A novel promoter for vascular endothelial growth factor receptor (flt-1) that confers endothelial-specific gene expression

CRISPR/Cas9-mediated mutations in both a cAMP response element and an ETS-binding site suppress FLT1 gene expression

The Fms-like tyrosine kinase-1 (FLT1) gene is expressed in various types of cells, including vascular endothelial cells and placental trophoblasts, and regulates angiogenesis, inflammation, and pregnancy. However, the basal transcriptional machinery of FLT1 is still not well understood. In this study, we first examined FLT1 promoter activity in three different types of cells, that is, trophoblast-derived cells, vascular endothelial-related cells, and HEK293 cells, using plasmid-based luciferase reporter assays, and showed that a cAMP-response element (CRE) and an ETS-binding site (EBS) are important for FLT1 expression in all cell types. To further examine the importance of these sites at the chromosomal level using HEK293 cells, we introduced CRISPR/Cas9-mediated mutations in these sites on the genomic DNA. HEK293 cells carrying these mutations clearly showed a significant decrease in endogenous FLT1 gene expression. These results suggest that CRE and EBS transcription regulatory elements are crucial for FLT1 gene expression in human tissues.

ETV2 and VEZF1 interaction and regulation of the hematoendothelial lineage during embryogenesis

Ets variant 2 (Etv2), a member of the Ets factor family, has an essential role in the formation of endothelial and hematopoietic cell lineages during embryonic development. The functional role of ETS transcription factors is, in part, dependent on the interacting proteins. There are relatively few studies exploring the coordinated interplay between ETV2 and its interacting proteins that regulate mesodermal lineage determination. In order to identify novel ETV2 interacting partners, a yeast two-hybrid analysis was performed and the C2H2 zinc finger transcription factor VEZF1 (vascular endothelial zinc finger 1) was identified as a binding factor, which was specifically expressed within the endothelium during vascular development. To confirm this interaction, co-immunoprecipitation and GST pull down assays demonstrated the direct interaction between ETV2 and VEZF1. During embryoid body differentiation, Etv2 achieved its peak expression at day 3.0 followed by rapid downregulation, on the other hand Vezf1 expression increased through day 6 of EB differentiation. We have previously shown that ETV2 potently activated Flt1 gene transcription. Using a Flt1 promoter-luciferase reporter assay, we demonstrated that VEZF1 co-activated the Flt1 promoter. Electrophoretic mobility shift assay and Chromatin immunoprecipitation established VEZF1 binding to the Flt1 promoter. Vezf1 knockout embryonic stem cells had downregulation of hematoendothelial marker genes when undergoing embryoid body mediated mesodermal differentiation whereas overexpression of VEZF1 induced the expression of hematoendothelial genes during differentiation. These current studies provide insight into the co-regulation of the hemato-endothelial lineage development via a co-operative interaction between ETV2 and VEZF1.

Global DNA and protein interactomes of FLT1P1 (Fms-related tyrosine kinase 1 pseudogene 1) revealed its molecular regulatory functions associated with preeclampsia

BACKGROUND

Preeclampsia (PE) is one of the most serious pregnancy complications with unknown pathogenesis. Emerging evidence has demonstrated that Fms-related tyrosine kinase 1 (FLT1) is highly involved in PE development. As a pseudogene of FLT1, FLT1P1 increased in PE samples. However, its functions remain largely unknown.

METHODS AND RESULTS

In this study, co-expression analysis was performed to identify the potential target genes of FTL1P1. Then chromatin isolation using RNA purification (ChIRP) method was employed to explore the interactomes of FLT1P1, including interacting with DNA fragments and proteins. We found that in PE samples, both FLT1P1 and FLT1 were highly expressed and closely correlated. ChIRP-protein data revealed that FLT1P1 interacts with translation- and transcription-related proteins, including 4 transcription factors (TFs). ChIRP-DNA analysis revealed that FLT1P1 preferentially interacted with DNA fragments downstream of transcription start sites (TSSs). Functional analysis of its interacting genes revealed that they were enriched in transcriptional regulation and apoptosis-related pathways. Twenty-six TFs, including CREB1 and SRF, were extracted from the potential FLT1P1-interacting gene sets and were potential targets of FLT1P1. CREB1 could bind to FLT1 promoter, and was negatively correlated with FLT1 at the expression level, making it a potential regulator of FLT1.

CONCLUSIONS

Our study extensively investigated the interactome profiles of FLT1P1, especially the prompter region of TF gene CREB1, and revealed the potential molecular regulatory mechanisms of FLT1 expression in PE samples. Our results provide a novel view of PE pathogenesis, and suggest that FLT1P1 could serve as a potential therapeutic target in PE diagnosis and treatment.

Directed evolution of AAV accounting for long-term and enhanced transduction of cardiovascular endothelial cells in vivo

Cardiac endothelial cells (ECs) are important targets for cardiovascular gene therapy. However, the approach of stably transducing ECs in vivo using different vectors, including adeno-associated virus (AAV), remains unexamined. Regarding this unmet need, two AAV libraries from DNA shuffling and random peptide display were simultaneously screened in a transgenic mouse model. Cardiac ECs were isolated by cell sorting for salvage of EC-targeting AAV. Two AAV variants, i.e., EC71 and EC73, enriched in cardiac EC, were further characterized for their tissue tropism. Both of them demonstrated remarkably enhanced transduction of cardiac ECs and reduced infection of liver ECs in comparison to natural AAVs after intravenous injection. Significantly, persistent transgene expression was maintained in mouse cardiac ECs in vivo for at least 4 months. The EC71 vector was selected for delivery of the endothelial nitric oxide synthase (eNOS) gene into cardiac ECs in a mouse model of myocardial infarction. Enhanced eNOS activity was observed in the mouse heart and lung, which was correlated with partially improved cardiac function. Taken together, two AAV capsids were evolved with more efficient transduction in cardiovascular endothelium in vivo, but their endothelial tropism might need to be further optimized for practical application to cardiac gene therapy.

Transcription factor AP2A affects sFLT1 expression and decidualization in decidual stromal cells: Implications to preeclampsia pathology

Preeclampsia (PE) yields a spectrum of phenotypic expression, leading to varying degrees of hypertension, maternal renal dysfunction and placental insufficiency with resultant maternal and neonatal morbidity. Increased sFLT1 expression contributing to angiogenic factor imbalance, placental hypoxia, failed immune adaptation to the fetus and defective decidualization are among the commonly proposed theories of PE pathogenesis. Recently researchers have focused their attention on the events that occur at the maternal fetal interface as potential contributors to PE pathogenesis. Decidual stromal cells (DSC) isolated from preeclamptic women show diminished ability to decidualize upon stimulation and reduced capacity to downregulate sFlt-1 levels. In this study, we sought to gain insight into the molecular mechanism(s) involved in the aberrant decidualization capacity of PE DSC. Our findings using qRT-PCR show that PE DSCs have 6-fold higher basal levels of transcription factor AP2A (TFAP2A) RNA compared to women without PE and that expression of TFAP2A increases during decidualization but only in DSCs of normotensive (NT) women. Silencing of TFAP2A using Trilencer siRNA upregulated sFLT1 expression only in NT-DSCs but suppressed the expression of decidualization markers PRL, IGFBP1 and their regulator FOXO1 in cells from both groups. Collectively, our observations suggest that TFAP2A acts as a repressor of sFLT1 and plays a necessary role in decidualization possibly through interacting with another factor that is aberrantly expressed in PE DSCs.

Adeno-Associated Virus Technologies and Methods for Targeted Neuronal Manipulation

Cell-type-specific expression of molecular tools and sensors is critical to construct circuit diagrams and to investigate the activity and function of neurons within the nervous system. Strategies for targeted manipulation include combinations of classical genetic tools such as Cre/loxP and Flp/FRT, use of cis-regulatory elements, targeted knock-in transgenic mice, and gene delivery by AAV and other viral vectors. The combination of these complex technologies with the goal of precise neuronal targeting is a challenge in the lab. This report will discuss the theoretical and practical aspects of combining current technologies and establish best practices for achieving targeted manipulation of specific cell types. Novel applications and tools, as well as areas for development, will be envisioned and discussed.

Retinoic Acid Is a Negative Regulator of sFLT1 Expression in Decidual Stromal Cells, and Its Levels Are Reduced in Preeclamptic Decidua

sFLT1 (soluble VEGF [vascular endothelial growth factor] receptor-1) levels are increased in preeclampsia-a pathological condition of pregnancy. The mechanism of sFLT1 overexpression by gestational tissues, particularly the decidua, remains unknown. Mass spectrometry measurement of the active retinoid metabolite, all-trans retinoic acid (RA), showed significantly lower levels of RA in preeclamptic versus normotensive decidua. In this study, we investigated the involvement of RA in regulating decidual sFLT1 expression. When decidual stromal cells (DSCs) isolated from the decidua basalis of normotensive and preeclampsia placentas were treated with BMS493-a pan-RAR (RA nuclear receptor) antagonist-upregulation of sFLT1 expression was observed. Conversely, treatment with RA resulted in downregulation of sFLT1 in normotensive DSCs and preeclampsia DSCs. Unlike treatment with cAMP, which induces decidualization while downregulating sFLT1, RA treatment did not alter DSC expression of prolactin-a marker of decidualization-or FOXO1 (forkhead box protein 01)-a transcription factor required for prolactin upregulation. TFAP2A (transcription factor AP-2-alpha [activating enhancer-binding protein 2 alpha]), a different transcription factor was upregulated in normotensive DSCs but not in preeclampsia DSCs after RA treatment. Collectively, our data show that RA suppresses sFLT1 expression in DSCs independently of cellular decidualization. These findings suggest that reduced decidual RA levels may contribute to preeclampsia pathogenesis by allowing sFLT1 accumulation at the maternal-fetal interface.

Dihydroartemisinin enhances VEGFR1 expression through up-regulation of ETS-1 transcription factor

Angiogenesis is required for tumor growth. Dihydroartemisinin (DHA), a the effective anti-malarial derivative of artemisinin, demonstrated potent anti-angiogenic activities that closely related to the regulation of vascular endothelial growth factor (VEGF) signaling cascade. VEGF receptor 1 (VEGFR1), a receptor in endothelial cells (ECs), coordinately regulate angiogenic activity triggered by ligand-receptor binding. Here we aimed to explore the effects of DHA on VEGFR1 expression in ECs. We found that DHA significantly increases VEGFR1 expression in human umbilical vein endothelial cells (HUVECs). In addition, DHA significantly upregulates the level of V-Ets Avian Erythroblastosis Virus E26 Oncogene Homolog 1 (ETS-1), a transcriptional factor which binds to the human VEGFR1 promoter. ChIP assay showed that DHA increases ETS-1 binding to the -52 ETS motif on the VEGFR1 promoter. Knockdown of ETS-1 by RNA interference abolished DHA-induced increase of VEGFR1 expression. Taken together, we demonstrated that DHA elevates VEGFR1 expression via up-regulation of ETS-1 transcription in HUVECs.

Treatment of hypertension by increasing impaired endothelial TRPV4-KCa2.3 interaction

The currently available antihypertensive agents have undesirable adverse effects due to systemically altering target activity including receptors, channels, and enzymes. These effects, such as loss of potassium ions induced by diuretics, bronchospasm by beta‐blockers, constipation by Ca²⁺ channel blockers, and dry cough by ACEI, lead to non‐compliance with therapies (Moser, 1990). Here, based on new hypertension mechanisms, we explored a new antihypertensive approach. We report that transient receptor potential vanilloid 4 (TRPV4) interacts with Ca²⁺‐activated potassium channel 3 (KCa2.3) in endothelial cells (ECs) from small resistance arteries of normotensive humans, while ECs from hypertensive patients show a reduced interaction between TRPV4 and KCa2.3. Murine hypertension models, induced by high‐salt diet, N(G)‐nitro‐l‐arginine intake, or angiotensin II delivery, showed decreased TRPV4‐KCa2.3 interaction in ECs. Perturbation of the TRPV4‐KCa2.3 interaction in mouse ECs by overexpressing full‐length KCa2.3 or defective KCa2.3 had hypotensive or hypertensive effects, respectively. Next, we developed a small‐molecule drug, JNc‐440, which showed affinity for both TRPV4 and KCa2.3. JNc‐440 significantly strengthened the TRPV4‐KCa2.3 interaction in ECs, enhanced vasodilation, and exerted antihypertensive effects in mice. Importantly, JNc‐440 specifically targeted the impaired TRPV4‐KCa2.3 interaction in ECs but did not systemically activate TRPV4 and KCa2.3. Together, our data highlight the importance of impaired endothelial TRPV4‐KCa2.3 coupling in the progression of hypertension and suggest a novel approach for antihypertensive drug development.

RNA activating-double stranded RNA targeting flt-1 promoter inhibits endothelial cell proliferation through soluble FLT-1 upregulation

Short-activating RNA (saRNA), which targets gene promoters, has been shown to increase the target gene expression. In this study, we describe the use of an saRNA (Flt a-1) to target the flt-1 promoter, leading to upregulation of the soluble isoform of Flt-1 and inhibition of angiogenesis. We demonstrate that Flt a-1 increased sFlt-1 mRNA and protein levels, while reducing VEGF expression. This was associated with suppression of human umbilical vascular endothelial cell (HUVEC) proliferation and cell cycle arrest at the G0/G1 phase. HUVEC migration and tube formation were also suppressed by Flt a-1. An siRNA targeting Flt-1 blocked the effects of Flt a-1. Flt a-1 effects were not mediated via argonaute proteins. However, trichostatin A and 5'-deoxy-5'-(methylthio) adenosine inhibited Flt a-1 effects, indicating that histone acetylation and methylation are mechanistically involved in RNA activation of Flt-1. In conclusion, RNA activation of sFlt-1 can be used to inhibit angiogenesis.

Cyclic AMP Response Element Binding Protein Mediates Pathological Retinal Neovascularization via Modulating DLL4-NOTCH1 Signaling

Retinal neovascularization is the most common cause of moderate to severe vision loss in all age groups. Despite the use of anti-VEGFA therapies, this complication continues to cause blindness, suggesting a role for additional molecules in retinal neovascularization. Besides VEGFA and VEGFB, hypoxia induced VEGFC expression robustly. Based on this finding, we tested the role of VEGFC in pathological retinal angiogenesis. VEGFC induced proliferation, migration, sprouting and tube formation of human retinal microvascular endothelial cells (HRMVECs) and these responses require CREB-mediated DLL4 expression and NOTCH1 activation. Furthermore, down regulation of VEGFC levels substantially reduced tip cell formation and retinal neovascularization in vivo. In addition, we observed that CREB via modulating the DLL4-NOTCH1 signaling mediates VEGFC-induced tip cell formation and retinal neovascularization. In regard to upstream mechanism, we found that down regulation of p38β levels inhibited hypoxia-induced CREB-DLL4-NOTCH1 activation, tip cell formation, sprouting and retinal neovascularization. Based on these findings, it may be suggested that VEGFC besides its role in the regulation of lymphangiogenesis also plays a role in pathological retinal angiogenesis and this effect depends on p38β and CREB-mediated activation of DLL4-NOTCH1 signaling.

Feedback Mechanisms Regulate Ets Variant 2 (Etv2) Gene Expression and Hematoendothelial Lineages

Etv2 is an essential transcriptional regulator of hematoendothelial lineages during embryogenesis. Although Etv2 downstream targets have been identified, little is known regarding the upstream transcriptional regulation of Etv2 gene expression. In this study, we established a novel methodology that utilizes the differentiating ES cell and embryoid body system to define the modules and enhancers embedded within the Etv2 promoter. Using this system, we defined an autoactivating role for Etv2 that is mediated by two adjacent Ets motifs in the proximal promoter. In addition, we defined the role of VEGF/Flk1-Calcineurin-NFAT signaling cascade in the transcriptional regulation of Etv2. Furthermore, we defined an Etv2-Flt1-Flk1 cascade that serves as a negative feedback mechanism to regulate Etv2 gene expression. To complement and extend these studies, we demonstrated that the Flt1 null embryonic phenotype was partially rescued in the Etv2 conditional knockout background. In summary, these studies define upstream and downstream networks that serve as a transcriptional rheostat to regulate Etv2 gene expression.

Increased size and cellularity of advanced atherosclerotic lesions in mice with endothelial overexpression of the human TRPC3 channel

In previous in vitro studies, we showed that Transient Receptor Potential Canonical 3 (TRPC3), a calcium-permeable, nonselective cation channel endowed with high constitutive function, is an obligatory component of the inflammatory signaling that controls expression of the vascular cell adhesion molecule-1 (VCAM-1) and monocyte adhesion to coronary artery endothelial cells. Also, TRPC3 expression in these cells was found to be up-regulated by proatherogenic factors, which enhanced inflammation and VCAM-1 expression. However, it remained to be determined whether these in vitro findings were of relevance to atherosclerotic lesion development in vivo. To answer this important question in the present work, we generated mice with endothelial-specific overexpression of human TRPC3 in an Apoe knockout background (TgEST3ApoeKO) and examined lesions in the aortic sinus following 10 and 16 wk on a high-fat diet. No significant differences were found in size or complexity of early stage lesions (10 wk). However, advanced plaques (16 wk) from TgEST3ApoeKO mice exhibited a significant increase in size and macrophage content compared with nontransgenic littermate controls. Remarkably, this change was correlated with increased VCAM-1 and phospho-IkBα immunoreactivity along the endothelial lining of lesions from transgenic animals compared with controls. These findings validate the in vivo relevance of previous in vitro findings and represent, to our knowledge, the first in vivo evidence for a proatherogenic role of endothelial TRPC3.

[Regulation of endothelial cell-specific Robo4 gene expression by DNA methylation and non-lineage specific transcription factors]

Studies of tissue-specific gene expression have suggested that tissue-specific transcription factors or tissue-specific combinations of non-cell-type-specific transcription factors regulate tissue-specific gene expression. Although the studies of endothelial cell (EC)-specific gene expression has identified several transcriptional activators such as SP1, ETS family proteins, and GATA proteins, their expression and combinations are not likely to be EC-specific. To investigate the mechanism of EC-specific gene expression, we analyzed the regulation mechanism of an EC-specific gene, Roundabout4 (Robo4). We identified the 3-kb Robo4 promoter and several transcription factors including SP1 and GABP that bind to the Robo4 promoter and promote Robo4 gene expression. However, we could not explain the mechanism for EC-specific Robo4 gene expression with only those factors because their expression and combination are not EC-specific. Therefore, we hypothesized the contribution of other mechanisms, especially epigenetic control, to Robo4 gene regulation and demonstrated the importance of DNA methylation for EC-specific Robo4 expression. In this review, we summarize our recent studies and discuss the novel regulation model of Robo4 gene expression by transcription factors and DNA methylation.

Cyclic adenosine monophosphate-response element-binding protein mediates the proangiogenic or proinflammatory activity of gremlin

OBJECTIVE

Angiogenesis and inflammation are closely related processes. Gremlin is a novel noncanonical vascular endothelial growth factor receptor-2 (VEGFR2) ligand that induces a proangiogenic response in endothelial cells (ECs). Here, we investigated the role of the cyclic adenosine monophosphate-response element (CRE)-binding protein (CREB) in mediating the proinflammatory and proangiogenic responses of ECs to gremlin.

APPROACH AND RESULTS

Gremlin induces a proinflammatory response in ECs, leading to reactive oxygen species and cyclic adenosine monophosphate production and the upregulation of proinflammatory molecules involved in leukocyte extravasation, including chemokine (C-C motif) ligand-2 (Ccl2) and Ccl7, chemokine (C-X-C motif) ligand-1 (Cxcl1), vascular cell adhesion molecule-1 (VCAM-1), and intercellular adhesion molecule-1 (ICAM-1). Accordingly, gremlin induces the VEGFR2-dependent phosphorylation, nuclear translocation, and transactivating activity of CREB in ECs. CREB activation mediates the early phases of the angiogenic response to gremlin, including stimulation of EC motility and permeability, and leads to monocyte/macrophage adhesion to ECs and their extravasation. All these effects are inhibited by EC transfection with a dominant-negative CREB mutant or with a CREB-binding protein-CREB interaction inhibitor that competes for CREB/CRE binding. Also, both recombinant gremlin and gremlin-expressing tumor cells induce proinflammatory/proangiogenic responses in vivo that are suppressed by the anti-inflammatory drug hydrocortisone. Similar effects were induced by the canonical VEGFR2 ligand VEGF-A165.

CONCLUSIONS

Together, the results underline the tight cross-talk between angiogenesis and inflammation and demonstrate a crucial role of CREB activation in the modulation of the VEGFR2-mediated proinflammatory/proangiogenic response of ECs to gremlin.

Variable promoter methylation contributes to differential expression of key genes in human placenta-derived venous and arterial endothelial cells

Background

The endothelial compartment, comprising arterial, venous and lymphatic cell types, is established prenatally in association with rapid phenotypic and functional changes. The molecular mechanisms underpinning this process in utero have yet to be fully elucidated. The aim of this study was to investigate the potential for DNA methylation to act as a driver of the specific gene expression profiles of arterial and venous endothelial cells.

Results

Placenta-derived venous and arterial endothelial cells were collected at birth prior to culturing. DNA methylation was measured at >450,000 CpG sites in parallel with expression measurements taken from 25,000 annotated genes. A consistent set of genomic loci was found to show coordinate differential methylation between the arterial and venous cell types. This included many loci previously not investigated in relation to endothelial function. An inverse relationship was observed between gene expression and promoter methylation levels for a limited subset of genes implicated in endothelial function, including NOS3, encoding endothelial Nitric Oxide Synthase.

Conclusion

Endothelial cells derived from the placental vasculature at birth contain widespread methylation of key regulatory genes. These are candidates involved in the specification of different endothelial cell types and represent potential target genes for environmentally mediated epigenetic disruption in utero in association with cardiovascular disease risk later in life.

PKA/CREB signaling triggers initiation of endothelial and hematopoietic cell differentiation via Etv2 induction

Ets family protein Etv2 (also called ER71 or Etsrp) is a key factor for initiation of vascular and blood development from mesodermal cells. However, regulatory mechanisms and inducing signals for Etv2 expression have been largely unknown. Previously, we revealed that cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) signaling enhanced differentiation of vascular progenitors into endothelial cells (ECs) and hematopoietic cells (HPCs) using an embryonic stem cell (ESC) differentiation system. Here, we show that PKA activation in an earlier differentiation stage can trigger EC/HPC differentiation through Etv2 induction. We found Etv2 was markedly upregulated by PKA activation preceding EC and HPC differentiation. We identified two cAMP response element (CRE) sequences in the Etv2 promoter and 5'-untranslated region and confirmed that CRE-binding protein (CREB) directly binds to the CRE sites and activates Etv2 transcription. Expression of a dominant negative form of CREB completely inhibited PKA-elicited Etv2 expression and induction of EC/HPCs from ESCs. Furthermore, blockade of PKA significantly inhibited Etv2 expression in ex vivo whole-embryo culture using Etv2-Venus knockin mice. These data indicated that PKA/CREB pathway is a critical regulator for the initiation of EC/HPC differentiation via Etv2 transcription. This early-stage molecular linkage between a triggering signal and transcriptional cascades for differentiation would provide novel insights in vascular and blood development and cell fate determination.

Resveratrol inhibits the release of soluble fms-like tyrosine kinase (sFlt-1) from human placenta

OBJECTIVE

Soluble vascular endothelial growth factor receptor-1 (also know as soluble fms-like tyrosine kinase [sFlt]-1) is a key causative factor of preeclampsia. Resveratrol, a plant phytoalexin, has antiinflammatory and cardioprotective properties. We sought to determine the effect of resveratrol on sFlt-1 release.

STUDY DESIGN

Human umbilical vein endothelial cells, transformed human trophoblast-8 (HTR/SVneo)-8/SVneo trophoblast cells, or placental explants were incubated with cytokines and/or resveratrol. Conditioned media were assayed for sFlt-1 by enzyme-linked immunosorbent assay and cell proteins used for Western blotting.

RESULTS

Resveratrol inhibited cytokine-induced release of sFlt-1 from normal placental explants and from preeclamptic placental explants. Preincubation of human umbilical vein endothelial cells or HTR-8/SVneo cells with resveratrol abrogated sFlt-1 release. Resveratrol prevented the up-regulation of early growth response protein-1 (Egr-1), a transcription factor necessary for induction of the vascular endothelial growth factor receptor-1 gene and caused up-regulation of heme oxygenase-1, a cytoprotective enzyme found to be dysfunctional in preeclampsia.

CONCLUSION

In summary, resveratrol can inhibit sFlt-1 release and up-regulate heme oxygenase-1; thus, may offer therapeutic potential in preeclampsia.

Optimizing adenoviral transduction of endothelial cells under flow conditions

PURPOSE

To target adenoviral vectors to cells of the vasculature and shielding vectors from inactivation by the immune system.

METHODS

Complexes of reporter gene expressing adenoviral vectors with positively charged magnetic nanoparticles were formed by electrostatic interaction in presence or absence of additional negatively charged poly(ethylene glycol)-based polymer. Transduction of HUVEC was analyzed in vitro under flow. Protection from inactivation by the immune system was analyzed by pre-incubation of AdV and complexes with neutralizing antibodies and subsequent reporter protein analysis of infected cells.

RESULTS

Physical association of AdV with MNP and polymers was demonstrated by radioactive labelling of components and co-sedimentation in a magnetic field. Ad-MNP+/-polymer resulted in efficient transduction of HUVEC, depending on MOI and flow rate in presence of magnetic field, whereas no transduction was observed without complex formation with MNP or in absence of magnetic field. Association with MNP did result in protection from neutralizing antibodies, with slightly increased protection provided by the polymer.

CONCLUSIONS

Complex formation of AdV with MNP is a viable means for targeting of vectors to areas of magnetic field gradient. Additional coating with polymer might proof useful in protection from inactivation by the immune system.

Plasmid-mediated gene therapy for cardiovascular disease

Gene transfer within the cardiovascular system was first demonstrated in 1989 yet, despite extensive basic-science and clinical research, unequivocal benefit in the clinical setting remains to be demonstrated. Potential reasons for this include the fact that recombinant viral vectors, used in the majority of clinical studies, have inherent problems with immunogenicity that are difficult to circumvent. Attention has turned therefore to plasmid vectors, which possess many advantages over viruses in terms of safety and ease of use, and many clinical studies have now been performed using non-viral technology. This review will provide an overview of clinical trials for cardiovascular disease using plasmid vectors, recent developments in plasmid delivery and design, and potential directions for this modality of gene therapy.

Cholesterol regulates VEGFR-1 (FLT-1) expression and signaling in acute leukemia cells

VEGF receptors 1 (FLT-1) and 2 (KDR) are expressed on subsets of acute myeloid leukemia (AML) and acute lymphoid leukemia cells, in which they induce cell survival, proliferation, and migration. However, little is known about possible cofactors that regulate VEGF receptor expression and activation on leukemia cells. Here we show that cholesterol accumulates in leukemia-rich sites within bone marrow of xenotransplanted severe combined immunodeficient (SCID) mice. Therefore, we hypothesized that cholesterol-rich domains might regulate FLT-1 signaling and chemotaxis of acute leukemias. We then showed that FLT-1 accumulates in discrete cholesterol-rich membrane domains where it associates with caveolin-1 and that placenta growth factor (PlGF)/VEGF stimulation promotes FLT-1 localization in such cholesterol-rich domains. Accordingly, FLT-1 localization and its phosphorylation are abrogated by methyl-β-cyclodextrin (MβCD), which removes cellular cholesterol, and by nystatin, an inhibitor of lipid-raft endocytosis. Mechanistically, cholesterol increases FLT-1 expression and promotes PlGF/VEGF-induced leukemia cells viability and also induces VEGF production by the leukemia cells in vitro. Taken together, we conclude that cholesterol regulates VEGF:VEGFR-1 signaling on subsets of acute leukemias, modulating cell migration, and viability, which may be crucial for disease progression. Finally, we provide evidence obtained from human AML samples that primary leukemia cells accumulate significantly more cholesterol than do normal cells and that cholesterol accumulation correlates with disease aggressiveness.

VE-statin/egfl7 expression in endothelial cells is regulated by a distal enhancer and a proximal promoter under the direct control of Erg and GATA-2

Angiogenesis is the process by which new blood vessels arise from existing ones by the budding out of endothelial cell capillaries from the luminal side of blood vessels. Blood vessel formation is essential for organ development during embryogenesis and is associated with several physiological and pathological processes, such as wound healing and tumor development. The VE-statin/egfl7 gene is specifically expressed in endothelial cells during embryonic development and in the adult. We studied here the regulatory mechanisms that control this tissue-specific expression. RT-qPCR analyses showed that the specificity of expression of VE-statin/egfl7 in endothelial cells is not shared with its closest neighbor genes notch1 and agpat2 on the mouse chromosome 2. Chromatin-immunoprecipitation analysis of histone modifications at the VE-statin/egfl7 locus showed that the chromatin is specifically opened in endothelial cells, but not in fibroblasts at the transcription start sites. A 13 kb genomic fragment of promoter was cloned and analyzed by gene reporter assays which showed that two conserved regions are important for the specific expression of VE-statin/egfl7 in endothelial cells; a −8409/−7563 enhancer and the −252/+38 region encompassing the exon-1b transcription start site. The latter contains essential GATA and ETS-binding sites, as assessed by linker-scanning analysis and site-directed mutagenesis. An analysis of expression of the ETS and GATA transcription factors showed that Erg, Fli-1 and GATA-2 are the most highly expressed factors in endothelial cells. Erg and GATA-2 directly control the expression of the endogenous VE-statin/egfl7 while Fli-1 probably exerts an indirect control, as assessed by RNA interference and chromatin immunoprecipitation. This first detailed analysis of the mechanisms that govern the expression of the VE-statin/egfl7 gene in endothelial cells pinpoints the specific importance of ETS and GATA factors in the specific regulation of genes in this cell lineage.

Hydrazone ligation strategy to assemble multifunctional viral nanoparticles for cell imaging and tumor targeting

Multivalent nanoparticle platforms are attractive for biomedical applications because of their improved target specificity, sensitivity, and solubility. However, their controlled assembly remains a considerable challenge. An efficient hydrazone ligation chemistry was applied to the assembly of Cowpea mosaic virus (CPMV) nanoparticles with individually tunable levels of a VEGFR-1 ligand and a fluorescent PEGylated peptide. The nanoparticles recognized VEGFR-1 on endothelial cell lines and VEGFR1-expressing tumor xenografts in mice, validating targeted CPMV as a nanoparticle platform in vivo.

Development of viral vectors for use in cardiovascular gene therapy

Cardiovascular disease represents the most common cause of mortality in the developed world but, despite two decades of promising pre-clinical research and numerous clinical trials, cardiovascular gene transfer has so far failed to demonstrate convincing benefits in the clinical setting. In this review we discuss the various targets which may be suitable for cardiovascular gene therapy and the viral vectors which have to date shown the most potential for clinical use. We conclude with a summary of the current state of clinical cardiovascular gene therapy and the key trials which are ongoing.

Differential roles for ETS, CREB, and EGR binding sites in mediating VEGF receptor 1 expression in vivo

Vascular endothelial growth factor receptor 1 (VEGFR1) is a marker for endothelial-specific gene expression. We previously reported that the human VEGFR1 promoter (between -748 and +284) contains information for expression in the intact endothelium of transgenic mice. The objective of this study was to dissect the cis-regulatory elements underlying VEGFR1 promoter activity in vitro and in vivo. In primary endothelial cells, binding sites for E74-like factor 1 (ELF-1; between -49 and -52), cyclic adenosine monophosphate response element binding (CREB; between -74 and -81), and early growth response factor 1/3 (EGR-1/3; between -16 to -25) were shown to play a positive role in gene transcription, whereas a putative E26 transformation-specificsequence (ETS) motif between -36 and -39 had a net negative effect on promoter activity. When targeted to the Hprt locus of mice, mutations of the ELF-1 binding site and the CRE element reduced promoter activity in the embryonic vasculature and resulted in a virtual loss of expression in adult endothelium. Postnatally, the EGR binding site mutant displayed significantly reduced promoter activity in a subset of vascular beds. In contrast, mutation of the -39 ETS site resulted in increased LacZ staining in multiple vascular beds. Together, these results provide new insights into the transcriptional regulatory mechanisms of VEGFR1.

Transcriptional targeting of tumor endothelial cells for gene therapy

It is well known that angiogenesis plays a critical role in the pathobiology of tumors. Recent clinical trials have shown that inhibition of angiogenesis can be an effective therapeutic strategy for patients with cancer. However, one of the outstanding issues in anti-angiogenic treatment for cancer is the development of toxicities related to off-target effects of drugs. Transcriptional targeting of tumor endothelial cells involves the use of specific promoters for selective expression of therapeutic genes in the endothelial cells lining the blood vessels of tumors. Recently, several genes that are expressed specifically in tumor-associated endothelial cells have been identified and characterized. These discoveries have enhanced the prospectus of transcriptionally targeting tumor endothelial cells for cancer gene therapy. In this manuscript, we review the promoters, vectors, and therapeutic genes that have been used for transcriptional targeting of tumor endothelial cells, and discuss the prospects of such approaches for cancer gene therapy.

[Genes that make the endothelial identity]

The endothelium is a tissue with a distinct identity due to the specific expression of molecular markers by endothelial cells. Further, the endothelium displays a structural heterogeneity illustrated by the expression of specific markers in arteries and in veins. Here, we present a review of the transcriptional and epigenetic mechanisms regulating the expression of the main markers of endothelial cells in man and mouse, demonstrating that there is no common and unique mechanism of specific expression of genes in these cells.

Transcriptional control of endothelial cell development

The transcription factors that regulate endothelial cell development have been a focus of active research for several years, and many players in the endothelial transcriptional program have been identified. This review discusses the function of several major regulators of endothelial transcription, including members of the Sox, Ets, Forkhead, GATA, and Kruppel-like families. This review also highlights recent developments aimed at unraveling the combinatorial mechanisms and transcription factor interactions that regulate endothelial cell specification and differentiation during vasculogenesis and angiogenesis.

Effect of antihypertensive therapy with alpha methyldopa on levels of angiogenic factors in pregnancies with hypertensive disorders

Background

Antihypertensive drugs are believed to lower blood pressure in pre-eclampsia by direct or central vasodilatory mechanisms. However, they could also act by decreasing production of anti-angiogenic proteins involved in the pathophysiology of hypertension and proteinuria in pre-eclampsia (PE). The aim of our study was to evaluate the impact of antihypertensive therapy with alpha methyldopa on maternal circulating levels and placental production of soluble fms-like tyrosine kinase 1 (sFlt-1), soluble endoglin (sEng), vascular endothelial growth factor (VEGF) and placental growth factor (PlGF) in hypertensive disorders of pregnancy.

Methodology/Principal Findings

In a study conducted at University College Hospital and the Homerton University Hospital in London, we recruited 51 women with PE, 29 with gestational hypertension (GH), and 80 matched normotensive controls. Eight (16%) of the women with PE had severe disease. Placental samples were obtained from a further 48 women (14 PE, 10 GH and 24 matched controls). Serum levels of angiogenic factors were measured before and 24–48 hours after commencing antihypertensive therapy with alpha methyldopa for clinical indications. The same parameters were measured in placental extracts. In both PE (P<0.0001) and GH (P<0.05), serum sFlt-1 was increased and PlGF reduced at all gestations (P<0.001) compared to controls. Serum sEng levels were also increased in PE. Placental concentration of sFlt-1 and sEng was significantly higher in women with PE compared to controls and women with GH (P<0.0001). The concentration of PlGF was significantly lower in the placental tissue of women with PE compared to GH (P = 0.008). Antihypertensive treatment was associated with a significant fall in serum and placental content of sFlt1 and sEng in PE only.

Conclusions

Our data suggest that alpha methyldopa may have a specific effect on placental and/or endothelial cell function in pre-eclampsia patients, altering angiogenic proteins.

Activation of the VEGFR1 chromatin domain: an angiogenic signal-ETS1/HIF-2alpha regulatory axis

Angiogenesis is induced by multiple growth factors including vascular endothelial growth factor (VEGF) and fibroblast growth factor 2 (FGF2). In vascular endothelium VEGF signals through two receptor-tyrosine kinases, VEGFR1 and VEGFR2. The VEGFR1 gene encodes both a receptor-tyrosine kinase and a secreted splice variant, soluble VEGFR1. Whereas VEGFR1 is essential for vascular development, mechanisms that regulate VEGFR1 expression in endothelial cells are poorly understood. We demonstrate here that in endothelial cells, FGF2 and epidermal growth factor (EGF) signaling induce VEGFR1 mRNA expression in a combinatorial fashion. EGF/FGF2-mediated VEGFR1 induction is mediated via functional interaction of transcription factors ETS1 and HIF-2alpha. Mechanistic analyses revealed that in endothelial cells EGF/FGF2 signaling induces ETS1 expression, increases HIF-2alpha protein level in absence of hypoxia, and recruits both ETS1 and HIF-2alpha to the VEGFR1 chromatin domain. Knockdown of ETS1 and HIF-2alpha by RNA interference inhibits EGF/FGF2-induced VEGFR1 expression, and loss of expression is associated with impaired RNA-polymerase II recruitment and histone modifications at the VEGFR1 promoter region. In addition, using a mouse embryonic stem cell in vitro differentiation system, we found that induction of VEGFR1 in embryoid bodies is also associated with ETS1 and HIF-2alpha recruitment to the VEGFR1 locus. These results establish an angiogenic signal-ETS1/HIF-2alpha axis that regulates the VEGFR1 chromatin domain to induce VEGFR1 transcription in endothelial cells and in differentiating embryonic stem cells.

The endothelial-specific regulatory mutation, Mvwf1, is a common mouse founder allele

Mvwf1 is a cis-regulatory mutation previously identified in the RIIIS/J mouse strain that causes a unique tissue-specific switch in the expression of an N-acetylgalactosaminyltransferase, B4GALNT2, from intestinal epithelium to vascular endothelium. Vascular B4galnt2 expression results in aberrant glycosylation of von Willebrand Factor (VWF) and accelerated VWF clearance from plasma. We now report that 13 inbred mouse strains share the Mvwf1 tissue-specific switch and low VWF phenotype, including five wild-derived strains. Genomic sequencing identified a highly conserved 97-kb Mvwf1 haplotype block shared by these strains that encompasses a 30-kb region of high nucleotide sequence divergence from C57BL6/J flanking B4galnt2 exon 1. The analysis of a series of bacterial artificial chromosome (BAC) transgenes containing B4galnt2 derived from the RIIIS/J or C57BL6/J inbred mouse strains demonstrates that the corresponding sequences are sufficient to confer the vessel (RIIIS/J) or intestine (C57BL6/J)-specific expression patterns. Taken together, our data suggest that the region responsible for the Mvwf1 regulatory switch lies within an approximately 30-kb genomic interval upstream of the B4galnt2 gene. The observation that Mvwf1 is present in multiple wild-derived strains suggests that this locus may be retained in wild mouse populations due to positive selection. Similar selective pressures could contribute to the high prevalence of von Willebrand disease in humans.

In vitro and in vivo analysis of expression cassettes designed for vascular gene transfer

Increasing the level and duration of transgene expression and restricting expression to vascular cells are important goals for clinically useful gene therapy vectors. We evaluated several promoters, enhancers and introns in endothelial, smooth muscle and liver cells in tissue culture and in vivo, comparing local delivery to the carotid artery with intravenous delivery to the liver. A 1800-bp fragment of the oxidized LDL receptor (LOX-1) promoter showed highest in vivo activity in the carotid artery, achieving 39% the activity of the reference cytomegalovirus promoter, with 188-fold greater specificity for carotid artery over liver. An enhancer from the Tie2 gene in combination with the intracellular adhesion molecule-2 promoter improved endothelial specificity of plasmid vectors, increased the expression from adenoviral vectors in cultured endothelial cells and doubled the specificity for carotid artery over liver in vivo. Adding a short intron to expression cassettes increased expression in both endothelial and smooth muscle cells in vitro; however, the eNOS enhancer failed to consistently increase the expression or endothelial specificity of the vector. In conclusion, elements from the LOX-1 promoter and Tie2 enhancer together with an intron can be used to improve vectors for vascular gene transfer.

In vivo transcriptional targeting into the retinal vasculature using recombinant baculovirus carrying the human flt-1 promoter

Background

Endothelial cells are a target for gene therapy because they are implicated in a number of vascular diseases. Recombinant baculovirus have emerged as novel gene delivery vectors. However, there is no information available concerning the use of endothelial-specific promoters in the context of the baculovirus genome. In the present study, we have generated a recombinant baculovirus containing the human flt-1 promoter (BacFLT-GFP) driving the expression of the green fluorescent protein. Transcriptional gene targeting was analyzed in vitro in different mammalian cell lines and in vivo in adult rat retinal vasculature.

Results

BacFLT-GFP evoked the highest levels of expression in the endothelial cell line BUVEC-E6E7-1, similar to those reached by recombinant baculovirus carrying the CMV promoter (112% relative to BacCMV-GFP, n = 4). Interestingly, BacFLT-GFP directed high levels of expression in rat glioma C6 and in human glioblastoma CH235 cells (34.78% and 47.86% relative to BacCMV-GFP, respectively). Histone deacetylase inhibitors such as butyrate or trichostatin A enhanced the transcriptional activity of both BacCMV-GFP and BacFLT-GFP. Thus, in this study histone deacetylation appears to be a central mechanism for the silencing of baculovirus, independently of the promoter utilized. In vivo transcriptional targeting was demonstrated in adult rat retinal vasculature by intravitreal delivery of BacFLT-GFP and immunohistochemical staining with von Willebrand factor (vWF). Analysis by fluorescence microscopy and deconvolved three-dimensional confocal microscopy of retinal whole mounts obtained after 3 days of baculovirus injection showed that most GFP-expressing cells localized to the inner limiting membrane (ILM) and ganglion cell layer (GCL) and colocalize with vWF (70%, n = 10) in blood vessels, confirming the endothelial phenotype of the transduced cells.

Conclusion

Taken together, our results indicate that the restricted expression in endothelial cells mediated by the flt-1 promoter is not affected by the context of the baculovirus genome and demonstrate the potential of using recombinant baculovirus for transcriptional targeted gene expression into the eye vasculature.

Upregulation of soluble vascular endothelial growth factor receptor 1 contributes to angiogenesis defects in the placenta of alpha 2B-adrenoceptor deficient mice

Alpha2-adrenoceptors are essential presynaptic regulators of norepinephrine release from sympathetic nerves. Previous studies in mice with targeted deletions in the 3 alpha2-adrenoceptor genes have indicated that these receptors are essential for embryonic development. In the present study, we searched for the alpha2-adrenoceptor subtype(s) involved in placental development and its molecular mechanism using mice carrying targeted deletions in alpha2-adrenoceptor genes. Congenic alpha2B-adrenoceptor-deficient mice (Adra2b-/-) developed a defect in fetal and maternal vessel formation in the placenta labyrinth at embryonic day 10.5. This defect was accompanied by reduced endothelial cell proliferation and decreased extracellular signal-regulated kinase 1/2 phosphorylation levels in Adra2b-/- as compared with Adra2b+/+ placentae. Microarray analysis of wild-type and mutant placentae (maternal genotype Adra2b+/-) revealed 179 genes, which were significantly up- or downregulated >1.5-fold in alpha2B-deficient placentae. The type 1 receptor for vascular endothelial growth factor (Flt1), which is coexpressed with alpha2B-adrenoceptors in spongiotrophoblast and giant cells of the placenta, was found to be 2.3-fold upregulated in alpha2B-deficient placentae. Neutralization of Flt1 and its soluble splice variant sFlt1 by a specific antibody in vivo prevented the vascular defect in alpha2B-deficient placentae at embryonic day 10.5. Thus, alpha2B-adrenoceptors are essential to suppress antiangiogenic (s)Flt1 in spongiotrophoblasts to control the coordinated formation of a vascular labyrinth of fetal and maternal blood vessels in the murine placenta during development.

beta2-microglobulin is a signaling and growth-promoting factor for human prostate cancer bone metastasis

The protein factor beta2-microglobulin (beta2M), purified from the conditioned medium of human prostate cancer cell lines, stimulated growth and enhanced osteocalcin (OC) and bone sialoprotein (BSP) gene expression in human prostate cancer cells by activating a cyclic AMP (cAMP)-dependent protein kinase A signaling pathway. When beta2M was overexpressed in prostate cancer cells, it induced explosive tumor growth in mouse bone through increased phosphorylated cAMP-responsive element binding protein (CREB) and activated CREB target gene expression, including OC, BSP, cyclin A, cyclin D1, and vascular endothelial growth factor. Interrupting the beta2M downstream signaling pathway by injection of the beta2M small interfering RNA liposome complex produced an effective regression of previously established prostate tumors in mouse bone through increased apoptosis as shown by immunohistochemistry and activation of caspase-9, caspase-3, and cleavage of poly(ADP-ribose) polymerase. These results suggest that beta2M signaling is an attractive new therapeutic target for the treatment of lethal prostate cancer bone metastasis.

Ets-1-dependent expression of vascular endothelial growth factor receptors is activated by latency-associated nuclear antigen of Kaposi's sarcoma-associated herpesvirus through interaction with Daxx

Vascular endothelial growth factor (VEGF) and its receptors are highly expressed in Kaposi's sarcoma (KS) lesion and play a key role in angiogenesis. Latency-associated nuclear antigen (LANA) of Kaposi's sarcoma-associated herpesvirus (KSHV/HHV8) has multiple functions related to viral latency and KSHV-induced oncogenesis. In this report, we have identified Daxx as a LANA-binding protein by co-immunoprecipitation analysis of HeLa cells stably expressing LANA. LANA associated with Daxx in a PEL cell line infected with KSHV. LANA and Daxx also bound in vitro, suggesting direct interaction. From the results of binding assays, a region containing the Glu/Asp-rich domain within LANA, and a central region including the second paired amphipathic helix within Daxx contributed to the interaction. To address the physiological significance of this interaction, we focused on a Daxx-mediated VEGF receptor gene regulation. We found that Daxx repressed Ets-1-dependent Flt-1/VEGF receptor-1 gene expression, and that LANA inhibited the repression by Daxx in a reporter assay. Analyses of flow cytometry and real-time PCR revealed that expression of VEGF receptor-1 and -2 in LANA-expressing human umbilical vein endothelial cells (HUVECs) significantly increased. Co-immunoprecipitation and immunoblotting experiments suggested that LANA-bound Daxx to inhibit the interaction between Daxx and Ets-1. Chromatin immunoprecipitation assays showed that Daxx associated with VEGF receptor-1 promoter in HUVECs, and that LANA expression reduced this association. These results suggested that LANA contributes to a high expression of VEGF receptors in KS lesion by interfering with the interaction between Daxx and Ets-1.

Transcriptional regulators of angiogenesis

Angiogenesis, the process by which new blood vessels develop from a pre-existing vascular network, is essential for normal development and in certain physiological states. Inadequate or excessive angiogenesis has been incriminated in a number of pathologic states. For example, vaso-occlusive disease arising from atherosclerosis can lead to ischemia, a situation in which enhanced angiogenesis would be beneficial. Conversely, overzealous angiogenesis can contribute to tumor development and in this case inhibition of angiogenesis is desirable. Thus, strategies to induce or inhibit angiogenesis are of considerable therapeutic interest.

Plasmid engineering for controlled and sustained gene expression for nonviral gene therapy

Gene therapy requires the introduction of genetic material in diseased cells with the aim of treating or ultimately curing a disease. Since the start of gene therapy clinical trials in 1990, gene therapy has proven to be possible, but studies to date have highlighted the difficulty of achieving efficient, specific, and long-term transgene expression. Efforts to improve gene therapy strategies over the past years were mainly aimed at solving the problem of delivery, without paying much attention to the optimization of the expression cassette. With the current understanding of the eukaryotic transcription machinery and advanced molecular biology techniques at our disposition, it has now become possible to create custom-made transgene expression cassettes optimized for gene therapy applications. In this review, we will discuss several strategies that have been explored to improve the level and duration of transgene expression, to increase control over expression, or to restrict transgene expression to specific cell types or tissues. Although still in its infancy, such strategies will eventually lead to improvement of nonviral gene therapy and expansion of the range of possible therapeutic applications.

Strategies to improve non-viral vectors – potential applications in clinical transplantation

Prevention of acute rejection has been well controlled with immunosuppressive drugs. However, the long-term control of rejection is less satisfactory and the side effects of chronic usage of these drugs are far from acceptable. Thus, more imaginative options for therapy need to be explored. Gene therapy has potential promise in preserving allografts, preventing rejection and inducing tolerance. Despite this initial promise in many animal models, the translation of gene therapy to the clinical arena has been slow. This may be related in part to the deficiencies in vector development. Existing viral vectors are efficient at transducing allografts, but they induce inflammatory and pathogenic effects. Although the alternative non-viral systems are relatively innocuous, they are less efficient at gene delivery. This review systematically analyses the limitations of non-viral vector technology and the strategies that have been developed to overcome these limitations. Future development of non-viral vectors may have potential application in clinical transplantation.

Use of replication-competent retroviral vectors in an immunocompetent intracranial glioma model

OBJECT

The authors had previously reported on a replication-competent retrovirus (RCR) that has been demonstrated to be stable, capable of effective transduction, and able to prolong survival in an intracranial tumor model in nude mice. The purpose of this study was further investigation of this gene therapy option.

METHODS

The transduction efficiency of RCR in RG2, an immunocompetent intracranial tumor model, was tested in Fischer 344 rats. The immune response to the RCR vector was expressed by the quantification of CD4, CD8, and CD11/b in tumors. The pharmaceutical efficacy of the suicide gene CD in converting prodrug 5-fluorocytosine (5-FC) to 5-fluorouracil (5-FU) was measured using fluorine-19 nuclear magnetic resonance (19F-NMR) spectroscopy. Animal survival data were plotted on Kaplan-Meier survival curves. Finally, the biodistribution of RCR was determined using quantitative real-time polymerase chain reaction (RT-PCR) for the detection of retroviral env gene. There was no evidence of viral transduction in normal brain cells. Neither severe inflammation nor immunoreaction occurred after intracranial injection of RCR-green fluorescent protein compared with phosphate-buffered saline (PBS). The 19F-NMR spectroscopy studies demonstrated that RCR-CD was able to convert 5-FC to 5-FU effectively in vitro. The infection of RG2 brain tumors with RCR-CD and their subsequent treatment with 5-FC significantly prolonged survival compared with that in animals with RG2 transduced tumors treated with PBS. In contrast to the nude mouse model, evidence of virus dissemination to the systemic organs after intracranial injection was not detected using RT-PCR.

CONCLUSIONS

The RCR-mediated suicide gene therapy described in this paper effectively transduced malignant gliomas in an immunocompetent in vivo rodent model, prolonging survival, without evidence of severe intracranial inflammation, and without local transduction of normal brain cells or systemic organs.

Conditionally replicative adenoviral vectors for malignant glioma

High-grade gliomas constitute an important challenge to modern medicine, and although great effort has been made to prolong patient survival, the prognosis for this disease remains poor. Due to recent discoveries in the molecular basis of gliomas, gene therapy is becoming a promising alternative. In this review, we discuss the use of conditionally replicative adenoviral vectors (CRAd) and their applications in neuro-oncology. Such vectors, when rendered conditionally replicative via transductional and transcriptional modifications, offer great promise for patients with malignant brain tumours. We review data from preclinical and clinical studies utilising such vectors and discuss the limitations and future perspectives of CRAd oncolytic therapy for malignant glioma.

An angiogenic switch in breast cancer involves estrogen and soluble vascular endothelial growth factor receptor 1

Estrogen is involved in breast tumorigenesis, but the precise mechanisms for its oncogenic and angiogenic actions are poorly understood. Angiogenesis is regulated, in part, by these critical components: vascular endothelial growth factor (VEGF) and its two receptors (VEGFR-1 and VEGFR-2). VEGFR-2 is a positive angiogenic signal transducer, whereas VEGFR-1, especially its soluble form (soluble VEGFR-1), is a negative regulator of VEGF availability. We found that breast epithelial cells express soluble VEGFR-1 and hypothesized that because estrogen can regulate expression of members of the VEGF family, it might stimulate angiogenesis in breast cancer by decreasing expression of soluble VEGFR-1. Soluble VEGFR-1 expression decreased in estrogen receptor (ER)-positive but not in ER-negative breast cancer cell lines treated with estrogen. Pretreatment of the cells with the ER antagonist ICI 182,780 blocked the effect. The estrogen-mediated decrease in soluble VEGFR-1 expression was accompanied by a statistically significant increase in angiogenesis in vivo. Our data suggest that inhibition of soluble VEGFR-1 expression represents a novel mechanism--an estrogen-driven angiogenic switch--possibly responsible for breast carcinoma progression.

Retroviral hybrid LTR vector strategy: functional analysis of LTR elements and generation of endothelial cell specificity

Transcriptional targeting is an important aspect of developing gene therapy vectors in order to restrict transgene expression to selected target cells. One approach, when using retroviral vectors, is to replace viral transcriptional control elements within the long terminal repeat (LTR) with sequences imparting the desired specificity. We have developed such hybrid LTR retroviruses, incorporating sequences from each of the human promoters for flt-1, ICAM-2 and KDR, as part of our antivascular cancer gene therapy strategy targeting tumour endothelial cells. The chosen fragments were used to replace the enhancer or combined enhancer and proximal promoter regions of the viral LTR. All showed activity in primary human breast microvascular endothelial cells, with viruses incorporating ICAM-2 sequences exhibiting the greatest specificity versus nonendothelial cells in vitro and a marked alteration of specificity towards endothelial cells in a subcutaneous xenograft model in vivo. Moreover, our study documents the effect of enhancer and/or proximal promoter deletion on LTR activity and reports that differential dependence in different cell lines can give the false impression of specificity if experiments are not adequately controlled. This finding also has implications for other retroviral vector designs seeking to provide transcriptional specificity and for their safety with respect to prevention of gene activation at sites of proviral integration.

Transductional and transcriptional targeting of cancer cells using genetically engineered viral vectors

Gene delivery vectors, including adenovirus (Ad) and adeno-associated virus (AAV), are inefficient and non-selective for cancer due to low levels of viral receptors with high levels on other tissues, including liver. We tested Ads and AAVs with the SIGYPLP-targeting peptide inserted into virus capsids for transduction in a panel of cancer cells. Six of twelve lines (C8161, PC-3, G-CCM, MKN-45, LnCAP and A549) were transduced, independently of native viral tropism. Furthermore the candidate cancer gene therapy promoter FLT-1 was active in three of these six cell lines. This offers the potential for dual targeting of selected cancer cells.

Aberrant methylation of the vascular endothelial growth factor receptor-1 gene in prostate cancer

Transcriptional silencing of cancer-related genes by DNA methylation is observed in various cancers. To identify genes controlled by methylation in prostate cancer, we used cDNA microarray analysis to investigate gene expression in prostate cancer cell lines LNCaP and DU145 treated with a methyltransferase inhibitor alone or together with a histone deacetylase inhibitor. We detected significant changes (3.4-5.7%) in gene expression in prostate cancer cell lines with the drug treatments. Among the affected genes, that for the vascular endothelial growth factor receptor 1 (VEGFR-1) was re-expressed in LNCaP and DU145 after the drug treatments. Bisulfite sequencing revealed the promoter and exon 1 of the VEGFR-1 to be hypermethylated in the cell lines. These results support the idea that methylation is associated with loss of VEGFR-1 mRNA expression in prostate cancer cell lines. Combined bisulfite restriction analysis (COBRA) showed the gene to be methylated in 24 (38.1%) of 63 primary local prostate cancer samples, while in all 13 benign prostate samples it was not. These findings indicate that methylation of VEGFR-1 is related with prostatic carcinogenesis.

Ets, Ap-1 and GATA factor families regulate the utrophin B promoter: potential regulatory mechanisms for endothelial-specific expression

Duchenne muscular dystrophy is caused by dystrophin deficiency, which can be prevented in the mdx mouse model by over-expression of an autosomal homologue, utrophin. Utrophin has two characterised full-length promoters, A and B. No data are available on the transcriptional regulation of B utrophin, which has been recently localised to the endothelium. Similar to characterised endothelial promoters, Ets and Ap-1 individually trans-activate the human B core promoter. Synergistic activation by GATA-2 and c-jun to the order of 20-fold was observed.

Airway vascular remodeling in asthma

Several characteristic changes occur in the bronchial wall in asthma, including specific changes to the vasculature. These result in an increase in vessel numbers per unit area, as well as increased vessel activity suggested by vasodilatation, vessel leakage, and cellular margination with transmigration to target tissues. This combined action in asthma leads to airway-wall thickening and reduced airflow. Each component of the vascular response has been shown to be controlled by a range of inflammatory mediators and growth factors. These factors are themselves regulated by a complex process initially involving gene expression, transcription, and translation at the molecular level, then subsequent protein release, binding to matrix elements, endothelial cell activation, and a proliferative endothelial response. Many commonly used airway medications are capable of modulating the vascular response to inflammatory stimuli. New therapies might improve airflow through better regulation of vessel growth, dilatation, and leakage in the airway wall.