Signal transduction by VEGF receptors in regulation of angiogenesis and lymphangiogenesis

The VEGF/VPF (vascular endothelial growth factor/vascular permeability factor) ligands and receptors are crucial regulators of vasculogenesis, angiogenesis, lymphangiogenesis and vascular permeability in vertebrates. VEGF-A, the prototype VEGF ligand, binds and activates two tyrosine kinase receptors: VEGFR1 (Flt-1) and VEGFR2 (KDR/Flk-1). VEGFR1, which occurs in transmembrane and soluble forms, negatively regulates vasculogenesis and angiogenesis during early embryogenesis, but it also acts as a positive regulator of angiogenesis and inflammatory responses, playing a role in several human diseases such as rheumatoid arthritis and cancer. The soluble VEGFR1 is overexpressed in placenta in preeclampsia patients. VEGFR2 has critical functions in physiological and pathological angiogenesis through distinct signal transduction pathways regulating proliferation and migration of endothelial cells. VEGFR3, a receptor for the lymphatic growth factors VEGF-C and VEGF-D, but not for VEGF-A, regulates vascular and lymphatic endothelial cell function during embryogenesis. Loss-of-function variants of VEGFR3 have been identified in lymphedema. Formation of tumor lymphatics may be stimulated by tumor-produced VEGF-C, allowing increased spread of tumor metastases through the lymphatics. Mapping the signaling system of these important receptors may provide the knowledge necessary to suppress specific signaling pathways in major human diseases.     

Restricted expression pattern of vegf-d in the adult and fetal mouse: high expression in the embryonic lung

Endothelial growth factors have become the target of intense research since the initial discovery of vascular endothelial growth factor (VEGF/VPF). At present, VEGF is established as a major inducer of angiogenesis in normal and pathological conditions. Recently several new members in the VEGF family have been described; VEGF-B/VRF, VEGF-C and VEGF-D. VEGF-D is most closely related to VEGF-C by virtue of the presence of N- and C-terminal extensions that are not found in other VEGF family members. We have here examined the expression pattern of vegf-d mRNA with in situ hybridization in developing and adult mice. This shows a restricted expression pattern, with high levels mainly in lung tissue. The expression in embryonic lung is upregulated prior to birth. Expression of vegf-d in other tissues, as well as in lung tissue of the E14 embryo, was either low or absent. This suggests that VEGF-D may be of special relevance for the vascularization of lung tissue during the last trimester of fetal development.     

Lymphangiogenesis and biological activity ov vascular endothelial growth factor-C]

Vascular endothelial growth factor (VEGF)-C is a new member of the VEGF family, a group of polypeptide growth factors which play key roles in the physiology and pathology of many aspects of the cardiovascular system, including vasculogenesis, hematopoiesis, angiogenesis and vascular permeability. VEGF signalling in endothelial cells occurs through three tyrosine kinase receptors (VEGFRs), expressed by endothelial cells and hematopoietic precursors. With respect to the first VEGF described, VEGF-A, which is an endothelial cell specific mitogen and key angiogenic factor, VEGF-C seems to play a major role in the development of the lymphatic system. This may reflect the different binding properties of VEGFs to VEGFRs, in that VEGF-A binds to VEGFR-1 and -2, whereas VEGF-C acts through VEGFR-3, whose expression becomes restricted to lymphatics and certain veins during development. However, the finding that VEGF-C also binds to and activates VEGFR-2 may explain why it induces angiogenesis under certain conditions, which makes it relevant to experimental or clinical settings in which one would wish to block or to stimulate angiogenesis. In this paper we briefly discuss current knowledge on the biological activity of VEGF-C, emphasizing that, as has already been shown for a number of other angiogenic factors, the biological effects of VEGF-C are strictly dependent on the activity of other angiogenic regulators present in the microenvironment of the responding endothelial cells.     

Biology of vascular endothelial growth factors

Angiogenesis is the process by which new blood vessels are formed from existing vessels. The vascular endothelial growth factors (VEGFs) are considered as key molecules in the process of angiogenesis. The VEGF family currently includes VEGF-A, -B, -C, -D, -E, -F and placenta growth factor (PlGF), that bind in a distinct pattern to three structurally related receptor tyrosine kinases, denoted VEGF receptor-1, -2, and -3. VEGF-C and VEGF-D also play a crucial role in the process of lymphangiogenesis. Here, we review the biology of VEGFs and evaluate their role in pathological angiogenesis and lymphangiogenesis.     

The comparison of VEGFR-1-binding domain of VEGF-A with modelled VEGF-C sheds light on receptor specificity

Receptor specificity determines the role of vascular endothelial growth factors (VEGFs), which either induce angiogenesis via VEGFR-1 and VEGFR-2 receptors or lymphangiogenesis via the VEGFR-3 receptor. Among the VEGFs, VEGF-A and VEGF-B predominantly induce angiogenesis while VEGF-C and VEGF-D induce lymphangiogenesis. The answer for the question of why VEGF-C and VEGF-D are not able to bind VEGFR-1 and behave as angiogenic growth factors may hide behind the details of the tertiary structures of these proteins. In the present study, the tertiary structure of human VEGF-C protein was modelled and the model was compared with the known human VEGF-A tertiary structure. In overall, the modelled structure highly resembled the structure of VEGF-A. The respective key residues that are involved in cysteine-knot motif formation in VEGF-A are similarly located and identically oriented in VEGF-C, indicating the presence of a VEGF-A-like homodimer. However, a VEGF-C homodimer created via monomer docking did not superimpose well with the VEGF-A homodimer. Rigid docking models of VEGF-C with the VEGFR-1 receptor revealed that in the VEGF-C–VEGFR-1 complex, the receptor–protein-interacting residues were not correctly oriented to induce angiogenesis via VEGFR-1. Mapping the electrostatic surface potentials to the protein surfaces revealed noteworthy number of dissimilarities between VEGF-A and VEGF-C, indicating that overall both proteins differ in their folding properties and stability.     

Differential mRNA and tissue expression of lymphangiogenic growth factors (VEGF-C and -D) and their receptor (VEGFR-3) during tail regeneration in a gecko

Lymphangiogenesis, the growth of new lymph vessels, has important roles in both normal and pathological lymphatic function. Despite recent advances, the precise molecular mechanisms behind the lymphangiogenic process remain unclear. The Australian marbled gecko, Christinus marmoratus, voluntarily drops its tail (autotomy) as a predator avoidance strategy. Following autotomy a new tail is regenerated including lymphatic drainage pathways. We examined the molecular control of lymphangiogenesis within the unique model of the regenerating gecko tail. Partial sequences were obtained of the gecko lymphangiogenic growth factors, vascular endothelial growth factor C (VEGF-C) and VEGF-D along with their receptor VEGFR-3. These were highly homologous to other vertebrates. Quantitative real-time polymerase chain reaction (PCR) demonstrated up-regulation of VEGF-C, VEGF-D and VEGFR-3 mRNA expression during the early and middle stages of tail regeneration (between 4 and 9 weeks following autotomy), in late regeneration (12 weeks) and during mid-regeneration (7 and 9 weeks), respectively. VEGF-C and VEGF-D immunostaining was observed lining some lymphatic-like and blood vessels in early–mid tail regeneration, indicating possible associations of the proteins with VEGFRs on endothelia. Keratinocytes and fibroblasts also showed positive staining of VEGF-C and VEGF-D in early–mid tail regeneration. Additionally, VEGF-C was localised in adipose tissue in all tail states examined. This work suggests that specific timings exist for the expression of the lymphangiogenic growth factors, VEGF-C and VEGF-D, and their receptor, VEGF-R3, throughout the regeneration of a functional lymphatic network. Along with localisation data, this suggests potential functions for the growth factors in lymphangiogenesis and angiogenesis throughout tail regeneration.     

VEGF—A和VEGF—C在皮肤恶性黑色素瘤表达的临床病理意义

目的：内皮细胞生长因子（Vascularendothelialgrowthfactor,VEGF）与恶性肿瘤转移密切相关,研究发现VEGF过度表达与恶性黑色素瘤转移有关,在本研究中通过研究VEGF在恶性黑色素瘤中的表达及与临床病理指标的相关性,为以VEGF为靶的抗转移治疗提供依据。方法：应用免疫组织化学技术检测恶性黑色素瘤中VEGF-A和VEGF-C表达,及与临床病理特点和生存状态的关系。结果：VEGF—A在皮肤恶性黑色素瘤中的阳性表达率是83．33％（30／36）,在色素痣中阳性表达率是15％（3／20）,两组间有显著性差异（P〈O．05）。VEGF—C在皮肤恶性黑色素瘤中的阳性表达率是88．9％（32／36）,在色素痣中阳性表达率是10％（2/20）,两组间有显著性差异（P〈0．01）。VEGF-A和VEGF—C表达与年龄、性别、肿瘤形态、肿瘤大小无显著关系,但与淋巴结转移和封闭血管环形成有关,VEGF-A和VEGF—C阳性病例淋巴结转移率和封闭血管环出现率显著高于VEGF-A和VEGF-C阴性病例。有统计学意义。对VEGF-A和VEGF-C表达与恶性黑色素瘤生存状态的关系分析显示,VEGF-A和VEGF-C表达阴性的病例的生存期和生存率均显著高于VEGF-A和VEGF-C表达阴性的病例,有统计学意义。结论：VEGF-A和VEGF-C表达与恶性黑色素瘤的淋巴结转移、血管形成和生存期相关,这两种蛋白过度表达反映黑色素瘤处于进展状态和预后差,可以作为黑色素瘤诊断、预后和复发预测的指标和靶向治疗的靶蛋白。     

Characterization of indolinones which preferentially inhibit VEGF-C- and VEGF-D-induced activation of VEGFR-3 rather than VEGFR-2.

VEGF-C and VEGF-D are lymphangiogenic factors that bind to and activate VEGFR-3, a fms-like tyrosine kinase receptor whose expression is limited almost exclusively to lymphatic endothelium in the adult. Processed forms of VEGF-C and VEGF-D can also activate VEGFR-2, a key player in the regulation of angiogenesis. There is increasing evidence to show that these receptor-ligand interactions play a pivotal role in a number of pathological situations. Inhibition of receptor activation by VEGF-C and VEGF-D could therefore be pharmaceutically useful. Furthermore, to understand the different roles of VEGF-C, VEGF-D, VEGFR-2 and VEGFR-3 in pathological situations it will be necessary to dissect the complex interactions of these ligands and their receptors. To facilitate such studies we cloned, sequenced and characterized the expression of rat VEGF-C and VEGF-D. We showed that Cys152-->Ser mutants of processed rat VEGF-C can activate VEGFR-3 but not VEGFR-2, while the corresponding mutation in rat VEGF-D inhibits its ability to activate both VEGFR-2 and VEGFR-3. We also synthesized and characterized indolinones that differentially block VEGF-C- and VEGF-D-induced VEGFR-3 kinase activity compared to that of VEGFR-2. These tools should be useful in analysing the different activities and roles of VEGF-C, VEGF-D and their ligands, and in blocking VEGFR-3-mediated lymphangiogenesis.     

卵巢上皮肿瘤淋巴转移与血管内皮生长因子C的表达

The aim of the present study was to explore the role of vascular endothelial growth factor-C (VEGF-C) in the process of angiogenesis, lymphangiogenesis and lymphatic metastasis in epithelial ovarian tumors. In situ hybridization and immunohistochemical staining for VEGF-C were performed in 30 epithelial ovarian carcinomas, 9 borderline tumors and 26 benign cystadenomas. Endothelial cells were immunostained with anti-VEGFR-3 pAb and anti-CD31 mAb, and VEGFR-3 positive vessels and microvessel density (MVD) were assessed by image analysis. VEGF-C mRNA and protein expression in ovarian epithelial carcinomas were significantly higher than that in borderline tumors and benign cystadenomas (p < 0.05 or p < 0.01). In ovarian epithelial carcinomas, VEGF-C protein expression, VEGFR-3 positive vessels and MVD were significantly higher in the cases of clinical stage III-IV and with lymphatic metastasis than those of clinical stage I-II and without lymphatic metastasis respectively (p < 0.05 or p < 0.01), VEGFR-3 positive vessels and MVD was significantly higher in the VEGF-C protein positive tumors than negative tumors (p < 0.05), VEGFR-3 positive vessels was significantly correlated with MVD(p < 0.01). These data suggest that VEGF-C might play a role in lymphatic metastasis via lymphangiogenesis and angiogenesis in epithelial ovarian carcinomas, and VEGF-C could be used as a biologic marker of metastasis in ovarian epithelial carcinomas.     

Microplate-based screening for small molecule inhibitors of neuropilin-2/vascular endothelial growth factor-C interactions

Vascular endothelial growth factor-C (VEGF-C) is a secreted growth factor essential for lymphangiogenesis. VEGF-C functions in both physiological and pathological lymphangiogenesis, particularly in tumor metastasis, making it an attractive therapeutic target. Members of two families of cell surface receptors transduce VEGF-C signals: neuropilin-2 (Nrp2) and VEGF-receptor (VEGFR)-2/3. Nrp2 is a promising target for inhibition because it is highly expressed in lymphatic vessels. Here we describe a microplate-based assay for discovery of VEGF-C/Nrp2 inhibitors. We optimize this assay for use in screening an inhibitor library and identify three novel Nrp2/VEGF-C binding inhibitors from the National Institutes of Health (NIH) Clinical Collection small molecule library.     

VEGF-C和VEGF-D在肝内胆管癌组织中的表达与淋巴结转移的关系及临床意义

目的:探讨胆管癌患者血管内皮生长因子C和D(vascular endothelial growth factor-C and-D,VEGF-C and VEGF-D)在胆管癌组织中的表达及其与肿瘤淋巴结转移的关系。方法:应用免疫组化SABC法及Real-time PCR法检测57例胆管癌组织和正常胆管组织中VEGF-C、VEGF-D蛋白及其mRNA的表达。结果:胆管癌组织VEGF-C和VEGF-D表达明显高于正常胆管组织(P<0.01),其中淋巴结转移组VEGF-C、VEGF-D的表达与淋巴结未转移组间统计学差异显著(P<0.05)。VEGF-C和VEGF-D在胆管癌组织中的表达与淋巴结转移有关(P<0.01)。结论:胆管癌细胞非摄入性高表达的VEGF-C和VEGF-D与淋巴结转移密切相关,可作为评估胆管癌患者预后的重要参考指标。     

Signalling via vascular endothelial growth factor receptor-3 is sufficient for lymphangiogenesis in transgenic mice

Vascular endothelial growth factor receptor-3 (VEGFR-3) has an essential role in the development of embryonic blood vessels; however, after midgestation its expression becomes restricted mainly to the developing lymphatic vessels. The VEGFR-3 ligand VEGF-C stimulates lymphangiogenesis in transgenic mice and in chick chorioallantoic membrane. As VEGF-C also binds VEGFR-2, which is expressed in lymphatic endothelia, it is not clear which receptors are responsible for the lymphangiogenic effects of VEGF-C. VEGF-D, which binds to the same receptors, has been reported to induce angiogenesis, but its lymphangiogenic potential is not known. In order to define the lymphangiogenic signalling pathway we have created transgenic mice overexpressing a VEGFR-3-specific mutant of VEGF-C (VEGF-C156S) or VEGF-D in epidermal keratinocytes under the keratin 14 promoter. Both transgenes induced the growth of lymphatic vessels in the skin, whereas the blood vessel architecture was not affected. Evidence was also obtained that these growth factors act in a paracrine manner in vivo. These results demonstrate that stimulation of the VEGFR-3 signal transduction pathway is sufficient to induce specifically lymphangiogenesis in vivo.     

VEGF-C和VEGF-D在肝内胆管癌组织中的表达与淋巴结转移的关系及临床意义

目的：探讨胆管癌患者血管内皮生长因子C和D（vascular endothelial growth factor-Cand．D,VEGF．CandVEGF．D）在胆管癌组织中的表达及其与肿瘤淋巴结转移的关系。方法：应用免疫组化SABC法及Real-timePCR法检测57例胆管癌组织和正常胆管组织中VEGF-C、vEGF-D蛋白及其mRNA的表达。结果：胆管癌组织VEGF—C和VEGF．D表达明显高于正常胆管组织（P〈0．叭）,其中淋巴结转移组VEGF-C、VEGF—D的表达与淋巴结未转移组间统计学差异显著（P〈0．05）。VEGF-C和VEGF-D在胆管癌组织中的表达与淋巴结转移有关（P〈0．01）。结论：胆管癌细胞非摄入性高表达的VEGF．C和VEGF．D与淋巴结转移密切相关,可作为评估胆管癌患者预后的重要参考指标。     

Vascular endothelial growth factor-C promotes the growth and invasion of gallbladder cancer via an autocrine mechanism

Vascular endothelial growth factor-C (VEGF-C) has a well-defined action on neoplastic lymphangiogenesis and angiogenesis through VEGF receptor-3 (VEGFR-3) and VEGFR-2, respectively, which are generally expressed in endothelial cells. The function of the VEGF-C/receptors pathway in tumor cell types is largely unknown. In this study, we examined the expression and role of VEGF-C/receptors in gallbladder cancer (GBC) cells. We examined the expression of VEGF-C in 50 surgical specimens from gallbladder cancer and three human gallbladder cancer cell lines. Both siRNA and neutralizing antibody to deplete the expression of VEGF-C were used to characterize the biological effect of VEGF-C in GBC NOZ cells. Furthermore, we examined the expression of its receptors, VEGFR-3 and VEGFR-2, in three human GBC cell lines. Our results are as follows: The expression of VEGF-C in the invasive marginal portion was significantly higher than the expression in the central portions. All the three GBC cell lines expressed VEGF-C. Treatment of NOZ cells with VEGF-C siRNA or a neutralizing antibody suppressed cell proliferation and invasion. Moreover, all the three GBC cell lines expressed VEGFR3, but only the NOZ cells expressed VEGFR-2 mRNA. Treatment of NOZ cells with a VEGFR-3 neutralizing antibody suppressed cell invasion, but treatment of NOZ cells with a VEGFR-2 neutralizing antibody suppressed cell proliferation and invasion. In conclusion, GBC cells express both VEGF-C and its receptors. VEGF-C may have a role in the progressive growth and invasion of human GBC through an autocrine mechanism.     

Vascular endothelial growth factor (VEGF)/VEGF-C mosaic molecules reveal specificity determinants and feature novel receptor binding patterns

Vascular endothelial growth factors (VEGFs) and their receptors play key roles in angiogenesis and lymphangiogenesis. VEGF activates VEGF receptor-1 (VEGFR-1) and VEGFR-2, whereas VEGF-C activates VEGFR-2 and VEGFR-3. We have created a library of VEGF/VEGF-C mosaic molecules that contains factors with novel receptor binding profiles, notably proteins binding to all three VEGF receptors ("super-VEGFs"). The analyzed super-VEGFs show both angiogenic and lymphangiogenic effects in vivo, although weaker than the parental molecules. The composition of the VEGFR-3 binding molecules and scanning mutagenesis revealed determinants of receptor binding and specificity. VEGFR-2 and VEGFR-3 showed striking differences in their requirements for VEGF-C binding; extracellular domain 2 of VEGFR-2 was sufficient, whereas in VEGFR-3, both domains 1 and 2 were necessary.     

Distinct characteristics of circulating vascular endothelial growth factor-a and C levels in human subjects

The mechanisms that lead from obesity to atherosclerotic disease are not fully understood. Obesity involves angiogenesis in which vascular endothelial growth factor-A (VEGF-A) plays a key role. On the other hand, vascular endothelial growth factor-C (VEGF-C) plays a pivotal role in lymphangiogenesis. Circulating levels of VEGF-A and VEGF-C are elevated in sera from obese subjects. However, relationships of VEGF-C with atherosclerotic risk factors and atherosclerosis are unknown. We determined circulating levels of VEGF-A and VEGF-C in 423 consecutive subjects not receiving any drugs at the Health Evaluation Center. After adjusting for age and gender, VEGF-A levels were significantly and more strongly correlated with the body mass index (BMI) and waist circumference than VEGF-C. Conversely, VEGF-C levels were significantly and more closely correlated with metabolic (e.g., fasting plasma glucose, hemoglobin A1c, immunoreactive insulin, and the homeostasis model assessment of insulin resistance) and lipid parameters (e.g., triglycerides, total cholesterol (TC), low-density-lipoprotein cholesterol (LDL-C), and non-high-density-lipoprotein cholesterol (non-HDL-C)) than VEGF-A. Stepwise regression analyses revealed that independent determinants of VEGF-A were the BMI and age, whereas strong independent determinants of VEGF-C were age, triglycerides, and non-HDL-C. In apolipoprotein E-deficient mice fed a high-fat-diet (HFD) or normal chow (NC) for 16 weeks, levels of VEGF-A were not significantly different between the two groups. However, levels of VEGF-C were significantly higher in HFD mice with advanced atherosclerosis and marked hypercholesterolemia than NC mice. Furthermore, immunohistochemistry revealed that the expression of VEGF-C in atheromatous plaque of the aortic sinus was significantly intensified by feeding HFD compared to NC, while that of VEGF-A was not. In conclusion, these findings demonstrate that VEGF-C, rather than VEGF-A, is closely related to dyslipidemia and atherosclerosis.     

Characterization of the interaction between endostatin short Peptide and VEGF receptor 3

Corneal angiogenesis and lymphangiogenesis are induced by vascular endothelial growth factors (VEGFs) signaling through its receptors VEGFR-1, -2, and -3. Endostatin is a peptide antagonist of these receptors that causes inhibition of bFGF-induced corneal angiogenesis and lymphangiogenesis. Here we show that binding of VEGF-C and endostatin to recombinant VEGFR-3 is competitive. Alignments of the primary amino acid sequences of VEGF-C and the C-terminal endostatin peptide (mEP: LEQKAASCHNSYIVLCIENSFMTSFSK) identified two conserved cysteine residues separated by seven amino acids. Peptides of VEGF-C and mEP containing these conserved residues bound toVEGFR-3. However, substitution of alanine for either of the cysteines in the mEP peptide perturbed the secondary structure, and this mutated peptide was unable to bind to VEGFR-3. Analysis by surface plasmon resonance demonstrated that the binding of the mEP peptide for recombinant VEGFR-3 had a Ka of 1.41x107M-1s-1, Kd of 0.6718 s-1, and a KD of 4.78x10-8M. Characterization of the mechanism of endostatin binding to VEGFR-3 may lead to the development of novel therapies for lymphangiogenesis-related disorders, such as transplant rejection, lymphedema, and cancer metastasis.