Interaction between hex and GATA transcription factors in vascular endothelial cells inhibits flk-1/KDR-mediated vascular endothelial growth factor signaling

GATA2 participates in protection against hypoxia-induced pulmonary vascular remodeling

The vascular endothelium is vital for cardio-pulmonary homeostasis and, thus, plays a crucial role in preventing life-threatening lung diseases. The transcription factor GATA2 is essential for hematopoiesis and maintaining vascular integrity. Heterozygous mutations in GATA2 can lead to a primary immunodeficiency syndrome with pulmonary manifestations. Some GATA2 haploinsufficient patients develop pulmonary hypertension (PH), characterized by vascular remodeling and occlusion of small pulmonary arteries. However, the mechanism underlying pulmonary vascular remodeling in GATA2 haploinsufficient patients remain unclear. To understand how GATA2 deficiency affects pulmonary artery homeostasis, we applied a chronic hypoxia-mediated PH model using inducible systemic Gata2 conditionally deficient (G2-CKO) mice. The G2-CKO mice exhibited augmented pulmonary vascular remodeling, with enhanced α-smooth muscle actin accumulation and increased apoptotic cells in the vascular wall upon chronic hypoxia. Transcript analysis and chromatin immunoprecipitation assays using mouse pulmonary vascular endothelial cells revealed that GATA2 directly regulates the expression of G6pdx (a crucial cytoprotective enzyme) and Bmp4 (a growth factor that mediates vascular homeostasis). These results suggest that GATA2-deficient lungs are vulnerable to the hypoxic stress due to a diminished cellular protective response, making G2-CKO mice more prone to vascular remodeling upon chronic hypoxia. These findings provide insights into the mechanisms underlying GATA2-haploinsufficiency-related pulmonary hypertension.

The Haematopoietically-expressed homeobox transcription factor: roles in development, physiology and disease

The Haematopoietically expressed homeobox transcription factor (Hhex) is a transcriptional repressor that is of fundamental importance across species, as evident by its evolutionary conservation spanning fish, amphibians, birds, mice and humans. Indeed, Hhex maintains its vital functions throughout the lifespan of the organism, beginning in the oocyte, through fundamental stages of embryogenesis in the foregut endoderm. The endodermal development driven by Hhex gives rise to endocrine organs such as the pancreas in a process which is likely linked to its role as a risk factor in diabetes and pancreatic disorders. Hhex is also required for the normal development of the bile duct and liver, the latter also importantly being the initial site of haematopoiesis. These haematopoietic origins are governed by Hhex, leading to its crucial later roles in definitive haematopoietic stem cell (HSC) self-renewal, lymphopoiesis and haematological malignancy. Hhex is also necessary for the developing forebrain and thyroid gland, with this reliance on Hhex evident in its role in endocrine disorders later in life including a potential role in Alzheimer's disease. Thus, the roles of Hhex in embryological development throughout evolution appear to be linked to its later roles in a variety of disease processes.

Adipose tissue angiogenesis genes are down-regulated by grape polyphenols supplementation during a human overfeeding trial

The adaptive response to overfeeding is associated with profound modifications of gene expression in adipose tissue to support lipid storage and weight gain. The objective of this study was to assess in healthy lean men whether a supplementation with polyphenols could interact with these molecular adaptations. Abdominal subcutaneous adipose tissue biopsies were sampled from 42 subjects participating to an overfeeding protocol providing an excess of 50% of their total energy expenditure for 31 days, and who were supplemented with 2 g/day of grape polyphenols or a placebo. Gene expression profiling was performed by RNA sequencing. Overfeeding led to a modification of the expression of 163 and 352 genes in the placebo and polyphenol groups, respectively. The GO functions of these genes were mostly involved in lipid metabolism, followed by genes involved in adipose tissue remodeling and expansion. In response to overfeeding, 812 genes were differentially regulated between groups. Among them, a set of 41 genes were related to angiogenesis and were downregulated in the polyphenol group. Immunohistochemistry targeting PECAM1, as endothelial cell marker, confirmed reduced angiogenesis in this group. Finally, quercetin and isorhamnetin, two polyphenol species enriched in the plasma of the volunteers submitted to the polyphenols, were found to inhibit human umbilical vein endothelial cells migration in vitro. Polyphenol supplementation do not prevent the regulation of genes related to lipid metabolism in human adipose tissue during overfeeding, but impact the angiogenesis pathways. This may potentially contribute to a protection against adipose tissue expansion during dynamic phase of weight gain.

Association of VEGF haplotypes with breast cancer risk in North-West Indians

BACKGROUND

Angiogenesis is a complex and coordinated process regulated by different growth factors and is one of the hallmark features of cancer. VEGF is one of the most important endothelial cell mitogen and has a critical role in normal physiological and tumor angiogenesis. The objective of this study was to investigate the potential association of haplotypes of six VEGF polymorphisms with breast cancer risk in North-West Indians.

METHODS

Samples of 250 breast cancer patients and 250 age and sex matched controls were genotyped for VEGF -2578C/A, -2549I/D, -460T/C, +405C/G, -7C/T and +936C/T polymorphisms. Haplotypes were generated to determine the better contribution of VEGF polymorphisms to breast cancer risk.

RESULTS

Haplotypes CDTCCC (OR = 0.56, 95%CI, 0.38-0.81; p = 0.003) and CDTGCC (OR = 0.63, 95%CI, 0.44-0.92; p = 0.018) of VEGF -2578C/A, -2549I/D, -460T/C, +405C/G, -7C/T and +936C/T polymorphisms were significantly associated with decreased risk of breast cancer. CDTCCC haplotype was also significantly associated with reduced risk of breast cancer in pre and post menopausal as well as both obese and non obese patients. Haplotype CDTGCC was marginally associated (p = 0.07) with reduced risk of breast cancer in non-obese patients as compared with non-obese controls where as haplotype AICGTC was marginally associated (p = 0.09) with reduced risk of breast cancer in obese patients when compared with non-obese patients. The CDTGCC haplotype was significantly associated with increased risk of breast cancer in premenopausal obese patients (OR = 1.98, 95%CI, 1.10-3.56; p = 0.02).

CONCLUSIONS

Our data indicated that CDTCCC and CDTGCC haplotypes of VEGF -2578C/A, -2549I/D, -460T/C, +405C/G, -7C/T and +936C/T polymorphisms were significantly associated with breast cancer risk in North-West Indians. Further studies on multiethnic groups with larger sample size are required to confirm our results.

A Novel GATA2 Protein Reporter Mouse Reveals Hematopoietic Progenitor Cell Types

The transcription factor (TF) GATA2 plays a key role in organ development and cell fate control in the central nervous, urogenital, respiratory, and reproductive systems, and in primitive and definitive hematopoiesis. Here, we generate a knockin protein reporter mouse line expressing a GATA2VENUS fusion from the endogenous Gata2 genomic locus, with correct expression and localization of GATA2VENUS in different organs. GATA2VENUS expression is heterogeneous in different hematopoietic stem and progenitor cell populations (HSPCs), identifies functionally distinct subsets, and suggests a novel monocyte and mast cell lineage bifurcation point. GATA2 levels further correlate with proliferation and lineage outcome of hematopoietic progenitors. The GATA2VENUS mouse line improves the identification of specific live cell types during embryonic and adult development and will be crucial for analyzing GATA2 protein dynamics in TF networks.

•

A novel GATA2VENUS fusion mouse line to report GATA2 protein expression

•

VENUS fusion does not alter GATA2 expression or disturb development or homeostasis

•

GATA2 expression identifies functionally distinct HSPC subpopulations

•

GATA2 expression unveils an earlier monocyte-mast cell lineage bifurcation point

Possible cooption of a VEGF-driven tubulogenesis program for biomineralization in echinoderms

Biomineralization is the process by which living organisms use minerals to form hard structures that protect and support them. Biomineralization is believed to have evolved rapidly and independently in different phyla utilizing preexisting components. The mechanistic understanding of the regulatory networks that drive biomineralization and their evolution is far from clear. Sea urchin skeletogenesis is an excellent model system for studying both gene regulation and mineral uptake and deposition. The sea urchin calcite spicules are formed within a tubular cavity generated by the skeletogenic cells controlled by vascular endothelial growth factor (VEGF) signaling. The VEGF pathway is essential for biomineralization in echinoderms, while in many other phyla, across metazoans, it controls tubulogenesis and vascularization. Despite the critical role of VEGF signaling in sea urchin spiculogenesis, the downstream program it activates was largely unknown. Here we study the cellular and molecular machinery activated by the VEGF pathway during sea urchin spiculogenesis and reveal multiple parallels to the regulation of vertebrate vascularization. Human VEGF rescues sea urchin VEGF knockdown, vesicle deposition into an internal cavity plays a significant role in both systems, and sea urchin VEGF signaling activates hundreds of genes, including biomineralization and interestingly, vascularization genes. Moreover, five upstream transcription factors and three signaling genes that drive spiculogenesis are homologous to vertebrate factors that control vascularization. Overall, our findings suggest that sea urchin spiculogenesis and vertebrate vascularization diverged from a common ancestral tubulogenesis program, broadly adapted for vascularization and specifically coopted for biomineralization in the echinoderm phylum.

NKL homeobox gene MSX1 acts like a tumor suppressor in NK-cell leukemia

NKL homeobox gene MSX1 is physiologically expressed in lymphoid progenitors and subsequently downregulated in developing T- and B-cells. In contrast, elevated expression levels of MSX1 persist in mature natural killer (NK)-cells, indicating a functional role in this compartment. While T-cell acute lymphoblastic leukemia (T-ALL) subsets exhibit aberrant overexpression of MSX1, we show here that in malignant NK-cells the level of MSX1 transcripts is aberrantly downregulated. Chromosomal deletions at 4p16 hosting the MSX1 locus have been described in NK-cell leukemia patients. However, NK-cell lines analyzed here showed normal MSX1 gene configurations, indicating that this aberration might be uncommon. To identify alternative MSX1 regulatory mechanisms we compared expression profiling data of primary normal NK-cells and malignant NK-cell lines. This procedure revealed several deregulated genes including overexpressed IRF4, MIR155HG and MIR17HG and downregulated AUTS2, EP300, GATA3 and HHEX. As shown recently, chromatin-modulator AUTS2 is overexpressed in T-ALL subsets where it mediates aberrant transcriptional activation of MSX1. Here, our data demonstrate that in malignant NK-cell lines AUTS2 performed MSX1 activation as well, but in accordance with downregulated MSX1 transcription therein we detected reduced AUTS2 expression, a small genomic deletion at 7q11 removing exons 3 and 4, and truncating mutations in exon 1. Moreover, genomic profiling and chromosomal analyses of NK-cell lines demonstrated amplification of IRF4 at 6p25 and deletion of PRDM1 at 6q21, highlighting their potential oncogenic impact. Functional analyses performed via knockdown or forced expression of these genes revealed regulatory network disturbances effecting downregulation of MSX1 which may underlie malignant development in NK-cells.

Misregulation of the proline rich homeodomain (PRH/HHEX) protein in cancer cells and its consequences for tumour growth and invasion

The proline rich homeodomain protein (PRH), also known as haematopoietically expressed homeobox (HHEX), is an essential transcription factor in embryonic development and in the adult. The PRH protein forms oligomeric complexes that bind to tandemly repeated PRH recognition sequences within or at a distance from PRH-target genes and recruit a variety of PRH-interacting proteins. PRH can also bind to other transcription factors and co-regulate specific target genes either directly through DNA binding, or indirectly through effects on the activity of its partner proteins. In addition, like some other homeodomain proteins, PRH can regulate the translation of specific mRNAs. Altered PRH expression and altered PRH intracellular localisation, are associated with breast cancer, liver cancer and thyroid cancer and some subtypes of leukaemia. This is consistent with the involvement of multiple PRH-interacting proteins, including the oncoprotein c-Myc, translation initiation factor 4E (eIF4E), and the promyelocytic leukaemia protein (PML), in the control of cell proliferation and cell survival. Similarly, multiple PRH target genes, including the genes encoding vascular endothelial growth factor (VEGF), VEGF receptors, Endoglin, and Goosecoid, are known to be important in the control of cell proliferation and cell survival and/or the regulation of cell migration and invasion. In this review, we summarise the evidence that implicates PRH in tumourigenesis and we review the data that suggests PRH levels could be useful in cancer prognosis and in the choice of treatment options.

Hhex Is Necessary for the Hepatic Differentiation of Mouse ES Cells and Acts via Vegf Signaling

Elucidating the molecular mechanisms involved in the differentiation of stem cells to hepatic cells is critical for both understanding normal developmental processes as well as for optimizing the generation of functional hepatic cells for therapy. We performed in vitro differentiation of mouse embryonic stem cells (mESCs) with a null mutation in the homeobox gene Hhex and show that Hhex^-/- mESCs fail to differentiate from definitive endoderm (Sox17⁺/Foxa2⁺) to hepatic endoderm (Alb⁺/Dlk⁺). In addition, hepatic culture elicited a >7-fold increase in Vegfa mRNA expression in Hhex^-/- cells compared to Hhex^+/+ cells. Furthermore, we identified VEGFR2⁺/ALB⁺/CD34^- in early Hhex^+/+ hepatic cultures. These cells were absent in Hhex^-/- cultures. Finally, through manipulation of Hhex and Vegfa expression, gain and loss of expression experiments revealed that Hhex shares an inverse relationship with the activity of the Vegf signaling pathway in supporting hepatic differentiation. In summary, our results suggest that Hhex represses Vegf signaling during hepatic differentiation of mouse ESCs allowing for cell-type autonomous regulation of Vegfr2 activity independent of endothelial cells.

Growth-promoting and tumourigenic activity of c-Myc is suppressed by Hhex

c-Myc transcription factor is a key protein involved in cellular growth, proliferation and metabolism. c-Myc is one of the most frequently activated oncogenes, highlighting the need to identify intracellular molecules that interact directly with c-Myc to suppress its function. Here we show that Hhex is able to interact with the basic region/helix-loop-helix/leucine zipper of c-Myc. Knockdown of Hhex increases proliferation rate in hepatocellular carcinoma cells, whereas Hhex expression cell-autonomously reduces cell proliferation rate in multiple cell lines by increasing G1 phase length through a c-Myc-dependent mechanism. Global transcriptomic analysis shows that Hhex counter-regulates multiple c-Myc targets involved in cell proliferation and metabolism. Concomitantly, Hhex expression leads to reduced cell size, lower levels of cellular RNA, downregulation of metabolism-related genes, decreased sensitivity to methotrexate and severe reduction in the ability to form tumours in nude mouse xenografts, all indicative of decreased c-Myc activity. Our data suggest that Hhex is a novel regulator of c-Myc function that limits c-Myc activity in transformed cells.

Dextran induces differentiation of circulating endothelial progenitor cells

Endothelial progenitor cells (EPCs) have been demonstrated to be effective for the treatment of cardiovascular diseases. However, the differentiation process from circulation to adhesion has not been clarified because circulating EPCs rarely attached to dishes in EPC cultures previously. Here we investigated whether immature circulating EPCs differentiate into mature adhesive EPCs in response to dextran. When floating‐circulating EPCs derived from ex vivo expanded human cord blood were cultured with 5% and 10% dextran, they attached to fibronectin‐coated dishes and grew exponentially. The bioactivities of adhesion, proliferation, migration, tube formation, and differentiated type of EPC colony formation increased in EPCs exposed to dextran. The surface protein expression rate of the endothelial markers vascular endothelial growth factor (VEGF)‐R1/2, VE‐cadherin, Tie2, ICAM1, VCAM1, and integrin αv/β3 increased in EPCs exposed to dextran. The mRNA levels of VEGF‐R1/2, VE‐cadherin, Tie2, endothelial nitric oxide synthase, MMP9, and VEGF increased in EPCs treated with dextran. Those of endothelium‐related transcription factors ID1/2, FOXM1, HEY1, SMAD1, FOSL1, NFkB1, NRF2, HIF1A, EPAS1 increased in dextran‐treated EPCs; however, those of hematopoietic‐ and antiangiogenic‐related transcription factors TAL1, RUNX1, c‐MYB, GATA1/2, ERG, FOXH1, HHEX, SMAD2/3 decreased in dextran‐exposed EPCs. Inhibitor analysis showed that PI3K/Akt, ERK1/2, JNK, and p38 signal transduction pathways are involved in the differentiation in response to dextran. In conclusion, dextran induces differentiation of circulating EPCs in terms of adhesion, migration, proliferation, and vasculogenesis. The differentiation mechanism in response to dextran is regulated by multiple signal transductions including PI3K/Akt, ERK1/2, JNK, and p38. These findings indicate that dextran is an effective treatment for EPCs in regenerative medicines.

VEGFA-dependent and -independent pathways synergise to drive Scl expression and initiate programming of the blood stem cell lineage in Xenopus

The first haematopoietic stem cells share a common origin with the dorsal aorta and derive from putative adult haemangioblasts in the dorsal lateral plate (DLP) mesoderm. Here we show that the transcription factor (TF) stem cell leukaemia (Scl/Tal1) is crucial for development of these adult haemangioblasts in Xenopus and establish the regulatory cascade controlling its expression. We show that VEGFA produced in the somites is required to initiate adult haemangioblast programming in the adjacent DLP by establishing endogenous VEGFA signalling. This response depends on expression of the VEGF receptor Flk1, driven by Fli1 and Gata2. Scl activation requires synergy between this VEGFA-controlled pathway and a VEGFA-independent pathway controlled by Fli1, Gata2 and Etv2/Etsrp/ER71, which also drives expression of the Scl partner Lmo2. Thus, the two ETS factors Fli1 and Etv6, which drives the VEGFA expression in both somites and the DLP, sit at the top of the adult haemangioblast gene regulatory network (GRN). Furthermore, Gata2 is initially activated by Fli1 but later maintained by another ETS factor, Etv2. We also establish that Flk1 and Etv2 act independently in the two pathways to Scl activation. Thus, detailed temporal, epistatic measurements of key TFs and VEGFA plus its receptor have enabled us to build a Xenopus adult haemangioblast GRN.

The dual roles of homeobox genes in vascularization and wound healing

Homeobox genes represent a family of highly conserved transcription factors originally discovered to regulate organ patterning during development. More recently, several homeobox genes were shown to affect processes in adult tissue, including angiogenesis and wound healing. Whereas a subset of members of the Hox-family of homeobox genes activate growth and migration to promote angiogenesis or wound healing, other Hox genes function to restore or maintain quiescent, differentiated tissue function. Pathological tissue remodeling is linked to differential expression of activating or stabilizing Hox genes and dysregulation of Hox expression can contribute to disease progression. Studies aimed at understanding the role and regulation of Hox genes have provided insight into how these potent morphoregulatory genes can be applied to enhance tissue engineering or limit cancer progression.

The HMG-box transcription factor Sox4b is required for pituitary expression of gata2a and specification of thyrotrope and gonadotrope cells in zebrafish

The pituitary is a complex gland comprising different cell types each secreting specific hormones. The extensive network of signaling molecules and transcription factors required for determination and terminal differentiation of specific cell types is still not fully understood. The SRY-like HMG-box (SOX) transcription factor Sox4 plays important roles in many developmental processes and has two homologs in zebrafish, Sox4a and Sox4b. We show that the sox4b gene is expressed in the pituitary anlagen starting at 24 h after fertilization (hpf) and later in the entire head region including the pituitary. At 48 hpf, sox4b mRNA colocalizes with that for TSH (tshβ), glycoprotein subunit α (gsuα), and the Zn finger transcription factor Gata2a. Loss of Sox4b function, using morpholino knockdown or expression of a dominant-negative Sox4 mutant, leads to a drastic decrease in tshβ and gsuα expression and reduced levels of gh, whereas other anterior pituitary gland markers including prl, slβ, pomc, and lim3 are not affected. Sox4b is also required for expression of gata2a in the pituitary. Knockdown of gata2a leads to decreased tshβ and gsuα expression at 48 hpf, similar to sox4b morphants. Injection of gata2a mRNA into sox4b morphants rescued tshβ and gsuα expression in thyrotrope cells. Finally, sox4b or gata2a knockdown causes a significant decrease of gonadotropin expression (lhβ and fshβ) at 4 d after fertilization. In summary, our results indicate that Sox4b is expressed in zebrafish during pituitary development and plays a crucial role in the differentiation of thyrotrope and gonadotrope cells through induction of gata2a expression in the developing pituitary.

Downregulation of endothelial microRNA-200b supports cutaneous wound angiogenesis by desilencing GATA binding protein 2 and vascular endothelial growth factor receptor 2

OBJECTIVE

MicroRNAs (miRs) regulate angiogenesis by posttranscriptional silencing of target genes. The significance of angiostatic miR-200b in switching on skin wound angiogenesis was tested.

METHODS AND RESULTS

Wounding caused imminent and transient downregulation of miR-200b in dermal wound-edge endothelial cells. Derailing this injury response by lentiviral delivery of miR-200b in vivo impaired wound angiogenesis. Computational prediction, target reporter luciferase assay, and Western blot analysis provided first evidence that miR-200b targets globin transcription factor binding protein 2 (GATA2) and vascular endothelial growth factor receptor 2 (VEGFR2). Overexpression of GATA2 or VEGFR2 in endothelial cells rescued the angiostatic effect of miR-200b in vitro. Downregulation of miR-200b derepressed GATA2 and VEGFR2 expression to switch on wound angiogenesis, which was disrupted in diabetic wounds. Treatment of endothelial cells with tumor necrosis factor-α, a proinflammatory cytokine abundant in diabetic wounds, induced miR-200b expression, silenced GATA2 and VEGFR2, and suppressed angiogenesis. These outcomes were attenuated using anti-miR-200b strategy. Neutralization of tumor necrosis factor-α in the diabetic wounds improved wound angiogenesis and closure, which was accompanied by downregulation of miR-200b expression and desilencing of GATA2 and VEGFR2.

CONCLUSIONS

Injury-induced repression of miR-200b turned on wound angiogenesis. In mice with diabetes mellitus,excessive tumor necrosis factor-α induced miR-200b blunting proangiogenic functions of GATA2 and VEGFR2.

VEGFR2 expression and TGF-β signaling in initial and recurrent high-grade human glioma

OBJECTIVE

Bevacizumab has promising activity against glioma, although reasons for poor efficacy and variable response rates in certain patients are unclear. Vascular endothelial growth factor receptor 2 (VEGFR2) is heterogeneously expressed within the microvasculature of various malignancies. Moreover, transforming growth factor β (TGF-β), a negative prognostic factor for glioma, is intimately involved in angiogenesis including VEGFR2 regulation. Our objective was to associate expression of VEGFR2 and TGF-β activity with clinicopathological features of human glioma.

METHODS

Expression patterns determined by immunohistochemistry for VEGFR2 and phosphorylated Smad2 in human gliomas were compared to overall survival, progression-free survival (PFS), initial versus recurrent tumors and tumor grade.

RESULTS

Endothelial VEGFR2 expression was low or undetectable in normal tissue but the proportion of VEGFR2-positive vessels increased with tumor grade. Decreased PFS was associated with tumors whose vessels had increased proportions of VEGFR2 at recurrence. Neither parenchymal nor endothelial cell p-Smad2 was associated with tumor grade; however, the former was negatively correlated with overall survival in glioblastoma multiforme.

CONCLUSIONS

The molecular phenotype of the vasculature based on the status of VEGFR2 but not p-Smad2 is related to aspects of glioma progression and patient response. Changes in VEGFR2-positive vessels may account for variable therapeutic efficacy of anti-angiogenic agents.

Colorectal carcinoma cell production of transforming growth factor beta decreases expression of endothelial cell vascular endothelial growth factor receptor 2

BACKGROUND

Vascular endothelial growth factor (VEGF) signaling is a target for antiangiogenic cancer therapy. The authors have previously observed that up to 40% of vessels in colorectal carcinoma (CRC) tumors are negative for VEGF receptor 2 (VEGFR2) expression. Differential activity of transforming growth factor beta (TGF-β) is a potential contributor to this receptor heterogeneity because TGF-β contributes to both angiogenesis and CRC tumor progression.

METHODS

The authors analyzed VEGFR2 expression by Western blotting, and TGF-β expression in endothelial and CRC cell lines, respectively. In addition, they immunostained endothelial cells in CRC xenografts to find an association between VEGFR2 and TGF-β levels or activity.

RESULTS

In bovine aortic endothelial cells (BAECs), TGF-β1 significantly repressed VEGFR2 protein in a time-dependent and dose-dependent fashion (P < .05). Serum-free conditioned media from various malignant human CRC cell lines (HCT116, 379.2, Dks8, and DLD1) induced down-regulation of VEGFR2 in BAECs. This effect was proportional to the total levels of TGF-β1 and TGF-β2 and was blocked by SB-431542 and SD-208, TGF-β receptor I inhibitors. Immunofluorescence staining of subcutaneous mouse xenografts of HCT116, 379.2, Dks8, and SW480 cells revealed vessels with an inverse relationship between TGF-β activity and VEGFR2 expression. Oxygen and bone morphogenetic protein 9 levels were shown to modulate TGF-β-induced VEGFR2 down-regulation.

CONCLUSIONS

In combination with other factors, TGF-β may contribute to the vascular heterogeneity in human colorectal tumors.

Epigenetically coordinated GATA2 binding is necessary for endothelium-specific endomucin expression

GATA2 is well recognized as a key transcription factor and regulator of cell-type specificity and differentiation. Here, we carried out comparative chromatin immunoprecipitation with comprehensive sequencing (ChIP-seq) to determine genome-wide occupancy of GATA2 in endothelial cells and erythroids, and compared the occupancy to the respective gene expression profile in each cell type. Although GATA2 was commonly expressed in both cell types, different GATA2 bindings and distinct cell-specific gene expressions were observed. By using the ChIP-seq with epigenetic histone modifications and chromatin conformation capture assays; we elucidated the mechanistic regulation of endothelial-specific GATA2-mediated endomucin gene expression, that was regulated by the endothelial-specific chromatin loop with a GATA2-associated distal enhancer and core promoter. Knockdown of endomucin markedly attenuated endothelial cell growth, migration and tube formation. Moreover, abrogation of GATA2 in endothelium demonstrated not only a reduction of endothelial-specific markers, but also induction of mesenchymal transition promoting gene expression. Our findings provide new insights into the correlation of endothelial-expressed GATA2 binding, epigenetic modification, and the determination of endothelial cell specificity.

PRH/Hhex controls cell survival through coordinate transcriptional regulation of vascular endothelial growth factor signaling

The proline-rich homeodomain protein (PRH) plays multiple roles in the control of gene expression during embryonic development and in the adult. Vascular endothelial growth factor (VEGF) is a mitogen that stimulates cell proliferation and survival via cell surface receptors including VEGFR-1 and VEGFR-2. VEGF signaling is of critical importance in angiogenesis and hematopoiesis and is elevated in many tumors. Here we show that PRH binds directly to the promoter regions of the Vegf, Vegfr-1, and Vegfr-2 genes and that in each case PRH represses transcription. We demonstrate that overexpression or knockdown of PRH directly impinges on the survival of both leukemic and tumor cells and that the modulation of VEGF and VEGF receptor signaling by PRH mediates these effects. Our findings demonstrate that PRH is a key regulator of the VEGF signaling pathway and describe a mechanism whereby PRH plays an important role in tumorigenesis and leukemogenesis.

Interaction between Hhex and SOX13 modulates Wnt/TCF activity

Fine-tuning of the Wnt/TCF pathway is crucial for multiple embryological processes, including liver development. Here we describe how the interaction between Hhex (hematopoietically expressed homeobox) and SOX13 (SRY-related high mobility group box transcription factor 13), modulates Wnt/TCF pathway activity. Hhex is a homeodomain factor expressed in multiple endoderm-derived tissues, like the liver, where it is essential for proper development. The pleiotropic expression of Hhex during embryonic development and its dual role as a transcriptional repressor and activator suggest the presence of different tissue-specific partners capable of modulating its activity and function. While searching for developmentally regulated Hhex partners, we set up a yeast two-hybrid screening using an E9.5-10.5 mouse embryo library and the N-terminal domain of Hhex as bait. Among the putative protein interactors, we selected SOX13 for further characterization. We found that SOX13 interacts directly with full-length Hhex, and we delineated the interaction domains within the two proteins. SOX13 is known to repress Wnt/TCF signaling by interacting with TCF1. We show that Hhex is able to block the SOX13-dependent repression of Wnt/TCF activity by displacing SOX13 from the SOX13 x TCF1 complex. Moreover, Hhex de-repressed the Wnt/TCF pathway in the ventral foregut endoderm of cultured mouse embryos electroporated with a SOX13-expressing plasmid. We conclude that the interaction between Hhex and SOX13 may contribute to control Wnt/TCF signaling in the early embryo.

Critical role for GATA3 in mediating Tie2 expression and function in large vessel endothelial cells

Endothelial phenotypes are highly regulated in space and time by both transcriptional and post-transcriptional mechanisms. There is increasing evidence that the GATA family of transcription factors function as signal transducers, coupling changes in the extracellular environment to changes in downstream target gene expression. Here we show that human primary endothelial cells derived from large blood vessels express GATA2, -3, and -6. Of these factors, GATA3 was expressed at the highest levels. In DNA microarrays of human umbilical vein endothelial cells (HUVEC), small interfering RNA-mediated knockdown of GATA3 resulted in reduced expression of genes associated with angiogenesis, including Tie2. At a functional level, GATA3 knockdown inhibited angiopoietin (Ang)-1-mediated but not vascular endothelial cell growth factor (VEGF)-mediated AKT signaling, cell migration, survival, and tube formation. In electrophoretic gel mobility shift assays and chromatin immunoprecipitation, GATA3 was shown to bind to regulatory regions within the 5'-untranslated region of the Tie2 gene. In co-immunoprecipitation and co-transfection assays, GATA3 and the Ets transcription factor, ELF1, physically interacted and synergized to transactivate the Tie2 promoter. GATA3 knockdown blocked the ability of Ang-1 to attenuate vascular endothelial cell growth factor stimulation of vascular cell adhesion molecule-1 expression and monocytic cell adhesion. Moreover, exposure of human umbilical vein endothelial cells to tumor necrosis factor-alpha resulted in marked down-regulation of GATA3 expression and reduction in Tie2 expression. Together, these findings suggest that GATA3 is indispensable for Ang-1-Tie2-mediated signaling in large vessel endothelial cells.

CK2 phosphorylation of the PRH/Hex homeodomain functions as a reversible switch for DNA binding

The proline-rich homeodomain protein (PRH/Hex) regulates transcription by binding to specific DNA sequences and regulates mRNA transport by binding to translation initiation factor eIF4E. Protein kinase CK2 plays multiple roles in the regulation of gene expression and cell proliferation. Here, we show that PRH interacts with the β subunit of CK2 in vitro and in cells and that CK2 phosphorylates PRH. Phosphorylation of PRH by CK2 inhibits the DNA binding activity of this protein and dephosphorylation restores DNA binding indicating that this modification acts as a reversible switch. We show that phosphorylation of the homeodomain is sufficient to block DNA binding and we identify two amino acids within this the domain that are phosphorylated by CK2: S163 and S177. Site-directed mutagenesis demonstrates that mutation of either of these residues to glutamic acid partially mimics phosphorylation but is insufficient to completely block DNA binding whereas an S163E/S177E double mutation severely inhibits DNA binding. Significantly, the S163E and S177E mutations and the S163E/S177E double mutation all inhibit the ability of PRH to regulate transcription in cells. Since these amino acids are conserved between many homeodomain proteins, our results suggest that CK2 may regulate the activity of several homeodomain proteins in this manner.

A mechanosensitive transcriptional mechanism that controls angiogenesis

Angiogenesis is controlled by physical interactions between cells and extracellular matrix as well as soluble angiogenic factors, such as VEGF. However, the mechanism by which mechanical signals integrate with other microenvironmental cues to regulate neovascularization remains unknown. Here we show that the Rho inhibitor, p190RhoGAP (also known as GRLF1), controls capillary network formation in vitro in human microvascular endothelial cells and retinal angiogenesis in vivo by modulating the balance of activities between two antagonistic transcription factors, TFII-I (also known as GTF2I) and GATA2, that govern gene expression of the VEGF receptor VEGFR2 (also known as KDR). Moreover, this new angiogenesis signalling pathway is sensitive to extracellular matrix elasticity as well as soluble VEGF. This is, to our knowledge, the first known functional cross-antagonism between transcription factors that controls tissue morphogenesis, and that responds to both mechanical and chemical cues.

The PRH/Hex repressor protein causes nuclear retention of Groucho/TLE co-repressors

The PRH (proline-rich homeodomain) [also known as Hex (haematopoietically expressed homeobox)] protein is a transcription factor that functions as an important regulator of vertebrate development and many other processes in the adult including haematopoiesis. The Groucho/TLE (transducin-like enhancer) family of co-repressor proteins also regulate development and modulate the activity of many DNA-binding transcription factors during a range of diverse cellular processes including haematopoiesis. We have shown previously that PRH is a repressor of transcription in haematopoietic cells and that an Eh-1 (Engrailed homology) motif present within the N-terminal transcription repression domain of PRH mediates binding to Groucho/TLE proteins and enables co-repression. In the present study we demonstrate that PRH regulates the nuclear retention of TLE proteins during cellular fractionation. We show that transcriptional repression and the nuclear retention of TLE proteins requires PRH to bind to both TLE and DNA. In addition, we characterize a trans-dominant-negative PRH protein that inhibits wild-type PRH activity by sequestering TLE proteins to specific subnuclear domains. These results demonstrate that transcriptional repression by PRH is dependent on TLE availability and suggest that subnuclear localization of TLE plays an important role in transcriptional repression by PRH.

Significance of NF-kappaB/GATA axis in tumor necrosis factor-alpha-induced expression of 6-sulfated cell recognition glycans in human T-lymphocytes

Sulfated glycans play critical roles in various cell recognition events among leukocytes. The 6-sulfated lactosamine glycans in particular have been widely noted for their importance because they are involved in cell recognition events mediated by cell-adhesion molecules such as selectins and sialic acid-recognizing molecules such as siglecs and also in the activation of CD44 in binding to extracellular matrix hyaluronate. A pro-inflammatory cytokine, tumor necrosis factor-alpha, induces expression of 6-sulfated glycans on human leukocytes. Here we report that the transcription of the GlcNAc6ST-1 gene, the gene encoding a sulfotransferase for 6-sulfated glycan synthesis, is induced in human T-lymphoid cells through tandem NF-kappaB and GATA motifs in its 5'-regulatory region. Results of our reporter assays, immunoprecipitation, and chromatin immunoprecipitation analyses indicated that GATA-3 and/or GATA-2, but not GATA-1, associates with NF-kappaB in a transcription factor complex on the 5'-regulatory region of the gene and acts synergistically with NF-kappaB in triggering GlcNAc6ST-1 transcription. Recently, a skin-homing subset of helper memory T cells exhibiting the Th2 marker CCR4 was shown to specifically express 6-sulfated glycans. The transactivation mechanism described here suggested that GlcNAc6ST-1 transcription is coordinated with the NF-kappaB/GATA-3 axis, which is known to figure heavily in Th2 cell differentiation. In line with this, in vitro differentiation of human T cells to Th2 cells was found to significantly induce GlcNAc6ST-1 transcription and 6-sulfated glycan expression.

Homeobox genes in normal and abnormal vasculogenesis

Homeobox containing genes are a family of transcription factors regulating normal development and controlling primary cellular processes (cell identity, cell division and differentiation) recently enriched by the discovery of their interaction with miRNAs and ncRNAs. Class I human homeobox genes (HOX genes) are characterized by a unique genomic network organization: four compact chromosomal loci where 39 sequence corresponding genes can be aligned with each other in 13 antero-posterior paralogous groups. The cardiovascular system is the first mesoderm organ-system to be generated during embryonic development; subsequently it generates the blood and lymphatic vascular systems. Cardiovascular remodelling is involved through homeobox gene regulation and deregulation in adult physiology (menstrual cycle and wound healing) and pathology (atherosclerosis, arterial restenosis, tumour angiogenesis and lymphangiogenesis). Understanding the role played by homeobox genes in endothelial and smooth muscle cell phenotype determination will be crucial in identifying the molecular processes involved in vascular cell differentiation, as well as to support future therapeutic strategies. We report here on the current knowledge of the role played by homeobox genes in normal and abnormal vasculogenesis and postulate a common molecular mechanism accounting for the involvement of homeobox genes in the regulation of the nuclear export of specific transcripts potentially capable of generating endothelial phenotype modification involved in new vessel formation.

Molecular hallmarks of endogenous chromatin complexes containing master regulators of hematopoiesis

Combinatorial interactions among trans-acting factors establish transcriptional circuits that orchestrate cellular differentiation, survival, and development. Unlike circuits instigated by individual factors, efforts to identify gene ensembles controlled by multiple factors simultaneously are in their infancy. A paradigm has emerged in which the important regulators of hematopoiesis GATA-1 and GATA-2 function combinatorially with Scl/TAL1, another key regulator of hematopoiesis. The underlying mechanism appears to involve preferential assembly of a multimeric complex on a composite DNA element containing WGATAR and E-box motifs. Based on this paradigm, one would predict that GATA-2 and Scl/TAL1 would commonly co-occupy such composite elements in cells. However, chromosome-wide analyses indicated that the vast majority of conserved composite elements were occupied by neither GATA-2 nor Scl/TAL1. Intriguingly, the highly restricted set of GATA-2-occupied composite elements had characteristic molecular hallmarks, specifically Scl/TAL1 occupancy, a specific epigenetic signature, specific neighboring cis elements, and preferential enhancer activity in GATA-2-expressing cells. Genes near the GATA-2-Scl/TAL1-occupied composite elements were regulated by GATA-2 or GATA-1, and therefore these fundamental studies on combinatorial transcriptional mechanisms were also leveraged to discover novel GATA factor-mediated cell regulatory pathways.

PRH/Hex: an oligomeric transcription factor and multifunctional regulator of cell fate

The PRH (proline-rich homeodomain) [also known as Hex (haematopoietically expressed homeobox)] protein is a critical regulator of vertebrate development. PRH is able to regulate cell proliferation and differentiation and is required for the formation of the vertebrate body axis, the haematopoietic and vascular systems and the formation of many vital organs. PRH is a DNA-binding protein that can repress and activate the transcription of its target genes using multiple mechanisms. In addition, PRH can regulate the nuclear transport of specific mRNAs making PRH a member of a select group of proteins that control gene expression at the transcriptional and translational levels. Recent biophysical analysis of the PRH protein has shown that it forms homo-oligomeric complexes in vivo and in vitro and that the proline-rich region of PRH forms a novel dimerization interface. Here we will review the current literature on PRH and discuss the complex web of interactions centred on this multifunctional protein.

Regulation and function of homeodomain proteins in the embryonic and adult vascular systems

During embryonic development, the cardiovascular system first forms and then gives rise to the lymphatic vascular system. Homeobox genes are essential for both the development of the blood and lymphatic vascular systems, as well as for their maintenance in the adult. These genes all encode proteins that are transcription factors that contain a well conserved DNA binding motif, the homeodomain. It is through the homeodomain that these transcription factors bind to the promoters of target genes and regulate their expression. Although many homeodomain proteins have been found to be expressed within the vascular systems, little is known about their downstream target genes. This review highlights recent advances made in the identification of novel genes downstream of the homeodomain proteins that are necessary for regulating vascular cellular processes such as proliferation, migration, and endothelial tube formation. Factors known to regulate the functions of vascular cells via modulating the expression of homeobox genes will be discussed. We will also review current methods used to identify and characterize downstream target genes of homeodomain proteins.

A Gata2 intronic enhancer confers its pan-endothelia-specific regulation

GATA-2, a transcription factor that has been shown to play important roles in multiple organ systems during embryogenesis, has been ascribed the property of regulating the expression of numerous endothelium-specific genes. However, the transcriptional regulatory hierarchy governing Gata2 activation in endothelial cells has not been fully explored. Here, we document GATA-2 endothelial expression during embryogenesis by following GFP expression in Gata2-GFP knock-in embryos. Using founder transgenic analyses, we identified a Gata2 endothelium enhancer in the fourth intron and found that Gata2 regulation by this enhancer is restricted to the endocardial, lymphatic and vascular endothelium. Whereas disruption of three ETS-binding motifs within the enhancer diminished its activity, the ablation of its single E box extinguished endothelial enhancer-directed expression in transgenic mice. Development of the endothelium is known to require SCL (TAL1), and an SCL-E12 (SCL-Tcfe2a) heterodimer can bind the crucial E box in the enhancer in vitro. Thus, GATA-2 is expressed early in lymphatic, cardiac and blood vascular endothelial cells, and the pan-endothelium-specific expression of Gata2 is controlled by a discrete intronic enhancer.

Context-dependent GATA factor function: combinatorial requirements for transcriptional control in hematopoietic and endothelial cells

GATA factors are fundamental components of developmentally important transcriptional networks. By contrast to common mechanisms in which transacting factors function directly at promoters, the hematopoietic GATA factors GATA-1 and GATA-2 often assemble dispersed complexes over broad chromosomal regions. For example, GATA-1 and GATA-2 occupy five conserved regions over approximately 100 kb of the Gata2 locus in the transcriptionally repressed and active states, respectively, in erythroid cells. Since it is unknown whether the individual complexes exert qualitatively distinct or identical functions to regulate Gata2 transcription in vivo, we compared the activity of the -3.9 and +9.5 kb sites of the Gata2 locus in transgenic mice. The +9.5 site functioned as an autonomous enhancer in the endothelium and fetal liver of embryonic day 11 embryos, whereas the -3.9 site lacked such activity. Mechanistic studies demonstrated critical requirements for a GATA motif and a neighboring E-box within the +9.5 site for enhancer activity in endothelial and hematopoietic cells. Surprisingly, whereas this GATA-E-box composite motif was sufficient for enhancer activity in an erythroid precursor cell line, its enhancer function in primary human endothelial cells required additional regulatory modules. These results identify the first molecular determinant of Gata2 transcription in vascular endothelium, composed of a core enhancer module active in both endothelial and hematopoietic cells and regulatory modules preferentially required in endothelial cells.

Interaction of GATA-3/T-bet transcription factors regulates expression of sialyl Lewis X homing receptors on Th1/Th2 lymphocytes

Selectin-dependent cell adhesion mediates inflammatory extravasation and routine homing of lymphocytes. Most resting peripheral T lymphocytes lack expression of sialyl Lewis X, the carbohydrate ligand for selectins, and are induced to strongly express it upon activation. T helper 1 (Th1) cells are known to more preferentially express sialyl Lewis X as compared with T helper 2 (Th2) cells upon activation. The molecular basis for this preferential expression, however, has not been elucidated to date. Here we show that the gene for fucosyltransferase VII (FUT7), the rate-limiting enzyme for sialyl Lewis X synthesis, is a unique example of the human genes with binding sites for both GATA-3 and T-bet, two opposing factors for Th1 and Th2 development, and is regulated transcriptionally by a balance of the two interacting transcription factors. T-bet promotes and GATA-3 represses FUT7 transcription. Our results indicated that T-bet interferes with the binding of GATA-3 to its target DNA, and also that GATA-3 significantly interferes with the binding of T-bet to the FUT7 promoter. T-bet has a binding ability to GATA-3, CBP/P300, and Sp1 to form a transcription factor complex, and GATA-3 regulates FUT7 transcription by phosphorylation-dependently recruiting histone deacetylase (HDAC)-3/HDAC-5 and by competing with CBP/P300 in binding to the N terminus of T-bet. Suppression of GATA-3 activity by dominant-negative GATA-3 or repressor of GATA (ROG) was necessary to attain a maximum expression of FUT7 and sialyl Lewis X in human T lymphoid cells. These results indicate that the GATA-3/T-bet transcription factor complex regulates the cell-lineage-specific expression of the lymphocyte homing receptors.

Wilms' tumor 1-associating protein regulates G2/M transition through stabilization of cyclin A2 mRNA

Wilms' tumor 1-associating protein (WTAP) has been reported to be a ubiquitously expressed nuclear protein. Although a relation to splicing factors has been postulated, its actual physiological function still remains to be elucidated. To investigate the role of WTAP, we generated WTAP-knockout mice and performed small interfering RNA (siRNA)-mediated knockdown analyses in primary cultured cells. In DNA microarrays using human umbilical vein endothelial cells, WTAP-targeted siRNA treatment resulted in markedly reduced expression of cell-cycle-related genes. siRNA-mediated WTAP knockdown down-regulated the stability of cyclin A2 mRNA through a nine-nucleotide essential sequence in cyclin A2 mRNA 3' UTR. WTAP knockdown induced G2 accumulation, which is partially rescued by adenoviral overexpression of cyclin A2. Moreover, WTAP-null mice exhibited proliferative failure with death resulting at approximately embryonic day 6.5, an etiology almost identical to cyclin A2-null mice. Collectively, these findings establish WTAP as an essential factor for the stabilization of cyclin A2 mRNA, thereby regulating G2/M cell-cycle transition.

New variations of the EDNRB gene and its association with sporadic Hirschsprung's disease in Korea

BACKGROUND/PURPOSE

The endothelin receptor B (EDNRB) signaling pathway, which is the second major susceptible gene for Hirschsprung's disease (HSCR), is crucial for the development of the enteric nervous system. The allele frequency of polymorphisms was mostly tested in the American and European population, but the data of an ethnically diverse, non-Caucasian population are unclear. To further investigate the variants and haplotypes of the EDNRB gene, this study examined sequence variations in Korean patients with sporadic HSCR.

METHODS

All 8 exons and intron/exon boundaries of the EDNRB gene in 18 Korean patients with sporadic HSCR and 84 healthy individuals were screened using PCR amplification and direct sequencing.

RESULTS

A total of 8 different nucleotide substitutions were identified. Of these, 4 were new variants (promoter-116C>T; 5'UTR-121G>T; IVS4+62C>A; IVS5+121G>C) and the others were previously described variants. The distribution of variations was even different from that reported for Chinese and Japanese subjects as well as other ethnic groups. This study also analyzed the haplotypes for an association between the variants identified with HSCR.

CONCLUSIONS

This study identified additional sequence variants of the EDNRB gene, but the estimated EDNRB haplotypes did not show any disease risk.

Oligomerisation of the developmental regulator proline rich homeodomain (PRH/Hex) is mediated by a novel proline-rich dimerisation domain

Homeodomain proteins regulate multiple developmental pathways by altering gene expression temporally and in a tissue-specific fashion. The Proline Rich Homeodomain protein (PRH/Hex) is a transcription factor and an essential regulator of embryonic development and haematopoiesis. Recent discoveries have implicated self-association as an important feature of transcription factor function. Here, we show using a variety of techniques including gel-filtration, analytical ultracentrifugation, electron microscopy and in vitro cross-linking, that purified recombinant PRH is oligomeric and we use in vivo cross-linking to confirm that this protein exists as oligomers in cells. This is the first demonstration that a homeodomain protein can oligomerise in vivo. Consistent with these findings we show that a fraction of endogenous and exogenous PRH appears as discrete foci within the nucleus and at the nuclear periphery. The N-terminal domain of PRH is involved in the regulation of cell proliferation and transcriptional repression and can make multiple protein-protein interactions. We show that this region of PRH contains a novel proline-rich dimerisation domain that mediates oligomerisation. We propose a model that explains how PRH forms oligomers and we discuss how these oligomers might control transcription.

Pituitary-specific Gata2 knockout: effects on gonadotrope and thyrotrope function

GATA2 is expressed in the pituitary during development and in adult gonadotropes and thyrotropes. It is proposed to be important for gonadotrope and thyrotrope cell fate choice and for TSH production. To test this idea, we produced a pituitary-specific knockout of Gata2, designed so that the DNA-binding zinc-finger region is deleted in the presence of a pituitary-specific recombinase transgene. These mice have reduced secretion of gonadotropins basally and in response to castration challenge, although the mice are fertile. GATA2 deficiency also compromises thyrotrope function. Mutants have fewer thyrotrope cells at birth, male Gata2-deficient mice exhibit growth delay from 3-9 wk of age, and adult mutants produce less TSH in response to severe hypothyroidism after radiothyroidectomy. Therefore, Gata2 appears to be dispensable for gonadotrope and thyrotrope cell fate and maintenance, but important for optimal gonadotrope and thyrotrope function. Gata2-deficient mice exhibit elevated levels of Gata3 transcripts in the pituitary gland, suggesting that GATA3 can compensate for GATA2.

Induction of Cells Expressing Vascular Endothelium Markers from Undifferentiated Xenopus Presumptive Ectoderm by Co-treatment with Activin and Angiopoietin-2

Activin is a potent inducer of mesoderm in amphibian embryos. We previously reported that low concentrations of activin could induce the formation of blood cells from Xenopus explants (animal caps). Both hematopoietic and vascular endothelial cell lineages are believed to share a common precursor, termed hemangioblasts. In this study, we tried to induce differentiation of vascular endothelial cells in aggregates derived from Xenopus animal caps. Aggregates formed from cells that were co-treated with activin and angiopoietin-2 expressed the vascular endothelial markers, X-msr, Xtie2 and Xegfl7. However, none of these aggregates expressed the hematopoietic marker genes, globin alpha T3, alpha T5, alpha A or GATA-1. We used microarray analysis to compare the gene expression profiles of aggregates treated with activin alone or with activin and angiopoietin. The combination, but not activin alone, induced expression of vascular-related genes such as Xl-fli and VEGF. These results demonstrate that treatment of dissociated animal cap cells with activin and angiopoietin-2 can induce differentiation of endothelial cells, and provides a promising model system for the in vitro study of blood vessel induction in vertebrates.

Impaired revascularization in a mouse model of type 2 diabetes is associated with dysregulation of a complex angiogenic-regulatory network

OBJECTIVE

Diabetes is a risk factor for the development of cardiovascular diseases associated with impaired angiogenesis or increased endothelial cell apoptosis.

METHODS AND RESULTS

Here it is shown that angiogenic repair of ischemic hindlimbs was impaired in Lepr(db/db) mice, a leptin receptor-deficient model of diabetes, compared with wild-type (WT) C57BL/6 mice, as evaluated by laser Doppler flow and capillary density analyses. To identify molecular targets associated with this disease process, hindlimb cDNA expression profiles were created from adductor muscle of Lepr(db/db) and WT mice before and after hindlimb ischemia using Affymetrix GeneChip Mouse Expression Set microarrays. The expression patterns of numerous angiogenesis-related proteins were altered in Lepr(db/db) versus WT mice after ischemic injury. These transcripts included neuropilin-1, vascular endothelial growth factor-A, placental growth factor, elastin, and matrix metalloproteinases implicated in blood vessel growth and maintenance of vessel wall integrity.

CONCLUSIONS

These data illustrate that impaired ischemia-induced neovascularization in type 2 diabetes is associated with the dysregulation of a complex angiogenesis-regulatory network.

Molecular determinants of NOTCH4 transcription in vascular endothelium

The process whereby the primitive vascular network develops into the mature vasculature, known as angiogenic vascular remodeling, is controlled by the Notch signaling pathway. Of the two mammalian Notch receptors expressed in vascular endothelium, Notch1 is broadly expressed in diverse cell types, whereas Notch4 is preferentially expressed in endothelial cells. As mechanisms that confer Notch4 expression were unknown, we investigated how NOTCH4 transcription is regulated in human endothelial cells and in transgenic mice. The NOTCH4 promoter and the 5' portion of NOTCH4 assembled into an endothelial cell-specific histone modification pattern. Analysis of NOTCH4 primary transcripts in human umbilical vein endothelial cells by RNA fluorescence in situ hybridization revealed that 36% of the cells transcribed one or both NOTCH4 alleles. The NOTCH4 promoter was sufficient to confer endothelial cell-specific transcription in transfection assays, but intron 1 or upstream sequences were required for expression in the vasculature of transgenic mouse embryos. Cell-type-specific activator protein 1 (AP-1) complexes occupied NOTCH4 chromatin and conferred endothelial cell-specific transcription. Vascular angiogenic factors activated AP-1 and reprogrammed the endogenous NOTCH4 gene in HeLa cells from a repressed to a transcriptionally active state. These results reveal an AP-1-Notch4 pathway, which we propose to be crucial for transducing angiogenic signals and to be deregulated upon aberrant signal transduction in cancer.

A null mutation of Hhex results in abnormal cardiac development, defective vasculogenesis and elevated Vegfa levels

The homeobox gene Hhex has recently been shown to be essential for normal liver, thyroid and forebrain development. Hhex(-/-) mice die by mid-gestation (E14.5) and the cause of their early demise remains unclear. Because Hhex is expressed in the developing blood islands at E7.0 in the endothelium of the developing vasculature and heart at E9.0-9.5, and in the ventral foregut endoderm at E8.5-9.0, it has been postulated to play a critical role in heart and vascular development. We show here, for the first time, that a null mutation of Hhex results in striking abnormalities of cardiac and vascular development which include: (1) defective vasculogenesis, (2) hypoplasia of the right ventricle, (3) overabundant endocardial cushions accompanied by ventricular septal defects, outflow tract abnormalities and atrio-ventricular (AV) valve dysplasia and (4) aberrant development of the compact myocardium. The dramatic enlargement of the endocardial cushions in the absence of Hhex is due to decreased apoptosis and dysregulated epithelial-mesenchymal transformation (EMT). Interestingly, vascular endothelial growth factor A (Vegfa) levels in the hearts of Hhex(-/-) mice were elevated as much as three-fold between E9.5 and E11.5, and treatment of cultured Hhex(-/-) AV explants with truncated soluble Vegfa receptor 1, sFlt-1, an inhibitor of Vegf signaling, completely abolished the excessive epithelial-mesenchymal transformation seen in the absence of Hhex. Therefore, Hhex expression in the ventral foregut endoderm and/or the endothelium is necessary for normal cardiovascular development in vivo, and one function of Hhex is to repress Vegfa levels during development.

Vascular Endothelial Growth Factor- and Thrombin-induced Termination Factor, Down Syndrome Critical Region-1, Attenuates Endothelial Cell Proliferation and Angiogenesis

Activation and dysfunction of the endothelium underlie many vascular disorders including atherosclerosis, tumor growth, and inflammation. Endothelial cell activation is mediated by many different extra-cellular signals, which result in overlapping yet distinct patterns of gene expression. Here we show, in DNA microarray analyses, that vascular endothelial growth factor (VEGF) and thrombin result in dramatic and rapid upregulation of Down syndrome critical region (DSCR)-1 gene encoding exons 4-7, a negative feedback regulator of calcium-calcineurin-NF-AT signaling. VEGF- and thrombin-mediated induction of DSCR-1 involves the cooperative binding of NF-ATc and GATA-2/3 to neighboring consensus motifs in the upstream promoter. Constitutive expression of DSCR-1 in endothelial cells markedly impaired NF-ATc nuclear localization, proliferation, and tube formation. Under in vivo conditions, overexpression of DSCR-1 reduced vascular density in matrigel plugs and melanoma tumor growth in mice. Taken together, these findings support a model in which VEGF- and thrombin-mediated induction of endothelial cell proliferation triggers a negative feedback loop consisting of DSCR-1 gene induction and secondary inhibition of NF-AT signaling. As a natural brake in the angiogenic process, this negative pathway may lend itself to therapeutic manipulation in pathological states.

Up-regulation of vascular endothelial growth factor (VEGF) in small-for-size liver grafts enhances macrophage activities through VEGF receptor 2-dependent pathway

This study aims to investigate the potential role of vascular endothelial growth factor (VEGF) and VEGF-R2 (fetal liver kinase (Flk)-1) in mediating macrophage activities in small-for-size liver transplantation. A rat orthotopic liver transplantation model was performed using either whole, 50, or 30% liver grafts (both 50 and 30% were regarded as small-for-size) in syngeneic or allogeneic combinations, respectively. Firstly, the mRNA and protein levels of VEGF and Flk-1 in liver grafts were detected by RT-PCR and Western blot, and the number of Flk-1(+) macrophages (labeled by ED1) was determined by flow cytometry. It was found that the small-for-size isografts and allografts presented higher levels of VEGF and Flk-1 expression than the whole isograft and allograft. In addition, a higher number of Flk-1(+)ED1(+) cells were detected in the small-for-size isografts and allografts than the whole isograft and allograft. Secondly, our study revealed that macrophage cell lines did not initially express detectable Flk-1, but could be induced by VEGF, and the inducible expression of Flk-1 in macrophages was related to their migration and proliferation activities. Finally, our study demonstrated that the induction of Flk-1 expression on macrophages by VEGF was associated with the expression of NF-kappaB and heat shock protein 90. In conclusion, the present study showed that the up-regulated expression of VEGF and its interaction with Flk-1 in small-for-size liver grafts might facilitate the activities of macrophages.