesis by ligating endothelial integrins alpha(v)beta(3) and alpha(6)beta(1). On tumor cells, full-length TF is constitutively associated with laminin-binding beta(1) integrins that support TF-VIIa-PAR2 signaling leading to upregulation of pro-angiogenic and immune modulatory cytokines and growth factors. Deficiency of PAR2, but not of the thrombin receptor PAR1, delays spontaneous breast cancer development and the angiogenic switch in mice. In addition, human xenograft breast cancer growth and angiogenesis is suppressed by selective antibody inhibition of TF-VIIa-PAR2 signaling, but not by blocking TF initiated coagulation. Thus, interruption of TF signaling represents a potential anti-angiogenic strategy that does not carry an increased risk of bleeding associated with prolonged inhibition of the TF coagulation pathway.

Vitamin A metabolite, all-trans-retinoic acid, mediates alternative splicing of protein kinase C deltaVIII (PKCdeltaVIII) isoform via splicing factor SC35

Vitamin A metabolite, all-trans-retinoic acid (RA), induces cell growth, differentiation, and apoptosis and has an emerging role in gene regulation and alternative splicing events. Protein kinase Cdelta (PKCdelta), a serine/threonine kinase, has a role in cell proliferation, differentiation, and apoptosis. We reported an alternatively spliced variant of human PKCdelta, PKCdeltaVIII that functions as a pro-survival protein (1). RA regulates the splicing and expression of PKCdeltaVIII via utilization of a downstream 5' splice site of exon 10 on PKCdelta pre-mRNA. Here, we further elucidate the molecular mechanisms involved in RA regulation of alternative splicing of PKCdeltaVIII mRNA. Overexpression and knockdown of the splicing factor SC35 (i.e. SRp30b) indicated that it is involved in PKCdeltaVIII alternative splicing. To identify the cis-elements involved in 5' splice site selection we cloned a minigene, which included PKCdelta exon 10 and its flanking introns in the pSPL3 splicing vector. Alternative 5' splice site utilization in the minigene was promoted by RA. Further, co-transfection of SC35 with PKCdelta minigene promoted selection of 5' splice site II. Mutation of the SC35 binding site in the PKCdelta minigene abolished RA-mediated utilization of 5' splice splice II. RNA binding assays demonstrated that the enhancer element downstream of PKCdelta exon 10 is a SC35 cis-element. We conclude that SC35 is pivotal in RA-mediated PKCdelta pre-mRNA alternative splicing. This study demonstrates how a nutrient, vitamin A, via its metabolite RA, regulates alternative splicing and thereby gene expression of the pro-survival protein PKCdeltaVIII.

The immunoconjugate "icon" targets aberrantly expressed endothelial tissue factor causing regression of endometriosis

Endometriosis is a major cause of chronic pain, infertility, medical and surgical interventions, and health care expenditures. Tissue factor (TF), the primary initiator of coagulation and a modulator of angiogenesis, is not normally expressed by the endothelium; however, prior studies have demonstrated that both blood vessels in solid tumors and choroidal tissue in macular degeneration express endothelial TF. The present study describes the anomalous expression of TF by endothelial cells in endometriotic lesions. The immunoconjugate molecule (Icon), which binds with high affinity and specificity to this aberrant endothelial TF, has been shown to induce a cytolytic immune response that eradicates tumor and choroidal blood vessels. Using an athymic mouse model of endometriosis, we now report that Icon largely destroys endometriotic implants by vascular disruption without apparent toxicity, reduced fertility, or subsequent teratogenic effects. Unlike antiangiogenic treatments that can only target developing angiogenesis, Icon eliminates pre-existing pathological vessels. Thus, Icon could serve as a novel, nontoxic, fertility-preserving, and effective treatment for endometriosis.

Tissue factor and PAR2 signaling in the tumor microenvironment

Diverse oncogenic transformations result in the constitutive expression of tissue factor (TF) in cancer cells. The local and systemic activation of the coagulation cascade has long been a recognized hallmark for aggressive cancer, but genetic mouse models and new experimental therapeutics have only recently demonstrated crucial roles for TF initiated cell signaling in the pathogenesis of cancer. On tumor cells, the TF-VIIa binary complex mediates activation of protease activated receptor (PAR) 2 and thereby shapes the tumor microenvironment by inducing an array of proangiogenic and immune modulating cytokines, chemokines, and growth factors. PAR2 also uniquely triggers tumor cell migration by G protein-independent pathways through beta-arrestin scaffolding. Metastatic tumor cells use additional signaling networks of the coagulation cascade by activating PAR1 through thrombin or the ternary TF-VIIa-Xa signaling complex in the vascular and potentially lymphatic system. Selective antagonists of TF-VIIa-PAR2 signaling may be used as antiangiogenic therapy without increasing the risk of bleeding, whereas coagulation and associated signaling pathways on platelets and other host cells may be targeted for therapeutic benefit in advanced cancer and metastatic disease.

Tissue factor in tumour progression

The linkage between activation of the coagulation system and cancer is well established, as is deregulation of tissue factor (TF) by cancer cells, their vascular stroma and cancer-associated inflammatory cells. TF is no longer perceived as an 'alternative' coagulation factor, but rather as a central trigger of the coagulation cascade and an important cell-associated signalling receptor activated by factor VIIa, and interacting with several other regulatory entities, most notably protease-activated receptors (PAR-1 and PAR-2). Preclinical studies revealed the role of oncogenic transformation and tumour micro-environment as TF regulators in cancer, along with the impact of this receptor on gene expression, tumour growth, metastasis, angiogenesis and, possibly, formation of the cancer stem cell niche. Increasing interest surrounds the shedding of TF-containing microvesicles from cancer cells, their entry into the circulation and their role in the intercellular transfer of TF activity, cancer coagulopathy and other processes. Recent data also suggest differential roles of cell autonomous versus global effects of TF in various settings. Questions are raised regarding the consequences of TF expression by tumour cells themselves and by their associated host stroma. Progress in these areas may soon begin to impact on clinical practice and, as such, raises several important questions. Can TF be exploited as a therapeutic target in cancer? Where and when may this be safe and beneficial? Is expression of TF in various disease settings useful as a biomarker of cancer progression or the associated hypercoagulability? What clinical questions related to TF are especially worthy of further exploration, at present and in the near future? Some of these developments and questions will be discussed in this chapter.

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.

Bone marrow cells produce a novel TSHbeta splice variant that is upregulated in the thyroid following systemic virus infection

Although cells of the immune system can produce thyroid-stimulating hormone (TSH), the significance of that remains unclear. Using 5' rapid amplification of cDNA ends (RACE), we show that mouse bone marrow (BM) cells produce a novel in-frame TSHbeta splice variant generated from a portion of intron 4 with all of the coding region of exon 5, but none of exon 4. The TSHbeta splice variant gene was expressed at low levels in the pituitary, but at high levels in the BM and the thyroid, and the protein was secreted from transfected Chinese hamster ovary (CHO) cells. Immunoprecipitation identified an 8 kDa product in lysates of CHO cells transfected with the novel TSHbeta construct, and a 17 kDa product in lysates of CHO cells transfected with the native TSHbeta construct. The splice variant TSHbeta protein elicited a cAMP response from FRTL-5 thyroid follicular cells and a mouse alveolar macrophage (AM) cell line. Expression of the TSHbeta splice variant, but not the native form of TSHbeta, was significantly upregulated in the thyroid during systemic virus infection. These studies characterize the first functional splice variant of TSHbeta, which may contribute to the metabolic regulation during immunological stress, and may offer a new perspective for understanding autoimmune thyroiditis.

Venous thromboembolic events and organ-specific occult cancers: a review and meta-analysis

BACKGROUND

Despite a recognized association between venous thromboembolic events (VTE) and cancer, little is known about the strength and the features of this association. We performed a meta-analysis in order to clarify this issue.

METHODS

We retrieved data from 40 reports published between 1982 and 2007: 12 contained cancer risk estimates for patients with either idiopathic or secondary VTE vs. subjects without VTE and 17 for patients with idiopathic vs. secondary VTE. We also pooled risk estimates from four cohort studies to assess the association between VTE and specific forms of cancer and conducted a proportional incidence study, based on the remaining 28 reports, which did not provide risk estimates.

RESULTS

The pooled relative risk (RR) of cancer was 3.2 [95% confidence interval (95% CI) 2.4-4.5] for patients with any form of VTE vs. no VTE, 2.7 (95% CI 1.9-3.9) for patients with idiopathic vs. no VTE and 3.8 (95% CI 2.6-5.4) for patients with idiopathic vs. secondary VTE. In the pooled cohort studies, RRs for VTE vs. no VTE were significantly elevated for cancers of the ovary (RR 7.0), pancreas (RR 6.1), liver (RR 5.6), blood (4.2), brain (RR 3.8), kidney (RR 3.4), lung (3.1), colon (2.9), and esophagus (2.1). In the proportional incidence study, cancers of the pancreas, colon, and blood were significantly more frequently observed than in the general population.

CONCLUSIONS

Overall we found a 3-fold excess risk of occult cancer in patients with VTE. The risk varies according to tumor site and is highest for cancers of the ovary, pancreas, and liver.

Tissue factor, angiogenesis and tumour progression

Tissue factor, the primary initiator of the coagulation cascade, maintains vascular integrity in response to injury. It is now recognised that, in addition to the role as a procoagulant activator, tissue factor participates in many tumour-related processes that contribute to malignant disease progression. The present review details the recent evidence supporting a role for tissue factor in tumour haemostasis, angiogenesis, metastasis and malignant cell survival. Furthermore, future research directions are discussed that may enhance our understanding of the role and regulation of this protein, which could ultimately lead to the innovative design and development of new anticancer therapies.

Alternatively spliced human tissue factor promotes tumor growth and angiogenesis in a pancreatic cancer tumor model

INTRODUCTION

Tissue Factor (TF) expression is observed in many types of cancer, associated with more aggressive disease, and thrombosis. Alternatively-spliced human tissue factor (asHTF) has recently been identified in which exon 5 is deleted. asHTF is soluble due to the substitution of the transmembrane and cytoplasmic domains of exon 6 with a unique COOH-terminal domain.

MATERIALS AND METHODS

We examine the expression and function of asHTF and full-length Tissue Factor ((FL)TF) in six human pancreatic cancer cells. Further, we transfected asHTF, (FL)TF, and control expression vectors into a non-expressing, human pancreatic cancer line (MiaPaCa-2). We studied the procoagulant activity of asHTF and (FL)TF and the effect on tumor growth in mice.

RESULTS

asHTF is expressed in 5 of 6 human pancreatic cancer cell lines, but not in normal human fibroblasts, nor the MiaPaCa-2 line. (FL)TF conferred procoagulant activity, but asHTF did not. Transfected cells were injected subcutaneously in athymic mice. Interestingly, compared with control transfection, (FL)TF expression was associated with reduced tumor growth (mean 7 mg vs 85 mg), while asHTF-expression was associated with enhanced tumor growth (mean 389 mg vs. 85 mg). asHTF expression resulted in increased mitotic index and microvascular density.

CONCLUSIONS

These data suggests that asHTF expression promotes tumor growth, and is associated with increased tumor cell proliferation and angiogenesis in vivo. Our results raise a new perspective on the understanding of the relationship between TF expression and cancer growth, by showing a dissociation of the procoagulant activity of (FL)TF and the cancer-promoting activity of asHTF.

Identification of a novel antiapoptotic human protein kinase C delta isoform, PKCdeltaVIII in NT2 cells

Protein kinase C (PKC) delta plays an important role in cellular proliferation and apoptosis where it is involved in the caspase-3 mediated apoptotic pathway. Cleavage of PKCdeltaI by caspase-3 releases a catalytically active C-terminal fragment that is sufficient to induce apoptosis. In this paper, we identified a novel human PKCdelta isozyme, PKCdeltaVIII (Genbank accession number DQ516383) in human teratocarcinoma (NT2) cells that differentiate into hNT neurons upon retinoic acid (RA) treatment. Expression of PKCdeltaVIII was confirmed by real-time RT-PCR analysis, and we observed that after an initial peak at 24 h following RA treatment, its expression gradually declined with prolonged RA treatment. PKCdeltaVIII is generated via the utilization of an alternative 5' splice site, and this results in an insertion of 31 amino acids in the caspase-3 recognition sequence DMQD. The function of PKCdeltaVIII was examined by subcloning it into an expression vector and raising an antibody specific to PKCdeltaVIII. Using in vivo and in vitro assays, we demonstrated that PKCdeltaVIII is resistant to caspase-3 cleavage. Next, we sought to determine the role of PKCdeltaVIII in apoptosis in NT2 cells. Overexpression of PKCdeltaVIII and knockdown using PKCdeltaVIII siRNA suggest an antiapoptotic function for the PKCdeltaVIII isozyme. We demonstrate that antisense oligonucleotides (ASO) directed toward the 5' splice site I promote the expression of the PKCdeltaVIII isozyme. Our results indicated that ASO mediated PKCdeltaVIII expression rescued NT2 cells from etoposide-induced apoptosis. We conclude that the novel human PKCdeltaVIII splice variant functions as an antiapoptotic protein in NT2 cells.

Vaccination against prostate cancer using a live tissue factor deficient cell line in Lobund-Wistar rats

Reducing expression of the tissue factor gene in prostate adenocarcinoma cells (PAIII) results in a cell line that, in vivo, mimics the growth of wildtype (wt) PAIII. However, instead of continuing to grow and metastasize as wt PAIII tumors do, tissue factor deficient PAIII (TFD PAIII) masses spontaneously regress after several weeks. Although whole cell vaccines are typically inactivated prior to administration to prevent proliferation within the host, numerous studies have suggested that exposure to live, attenuated, whole tumor cells, and the extracellular microenvironment they recruit, increases immunotherapeutic potential. Here, we provide support for this notion, and a strategy through which to implement it, by demonstrating that subcutaneous vaccinations with the TFD PAIII protect the Lobund-Wistar rat against subsequent wt PAIII cell challenge. TFD PAIII immunized rats suffered significantly less metastasis of wt PAIII challenge tumors compared to unvaccinated naïve controls rats. These results offer the intriguing possibility that the TFD PAIII vaccine is an effective system for the prevention and, possibly, the treatment of prostate cancer.

Alternatively Spliced Tissue Factor: A Previously Unknown Piece in the Puzzle of Hemostasis

Alternatively spliced tissue factor (asTF) has recently been discovered as a soluble form of tissue factor (TF), which circulates in blood and exhibits procoagulant activity. This soluble TF variant expanded the concept of circulating TF by a further element. Up to 30% of the TF antigen found in circulating blood was proposed to be derived from alternative splicing. We showed that cytokines induced the expression of asTF and the release from endothelial cells. The use of plasma asTF as a clinical marker for an inflammation-associated dysregulated hemostasis may therefore be a novel approach in predicting the patients' prognosis. This review covers the latest findings in the field of soluble TF focusing on asTF and its potential role besides the one in coagulation.