Vascular endothelial growth factor. Regulation by cell differentiation and activated second messenger pathways

ACTH-regulated expression of vascular endothelial growth factor in the adult bovine adrenal cortex: a possible role in the maintenance of the microvasculature

Endothelial cells lining vessels of endocrine tissues are fenestrated. Interactions with the local environment via either soluble factors or cell-cell interactions appear to govern this terminal endothelial differentiation. Adrenocorticotropin (ACTH) has previously been reported to modulate endothelial fenestration in the rat adrenal cortex. Since vascular endothelial growth factor (VEGF) has been characterized as a potent inducer of endothelial fenestration, we aimed to characterize the status of VEGF expression in the bovine adult adrenal cortex and asked whether ACTH may regulate VEGF expression. By immunohistochemical analysis, we observed VEGF expression in steroidogenic cells from both zona glomerulosa and zona fasciculata of the bovine adrenal cortex. Double-labeling experiments performed on isolated cells in primary culture revealed VEGF immunoreactivity, essentially colocalized with the Golgi apparatus. The expression of two predominant VEGF isoforms, VEGF(121) and VEGF(165), was observed by RT-PCR analysis. ACTH (10 nM) was found to rapidly (within 2-4 h) increase the abundance of these VEGF transcripts, as assessed by both RT-PCR and Northern blot analysis. In parallel, ACTH significantly induced VEGF secretion into the medium of fasciculata cells in primary culture. Thus, our data are consistent with the involvement of ACTH, through its regulation of VEGF expression, in the maintenance of the adult adrenal cortex endothelium.

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.

Multilocular fat cells in WAT of CL-316243-treated rats derive directly from white adipocytes

Multilocular, mitochondria-rich adipocytes appear in white adipose tissue (WAT) of rats treated with the beta3-adrenoceptor agonist, CL-316243 (CL). Objectives were to determine whether these multilocular adipocytes derived from cells that already existed in the WAT or from proliferation of precursor cells and whether new mitochondria contained in them were typical brown adipocyte mitochondria. Use of 5-bromodeoxyuridine to identify cells that had undergone mitosis during the CL treatment showed that most multilocular cells derived from cells already present in the WAT. Morphological techniques showed that at least a subpopulation of unilocular adipocytes underwent conversion to multilocular mitochondria-rich adipocytes. A small proportion of multilocular adipocytes ( approximately 8%) was positive for UCP1 by immunohistochemistry. Biochemical techniques showed that mitochondrial protein recovered from WAT increased 10-fold and protein isolated from brown adipose tissue (BAT) doubled in CL-treated rats. Stained gels showed a different protein composition of new mitochondria isolated from WAT from that of mitochondria isolated from BAT. Western blotting showed new mitochondria in WAT to contain both UCP1, but at a much lower concentration than in BAT mitochondria, and UCP3, at a higher concentration than that in BAT mitochondria. We hypothesize that multilocular adipocytes present at 7 days of CL treatment have two origins. First, most come from convertible unilocular adipocytes that become multilocular and make many mitochondria that contain UCP3. Second, some come from a cell that gives rise to more typical brown adipocytes that express UCP1.

Treatment with soluble VEGF receptor reduces disease severity in murine collagen-induced arthritis

Maintenance of the invasive pannus in rheumatoid arthritis is an integral part of disease progression. The synovial vasculature plays an important role in the delivery of nutrients, oxygen, and inflammatory cells to the synovium. Vascular endothelial growth factor (VEGF), an endothelial mitogen expressed by cells within the synovial membrane, is thought to contribute to the formation of synovial blood vessels. Our objective in this study was to measure the kinetics of VEGF production in a murine model of collagen-induced arthritis and to determine whether VEGF blockade reduces disease progression. Synovial cells isolated from the knee joints of naive or sham-immunized mice, or from mice immunized with collagen but without arthritis, released little or no detectable VEGF. Onset of arthritis was associated with expression of VEGF mRNA and protein. The levels of VEGF secreted by synovial cells isolated from the joints of mice with severe arthritis were significantly higher than from mice with mild disease. To block VEGF activity, animals were treated after arthritis onset with a soluble form of the Flt-1 VEGF receptor (sFlt), which was polyethylene glycol (PEG)-linked to increase its in vivo half-life. Treatment of arthritic mice with sFlt-PEG significantly reduced both clinical score and paw swelling, compared with untreated or control-treated (heat-denatured sFlt-PEG) animals. There was also significantly less joint inflammation and reduced bone and cartilage destruction in sFlt-PEG-treated animals, as assessed by histology. Our data demonstrate that, in collagen-induced arthritis, expression of the potent angiogenic cytokine VEGF correlates with disease severity. Furthermore, specific blockade of VEGF activity results in attenuation of arthritis in both macroscopic and microscopic parameters. These observations indicate that blood vessel formation is integral to the development of arthritis and that blockade of VEGF activity might be of therapeutic benefit in rheumatoid arthritis.

Coexpression of neuropilin-1, Flk1, and VEGF(164) in developing and mature mouse kidney glomeruli

Neuropilin-1, a neuronal cell surface semaphorin III receptor protein important for axonal guidance in developing peripheral nervous system efferents, has also been identified as a vascular endothelial growth factor (VEGF) receptor on endothelial cells. To evaluate its expression in kidney, we carried out RT-PCR on newborn and adult total renal RNAs. A 403-bp product, which was predicted to be that from neuropilin-1 mRNA, was found in both samples. Nucleotide sequencing confirmed that these products encoded neuropilin-1. Northern analysis of newborn and adult kidney RNA showed specific hybridization to appropriately sized bands of approximately 6 kb. In situ hybridization with a mouse-specific antisense neuropilin-1 (35)S-cRNA probe showed distinct glomerular localization on sections from both newborns and adults. Similar patterns of hybridization were seen in sections treated with antisense cRNA probes against another VEGF receptor, Flk1, and with VEGF probes. However, the VEGF hybridization signal was markedly less in adult glomeruli than those for neuropilin-1 and Flk1. Because neuropilin-1 specifically binds VEGF(165) in humans, we carried out RT-PCR on mouse kidney RNA with primers that amplified the three alternatively spliced isoforms of VEGF mRNA. Our analysis showed that for both newborn and adult kidneys, the relative abundance of VEGF mRNA was VEGF(164) >> VEGF(120) > VEGF(188). We conclude that the expression of neuropilin-1, in conjunction with Flk1 and VEGF(164), jointly contributes to the development and maintenance of glomerular capillaries.

Induction of angiogenesis by implantation of encapsulated primary myoblasts expressing vascular endothelial growth factor

BACKGROUND

We previously demonstrated that intramuscular implantation of primary myoblasts engineered to express vascular endothelial growth factor (VEGF) constitutively resulted in hemangioma formation and the appearance of VEGF in the circulation. To investigate the potential for using allogeneic myoblasts and the effects of delivery of VEGF-expressing myoblasts to non-muscle sites, we have enclosed them in microcapsules that protect allogeneic cells from rejection, yet allow the secretion of proteins produced by the cells.

METHODS

Encapsulated mouse primary myoblasts that constitutively expressed murine VEGF164, or encapsulated negative control cells, were implanted either subcutaneously or intraperitoneally into mice.

RESULTS

Upon subcutaneous implantation, capsules containing VEGF-expressing myoblasts gave rise to large tissue masses at the implantation site that continued to grow and were composed primarily of endothelial and smooth muscle cells directly surrounding the capsules, and macrophages and capillaries further away from the capsules. Similarly, when injected intraperitoneally, VEGF-producing capsules caused significant localized inflammation and angiogenesis within the peritoneum, and ultimately led to fatal intraperitoneal hemorrhage. Notably, however, VEGF was not detected in the plasma of any mice.

CONCLUSIONS

We conclude that encapsulated primary myoblasts persist and continue to secrete VEGF subcutaneously and intraperitoneally, but that the heparin-binding isoform VEGF164 exerts localized effects at the site of production. VEGF secreted from the capsules attracts endothelial and smooth muscle cells in a macrophage-independent manner. These results, along with our previous results, show that the mode and site of delivery of the same factor by the same engineered myoblasts can lead to markedly different outcomes. Moreover, the results confirm that constitutive delivery of high levels of VEGF is not desirable. In contrast, regulatable expression may lead to efficacious, safe, and localized VEGF delivery by encapsulated allogeneic primary myoblasts that can serve as universal donors.

Stretch-induced upregulation of VEGF gene expression in murine pulmonary culture: a role for angiogenesis in lung development

BACKGROUND/PURPOSE

The authors' have shown pulmonary alveolarization (capillary and alveolar growth) both after fetal tracheal occlusion and postnatal pulmonary distension. The trophic and developmental mechanisms responsible for this growth remain largely unknown; however, experimental systems have defined an enhanced expression of angiogenic proteins in response to tissue stretch. The authors hypothesize that the stimulation of pulmonary alveolarization after stretch is secondary to upregulation of the potent endothelial cell mitogen vascular endothelial growth factor (VEGF) and that the endothelial cell represents the central stimulus of parenchymal growth.

METHODS

A mixed primary pulmonary cell culture obtained by enzymatic digestion of fetal, neonatal, and adult mouse lung was plated on Bioflex elastomer bottom plates, grown to confluence, rendered quiescent, and subjected to continuous cycles of stretch-relaxation with nonstretched cells as controls. Cells were harvested at time-points 0, 30 minutes, 2 hours, 4 hours, 8 hours, and 24 hours. RNA was extracted and VEGF gene expression analyzed by semiquantitative reverse transcription polymerase chain reaction (RT-PCR). Similar cell groups were harvested, processed, and analyzed utilizing Western Blot techniques. VEGF PCR of mRNA isolated from fetal sheep subjected to surgical creation of diaphragmatic hernia both with (DH-TL) and without (DH) tracheal ligation also was analyzed.

RESULTS

VEGF mRNA isoforms 120, 164, and 188 showed increased expression in all stretched groups, which was noted by 30 minutes with maximal expression seen at 2 to 4 hours and a return to baseline expression by 24 hours. VEGF protein was similarly elevated in all stretched cell groups. In preliminary studies, DH/TL sheep showed upregulation of VEGF compared with DH sheep alone.

CONCLUSIONS

These data show in an in vitro system that "pulmonary stretch" upregulates VEGF mRNA and protein expression supporting the role of angiogenesis in the stretch-induced pulmonary alveolarization. The authors speculate that such angiogenic activity is a rate-limiting factor in stimulating alveolar epithelial development, and as a treatment modality, therapeutic angiogenesis may provide a noninvasive method with which to treat pulmonary hypoplasia.

Vascular endothelial growth factor expression and regulation of murine collagen-induced arthritis

We have examined the expression and function of the angiogenic factor, vascular endothelial growth factor (VEGF) during the evolution of type II collagen-induced arthritis (CIA). Biologically active VEGF was expressed along a time course that paralleled the expression of two specific VEGF receptors, Flk-1 and Flt-1, and the progression of joint disease. Moreover, levels of VEGF expression correlated with the degree of neovascularization, as defined by vWF levels, and arthritis severity. Macrophage- and fibroblast-like cells, which infiltrated inflamed sites and were then activated by other inflammatory mediators, are probably important sources of VEGF and may thus regulate angiogenesis during the development of CIA. Administration of anti-VEGF antiserum to CIA mice before the onset of arthritis delayed the onset, reduced the severity, and diminished the vWF content of arthritic joints. By contrast, administration of anti-VEGF antiserum after the onset of the disease had no effect on the progression or ultimate severity of the arthritis. These data suggest that VEGF plays a crucial role during an early stage of arthritis development, affecting both neovascularization and the progression of experimentally induced synovitis.

Norepinephrine induces vascular endothelial growth factor gene expression in brown adipocytes through a beta -adrenoreceptor/cAMP/protein kinase A pathway involving Src but independently of Erk1/2

To identify the signaling pathway that mediates the adrenergic stimulation of the expression of the gene for vascular endothelial growth factor (VEGF) during physiologically induced angiogenesis, we examined mouse brown adipocytes in primary culture. The endogenous adrenergic neurotransmitter norepinephrine (NE) induced VEGF expression 3-fold, in a dose- and time-dependent manner (EC(50) approximately 90 nm). Also, the hypoxia-mimicking agent cobalt, as well as serum and phorbol ester, induced VEGF expression, but the effect of NE was additive to each of these factors, implying that a separate signaling mechanism for the NE-mediated induction was activated. The NE effect was abolished by propranolol and mimicked by isoprenaline or BRL-37344 and was thus mediated via beta-adrenoreceptors. The NE-induced VEGF expression was fully cAMP mediated, an effect which was inhibited by H-89 and thus was dependent on protein kinase A activity. Involvement of other adrenergic signaling pathways (alpha(1)-adrenoreceptors, Ca(2+), protein kinase C, alpha(2)-adrenoreceptors, and pertussis toxin-sensitive G(i)-proteins) was excluded. The specific inhibitor of Src tyrosine kinases, PP2, markedly reduced the stimulation by NE, which demonstrates that a cAMP-dependent Src-mediated pathway is positively connected to VEGF expression. However, inhibition of Erk1/2 MAP kinases by PD98059 was without effect. NE did not prolong VEGF mRNA half-life and its effect was thus transcriptional, and was independent of protein synthesis. These results demonstrate that adrenergic stimulation, through beta-adrenoreceptor/cAMP/protein kinase A signaling, recruits a pathway that branches off from the NE-activated Src-Erk1/2 cascade to enhance transcription of the VEGF gene.

Interaction between human monocytes and vascular smooth muscle cells induces vascular endothelial growth factor expression

The objective of this study was to investigate whether synthesis of vascular endothelial growth factor (VEGF), a major mitogen for vascular endothelial cells, was induced by a cell-to-cell interaction between monocytes and vascular smooth muscle cells (VSMCs). Human VSMCs and THP-1 cells (human monocytoid cell) were cocultured. VEGF levels in the coculture medium were determined by enzyme-linked immunosorbent assay. Northern blot analysis of VEGF mRNA was performed using a specific cDNA probe. Immunohistochemistry was performed to determine which types of cell produce VEGF. Adding THP-1 cells to VSMCs for 24 h increased VEGF levels of the culture media, 8- and 10-fold relative to those of THP-1 cells and VSMCs alone, respectively. Northern blot analysis showed that VEGF mRNA expression was induced in the cocultured cells and peaked after 12 h. Immunohistochemistry disclosed that both types of cell in the coculture produced VEGF. Separate coculture experiments revealed that both direct contact and a soluble factor(s) contributed to VEGF production. Neutralizing anti-interleukin (IL)-6 antibody inhibited VEGF production by the coculture of THP-1 cells and VSMCs. A cell-to-cell interaction between monocytes and VSMCs induced VEGF synthesis in both types of cell. An IL-6 mediated mechanism is at least partially involved in VEGF production by the cocultures. Local VEGF production induced by a monocyte-VSMC interaction may play an important role in atherosclerosis and vascular remodeling.

Human adipocyte proteomics--a complementary way of looking at fat

As little as 100 years ago, and for some of the world’s population even today, starvation was and is a predominant component of our nutritional state. Adipose evolved as an efficient energy storage depot to sustain life during such prolonged periods of fasting. However, adipose has been largely overlooked in the study of the process of controlling energy balance. Interest in adipose has increased in parallel with adiposity in modern affluent western society. In the last decade, it has become apparent that adipose is an active player in the management of energy storage, transfer and utilisation, rather than just a passive storage facility. Genomics has facilitated the renaissance of a new understanding of the repertoire of genes expressed in adipose and has supported its regulatory role in energy metabolism. However, significant differences exist between rodent and human adipose biology which have led to some unexpected failures in clinical trials. Recently, leptin showed great promise in rodents as an anti-obesity therapeutic, but has not readily translated to human therapy. We propose that the study of human adipose will greatly facilitate the understanding of human adipose pathologies and metabolic imbalances. Genomics approaches will continue to yield novel genes expressed in adipose; however, it will become increasingly important to study the expression of the proteome to relate these genes to function. We have chosen to focus this review on the secreted proteome of human adipose, as this most directly reflects the endocrine role of this tissue in metabolism.

Expression of vascular endothelial growth factors and their receptors during osteoblast differentiation

Endochondral bone formation is regulated by systemically and locally acting growth factors. A role for vascular endothelial growth factor (VEGF) in this process has recently been proposed, because inactivation of VEGF inhibits endochondral bone formation via inhibition of angiogenesis. Despite the known effect of VEGF as specific endothelial growth factor, its effects on osteoblast differentiation have not been studied. We, therefore, examined the expression of VEGF-A, -B, -C, and -D and their receptors in a model of osteoblast differentiation using the mouse preosteoblast-like cell line KS483. Early in differentiation, KS483 cells express low levels VEGF-A, -B, and -D messenger RNA, whereas during mineralization, KS483 cells express high levels. In addition, expression of the VEGF receptors, VEGFR1, VEGFR2, and VEGF165R/neuropilin, coincided with expression of their ligands, being maximally expressed during mineralization. VEGF-A production during osteoblast differentiation was stimulated by insulin-like growth factor I that enhances osteoblast differentiation and was inhibited by PTH-related peptide that inhibits osteoblast differentiation. Furthermore, continuous treatment of KS483 cells with recombinant human VEGF-A stimulated nodule formation. Although treatment of KS483 cells with soluble FLT1, an agent that blocks binding of VEGF-A and -B to VEGFR1, did not inhibit nodule formation, this observation does not exclude involvement of VEGFR2 in the regulation of osteoblast differentiation. As it is known that VEGF-A, -C, and -D can act through activation of VEGFR2, other isoforms might compensate for VEGF-A loss. The expression pattern of VEGFs and their receptors shown here suggests that VEGFs play an important role in the regulation of bone remodeling by attracting endothelial cells and osteoclasts and by stimulating osteoblast differentiation.

Lipopolysaccharide augments expression and secretion of vascular endothelial growth factor in rat ventricular myocytes

Vascular endothelial growth factor (VEGF), also known as vascular permeability factor, is highly expressed in the myocardium under various stimuli including hypoxia and ischemia. On the other hand, lipopolysaccharide (LPS) causes systemic inflammatory response syndrome (SIRS), which consists of systemic pathophysiological changes related to vascular hyperpermeability. To test the hypothesis that VEGF is one of the important mediators of SIRS, we examined effects of LPS on the VEGF expression and secretion in cultured neonatal rat ventricular myocytes. LPS (10 microg/ml) rapidly (within 1 h) augmented the levels of VEGF mRNA in these cells. Pharmacological inhibition of nucleic factor-kappaB or tyrosine kinases did not affect the LPS-induced augmentation of VEGF mRNA expression, while these treatments markedly suppressed the up-regulation of inducible nitric oxide synthase (iNOS) expression by LPS. The VEGF concentrations in the conditioned media were also significantly increased by the LPS treatment of 6 h. In conclusion, LPS augments VEGF expression and secretion in rat ventricular myocytes, suggesting that VEGF may be involved in pathogenesis of SIRS. LPS may induce VEGF mRNA through the signaling pathways that are distinct from those responsible for the iNOS induction.

Effects of intraocular or systemic administration of neutralizing antibody against vascular endothelial growth factor on the murine experimental model of retinopathy

Vascular endothelial growth factor (VEGF), the strongest known angiogenic cytokine and also a potent enhancer of vascular permeability, is closely associated with diabetic ocular complications and other intraocular neovascular diseases. The therapeutic effect of VEGF-neutralizing antibody on oxygen-induced retinopathy in an experimental murine model of proliferative retinopathy was investigated. Intraocular and systemic injection of the antibody resulted in 46% and 18% reductions in the number of nuclei of newly formed vessels of this model, respectively. The results demonstrated that a neutralizing antibody against VEGF was highly effective in the treatment of intraocular neovascularization and suggested possible modes of therapy in human intraocular neovascular diseases, including diabetic proliferative retinopathy.

Expression of vascular endothelial growth factor induces an invasive phenotype in human squamous cell carcinomas

Inhibition of the vascular endothelial growth factor (VEGF) receptor Flk-1 has been shown to prevent invasion of experimental squamous cell carcinomas (SCC). To directly investigate the role of VEGF in tumor invasion, we stably transfected human SCC-13 cells, which are characterized by a noninvasive phenotype in vivo, with expression vectors containing murine VEGF(164) in sense (SCC/VEGF+) or antisense (SCC/VEGF-) orientation or with vector alone (SCC/vec). SCC/vec cells formed slowly growing, well-differentiated tumors with well-defined borders between tumor and stroma, after intradermal or subcutaneous injection. In contrast, SCC/VEGF+ tumors were characterized by rapid tumor growth, with small cell groups and single cells invading into the surrounding tissue, and by admixture of blood vessels and tumor cells in areas of tumor invasion. We detected an increase in tumor vessel density and size in VEGF-overexpressing tumors, resulting in a more than fourfold increase in total vascular areas. In contrast, SCC/VEGF- clones formed noninvasive, sharply circumscribed tumors with reduced vascular density. These findings demonstrate that selective VEGF overexpression was sufficient to induce tumor invasiveness, and they provide further evidence for an active role of the tumor stroma in cancer progression.

Vascular endothelial growth factor (VEGF) in cartilage neovascularization and chondrocyte differentiation: auto-paracrine role during endochondral bone formation

Vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) induces endothelial cell migration and proliferation in culture and is strongly angiogenic in vivo. VEGF synthesis has been shown to occur in both normal and transformed cells. The receptors for the factor have been shown to be localized mainly in endothelial cells, however, the presence of VEGF synthesis and the VEGF receptor in cells other than endothelial cells has been demonstrated. Neoangiogenesis in cartilage growth plate plays a fundamental role in endochondral ossification. We have shown that, in an avian in vitro system for chondrocyte differentiation, VEGF was produced and localized in cell clusters totally resembling in vivo cartilage. The factor was synthesized by hypertrophic chondrocytes and was released into their conditioned medium, which is highly chemotactic for endothelial cells. Antibodies against VEGF inhibited endothelial cell migration induced by chondrocyte conditioned media. Similarly, endothelial cell migration was inhibited also by antibodies directed against the VEGF receptor 2/Flk1 (VEGFR2). In avian and mammalian embryo long bones, immediately before vascular invasion, VEGF was distinctly localized in growth plate hypertrophic chondrocytes. In contrast, VEGF was not observed in quiescent and proliferating chondrocytes earlier in development. VEGF receptor 2 colocalized with the factor both in hypertrophic cartilage in vivo and hypertrophic cartilage engineered in vitro, suggesting an autocrine loop in chondrocytes at the time of their maturation to hypertrophic cells and of cartilage erosion. Regardless of cell exposure to exogenous VEGF, VEGFR-2 phosphorylation was recognized in cultured hypertrophic chondrocytes, supporting the idea of an autocrine functional activation of signal transduction in this non-endothelial cell type as a consequence of the endogenous VEGF production. In summary we propose that VEGF is actively responsible for hypertrophic cartilage neovascularization through a paracrine release by chondrocytes, with invading endothelial cells as a target. Furthermore, VEGF receptor localization and signal transduction in chondrocytes strongly support the hypothesis of a VEGF autocrine activity also in morphogenesis and differentiation of a mesoderm derived cell.

The 3T3-L1 fibroblast to adipocyte conversion is accompanied by increased expression of angiopoietin-1, a ligand for tie2

The tie2 receptor tyrosine kinase plays a key role in angiogenesis, and the remodeling and maturation of blood vessels. In this study we have used a factor-dependent cell line (Ba/F3) expressing a chimeric receptor containing the extracellular domain of mouse tie2 and the transmembrane and cytoplasmic domain of the erythropoietin receptor to identify specific binding activity associated with an adipogenic sub-line of 3T3 fibroblasts (3T3-L1). 3T3-L1 fibroblasts are capable of undergoing differentiation to adipocytes under specific culture conditions. When compared to 3T3-L1 cells, the adipocyte differentiated cultures, which contain both pre-adipocytes and adipocytes, exhibited a significantly increased ability to support the growth of Ba/F3 cells expressing the chimeric receptor. Using probes specific for two recently described ligands for tie2, Ang-1 and Ang-2, we have shown that mRNA encoding Ang-1 is upregulated when 3T3-L1 fibroblasts are differentiated to adipocytes. These results suggest that the levels of Ang-1 protein and mRNA in 3T3-L1 cells can be regulated by cellular differentiation in adipose development.

Mice lacking HSP90beta fail to develop a placental labyrinth

The 90 kDa heat-shock proteins (HSP90s) play important roles during stress situations as general chaperones and under physiological conditions in the conformational activation of specific protein substrates. Vertebrates express two cytosolic HSP90s (HSP90alpha and HSP90beta) ubiquitously. We have mutated the Hsp90beta gene in murine embryonic stem cells and generated Hsp90beta mutant mice. Heterozygous animals were phenotypically normal. Interestingly, homozygous embryos developed normally until embryonic day 9.0/9.5. Then, although Hsp90beta is expressed ubiquitously, they exhibited phenotypic abnormalities restricted to the placenta. The mutant concepti failed to form a fetal placental labyrinth and died a day later. Fusion between the allantois and the chorionic plate occurred, allantoic blood vessels invaded the chorion, but then did not expand. Mutant trophoblast cells failed to differentiate into trilaminar labyrinthine trophoblast. Despite conspicuous similarities between HSP90alpha and HSP90beta at the molecular level, our data suggest that HSP90beta has a key role in placenta development that cannot be performed by the endogenous HSP90alpha alone. Analysis of chimeric concepti consisting of mutant embryos and tetraploid embryos or ES cells revealed that wild-type allantois was able to induce mutant trophoblast to differentiate. In contrast, trophoblast wild type at the Hsp90beta locus was unable to differentiate when in contact with mutant allantois. Therefore, the primary defect caused by the Hsp90beta mutation resided in the allantois. The allantois mesoderm is thought to induce trophoblast differentiation. Our results show that Hsp90beta is a necessary component of this induction process.

Cross talk between adipocytes and their precursors: relationships with adipose tissue development and blood pressure

Adipose tissue is an important source of angiotensinogen (AT). A possible involvement of increased plasma AT has been proposed in hypertension in obese patients, but growing evidence suggests also that the local renin-angiotensinogen system (RAS), giving rise to angiotensin II (AngII), may act as a distinct system from the plasma RAS. AngII stimulates in vitro the production and release of prostacyclin from adipocytes which in turn promotes the differentiation of precursor cells into new adipocytes (Darimont et al. 1994, Endocrinology 138: 1092-1096). Cross talk between adipocytes and precursor cells has been validated ex vivo and in vivo as (1) AngII stimulates specifically prostacyclin production, (2) both carbacyclin, a stable analogue of prostacyclin, and AngII promote the formation of new fat cells, and (3) AT (-/-) mice, which have decreased blood pressure (Tanimoto et al. 1994, J. Biol. Chem. 269: 31334-31336), exhibit both hypertrophy and hypoplasia of adipose tissue compared to wild-type mice (collaboration with Prof. A. Fukamizu, Tsukuba University, Japan). Altogether the data are consistent with an autocrine/paracrine mechanism implicating AT, AngII, and prostacyclin in adipose tissue development and suggest a new role for local AngII in addition to that of systemic AngII in blood pressure. Hormonal regulation of AT production from adipose tissue is also discussed.

Oligonucleotide NX1838 inhibits VEGF165-mediated cellular responses in vitro

VEGF (vascular endothelial growth factor) overproduction has been identified as a major factor underlying pathological angiogenesis in vivo, including such conditions as psoriasis, macular degeneration, and tumor proliferation. Endothelial cell tyrosine kinase receptors, KDR and Flt-1, have been implicated in VEGF responses including cellular migration, proliferation, and modulation of vascular permeability. Therefore, agents that limit VEGF-cellular interaction are likely therapeutic candidates for VEGF-mediated disease states (particularly agents blocking activity of VEGF165, the most frequently occurring VEGF isoform). To that end, a nuclease-resistant, VEGF165-specific aptamer NX1838 (2'-fluoropyrimidine, RNA-based oligonucleotide/40-kDa-PEG) was developed. We have assessed NX1838 inhibition of a variety of cellular events associated with VEGF, including cellular binding, signal transduction, calcium mobilization, and induction of cellular proliferation. Our data indicate that NX1838 inhibits binding of VEGF to HUVECs (human umbilical vein endothelial cells) and dose-dependently prevents VEGF-mediated phosphorylation of KDR and PLCgamma, calcium flux, and ultimately VEGF-induced cell proliferation. NX1838-inhibition of VEGF-mediated cellular events was comparable to that observed with anti-VEGF monoclonal antibody, but was ineffective as an inhibitor of VEGF121-induced HUVEC proliferation. These findings, coupled with nuclease stability of the molecule, suggest that NX1838 may provide therapeutic utility in vivo.

Vascular endothelial growth factor in pleural fluid

STUDY OBJECTIVES

The purpose of this study was to analyze the relationship of the pleural fluid vascular endothelial growth factor (VEGF) level with the diagnostic category and with the pleural fluid characteristics in a group of 70 patients.

DESIGN

The VEGF levels of consecutive patients undergoing therapeutic thoracentesis were determined with an enzyme-linked immunosorbent assay.

SETTING

University-affiliated tertiary care center.

RESULTS

The median level of pleural fluid VEGF in the patients with congestive heart failure (150 pg/mL) was significantly (p < 0.05) lower than the median level in the patients with coronary artery bypass grafting (357 pg/mL), which in turn was significantly lower (p < 0.05) than the median levels in the patients with malignancy (1,097 pg/mL). The overlap between groups, however, limits the diagnostic usefulness of pleural fluid VEGF levels. The VEGF level was most closely correlated with the lactate dehydrogenase level (r = 0.42, p < 0.001) and was also significantly correlated with the total pleural fluid protein level. The median VEGF levels in the pleural fluid of patients with breast cancer were significantly lower (p = 0.017) than in those with lung cancer. The VEGF level was very high (3,294 pg/mL) in the one patient with pulmonary embolism.

CONCLUSIONS

We conclude that the VEGF levels in pleural fluid differ significantly from one diagnostic category to another with the highest median levels occurring in patients with malignant pleural effusions. We speculate that VEGF may be responsible for the pleural fluid accumulation in at least some situations.

Role of vascular endothelial growth factor in the regulation of angiogenesis

Compelling evidence indicates that vascular endothelial growth factor (VEGF) is a fundamental regulator of normal and abnormal angiogenesis. The loss of a single VEGF allele results in defective vascularization and early embryonic lethality. VEGF plays also a critical role in kidney development, and its inactivation during early postnatal life results in the suppression of glomerular development and kidney failure. Recent evidence indicates that VEGF is also essential for angiogenesis in the female reproductive tract and for morphogenesis of the epiphyseal growth plate and endochondral bone formation. Substantial experimental evidence also implicates VEGF in pathological angiogenesis. Anti-VEGF monoclonal antibodies or other VEGF inhibitors block the growth of several human tumor cell lines in nude mice. Furthermore, the concentrations of VEGF are elevated in the aqueous and vitreous humors of patients with proliferative retinopathies such as the diabetic retinopathy. In addition, VEGF-induced angiogenesis results in a therapeutic benefit in several animal models of myocardial or limb ischemia. Currently, both therapeutic angiogenesis using recombinant VEGF or VEGF gene transfer and inhibition of VEGF-mediated pathological angiogenesis are being pursued clinically.

Transforming growth factor-beta signalling in extraembryonic mesoderm is required for yolk sac vasculogenesis in mice

We have analysed the function of transforming growth factor beta (TGF-beta) in yolk sac development in mice by generating somatic chimaeras in which the extraembryonic mesoderm, which gives rise to the endothelial and haematopoietic cells of the yolk sac vasculature, is derived from embryonic stem (ES) cells. The ES cells were stably transfected and express either the full-length type II binding receptor or a kinase-deficient mutant of this receptor. Examination of yolk sacs from chimaeras between E8.5 and 9.5, and analysis of marker expression in embryoid bodies from these mutant ES cell lines in prolonged suspension culture demonstrated that (1) a major function of TGF-beta in yolk sac mesoderm is to regulate production and deposition of fibronectin in the extracellular matrix that maintains yolk sac integrity, (2) TGF-beta signalling is not required for differentiation of extraembryonic mesoderm into endothelial cells but is necessary for their subsequent organisation into robust vessels, and (3) TGF-beta signalling must be tightly regulated for the differentiation of primitive haematopoietic cells to take place normally. Together, these results show that defective TGF-beta signalling in the extraembryonic mesoderm alone is sufficient to account for the extraembryonic phenotype reported previously in TGF-beta1(−/−) mice (Dickson, M. C., Martin, J. S., Cousins, F. M., Kulkarni, A. B., Karlsson, S. and Akhurst, R. J. (1995) Development 121, 1845–1854).

Adenosine upregulates VEGF expression in cultured myocardial vascular smooth muscle cells

We tested whether adenosine has differential effects on vascular endothelial growth factor (VEGF) expression under normoxic and hypoxic conditions, and whether A(1) or A(2) receptors (A(1)R; A(2)R) mediate these effects. Myocardial vascular smooth muscle cells (MVSMCs) from dog coronary artery were exposed to hypoxia (1% O(2)) or normoxia (20% O(2)) in the absence and presence of adenosine agonists or antagonists for 18 h. VEGF protein levels were measured in media with ELISA. VEGF mRNA expression was determined with Northern blot analysis. Under normoxic conditions, the adenosine A(1)R agonists, N(6)-cyclopentyladenosine and R(-)-N(6)-(2-phenylisopropyl)adenosine did not increase VEGF protein levels at A(1)R stimulatory concentrations. However, adenosine (5 microM) and the adenosine A(2)R agonist N(6)-[2-(3, 5-dimethoxyphenyl)-2-(2-methylphenyl)]ethyl adenosine (DPMA; 100 nM) increased VEGF protein levels by 51 and 132% and increased VEGF mRNA expression by 44 and 90%, respectively, in cultured MVSMCs under normoxic conditions. Hypoxia caused an approximately fourfold increase in VEGF protein and mRNA expression, which could not be augmented with exogenous adenosine, A(2)R agonist (DPMA), or A(1)R agonist [1,3-diethyl-8-phenylxanthine (DPX)]. The A(2)R antagonist 8-(3-chlorostyryl)-caffeine completely blocked adenosine-induced VEGF protein and mRNA expression and decreased baseline VEGF protein levels by up to approximately 60% under normoxic conditions but only by approximately 25% under hypoxic conditions. The A(1)R antagonist DPX had no effect. These results are consistent with the hypothesis that 1) adenosine increases VEGF protein and mRNA expression by way of A(2)R. 2) Adenosine plays a major role as an autocrine factor regulating VEGF expression during normoxic conditions but has a relatively minor role during hypoxic conditions. 3) Endogenous adenosine can account for the majority of basal VEGF secretion by MVSMCs under normoxic conditions and could therefore be a maintenance factor for the vasculature.

Role of angiogenic factors: coexpression of interleukin-8 and vascular endothelial growth factor in patients with head and neck squamous carcinoma

OBJECTIVE/HYPOTHESIS

Angiogenesis has been used as a prognostic indicator in a variety of cancers and is believed to be controlled by angiogenic factors, including the cytokines interleukin-8 (IL-8) and vascular endothelial growth factor (VEGF). We hypothesized that the in vivo coexpression of both IL-8 and VEGF in head and neck tumors contributes to perpetuating tumor growth and metastasis by enhancing angiogenesis.

METHODS

Immunohistochemical analysis for IL-8 and VEGF was performed using specimens from 33 cancer patients and 6 control patients. We quantitatively evaluated levels of IL-8 and VEGF in tumor tissue homogenates from those same patients using enzyme-linked immunosorbent assay and radioimmunoassay. Comprehensive histories of each patient were taken and later analyzed for clinical correlations with IL-8 or VEGF levels.

RESULTS

IL-8 and VEGF were found to be colocalized within the head and neck squamous cell carcinoma (HNSCCA) tumor cells. In the head and neck tumor specimens, IL-8 levels ([38,152+/-1.8]x10(5) pg/mg total protein [TP]) were 22-fold greater than controls (1,721+/-2,122 pg/mg TP). The tumor levels of VEGF (1,304+/-6,037 pg/mg TP) were nearly fourfold higher than the controls (317+/-400 pg/mg TP. Interleukin-8 and VEGF levels were found to have a positive correlation (P< or = .0001). Patients exhibiting high levels in picograms per milligram of TP and/or number of moles of IL-8 and VEGF were found to clinically have more aggressive disease manifested by higher TNM stage, more recurrences, and shorter disease-free intervals (P< or =.03)

CONCLUSIONS

Marked increase in HNSCCA of IL-8 and VEGF underscores the importance of these angiogenic factors in this disease. Understanding the roles and interplay of angiogenic factors such as IL-8 and VEGF may have value in the treatment of HNSCCA.

Roles of trk family neurotrophin receptors in medullary thyroid carcinoma development and progression

Although initiating mutations in the ret protooncogene have been found in familial and sporadic medullary thyroid carcinoma (MTC), the molecular events underlying subsequent tumor progression stages are unknown. We now report that changes in trk family neurotrophin receptor expression appear to be involved in both preneoplastic thyroid C cell hyperplasia and later tumor progression. Only a subset of normal C cells expresses trk family receptors, but, in C cell hyperplasia, the affected cells consistently express trkB, with variable expression of trkA and trkC. In later stages of gross MTC tumors, trkB expression was substantially reduced, while trkC expression was increased and often intense. In a cell culture model of MTC, exogenous trkB expression resulted in severely impaired tumorigenicity and was associated with 11-fold lower levels of the angiogenesis factor vascular endothelial growth factor. These results suggest that trk family receptor genes participate in MTC development and progression, and, in particular, that trkB may limit MTC tumor growth by inhibition of angiogenesis.

Expression of vascular endothelial growth factor promotes colonization, vascularization, and growth of transplanted hepatic tissues in the mouse

A complex vascular network forms an important component of the liver architecture. This network is essential for the supply of oxygen and nutrients to cells and delivery of molecules for metabolic exchange. In this study, we attempted to construct a vascular network in transplanted hepatic tissues and examined the effect of such network on tissue formation. Primary hepatocytes of adult mice were transfected with vascular endothelial growth factor (VEGF) gene in vitro then transplanted with collagen beads intraperitoneally in mice. VEGF-transfected hepatocytes secreted sufficient protein of the transgene in vitro to induce proliferation of endothelial cells. In vivo, VEGF-transfected hepatocytes formed a large number of colonies and developed a significant vascular network in established tissues compared with control tissues. In addition, hepatocytes of VEGF-transfected, established tissues proliferated and formed a substantial parenchymal region. These hepatocytes were also functional as confirmed by the production of albumin. Our results suggested that VEGF expression conferred not only the formation of a vascular network but also promoted tissue formation. Our study showed that ex vivo gene transfection into hepatocytes is a useful method for the induction of liver reconstitution in vivo.

Systemic hypoxia changes the organ-specific distribution of vascular endothelial growth factor and its receptors

Vascular endothelial growth factor (VEGF) plays a key role in physiological blood vessel formation and pathological angiogenesis such as tumor growth and ischemic diseases. Hypoxia is a potent inducer of VEGF in vitro. Here we demonstrate that VEGF is induced in vivo by exposing mice to systemic hypoxia. VEGF induction was highest in brain, but also occurred in kidney, testis, lung, heart, and liver. In situ hybridization analysis revealed that a distinct subset of cells within a given organ, such as glial cells and neurons in brain, tubular cells in kidney, and Sertoli cells in testis, responded to the hypoxic stimulus with an increase in VEGF expression. Surprisingly, however, other cells at sites of constitutive VEGF expression in normal adult tissues, such as epithelial cells in the choroid plexus and kidney glomeruli, decreased VEGF expression in response to the hypoxic stimulus. Furthermore, in addition to VEGF itself, expression of VEGF receptor-1 (VEGFR-1), but not VEGFR-2, was induced by hypoxia in endothelial cells of lung, heart, brain, kidney, and liver. VEGF itself was never found to be up-regulated in endothelial cells under hypoxic conditions, consistent with its paracrine action during normoxia. Our results show that the response to hypoxia in vivo is differentially regulated at the level of specific cell types or layers in certain organs. In these tissues, up- or down-regulation of VEGF and VEGFR-1 during hypoxia may influence their oxygenation after angiogenesis or modulate vascular permeability.

Hypoxia-mediated regulation of gene expression in mammalian cells

The molecular mechanism underlying oxygen sensing in mammalian cells has been extensively investigated in the areas of glucose transport, glycolysis, erythropoiesis, angiogenesis and catecholamine metabolism. Expression of functionally operative representative proteins in these specific areas, such as the glucose transporter 1, glycolytic enzymes, erythropoietin, vascular endothelial growth factor and tyrosine hydroxylase are all induced by hypoxia. Recent studies demonstrated that both transcriptional activation and post-transcriptional mechanisms are important to the hypoxia-mediated regulation of gene expression. In this article, the cis-acting elements and trans-acting factors involved in the transcriptional activation of gene expression will be reviewed. In addition, the mechanisms of post-transcriptional mRNA stabilization will also be addressed. We will discuss whether these two processes of regulation of hypoxia-responsive genes are mechanistically linked and co-operative in nature.

VEGF gene delivery to muscle: potential role for vasculogenesis in adults

Constitutive expression of VEGF after implantation of genetically engineered myoblasts into non-ischemic muscle led to an increase in vascular structures. Previously, effects of VEGF delivery to adult muscle have only been reported in ischemic tissues. The resulting vascular structures were reminiscent of those formed during embryonic vasculogenesis, rather than angiogenesis, sprouting from preexisting vessels. Initially, VEGF caused an accumulation of endothelial cells and macrophages, followed by networks of vascular channels and hemangiomas with locally high serum VEGF levels. No effects were evident in adjacent tissue or contralateral legs, where low serum VEGF was detected. These data suggest that the induction by VEGF of angiogenesis or vasculogenesis may be dose-dependent. Furthermore, VEGF expression must be carefully modulated, as overexpression is deleterious.

Evidence for mRNA expression of vascular endothelial growth factor by X-ray irradiation in a lung squamous carcinoma cell line

Vascular endothelial growth factor (VEGF) is a multipotent cytokine which plays an important role in various angiogenic conditions as well as in some tumor behaviors. Here we examined the induction of VEGF mRNA by X-ray irradiation in a lung squamous cell carcinoma cell line (RERF-LC-AI). Irradiating the cells with 15 Gy X-rays significantly increased the mRNA expression up to 2.5-fold of control at a post-irradiation time of 16-24 h. The induction of VEGF mRNA by X-ray irradiation was completely blocked by treating cells with either genistein (Src tyrosine kinase inhibitor) or H7 (protein kinase C inhibitor). This suggests that the mechanism of induction might be concerned with the pathway which triggers Src tyrosine kinase of the cell surface and the protein kinase C pathway.

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.

Mast cells can secrete vascular permeability factor/ vascular endothelial cell growth factor and exhibit enhanced release after immunoglobulin E-dependent upregulation of fc epsilon receptor I expression

Vascular permeability factor/vascular endothelial cell growth factor (VPF/VEGF) can both potently enhance vascular permeability and induce proliferation of vascular endothelial cells. We report here that mouse or human mast cells can produce and secrete VPF/VEGF. Mouse mast cells release VPF/VEGF upon stimulation through Fcepsilon receptor I (FcepsilonRI) or c-kit, or after challenge with the protein kinase C activator, phorbol myristate acetate, or the calcium ionophore, A23187; such mast cells can rapidly release VPF/VEGF, apparently from a preformed pool, and can then sustain release by secreting newly synthesized protein. Notably, the Fc epsilonRI-dependent secretion of VPF/VEGF by either mouse or human mast cells can be significantly increased in cells which have undergone upregulation of Fc epsilonRI surface expression by a 4-d preincubation with immunoglobulin E. These findings establish that at least one cell type, the mast cell, can be stimulated to secrete VPF/VEGF upon immunologically specific activation via a member of the multichain immune recognition receptor family. Our observations also identify a new mechanism by which mast cells can contribute to enhanced vascular permeability and/or angiogenesis, in both allergic diseases and other settings.

Hypoxia and endothelin-1 induce VEGF production in human vascular smooth muscle cells

Vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) is a secreted mitogen for vascular endothelial cells, and it promotes vascular permeability and neovascularization in vivo. We investigated the mechanisms by which low oxygen tension modulates the expression of VEGF in human aortic vascular smooth muscle cells (h-SMC) in vitro. Moreover, we measured VEGF levels in the cultured medium with or without endothelin-1 (ET-1) using a newly developed, highly sensitive, enzyme-linked immunosorbent assay. Hypoxia resulted in a substantial induction of VEGF transcripts at 3 and 24 hr. VEGF levels were significantly higher when h-SMC were cultured in medium containing ET-1 than when cultured in medium without ET-1. In conclusion, hypoxia and ET-1 constitute potent stimuli for VEGF production in h-SMC.

Stimulatory interaction between vascular endothelial growth factor and endothelin-1 on each gene expression

The precise regulation of cell growth in the vascular wall maintains vascular integrity, and its disruption leads to cardiovascular disorders including atherosclerosis and restenosis. Vascular endothelial growth factor (VEGF) is a specific mitogen for endothelial cells, and endothelin-1 (ET-1) is known to stimulate the proliferation of smooth muscle cells. The aim of this study was to explore a potential interaction between VEGF and ET-1 on each expression in vascular cells. VEGF enhanced preproET-1 mRNA expression and ET-1 secretion in bovine aortic endothelial cells (BAECs). Similarly, in rat vascular smooth muscle cells (VSMCs), ET-1 enhanced VEGF mRNA expression and stimulated VEGF secretion. ET-1-induced VEGF mRNA expression was abolished by a selective ET(A) receptor antagonist, BQ-485, but not by an ET(B)-selective blocker, BQ-788. It was also inhibited by pretreatment with actinomycin D but not by pretreatment with cycloheximide. Furthermore, the actinomycin D chase experiment revealed that ET-1 did not alter VEGF mRNA stability. Coculture of BAECs and VSMCs enhanced both ET-1 and VEGF gene expression in these cells, and the conditioned media from BAECs and VSMCs reproduced the augmentation of each gene expression, which was partially inhibited by BQ-485 or an antibody specific to VEGF. Our results indicate that VEGF and ET-1 have stimulatory interactions on each expression, which may play an important role in concomitant proliferation of endothelial and smooth muscle cells in the vascular wall.

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.

Upregulation of vascular endothelial growth factor by angiotensin II in rat heart endothelial cells

Vascular endothelial growth factor (VEGF) is a potent mitogen for endothelial cells and a vascular permeability factor. In this study we found that the addition of angiotensin II (AII) to rat heart endothelial cells induced VEGF mRNA production. VEGF mRNA levels reached a plateau within 2 h after the addition of AII and decreased after 4 h. The induction was superinduced by cycloheximide and blocked by actinomycin D. Losartan, an AT1 receptor antagonist, abolished the induction of VEGF mRNA by AII, whereas PD 123319, an AT2 receptor antagonist, had no effect on VEGF mRNA induction. H7, a protein kinase C inhibitor, blocked the induction. RT-PCR experiments showed two mRNA species (VEGF 120 and VEGF 164) in these cells and both species were stimulated by AII. Transient transfection experiment showed that VEGF promoter activity was increased 2.2-fold upon AII stimulation. Electrophoretic mobility shift assay revealed an enhanced binding of transcription factors AP-1 and NF-kappa B. Immunoblot analysis showed that the amount of secreted VEGF was elevated in the medium 8 h after AII stimulation. Our results demonstrate for the first time that the upregulation of VEGF by AII may play a significant role in AII-induced hyperpermeability.

A novel alternatively spliced form of murine vascular endothelial growth factor, VEGF 115

Murine immortal fibroblasts express a form of vascular endothelial growth factor (VEGF) that was cloned, characterized and named VEGF 115. It differs from VEGF 120 by 37 amino acids at the carboxyl terminus. VEGF 115-specific sequence reacted to a single transcript in mouse tissues. Reverse transcription-polymerase chain reaction was performed in mouse tissues and in fibroblasts of normal and immortal divisional phenotypes. The data from mouse tissues suggested that VEGF 115 is not a tissue-specific isoform of VEGF 120, whereas a functional relevance with immortalization is indicated from the latter. The novel cDNA was expressed in Escherichia coli, and the His-tagged VEGF 115 (17.2 kDa) thus obtained was recognized by anti-VEGF antibody. A mammalian expression plasmid, pCMVneo+, encoding for VEGF 115 was transfected to NIH 3T3 cells, and the conditioned medium of stable transfectants was found to have fibroblast growth factor-replacing activity for human umbilical vein endothelial cells. Two independent genomic P1 clonings with primers specific for VEGF 164 and VEGF 115, respectively, resulted in isolation of identical P1 clones. We analyzed these three P1 clones on Southern blots with common and specific probes for VEGF 164 and VEGF 115. The results support the hypothesis that VEGF 115 is a new alternatively spliced form of mouse VEGF.

Human FIGF: cloning, gene structure, and mapping to chromosome Xp22.1 between the PIGA and the GRPR genes

We report the identification, structural characterization, and mapping of the human FIGF gene. FIGF is the human homologue of mouse figf (c-fos-induced growth factor), a new member of the platelet-derived growth factor/vascular endothelial growth factor (PDGF/VEGF) family. It codes for a secreted factor with mitogenic and morphogenic activity on fibroblast cells. The predicted amino acid sequence of FIGF is 84% identical to that of the mouse protein, and it is highly conserved (up to 40%) in the dimerization domain with respect to the VEGF members of the family. The 2.5-kb mRNA of FIGF was detected in adult lung and heart tissues. The gene spans about 50 kb and is organized into seven exons and six introns. The FIGF promoter contains an optimal AP-1-binding site and lacks a canonical TATA box. Fluorescence in situ hybridization mapped FIGF to chromosomal region Xp22.1. The subsequent identification of YAC positive clones from this region allowed us to refine the map and localize FIGF centromeric to the phosphatidylinositol glycan complementation class A (PIGA) gene and telomeric to the gastrin-releasing peptide receptor (GRPR) gene. FIGF and PIGA genes lie next to each other in a head-to-tail orientation, with the FIGF polyadenylation signal about 12 kb from the PIGA transcriptional start site.

Vascular endothelial growth factor mRNA in pericytes is upregulated by phorbol myristate acetate

Increased microvascular permeability, which occurs in conditions such as the adult respiratory distress syndrome and diabetes mellitus, is related to physicochemical alterations in the microvascular barrier. We postulate that, in part, capillary pericytes affect microvascular permeability via production of a vasoactive cytokine, viz, vascular endothelial growth factor (VEGF), also known as vascular permeability factor. The goal of the present study was to evaluate the effects of phorbol myristate acetate (PMA), a substance known to produce nonhydrostatic pulmonary edema in intact animals, on VEGF gene expression in pericyte cultures. Microvascular pericytes were isolated from bovine retinas using magnetic microspheres coated with 3G5 monoclonal antibody. Pericyte identity was confirmed both morphologically and by immunostaining for alpha-smooth muscle actin and 3G5 ganglioside. The cultured pericytes were stimulated with N(omega)-nitro-L-arginine methyl ester (L-NAME, 1 x 10(-4) mmol/L), angiotensin II (1 x 10(-6) mmol/L), and PMA (5 x 10(-8) mmol/L), selected because of their ability to upregulate VEGF mRNA expressions in other cell types. Northern blot analysis was performed using [32P]dCTP labeled human VEGF cDNA (Genentech). Lane-loading differences were normalized using mouse GAPDH control cDNA probe. VEGF mRNA expression was upregulated by PMA (10(-9) to 10(-6) mol/L) in a dose-dependent manner, whereas neither L-NAME nor angiotensin II affected VEGF mRNA expression in pericytes. These results support the hypothesis that pericytes increase permeability of the endothelial barrier through increased VEGF production.

Prostaglandins induce vascular endothelial growth factor in a human monocytic cell line and rat lungs via cAMP

Prostaglandins have emerged as a therapeutic option for patients with peripheral vascular disease as well as pulmonary hypertension as a means to increase blood flow. We tested the hypothesis that prostaglandins regulate vascular endothelial growth factor (VEGF) expression in the human monocytic THP-1 cell line and in isolated perfused rat lungs. Our data show that the stable PGI2-analogue iloprost induces VEGF gene expression (predominantly VEGF121, but also VEGF165 isoforms) and VEGF protein synthesis in THP-1 cells. This effect is abolished by dexamethasone and by Rp-cAMP, a specific inhibitor of cAMP-dependent protein kinase (PKA) activation. The calcium channel blocker diltiazem has no effect on the iloprost-induced VEGF gene expression, and depletion of intracellular Ca2+ stores by long-term exposure (16 h) of THP-1 cells to thapsigargin does not inhibit iloprost-induced VEGF gene expression, suggesting that an increase in intracellular Ca2+ is not essential for VEGF gene induction by iloprost. However, an increase of intracellular Ca2+ by a short-term (2 h) exposure of THP-1 cells to thapsigargin or to the calcium-ionophore A23187 increases VEGF mRNA levels, indicating that a change in intracellular Ca2+ by itself can alter VEGF gene expression. The effects of thapsigargin or A23187 on VEGF gene expression are also mediated via cAMP-PKA since they are inhibited by Rp-cAMP. In isolated perfused rat lungs, PGI2 and PGE2 increases VEGF mRNA abundance whereas Rp-cAMP inhibits the prostaglandin-induced VEGF gene activation. Thus, our data suggest that prostaglandins stimulate VEGF gene expression in monocytic cells and in rat lungs via a cAMP-dependent mechanism.

Vascular endothelial growth factor, placenta growth factor and their receptors in isolated human trophoblast

The expression of the angiogenic growth factors, vascular endothelial cell growth factor (VEGF) and placenta growth factor (PIGF) was demonstrated in isolated human term cytotrophoblast and in vitro differentiated syncytiotrophoblast. RNase protection assays demonstrated VEGF expression in both cytotrophoblast and syncytiotrophoblast while prominent PIGF expression was detected in both types of trophoblast by Northern blot analyses. VEGF expression increased approximately eightfold in trophoblast cultured under hypoxic conditions (1 per cent O2) yet PIGF expression decreased 73 +/- 5.5 per cent in the same trophoblast. These results suggest distinct regulatory mechanisms govern expression of VEGF and PIGF in trophoblast. Characterization of the VEGF/PIGF receptors, KDR and flt-1, revealed the presence of flt-1 mRNA in isolated cytotrophoblast and in vitro differentiated syncytiotrophoblast. KDR was not detected in the isolated trophoblast. Exogenous rhVEGF induced c-Jun N-terminal kinase (JNK) activity in the normal trophoblast indicating that the flt-1 receptors on trophoblast are functional. Trophoblast-derived VEGF/PIGF could act in a paracrine fashion to promote uterine angiogenesis and vascular permeability within the placental bed. In addition, presence of function flt-1 on normal trophoblast suggests that VEGF/PIGF functions in an autocrine manner to perform an as yet undefined role in trophoblast invasion, differentiation, and/or metabolic activity during placentation.

Vascular endothelial growth factor expression in head and neck squamous cell carcinoma

BACKGROUND

Angiogenesis is an essential process required for growth and metastasis in cancer. In breast, gastric, and prostate cancer, vascular endothelial growth factor (VEGF) has been implicated in angiogenesis; however, little is known about VEGF in HNSCC. In this study, we hypothesize that VEGF is present in elevated levels in HNSCC and may therefore play a role in promoting angiogenesis.

METHODS

We obtained tumor tissue from 63 HNSCC patients undergoing primary resection. All tissue samples were analyzed by immunohistochemistry (IHC) techniques for the presence and localization of VEGF; however, only 36 had sufficient amounts of tissue for quantitative analysis of VEGF by ELISA. Nine control specimens taken from patients undergoing uvulopalatopharyngoplasty were also analyzed.

RESULTS

In all 63 of our patient samples we found VEGF to be present and localized to the cancer cells and endothelial cells. The poorly differentiated cancer cells stained more intensely in comparison with the well-differentiated ones. There was a 20-fold increase in the patient levels when compared with controls levels (P > or =0.05). Analysis by enzyme-linked immunosorbent assay revealed elevated mean levels of VEGF (241 +/- 326 pg/mg total protein [TP]) with a range of 2 to 1484 pg/mg TP. The control specimens had mean levels of 13 +/- 11 pg/mg TP and a range of 1 to 78 pg/mg TP. Patients who exhibited higher levels of VEGF tended to have a higher rate of disease recurrence (P < or =0.048) and shorter disease-free interval (P < or =0.05).

CONCLUSIONS

The expression of VEGF in elevated levels in the HNSCC tumor microenvironment appears to be associated with more aggressive disease. Based on our results, VEGF may be an important angiogenic factor associated with cancer cells and endothelial cells in HNSCC. Further studies are needed to better define the role of VEGF in HNSCC and its role as a potential target for therapeutic intervention.

Contact allergens and sodium lauryl sulphate upregulate vascular endothelial growth factor in normal keratinocytes

In allergic and irritant contact dermatitis, keratinocytes are major target cells that can be activated to take part in local reactions by secreting soluble mediators. Among the growth factors produced by keratinocytes, vascular endothelial growth factor (VEGF) is a powerful inducer of permeability of endothelial cells, and is involved in inflammation. We determined whether different contact allergens, dinitrosulphobenzene (DNSB), para-phenylenediamine (pPD) and the metals nickel and chromium, as distinct from cobalt, which has been shown to mimic the effects of hypoxia, can modify the basal level of VEGF in normal human keratinocytes when tested at various, non-toxic concentrations. The effects of an irritant, sodium lauryl sulphate (SLS), and of hydrocortisone were also tested. Our results showed an intense dose-dependent upregulation of VEGF release by keratinocytes after treatments by metals, pPD and SLS. DNSB induced only a moderate increase of VEGF. Hydrocortisone reduced the basal level as well as the nickel-induced upregulation of VEGF. These findings suggest that contact allergens and irritants probably upregulate VEGF in keratinocytes by different mechanisms and may contribute directly to the microvascular hyperpermeability which characterizes both contact and irritant dermatitis.

Molecular cloning of a novel vascular endothelial growth factor, VEGF-D

We have identified and characterized a novel vascular endothelial growth factor (VEGF), VEGF-D, which is structurally related to vascular endothelial growth factor C. A full-length cDNA for human VEGF-D was cloned following the identification of an EST obtained through a TFASTA search of public EST databases. The murine VEGF-D was subsequently isolated from a mouse lung cDNA library. The human VEGF-D gene was mapped to human chromosome Xp22.31. Both human and mouse VEGF-D are strongly expressed in lung and encode the eight cysteine residues that are highly conserved among the members of this family. The high level of conservation between mouse and human VEGF-D may emphasize the biological importance of this gene. Recently the murine gene, FIGF, which is identical to mouse VEGF-D, was reported.