Vascular endothelial growth factor: a new member of the platelet-derived growth factor gene family

Lymphatic versus blood vascular endothelial growth factors and receptors in humans

Three different growth factor systems have been described acting via endothelial cell-specific receptor tyrosine kinases (RTKs). These are vascular endothelial growth factors (VEGFs), angiopoietins, and ephrins. Recent studies on gene targeting suggest that they play critical roles in embryonic development and contribute to the integrity and responses to environmental factors in the adult vasculature. Coagulation, inflammation, immune response regulation, vascular tone, stromal component synthesis, and angiogenesis are all dependent on the physiological and pathological events that affect endothelial cells in the heart, arteries, veins, and lymphatic vessels. Angiogenesis, the formation of new blood vessels from preexisting ones, takes place in adults only during hormonal control of female reproduction. All other activation of angiogenesis in adulthood occurs in response to injury or pathological processes such as tumorigenesis, diabetes, or inflammatory conditions. Insufficient growth of collateral vessels is a major problem in atherosclerotic cardiovascular disease. Controlled stimulation of angiogenesis would be of therapeutic value. Lymphangiogenesis, the mechanisms involved in the development of lymphatic vessels, was studied intensively nearly a century ago, although since then it has been neglected, perhaps because, unlike the disorders of blood vessels, those of the lymphatic vessels are seldom life-threatening. Interrupting this one-way system can cause severe disorders, including liver dysfunction, genetic disease (e.g., Milroys disease), and degenerative disease (e.g., primary lymphangiosclerosis). Recently, novel growth factors, receptors, cell surface proteins, and transcription factors have been found which play a role in the lymphatic endothelium. These are VEGF-C, VEGF-D, VEGFR-3, LYVE-1, podoplanin, and Prox-1. Until recently lymphatic vessels have been difficult to study due to a lack of appropriate tools. Monoclonal antibodies raised against VEGFR-3 and against its ligands, VEGF-C and VEGF-D, have offered an insight into expression studies in tissues. In this review, we summarize the recent data on VEGFs in the human vasculature.

VEGF(165) requires extracellular matrix components to induce mitogenic effects and migratory response in breast cancer cells

The expression of VEGF and the relapse-free survival rate of breast cancer patients are inversely related. While VEGF induces the proliferation and migration of vascular endothelial cells, its function in breast cancer cells is not well studied. We reported previously that fibronectin increased VEGF-dependent migration in breast cancer cells. Since VEGF has an extracellular matrix (ECM)-binding domain and possesses binding affinity for heparin, we sought to determine the effects of VEGF in breast cancer cells and the role of heparin and/or fibronectin in VEGF-induced signaling. Cells grown on plastic were compared to those grown on fibronectin or to those grown on plastic in the presence of heparin, and analysed for intracellular signaling, proliferation and migration in response to VEGF(165). Both heparin and fibronectin enhanced the binding of VEGF to T47D cells. After treatment with VEGF, [(3)H]thymidine incorporation, c-fos induction, and the number of migrating cells were significantly higher ( approximately twofold) in cells grown on fibronectin or in cells grown on plastic in the presence of heparin when compared to those grown on plastic only. Likewise, tyrosine phosphorylation of VEGF receptors, MAPK activity and PI3-kinase activity were all several-fold higher in cells seeded on fibronectin or in the presence of heparin as compared to cells exposed to VEGF alone. VEGF-dependent c-fos induction was found to be regulated through a MAPK-dependent, but PI3-kinase-independent pathway. In contrast, the migration of T47D cells in response to VEGF, in the presence of ECM, was regulated through PI3-kinase. Therefore, VEGF requires ECM components to induce a mitogenic response and cell migration in T47D breast cancer cells.

Platelet-derived growth factor C (PDGF-C), a novel growth factor that binds to PDGF alpha and beta receptor

We have characterized platelet-derived growth factor (PDGF) C, a novel growth factor belonging to the PDGF family. PDGF-C is a multidomain protein with the N-terminal region homologous to the extracellular CUB domain of neuropilin-1, and the C-terminal region consists of a growth factor domain (GFD) with homology to vascular endothelial growth factor (25%) and PDGF A-chain (23%). A serum-sensitive cleavage site between the two domains allows release of the GFD from the CUB domain. Competition binding and immunoprecipitation studies on cells bearing both PDGF alpha and beta receptors reveal a high affinity binding of recombinant GFD (PDGF-CC) to PDGF receptor-alpha homodimers and PDGF receptor-alpha/beta heterodimers. PDGF-CC exhibits greater mitogenic potency than PDGF-AA and comparable or greater mitogenic activity than PDGF-AB and PDGF-BB on several mesenchymal cell types. Analysis of PDGF-CC in vivo in a diabetic mouse model of delayed wound healing showed that PDGF-CC significantly enhanced repair of a full-thickness skin excision. Together, these studies describe a third member of the PDGF family (PDGF-C) as a potent mitogen for cells of mesenchymal origin in in vitro and in vivo systems with a binding pattern similar to PDGF-AB.

Differentiation-dependent expression of connective tissue growth factor and lysyl oxidase messenger ribonucleic acids in rat granulosa cells

Searching for novel genes involved in tissue remodeling during ovarian folliculogenesis, we carried out differential display RT-PCR (DDRT-PCR) on RNA from gonadotropin-stimulated rat granulosa cells (GC). GC from preantral and early antral follicles in immature rat ovaries were cultured in serum-free medium containing no hormone (control), recombinant human FSH (10 ng/ml), 5alpha-dihydrotestosterone (DHT; 10(-6) M), or FSH plus DHT. Total cellular RNA was extracted from cells at 6, 12, 24, and 48 h of treatment for DDRT-PCR analysis, corresponding to an estimated 60% saturation of the messenger RNA (mRNA) population. Six distinct complementary DNA clones were obtained that reproduced the DDRT-PCR profile on a Northern blot of the corresponding RNA samples. Two of these clones detected transcripts that were strongly down-regulated by FSH. One corresponded to connective tissue growth factor (CTGF), a cysteine-rich secreted protein related to platelet-derived growth factor that is implicated in mitogenesis and angiogenesis, and a second was identical to lysyl oxidase (LO), a key participant in extracellular matrix deposition. In detailed expression studies, Northern analysis revealed a single, approximately 2.5-kb CTGF transcript maximally suppressed within 3 h of exposure to FSH with or without DHT and two LO transcripts ( approximately 3.8 and approximately 5.2 kb) maximally suppressed at 6 h. DHT alone did not affect CTGF mRNA, but strongly enhanced LO mRNA relative to the control value. In vivo, CTGF and LO transcripts were significantly suppressed in GC 48 h after equine CG injection (10 IU, ip) compared with untreated controls and were further reduced 12 h after administration of additional 10 IU hCG to induce luteinization. In situ hybridization confirmed GC in preantral/early antral follicles as principal sites of CTGF and LO mRNA expression. We conclude that expression of CTGF and LO mRNAs is inversely related to GC differentiation. The encoded proteins probably have roles in the regulation of tissue remodeling and extracellular matrix formation during early follicular development.

Aberrantly glycosylated IgA molecules downregulate the synthesis and secretion of vascular endothelial growth factor in human mesangial cells

To gain insight into the glomerular capillary repair mechanisms in immunoglobulin A (IgA) nephropathy, we focused on vascular endothelial growth factor (VEGF-A) and nitric oxide (NO). Because abnormal glycosylation of serum IgA has been shown in IgA nephropathy, we examined whether VEGF-A and NO production by mesangial cells (MCs) could be modulated by aberrantly glycosylated (desialylated or degalactosylated) IgA. VEGF-A and NO synthase (NOS) gene expression were examined by reverse-transcriptase polymerase chain reaction (RT-PCR) or Northern blot analysis, and VEGF-A peptide, by capture enzyme-linked immunosorbent assay and NOS activity as production of tritium ([(3)H]) citrulline from [(3)H] arginine. Semiquantitative densitometric analysis of RT-PCR experiments showed a significant downregulation of VEGF-A messenger RNA (mRNA) in MCs incubated with aberrantly glycosylated IgA. This resulted in decreased release of VEGF-A in culture medium (P: < 0. 01). NOS activity and inducible NOS (iNOS) mRNA were enhanced by aberrantly glycosylated IgA (both P: < 0.01). No modulation of constitutive NOS mRNA was found. The depression of the VEGF-A production induced by aberrantly glycosylated IgA was mediated by NO because it was completely reversed by the NOS inhibitor, N:omega-nitro-L-arginine methyl ester. The NO donor, sodium nitroprusside, induced a bimodal modulation of VEGF; although low concentrations (0.0001 nmol/L) increased VEGF-A synthesis, greater concentrations (1,000 nmol/L) depressed it. In conclusion, we report negative control of VEGF-A synthesis in MCs by aberrantly glycosylated IgA, mediated by enhanced iNOS activity. We speculate that both increased iNOS activity and depressed VEGF-A synthesis might have a role in impairing vascular repair and favor sclerosis in IgA nephropathy.

Role of vasoactive factors in the pathogenesis of early changes in diabetic retinopathy

Several interactive and mutually perpetuating abnormal biochemical pathways, such as protein kinase C (PKC) activation, augmented polyol pathway, and non-enzymatic glycation, may be activated as a result of sustained hyperglycemia in diabetes. These abnormal pathways may in turn influence several vasoactive factors, which are probably instrumental in the production of functional and morphological changes in the retina in diabetes. The vasoactive factors such as endothelins, nitric oxide, vascular endothelial growth factors, etc., are of importance in mediating functional and structural alterations in early diabetic retinopathy. Intricate and interactive regulatory mechanism(s) among these factors may control ultimate availability of these molecules to produce biologically significant effects. A better understanding of these factors and their interactions would aid the development of adjuvant therapies for the treatment of diabetic retinopathy.

Expression and tissue concentration of vascular endothelial growth factor, its receptors, and localization in the bovine corpus luteum during estrous cycle and pregnancy

The presence of vascular endothelial growth factor (VEGF) in the ovary has been reported in a number of species. The objective of the present study was to demonstrate the expression of VEGF, VEGF receptor (R)-1, and VEGFR-2 in detail by different methodological approaches in bovine corpora lutea (CL) obtained from different stages of the estrous cycle and during pregnancy. VEGF and VEGF receptor transcripts were analyzed by reverse transcription-polymerase chain reaction (RT-PCR) and ribonuclease protection assay. All components of the VEGF system were found in the bovine CL during the estrous cycle and pregnancy. Analysis of VEGF transcript by RT-PCR shows that CL tissues expressed predominantly the smallest isoforms (VEGF(121) and VEGF(165)). The highest mRNA expression for VEGF and VEGFR-2 mRNA was detected during the early luteal phase, followed by a significant decrease of expression during the mid and late luteal phase and a further decrease of VEGF mRNA after regression. During pregnancy, high levels of expression were always present. In contrast, no significant change in VEGFR-1 mRNA expression during the estrous cycle and pregnancy was found. The VEGF protein concentration in CL tissue was significantly higher (20.9-23.4 ng/g wet weight) during the early luteal phase (Days 1-7), followed by a decrease at the late luteal phase (14.3-18.7 ng/g wet weight) and, especially, after CL regression (2.8 ng/g wet weight). However, relatively high levels were found during pregnancy (10.1 ng/g wet weight). As achieved by immunohistochemistry, VEGF protein was localized predominantly in luteal cells. High VEGF protein and transcript concentrations and increased VEGFR-2 expression during the early luteal phase coincided with luteal vascularization. These results suggest an important role of VEGF in angiogenesis of the newly formed CL. The high VEGF mRNA expression and protein levels during matured vasculature in the mid-stage CL and pregnancy also suggest also a survival function for endothelial cells.

Heregulin selectively upregulates vascular endothelial growth factor secretion in cancer cells and stimulates angiogenesis

The interaction between the erbB tyrosine kinase receptors and their ligands plays an important role in tumor growth via the regulation of autocrine and paracrine loops. We report the effect of heregulin beta1, the ligand for erbB-3 and erbB-4 receptors, on the regulation of vascular endothelial growth factor (VEGF) expression, using a panel of breast and lung cancer cell lines with constitutive erbB-2 overexpression or engineered to stably overexpress the erbB-2 receptor. We demonstrate that heregulin beta1 induces VEGF secretion in most cancer cell lines, while no significant effect was observed in normal human mammary and bronchial primary cells. Overexpression of erbB-2 receptor results in induction of the basal level of VEGF and exposure to heregulin further enhances VEGF secretion. This is associated with increased VEGF mRNA expression. In contrast, VEGF induction is significantly decreased in a T47D cell line where erbB-2 is functionally inactivated. Conditioned media from heregulin-treated cancer cells, but not from normal cells, stimulates endothelial cell proliferation; this paracrine stimulation is inhibited by co-exposure to a specific VEGF neutralizing antibody. Furthermore, heregulin-mediated angiogenesis is observed in the in vivo CAM assay. This study reports the first evidence of VEGF regulation by heregulin in cancer cells. Oncogene (2000) 19, 3460 - 3469

Ultraviolet-A-induced transactivation of the vascular endothelial growth factor gene in HaCaT keratinocytes is conveyed by activator protein-2 transcription factor

Ultraviolet-A radiation represents a significant proportion of the ultraviolet solar spectrum that was recently shown to affect gene expression of epidermal keratinocytes by molecular mechanisms distinct from ultraviolet-B radiation. As ultraviolet-A either alone or in combination with ultraviolet-B may contribute to photocarcinogenesis, we aimed to explore the biologic effects of ultraviolet-A radiation on vascular endothelial growth factor gene expression by the immortalized keratinocyte cell line HaCaT. As keratinocyte-derived vascular endothelial growth factor not only provides the major cutaneous angiogenic activity but may also augment the malignant phenotype of tumor cells, we studied the molecular mechanisms of ultraviolet-A-induced vascular endothelial growth factor expression in HaCaT cells, serving as a transformed preneoplastic epithelial cell line. Whereas ultraviolet-B-mediated vascular endothelial growth factor expression has been previously indicated to be conveyed by indirect mechanisms, ultraviolet-A rapidly induced vascular endothelial growth factor mRNA expression in a fashion comparable to that seen with the transforming growth factor alpha, representing a direct and potent activator of vascular endothelial growth factor gene transcription. Ultraviolet-A was found to readily induce vascular endothelial growth factor promoter-based reporter gene constructs through a consensus element for activator protein-2 transcription factor. The critical role of activator protein-2 was substantiated by demonstration of ultraviolet-A-induced activator-protein-2-dependent nuclear DNA binding activity to this site, and by inhibition of ultraviolet-A-mediated vascular endothelial growth factor gene transcription through insertion of a critical mutation within the activator protein-2 sequence. Together, our data further elucidate photobiologic aspects of ultraviolet-A-induced gene expression by characterizing mechanisms of vascular endothelial growth factor upregulation at the molecular level. In addition, our experiments support the concept of a more general importance of activator protein-2 in ultra- violet-A-mediated responses by keratinocytes or keratinocyte-derived cell lines.

VEGF receptor signaling in tumor angiogenesis

The growth of human tumors and development of metastases depend on the de novo formation of blood vessels. The formation of new blood vessels is tightly regulated by specific growth factors that target receptor tyrosine kinases (RTKs). Vascular endothelial growth factor (VEGF) and the Flk-1/KDR RTK have been implicated as the key endothelial cell-specific factor signaling pathway required for pathological angiogenesis, including tumor neovascularization. Inhibition of the VEGF tyrosine kinase signaling pathway blocks new blood vessel formation in growing tumors, leading to stasis or regression of tumor growth. Advances in understanding the biology of angiogenesis have led to the development of several therapeutic modalities for the inhibition of the VEGF tyrosine kinase signaling pathway. A number of these modalities are under investigation in clinical studies to evaluate their potential to treat human cancers.

Cardiac angiogenesis and gene therapy: a strategy for myocardial revascularization

Angiogenesis, the de novo formation of new vasculature, is a critical response to ischemia that provides neovascularization of ischemic tissues. In therapeutic angiogenesis, an angiogen--a mediator that induces angiogenesis--is delivered to targeted tissues, augmenting the native angiogenic process and enhancing reperfusion of ischemic tissues. Gene transfer is a novel means of providing therapeutic angiogenesis: the cDNA coding for specific angiogens, rather than the proteins themselves, is administered to the tissues in which angiogenesis is desired. This review is focused on therapeutic angiogenesis based on gene transfer strategies for the provision of myocardial revascularization.

Expression of vascular endothelial growth factor (VEGF) and its corresponding receptors (flt-1 and flk-1) in the bovine oviduct

Vascular endothelial growth factor (VEGF) functions as a potent angiogenic protein as well as in regulating permeability. Reverse transcription-polymerase chain reaction (RT-PCR) and ribonuclease protection assay (RPA) were used to show that the bovine oviduct expresses VEGF and its two receptors flk-1 and flt-1. Expression of VEGF was relatively stable during the estrous cycle. In contrast, both receptor transcripts showed cycle-dependent variations with significantly increased flt-1 mRNA amounts before ovulation. Immunohistochemical studies localized VEGF mainly on the epithelial surface of oviducts. Protein concentrations of VEGF in oviductal flushings were significantly higher (mean +/- SEM: 2.8 +/- 0.8 ng/ml) during the pre-ovulatory phase when compared with the other estrous cycle stages (1.0 +/- 0.25 ng/ml). In conclusion, all components of a functional VEGF-system in the bovine oviduct were found to undergo specific modulations during the cycle. We suggest that VEGF may be involved in creating an optimal local environment for fertilization or the developing embryo by modulating permeability within the bovine oviduct.

Safety of direct myocardial administration of an adenovirus vector encoding vascular endothelial growth factor 121

A gene therapy strategy involving direct myocardial administration of an adenovirus (Ad) vector encoding the vascular endothelial growth factor 121 cDNA (Ad(GV)VEGF121.10) has been shown to be capable of "biological revascularization" of ischemic myocardium in an established porcine model [Mack, C.A. (1998). J. Thorac. Cardiovasc. Surg. 115, 168-177]. The present study evaluates the local and systemic safety of this therapy in this porcine ischemia model and in normal mice. Myocardial ischemia was induced in Yorkshire swine with an ameroid constrictor 21 days prior to vector administration. Ad(GV)VEGF121.10 (10(9) or 10(10) PFU), Ad5 wild type (10(9) PFU), AdNull (control vector with no transgene; 10(9) PFU), saline, or no injection (naive) was administered in 10 sites in the ischemic, circumflex distribution of the myocardium. Toxicity was assessed by survival, serial echocardiography, blood analyses, and myocardial and liver histology at 3 and 28 days after vector administration. All pigs survived to sacrifice, except for one animal in the Ad(GV)VEGF121.10 (10(10) PFU) group, which died as a result of oversedation. Echocardiograms of Ad(GV)VEGF121.10-treated pigs demonstrated no differences in pericardial effusion, mitral valve regurgitation, or regional wall motion compared with control pigs. Intramyocardial administration of Ad(GV)VEGF121.10 included only minimal myocardial inflammation and necrosis, and no hepatic inflammation or necrosis. Only a mild elevation of the white blood cell count was encountered on day 3, which was transient and self-limited in the Ad(GV)VEGF121.10 group as compared with the saline-treated animals. As a measure of inadvertent intravascular administration of vector, normal C57/BL6 mice received intravenous Ad(GV)VEGF121.10 (10(4), 10(6), 5 x 10(7), or 10(9) PFU), AdNull (5 x 10(7) or 10(9) PFU), or saline. Toxicity was assessed by survival, blood analyses, and organ histology at 3 and 7 days after vector administration. A separate group of C57/BL6 mice received intravenous AdmVEGF164 (Ad vector encoding the murine VEGF164 cDNA), Ad(GV)VEGF121.10, AdNull (10(8) PFU each group), or saline to assess duration of expression and safety of a homologous transgene. All mice survived to sacrifice except for 40% of the mice in the highest (10(9) PFU; a dose more than 10(3)-fold higher by body weight than the efficacious dose in pigs) Ad(GV)VEGF121.10 dose group, which died on days 5-6 after vector administration. The only differences seen in the blood analyses between treated and control mice were in the very high Ad(GV)VEGF121.10 dose group (10(9) PFU), which demonstrated an anemia as well as an increase in alkaline phosphatase when compared with all other treatment groups. Hepatic VEGF levels by ELISA in AdmVEGF164-treated mice did not persist beyond 14 days after vector administration, suggesting that persistent expression of a homologous VEGF gene transferred with an Ad vector is not a significant safety risk. Although this is not a chronic toxicity study, these data demonstrate the safety of direct myocardial administration of Ad(GV)VEGF121.10, and support the potential use of this strategy to treat human myocardial ischemia.

Vascular endothelial growth factor in acute Kawasaki disease

Vascular endothelial growth factor (VEGF), also known as vascular permeability factor, is an important regulator of angiogenesis and blood vessel permeability. Kawasaki disease (KD) is characterized by systemic vasculitis with increased vascular permeability, implying a possible role of VEGF in KD. To elucidate the involvement of VEGF in the pathogenesis of KD, we investigated 30 patients with acute KD, comparing the time course of plasma VEGF levels (n = 123) with clinical symptoms and laboratory findings. Compared with control values, the peak levels of plasma VEGF were significantly elevated (38+/-26 vs 244+/-248 pg/ml, p <0.001). The VEGF levels at the appearance of skin rash and/or edema of hands and feet were also elevated to 176+/-163 pg/ml (p <0.001). In 7 patients (23%), the plasma VEGF levels remained increased after the resolution of the skin rash and peripheral edema. The VEGF levels were independent of gamma globulin therapy and levels of serum albumin and C-reactive protein. We also measured the plasma levels of transforming growth factor-beta1 (TGF-beta1) and tumor necrosis factor alpha, both of which can upregulate VEGF in vitro. The plasma levels of VEGF were highly correlated with those of TGF-beta1 (n = 63, r = 0.73, p <0.001) but not with those of tumor necrosis factor alpha. These findings suggest that the production of VEGF is increased and may be upregulated by TGF-beta1 in acute KD. VEGF may be involved in the hyperpermeability of local blood vessels in acute KD.

Hepatocyte growth factor/scatter factor (HGF/SF) induces vascular permeability factor (VPF/VEGF) expression by cultured keratinocytes

Skin expression of the endothelial cell-specific vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) as an outstanding mediator of physiologic and pathologic angiogenesis has been previously demonstrated to be subject to regulation by distinct stimuli. We explored whether the multifunctional hepatocyte growth factor/scatter factor (HGF/SF) may mediate its angiogenic properties in part through paracrine induction of cutaneous VPF/VEGF synthesis. In these studies, we demonstrate that HGF/SF functions as a potent inducer of VPF/VEGF expression by human epidermal keratinocytes and by different epithelial-derived cells in vitro. VPF/VEGF mRNA and protein expression are regulated by HGF/SF in both a concentration- and a time-dependent fashion. Examination of mRNA half-lives does not reveal an increase in VPF/VEGF mRNA stability after HGF/SF stimulation. Thus, HGF/SF-induced VPF/VEGF mRNA expression appears to be largely dependent on enhanced gene transcription. In analyses of transiently transfected 5'-deletional reporter gene constructs, we identified a GC-rich VPF/VEGF promoter element that conveys transcriptional activation in response to HGF/SF. This sequence, located between nucleotides -88 and -70, is critical for both constitutive and HGF/SF-induced transcriptional activity. Together, our observations support a model in which HGF/SF mediates angiogenic properties in part through paracrine induction of VPF/VEGF synthesis by keratinocytes. In addition to cutaneous inflammation and wound healing, our findings have potential significance for vascular hyperpermeability and angiogenesis in tumor growth.

Expression of VEGF in routinely fixed material using a new monoclonal antibody VG1

The aim of this study was to raise and characterize a monoclonal antibody reactive with VEGF (vascular endothelial growth factor) in routinely fixed specimens and to use it to investigate its tissue distribution in normal and pathological specimens. Recombinant VEGF 189 protein was used to raise a monoclonal antibody. The specificity of the antibody was confirmed using COS cells transfected with cDNA coding for VEGF 121, 165 and 189 protein and by western blotting studies. The resulting antibody VG1 was shown to react with the 121, 165 and 189 isoforms of VEGF protein in routinely processed material. In normal tissues, there was strong staining of endometrial and salivary glands and of the mucosa of the gastro-intestinal tract. In tumours, a proportion of the neoplastic cells in lung and breast cancer and in melanoma were labelled. In all tissues, whether normal or malignant, striking VEGF positivity was seen in plasma in vessels and stroma. This study has shown that antibody VG1 detects the 121, 165 and 189 VEGF isoforms in routinely fixed specimens. The results of the normal tissue and tumour labelling are in agreement with other studies using alternative methods of detection. This should be a useful and reliable reagent for studies of VEGF and angiogenesis in human pathological material.

Estrogen-dependent production of erythropoietin in uterus and its implication in uterine angiogenesis

Although erythropoietin (Epo) has been shown to possess in vitro angiogenic activity, its physiological significance has not been demonstrated. Normally angiogenesis does not occur actively in adults but an exception is the female reproductive organ. In the uterine endometrium, angiogenesis takes place actively for supporting the endometrial growth that occurs during transition from the diestrus to estrous stage. This transition is under control of 17beta-estradiol (E2), an ovarian hormone, and can be mimicked by injection of E2 to ovariectomized (OVX) mouse. Thus, the uterus is a pertinent site to examine the Epo function in angiogenesis. We found that Epo protein and its mRNA were produced in an E2-dependent manner, when the uterus from OVX mouse was cultured in vitro. The de novo protein synthesis was not needed for E2 induction of Epo mRNA. Administration of E2 to OVX mouse induced a rapid and transient increase in Epo mRNA in the uterus. Injection of Epo into the OVX mouse uterine cavity promoted blood vessel formation in the endometrium. Furthermore, injection of the soluble Epo receptor capable of binding with Epo into the uterine cavity of non-OVX mouse in diestrus stage inhibited the endometrial transition to proestrus stage, whereas heat-inactivated soluble Epo receptor allowed the transition to occur. These results, combined with our finding that the endothelial cells in uterine endometrium express Epo receptor, strongly suggest that Epo is an important factor for the E2-dependent cyclical angiogenesis in uterus.

The alpha-helical domain near the amino terminus is essential for dimerization of vascular endothelial growth factor

Vascular endothelial growth factor (VEGF) is an endothelial cell-specific mitogen and a key mediator of aberrant endothelial cell proliferation and vascular permeability in a variety of human pathological situations such as tumor angiogenesis, diabetic retinopathy, or psoriasis. By amino-terminal deletion analysis and by site-directed mutagenesis we have identified a new domain within the amino-terminal alpha-helix that is essential for dimerization of VEGF. VEGF121 variants containing amino acids 8 to 121 or 14 to 121, respectively, either expressed in Escherichia coli and refolded in vitro, or expressed in Chinese hamster ovary cells, were in a dimeric conformation and showed full binding activity to VEGF receptors and stimulation of endothelial cell proliferation as compared with wild-type VEGF. In contrast, a VEGF121 variant covering amino acids 18 to 121, as well as a variant in which the hydrophobic amino acids Val14, Val15, Phe17, and Met18 within the amphipathic alpha-helix near the amino terminus were replaced by serine, failed to form biological active VEGF dimers. From these data we conclude that a domain between amino acids His12 and Asp19 within the amino-terminal alpha-helix is essential for formation of VEGF dimers, and we propose hydrophobic interactions between VEGF monomers to stabilize or favor dimerization.

Neuropilin-1 is expressed by endothelial and tumor cells as an isoform-specific receptor for vascular endothelial growth factor

Vascular endothelial growth factor (VEGF), a major regulator of angiogenesis, binds to two receptor tyrosine kinases, KDR/Flk-1 and Flt-1. We now describe the purification and the expression cloning from tumor cells of a third VEGF receptor, one that binds VEGF165 but not VEGF121. This isoform-specific VEGF receptor (VEGF165R) is identical to human neuropilin-1, a receptor for the collapsin/semaphorin family that mediates neuronal cell guidance. When coexpressed in cells with KDR, neuropilin-1 enhances the binding of VEGF165 to KDR and VEGF165-mediated chemotaxis. Conversely, inhibition of VEGF165 binding to neuropilin-1 inhibits its binding to KDR and its mitogenic activity for endothelial cells. We propose that neuropilin-1 is a novel VEGF receptor that modulates VEGF binding to KDR and subsequent bioactivity and therefore may regulate VEGF-induced angiogenesis.

Circulating vascular endothelial growth factor in patients with colorectal cancer

OBJECTIVE

The expression of vascular endothelial growth factor (VEGF), a glycoprotein that selectively promotes proliferation of endothelial cells, has been associated with cancer development. The aim of the present study was to determine whether serum levels of VEGF correlate with disease progression in patients with colorectal cancer.

METHODS

VEGF levels were measured by a highly sensitive enzyme-linked immunosorbent assay in sera from 67 patients with colorectal cancer, 14 patients with colorectal adenomas, and 72 healthy volunteers, and in tissue homogenates from 10 patients with colorectal cancer.

RESULTS

Serum VEGF levels were significantly higher in patients with colorectal cancer than in patients with colorectal adenomas or in normal controls (p < 0.01). In patients with colorectal cancer, serum VEGF levels were significantly associated with Dukes stage (p < 0.01) and with carcinoembryonic antigen levels (r = 0.725, p < 0.001). Patients with hepatic and/or lymph node metastasis had higher serum VEGF levels than those without. Surgical resection of the colorectal tumor led to a decrease in serum VEGF levels whether or not metastasis was present (p < 0.05). The tumor-bearing tissue contained significantly more VEGF than normal-appearing mucosa (p < 0.05).

CONCLUSIONS

VEGF is involved in the development of colorectal cancer. Measurement of VEGF in the serum may be a useful noninvasive clinical marker for evaluating the disease status.

Ovine vascular endothelial growth factor: nucleotide sequence and expression in fetal tissues

To examine the role of vascular endothelial growth factor (VEGF) in mediating angiogenesis and vascular permeability during fetal development, we determined the gene expression of VEGF in ovine fetal tissues. Further, we cloned and sequenced the ovine VEGF cDNA encoding VEGF164 from sheep placenta. VEGF protein was localized in epithelial cells of the placenta and fetal kidney, and in hepatocytes of the fetal liver. By Northern analysis, a major VEGF mRNA species of 3.7 kb was identified in all tissues examined, with abundance highest in the lung and lowest in the liver. The most prominent molecular form expressed in ovine fetal tissues appeared to be VEGF164 with low levels of expression of VEGF120 and VEGF188. Cloning and sequence analysis of the most abundant form of ovine VEGF cDNA in the placenta confirmed the prediction of a 164-amino acid peptide, with a putative N-terminal signal sequence of 26 amino acids. Comparison of the VEGF cDNA sequence among different species revealed that VEGF is highly conserved suggesting an important role in development.

Automated evaluation of angiogenic effects mediated by VEGF and PlGF homo- and heterodimers

The effects of growth factors on the blood vessel pattern of chick chorioallantoic membrane (CAM) were assessed with a fast and automated method (extended counting method, XCM; Sandau, 1996) that measures complexity, without assumptions about a fractal structure. XCM is a reliable measure of complexity not only in theory but also in practice: (1) it is robust with respect to thresholding; (2) it shows reduced variance due to pattern translation and rotation; (3) its properties come close to requirements of fractal geometry. It hence is superior to established fractal methods for distinguishing effects induced by various isoforms of vascular endothelial growth factor (VEGF121 and VEGF165), placenta growth factor (PlGF) isoforms, and control treatment. We here show that VEGF homo- and heterodimers and VEGF121/PlGF1 heterodimers increase vascular complexity, whereas PlGF1 and PlGF2 are not effective. PlGF1 and VEGF121 did not mutually influence each other when applied in adjacent fields on the same CAM. Since blood vessels in the CAM originate via nonfractal growth processes, their growth should be analyzed accordingly.

Differential hormonal regulation of vascular endothelial growth factors VEGF, VEGF-B, and VEGF-C messenger ribonucleic acid levels in cultured human granulosa-luteal cells

The development of ovarian follicles and subsequent corpus luteum formation is accompanied by very active angiogenesis. Ovarian granulosa cells produce vascular endothelial growth factor (VEGF), which is a potent endothelial cell mitogen and an angiogenic agent. The complementary DNAs of two other factors structurally related to VEGF, namely VEGF-B and VEGF-C, were recently cloned, but little is known of their regulation in the ovary. We first studied the expression of the messenger RNAs (mRNAs) of the three VEGF isotypes in freshly isolated human granulosa-luteal (GL) cells obtained at oocyte retrieval for in vitro fertilization. The hormonal regulation of these mRNAs was subsequently studied in primary cultures of human GL cells. Analysis of cultured GL cell RNA by reverse transcription-PCR revealed that these cells express the alternatively spliced transcripts representing 121-, 145-, and 165-amino acid VEGF isoforms. Northern blot hybridization analyses indicated that transcripts of 4.5 and 3.7 kilobases for VEGF, and 1.4 and 2.4 kilobases for VEGF-B and VEGF-C, respectively, are expressed in human GL cells. The basal VEGF mRNA levels declined steadily, whereas VEGF-B mRNA levels were rather invariant over a 10-day culture period of GL cells. In contrast, VEGF-C mRNA levels increased toward the end of culture. For studying the hormonal regulation of VEGF isotype mRNAs, GL cells were treated with hCG, recombinant human FSH, PGE2, as well as 8-bromo-cAMP and 12-O-tetradecanoylphorbol 13-acetate, which activate protein kinase A- and protein kinase C-dependent signaling pathways, respectively. All test agents stimulated the expression of VEGF mRNA levels in a concentration-dependent manner. Time-course studies indicated that all treatments induced VEGF mRNA levels as early as incubation for 2 h, and the effect was sustained up to 48 h. VEGF-B mRNA levels were not regulated by any of the test agents. However, we found that hCG and 8-bromo-cAMP decreased VEGF-C mRNA levels with a maximal response observed at 24 and 48 h after cellular treatment. We conclude that the mRNAs of VEGF, VEGF-B, and VEGF-C are expressed in human GL cells and that their mRNA steady state levels are regulated in cultured human GL cells in an isotype-specific manner. The differential regulation of VEGF, VEGF-B, and VEGF-C in human GL cells suggests that distinct VEGF isotypes may play different roles during the vascularization of the human ovarian follicle and corpus luteum.

Increased expression of vascular endothelial growth factor in human hepatocellular carcinoma

BACKGROUND/AIMS

Angiogenesis is critical for the development and progression of solid tumors. The purpose of this study was to evaluate the possible role of vascular endothelial growth factor (which is considered to be one of the most important factors involved in tumor-associated angiogenesis), in human hepatocellular carcinoma.

METHODS

Vascular endothelial growth factor gene and protein expression were analyzed by means of Northern hybridization and immunohistochemical methods in 5 hepatocellular carcinoma cell lines. Secretion of vascular endothelial growth factor was evaluated by immunoblotting of conditioned medium of these hepatocellular carcinoma cells. Further, we compared the level of vascular endothelial growth factor expression in hepatocellular carcinoma tissues along with that in surrounding tumor-free tissues obtained from 20 patients. We also analyzed mRNA expression of Flt-1, one of the vascular endothelial growth factor specific high-affinity receptors, in hepatocellular carcinoma cell lines.

RESULTS

Northern hybridization analysis and immunohistochemistry revealed that all cultured hepatocellular carcinoma cells exhibited a high level of vascular endothelial growth factor mRNA. In addition, vascular endothelial growth factor secretion by Hep G2, one of the hepatocellular carcinoma cell lines, was shown by Western blot. In vivo, we observed vascular endothelial growth factor expression in both hepatocellular carcinoma and non-hepatocellular carcinoma tissues. However, in 12 of 20 cases, vascular endothelial growth factor mRNA levels were significantly up-regulated in hepatocellular carcinoma tissues. In the majority of cases (10 out of 12 cases) with abundant tumor vascularity, vascular endothelial growth factor mRNA up-regulation in hepatocellular carcinoma tissues was observed. We failed to detect Flt-1 mRNA expression in hepatocellular carcinoma cells.

CONCLUSIONS

This study suggests that the possibility that hepatocellular carcinoma cells overexpress the vascular endothelial growth factor gene and protein. These findings support the hypothesis that vascular endothelial growth factor is one of the important factors involved in the angiogenesis of hepatocellular carcinoma, and may even be involved in the development and/or progression of hepatocellular carcinoma itself.

Isolation from fetal bovine serum of a fragment b of complement factor B-like protein improving a long-term survival of human endothelial cells

It is known that serum is a most important factor supporting cell survival and growth. Particularly, the deprivation of serum would result in the death of human endothelial cell. Our previous paper reported an endothelial cell-viability maintaining factor (EC-VMFa) purified from fetal bovine serum and identified as an apolipoprotein. In the present further study, it is demonstrated that another potent serum factor (refer as EC-VMFb) is also possessed of the endothelial cell-viability maintaining activity, improving a long-term survival of human endothelial cells in serum-free medium. EC-VMFb has a molecular weight of 66,000 (reduced and nonreduced), pI of 4.5 and has been identified as fragment b of complement factor B (Bb)-like protein by amino-terminal amino acid sequence.

Expression of vascular endothelial growth factor and its receptors in pilocytic astrocytoma

Vascular endothelial growth factor (VEGF), a potent angiogenic and vascular permeability factor, is important in the angiogenesis of glioblastoma. A major difference between pilocytic astrocytoma, a grade I tumor, and the grade II fibrillary astrocytoma is the vascular proliferation, highly vascularized stroma, and great propensity for cyst formation in the former. In order to explore factors regulating such angiogenesis and cyst formation in pilocytic astrocytoma, we examined expression of VEGF and its receptors (KDR and Flt-1) using in situ hybridization. In all 14 cases a high level of VEGF transcripts could be demonstrated. These were found in specific regions, namely, in the tumor cyst wall, in areas of hyaline cystic degeneration, in stellate reticulated astrocytes around microcysts in the biphasic compact and loose areas, and in tumor cells with degenerative pleomorphic multicoated nuclei. KDR and Flt-1 were expressed in the tumor vasculature, with particularly high levels seen in coiled young proliferating vessels, especially those in the cyst wall. Given the known angiogenic and vascular permeability activities of VEGF, we propose that VEGF plays an important role in molding the characteristic morphologic features of this tumor, namely, the formation of cysts, microcystic pattern, hyaline cystic degeneration, hyaline vessels, and vascular proliferation. Mechanisms that block the VEGF pathway could constitute a potential therapeutic strategy for the treatment of this tumor.

VEGF145, a secreted vascular endothelial growth factor isoform that binds to extracellular matrix

A vascular endothelial growth factor (VEGF) mRNA species containing exons 1-6 and 8 of the VEGF gene was found to be expressed as a major VEGF mRNA form in several cell lines derived from carcinomas of the female reproductive system. This mRNA is predicted to encode a VEGF form of 145 amino acids (VEGF145). Recombinant VEGF145 induced the proliferation of vascular endothelial cells and promoted angiogenesis in vivo. VEGF145 was compared with previously characterized VEGF species with respect to interaction with heparin-like molecules, cellular distribution, VEGF receptor recognition, and extracellular matrix (ECM) binding ability. VEGF145 shares with VEGF165 the ability to bind to the KDR/flk-1 receptor of endothelial cells. It also binds to heparin with an affinity similar to that of VEGF165. However, VEGF145 does not bind to two additional endothelial cell surface receptors that are recognized by VEGF165 but not by VEGF121. VEGF145 is secreted from producing cells as are VEGF121 and VEGF165. However, VEGF121 and VEGF165 do not bind to the ECM produced by corneal endothelial cells, whereas VEGF145 binds efficiently to this ECM. Basic fibroblast growth factor (bFGF)-depleted ECM containing bound VEGF145 induces proliferation of endothelial cells, indicating that the bound VEGF145 is active. The mechanism by which VEGF145 binds to the ECM differs from that of bFGF. Digestion of the ECM by heparinase inhibited the binding of bFGF to the ECM and released prebound bFGF, whereas the binding of VEGF145 was not affected by heparinase digestion. It therefore seems that VEGF145 possesses a unique combination of biological properties distinct from those of previously characterized VEGF species.

Transforming growth factor-alpha-induced transcriptional activation of the vascular permeability factor (VPF/VEGF) gene requires AP-2-dependent DNA binding and transactivation

The endothelial cell-specific mitogen vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) represents a central regulator of cutaneous angiogenesis. Increased VPF/VEGF expression has recently been reported in psoriatic skin and healing wounds, both conditions in which transforming growth factor-alpha (TGF alpha) and its ligand, the epidermal growth factor receptor, are markedly up-regulated. Since TGF alpha strongly induces VPF/VEGF synthesis in keratinocytes, TGF alpha-mediated VPF/VEGF expression is likely to play a significant role in the initiation and maintenance of increased vascular hyperpermeability and hyperproliferation in skin biology. The objectives of the present studies were to determine the molecular mechanisms responsible for TGF alpha-induced transcriptional activation of the VPF/VEGF gene. We have identified a GC-rich TGF alpha-responsive region between -88 bp and -65 bp of the VPF/VEGF promoter that is necessary for constitutive and TGF alpha-inducible transcriptional activation. In electrophoretic mobility shift assays, this region binds Sp1-dependent protein complexes constitutively and an additional TGF alpha-inducible protein complex that is distinct from Sp1 protein. Both AP-2 and Egr-1 transcription factors were detected as components of the TGF alpha-inducible protein complex in supershift EMSA studies. In co-transfection studies, an AP-2 but not an Egr-1 expression vector activated VPF/VEGF transcription, thus indicating that AP-2 protein is functionally important in TGF alpha-induced VPF/VEGF gene expression. By clarifying regulatory mechanisms that are critical for angiogenic processes in the skin, these studies may form the basis for new therapeutic strategies to modulate VPF/VEGF expression in cutaneous inflammation and wound healing.

VEGF and bFGF mRNA are expressed in ethylnitrosourea-induced experimental rat gliomas

1. Which angiogenic growth factors actually mediate tumor growth in ethylnitrosourea (ENU)-induced gliomas in rats was examined. 2. In situ hybridization histochemistry with digoxigenin-labeled oligonucleotide probes was used to investigate the cellular expression and distribution of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) mRNAs in ENU-induced gliomas. 3. Both VEGF and bFGF mRNAs were not detected in normal gial cells but in ENU-induced glioma cells. 4. Our results suggest that the growth of ENU-induced glioma may be regulated by multiple angiogenic growth factors and that these gliomas may proliferate by synthesizing such growth factors.

Regional angiogenesis induced in nonischemic tissue by an adenoviral vector expressing vascular endothelial growth factor

The feasibility of a single administration of a replication-deficient adenovirus (Ad) vector encoding the cDNA for human vascular endothelial growth factor (VEGF) (AdCMV.VEGF) to induce neovascularization in vivo in normal tissue was evaluated in retroperitoneal adipose tissue. Following administration of AdCMV.VEGF (10(9) pfu/50 microliters), maximal VEGF cDNA expression was observed at 2-5 days in the injected adipose tissue. No VEGF protein was detected at > or = 10 days in injected adipose tissue, and there was no increase in serum VEGF levels at any time. In vivo quantification of the number of blood vessels using 30x visualization of the adipose tissue demonstrated an increase in vessel number by 10 days, plateauing by 30 days with a 123% increase in vessel number compared to the control vector AdCMV.Null, despite the fact that no VEGF protein was detected after 5 days. Consistent with the in vivo data, histologic quantification of capillary number demonstrated an increase by day 5, reaching a 38% increase over AdCMV.Null by day 30. These observations demonstrate that an Ad vector carrying the VEGF cDNA is capable of inducing the growth of new blood vessels in a regional fashion in a relatively avascular, normal organ. This suggests in vivo Ad-mediated gene transfer may be useful for therapeutic angiogenesis in the treatment of ischemic cardiovascular disease.

Platelet-derived growth factor and vascular endothelial growth factor expression in disc herniation tissue: and immunohistochemical study

Angiogenesis is essential in tissue growth and regeneration. There are several factors that are able to stimulate vascular endothelial cell growth, including platelet-derived growth factor (PDGF) and vascular endothelial growth factor (VEGF). Disc herniation tissue (DHT) contains vascular ingrowth, which promotes granulation tissue formation. In this study we observed 50 disc herniations for PDGF and VEGF immunoreactivity. PDGF immunopositivity was detected in 38 samples (78%). In 28 samples (56%) there were PDGF immunopositive capillaries, PDGF immunopositive disc cells were detected in 19 samples (38%) and PDGF immunopositive fibroblasts in 6 DHT samples (12%). VEGF immunopositive capillaries were identified in 44 DHT samples (88%). For neither growth factor was immunopositivity dependent on preoperative radicular pain duration. In extrusions (n = 25) VEGF immunopositive capillaries were detected in 23 samples (92%) and PDGF immunopositivity in 21 samples (84%). PDGF immunopositivity was more commonly associated with capillaries than with nuclei of disc cells. In sequesters (n = 20) VEGF immunopositive capillaries were identified in all samples and PDGF immunopositivity in 16 (80%). As in extrusions, PDGF immunoreaction was more prevalent in capillaries than in disc cells. Patient age did not relate to VEGF expression. In all age groups it was higher than 80%. Thus capillaries in disc herniation tissue are evidently newly formed and our results demonstrate that PDGF and VEGF participate in the neovascularization process. The presence of PDGF in fibroblasts and in disc cells suggests that this growth factor regulates the function of these cells, possibly the proliferation of the cells and the production of extracellular matrix components.

Vascular endothelial growth factor messenger ribonucleic acid expression in human ovarian and endometrial cancer

Vascular endothelial growth factor (VEGF) is a previously discovered angiogenic factor that seems to influence the neoangiogenesis of neoplastic and non-neoplastic tissues. Substantial experimental evidence links tumor growth and metastasis with blood vessel formation. Tumor angiogenesis can be induced by factors released by the tumor cells themselves. A variety of transformed cell lines expresses the VEGF transcript and secretes an EGF-like protein, suggesting that this angiogenic factor may be one of the mediators of tumor angiogenesis. By Northern blot analysis and in situ hybridization, we investigated the expression of VEGF transcript in human ovarian and endometrial neoplasms. Messenger RNA encoding VEGF was detected in all tissues studied and was more densely expressed in endometrial carcinoma. VEGF expression was also identified in cells obtained from ovarian and endometrial ascitic fluid. VEGF mRNA, detected by in situ hybridization, was identified in the epithelial cells of endometrial adenocarcinoma. This distribution was localized primarily in the apices of the papillae. The prominence of VEGF mRNA levels in human ovarian and endometrial tumors demonstrates that VEGF may be involved in promoting tumor angiogenesis and stroma generation, acting as an endothelial cell mitogen.

Vascular endothelial growth factor and its receptors

Vascular endothelial growth factor (VEGF) is a prime regulator of endothelial cell proliferation, angiogenesis, vasculogenesis and vascular permeability. Its activity is mediated by the high affinity tyrosine kinase receptors, KDR/Fik-1 and Fit-1. In this article, recently discovered structural, molecular and biological properties of VEGF are described. Among the topics discussed are VEGF and VEGF receptor structure and bioactivity, the regulation of VEGF expression, the role of VEGF and its receptors in vascular development, and the involvement of VEGF and its receptors in normal and pathological (ocular and tumor) angiogenesis.

Expression of vascular endothelial growth factor in human myocardial infarction

To define mechanisms that may influence collateral circulation and angiogenesis, we investigated vascular endothelial growth factor (VEGF) mRNA expression in human hearts. In non-ischemic human hearts, VEGF mRNA was not detected in vessels, but was found in cardiomyocytes. In hearts with myocardial infarction, the intensity of the VEGF signal was much higher in smooth muscle cells of arterioles adjacent to necrosis and in infiltrating macrophages than in myocytes around the site of the necrosis. This study suggests that levels of VEGF expression are high in smooth muscle cells and macrophages around infarcted areas after myocardial infarction and that VEGF may play a role in promoting collateral circulation and angiogenesis in human ischemic hearts.

Embryonic angiogenesis: a review

Supply with nutrients is essential from early embryonic stages onwards. Therefore, circulatory organs form the first functioning organ system. With the exception of the heart, this system is at first formed by only one cell type, the endothelial cell. Emergence, behavior, and differentiation of endothelial cells are discussed in this review. At first, endothelial cells develop from angioblasts (primary angiogenesis/angioblastic development), later they develop from preexisting endothelial cells (secondary angiogenesis/angiotrophic growth). The composition of the extracellular matrix may promote or inhibit angiogenesis. Various growth factors which can be bound to the extracellular matrix may have been found, but only two of them (VEGF, P1GF) seem to influence endothelial cell behavior directly. Heterogeneity and organ-typical differentiation of endothelial cells seem to be dependent on cell-cell signaling within each organ.

Retinal vascular endothelial growth factor (VEGF) mRNA expression is altered in relation to neovascularization in oxygen induced retinopathy

The temporal and spatial expression of vascular endothelial cell growth factor (VEGF) mRNA was studied in normal developing cat retina, and in oxygen induced retinopathy. Unexposed control and oxygen-exposed animals (80 h of 80% oxygen from day 3, n = 16) were studied at 1, 2, 4, and 6 weeks after birth. India ink injected retinal flat mounts were used to study vessel progression, and in situ hybridizations using retinal cross sections were used to assess VEGF mRNA accumulation. In controls, as the retina matured, VEGF mRNA hybridization was evident in the ganglion cell layer in a scattered line of distinct cells prior to the ingrowth of vessels, involved the most cells in regions just peripheral to invading vessels and persisted in a fewer positive cells, widely spaced in the vascularized retinas of control, six week animals. In the inner nuclear layer, hybridization initially appeared diffusely and later became localized to a narrow portion of that layer and persisted there. In animals with oxygen induced retinopathy, a substantial increase in hybridization was observed in both the ganglion cell and inner nuclear layers of the avascular retina anterior to the advancing neovascularization. VEGF hybridization decreased abruptly to background levels in both layers at the point were neovascularization met avascular retina. By six weeks, when the neovascularization reached the ora, there was a return of VEGF mRNA in the inner nuclear layer which was similar to normal control expression. A low level of unchanging expression was also observed in the retinal pigment epithelium in both groups at all ages. These results indicate that VEGF mRNA abundance is regulated during retinal vascularization and is increased in relation to oxygen induced neovascularization, suggesting that VEGF may play an important role in both normal retinal vessel development and in the pathophysiology of retinopathy of prematurity.

Heparin-binding epidermal growth factor-like growth factor: p91 activation induction of plasminogen activator/inhibitor, and tubular morphogenesis in human microvascular endothelial cells

Epidermal growth factor (EGF) or transforming growth factor-alpha (TGF-alpha) stimulates cell migration, proliferation and the formation of tube-like structures of human microvascular endothelial cells in culture. Heparin-binding EGF-like growth factor(HB-EGF), which shows 35% homology with EGF/TGF-alpha, is a member of the EGF family, and it is ubiquitous in many tissues and organs. We examined whether or not HB-EGF induced angiogenic responses in human microvascular endothelial cells. HB-EGF inhibited the binding of (125) I-EGF to the EGF receptor and induced autophosphorylation of the receptor on endothelial cells. Exogenous HB-EGF induced the loss of more than 70% of the EGF receptor from the cell surface within 30 min, with similar kinetics to that of EGF. The level of c-fos mRNA markedly increased at 30 min in response to HB-EGF as well as EGF. A gel shift assay demonstrated the activation of the transcription factor p91 by HB-EGF and EGF. This factor directly interacts with EGF receptor and mediates the activation of c-fos gene promoter. HB-EGF enhanced the mRNA expression of tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor-1 (PAI-1) mRNA. However, the enhancement of t-PA and PAI-1 by HB-EGF was less than that by EGF. Heparitinase/chlorate, which digests the heparan sulfate proteoglycan of the endothelial cell surface, restored both t-PA and PAI-1 mRNA levels in response to HB-EGF in a manner similar to that by EGF. HB-EGF at 10 ng/ml developed tube-like structures in type I collagen gel at similar levels to that of EGF at 10 ng/ml, suggesting that HB-EGF is also a potent angiogenic factor in the model system for angiogenesis. The tubulogenesis activity of HB-EGF is discussed in relation to the expression of the t-PA and PAI-1 genes.

Purification and characterization of an endothelial cell-viability maintaining factor from fetal bovine serum

Serum is an essential requirement for the growth and long-term survival of human endothelial cells, even in the presence of such defined elements such as polypeptide growth factors and hormones. A polypeptide from fetal bovine serum was isolated and characterized on the basis of long-term survival of human endothelial cells in serum-free culture. The endothelial cell viability maintaining factor has been purified to homogeneity by a combination of polyethylene glycol precipitation, hydroxylapatite, gel permeation and reverse-phase high performance liquid chromatography. The final purified endothelial cell viability maintaining factor has a molecular weight of 65,000 (reduced) and has been identified as bovine apolipoprotein H by amino-terminal amino acid sequence analysis and Western blot analysis. Endothelial cell viability maintaining factor improved a long-term viability of human endothelial cells at maximal concentrations of 2.5-5 micrograms protein/ml in serum-free medium.

Vascular endothelial growth/permeability factor expression in human glioma specimens: correlation with vasogenic brain edema and tumor-associated cysts

Peritumoral vasogenic brain edema (PVBE) is a common accompaniment of malignant gliomas. It results from microvascular extravasation of plasma fluid and proteins through the interendothelial spaces. Tumor-associated cysts (TACs) are observed more commonly with benign gliomas that are not associated with PVBE. This study investigates the hypothesis that these morphologically distinct epiphenomena of microvascular extravasation are linked by a common pathophysiological mechanism involving vascular endothelial growth/permeability factor (VEG/PF), which has been implicated in vascular leak phenomena including ascites, malignant effusions, and brain edema. Furthermore, VEG/PF has been isolated from cultured glioma cells, and both VEG/PF protein and messenger RNA transcripts are expressed in brain tumor tissue. To further elucidate the relationship of VEG/PF to PVBE and TACs, the authors examined 34 pathological specimens for VEG/PF expression. Nineteen primary low-grade tumors, 11 primary high-grade tumors, and four gliosis controls were immunostained with a polyclonal anti-VEG/PF immunoglobulin G antibody. Magnetic resonance imaging was used to quantitate PVBE and to determine the presence of TACs and tumor enhancement. The study revealed that eight VEG/PF-negative specimens exhibited no significant edema, whereas 26 VEG/PF-positive tumors exhibited either significant PVBE or TACs. Notably, eight of nine benign TACs that were not associated with PVBE immunostained positive for VEG/PF. These data indicate a high degree of correlation between VEG/PF expression by gliomas and the occurrence of PVBE or TACs, irrespective of tumor grade, thus supporting VEG/PF's pivotal role as the common pathophysiological link between these processes.

Vascular endothelial growth factor gene expression in ovine placenta and fetal membranes

OBJECTIVE

The purpose of this study was to explore the gene expression of vascular endothelial growth factor (VEGF) in placental cotyledon, chorion, and amnion of the ovine fetus.

STUDY DESIGN

Time-dated pregnant sheep with singleton or twin fetuses at a gestational age ranging from 100 to 140 days were used for the study. Placental cotyledonary, chorionic, and amniotic tissues were collected and processed for messenger ribonucleic acid analysis by Northern blotting and reverse transcription-polymerase chain reaction.

RESULTS

By use of a phosphorus 32-labeled human VEGF complementary deoxyribonucleic acid probe, a prominent VEGF messenger ribonucleic acid transcript of 3.7 kb was detected in the cotyledon, chorion, and amnion. A minor band of 1.7 kb was also found but only in the cotyledon and chorion. The abundance of messenger ribonucleic acid encoding VEGF was highest (p < 0.001) in the cotyledon and lowest in the amnion. In these tissues polymerase chain reaction-amplified products corresponding to VEGF121, VEGF165, VEGF189, and VEGF206 were identified by ethidium bromide. In addition, a polymerase chain reaction fragment corresponding to VEGF145 was observed. These fragments produced specific hybridization signals with the human VEGF radioactive probe where the intensity of the signal was strongest for VEGF165 and weakest for VEGF189.

CONCLUSIONS

VEGF gene expression was detected in the cotyledon, chorion, and amnion of the near-term ovine fetus. These findings suggest that vascular endothelial growth factor may play a role in the induction of angiogenesis and promotion of permeability in the microvessels that perfuse the placental and fetal membranes.

Hypoxic induction of vascular endothelial growth factor (VEGF) in human epithelial cells is mediated by increases in mRNA stability

Vessel growth is often associated with ischemia. VEGF, a potent angiogenic factor, has been shown to be induced by low oxygen concentrations. These studies were conducted to investigate the molecular basis of the hypoxia-induced increase in VEGF mRNA. Run-on analysis of VEGF revealed a minimal increase in the rate of gene transcription in a human retinal epithelial cell line grown under hypoxic conditions. Examination of VEGF mRNA stability revealed that the half-life of VEGF transcripts under normoxia was short, 30-45 min, but was dramatically increased to 6-8 h in cells grown under hypoxia. Cobalt chloride, which elevates VEGF and has been suggested to be similar to hypoxia in its mechanism of action, had only a slight effect on decay rate. We postulate that hypoxia-induced increases in mRNA stability provide the sustained increases in VEGF mRNA levels necessary to support a neovascular response.

Platelet factor-4 inhibits the mitogenic activity of VEGF121 and VEGF165 using several concurrent mechanisms

The 121-amino acid form of vascular endothelial growth factor (VEGF121) and the 165-amino acid form (VEGF165) are mitogenic for vascular endothelial cells and induce angiogenesis in vivo. VEGF165 possesses a heparin binding ability and in the absence of heparin-like molecules does not bind efficiently to the VEGF receptors of vascular endothelial cells. The binding of 125I-VEGF165 to the VEGF receptors of endothelial cells, and the heparin-dependent binding of 125I-VEGF165 to a soluble extracellular domain of the VEGF receptor KDR/flk-1, were inhibited by the angiogenesis inhibitor platelet factor-4 (PF4). In contrast, PF4 was not able to inhibit the binding of VEGF121, a VEGF isoform which lacks a heparin binding capacity, to the VEGF receptors of the cells or to KDR/flk-1. These results indicate that PF4 may inhibit VEGF165 binding to VEGF receptors by disrupting the interaction of VEGF165 with cell surface heparan sulfates. Since PF4 mutants lacking a heparin binding ability retain their anti-angiogenic activity, alternative inhibitory mechanisms were also examined. 125I-PF4 bound with high affinity (Kd 5 x 10(-9) M) to VEGF165-coated wells. The binding of 125I-PF4 to the VEGF165-coated wells was inhibited by several types of heparin binding proteins, including unlabeled PF4 and unlabeled VEGF165. The binding was not inhibited by proteins which lack a heparin binding capacity, nor was it inhibited by VEGF121. Heparinase did not inhibit the binding of 125I-PF4 to VEGF165, indicating that heparin-like molecules are not required. These experiments suggest that PF4 can bind to heparin binding proteins such as VEGF165 leading to an inhibition of their receptor binding ability. In agreement with these results, we have observed that PF4 inhibits efficiently the VEGF165 induced proliferation of vascular endothelial cells. Unexpectedly, PF4 also inhibited efficiently the VEGF121-induced proliferation of the cells, indicating that PF4 can disrupt VEGF receptor mediated signal transduction using an unknown mechanism which does not interfere with VEGF121 binding.

Transcriptional regulation of the rat vascular endothelial growth factor gene by hypoxia

Vascular endothelial growth factor (VEGF), a potent angiogenic factor and endothelial cell-specific mitogen, is up-regulated by hypoxia. However, the mechanism(s) responsible for hypoxic induction of VEGF has not been clearly delineated. We report that the steady state VEGF mRNA levels are increased 12 +/- 0.6-fold, but the transcriptional rate for VEGF is increased only 3.1 +/- 0.6-fold by hypoxia in PC12 cells. In order to investigate cis-regulatory sequences which mediate this response to hypoxia, we cloned the rat genomic sequences encoding VEGF and identified a 28-base pair element in the 5' promoter that mediates hypoxia-inducible transcription in transient expression assays. This element has sequence and protein binding similarities to the hypoxia-inducible factor 1 binding site within the erythropoietin 3' enhancer. Post-transcriptional mechanisms have also been suggested to play a role in the hypoxic induction of VEGF. Evidence is provided that a frequently used polyadenylation site is 1.9 kilobases downstream from the translation termination codon for rat VEGF. This site is 1.5 kilobases further downstream from the polyadenylation site previously reported for VEGF. This new finding reveals sequence motifs in the 3'-untranslated region that may mediate VEGF mRNA stability.