VEGF121, a vascular endothelial growth factor (VEGF) isoform lacking heparin binding ability, requires cell-surface heparan sulfates for efficient binding to the VEGF receptors of human melanoma cells

Vascular endothelial growth factor 121 and 165 in the subacromial bursa are involved in shoulder joint contracture in type II diabetics with rotator cuff disease

Vascular endothelial growth factor (VEGF) is a glycoprotein that plays an important role in neovascularization and increases vascular permeability. We reported that VEGF is involved in motion pain of patients with rotator cuff disease by causing synovial proliferation in the subacromial bursa (SAB). The present study investigates whether VEGF is also involved in the development of shoulder contracture in diabetics with rotator cuff disease. We examined 67 patients with rotator cuff disease, including 36 with complete cuff tears, 20 with incomplete tears, and 11 without apparent tears (subacromial bursitis). The patients were into groups according to the presence or absence of diabetes (14 type II diabetics and 53 non-diabetics). Specimens of the synovium of the SAB were obtained from all patients during surgery. Expression of the VEGF gene in the synovium of the subacromial bursa was evaluated by using the reverse transcriptase polymerase chain reaction. The VEGF protein was localized by immunohistochemistry, and the number of vessels was evaluated based on CD34 immunoreactivity. The results showed that VEGF mRNA was expressed in significantly more diabetics (100%, 14/14) than in non-diabetics (70%, 37/53) (P=0.0159, Fisher's test). Investigation of VEGF isoform expression revealed VEGF121 in all 14 diabetics and in 37 of the 53 non-diabetics, VEGF165 in 12 of the 14 diabetics and in 21 of the 53 non-diabetics, and VEGF189 in 1 of the 14 diabetics and in 2 of the 53 non-diabetics. No VEGF206 was expressed in either group. VEGF protein was localized in both vascular endothelial cells and synovial lining cells. The mean number of VEGF-positive vessels and the vessel area were also significantly greater in the diabetics (p<0.015, Mann-Whitney U test). Synovial proliferation and shoulder joint contracture were more common in the diabetics (P=0.0329 and P=0.073, respectively; Fisher's test). The mean preoperative range of shoulder motion significantly differed in terms of elevation between two groups: 103.8 degrees in diabetics and 124.9 degrees in no diabetics (p=0.0039 Mann-Whitney U test). In contrast, external rotation did not significantly differ: 44 degrees in diabetics and 49 degrees in non-diabetics (p=0.4957, Mann-Whitney U test). These results suggest that VEGF121 and VEGF165 expression in the SAB is responsible for the development of shoulder joint contracture, especially in elevation, among type II diabetic patients with rotator cuff disease.

Tumour vascular endothelial growth factor (VEGF) mRNA in relation to serum VEGF protein levels and tumour progression in human renal cell carcinoma

Angiogenesis is gaining interest because of its importance in tumour growth and metastasis. Renal cell carcinoma (RCC) is known to be a well-vascularized tumour. The aim of this study was to evaluate the expression of VEGF mRNA and receptor flt-1 mRNA (VEGF R1) in a clinical material of RCCs compared with clinicopathological variables and serum VEGF levels. Total RNA was extracted from snap-frozen tumour tissue obtained from 61 patients. Expression of mRNA for VEGF121, VEGF165 and flt-1 were analysed using quantitative RT-PCR. Relative VEGF mRNA levels, corrected for corresponding cyclophilin value, were related to stage, grade, RCC type and survival time. Serum VEGF165 protein was analysed using a quantitative ELISA. Papillary RCC had significantly lower VEGF121 and flt-1 mRNA levels compared with conventional RCC (p=0.001). VEGF121 mRNA levels were significantly lower in locally advanced tumours in relation to tumours limited to the kidney and those with metastatic disease (p=0.047 and p=0.036). This statistical difference disappeared when only conventional RCCs were evaluated. No association was found between VEGF mRNA levels and nuclear grade. Patients with lower VEGF121 mRNA levels had significantly longer survival time compared with those with higher levels (when adjusted to stage, p=0.0097, log rank test). There was an inverse relation between VEGF165 mRNA and serum VEGF165 levels. The trend to lower VEGF121 mRNA levels in locally advanced RCC indicate that angiogenic activity and degradation might be up-regulated in tumours with a high ability to invade. The association with tumour progression shows that VEGF is a promising angiogenic factor especially important in conventional RCCs. VEGF expression might possibly be of help to identify RCCs susceptible for anti-angiogenic therapies.

Differential expression of vascular endothelial growth factor-A isoforms at different stages of melanoma progression

Vascular endothelial growth factor-A (VEGF-A) is an important mediator of angiogenesis in normal and neoplastic tissues. Total VEGF-A levels have been associated with melanoma progression, but the relative contributions of each isoform is unknown. To determine whether differences in the production of any or all of the major VEGF-A isoforms are related to stage of progression, we compared message levels for the three major isoforms of VEGF in melanoma specimens from different stages of progression.Primary melanomas (N = 18), primary recurrences (N = 5), regional dermal metastases (N = 11), nodal metastases (N = 12), normal lymph nodes (N = 18), and distant metastases (N = 9) were prospectively collected. Samples from the horizontal and vertical growth phases of primary tumors were also collected from five additional patients. Message levels for the three major VEGF-A isoforms were measured using real-time quantitative reverse-transcriptase polymerase chain reaction and normalized to beta-actin mRNA levels. There was a marked increase in the expression of all three VEGF-A isoforms from the vertical growth phase tissue as compared with the horizontal growth phase tissue. Primary tumors, local recurrences, regional dermal metastases, nodal metastases, and distant metastases all produced more VEGF(121) and VEGF(165) than negative nodes. Nodal metastases produced the highest level of these two isoforms, higher even than distant metastases. There was no significant difference in VEGF(189) message among the groups. Melanomas in the vertical growth phase produce more VEGF-A (all isoforms) than in the horizontal growth phase. Nodal metastases produce the highest levels of VEGF(121) and VEGF(165), but not VEGF(189) as compared with other stages of progression. These data suggest that the soluble forms of VEGF-A might be an important factor in melanoma metastasis to regional lymph nodes.

Targeted in vivo labeling of receptors for vascular endothelial growth factor: approach to identification of ischemic tissue

BACKGROUND

A method for identifying tissue experiencing hypoxic stress due to atherosclerotic vascular disease would be clinically useful. Vascular endothelial growth factor-121 (VEGF121) is an angiogenic protein secreted in response to hypoxia that binds to VEGF receptors overexpressed by ischemic microvasculature. We tested the hypothesis that VEGF receptors could serve as markers for ischemic tissue and hence provide a target for imaging such tissue with radiolabeled human VEGF121.

METHODS AND RESULTS

A rabbit model of unilateral hindlimb ischemia was created by femoral artery excision (n=14). Control rabbits (n=5) underwent identical surgery without femoral excision. On postoperative day 10, rabbits were intravenously administered 100 microCi of 111In-labeled recombinant human VEGF121, and biodistribution studies and planar imaging were conducted at 3, 24, and 48 hours. On postmortem gamma counting, there was greater accumulation of 111In-labeled VEGF121 in ischemic than in control tissue (P<0.02). Differential uptake of isotope by ischemic muscle was not seen in rabbits injected with 125I-labeled human serum albumin (n=6). Radioactivity imaged in hindlimb regions of interest was significantly higher in ischemic muscle than in sham-operated and contralateral nonoperated hindlimb at 3 hours (P<0.02). Immunohistochemical staining confirmed upregulation of VEGF receptors in ischemic skeletal muscle.

CONCLUSIONS

Identification of the ischemic state via targeted radiolabeling of hypoxia-induced angiogenic receptors is possible. This approach could be useful for monitoring the efficacy of revascularization strategies such as therapeutic angiogenesis.

Basement membranes: structure, assembly and role in tumour angiogenesis

In recent years, the basement membrane (BM)--a specialized form of extracellular matrix (ECM)--has been recognized as an important regulator of cell behaviour, rather than just a structural feature of tissues. The BM mediates tissue compartmentalization and sends signals to epithelial cells about the external microenvironment. The BM is also an important structural and functional component of blood vessels, constituting an extracellular microenvironment sensor for endothelial cells and pericytes. Vascular BM components have recently been found to be involved in the regulation of tumour angiogenesis, making them attractive candidate targets for potential cancer therapies.

Bone tissue engineering: recent advances and promising therapeutic agents

Bone regeneration can be accomplished with growth factors, cells and delivery systems. This review is a summary of these components that may be used for tissue regeneration. Support for the potential therapeutic applications of transcription factors in bone tissue engineering will also be discussed.

VEGF162, a new heparin-binding vascular endothelial growth factor splice form that is expressed in transformed human cells

The splice forms of vascular endothelial growth factor (VEGF) differ in biological properties such as the receptor types that they recognize and their interaction with heparan sulfate proteoglycans. We have identified a new VEGF mRNA splice form encoding a VEGF species containing 162 amino acids (VEGF(162)) in human A431 ovarian carcinoma cells. This novel mRNA contains the peptides encoded by exons 1-5, 6A, 6B, and 8 of the VEGF gene. Recombinant VEGF(162) is biologically active. It induces proliferation of endothelial cells in vitro and angiogenesis in vivo as determined by the alginate bead assay. VEGF(162) binds less efficiently than VEGF(145) but more efficiently than VEGF(165) to a natural basement membrane produced by corneal endothelial cells. VEGF(138), an artificial VEGF form that contains exon 6B but lacks exons 6A and 7, did not bind to this basement membrane at all, indicating that exon 6B probably interferes with the interaction of exon 6A with heparin and heparan sulfate proteoglycans.

Vector-based RNAi, a novel tool for isoform-specific knock-down of VEGF and anti-angiogenesis gene therapy of cancer

Vascular endothelial growth factor (VEGF) carries out multifaceted functions in tumor development, and it exists as at least five isoforms with distinct biologic activities and clinical implications. Several strategies have been developed to block VEGF for cancer therapy; however, the approach to target-specific VEGF isoform(s) has not been explored to date. In the present study, we show that DNA vector-based RNA interference (RNAi), in which RNAi sequences targeting murine VEGF isoforms are inserted downstream of an RNA polymerase III promoter, has potential applications in isoform-specific "knock-down" of VEGF. Large molecular weight VEGF isoforms were specifically reduced in vitro in the presence of isoform-specific RNAi constructs. Additionally, H1 promoter may be superior to U6 promoter when used for vector-based RNAi of VEGF isoforms. This strategy provides a novel tool to study the function of various VEGF isoforms and may contribute to VEGF isoform-specific treatment in cancer.

Oncogenic transformation induces tumor angiogenesis: a role for PAR1 activation

The formation of new blood vessels is a critical determinant of tumor progression. We find that Par1 gene expression plays a central role in blood vessel recruitment in animal models. By in vivo injection of either Matrigel plugs containing Par1-expressing cells or of rat prostatic carcinoma cells transfected with tetracycline-inducible Par1 expression vectors, we show that Par1 significantly enhances both angiogenesis and tumor growth. Several vascular endothelial growth factor (VEGF) splice forms are induced in cells expressing Par1. Activation of PAR1 markedly augments the expression of VEGF mRNAs and of functional VEGFs as determined by in vitro assays for endothelial tube alignment and bovine aortic endothelial cell proliferation. Because neutralizing anti-VEGF antibodies potently inhibited Par1-induced endothelial cell proliferation, we conclude that Par1-induced angiogenesis requires VEGF. Specific inhibitors of protein kinase C (PKC), Src, and phosphatidylinositol 3-kinase (PI3K) inhibit Par1-induced VEGF expression, suggesting the participation of these kinases in the process. We also show that oncogenic transformation by genes known to be part of PAR1 signaling machinery is sufficient to increase VEGF expression in NIH 3T3 cells. These data support the novel notion that initiation of cell signaling either by activating PAR1 or by the activated forms of oncogenes is sufficient to induce VEGF and hence angiogenesis.

Vascular endothelial growth factor isoforms and their receptors are expressed in human osteoarthritic cartilage

To assess the possible involvement of vascular endothelial growth factor (VEGF) in the pathology of osteoarthritic (OA) cartilage, we examined the expression of VEGF isoforms and their receptors in the articular cartilage, and the effects of VEGF on the production of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) in OA chondrocytes. Reverse transcriptase-polymerase chain reaction analyses demonstrated that mRNAs for three VEGF isoforms (VEGF(121), VEGF(165), and VEGF(189)) are detectable in all of the OA and normal (NOR) cartilage samples. However, the mRNA expression of their receptors (VEGFR-1 = Flt-1, VEGFR-2 = KDR and neuropilin-1) was recognized only in the OA samples. The protein expression of VEGFR-1 and VEGFR-2 in OA chondrocytes was also demonstrated by immunohistochemistry of the OA cartilage tissue and cultured OA chondrocytes. In situ hybridization and immunohistochemistry indicated that VEGF is expressed in the chondrocytes in the superficial and transitional zones of OA cartilage. A linear correlation was obtained between VEGF immunoreactivity and Mankin scores in the cartilage (r = 0.906, P < 0.001). The production levels of VEGF determined by enzyme-linked immunosorbent assay were significantly 3.3-fold higher in OA than in NOR samples (P < 0.001). Among MMP-1, -2, -3, -7, -8, -9, and -13, TIMP-1 and -2 measured by their sandwich enzyme immunoassay systems, the production of MMP-1 and MMP-3 but not TIMP-1 or TIMP-2 was significantly enhanced by the treatment of cultured OA chondrocytes with VEGF (P < 0.05), whereas no such effect was obtained with cultured NOR chondrocytes. These results demonstrate that VEGF and its receptors are expressed in OA cartilage, and suggest the possibility that VEGF is implicated for the destruction of OA articular cartilage through the increased production of MMPs.

Anti-angiogenic agents for the treatment of brain tumors

It is accepted that novel therapeutic approaches are needed for the majority of patients with malignant brain tumors. The vascularity of many primary brain tumors and the encouraging preclinical studies suggest that antiangiogenic agents have the potential to become an important component of multimodality treatment of patients with brain tumors. The understanding of the biology of angiogenesis is improving rapidly, offering the hope for more specific vascular targeting of brain tumor neovasculature. Neuroimaging techniques evaluating the angiogenic process and the impact of antiangiogenic agents will be an important tool for the rapid development of these novel therapeutic agents.

Plasma vascular endothelial growth factor (VEGF) levels after intramuscular and intramyocardial gene transfer of VEGF-1 plasmid DNA

The purpose of this study was to document the kinetics of vascular endothelial growth factor (VEGF) protein release into the systemic circulation after phVEGF gene transfer for therapeutic angiogenesis. VEGF plasma levels were measured by ELISA in 64 patients undergoing gene transfer of plasmid DNA: intramuscular in 34 patients with peripheral artery disease, and intramyocardial in 30 patients with coronary disease. Baseline plasma VEGF was highly variable and not normally distributed. After intramuscular gene transfer, median plasma VEGF rose slightly, although significantly, by 7 days (38 to 41 pg/ml, p < 0.05), but was not different from baseline at 14, 21, or 28 days. After intramyocardial gene transfer, median plasma VEGF levels were significantly elevated compared with baseline on days 2, 3, and 7 (39, 38, and 45 pg/ml, respectively, each p < 0.05 vs. baseline value of 21 pg/ml). Day 7 plasma levels did not differ significantly as a function of phVEGF dose, or between intramyocardial and intramuscular injections (1.8 and 1.3 times baseline levels, respectively, p = 0.6), despite an almost 10-fold difference in mean phVEGF dose. Intramuscular and intramyocardial phVEGF injections result in significant, although modest, elevations of circulating gene product for <14 days, with no relationship to injected dose. While a statistically significant increase in circulating VEGF level can provide evidence of successful gene transfer for groups of patients, interpretation of results for individual subjects is complicated by wide variation in baseline VEGF and low circulating levels compared with baseline after gene transfer.

VEGF-165 serum levels and tyrosinase expression in melanoma patients: correlation with the clinical course

Vascular endothelial growth factor (VEGF) is known to play a crucial role in the growth and metastatization of solid tumours. In cancer patients, high VEGF serum levels correlate with tumour status and prognosis, but to date few data have been reported concerning VEGF in melanoma patients. In the present study, immunoenzymatic and reverse transcription-polymerase chain reaction (RT-PCR) techniques were used to detect VEGF-165 serum levels and the presence of tyrosinase mRNA, respectively, in the peripheral blood of a cohort of 155 melanoma patients at different clinical stages (30 stage I, 40 stage II, 40 stage III and 45 stage IV; AJCC classification). Data were compared with both the extent of the disease and the clinical course. The aim was to assess the relationship between VEGF serum levels, the presence of detectable circulating melanoma cells and melanoma progression. A significant increase in VEGF serum levels was found in melanoma patients, in particular in those with metastatic disease; a higher incidence of relapses was found in stage I-III disease-free patients who showed an increase in VEGF during follow-up. VEGF serum levels were significantly higher in patients with detectable circulating melanoma cells than in those with negative tyrosinase mRNA expression. The finding of both an increase in VEGF and the presence of detectable melanoma cells during follow-up was associated with a relapse rate of 81%. The relapse rate was significantly lower when either of the two parameters were present separately. Multivariate analysis of both overall survival and time-to-progression selected baseline tyrosinase expression in peripheral blood but not VEGF serum levels as an independent prognostic factor.

Expression and endocytosis of VEGF and its receptors in human colonic vascular endothelial cells

Normal human colonic microvascular endothelial cells (HUCMEC) have been isolated from surgical specimens by their adherence to Ulex europaeus agglutinin bound to magnetic dynabeads that bind alpha-L-fucosyl residues on the endothelial cell membrane. Immunocytochemistry demonstrated the presence of a range of endothelial-specific markers on HUCMEC, including the von Willebrand factor, Ulex europaeus agglutinin, and platelet endothelial cell adhesion molecule-1. The growing cells form monolayers with the characteristic cobblestone morphology of endothelial cells and eventually form tube-like structures. HUCMEC produce vascular endothelial growth factor (VEGF) and express the receptors, kinase insert domain-containing receptor (KDR) and fms-like tyrosine kinase, through which VEGF mediates its actions in the endothelium. VEGF induces the tyrosine phosphorylation of KDR and a proliferative response from HUCMEC comparable to that elicited from human umbilical vein endothelial cells (HUVEC). On binding to HUCMEC or HUVEC, (125)I-labeled VEGF internalizes or dissociates to the medium. Once internalized, (125)I-labeled VEGF is degraded and no evidence of ligand recycling was observed. However, significantly less VEGF is internalized, and more is released to the medium from HUCMEC than HUVEC. Angiogenesis results from the proliferation and migration of microvascular, not large-vessel, endothelial cells. The demonstration that microvascular endothelial cells degrade less and release more VEGF to the medium than large-vessel endothelial cells identifies a mechanism permissive of the role of microvascular cells in angiogenesis.

Pathological significance of vascular endothelial growth factor A isoform expression in human cancer

Vascular endothelial growth factor (VEGF) is a highly specific factor for vascular endothelial cells. Five VEGF-A isoforms (splice variants 121, 145, 165, 189 and 206) are generated as a result of alternative splicing from a single VEGF-A gene. These differ in their molecular weights and in biological properties such as their ability to bind to cell-surface heparan sulfate proteoglycans. Deregulated VEGF-A expression contributes to the development of solid tumors by promoting tumor angiogenesis. More specifically, VEGF-A189 expression is related to angiogenesis and prognosis in certain human solid tumors. VEGF-A189 expression is also related to the xenotransplantability of human cancers into immunodeficient mice in vivo. Consequently, inhibition of VEGF-A or VEGF-A189 signaling regulates the development and metastasis of a variety of tumors. This review focuses on recent studies of the mechanisms by which VEGF-A regulates angiogenesis in the cancer stroma and on our recent findings concerning the potential mechanisms of VEGF-A189 expression on tumor growth and metastasis.

B-CLL cells are capable of synthesis and secretion of both pro- and anti-angiogenic molecules

Initial work has shown that clonal B cells from B-chronic lymphocytic leukemia (B-CLL) are able to synthesize pro-angiogenic molecules. In this study, our goal was to study the spectrum of angiogenic factors and receptors expressed in the CLL B cell. We used ELISA assays to determine the levels of basic fibroblast growth factors (bFGF), vascular endothelial growth factor (VEGF), endostatin, interferon-alpha (IFN-alpha) and thrombospondin-1 (TSP-1) secreted into culture medium by purified CLL B cells. These data demonstrated that CLL B cells spontaneously secrete a variety of pro- and anti-angiogenic factors, including bFGF (23.9 pg/ml +/- 7.9; mean +/- s.e.m.), VEGF (12.5 pg/ml +/- 2.3) and TSP-1 (1.9 ng/ml +/- 0.3). Out of these three factors, CLL B cells consistently secreted bFGF and TSP-1, while VEGF was expressed in approximately two-thirds of CLL patients. Of interest, hypoxic conditions dramatically upregulated VEGF expression at both the mRNA and protein levels. We also employed ribonuclease protection assays to assay CLL B cell expression of a variety of other angiogenesis-related molecules. These analyses revealed that CLL B cells consistently express mRNA for VEGF receptor 1 (VEGFR1), thrombin receptor, endoglin, and angiopoietin. Further analysis of VEGFR expression by RT-PCR revealed that CLL B cells expressed both VEGFR1 mRNA and VEGFR2 mRNA. In summary, these data collectively indicate that CLL B cells express both pro- and anti-angiogenic molecules and several vascular factor receptors. Because of the co-expression of angiogenic molecules and receptors for some of these molecules, these data suggest that the biology of the leukemic cells may also be directly impacted by angiogenic factors as a result of autocrine pathways of stimulation.

Different effects of glucose starvation on expression and stability of VEGF mRNA isoforms in murine ovarian cancer cells

Vascular endothelial growth factor (VEGF) has been implicated as a potent regulator of angiogenesis in tumors, and its protein exists as at least five isoforms with distinct biologic activities and clinical significance. Tumors under metabolic stress conditions dramatically increase VEGF expression due to both increased transcription and decreased mRNA degradation. However, it is not known how stress conditions regulate expression of each VEGF isoform. Here, we report a novel Taqman real-time RT-PCR strategy for quantification of all murine VEGF isoforms and find that (1) glucose starvation dramatically up-regulates the mRNA level of all VEGF isoforms, with the three abundant isoforms, VEGF120, VEGF164, and VEGF188, increasing at a similar rate, while the rare isoform VEGF144 is more markedly up-regulated; (2) glucose starvation induces a significant increase of the relative abundance of VEGF144 mRNA, but not the more prevalent isoforms VEGF120, VEGF164, and VEGF188, compared to total VEGF; and (3) the stability of each isoform mRNA differs under the control conditions as well as glucose starvation. The latter significantly stabilizes mRNA of all VEGF isoforms at a different rate, with VEGF144 most significantly stabilized. Our results indicate that under metabolic stress conditions VEGF144 is the most dramatically up-regulated VEGF isoform, probably through mechanism(s) different from the three abundant VEGF isoforms.

New cytokine delivery system using gelatin microspheres containing interleukin-10 for experimental inflammatory bowel disease

Interleukin (IL)-10 is an anti-inflammatory cytokine that suppresses the T helper 1 immune response and down-regulates macrophages and monocytes. The therapeutic effect of systemic administration of IL-10 for patients with inflammatory bowel disease, however, has not been satisfactory. We examined whether rectal administration of gelatin microspheres (GM) containing IL-10 (GM-IL-10) prevents colitis in IL-10-deficient (IL-10(-/-)) mice. GM-IL-10 and IL-10 alone were administered rectally. The colon was examined macroscopically and microscopically. IL-12 mRNA expression and CD40 expression in Mac-1-positive cells were also examined. Macroscopic and microscopic examination revealed marked improvement of colitis in IL-10(-/-) mice treated with GM-IL-10. mRNA expression of IL-12 in Mac-1-positive cells in GM-IL-10-treated mice was significantly decreased compared with that in the mice treated with IL-10 alone. Additionally, CD40 expression in Mac-1-positive cells in GM-IL-10-treated mice was decreased more prominently than in mice treated with IL-10 alone. The therapeutic effects of GM-IL-10 were associated with decreased expression of IL-12 mRNA and down-regulation of CD40 expression in Mac-1-positive cells. GM-IL-10 might be useful for treatment of patients with inflammatory bowel disease.

Connective tissue growth factor binds vascular endothelial growth factor (VEGF) and inhibits VEGF-induced angiogenesis

Vascular endothelial growth factor (VEGF) is a strong angiogenic mitogen and plays important roles in angiogenesis under various pathophysiological conditions. The in vivo angiogenic activity of secreted VEGF may be regulated by extracellular inhibitors, because it is also produced in avascular tissues such as the cartilage. To seek the binding inhibitors against VEGF, we screened the chondrocyte cDNA library by a yeast two-hybrid system by using VEGF165 as bait and identified connective tissue growth factor (CTGF) as a candidate. The complex formation of VEGF165 with CTGF was first established by immunoprecipitation from the cells overexpressing both binding partners. A competitive affinity-binding assay also demonstrated that CTGF binds specifically to VEGF165 with two classes of binding sites (Kd = 26 +/- 11 nM and 125 +/- 38 nM). Binding assay using deletion mutants of CTGF indicated that the thrombospondin type-1 repeat (TSP-1) domain of CTGF binds to the exon 7-coded region of VEGF165 and that the COOH-terminal domain preserves the affinity to both VEGF165 and VEGF121. The interaction of VEGF165 with CTGF inhibited the binding of VEGF165 to the endothelial cells and the immobilized KDR/IgG Fc; that is, a recombinant protein for VEGF165 receptor. By in vitro tube formation assay of endothelial cells, full-length CTGF and the deletion mutant possessing the TSP-1 domain inhibited VEGF165-induced angiogenesis significantly in the complex form. This antiangiogenic activity of CTGF was demonstrated further by in vivo angiogenesis assay by using Matrigel injection model in mice. These data demonstrate for the first time that VEGF165 binds to CTGF through a protein-to-protein interaction and suggest that the angiogenic activity of VEGF165 is regulated negatively by CTGF in the extracellular environment.

VEGF receptor signal transduction

The family of vascular endothelial growth factors (VEGFs) currently includes VEGF-A, -B, -C, -D, -E, and placenta growth factor (PlGF). Several of these factors, notably VEGF-A, exist as different isoforms, which appear to have unique biological functions. The VEGF family proteins bind in a distinct pattern to three structurally related receptor tyrosine kinases, denoted VEGF receptor-1, -2, and -3. Neuropilins, heparan-sulfated proteoglycans, cadherins, and integrin alphavbeta3 serve as coreceptors for certain but not all VEGF proteins. Moreover, the angiogenic response to VEGF varies between different organs and is dependent on the genetic background of the animal. Inactivation of the genes for VEGF-A and VEGF receptor-2 leads to embryonal death due to the lack of endothelial cells. Inactivation of the gene encoding VEGF receptor-1 leads to an increased number of endothelial cells, which obstruct the vessel lumen. Inactivation of VEGF receptor-3 leads to abnormally organized vessels and cardiac failure. Although VEGF receptor-3 normally is expressed only on lymphatic endothelial cells, it is up-regulated on vascular as well as nonvascular tumors and appears to be involved in the regulation of angiogenesis. A large body of data, such as those on gene inactivation, indicate that VEGF receptor-1 exerts a negative regulatory effect on VEGF receptor-2, at least during embryogenesis. Recent data imply a positive regulatory role for VEGF receptor-1 in pathological angiogenesis. The VEGF proteins are in general poor mitogens, but binding of VEGF-A to VEGF receptor-2 leads to survival, migration, and differentiation of endothelial cells and mediation of vascular permeability. This review outlines the current knowledge about the signal transduction properties of VEGF receptors, with focus on VEGF receptor-2.

Role of heparan sulfate as a tissue-specific regulator of FGF-4 and FGF receptor recognition

FGF signaling uses receptor tyrosine kinases that form high-affinity complexes with FGFs and heparan sulfate (HS) proteoglycans at the cell surface. It is hypothesized that assembly of these complexes requires simultaneous recognition of distinct sulfation patterns within the HS chain by FGF and the FGF receptor (FR), suggesting that tissue-specific HS synthesis may regulate FGF signaling. To address this, FGF-2 and FGF-4, and extracellular domain constructs of FR1-IIIc (FR1c) and FR2-IIIc (FR2c), were used to probe for tissue-specific HS in embryonic day 18 mouse embryos. Whereas FGF-2 binds HS ubiquitously, FGF-4 exhibits a restricted pattern, failing to bind HS in the heart and blood vessels and failing to activate signaling in mouse aortic endothelial cells. This suggests that FGF-4 seeks a specific HS sulfation pattern, distinct from that of FGF-2, which is not expressed in most vascular tissues. Additionally, whereas FR2c binds all FGF-4-HS complexes, FR1c fails to bind FGF-4-HS in most tissues, as well as in Raji-S1 cells expressing syndecan-1. Proliferation assays using BaF3 cells expressing either FR1c or FR2c support these results. This suggests that FGF and FR recognition of specific HS sulfation patterns is critical for the activation of FGF signaling, and that synthesis of these patterns is regulated during embryonic development.

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.

Vascular endothelial growth factor receptor 2 (VEGFR2) expression in squamous cell carcinomas of the head and neck

OBJECTIVES

Vascular endothelial growth factor receptor 2 (VEGFR2; Flk-1 [fetal liver kinase]/KDR [kinase insert domain containing receptor]) has been identified as a high affinity receptor for vascular endothelial growth factor (VEGF) on vascular endothelium. Head and neck squamous cell carcinomas (HNSCC) have already been shown to produce substantial amounts of VEGF. VEGFR2 is supposed to play a major role in tumor-neoangiogenesis.

METHODS

We investigated 24 tumor specimens and 4 HNSCC cultured tumor cell lines for the incidence and distribution of VEGFR2 by immunohistochemistry using monoclonal antibodies (mAbs) and RT-PCR.

RESULTS

Analysis of frozen sections by immunohistochemistry showed that in 90% of tumor specimens VEGFR2-positive cells were found which were associated with vascular endothelium. VEGFR2 was also expressed on tumor cells and vessels, which was confirmed by double immunolabeling of tumor cells with an a-cytokeratin mAb. Furthermore, 2 (JPPA, SCC9) of 4 HNSCC cultured tumor cell lines revealed positive VEGFR2 immunoreactivity. Synthesis of VEGFR2 mRNA on all 4 HNSCC cultured tumor cell lines (JPPA, SCC9, SCC25, and LFFR) and in 6 tumor specimens was confirmed by RT-PCR. In conclusion, our results showed that VEGFR2 is expressed in HNSCCs on tumor cells. VEGFR2 expression is associated with the beginning of vasculogenesis represented by accumulation of VEGFR2-positive cells budding into new vessels ("hot spots"). The focal expression pattern of VEGFR2 on tumor cells suggests an autocrine loop for VEGF in tumor cell growth.

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.

Vascular endothelial growth factor: acting as an autocrine growth factor for human gastric adenocarcinoma cell MGC803

Vascular endothelial growth factor (VEGF) is known to be a highly specific mitogen for endothelial cells through two high-affinity tyrosine kinase receptors, VEGFR-1 and VEGFR-2, which are almost specifically expressed in endothelial cells. However, recent findings showed that VEGF receptors may also expressed by nonendothelial cells, especially by tumor cells. To further understand the functional expression of VEGF receptors by nonendothelial cells, our preliminary screening detected the expression of VEGFR-2 in 115 different paraffin-embedded cancer specimens including 35 cases of bladder tumor, 30 cases of breast cancer, 25 cases of intestinal cancer, and 25 cases of lung cancer with immunohistochemistry. The results showed that VEGFR-2 was widely expressed in different tumor tissues. By reverse transcription PCR, NCI-H23, NCI-H460, MGC803, MDA-MB-231, 293, and MCF7 cells were evaluated for the mRNA expression of both VEGF and VEGFR-2. The data indicated that all these tumor cell lines expressed detectable amounts of VEGF mRNA, but only 293, MCF7, and MGC803 cells coexpressed VEGFR-2. Immunoblot analysis also demonstrated the expression of VEGFR-2 at protein level. We further demonstrate that exogenous rhVEGF(165) could stimulate cell growth in MGC803, a tumor cell line derived from gastric adenocarcinoma, in a dose- and time-dependent manner. Furthermore, the antibodies against rhVEGF(165) and VEGFR-2 could block rhVEGF(165)-mediated proliferation of MGC803 cells. These unexpected results provided direct evidence that VEGF may act as an autocrine growth factor to induce the proliferation of gastric adenocarcinoma cells as well as tumor angiogenic cells, thus suggesting a promising tumor therapeutic application based upon the VEGF system.

Expression of vascular endothelial growth factor family members in head and neck squamous cell carcinoma correlates with lymph node metastasis

BACKGROUND

The expression of vascular endothelial growth factor (VEGF)-A isoforms (121, 165, 189, 206), VEGF-B, VEGF-C and VEGF-D in both experimental and clinical models of head and neck squamous cell carcinoma (HNSCC) was determined and correlated with conventional clinicopathologic parameters, with particular reference to cervical nodal metastasis.

METHODS

The mRNA expression of VEGFs in 14 HNSCC cell lines was compared with 4 normal keratinocyte cultures and 10 fibroblast cultures using a semiquantitative reverse transcription polymerase chain reaction (RT-PCR) assay. Protein levels were determined by Western blotting and enzyme-linked immunosorbent assay (ELISA). The authors then examined the expression of VEGFs in tissues from 54 patients including histologically normal epithelium (n = 32), early invasive squamous cell carcinomas (SCCs) (n = 23), advanced primary SCCs (n = 31), and lymph node metastases (n = 27).

RESULTS

Increased levels of VEGF-A (all four isoforms) and VEGF-C were found in tumor cell lines compared with normal cells, whereas no differences in VEGF-B levels were found. VEGF-D expression, however, was lower in HNSCC cells. Studies in clinical samples showed highly significant increases in mRNA expression of all four isoforms of VEGF-A and VEGF-C in tumors versus normal epithelium. In contrast, the levels of VEGF-D were significantly decreased in tumors, and VEGF-B expression appeared similar in both normal and malignant tissues. Multivariate analysis demonstrated that an infiltrative mode of invasion and enhanced expression of VEGF-A (isoforms 121 and 165) and VEGF-C had predictive value for the presence of cervical nodal metastases.

CONCLUSIONS

Up-regulation of VEGF-A (two isoforms) and VEGF-C and down-regulation of VEGF-D have been common features in HNSCC. Thus VEGF-A and VEGF-C appeared to play a vital role in the metastatic process of HNSCC.

Einsiedel H, Geilen W, Seifert G, Eckert C, Henze G, Seeger K. Specific Reverse Transcription-PCR Quantification of Vascular Endothelial Growth Factor (VEGF) Splice Variants by LightCycler Technology

Background: Overexpression of vascular endothelial growth factor (VEGF) is associated with increased angiogenesis, growth and invasion in solid tumors, and hematologic malignancies. The expression of isoforms of VEGF, which mediate different effects, can be discriminated by splice-variant-specific quantitative reverse transcription-PCR (RT-PCR), but current methods have only modest sensitivity and precision and suffer from heteroduplex formation.

Methods: We used a real-time RT-PCR assay on the LightCycler system. Applicability for detection of different VEGF mRNAs and total VEGF message was tested on seven healthy tissues (each pooled from healthy donors) and seven correlated malignant tissues. Results were normalized to β2-microglobulin mRNA. Amplification of VEGF splice variants was performed exclusively with variant-specific reverse primers, whereas forward primer and fluorescent probe were common to obtain similar RT-PCR kinetics.

Results: Highly specific detection of VEGF splice variants was achieved with minor intra- and interassay variation (&lt;0.22 threshold cycle). Total VEGF expression was higher in malignant tissues. In healthy tissues, the mRNA encoding diffusible variants VEGF121 and VEGF165 constituted on average 78% (SD = 9.3%) of the total VEGF message, and the cell-adherent variant VEGF189 constituted on average 22% (SD = 5.4%). In contrast, in malignant tissues VEGF121 and VEGF165 accounted for 94% (SD = 7.6%) and VEGF189 only 6% (SD = 3.7%).

Conclusions: Because of the ability for quantification of VEGF splice variants with high specificity, sensitivity, and reproducibility, this new LightCycler assay is superior to conventional semiquantitative competitive RT-PCR and immunological assays and may contribute to better understanding of VEGF-mediated angiogenesis.

Characterization of (123)I-vascular endothelial growth factor-binding sites expressed on human tumour cells: possible implication for tumour scintigraphy

To explore the possibility of vascular endothelial growth factor (VEGF) receptor scintigraphy of primary tumours and their metastases, we analysed the binding properties of (123)I-labelled VEGF(165) ((123)I-VEGF(165)) and (123)I-VEGF(121) to human umbilical vein endothelial cells (HUVECs), several human tumour cell lines (HMC-1, A431, KU812, U937, HEP-1, HEP-G2, HEP-3B and Raji), a variety of primary human tumours (n = 40) and some adjacent non-neoplastic tissues as well as normal human peripheral blood cells in vitro. Two classes of high-affinity (123)I-VEGF(165)-binding site were found on the cell surface of HUVECs. In contrast, one class of high-affinity binding sites for (123)I-VEGF(165) was found on HMC-1, A431, HEP-1, HEP-G2, HEP-3B and U937 cells as well as many primary tumours. For (123)I-VEGF(121), a single class of high-affinity binding site was found on certain cell lines (HUVEC, HEP-1 and HMC-1) and distinct primary tumours (primary melanomas, ductal breast cancers and ovarian carcinomas as well as meningiomas). Tumour cells expressed significantly higher numbers of VEGF receptors compared with normal peripheral blood cells and adjacent non-neoplastic tissues. Immunohistochemical staining revealed that the VEGF receptor Flk-1 is expressed to a much higher extent within malignant tissues compared with neighbouring non-neoplastic cells. We observed significantly greater specific binding of (123)I-VEGF(165) and (123)I-VEGF(121) to a variety of human tumour cells/tissues compared with the corresponding normal tissues or normal peripheral blood cells. In comparison with (123)I-VEGF(121), (123)I-VEGF(165) bound to a higher number of different tumour cell types with a higher capacity. Thus, (123)I-VEGF(165) may be a potentially useful tracer for in vivo imaging of solid tumours.

The splice variants of vascular endothelial growth factor (VEGF) and their receptors

Vascular endothelial growth factor (VEGF) is a secreted mitogen highly specific for cultured endothelial cells. In vivo VEGF induces microvascular permeability and plays a central role in both angiogenesis and vasculogenesis. VEGF is a promising target for therapeutic intervention in certain pathological conditions that are angiogenesis dependent, most notably the neovascularisation of growing tumours. Through alternative mRNA splicing, a single gene gives rise to several distinct isoforms of VEGF, which differ in their expression patterns as well as their biochemical and biological properties. Two VEGF receptor tyrosine kinases (VEGFRs) have been identified, VEGFR-1 (Flt-1) and VEGFR-2 (KDR/Flk-1). VEGFR-2 seems to mediate almost all observed endothelial cell responses to VEGF, whereas roles for VEGFR-1 are more elusive. VEGFR-1 might act predominantly as a ligand-binding molecule, sequestering VEGF from VEGFR-2 signalling. Several isoform-specific VEGF receptors exist that modulate VEGF activity. Neuropilin-1 acts as a co-receptor for VEGF(165), enhancing its binding to VEGFR-2 and its bioactivity. Heparan sulphate proteoglycans (HSPGs), as well as binding certain VEGF isoforms, interact with both VEGFR-1 and VEGFR-2. HSPGs have a wide variety of functions, such as the ability to partially restore lost function to damaged VEGF(165) and thereby prolonging its biological activity.

Targeting avian leukosis virus subgroup A vectors by using a TVA-VEGF bridge protein

Previously, we have demonstrated that bridge proteins comprised of avian leukosis virus (ALV) receptors fused to epidermal growth factor (EGF) can be used to selectively target retroviral vectors with ALV envelope proteins to cells expressing EGF receptors. To determine whether another type of ligand incorporated into an ALV receptor-containing bridge protein can also function to target retroviral infection, the TVA-VEGF110 bridge protein was generated. TVA-VEGF110 consists of the extracellular domain of the TVA receptor for ALV subgroup A (ALV-A), fused via a proline-rich linker peptide to a 110-amino-acid form of vascular endothelial growth factor (VEGF). This bridge protein bound specifically to its cell surface receptor, VEGFR-2, and efficiently mediated the entry of an ALV-A vector into cells. These studies indicate that ALV receptor-ligand bridge proteins may be generally useful tools for retroviral targeting approaches.

Vascular endothelial growth factor 189 mRNA isoform expression specifically correlates with tumor angiogenesis, patient survival, and postoperative relapse in non-small-cell lung cancer

PURPOSE

The purpose of this study was to evaluate the correlation between the expression of four different vascular endothelial growth factor (VEGF) mRNA isoforms (VEGF121, VEGF165, VEGF 189, and VEGF206) and the clinicopathologic characteristics, tumor angiogenesis, and outcome of patients with non-small-cell lung cancer.

PATIENTS AND METHODS

We examined the expression of four different VEGF mRNA isoforms in 57 non-small-cell lung cancers using reverse transcriptase polymerase chain reaction and the tumor angiogenesis using immunohistochemical staining.

RESULTS

All 57 lung cancer samples expressed the VEGF121, VEGF165, and VEGF189 mRNA isoforms, and three expressed the VEGF206 mRNA isoform. A high tumoral VEGF189 mRNA isoform expression ratio was associated with a high intratumoral microvessel count (P = .013), short survival (< 24 months; P = .001), and early postoperative relapse (< 12 months; P = .001). Survival and postoperative relapse time were significantly shorter in patients with a high compared with a low tumor VEGF189 mRNA isoform expression ratio (P = .0001 and P = .0086, respectively, log-rank test). In contrast, the VEGF165 and VEGF 206 mRNA isoform expression ratios showed no statistical correlation with tumor angiogenesis, postoperative relapse time, or survival. A high VEGF121 mRNA isoform expression ratio was associated with short survival (< 24 months) and early relapse (< 12 months). Multivariate analysis showed that VEGF 189 mRNA isoform expression, microvessel count, and nodal status were the most important independent prognostic factors for patient survival and postoperation recurrence.

CONCLUSION

The VEGF189 mRNA isoform expression ratio shows a greater correlation with tumor angiogenesis, postoperative relapse time, and survival than do the expression ratios for the VEGF121, VEGF165, and VEGF206 mRNA isoforms and can be used as a prognostic indicator for patients with non-small-cell lung cancers.

Developmental expression of vascular endothelial growth factor in the masseter muscle of rats

Developmental changes in vascular endothelial growth factor (VEGF) in rat masseter after birth were investigated. VEGF was extracted efficiently and reproducibly from muscle homogenate with low concentrations of non-ionic detergents, such as Triton X-100, Nonidet P-40, and Tween 20. The amount of VEGF measured by enzyme-linked immunosorbent assay (ELISA) increased markedly by approximately 9-fold, from day 8 to 35 after birth. The increase in VEGF was closely correlated with the development of the capillary network, as shown by the capillary to muscle fibre ratio (C/F ratio). Immunoblotting revealed that the predominant molecular species of VEGF concentrated with heparin-sepharose beads was VEGF(188). These results suggest that VEGF plays an important part in the development and maintenance of the capillary network in the rat masseter.

Human melanoma cells secrete and respond to placenta growth factor and vascular endothelial growth factor

The vascular endothelial growth factor is produced by a large variety of human tumors, including melanoma, in which it appears to play an important role in the process of tumor-induced angiogenesis. Little information is available on the role of placenta growth factor, a member of the vascular endothelial growth factor family of cytokines, in tumor angiogenesis, even though placenta growth factor/vascular endothelial growth factor heterodimers have been recently isolated from tumor cells. To investigate the role of placenta growth factor and vascular endothelial growth factor homodimers and heterodimers in melanoma angiogenesis and growth, 19 human melanoma cell lines derived from primary or metastatic tumors were characterized for the expression of these cytokines and their receptors. Release of placenta growth factor and vascular endothelial growth factor polypeptides into the supernatant of human melanoma cells was demonstrated. Reverse transcriptase polymerase chain reaction analysis showed the presence of mRNAs encoding at least three different vascular endothelial growth factor isoforms (VEGF(121), VEGF(165), and VEGF(189)) and transcripts for two placenta growth factor isoforms (PlGF-1 and PlGF-2) in human melanoma cells. In addition, placenta growth factor expression in human melanoma in vivo was detected by immunohistochemical staining of tumor specimens. Both primary and metastatic melanoma cells were found to express the mRNAs encoding for vascular endothelial growth factor and placenta growth factor receptors (KDR, Flt-1, neuropilin-1, and neuropilin-2), and exposure of melanoma cells to these cytokines resulted in a specific proliferative response, supporting the hypothesis of a role of these angiogenic factors in melanoma growth. J Invest Dermatol 115:1000-1007 2000

Ribozyme approach to downregulate vascular endothelial growth factor (VEGF) 189 expression in non-small cell lung cancer (NSCLC)

The aim of this study was to further clarify the role of the cell-associated isoform of vascular endothelial growth factor (VEGF189) on tumour growth and vascularity. Five isoforms of VEGF have been identified with different biological activities. VEGF121, VEGF145, VEGF165, VEGF189, VEGF206 are generated by alternative splicing. We used a hammerhead-type ribozyme (V189Rz) to suppress VEGF189 mRNA. The V189Rz specifically cleaved exon 6 of VEGF189 mRNA, but showed no activity against the VEGF121 or VEGF165 isoforms. The V189Rz was introduced into the human non-small cell lung cancer (NSCLC) cell line (OZ-6/VR). The expression level of VEGF189 mRNA was decreased in the OZ-6/VR cells, while VEGF121 and 165 expression was unaltered. The OZ-6/VR cells xenotransplanted into nude mice showed markedly reduced vascularisation and growth, whereas the cell line did not show any decreased growth under tissue culture conditions. The OZ-6/VR cells (1 x 10(5) cells/mouse) formed no tumours, whereas the parental OZ-6 cells formed large tumours within 8 weeks. The specific suppression of VEGF189 by the ribozyme decreased vascularity and xenotransplantability of the lung cancer cell line. Thus, the cell-associated isoform of VEGF, VEGF189, might have a key role in stromal vascularisation and the growth of NSCLC xenografts in vivo.

Protein tyrosine kinases in malignant melanoma

Protein tyrosyl phosphorylation is an essential component in intracellular signalling, with diverse and crucial functions including mediation of cell proliferation, survival, death, differentiation, migration and attachment. It is regulated by the balance between the activities of protein tyrosine kinases (PTKs) and protein tyrosine phosphatases. A number of PTKs are encoded by proto-oncogenes or viral oncogenes, and are thus strongly implicated in cancer. While a role for PTKs in human melanoma is less firmly established, human melanomas or melanoma cells have been reported to contain more tyrosine phosphate than normal melanocytes, and some receptor PTKs (EPH-A2/ ECK and EPH-B3) are overexpressed in over 90% of melanoma cell lines. Other specific PTKs are also frequently overexpressed, including KDR and fibroblast growth factor receptor-4 (FGF-R4), while, interestingly, yet others, such as KIT and FES, are consistently downregulated in melanoma cell lines. All of these differentially expressed PTKs are candidates for gene products important in melanoma development. In addition, PTKs expressed in significant amounts in both benign and malignant melanocytes, such as insulin-like growth factor-1 receptor (IGF1-R), FGF-R1, HER2/NEU and FAK, are likely to play a role in melanoma genesis and progression.

Neuropilin-2 is a receptor for the vascular endothelial growth factor (VEGF) forms VEGF-145 and VEGF-165 [corrected]

Neuropilin-1 (np-1) and neuropilin-2 (np-2) are receptors for axon guidance factors belonging to the class 3 semaphorins. np-1 also binds to the 165-amino acid heparin-binding form of VEGF (VEGF(165)) but not to the shorter VEGF(121) form, which lacks a heparin binding ability. We report that human umbilical vein-derived endothelial cells express the a17 and a22 splice forms of the np-2 receptor. Both np-2 forms bind VEGF(165) with high affinity in the presence of heparin (K(D) 1.3 x 10(-10) m) but not VEGF(121). np-2 also binds the heparin-binding form of placenta growth factor. These binding characteristics resemble those of np-1. VEGF(145) is a secreted heparin binding VEGF form that contains the peptide encoded by exon 6 of VEGF but not the peptide encoded by exon 7, which is present in VEGF(165). VEGF(145) binds to np-2 with high affinity (K(D) 7 x 10(-10) m). Surprisingly, VEGF(145) did not bind to np-1. Indeed, VEGF(145) does not bind to MDA-MB-231 breast cancer cells, which predominantly express np-1. By contrast, VEGF(145) binds to human umbilical vein-derived endothelial cells, which express both np-1 and np-2. The binding of VEGF(165) to porcine aortic endothelial cells expressing recombinant np-2 did not affect the proliferation or migration of the cells. Nevertheless, it is possible that VEGF-induced np-2-mediated signaling will take place only in the presence of other VEGF receptors such as VEGF receptor-1 or VEGF receptor-2.

Arginine-rich anti-vascular endothelial growth factor peptides inhibit tumor growth and metastasis by blocking angiogenesis

Tumor angiogenesis is a critical step for the growth and metastasis of solid tumors. Vascular endothelial growth factor (VEGF) is a specific and potent angiogenic factor and contributes to the development of solid tumors by promoting tumor angiogenesis. Therefore, it is a prime therapeutic target for the development of antagonists for treatment of cancer. We identified from peptide libraries arginine-rich hexapeptides that inhibit the interaction of VEGF(165) with VEGF receptor (IC(50) = 2-4 micrometer). They have no effect on binding of basic fibroblast growth factor to cellular receptor. The hexapeptides inhibit the proliferation of human umbilical vein endothelial cells induced by VEGF(165) without toxicity. The peptides bind to VEGF and inhibit binding of both VEGF(165) and VEGF(121), suggesting that the peptides interact with the main body of VEGF but not the heparin-binding domain that is absent in VEGF(121). The identified peptides block the angiogenesis induced by VEGF(165) in vivo in the chick chorioallantoic membrane and the rabbit cornea. Furthermore, one of the hexapeptides, RRKRRR, blocks the growth and metastasis of VEGF-secreting HM7 human colon carcinoma cells in nude mice. Based on our results, the arginine-rich hexapeptides may be effective for the treatment of various human tumors and other angiogenesis-dependent diseases that are related to the action of VEGF and could also serve as leads for development of more effective drugs.

Vascular endothelial growth factor expression under ischemic stress in human meningiomas

Vascular endothelial growth factor (VEGF) is an endothelial cell-specific antigen and angiogenic factor that plays a role in angiogenesis. We analyzed the expression of four VEGF mRNA isoforms in meningiomas. Among 35 meningiomas, 11 came from patients who underwent complete (n=4) or partial (n=7206=189 in all samples. However, the VEGF121 and 165 isoforms were significantly upregulated in samples from patients who underwent partial preoperative embolization. The diffusible VEGF121 isoform may be important for vascularity and edema formation in meningiomas.

Comparison of the rates of deamidation, diketopiperazine formation and oxidation in recombinant human vascular endothelial growth factor and model peptides

In this work, we examine the way in which stability information obtained from studies on small model peptides correlates with similar information acquired from a protein. The rates of deamidation, oxidation, and diketopiperazine reactions in model peptide systems were compared to those of recombinant human vascular endothelial growth factor (rhVEGF). The N-terminal residues of rhVEGF, a potent mitogen in angiogenesis, are susceptible to the aforementioned reactions. The degradation of the peptides L-Ala-L-Pro-L-Met (APM) and Gly-L-Gln-L-Asn-L-His-L-His (GQNHH), residues 1-3 and 8-12 of rhVEGF, respectively, and rhVEGF were examined at pH 5 and 8 at 37 degrees C. Capillary electrophoresis and high-performance liquid chromatography (HPLC) stability-indicating assays were developed to monitor the degradation of the penta- and tripeptides, respectively. The degradation of rhVEGF was determined by tryptic mapping and quantified by RP-HPLC. The rates of degradation of both peptides and the protein followed apparent first-order kinetics and increased with increasing pH. The tripeptide APM underwent diketopiperazine formation (Ala-Pro-diketopiperazine) and oxidation of the Met residue, whereas the pentapeptide GQNHH degraded via the deamidation pathway. The results indicate that the rates of deamidation and oxidation of the protein are comparable to those observed in the model peptides at both pH values. However, the rate of the diketo-piperazine reaction was slower in the protein than in the model peptide, which may be the result of differences in the cis-trans equilibrium of the X-Pro peptide bonds in the 2 molecules.

Microphthalmia transcription factor. A sensitive and specific melanocyte marker for MelanomaDiagnosis

Malignant melanomas do not uniformly retain expression of melanocytic gene products-an observation associated with diagnostic dilemmas. Microphthalmia transcription factor (Mitf) is a melanocytic nuclear protein critical for the embryonic development and postnatal viability of melanocytes. It serves as a master regulator in modulating extracellular signals, such as those triggered by alpha-MSH and c-Kit ligand. Because of its central role in melanocyte survival and to assess its potential use as a histopathological marker for melanoma, Mitf expression was examined in histologically confirmed human melanoma specimens. Western blot analysis of melanoma cell lines revealed consistent expression of two Mitf protein isoforms differing by MAP kinase-mediated phosphorylation. In a series of 76 consecutive human melanoma surgical specimens, 100% stained positively for Mitf with a nuclear pattern of reactivity. In a side-by-side comparison, Mitf staining was positive in melanomas that failed to stain for either HMB-45 or S-100, the most common currently used melanoma markers. Of 60 non-melanoma tumors, none displayed nuclear Mitf staining and two displayed cytoplasmic staining. Although Mitf does not distinguish benign from malignant melanocytic lesions, for invasive neoplasms it appears to be a highly sensitive and specific histopathological melanocyte marker for melanoma.

Bioactivity of anti-angiogenic ribozymes targeting Flt-1 and KDR mRNA

Vascular endothelial growth factor (VEGF) and its receptors Flt-1 and KDR play important roles in physiological and pathological angiogenesis. Ribozymes that target the VEGF receptor mRNAs were developed and their biological activities in cell culture and an animal model were assessed. Ribozymes targeting Flt-1 or KDR mRNA sites reduced VEGF-induced proliferation of cultured human vascular endothelial cells and specifically lowered the level of Flt-1 or KDR mRNA present in the cells. Anti- Flt-1 and KDR ribozymes also exhibited anti-angiogenic activity in a rat corneal pocket assay of VEGF-induced angiogenesis. This report illustrates the anti-angiogenic potential of these ribozymes as well as their value in studying VEGF receptor function in normal and pathophysiologic states.

Cell-retained isoforms of vascular endothelial growth factor (VEGF) are correlated with poor prognosis in osteosarcoma

Vascular endothelial growth factor (VEGF) is a major angiogenic factor. Osteosarcoma is characterised by hypervascularity and metastatic potential. We examined VEGF mRNA expression, VEGF isoform pattern and VEGF receptor (flt-1 and KDR) by RT-PCR analysis in 30 osteosarcomas. All 30 osteosarcomas expressed VEGF mRNA. 17 osteosarcomas (57%) expressed flt-1 mRNA, whilst 20 (67%) expressed KDR mRNA. 6/30 (20%) osteosarcomas were positive for VEGF121 only, 8 (27%) for VEGF121 + VEGF165, and 16 (53%) for VEGF121 + VEGF165 + VEGF189. Patients with osteosarcomas with VEGF165 (n = 24) had significantly poorer prognosis in comparison with those without VEGF165 (P = 0.022, Wilcoxon's test). The osteosarcomas with VEGF165 had significantly increased vascularity assessed on sections immunostained for CD34 (P < 0.001, Mann-Whitney U test). Although VEGF165 is a soluble isoform, it is also retained on the cellular surface. These results suggest that cell-retained VEGF isoforms (VEGF165, VEGF189) might be essential for neovascularisation in osteosarcoma, whilst the soluble VEGF121 isoform is not sufficient to stimulate neovascularisation in this type of neoplasm.

Effect of vascular endothelial growth factor on hepatic regenerative activity following partial hepatectomy in rats

BACKGROUND/AIMS

Vascular endothelial growth factor (VEGF) is an angiogenic factor with a growth-promoting effect that is thought to be restricted to vascular endothelial cells. Its essential role during liver regeneration has yet to be determined. The aim of this study was to document the effect of exogenous VEGF administration on liver regeneration in rats undergoing submaximal hepatic resections.

METHODS

Adult male Sprague-Dawley rats (n = 4/group) undergoing 30% partial hepatectomy were administered 200 ng VEGF165 intravenously and were sacrificed at 24, 36, and 48 h postoperatively. Liver regeneration was monitored by measuring the restituted liver mass, proliferating cell nuclear antigen (PCNA) immunostaining, and hepatic PCNA protein by Western blot.

RESULTS

Changes in restituted liver mass 48 h postsurgery were more prominent, but did not differ statistically between VEGF-treated and control rats (47% vs. 29%; p<0.06). Nevertheless, PCNA immunostaining showed increased labeling index of hepatocytes, apparent at 36 and 48 h after partial hepatectomy (38% vs. 18% [p<0.041 and 42% vs. 11% [p<0.021], respectively). Hepatic PCNA proteins measured by Western blot showed a 3-fold increase in VEGF-treated rats 48 h postsurgery compared with controls (p<0.01).

CONCLUSION

Exogenous VEGF administration early after partial hepatectomy stimulates liver regeneration in rats. Whether or not VEGF165 is a direct mitogen for hepatocytes remains to be determined.

Glypican-1 is a VEGF165 binding proteoglycan that acts as an extracellular chaperone for VEGF165

Glypican-1 is a member of a family of glycosylphosphatidylinositol anchored cell surface heparan sulfate proteoglycans implicated in the control of cellular growth and differentiation. The 165-amino acid form of vascular endothelial growth factor (VEGF165) is a mitogen for endothelial cells and a potent angiogenic factor in vivo. Heparin binds to VEGF165 and enhances its binding to VEGF receptors. However, native HSPGs that bind VEGF165 and modulate its receptor binding have not been identified. Among the glypicans, glypican-1 is the only member that is expressed in the vascular system. We have therefore examined whether glypican-1 can interact with VEGF165. Glypican-1 from rat myoblasts binds specifically to VEGF165 but not to VEGF121. The binding has an apparent dissociation constant of 3 x 10(-10) M. The binding of glypican-1 to VEGF165 is mediated by the heparan sulfate chains of glypican-1, because heparinase treatment abolishes this interaction. Only an excess of heparin or heparan sulfates but not other types of glycosaminoglycans inhibited this interaction. VEGF165 interacts specifically not only with rat myoblast glypican-1 but also with human endothelial cell-derived glypican-1. The binding of 125I-VEGF165 to heparinase-treated human vascular endothelial cells is reduced following heparinase treatment, and addition of glypican-1 restores the binding. Glypican-1 also potentiates the binding of 125I-VEGF165 to a soluble extracellular domain of the VEGF receptor KDR/flk-1. Furthermore, we show that glypican-1 acts as an extracellular chaperone that can restore the receptor binding ability of VEGF165, which has been damaged by oxidation. Taken together, these results suggest that glypican-1 may play an important role in the control of angiogenesis by regulating the activity of VEGF165, a regulation that may be critical under conditions such as wound repair, in which oxidizing agents that can impair the activity of VEGF are produced, and in situations were the concentrations of active VEGF are limiting.

Hypoxic regulation of vascular endothelial growth factor mRNA stability requires the cooperation of multiple RNA elements

Vascular endothelial growth factor (VEGF) is a key regulator of developmental, physiological, and tumor angiogenesis. Upregulation of VEGF expression by hypoxia appears to be a critical step in the neovascularization of solid cancers. The VEGF mRNA is intrinsically labile, but in response to hypoxia the mRNA is stabilized. We have systematically analyzed the regions in the VEGF mRNA that are responsible for its lability under normoxic conditions and for stabilization in response to hypoxia. We find that the VEGF mRNA not only contains destabilizing elements in its 3' untranslated region (3'UTR), but also contains destabilizing elements in the 5'UTR and coding region. Each region can independently promote mRNA degradation, and together they act additively to effect rapid degradation under normoxic conditions. Stabilization of the mRNA in response to hypoxia is completely dependent on the cooperation of elements in each of the 5'UTR, coding region, and 3'UTR. Combinations of any of two of these three regions were completely ineffective in responding to hypoxia, whereas combining all three regions allowed recapitulation of the hypoxic stabilization seen with the endogenous VEGF mRNA. We conclude that multiple regions in the VEGF mRNA cooperate both to ensure the rapid degradation of the mRNA under normoxic conditions and to allow stabilization of the mRNA in response to hypoxia. Our findings highlight the complexity of VEGF gene expression and also reveal a mechanism of gene regulation that could become the target for strategies of therapeutic intervention.

Normoxic and hypoxic regulation of vascular endothelial growth factor (VEGF) by astrocytoma cells is mediated by Ras

Vascular endothelial growth Factor (VEGF) has been identified as a key angiogenic factor involved in the growth and malignant progression of tumours. Glioblastoma multiforme (GBM) are the most common primary human brain tumours, histo-pathologically characterized by intense tumour angiogenesis. GBMs do not harbour oncogenic Ras mutations, but there is a functional up-regulation of Ras signaling through activation of receptor tyrosine kinases overexpressed by these tumours. We demonstrate that Ras pathway activation regulates VEGF secretion in astrocytoma cell lines. Ras pathway inhibition was carried out using genetic and pharmacologic techniques. Astrocytoma cells that were transfected to express the dominant inhibitory mutant H-Ras(N17) demonstrated a reduction in VEGF secretion under both normoxic and hypoxic conditions. Cells treated with the farnesyl transferase inhibitor L-744,832 demonstrated similar reductions in VEGF secretion. Furthermore, astrocytoma cells expressing a constitutively phosphorylated and truncated EGF-R common in GBMs (EGFRvIII or p140(EGF-R)) demonstrate further elevations in Ras activation, resulting in a further increase in VEGF secretion. We have previously demonstrated that activation of Ras plays a vital role in transducing mitogenic signals in human malignant astrocytoma cells. Our present results further extend the role of Ras activation in modulating tumour angiogenesis in these tumours. We propose that Ras may contribute to the angiogenic switch in astrocytomas.