Novel human vascular endothelial growth factor genes VEGF-B and VEGF-C localize to chromosomes 11q13 and 4q34, respectively

The role of VEGF in Cancer angiogenesis and tumorigenesis: Insights for anti-VEGF therapy

Vascular endothelial growth factor (VEGF) is a critical regulator of angiogenesis, playing a pivotal role in both physiological and pathological processes. It promotes the formation of new blood vessels and activates downstream signaling pathways that regulate endothelial cell function. This review highlights recent advancements in the understanding of VEGF's molecular structure and its isoforms, as well as their implications in disease progression. It also explores the mechanisms of VEGF inhibitors. While VEGF inhibitors show promise in the treatment of cancer and other diseases, their clinical use faces significant challenges, including drug resistance, side effects, and complex interactions with other signaling pathways. To address these challenges, future research should focus on: (i) enhancing the understanding of VEGF subtypes and their distinct roles in various diseases, supporting the development of personalized treatment strategies; (ii) developing combination therapies that integrate VEGF inhibitors with other targeted treatments to overcome resistance and improve efficacy; (iii) optimizing drug delivery systems to reduce off-target effects and enhance therapeutic outcomes. These approaches aim to improve the effectiveness and safety of VEGF-targeted therapies, offering new possibilities for the treatment of VEGF-related diseases.

Soluble FLT-1 in angiogenesis: pathophysiological roles and therapeutic implications

Fine-tuning angiogenesis, the development of new blood vessels, is essential for maintaining a healthy circulatory and lymphatic system. The small glycoprotein vascular endothelial growth factors (VEGF) are the key mediators in this process, binding to their corresponding membrane-bound VEGF receptors (VEGFRs) to activate angiogenesis signaling pathways. These pathways are crucial throughout human life as they are involved in lymphatic and vascular endothelial cell permeability, migration, proliferation, and survival. Neovascularization, the formation of abnormal blood vessels, occurs when there is a dysregulation of angiogenesis and can result in debilitating disease. Hence, VEGFRs have been widely studied to understand their role in disease-causing angiogenesis. VEGFR1, also known as Fms-like tyrosine kinase-1 (FLT-1), is also found in a soluble form, soluble FLT-1 or sFLT-1, which is known to act as a VEGF neutralizer. It is incorporated into anti-VEGF therapy, designed to treat diseases caused by neovascularization. Here we review the journey of sFLT-1 discovery and delve into the alternative splicing mechanism that creates the soluble receptor, its prevalence in disease states, and its use in current and future potential therapies.

Chronic Encapsulated Expanding Hematomas After Stereotactic Radiosurgery for Intracranial Arteriovenous Malformations: An International Multicenter Case Series

BACKGROUND

Stereotactic radiosurgery (SRS) offers a minimally invasive treatment modality for appropriately selected intracranial arteriovenous malformations (AVMs). Recent reports have described the development of rare, delayed chronic encapsulated expanding hematomas (CEEHs) at the site of an angiographically confirmed obliterated AVM.

OBJECTIVE

To elucidate the incidence, characteristics, and management of CEEH in patients with AVM after SRS.

METHODS

The records of all patients who underwent SRS for an intracranial AVM at 4 institutions participating in the International Radiosurgery Research Foundation between 1987 and 2021 were retrospectively reviewed. Data regarding characteristics of the AVM, SRS treatment parameters, CEEH presentation, management, and outcomes were collected and analyzed.

RESULTS

Among 5430 patients, 15 developed a CEEH at a crude incidence of 0.28%. Nine patients were female, and the mean age was 43 ± 14.6 years. Nine patients underwent surgical evacuation, while 6 were managed conservatively. The median CEEH development latency was 106 months after SRS. The patients were followed for a median of 32 months, and 9 patients improved clinically, while 6 patients remained stable. No intraoperative complications were reported after CEEH resection, although 1 patient recovered from postoperative meningitis requiring intravenous antibiotics.

CONCLUSION

CEEH is a rare, late complication of AVM SRS with an incidence of 0.28% and a median latency of 106 months. In the presence of a delayed and symptomatic expanding hematoma in the bed of an angiographically obliterated AVM, surgical resection resulted in clinical improvement in most patients. Conservative management is possible in asymptomatic patients with stable, small-sized hematomas in deeply seated locations.

The Role of Periostin in Angiogenesis and Lymphangiogenesis in Tumors

Simple Summary

Cancers are common diseases that affect people of all ages worldwide. For this reason, continuous attempts are being made to improve current therapeutic options. The formation of metastases significantly decreases patient survival. Therefore, understanding the mechanisms that are involved in this process seems to be crucial for effective cancer therapy. Cancer dissemination occurs mainly through blood and lymphatic vessels. As a result, many scientists have conducted a number of studies on the formation of new vessels. Many studies have shown that proangiogenic factors and the extracellular matrix protein, i.e., periostin, may be important in tumor angio- and lymphangiogenesis, thus contributing to metastasis formation and worsening of the prognosis.

Abstract

Periostin (POSTN) is a protein that is part of the extracellular matrix (ECM) and which significantly affects the control of intracellular signaling pathways (PI3K-AKT, FAK) through binding integrin receptors (αvβ3, αvβ5, α6β4). In addition, increased POSTN expression enhances the expression of VEGF family growth factors and promotes Erk phosphorylation. As a result, this glycoprotein controls the Erk/VEGF pathway. Therefore, it plays a crucial role in the formation of new blood and lymphatic vessels, which may be significant in the process of metastasis. Moreover, POSTN is involved in the proliferation, progression, migration and epithelial-mesenchymal transition (EMT) of tumor cells. Its increased expression has been detected in many cancers, including breast cancer, ovarian cancer, non-small cell lung carcinoma and glioblastoma. Many studies have shown that this protein may be an independent prognostic and predictive factor in many cancers, which may influence the choice of optimal therapy.

Snake venom vascular endothelial growth factors (svVEGFs): Unravelling their molecular structure, functions, and research potential

Vascular endothelial growth factor (VEGF) is a key regulator of angiogenesis, a physiological process characterized by the formation of new vessels from a preexisting endothelium. VEGF has also been implicated in pathologic states, such as neoplasias, intraocular neovascular disorders, among other conditions. VEGFs are distributed in seven different families: VEGF-A, B, C, D, and PIGF (placental growth factor), which are identified in mammals; VEGF-E, which are encountered in viruses; and VEGF-F or svVEGF (snake venom VEGF) described in snake venoms. This is the pioneer review of svVEGF family, exploring its distribution among the snake venoms, molecular structure, main functions, and potential applications.

Intersecting Mechanisms of Hypoxia and Prostaglandin E2-Mediated Inflammation in the Comparative Biology of Oral Squamous Cell Carcinoma

The importance of inflammation in the pathogenesis of cancer was first proposed by Rudolph Virchow over 150 years ago, and our understanding of its significance has grown over decades of biomedical research. The arachidonic acid pathway of inflammation, including cyclooxygenase (COX) enzymes, PGE2 synthase enzymes, prostaglandin E2 (PGE2) and PGE2 receptors has been extensively studied and has been associated with different diseases and different types of cancers, including oral squamous cell carcinoma (OSCC). In addition to inflammation in the tumour microenvironment, low oxygen levels (hypoxia) within tumours have also been shown to contribute to tumour progression. Understandably, most of our OSCC knowledge comes from study of this aggressive cancer in human patients and in experimental rodent models. However, domestic animals develop OSCC spontaneously and this is an important, and difficult to treat, form of cancer in veterinary medicine. The primary goal of this review article is to explore the available evidence regarding interaction between hypoxia and the arachidonic acid pathway of inflammation during malignant behaviour of OSCC. Overlapping mechanisms in hypoxia and inflammation can contribute to tumour growth, angiogenesis, and, importantly, resistance to therapy. The benefits and controversies of anti-inflammatory and anti-angiogenic therapies for human and animal OSCC patients will be discussed, including conventional pharmaceutical agents as well as natural products.

Structural Studies on an Anti-Angiogenic Peptide Using Molecular Modeling

BACKGROUND

Development of VEGF antagonists, which inhibit its interaction with the receptors, is a widely used strategy for the inhibition of angiogenesis and tumor growth.

OBJECTIVES

In the present study, a VEGFR-1 antagonistic peptide was designed and its potential for binding to VEGFR-1 and VEGFR-2 was evaluated by theoretical studies.

MATERIALS AND METHODS

Based on the X-ray structure of VEGF-B/VEGFR-1 D2 (PDB ID: 2XAC), an antagonistic peptide (known as VGB1) was designed, and its model structure was constructed using homology modeling in the MODELLER, version 9.16. The validity of the modeled structures was estimated employing several web tools. Finally, one model was chosen and molecular dynamics (MD) simulation was applied using the GROMACS package, version 5.1.4, to allow conformational relaxation of the structure. Next, docking process of the peptide with VEGFR-1 and VEGFR-2 was performed by HADDOCK web server and the docking structures were optimized by MD simulation for 20 ns. The far-UV circular dichroism (CD) spectrum of VGB1 was recorded to evaluate the overall structure of the peptide.

RESULTS

The far-UV CD spectrum indicated that VGB1 contains α helix structure. The results from docking studies suggested that Van der Waals and nonpolar interactions play the most important role in the peptide binding to VEGFR-1. In addition, our results implicated the relevance of both Van der Waals and electrostatic interactions in the formation of complex between VGB1 and VEGFR-2. In addition to the common binding residues in the corresponding region of VEGF-A and VEGF-B, additional binding residues also were predicted for the interaction of VGB1 with VEGFR-1 and VEGFR-2.

CONCLUSIONS

The results of MD and molecular docking simulations predicted that VGB1 recognizes both VEGFR-1 and VEGFR-2, which may lead to the prevention of the downstream signaling triggered by these receptors.

Resistance Mechanisms to Anti-angiogenic Therapies in Cancer

Tumor growth and metastasis rely on tumor vascular network for the adequate supply of oxygen and nutrients. Tumor angiogenesis relies on a highly complex program of growth factor signaling, endothelial cell (EC) proliferation, extracellular matrix (ECM) remodeling, and stromal cell interactions. Numerous pro-angiogenic drivers have been identified, the most important of which is the vascular endothelial growth factor (VEGF). The importance of pro-angiogenic inducers in tumor growth, invasion and extravasation make them an excellent therapeutic target in several types of cancers. Hence, the number of anti-angiogenic agents developed for cancer treatment has risen over the past decade, with at least eighty drugs being investigated in preclinical studies and phase I-III clinical trials. To date, the most common approaches to the inhibition of the VEGF axis include the blockade of VEGF receptors (VEGFRs) or ligands by neutralizing antibodies, as well as the inhibition of receptor tyrosine kinase (RTK) enzymes. Despite promising preclinical results, anti-angiogenic monotherapies led only to mild clinical benefits. The minimal benefits could be secondary to primary or acquired resistance, through the activation of alternative mechanisms that sustain tumor vascularization and growth. Mechanisms of resistance are categorized into VEGF-dependent alterations, non-VEGF pathways and stromal cell interactions. Thus, complementary approaches such as the combination of these inhibitors with agents targeting alternative mechanisms of blood vessel formation are urgently needed. This review provides an updated overview on the pathophysiology of angiogenesis during tumor growth. It also sheds light on the different pro-angiogenic and anti-angiogenic agents that have been developed to date. Finally, it highlights the preclinical evidence for mechanisms of angiogenic resistance and suggests novel therapeutic approaches that might be exploited with the ultimate aim of overcoming resistance and improving clinical outcomes for patients with cancer.

Vascular endothelial growth factor C is an indicator of lymph node metastasis in thoracic esophageal squamous cellcarcinomas and its role in long-term survival after surgery

BACKGROUND

To define the role of vascular endothelial growth factor C (VEGF-C) on lymph node (LN) metastasis of human esophageal squamous cell carcinoma (ESCC), and to investigate its impact on overall survival.

METHODS

Real-time polymerase chain reaction was introduced to quantify the expression of VEGF-CmRNA. One hundred and eight samples (59 tumor tissue and 59 paired normal tissue) were analyzed.

RESULTS

VEGF-CmRNA expression was significantly higher in tumor tissues than in normal mucosa (P = 0.02). VEGF-CmRNA expression was significantly higher in LN (+) patients than in LN (-) patients (P = 0.04). VEGF-CmRNA expression was related to a positive LN number (P = 0.06) and a positive LN station number (P = 0.04). VEGF-CmRNA expression was significantly higher in stage III and IV patients than in stage I and II patients (P = 0.03). A logistic regression model showed that VEGF-CmRNA and T status were independent risk factors for LN metastasis(P < 0.05). In univariate analysis, survival tended to be poorer in the VEGF-CmRNA high expression group (22.0 months vs. 44.0 months, P = 0.08). A Cox regression model revealed that a positive LN station number was the only independent risk factor for overall survival (P < 0.01).

CONCLUSION

VEGF-C was a useful indicator for LN metastasis in human ESCC, and it might have some influence on long-term survival by affecting LN metastasis.

Roles of vascular endothelial growth factor in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal devastating neurodegenerative disorder, involving progressive degeneration of motor neurons in spinal cord, brainstem, and motor cortex. Riluzole is the only drug approved in ALS but it only confers a modest improvement in survival. In spite of a high number of clinical trials no other drug has proved effectiveness. Recent studies support that vascular endothelial growth factor (VEGF), originally described as a key angiogenic factor, also plays a key role in the nervous system, including neurogenesis, neuronal survival, neuronal migration, and axon guidance. VEGF has been used in exploratory clinical studies with promising results in ALS and other neurological disorders. Although VEGF is a very promising compound, translating the basic science breakthroughs into clinical practice is the major challenge ahead. VEGF-B, presenting a single safety profile, protects motor neurons from degeneration in ALS animal models and, therefore, it will be particularly interesting to test its effects in ALS patients. In the present paper the authors make a brief description of the molecular properties of VEGF and its receptors and review its different features and therapeutic potential in the nervous system/neurodegenerative disease, particularly in ALS.

The VEGF signaling pathway in cancer: the road ahead

The vascular endothelial growth factor (VEGF) family of soluble protein growth factors consists of key mediators of angiogenesis and lymphangiogenesis in the context of tumor biology. The members of the family, VEGF-A (also known as VEGF), VEGF-B, VEGF-C, VEGF-D, and placenta growth factor (PIGF), play important roles in vascular biology in both normal physiology and pathology. The generation of a humanized neutralizing antibody to VEGF-A (bevacizumab, also known as Avastin) and the demonstration of its benefit in numerous human cancers have confirmed the merit of an anti-angiogenesis approach to cancer treatment and have validated the VEGF-A signaling pathway as a therapeutic target. Other members of the VEGF family are now being targeted, and their relevance to human cancer and the development of resistance to anti-VEGF-A treatment are being evaluated in the clinic. Here, we discuss the potential of targeting VEGF family members in the diagnosis and treatment of cancer.

The role of the VEGF-C/VEGFRs axis in tumor progression and therapy

Vascular endothelial growth factor C (VEGF-C) has been identified as a multifaceted factor participating in the regulation of tumor angiogenesis and lymphangiogenesis. VEGF-C is not only expressed in endothelial cells, but also in tumor cells. VEGF-C signaling is important for progression of various cancer types through both VEGF receptor-2 (VEGFR-2) and VEGF receptor-3 (VEGFR-3). Likewise, both receptors are expressed mainly on endothelial cells, but also expressed in tumor cells. The dimeric VEGF-C undergoes a series of proteolytic cleavage steps that increase the protein binding affinity to VEGFR-3; however, only complete processing, removing both the N- and C-terminal propeptides, yields mature VEGF-C that can bind to VEGFR-2. The processed VEGF-C can bind and activate VEGFR-3 homodimers and VEGFR-2/VEGFR-3 heterodimers to elicit biological responses. High levels of VEGF-C expression and VEGF-C/VEGFRs signaling correlate significantly with poorer prognosis in a variety of malignancies. Therefore, the development of new drugs that selectively target the VEGF-C/VEGFRs axis seems to be an effective means to potentiate anti-tumor therapies in the future.

An investigation of growth factors and lactoferrin in naturally occurring ovine pulmonary adenomatosis

Ovine pulmonary adenomatosis (OPA), also known as jaagsiekte, is a transmissible beta retrovirus-induced lung tumour of sheep that has several features resembling human bronchoalveolar carcinoma (BAC). Angiogenesis has been suggested to be one of the most important factors underlying tumour growth and invasion. This process involves the action of growth factors including vascular endothelial growth factor (VEGF)-C, basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF)-C and its receptor (PDGFR-α). Bovine lactoferrin (bLF), an iron and heparin-binding glycoprotein secreted into various biological fluids, has been implicated in innate immunity and has anti-inflammatory and anti-tumour functions. Tissues from 16 cases of OPA were compared with tissues from seven healthy control sheep by immunohistochemistry. Expression of the markers was assessed semi-quantitatively by ascribing an immunoreactivity score (IRS) with a maximum value of 300. VEGF-C, bFGF, PDGF-C, PDGFR-α and bLF signals were detected in 10/16, 15/16, 12/16, 15/16 and 10/16 of the OPA cases studied, respectively. bLF expression was weak in the neoplastic epithelial cells (IRS 21.4 ± 10.0) in contrast to high levels detected in infiltrating macrophages and plasma cells (IRS 141.3 ± 24.8 and 140.0 ± 25.1, respectively). The PDGFR-α IRS was elevated for neoplastic epithelial cells (108.9 ± 18.2) and was lowest for macrophages and plasma cells (20.4 ± 13.1 and 13.7 ± 12.4, respectively). These results suggest that bFGF, VEGF-C and PDGF-C have roles in the pathogenesis of OPA. bLF may activate macrophages and plasma cells in these lesions, but limited expression of bLF by neoplastic cells may be a consequence of defective or impaired function of this molecule.

The vascular endothelial growth factor family in adverse pregnancy outcomes

BACKGROUND

Pre-eclampsia, small-for-gestational-age infants, preterm birth and recurrent miscarriage complicate a significant number of pregnancies. The vascular endothelial growth factor (VEGF) family of angiogenic growth factors is implicated in the pathophysiology of these complications. We aimed to elucidate the role of these angiogenic factors in placentation and to evaluate the predictive value of their protein concentrations and genetic variations in pregnancy complications.

METHODS

We performed a systematic search of PubMed, and retrieved original articles. The search included a combination of terms such as VEGF-A, placental growth factor (PlGF), kinase insert domain receptor, fms-like-tyrosine-kinase receptor 1, soluble fms-like-tyrosine-kinase receptor 1, pre-eclampsia, small-for-gestational-age infants, preterm birth, recurrent miscarriage, placenta, prediction and polymorphisms.

RESULTS

This review summarizes the current knowledge of the roles of the VEGF family in early placentation and of the abnormalities in maternal plasma and placental expression of angiogenic proteins in adverse pregnancy outcomes compared with normal pregnancy. PlGF and sFLT-1 in combination with other clinical and biochemical markers in late first or second trimester appear to predict early-onset pre-eclampsia with a high sensitivity and specificity. However, VEGF family proteins do not have sufficient power to accurately predict late-onset pre-eclampsia, small-for-gestational age pregnancies or preterm birth. Functional polymorphisms in these angiogenic genes are implicated in pregnancy complications, but their contribution appears to be minor.

CONCLUSIONS

Although the VEGF family has important roles in normal and complicated pregnancy, the current predictive value of the VEGF family as biomarkers appears to be limited to early-onset pre-eclampsia.

The effects of vascular endothelial growth factor C knockdown in esophageal squamous cell carcinoma

PURPOSE

We investigated the role of vascular endothelial growth factor C (VEGF-C) in esophageal squamous cell carcinoma (ESCC) by knocking down VEGF-C expression in the ESCC cell line EC9706.

METHODS

Immunohistochemistry and in situ hybridization techniques were used to detect the expression of VEGF-C expression in ESCC tissues. We also investigated the relationship between VEGF-C expression and lymph node metastasis. We designed a siRNA expression plasmid for VEGF-C and transfected it into EC9706 cells. Stable clones were selected, and VEGF-C expression was analyzed by RT-PCR and western blotting. Cells were inoculated into nude mice. The expression of VEGF-C in the resulting tumors was analyzed by immunohistochemistry and in situ hybridization.

RESULTS

VEGF-C is highly expressed in ESCC and correlated with lymph node metastasis, as high levels were observed in patients presenting with lymph node metastases relative to those who did not (P < 0.01). Transfection with VEGF-C-siRNA decreased the expression of VEGF-C mRNA and protein. ESCC cells stably transfected with VEGF-C-siRNA expressed very low levels of VEGF-C (P < 0.01 compared with control). This knockdown effect persisted when the cells were inoculated into nude mice and allowed to form tumors.

CONCLUSIONS

The siRNA-targeted knockdown of VEGF-C led to a significant reduction in VEGF-C expression. This siRNA technique could be used for gene therapy in ESCC.

Tying the knot: the cystine signature and molecular-recognition processes of the vascular endothelial growth factor family of angiogenic cytokines

The cystine-knot motif, made up of three intertwined disulfide bridges, is a unique feature of several toxins, cyclotides and growth factors, and occurs in a variety of species, including fungi, insects, molluscs and mammals. Growth factor molecules containing the cystine-knot motif serve as ligands for a diverse range of receptors and play an important role in extracellular signalling. This superfamily of polypeptides comprises several homodimeric and heterodimeric molecules that are central characters in both health and disease. Amongst these molecules are a group of proteins that belong to the vascular endothelial growth factor (VEGF) subfamily. The members of this family are known angiogenic factors that regulate processes leading to blood vessel formation in physiological and pathological conditions. The focus of the present review is on the structural characteristics of proteins that belong to the VEGF family and on signal-transduction pathways that become initiated via the VEGF receptors.

The effect of the expression of vascular endothelial growth factor (VEGF)-C and VEGF receptor-3 on the clinical outcome in patients with gastric carcinoma

AIMS

We aimed to investigate the relationship among VEGF-C/VEGFR-3 expression, lymphatic metastasis and patient prognosis in gastric carcinoma.

MATERIAL AND METHODS

VEGF-C and VEGFR-3 expression in gastric carcinoma tissues obtained from 204 patients who underwent curative gastrectomy (105 cases presented with lymph node metastasis and 99 cases without metastasis) was examined immunohistochemically. There was no significant difference in the other clinicopathologic variables except for postoperative pathological tumor stage (pT) and TNM stage between the two groups. The results were statistically processed.

RESULTS

The results showed that VEGF-C was located mainly in the cytoplasm of tumor cells and VEGFR-3 was found predominantly in the endothelium of lymphatic vessels. VEGF-C and VEGFR-3 expression was more frequent in gastric carcinoma tissues than that in normal gastric tissues, 54.90% and 35.29% respectively, which revealed that the expression of VEGF-C and VEGFR-3 was significantly stronger in patients with lymph node metastasis than in those without metastasis. Patients who had positive staining for VEGF-C showed significantly less favorable survival rates compared with patients who had negative staining for VEGF-C. The survival rates of patients who had positive staining for VEGFR-3 also were significantly lower compared with patients who had negative staining for VEGFR-3. Patients who had positive staining for both VEGF-C and VEGFR-3 exhibited the most unfavorable prognosis. Multivariate analysis demonstrated that the expression of VEGF-C and VEGFR-3 was an independent prognostic determinant. In addition, faint to moderate VEGF-C expression was detected in normal gastric epithelial cells (18/204, 8.9%).

CONCLUSIONS

VEGF-C and VEGFR-3 expression could serve as a prognostic biomarker in patients with gastric carcinoma.

Role and therapeutic potential of VEGF in the nervous system

The development of the nervous and vascular systems constitutes primary events in the evolution of the animal kingdom; the former provides electrical stimuli and coordination, while the latter supplies oxygen and nutrients. Both systems have more in common than originally anticipated. Perhaps the most striking observation is that angiogenic factors, when deregulated, contribute to various neurological disorders, such as neurodegeneration, and might be useful for the treatment of some of these pathologies. The prototypic example of this cross-talk between nerves and vessels is the vascular endothelial growth factor or VEGF. Although originally described as a key angiogenic factor, it is now well established that VEGF also plays a crucial role in the nervous system. We describe the molecular properties of VEGF and its receptors and review the current knowledge of its different functions and therapeutic potential in the nervous system during development, health, disease and in medicine.

Preoperative serum levels of serum VEGF-C is associated with distant metastasis in colorectal cancer patients

PURPOSE

Vascular endothelial growth factor-C (VEGF-C) is one of the most potent lymphangiogenic members of the VEGF family that has been associated with lymph node metastasis and poor prognosis in patients with colorectal cancer (CRC). In this study, we evaluated the relationship of preoperative serum VEGF-C (sVEGF-C) and survival in CRC patients.

MATERIALS AND METHODS

sVEGF-C levels were determined, prior to resection, in a cohort of 120 newly presenting patients with CRC by quantitative ELISA.

RESULTS

Patients who had positive lymph node involvement and higher Dukes' staging (C&D) were associated with shorter time to metastases as expected (p = 0.002 and 0.001, respectively). Patients with distant metastasis had significantly lower levels of sVEGF-C than those without histopathologically proven disease (p = 0.004). However, there was no significant difference in the median sVEGF-C level in patients with or without lymph node metastatic involvement (91 pg/ml vs. 124 pg/ml; p = 0.81). Patients with a sVEGF-C concentration less than the median value (103 pg/ml) showed a poorer overall survival than patients with sVEGF-C levels greater than the median; but this was not statistically significant.

CONCLUSIONS

In this study, low sVEGF-C levels are associated with distant metastasis; hence, preoperative levels may aid in the selection of CRC patients who require further investigation.

Aortic adventitial angiogenesis and lymphangiogenesis promote intimal inflammation and hyperplasia

INTRODUCTION

Adventitial inflammation is known to influence neointimal formation and vascular remodeling. The present study was aimed to clarify the relationship between neointima hyperplasia and adventitial angiogenesis and lymphangiogenesis after balloon-induced aortic endothelial injury.

METHODS

Seventy male Wistar rats were randomly divided into six interventional groups and one control group. The intimal area/medial area ratio (I/M ratio), the adventitial macrophage index, and the number of adventitial microvessels (Ad-MV) and lymphatic vessels (Ad-LV) in the aorta were measured, and the mRNA expressions of VEGF-A, VEGFR-1, VEGF-C, VEGFR-3, PDGF-B, and PDGFR-beta in the aortic wall were quantified by real-time RT-PCR.

RESULTS

Compared with the control group, the I/M ratio, macrophage index, Ad-MV, Ad-LV, and the mRNA expressions of VEGF-A, VEGFR-1, VEGF-C, VEGFR-3, PDGF-B, and PDGFR-beta in interventional groups increased significantly after balloon-induced injury. I/M ratio showed significant correlations with Ad-MV and Ad-LV after balloon intervention. Multiple linear regression analysis indicated that Ad-MV and Ad-LV were independent factors of intimal hyperplasia.

CONCLUSION

Adventitial angiogenesis and lymphangiogenesis are induced by intimal inflammation after balloon injury, and these neogenetic vessels in turn promote intimal inflammation and hyperplasia probably via delivery and activation of inflammatory cells.

Current insights on the biology and clinical aspects of VEGF regulation

Vascular endothelial growth factor (VEGF) is a key molecule that orchestrates the formation and function of vascular networks. Impaired regulation of angiogenesis is implicated in a number of pathologic states. For instance, neoplasias exhibit uncontrolled angiogenesis, whereas ischemia and states of vascular insufficiency involve reduced VEGF activity. As the role of VEGF has been elucidated in these disease processes, its therapeutic role has been developed. The Food and Drug Administration has approved several anti-VEGF agents for treating colorectal, lung, and kidney cancer. VEGF-inducing agents have also been used experimentally to induce angiogenesis in patients with critical limb ischemia. As more knowledge is gathered about the biology of VEGF and its receptors, there is greater promise for therapeutic modulation of VEGF expression. The purpose of this review is to describe the various therapeutic and biologic factors that regulate the expression of VEGF.

Correlations of the expression of vascular endothelial growth factor B and its isoforms in hepatocellular carcinoma with clinico-pathological parameters

BACKGROUND

The vascular endothelial growth factor (VEGF) is involved in the growth of cancer cells through angiogenesis. At present the role of VEGF-B has not been clarified completely. We investigated correlations of the expression of VEGF-B and its isoforms, VEGF-B167 and VEGF-B186, by alternative splicing in hepatocellular carcinoma (HCC) with the pathological findings and prognosis.

METHODS

Forty-eight patients with HCC were investigated. We examined the mRNA expression of total VEGF-B, VEGF-B167 and VEGF-B186 in primary HCC and non-cancerous tissues using quantitative real-time reverse transcription polymerase chain reaction (RT-PCR) analysis.

RESULTS

In 16 (33.3%) of 48 HCCs, the expression of total VEGF-B increased compared with the corresponding non-cancerous liver tissues. Regarding the isoforms, the expression of VEGF-B167 and VEGF-B186 was increased in 17 (35.4%) of 48 and 33 (68.75%) of 48 HCCs, respectively. Cases with high expression level of total VEGF-B in HCC significantly correlated with the advanced pathological stage (P < 0.018), tumor multiplicity (P < 0.033), vascular invasion (P < 0.045) and lack of capsule formation (P < 0.027). The result in VEGF-B167 was similar to total VEGF-B.

CONCLUSIONS

Our results indicated that the expression of VEGF-B is correlated with tumor growth and invasiveness in HCC. VEGF-B167 seemed to be the clinically dominant isoform.

The role of VEGF-C staining in predicting regional metastasis in melanoma

Sentinel lymph node status is the most important prognostic factor in primary melanoma. The number of melanoma-associated lymphatic vessels has been associated with sentinel lymph node status and survival. Vascular endothelial growth factor-C (VEGF-C) is found to promote tumour-associated lymphatic vessel growth. In many human neoplasms, VEGF-C expression in neoplastic cells or tumour-associated macrophages (TAMs) has been linked to lymphatic dissemination of tumour cells. Recent studies have suggested a correlation between VEGF-C expression in primary melanoma and the presence of lymph node metastasis. We performed VEGF-C immunohistochemical staining on melanoma tissues of 113 patients with known sentinel lymph node status. We showed that both high VEGF-C expression in melanoma cells and TAMs are positively associated with the presence of a positive sentinel lymph node. No correlation with Breslow thickness, Clark invasion level or ulceration could be detected. VEGF-C expression in melanoma cells was predictive of a shorter overall and disease-free survival, without being an independent predictor of survival. Our results confirm that VEGF-C expression in primary cutaneous melanoma plays a role in the lymphatic spread of the tumour.

VEGF: an essential mediator of both angiogenesis and endochondral ossification

During bone growth, development, and remodeling, angiogenesis as well as osteogenesis are closely associated processes, sharing some essential mediators. Vascular endothelial growth factor (VEGF) was initially recognized as the best-characterized endothelial-specific growth factor, which increased vascular permeability and angiogenesis, and it is now apparent that this cytokine regulates multiple biological functions in the endochondral ossification of mandibular condylar growth, as well as long bone formation. The complexity of VEGF biology is paralleled by the emerging complexity of interactions between VEGF ligands and their receptors. This narrative review summarizes the family of VEGF-related molecules, including 7 mammalian members, namely, VEGF, placenta growth factor (PLGF), and VEGF-B, -C, -D, -E, and -F. The biological functions of VEGF are mediated by at least 3 corresponding receptors: VEGFR-1/Flt-1, VEGFR-2/Flk-1, VEGFR-3/Flt-4 and 2 co-receptors of neuropilin (NRP) and heparan sulfate proteoglycans (HSPGs). Current findings on endochondral ossification are also discussed, with emphasis on VEGF-A action in osteoblasts, chondroblasts, and chondroclasts/osteoclasts and regulatory mechanisms involving oxygen tension, and some growth factors and hormones. Furthermore, the therapeutic implications of recombinant VEGF-A protein therapy and VEGF-A gene therapy are evaluated. Abbreviations used: VEGF, Vascular endothelial growth factor; PLGF, placenta growth factor; NRP, neuropilin; HSPGs, heparan sulfate proteoglycans; FGF, fibroblast growth factor; TGF, transforming growth factor; HGF, hepatocyte growth factor; TNF, tumor necrosis factor; ECM, extracellular matrix; RTKs, receptor tyrosine kinases; ERK, extracellular signal kinases; HIF, hypoxia-inducible factor.

Vascular endothelial growth factor family of ligands and receptors: review

VEGF signaling often represents a critical rate-limiting step in physiological angiogenesis. The VEGF family comprises seven secreted glycoproteins that are designated VEGF-A, VEGF-B, VEGF-C, VEGF-D, VEGF-E, placental growth factor (PlGF) and VEGF-F. The VEGF family members bind their cognate receptors. The receptors identified so far are designated VEGFR-1, VEGFR-2, VEGFR-3 and the neuropilins (NP-1 and NP-2). We review in this article the biology of the VEGF ligands and the receptors.

Molecular and functional diversity of vascular endothelial growth factors

Members of the vascular endothelial growth factor (VEGF) family are crucial regulators of neovascularization and are classified as cystine knot growth factors that specifically bind cellular receptor tyrosine kinases VEGFR-1, VEGFR-2, and VEGFR-3 with high but variable affinity and selectivity. The VEGF family has recently been expanded and currently comprises seven members: VEGF-A, VEGF-B, placenta growth factor (PlGF), VEGF-C, VEGF-D, viral VEGF (also known as VEGF-E), and snake venom VEGF (also known as VEGF-F). Although all members are structurally homologous, there is molecular diversity among the subtypes, and several isoforms, such as VEGF-A, VEGF-B, and PlGF, are generated by alternative exon splicing. These splicing isoforms exhibit differing properties, particularly in binding to co-receptor neuropilins and heparin. VEGF family proteins play multiple physiological roles, such as angiogenesis and lymphangiogenesis, while exogenous members (viral and snake venom VEGFs) display activities that are unique in physiology and function. This review will highlight the molecular and functional diversity of VEGF family proteins.

The biology of vascular endothelial growth factor-B (VEGF-B)

The formation of new blood vessels (angiogenesis) is critical for both embryonic development and a variety of normal postnatal physiological processes. Various pathological processes, most notably tumour growth and chronic inflammation, are also known to be dependent on the new vessel formation. Amongst the variety of factors that contribute to the regulation of this complex process, vascular endothelial growth factor (VEGF or VEGF-A) is arguably the most well characterised. The VEGF family of growth factors is now known to comprise of VEGF-A plus four additional members, including VEGF-B. In contrast to VEGF-A, surprisingly little is known about the precise biological role of VEGF-B. Unlike VEGF-A, which binds to the two receptor tyrosine kinases VEGFR-1 (Flt-1) and VEGFR-2 (Flk-1/KDR), VEGF-B binds only to VEGFR-1 and the functional significance of VEGFR-1 signalling has remained problematic. More recently, however, evidence has emerged suggesting a key role for VEGFR-1 signalling in pathological angiogenesis and this has raised the possibility that, like VEGF-A, VEGFR-1 specific ligands such as VEGF-B may provide for novel therapeutic strategies and/or represent new therapeutic targets. Here we review current knowledge of the biology of VEGF-B. We note that although analysis to date, including expression profiling and the generation of gene targetted mice, has provided only limited insights, future studies using recently generated recombinant proteins and antagonist monoclonal antibodies should provide for a more comprehensive understanding.

Vascular endothelial growth factor-C (VEGF-C) expression predicts lymph node metastasis of transitional cell carcinoma of the bladder

PURPOSE

It has been found that expression of vascular endothelial growth factor-C (VEGF-C) in several carcinomas is significantly associated with angiogenesis, lymphangiogenesis and regional lymph node metastasis. However, VEGF-C expression in bladder transitional cell carcinoma (TCC) has not yet been reported. To elucidate the role of VEGF-C in bladder TCC, we examined VEGF-C expression in bladder TCC and pelvic lymph node metastasis specimens obtained from patients who underwent radical cystectomy.

METHODS

Eighty-seven patients who underwent radical cystectomy for clinically organ-confined TCC of the bladder were enrolled in the present study. No neoadjuvant treatments, except transurethral resection of the tumor, were given to these patients. The VEGF-C expressions of 87 bladder tumors and 20 pelvic lymph node metastasis specimens were examined immunohistochemically and the association between VEGF-C expression and clinicopathological factors, including angiogenesis as evaluated by microvessel density (MVD), was also examined.

RESULTS

Vascular endothelial growth factor-C expression was found in the cytoplasm of tumor cells, but not in the normal transitional epithelium. Vascular endothelial growth factor-C expression was significantly associated with the pathological T stage (P = 0.0289), pelvic lymph node metastasis (P < 0.0001), lymphatic involvement (P = 0.0008), venous involvement (P = 0.0002) and high MVD (P = 0.0043). The multivariate analysis demonstrated that VEGF-C expression and high MVD in bladder TCC were independent risk factors influencing the pelvic lymph node metastasis. Moreover, the patients with VEGF-C-positive tumors had significantly poorer prognoses than those with the VEGF-C-negative tumors (P = 0.0087) in the univariate analysis. The multivariate analysis based on Cox proportional hazard model showed that the independent prognostic factors were patient age (P = 0.0132) and pelvic lymph node metastasis (P = 0.0333).

CONCLUSION

The present study suggests that VEGF-C expression is an important predictive factor of pelvic lymph node metastasis in bladder cancer patients.

Constitutive and inducible expression and regulation of vascular endothelial growth factor

Vascular endothelial growth factor (VEGF), which was originally discovered as vascular permeability factor, is critical to human cancer angiogenesis through its potent functions as a stimulator of endothelial cell survival, mitogenesis, migration, differentiation and self-assembly, as well as vascular permeability, immunosuppression and mobilization of endothelial progenitor cells from the bone marrow into the peripheral circulation. Genetic alterations and a chaotic tumor microenvironment, such as hypoxia, acidosis, free radicals, and cytokines, are clearly attributed to numerous abnormalities in the expression and signaling of VEGF and its receptors. These perturbations confer a tremendous survival and growth advantage to vascular endothelial cells as manifested by exuberant tumor angiogenesis and a consequent malignant phenotype. Understanding the regulatory mechanisms of both inducible and constitutive VEGF expression will be crucial in designing effective therapeutic strategies targeting VEGF to control tumor growth and metastasis. In this review, molecular regulation of VEGF expression in tumor cells is discussed.

Clinical significance of VEGF-C status in tumour cells and stromal macrophages in non-small cell lung cancer patients

Recent experimental studies have revealed that tumour-associated stromal macrophages as well as tumour cells express vascular endothelial growth factor C (VEGF-C), which plays important roles in lymphangiogenesis, which is a critical factor in the progression of many malignant tumours including non-small-cell lung cancer (NSCLC). However, no clinical study on VEGF-C expression in both stromal macrophages and tumour cells has been reported, and we conducted the present study to address the issue in resected NSCLC. A total of 206 patients with completely resected pathologic stage I-IIIA NSCLC were retrospectively reviewed. Expression of VEGF-C in primary lung tumour was assessed immunohistochemically. Expression of VEGF-C in tumour cells was high in 125 patients (60.7%), and that in stromal macrophages was positive in 136 patients (71.2%). The status of VEGF-C in tumour cells or in stromal macrophages was not correlated with nodal status or angiogenesis. The 5-year survival rate of high tumoral VEGF-C patients (60.7%) was significantly lower than that of low tumoral VEGF-C patients (39.3%) (P=0.046), and a multivariate analysis confirmed that tumoral VEGF-C status was a significant and independent prognostic factor. Moreover, tumour showing high VEGF-A and VEGF-C expression in tumour cells showed the poorest prognosis (5-year survival rate, 45.1%). The status of VEGF-C in stromal macrophages was not correlated with the prognosis. In conclusion, tumoral VEGF-C status, not stromal VEGF-C status, was a significant prognostic factor in resected NSCLC.

Angiogenesis and prostate cancer tumor growth

The initiation of new blood vessels through angiogenesis is critical to tumor growth. Tumor cells release soluble angiogenic factors that induce neovascularization, without which nutrients and oxygen would not be available to allow tumors to grow more than 2-3 mm in diameter. This "angiogenic switch" or angiogenic phenotype requires an imbalance between proangiogenic and antiangiogenic factors since the formation of new blood vessels is highly regulated. This review discusses angiogenesis mediators, and the potential for manipulation of angiogenic factors as a practical cancer therapy, particularly in prostate cancer.

Vascular endothelial growth factor is a chemoattractant for trophoblast cells

A role for angiogenic growth factors in trophoblast invasion has been postulated. Directional motility (chemotaxis) is an important function of trophoblast cells. We have previously shown that vascular endothelial growth factor (VEGF) increases the random movement of trophoblast cells although placental growth factor (PlGF) has no effect. Heparin inhibited this effect of VEGF. Motility of trophoblast cells has been proposed to be mediated by a nitric oxide (NO) pathway. We hypothesized that VEGF but not PlGF would be chemotactic for trophoblast cells. Chemotaxis of a first trimester extravillous trophoblast cell line, SGHPL-4, and primary isolates of first trimester and term trophoblast cells was measured using a Boyden chamber. Initial experiments to optimize the time of the experiment and identify a positive control were performed. Subsequent experiments ran for 20 h, used 0.5 per cent FBS or 10 ng/ml PDGF as negative and positive controls and were performed in triplicate. VEGF (1, 10 and 100 ng/ml+/-1 microg/ml heparin or +/-100 microM L-NAME) and PlGF (1, 10, 100 ng/ml) were tested. The chamber was placed in a 5 per cent CO(2) in air, 37 degrees C incubator. The number of cells in the lower chamber were counted. There was a dose dependent increase in chemotactic motility of the SGHPL-4 cell line and term trophoblast cells in response to VEGF. PlGF had no effect on the movement of the first trimester trophoblast cell line but did increase the motility of the term trophoblast cells in a dose dependent manner. Heparin increased the cellular motility of both cell types alone. It also further enhanced the chemoactivity of VEGF on the term trophoblast cells but not the cell line. L-NAME did not affect the VEGF-stimulated motility of the first trimester cell line. However, in the term trophoblast cells L-NAME increased the directional cellular motility in the absence of, or in the presence of low concentrations of VEGF. In conclusion, the first trimester and term trophoblast cells appeared to respond differently to the various factors tested in the present study that may reflect differential cellular function as gestation progresses.

Inhibition of breast carcinoma and trophoblast cell invasiveness by vascular endothelial growth factor

Vascular endothelial growth factor (VEGF) is a potent endothelial cell mitogen and angiogenic growth factor that enhances endothelial cell invasion through the extracellular matrix (ECM). While various cell types express VEGF receptors, little is known about the biological actions of VEGF on nonendothelial cells. Therefore, the main objective of the present study was to determine the effect of VEGF on the in vitro invasiveness and proliferation of human MDA-MB-231 breast carcinoma cells and human HTR-8/SVneo trophoblast cells. Reverse-transcriptase polymerase chain reaction analysis demonstrated the presence of transcripts encoding VEGF receptors (VEGFR) -1, -2, and -3 as well as neuropilins-1 and -2 in the trophoblast cells, and the presence of transcripts encoding VEGFR-2 and neuropilins-1 and -2 in the breast carcinoma cells. Both cell lines also expressed transcripts for VEGF-A, -B, -C and -D, as well as for placenta growth factor (PlGF). Although incubation with exogenous VEGF-A(165) or VEGF-A(121) did not affect the rate of proliferation of either the trophoblast or the breast carcinoma cells, incubation with these molecules reduced their ability to invade through reconstituted ECM (Matrigel). The effect of VEGF-A(165) on the invasiveness of both cell lines was inhibited by the inclusion of a neutralizing antibody to VEGF. Exogenous VEGF-A(165) also decreased the cell surface expression of the urokinase-type plasminogen activator (a molecule required for invasion) by the breast carcinoma and trophoblast cells. These results indicate that the biological actions of VEGF on certain cell types may differ from the effects of this molecule on vascular endothelial cells, and therefore are relevant to angiogenesis-based therapies.

Lymphangiogenesis in tumors: what do we know?

Lymphangiogenesis, the growth of new lymphatic vessels, has long been regarded as a putative efficient pathway to neoplastic metastization. However, until recently consistent data regarding reliable lymphatic endothelial cell markers were lacking. Moreover, the presence of new formed lymphatic vessels was considered a largely disputable concept. Now, this scenario has changed significantly, owing to consistent reports describing novel lymphatic endothelial cell (LEC) markers, the demonstration of new formed lymphatic vessels within the bulk of the tumor in animal models and human neoplasms, and the characterization of the VEGF-C/VEGFR-3 pathway. We herein review the major breakthroughs in the field of lymphangiogenesis, with special emphasis on novel and reliable LEC markers, such as prox-1, LYVE-1, and podoplanin, as well as on the pathological assessment of lymphangiogenesis as a putative prognostic factor for human neoplasms.

Clinical significance of vascular endothelial growth factor C and vascular endothelial growth factor receptor 3 in patients with nonsmall cell lung carcinoma

BACKGROUND

Vascular endothelial growth factor C (VEGF-C) plays an important role in lymphangiogenesis and activates VEGF receptor 3 (VEGFR-3). By contrast, lymphatic spread is an important prognostic factor in patients with nonsmall cell lung carcinoma (NSCLC). The objective of the current study was to determine whether the expression of VEGF-C and VEGFR-3 correlates with clinicopathologic factors and prognosis in patients with primary NSCLC.

METHODS

The authors conducted a retrospective review of 180 consecutive patients who underwent complete resection for NSCLC and who did not receive any chemotherapy or radiotherapy prior to surgery. Immunohistochemical staining for VEGF-C and VEGFR-3 was performed. The clinicopathologic implications of VEGF-C and VEGFR-3 expression were analyzed statistically.

RESULTS

Of 180 patients with NSCLC, 137 patients (76.1%) were positive for VEGF-C, and 40 patients (22.2%) were positive for VEGFR-3. VEGF-C expression was observed frequently in patients with adenocarcinoma (P = 0.026). For VEGFR-3 expression, significant correlations were demonstrated with age (P = 0.02), gender (P = 0.008), and histologic differentiation in patients with squamous cell carcinoma (P = 0.03). Patients who had positive staining for VEGF-C showed significantly less favorable survival rates compared with patients who had negative staining for VEGF-C (P = 0.003). The survival rates of patients who had positive staining for VEGFR-3 also were significantly lower compared with patients who had negative staining for VEGFR-3 (P < 0.001). Patients who had positive staining for both VEGF-C and VEGFR-3 exhibited the most unfavorable prognoses. Univariate analysis revealed the following prognostic factors: gender (P = 0.03), tumor status (T1,T2 vs. T3; P < 0.01), lymph node status (negative vs. positive; P < 0.01), tumor size (< or = 35 mm vs. > 35 mm; P < 0.01), disease stage (Stage I vs. Stages II and III; P < 0.01), VEGF-C expression (negative vs. positive; P < 0.01), VEGFR-3 expression (negative vs. positive; P < 0.01) and combined VEGF-C and/or VEGFR-3 expression (both positive vs. VEGF-C or VEGFR-3 positive; P < 0.01). Multivariate analysis demonstrated that VEGFR-3 expression was the only independent negative prognostic factor (P < 0.01).

CONCLUSIONS

VEGF-C and VEGFR-3 expression may be indicative of survival rates for patients with NSCLC.

Characterization of platelet-derived growth factor-C (PDGF-C): expression in normal and tumor cells, biological activity and chromosomal localization

The predicted platelet-derived growth factor-C (PDGF-C) polypeptide contains an N-terminal CUB-like domain and a C-terminal domain with homology to members of the PDGF/vascular endothelial growth factor (VEGF) family. PDGF-C mRNA is widely expressed in normal tissues and does not appear to be up-regulated in the tumor cell lines tested. The PDGF-C gene was mapped to human chromosome 4q31-32. PDGF-C protein and the CUB domain of PDGF-C expressed in Escherichia coli, were able to stimulate proliferation of human artery smooth muscle cells, but were inactive on umbilical vein endothelial cells, osteoblasts, fibroblasts, skeletal muscle cells (SkMC), bovine chondrocytes, and rat myocardium cells. Although the mitogenic activity of PDGF-C and the CUB domain was only observed at concentrations ranging from 1 to 10 microg/ml, substitution of Cys(124) by Ser or deletion of Cys(124) significantly reduced the mitogenic activity. Our data suggest a possible role of the CUB domain of PDGF-C in addition to its role in maintaining latency of the PDGF domain.

Placental expression of VEGF, PlGF and their receptors in a model of placental insufficiency-intrauterine growth restriction (PI-IUGR)

Placental development requires adequate and organized interaction of vascular growth factors and their receptors, including vascular endothelial growth factor (VEGF) and placental growth factor (PlGF). Both VEGF and PlGF, acting through the tyrosine kinase receptors VEGFR-1 and VEGFR-2, have been implicated in playing a role in ovine placental vascular development. The present studies describe the placental expression of components of the VEGF family at two maturational time points (55 and 90 days post coitus, dpc) in a hyperthermic-induced ovine model of placental insufficiency-intrauterine growth restriction (PI-IUGR). Both caruncular and cotyledonary VEGF and PlGF mRNA concentration increased with gestational age (P< 0.05), whereas only cotyledonary VEGF and PlGF protein concentration increased over gestation (P< 0.002). At 55 dpc, VEGF mRNA concentration was elevated in hyperthermic (HT) ewes, compared to control thermoneutral (TN) animals (TN; 0.52+/-0.08 vs HT; 1.27+/-0.17 VEGF/GAPDH, P< 0.001). At 90 dpc, expression of PlGF and VEGF mRNA was not altered by the HT treatment. Both TN cotyledonary VEGFR-1 and VEGFR-2 mRNA expression levels rose significantly over the period studied (P< 0.05 and P< 0.01 respectively). Receptor mRNA concentration in HT cotyledonary tissue was significantly reduced at 90 dpc (VEGFR-1; TN 0.21+/-0.02 vs HT 0.11+/-0.01 VEGFR-1/actin, P< 0.05, VEGFR-2; TN 0.18+/-0.05 vs HT 0.07+/-0.01 VEGFR-2/actin, P< 0.01). Soluble VEGFR-1 (sVEGFR-1) mRNA was not detected in these tissues. These alterations in growth factor and growth factor receptor mRNA expression, as a result of environmental heat stress early in placental development, could impair normal placental vascular development. Furthermore, alterations in VEGF, VEGFR-1 and VEGFR-2 mRNA expression, during the period of maximal placental growth, may contribute to the development of placental insufficiency, and ultimately intrauterine growth restriction.

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.

Co-expression of VEGF-C and its receptors, VEGFR-2 and VEGFR-3, in endothelial cells of lymphangioma. Implication in autocrine or paracrine regulation of lymphangioma

Lymphangioma has long been thought of as congenital malformations resulting from the failure of lymphatic vessels communicating with the venous system in the fetal period. Alternatively, it is proposed to be true neoplasm originated from the transformation of lymphatic endothelia. To extend the molecular basis of the pathogenesis of lymphangioma, we have characterized the expression of vascular endothelial growth factor (VEGF) and VEGF receptors (VEGFR) in 29 cases of lymphangioma by RNA in situ hybridization. Endothelial cells of lymphangioma co-express transcripts of VEGF-C and its receptors VEGFR-3 (Flt4) and VEGFR-2 (Flk1), which are not detectable in the adjacent connective tissue. In contrast, there is little or no expression of VEGF-C, VEGFR-3, and VEGFR-2 mRNA in endothelial cells of hemangiomas, angiosarcomas, or normal lymphatic vessels of the small or large intestines. The results suggest that VEGF-C and its receptors may take active parts in the formation of lymphangioma by autocrine or paracrine regulation.

Multiple forms of mouse vascular endothelial growth factor-D are generated by RNA splicing and proteolysis

The secreted glycoprotein vascular endothelial growth factor-D (VEGF-D) is angiogenic, lymphangiogenic, and promotes metastatic spread of tumor cells via lymphatic vessels. VEGF-D consists of a receptor-binding domain (VEGF homology domain) and N- and C-terminal propeptides. Proteolytic processing produces numerous forms of human VEGF-D, including fully processed derivatives (containing only the VEGF homology domain), partially processed, and unprocessed derivatives. Proteolysis is essential to generate human VEGF-D that binds the angiogenic receptor VEGF receptor-2 (VEGFR-2) and the lymphangiogenic receptor VEGFR-3 with high affinity. Here, we report that alternative use of an RNA splice donor site in exon 6 of the mouse VEGF-D gene produces two different protein isoforms, VEGF-D(358) and VEGF-D(326), with distinct C termini. The two isoforms were both expressed in all adult mouse tissues and embryonic stages of development analyzed. Both isoforms are proteolytically processed in a similar fashion to human VEGF-D to generate a range of secreted derivatives and bind and cross-link VEGFR-3 with similar potency. The isoforms are differently glycosylated when expressed in vitro. This study demonstrates that RNA splicing, protein glycosylation, and proteolysis are mechanisms for generating structural diversity of mouse VEGF-D.

Development of the avian lymphatic system

Recently, highly specific markers of the lymphatic endothelium have been found enabling us to reinvestigate the embryonic origin of the lymphatics. Here we present a review of our studies on the development of the lymphatic system in chick and quail embryos. We show that the lymphatic endothelium is derived from two sources: the embryonic lymph sacs and mesenchymal lymphangioblasts. Proliferation studies reveal a BrdU-labeling index of 11.5% of lymph sac endothelial cells by day 6.25, which drops to 3.5% by day 7. Lymphangioblasts are able to integrate into the lining of lymph sacs. Lymphatic endothelial cells express the vascular endothelial growth factor (VEGF) receptors-2 and -3. Their ligand, VEGF-C, is expressed almost ubiquitously in embryonic and fetal tissues. Elevated expression levels are found in the tunica media of large blood vessels, which usually serve as major routes for growing lymphatics. The homeobox gene, Prox1, is expressed in lymphatic but not in blood vascular endothelial cells throughout all stages examined, namely, in developing lymph sacs of day 6 embryos and in lymphatics at day 16. Experimental studies show the existence of lymphangioblasts in the mesoderm, a considerable time before the development of the lymph sacs. Lymphangioblasts migrate from the somites into the somatopleure and contribute to the lymphatics of the limbs. Our studies indicate that these lymphangioblasts already express Prox1.

Co-localization of vascular endothelial growth factor and its two receptors flt-1 and kdr in the mink placenta

Placental angiogenesis plays an important role in placental development and morphogenesis. Vascular endothelial growth factor (VEGF) is a well-known angiogenic growth factor, which has previously been localized in different epitheliochorial and haemochorial placenta types. In the present study VEGF and its Flt-1(VEGFR-1) and KDR (VEGFR-2) receptors were immunolocalized in the endotheliochorial mink placenta throughout gestation. VEGF, Flt-1 and KDR co-localized to fetal and maternal microvascular endothelial cells, but with a temporal difference, displaying KDR in endothelial cells throughout gestation, whereas the VEGF and Flt-1 maternal endothelial cell staining was most intense during late gestation. Additionally, KDR was found in vascular related mesenchymal cells. The VEGF-receptors were also localized in non-endothelial cells, e.g. the uterine luminal and glandular epithelium as well as the trophoblast. Our results are in agreement with former studies, showing the different effects of the Flt-1-and KDR receptors in respect of angiogenesis. More importantly, the present study of the endotheliochorial placenta localizes the VEGF-ligand-receptor system in non-endothelial cells, and thereby strengthen the hypothesis that VEGF, apart from its well-established angiogenic properties, must also have additional functional roles in the establishment and development of the placenta.

VEGF-B expression in human primary breast cancers is associated with lymph node metastasis but not angiogenesis

Angiogenesis is essential for tumour growth and metastasis. It is regulated by numerous angiogenic factors, one of the most important being vascular endothelial growth factor (VEGF). Recently VEGF-B, a new VEGF family member that binds to the tyrosine kinase receptor flt-1, has been identified. Although the importance of VEGF has been shown in many human tumour types, the contribution of VEGF-B to tumour neovascularization is unknown in any tumour type. This study therefore measured the mRNA level of VEGF-B and its receptor flt-1 by ribonuclease protection assay and the pattern of VEGF-B expression by immunohistochemistry in 13 normal breast samples and 68 invasive breast cancers. Flt-1 expression was significantly higher in tumours than in normal breast (p=0.02) but no significant difference was seen in VEGF-B between normal and neoplastic breast (p=0.3). There was a significant association between VEGF-B and node status (p=0.02) and the number of involved nodes (p=0.01), but not with age (p=0.7), size (p=0.6), oestrogen receptor (ER) (p=0.2), grade (p=0.5) or vascular invasion (p=0.16). No significant relationship was present between VEGF-B and flt-1 (p=0.2) or tumour vascularity (p=0.4). VEGF-B was expressed mostly in the cytoplasm of tumour cells, although occasional stromal components including fibroblasts and endothelial cells were also positive. No difference in VEGF-B expression was observed adjacent to regions of necrosis, in keeping with this VEGF family member not being hypoxically regulated. These findings suggest that VEGF-B may contribute to tumour progression by a non-angiogenic mechanism, possibly by increasing plasminogen activators and hence metastasis, as has been described in vitro. Measurement of VEGF-B together with other angiogenic factors may identify a poor prognostic patient group, which may benefit from anti-VEGF receptor therapy targeted to flt-1 (VEGFR1) as well as kdr (VEGFR2).

Vascular endothelial growth factor-C (VEGF-C) expression in human colorectal cancer tissues

Vascular endothelial growth factor-C (VEGF-C) functions specifically to induce lymphangiogenesis. We examined the relationship between expression of VEGF-C and clinicopathological features in patients with colorectal cancer. The expression of VEGF-C in the 99 primary tumours and 18 metastatic lymph nodes from colorectal cancer patients was examined immunohistochemically. To verify VEGF-C mRNA expression, reverse transcriptase-polymerase chain reaction (RT-PCR) was carried out. The expression of VEGF-C correlated with lymphatic involvement, lymph nodes metastasis, and depth of invasion. On the other hand, correlations were nil with regard to gender of the patients, histologic type, venous involvement, and liver metastasis. The expression of VEGF-C in metastatic lymph nodes was fairly consistent with this expression in the primary tumour. Survival time was shorter for VEGF-C positive groups than for VEGF-C negative ones, but with no statistically significant difference. RT-PCR findings revealed that the expression of VEGF-C mRNA correlated mostly with that of VEGF-C protein expression. VEGF-C may play an important role in lymphatic spread of colorectal cancer.