What is the role of vascular endothelial growth factor-related molecules in tumor angiogenesis?

Involvement of RhoA/Rho kinase signaling in VEGF-induced endothelial cell migration and angiogenesis in vitro

OBJECTIVE

Growth factor-induced angiogenesis involves migration of endothelial cells (ECs) into perivascular areas and requires active remodeling of the endothelial F-actin cytoskeleton. The small GTPase RhoA previously has been implicated in vascular endothelial growth factor (VEGF)-induced signaling pathways, but its role has not been clarified.

METHODS AND RESULTS

VEGF induced the activation of RhoA and recruited RhoA to the cell membrane of human ECs. This increase in RhoA activity is necessary for the VEGF-induced reorganization of the F-actin cytoskeleton, as demonstrated by adenoviral transfection of dominant-negative RhoA. Rho kinase mediated this effect of RhoA, as was demonstrated by the use of Y-27632, a specific inhibitor of Rho kinase. Inhibition of Rho kinase prevented the VEGF-enhanced EC migration in response to mechanical wounding but had no effect on basal EC migration. Furthermore, in an in vitro model for angiogenesis, inhibition of either RhoA or Rho kinase attenuated the VEGF-mediated ingrowth of ECs in a 3-dimensional fibrin matrix.

CONCLUSIONS

VEGF-induced cytoskeletal changes in ECs require RhoA and Rho kinase, and activation of RhoA/Rho kinase signaling is involved in the VEGF-induced in vitro EC migration and angiogenesis.

Prognostic and predictive indicators in operable breast cancer

Because of its biological heterogeneity and wide spectrum of responsiveness to different treatments, breast cancer is a complex disease of difficult clinical management. Over the past several years, knowledge of the molecular mechanisms regulating normal and aberrant cell growth leading to cancer has been enhanced. These advances have enabled the identification of an increasing number of surrogate biomarkers, which have been correlated with prognosis or used as predictors of response to specific treatments. Axillary nodal status, age, tumor size, pathologic grade, and hormone receptor status are the established prognostic and/or predictive factors for selection of adjuvant treatments. The role of new biomarkers, such as p53, HER2/neu, angiogenesis, and the proliferation index value, is promising; however, the clinical value of their determination must be provided by prospective clinical studies.

Vascular endothelial growth factor-D is an independent prognostic factor in epithelial ovarian carcinoma

We assessed the presence of vascular endothelial growth factor (VEGF)-C, VEGF-D and their receptor VEGFR-3 by immunohistochemistry in 59 epithelial ovarian carcinomas, 11 borderline tumours and 20 benign cystadenomas. VEGF-C and VEGF-D were generally expressed in tumour cells and also in endothelia adjacent to tumour nests which showed a strong staining for them. VEGFR-3 was expressed in lymphatic and vascular endothelial cells adjacent to tumour nests. Immunoreactivity was significantly more frequent as lesions progressed from a benign tumour to advanced carcinoma. A strong correlation was found between VEGF-C and VEGF-D detected in carcinoma and VEGFR-3 detected in neighbouring endothelial cells. Increased expression of VEGF-C, VEGF-D and VEGFR-3 was significantly associated with lymph node metastasis and peritoneal metastasis outside the pelvis. There was a significant correlation between the high levels of VEGF-C and VEGF-D proteins, and poor survival. The presence of VEGF-D was an independent prognostic indicator by multivariate analysis. We conclude that VEGF-C, VEGF-D and VEGFR-3 play an important role in lymphatic spread and intraperitoneal tumour development in ovarian carcinoma. Since VEGF-D was found to be an independent predictor of poor outcome, its measurement, together with other prognostic markers may improve prospective identification of patients with a poor prognosis.

Cockroach extract antigen increases bronchial airway epithelial permeability

BACKGROUND

The bronchial epithelial cells of airways are subject to recurrent environmental injury throughout the life of an individual. Recently, a high incidence of asthma has been reported in inner-city children. The increased incidence of asthma in inner-city children is thought to be caused, in part, by frequent exposure to allergens of the common household pest the cockroach.

OBJECTIVE

We sought to investigate whether cockroach extract antigen (CrAg) induces vascular permeability factor, also known as vascular endothelial growth factor (VEGF), and whether it increases permeability in bronchial airway epithelial cells (BAECs).

METHODS

We estimated CrAg-induced VEGF release in BAECs by using an ELISA and VEGF mRNA expression by using an RT-PCR reaction. The influence of CrAg on BAEC barrier function was estimated by measuring electrical resistance with an electric cell substrate impedance-sensing system.

RESULTS

Our results demonstrate that CrAg induces VEGF release in BAECs in a time-dependent manner. The VEGF induction was also confirmed by means of VEGF mRNA expression in CrAg-stimulated BAECs. CrAg decreased electrical resistance across BAEC monolayers. The maximum decrease in electrical resistance was noticed 6 hours after activation and reached a plateau thereafter. Neutralizing antibodies to VEGF significantly inhibited the decrease in BAEC electrical resistance caused by CrAg.

CONCLUSIONS

These data suggest that CrAg induces VEGF release in BAECs and alters bronchial airway permeability.

Differential gene expression of vascular endothelial growth factor isoforms and their receptors in the development of the rat masseter muscle

The capillary network in the masseter muscle develops dramatically with the differentiation of muscle fibres after birth, especially around weaning. Here, developmental changes in mRNA expression for four splicing variants of vascular endothelial growth factor (VEGF) and for two distinct VEGF receptors (Fms-like tyrosine kinase (Flt-1) and kinase insert domain-containing receptor/fetal liver kinase-1 (KDR/Flk-1)) were studied in rat masseter. The relative abundance of VEGF (120) mRNA was the highest, representing 35% of total VEGF mRNA on day 7 after birth and gradually decreased with age to become approximately 5% on day 37. In contrast, VEGF (188) mRNA was very low in the newborn rat, but increased sharply before weaning and reached 40-50% of the total on day 50. Neither VEGF (144) nor VEGF(164) mRNA showed any significant change in abundance after birth. The expression of KDR/Flk-1 mRNA was transiently high in the early postnatal stage and gradually decreased with age, Flt-1 mRNA was stably expressed at a constant level after birth. These findings suggest that different combinations of VEGF isoforms and their receptors regulate angiogenesis in the development of the masseter muscle.

Expression of vascular endothelial growth factor in canine mammary tumors

Vascular endothelial growth factor (VEGF) is a dimeric protein that stimulates angiogenesis in vitro and in vivo by inducing endothelial cell proliferation and migration. In this immunohistochemical study, VEGF-immunolabeled cells were counted in a series of 10 benign and 40 malignant canine mammary tumors. The morphologic pattern of VEGF positivity (intensity of immunolabeling and VEGF granule size and distribution) was also evaluated. A low number of cells weakly positive for VEGF with few and small granules polarized to the luminal pole was detected in benign neoplasms. In contrast, in malignancies a high number of VEGF-positive cells had strong immunolabeling, often with large granules found diffusely in the cytoplasm. This level of immunolabeling was more pronounced in the less differentiated, more malignant phenotypes (grade 3). Macrophages, which can synthesize VEGF, were strongly positive. Stromal and myoepithelial cells were negative. VEGF data were correlated statistically with intratumoral microvessel density (number of newly formed microvessels) and both measures were greater in less differentiated malignant neoplasms, demonstrating that angiogenesis and malignancy increase together. VEGF appears to be a powerful angiogenic factor in canine mammary tumors.

Tea catechins inhibit angiogenesis in vitro, measured by human endothelial cell growth, migration and tube formation, through inhibition of VEGF receptor binding

We have investigated whether tea catechins (EC, ECg, EGC, EGCg) have any inhibitory effects on angiogenesis and which step they affect during the process. The effects of catechins were tested on in vitro models of angiogenesis, namely, growth, migration and tube formation of human umbilical vein endothelial cells. All four catechins inhibited angiogenesis in vitro in the three different bioassays with concentrations ranging from 1.56 to 100 microM. Among the four catechins tested, epigallocatechin gallate (EGCg) was the most effective in inhibiting angiogenesis in all three assays. When these four catechins were tested on VEGF binding assay, only EGCg inhibited the binding of VEGF, a major angiogenesis inducing factor, to endothelial cells in a concentration dependent manner. These results indicate that while all four tea catechins inhibit the process of angiogenesis, EGCg alone can reduce the binding of VEGF to its receptors and thus affects the downstream signaling.

Angiogenic effects of extracellular human immunodeficiency virus type 1 Tat protein and its role in the pathogenesis of AIDS-associated Kaposi's sarcoma

The Tat protein of human immunodeficiency virus (HIV) type 1 is a transactivator of viral gene expression that is required for virus replication and spread. Moreover, Tat is released by acutely HIV-infected cells via a leaderless secretory pathway and in a biologically active form that exerts effects on both HIV-infected and uninfected cells from different organs and systems. This review focuses on the activities of extracellular Tat protein on endothelial cells, on angiogenesis, and on the pathogenesis of AIDS-associated angioproliferative diseases such as Kaposi's sarcoma. In particular, we discuss results from different groups indicating that Tat mimics the proangiogenic activities of extracellular matrix molecules and that it enhances the effects of angiogenic factors.

Expression of endothelial cell-associated molecules in AML cells

Recently, it has been clarified that interaction between hematopoietic cells and endothelial cells is important in normal hematopoiesis and leukemogenesis. In this study, we examined the relationship between AML cells and endothelial cells by analyzing the expression profile of angiogenic factors, angiopoietin-1 (Ang-1), Ang-2, Tie-2 (a receptor for angiopoietins) and vascular endothelial growth factor (VEGF). Our results demonstrated that CD7(+)AML expressed Ang-2 mRNA frequently and integrin-family adhesion molecules (CD11c and CD18) intensively, suggesting the close correlation with endothelial cells. On the other hand, in t(8;21) AML cells, expression of Ang-2 was infrequent and expression of integrin-family adhesion molecules (CD11b, CD11c and CD18) was weak, suggesting the sparse association with endothelial cells. As for CD7(+)AML cells, despite the frequent and intense expression of endothelial cell-associated molecules (such as Ang-2, CD11c and CD18), intensity of Tie-2 expression was quite low (P < 0.05). Ang-2 expressed in CD7(+)AML cells is not considered to act in an autocrine fashion, but to work on endothelial cells to "feed" leukemic cells. Although Ang-2 is recognized as a natural antagonist for Tie-2, our data presented here suggested the alternative role of Ang-2 in the relationship between endothelial cells and leukemia cells, at least in a subset of leukemia such as CD7(+)AML. These results were supported by the study using AML cell lines, KG-1 (CD7 negative) and its subline KG-1a (CD7 positive); KG-1 had mRNA expression profile of Ang-1(+)Ang-2(-)Tie-2(+), while KG-1a showed Ang-1(+)Ang-2(+)Tie-2(-). These difference in the expression profile of angiogenic factors between CD7(+)AML and t(8;21)AML may explain the characteristic morphological features of these leukemias (CD7(+)AML as blastic type and t(8;21)AML as differentiative type).

Effect of tenascin-X together with vascular endothelial growth factor A on cell proliferation in cultured embryonic hearts

Tenascin-X (TNX) is a large glycoprotein that appears in extracellular matrices. Previously, we demonstrated that TNX binds to vascular endothelial growth factors A and B (VEGF-A and -B) and that VEGF-B in combination with TNX induces DNA synthesis in endothelial cells via increased signals mediated by the VEGFR-1 receptor. In this study, we investigated the effect of TNX with VEGF-A on the cell proliferation in embryonic mouse heart explants from either wild-type (TNX+/+) or TNX-deficient (TNX-/-) mice. The addition of VEGF-A to the explants from TNX+/+ mice increased cell proliferation by 1.5 fold compared with that in TNX-/- mice, indicating that TNX with VEGF family member plays an important role in the control of endothelial cell proliferation in vivo.

The role of mast cell tryptase in neoangiogenesis of premalignant and malignant lesions of the uterine cervix

Recently, mast cell tryptase has been identified as another potent proangiogenic factor in tumors, along with fibroblast and vascular endothelial growth factors. Its role has been studied in a number of cancers, including carcinoma of the uterine cervix, with discordant results. Our aim was to study the expression of tryptase and bFGF in mast cells (MCs) during development of neoangiogenesis in premalignant and malignant lesions of the cervix. Biopsy specimens from 21 patients without cancer and from 63 patients with dysplasias and squamous cell carcinomas were used. They were stained with Alcian blue-safranin O (ABSO) and immunostained with specific antibodies against factor VIII, CD105, tryptase, and bFGF. Tryptase-positive mast cells increased with tumor progression and were close to newly formed blood vessels. Vascularization showed a linear increase from dysplasia to invasive cancer. We suggest that MC tryptase may upregulate neoangiogenesis in carcinogenesis of the uterine cervix.

Vascular endothelial growth factor C gene expression is closely related to invasion phenotype in gynecological tumor cells

OBJECTIVE

The correlation between the gene expression of various angiogenic factors and in vitro invasive activity in 16 human gynecological cancer cell lines was investigated.

METHODS

Semiquantitative reverse transcription polymerase chain reaction analysis was performed to investigate the mRNA expression levels of vascular endothelial growth factors (VEGF-A, -B, -C, and -D), basic fibroblast growth factor (bFGF), and matrix metalloproteinase (MMP)-2 with beta-actin coamplified as an internal standard. Tumor cell migration along a gradient of substratum-bound fibronectin and invasion into reconstituted basement membrane were evaluated by haptotactic migration and invasion assay.

RESULTS

Expression of VEGF-A mRNA was detected in all 16 cell lines, whereas the relative expression levels of other VEGF family members and bFGF, differed markedly among the cell lines. There was a statistical correlation between VEGF-C gene expression and the number of cells that migrated and invaded (P < 0.01). However, expression of mRNAs of other angiogenic factors did not correlate with motility and invasive activity of the cells. Moreover, there was a close correlation between VEGF-C and MMP-2 gene expression levels (P < 0.05).

CONCLUSION

Tumor cells that produce VEGF-C may have a higher invasive and metastatic potential because of their capacity to pass through tissue barriers.

Cellular interactions in vascular growth and differentiation

In nature, mammalian cells do not exist in isolation, but rather are involved in interactions with other cells and matrix. In this review, several aspects of cellular interactions that are important in vascular growth and development will be highlighted. The cardiovascular system is the earliest to develop in the embryo. A number of growth factors and their receptors mediate the complex stages of migration, assembly, organization, and stabilization of developing vessels. In the adult organism, normal angiogenesis is restricted primarily to tissue growth (such as muscle and fat), the wound healing process and the female reproductive system. However, pathological angiogenesis, such as with tumor growth, diabetic retinopathy, and arthritis, is of great concern. The identification and/or development of exogenous and endogenous angiogenesis inhibitors has added to the understanding of these pathological processes. In addition to cellular interactions via ligands and receptors, cells also interact directly through physical contacts. These interactions facilitate anchorage, communication, and permeability. Since vessels serve as non-leaky conduits for blood flow as well as interfaces for molecular diffusion, the physical interactions between the cells that make up vessels must be specific for the function at hand. Permeability is a specialized function of vessels and is mediated by intracellular mechanisms and intercellular interactions. Cells also interact with the surrounding extracellular matrix. Integrin-matrix interaction is a two-way exchange critical for angiogenesis. Matrix metalloproteinases and tissue inhibitors of matrix metalloproteinases play major roles in embryonic remodeling, adult injury, and pathological conditions. Several experimental model systems have been useful in our understanding of cellular interactions. These in vitro models incorporate heterotypic cell-cell interactions and/or allow cell-matrix interactions to occur.

Angiogenesis: pathological, prognostic, and growth-factor pathways and their link to trial design and anticancer drugs

Angiogenesis is essential for tumour growth, invasion, and metastasis. Tumour blood vessels show many differences from normal vessels and are not genetically unstable, so they form a potentially key area for therapy of all types of cancer including leukaemias. Here we review current knowledge on the multiple pathways controlling tumour angiogenesis and assess which are the most clinically relevant. We also review the clinical evidence that angiogenesis affects the behaviour of cancer. Retrospective studies on intratumoral vascularisation suggest that it is an independent prognostic factor that merits prospective validation. Also, the presence of vascular endothelial growth factor in high concentrations in primary cancers is associated with poor prognosis. Key targets for drug development, current clinical trials, and the problems of developing drugs that do not have direct cytotoxic effects are reviewed. Recommendations are made on organising and monitoring antiangiogenic trials.

Regulation of vascular endothelial growth factor transcription by endothelial PAS domain protein 1 (EPAS1) and possible involvement of EPAS1 in the angiogenesis of renal cell carcinoma

BACKGROUND

Endothelial PAS domain protein 1 (EPAS1) is a basic helix-loop-helix/PAS domain transcription factor that expressed most abundantly in highly vascularized organs. The authors examined the effect of transfection of EPAS1 cDNA on the endogenous expression of vascular endothelial growth factor (VEGF) in the 293 Tet-Off cell line and the possible involvement of EPAS1 in the angiogenesis of renal cell carcinoma (RCC).

METHODS

Complete cDNA of EPAS1 was cloned and transfected to cells from the 293 Tet-Off fetal kidney cell line, in which the expression of EPAS1 can be inhibited by doxycycline. The subsequent changes in expression pattern of VEGF and transferrin receptor (TfR), a target gene of hypoxia-inducible factor 1alpha (HIF-1alpha), were examined by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay. In addition, expression of EPAS1, HIF-1alpha, and VEGF were analyzed by semiquantitative RT-PCR in five RCC cell lines and in 13 RCC tissue samples. In situ hybridization was performed on 7 of the 13 RCC tissue samples.

RESULTS

Endogenous VEGF was increased significantly by the introduction of EPAS1 cDNA at both the mRNA level and the protein level. With the inhibition of EPAS1 by doxycycline treatment, the expression of VEGF was significantly decreased accordingly, whereas the expression of TfR was not affected. EPAS1 was detected in all of the RCC cell lines examined. In RCC tissue samples, EPAS1 mRNA and VEGF mRNA were increased significantly in tumor tissues compared with normal adjacent kidney tissues. In situ hybridization showed that EPAS1 and VEGF were coexpressed topographically in tumor tissues.

CONCLUSIONS

These results suggest that endogenous VEGF can be up-regulated transcriptionally by EPAS1, and EPAS1 may be involved in the angiogenesis of RCC.

Pitfalls in the Measurement of Circulating Vascular Endothelial Growth Factor

Background: Vascular endothelial growth factor (VEGF) is a protein with antiapoptotic, mitogenic, and permeability-increasing activities specific for vascular endothelium. VEGF mRNA, which has five isoforms, is produced by nonmalignant cells in response to hypoxia and inflammation and by tumor cells in constitutively high concentrations. Because VEGF plays a crucial role in physiological and pathophysiological angiogenesis, measurements of circulating VEGF are of diagnostic and prognostic value, e.g., in cardiovascular failures, inflammatory diseases, and malignancies. However, there are major quantitative differences in the published results. This review attempts to identify reasons for these disparities.

Approach: The literature was reviewed through a Medline search covering 1995 to 2000. A selection of exemplary references had to be made for this perspective overview.

Content: Data are included from studies on healthy humans, gynecological patients, and persons suffering from inflammatory or malignant diseases. The results indicate that competitive immunoassays detect the total amount of circulating VEGF, which enables observations regarding the increase in VEGF in pregnancy and preeclampsia to be made. In these cases, capture immunoassays utilizing neutralizing antibodies are insufficient because of an accompanying increase in VEGF-binding soluble receptors (sFlt-1). Measurements of circulating free VEGF are useful for study of malignant diseases, which are associated with both genetically and hypoxia-induced overproduction of VEGF. The VEGF isoform specificity of the antibodies is also critical because both VEGF121 and VEGF165 are secreted. It is important to consider that platelets and leukocytes release VEGF during blood clotting.

Conclusions: Future efforts should concentrate on the balance between free VEGF, total VEGF, and sFlt-1. Plasma, rather than serum, should be used for analysis.

In fibroblasts Vegf-D expression is induced by cell-cell contact mediated by cadherin-11

Vascular endothelial growth factors (VEGFs) are a highly conserved family of growth factors all angiogenic in vivo with mitogenic and chemotactic activity on endothelial cells. VEGFs are expressed in fibroblasts either in hypoxia or in response to growth factors. Here we report that, differently from the other members of the family, Vegf-D is induced by cell-cell contact. By in situ hybridization we demonstrated that noninteracting fibroblasts express low levels of Vegf-D mRNA, whereas contacting cells express high levels of Vegf-D transcripts. By immunostaining we observed that the surface protein cadherin-11 is localized at the opposite sites of interacting cell surfaces. Ca(2+) deprivation from the culture medium determined the loss of cadherin-11 from the cell surfaces and down-regulation of Vegf-D mRNA. Moreover, a cadherin-11 antisense RNA construct inhibited Vegf-D expression in confluent BALB/c fibroblasts, whereas in NIH 3T3 cells, which express low levels of cadherin-11, Vegf-D induction could be obtained by overexpression of cadherin-11. This suggests that cell interaction mediated by cadherin-11 induces the expression of the angiogenic factor Vegf-D in fibroblasts.

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).

Cytological evaluation of angiogenesis in endometrial aspirates

We conducted a comparative study of angiogenesis observed in endometrial aspirates according to histological type. Cytological specimens from 14 cases of proliferative phase endometrium, 21 cases of endometrial hyperplasia and 18 cases of well-differentiated endometrial adenocarcinoma were used in the investigation. Immunohistochemical staining was performed according to standard methods using CD34 monoclonal antibody, and new vessels were examined. New vessels were identified in all of the histological types, but no morphological differences were seen. New vessels were observed in more cases of adenocarcinoma than in cases of normal tissue or hyperplasia, and the differences were significant. The difference between the maximum and minimum rates of occurrence of cell clusters possessing new vessels tended to be greater in adenocarcinoma than in the other tissue types (P < 0.05). Based on the above findings, examination of new vessels appearing in aspirated endometrial specimens appeared to be of help in differential diagnosis, but it also seemed necessary to take changes due to the menstrual cycle etc. into consideration.

Clinical significance of determination of surrogate markers of angiogenesis in breast cancer

Compelling experimental and clinical data support the concept that breast carcinoma, as most of the other solid tumors, needs to develop the angiogenic phenotype for invasiveness, progression and metastasis. Several studies have determined intratumoral microvessel density by panendothelial markers and immunohistochemical techniques, with most of them showing that the degree of vascularity is associated with prognosis of the patients operated of early-stage invasive breast cancer. More recently, certain angiogenic peptides have been assessed in human breast cancer: vascular endothelial growth factor (VEGF), platelet derived-endothelial cell growth factor (PD-ECGF, also known as thymidine phosphorylase, TP) and fibroblast growth factor family (FGFs). Among these, the most studied is VEGF, which appears to be a powerful prognostic indicator. Little data are available on the clinical significance of naturally occurring antiangiogenic factors, with few studies reporting on interleukin-12 and thrombospondins. In vivo techniques for dynamic assessment of tumor blood network are presently under extensive research, in particular for monitoring activity of inhibitors of angiogenesis. The methods of assessment of angiogenic activity and the results of published clinical studies in peer reviewed Journals with a computerized overview of literature will be presented. Overall, the results of the reported studies suggest that human breast cancer is an angiogenic-dependent tumor for which antiangiogenic therapy represents a promising novel antitumoral therapeutic strategy.

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.

Extracellular matrix tenascin-X in combination with vascular endothelial growth factor B enhances endothelial cell proliferation

BACKGROUND

An extracellular matrix tenascin-X (TNX) is highly expressed in muscular tissues, especially heart and skeletal muscle, and is also prominent around blood vessels. The precise in vivo role of TNX remains to be elucidated. To identify proteins that interact with TNX in the extracellular environment, we searched for TNX-binding proteins using a yeast two-hybrid system.

RESULTS

We used mouse TNX-specific fibronectin type III repeats (mTNX/FNIII13-25) as a bait for the screening. We found that vascular endothelial growth factor B (VEGF-B) binds to mTNX/FNIII13-25. This interaction was confirmed by pull-down assays and co-immunoprecipitation assays. The full-length mTNX, as well as mTNX/FNIII13-25, interacted with both alternative splice isoforms VEGF-B186 and VEGF-B167. Furthermore, the full-length mTNX also bound to VEGF-A. The minimal region of TNX that interacts with VEGF-B was mapped to the FNIII repeats (FNIII13-25) but not to the other characteristic domains of TNX. The TNX-binding site of VEGF-B was located in the N-terminal 115-amino acid region. mTNX/FNIII13-25 did not prevent the interaction of VEGF-B with VEGFR-1 (VEGF receptor 1), and VEGF-B could simultaneously bind to both mTNX/FNIII13-25 and VEGFR-1. A conditioned medium from transfected 293T cells coexpressing full-length TNX and VEGF-B could promote DNA synthesis in bovine endothelial cells in which VEGFR-1 were expressed. VEGFR-1 phosphorylation triggered by VEGF-B186 were increased in cells plated with mTNX/FNIII13-25 or full-length mTNX, compared with cells plated with VEGF-B186 alone.

CONCLUSION

TNX interacts with VEGF-B and enhances the ability of VEGF-B to stimulate cell proliferation. This enhanced mitogenecity is caused by increased signals mediated by the VEGFR-1 receptor. This finding suggests a role for TNX in the regulation of the development of blood vessels such as vasculogenesis and angiogenesis.

Vascular endothelial growth factor-driven glioma growth and vascularization in an orthotopic rat model monitored by magnetic resonance imaging

OBJECTIVE

The goal of the present study was to develop an orthotopic in vivo model for the investigation of vascular endothelial growth factor (VEGF)-dependent glioma growth and vascularization.

METHODS

C6 glioma cells were infected with viruses encoding sense or antisense VEGF. Expression of the transgene was controlled by Northern blot analysis, Western blot analysis, and immunohistochemistry. Spheroids generated from both clones as well as from wild-type and mock-transfected cells were implanted in the brains of Sprague-Dawley rats. Growth and vascularization were assessed using magnetic resonance imaging after 7 and 11 days. Histology was studied using hematoxylin and eosin staining, immunohistochemistry with anti-von Willebrand staining, anti-VEGF, anti-CD8, and assessment of vessel density.

RESULTS

Cell proliferation, migration, and invasion in vitro were very similar in all cell clones. Sense gliomas demonstrated by far the fastest growth in vivo, with intense contrast enhancement meeting criteria for highly malignant tumors. Histological examination revealed masses of von Willebrand- and VEGF-positive tumor vessels with a high vessel density. Antisense gliomas depicted the radiological features of low-grade gliomas, with slow growth and poor vascularization, although they were highly infiltrative. Wild-type and mock-transfected gliomas demonstrated similar growth and vascularization patterns intermediate between sense and antisense gliomas. Any influence of the allogeneic response of the hosts on different tumor sizes could be excluded.

CONCLUSION

Our model elucidates glioma growth and vascularization as strongly VEGF dependent, which is consistent with human gliomas. Thus, this model is suitable for testing antiangiogenic strategies to interfere with the VEGF/VEGF receptor system, as well as for exploring VEGF-independent mechanisms using the antisense-transfected clone.

Development of laminin receptor agonists: identification of important functional residues by alanine scanning

An antagonist of cellular adhesion and motility, acetyl-C-[S-Acm]-VIGYSGDRC-[S-Acm]-NH(2) (mEGF(33-42)), shares homology with the agonist sequence CDPGYIGSR-NH(2). It has been proposed that the latter peptide binds to the high affinity 67 kDa laminin receptor. Both peptides have equal affinities for the receptor and similar conformations have been derived for both. We have examined the importance of individual non-homologous residues with respect to receptor binding and antagonistic properties of mEGF(33-42). Alanine scanning of non-conserved residues in the N-terminal half of mEGF(33-42) caused loss of biological activity with respect to cell attachment, receptor binding and migratory response. Substitution of alanine for serine (position 6) caused loss of laminin-specific cell attachment and receptor binding activities. However, the peptide did stimulate migration suggesting that this peptide may be a non-specific stimulator of migration. In contrast, alanine substitution for the C-terminal Cys-S-Acm had no apparent effect on the attachment or receptor binding activities of the peptide but generated an agonist from the antagonist parent. Comparison of the modelled folds of the alanine containing peptides revealed the presence of significant helical content in those peptides capable of stimulating migration and suggests that a reduction in bulk in the N-terminal residues is not conducive to adopting a productive binding conformation.

Prognostic value of vascular endothelial growth factor in breast cancer

Angiogenesis, the process leading to the formation of new blood vessels from a preexisting vascular network, is necessary for tumor growth, invasion, and metastasis. Data from experimental and clinical studies indicate that breast carcinoma is an angiogenesis-dependent tumor. Most retrospective studies evaluating the prognostic value of determination of intratumoral microvessel density (IMD) at the vascular "hot spot" (a surrogate marker of angiogenesis) found that IMD is a significant and independent prognostic indicator in patients with both node-negative and node-positive breast cancers. More recently, the expression of certain endothelial growth factors has been tested. Among these, vascular endothelial growth factor (VEGF), the most potent endothelial cell mitogen and also a regulator of vascular permeability, is emerging as a powerful new prognostic tool. Eight of the nine published retrospective studies reported that VEGF is significantly associated with relapse-free survival, overall survival, or both. Patients with early stage breast cancer who have tumors with elevated levels of VEGF have a higher likelihood of recurrence or death than patients with low-angiogenic tumors, even if treated with conventional adjuvant therapy. High levels of VEGF can differentiate the subgroups of patients with breast cancer with poor prognosis who benefit minimally from conventional adjuvant therapy but who may benefit from validated anti-VEGF treatments.

Angiogenesis in head and neck squamous cell carcinoma

Tumour angiogenesis has recently attracted a great deal of attention as a critical part of oncogenesis and a necessary prerequisite for a malignant phenotype. Research into this process not only offers new insights into tumour biology but is also leading to the development of realistic novel and minimally toxic anti-tumour therapies. Various pro-angiogenic and anti-angiogenic cytokines and pathways have been characterized and their interrelationships are becoming increasingly complex as new findings are made. This article reviews the current understanding of tumour angiogenesis, the basic mechanisms involved and the more important and investigated pathways and proteins involved.

The detection and comparison of angiogenesis-associated factors in pyogenic granuloma by immunohistochemistry

BACKGROUND

Pyogenic granuloma is a benign inflammatory lesion demonstrating obvious activity of angiogenesis. Female steroid hormones are believed to play important roles in the etiology because the lesion is frequently found in females with high levels of sex hormones. Few molecular mechanisms of the pathogenesis have been proposed and proven. The purpose of this study was to detect and compare the expression of angiogenesis-associated factors among healthy gingiva, gingiva from periodontitis, and pyogenic granuloma to clarify the pathogenesis of pyogenic granuloma.

METHODS

Fifteen specimens were collected from each of 3 groups of gingiva (healthy gingiva, periodontitis, and pyogenic granuloma). The subjects were age and gender matched. The specimens were processed for immunohistochemistry to detect and compare the expression of 2 angiogenesis enhancers, i.e., vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF), 2 angiogenesis inhibitors, i.e., angiostatin and thrombospondin-1 (TSP-1), and estrogen receptor (ER). Using the subject as the unit of statistical analysis, either analysis of variance or chi-square analysis was employed to show the statistically significant difference at a level P <0.05.

RESULTS

The pyogenic granuloma group expressed significantly more VEGF and bFGF than healthy gingiva and periodontitis. The positive staining of VEGF was mostly localized in the cytoplasm of macrophages and fibroblasts while that of bFGF was in the extracellular matrix of lamina propria. Angiostatin was expressed significantly less in pyogenic granuloma than the other 2 groups and was mostly localized in the nuclei of endothelial cells and epithelial cells. There was no significant difference in the expression of TSP-1 and ER among the 3 groups.

CONCLUSIONS

The results of this research suggest that the etiology of pyogenic granuloma is due to the imbalance between angiogenesis enhancers and inhibitors. Whether and how the angiogenesis-associated factors are regulated by female steroid hormones remain to be answered.

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

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

Insights into the molecular pathogenesis of atherosclerosis and therapeutic strategies using gene transfer

Gene therapy for the treatment of atherosclerosis and related diseases has shown its potential in animal models and in the first human trials. Gene transfer to the vascular system can be performed both via intravascular and extravascular periadventitial routes. Intravascular gene transfer can be done with several types of catheters under fluoroscopic control. Extravascular gene transfer, on the other hand, provides a well-targeted gene delivery route available during vascular surgery. It can be done with direct injection or by using perivascular cuffs or surgical collagen sheets. Ex vivo gene delivery via transfected smooth muscle cells or endothelial cells might be useful for the production of secreted therapeutic compounds. Gene transfer to the liver has been used for the treatment of hyperlipidemia. The first clinical trials for the induction of therapeutic angiogenesis in ischemic myocardium or peripheral muscles with VEGF or FGF gene transfer are under way and preliminary results are promising. VEGF has also been used for the prevention of postangioplasty restenosis because of its capability to induce endothelial repair and production of NO and prostacyclin. However, further basic research is needed to fully understand the pathophysiological mechanisms involved in conditions related to atherosclerosis. Also, further development of gene transfer vectors and gene delivery techniques will improve the efficacy and safety of human gene therapy.

Prevention of breast cancer

With the advent of screening and the increased incidence of breast cancer, concern for the prevention of breast cancer has become forefront in today's society. Determining individual risk is the key to prescribing prevention. Prevention of breast cancer is still under clinical investigation with only one drug, tamoxifen, showing benefit in high risk patients. This paper reviews the possible sites for prevention of neoplastic transformation via biomarkers in a breast cell as well as the investigational drugs and their potential use in the chemoprevention of breast cancer.

Prognosis of breast-carcinoma lymphagenesis evaluated by immunohistochemical investigation of vascular-endothelial-growth-factor receptor 3

Very few studies have yet addressed the question of the existence and role of lymphagenesis in tumor growth; it is generally overshadowed by the greater emphasis placed on the blood vascular system. Monoclonal antibodies against vascular endothelial-growth-factor receptor 3 (VEGFR3) have been shown to provide a specific antigenic marker for lymphatic endothelium. By comparison with the microvascular count (MVC), we investigated the prognostic value of the microlymphatic count (MLC) in a series of 60 cases of 2-cm-diameter breast carcinomas. The mean value of MVC was 72.5 and of MLC, 40.5. There was no quantitative correlation between these 2 parameters. The MVC but not the MLC had a prognostic value in overall survival. Neither the MLC nor the MVC had any correlation with axillary-lymph-node invasion.

Vascular endothelial growth factor and platelet-derived endothelial cell growth factor expression are implicated in the angiogenesis of endometrial cancer

Although many angiogenic factors have been described, it is not well defined which factors are expressed in endometrial cancer. The object of this study was to examine mRNA levels of the two angiogenic factors, vascular endothelial growth factor (VEGF) and platelet-derived endothelial cell growth factor (PD-ECGF) in endometrial cancer tissues and their association with clinicopathological features including microvessel density. The level of VEGF and PD-ECGF mRNAs was assessed by semi-quantitative reverse transcription-polymerase chain reaction using beta-actin as an internal standard in 38 patients with endometrial cancer. Microvessel counts were also assessed by immunostaining for factor VIII-related antigen in the most vascularised area of the specimen. VEGF/beta-actin ratios of non-endometrioid tumours were significantly higher than those of endometrioid tumours (P = 0.013). VEGF/beta-actin ratios of cases with lymph-vascular space involvement were significantly higher than those of cases without lymph-vascular space involvement (P = 0.021). Although it was not statistically significant, PD-ECGF/beta-actin ratios in grade 3 tumours were higher than those in grade 1 and 2 tumours (P = 0.066). The microvessel density was significantly correlated with the level of VEGF and PD-ECGF mRNA expression (P = 0.041 and P < 0.0001, respectively). Our findings provide evidence that the expression of both VEGF and PD-ECGF is involved in the promotion of angiogenesis in endometrial cancer. In addition, VEGF and PD-ECGF might contribute to the aggressive potential of high grade tumours or certain histological subtypes with unfavourable prognosis through the induction of angiogenesis.

Placenta growth factor and vascular endothelial growth factor B and C expression in microvascular endothelial cells and pericytes. Implication in autocrine and paracrine regulation of angiogenesis

We have shown previously that vascular endothelial growth factor (VEGF) synthesized by the cellular constituents of small vessels per se, viz. endothelial cells and pericytes, participates in the hypoxia-driven proliferation of both cell types (Nomura, M., Yamagishi, S., Harada, S., Hayashi, Y., Yamashima, T., Yamashita, J., Yamamoto, H. (1995) J. Biol. Chem. 270, 28316-28324; Yamagishi, S., Yonekura, H., Yamamoto, Y., Fujimori, H., Sakurai, S., Tanaka, N., and Yamamoto, H. (1999) Lab. Invest. 79, 501-509). In this study, we examined the expression of the recently isolated VEGF gene family members (placenta growth factor (PlGF), VEGF-B, and VEGF-C) in human dermal microvascular endothelial cells and bovine retinal pericytes cultured under various oxygen tensions. Quantitative reverse transcription-polymerase chain reaction analyses demonstrated that the two cell types possess not only VEGF (VEGF-A) mRNA, but also VEGF-B, VEGF-C, and PlGF mRNAs. Among them, only VEGF-A mRNA was induced under hypoxia. Competitive reverse transcription-polymerase chain reaction showed that, under normoxic conditions, the rank order of mRNA content in endothelial cells was PlGF > VEGF-B > VEGF-C > VEGF-A and that mRNA coding for PlGF was expressed at >100-fold higher levels than VEGF-A mRNA. In pericytes, the rank order was VEGF-C > VEGF-A > VEGF-B > PlGF, and approximately 7-fold higher levels of VEGF-C mRNA compared with VEGF-A mRNA were noted in this cell type. Furthermore, antisense inhibition of PlGF protein production lowered the endothelial cell synthesis of DNA under hypoxic conditions. The results suggest that these VEGF family members may also take active parts in angiogenesis.

VEGF stimulates tyrosine phosphorylation of beta-catenin and small-pore endothelial barrier dysfunction

The purpose of this study was to test the hypothesis that tyrosine phosphorylation signaling events and protein kinase C (PKC) activation mediate vascular endothelial growth factor-A(165) (VEGF)-induced endothelial cell (EC) proliferation and barrier dysfunction in bovine pulmonary artery EC monolayers. A size-selective permeability assay showed that VEGF stimulated a delayed, prolonged (6-45 h), concentration-dependent (50-200 ng/ml, approximately 1-4 nM) increase in the number of predominantly small-"pore" transport pathways (<60 A) across EC monolayers. The tyrosine kinase inhibitor herbimycin A (HA) and the selective PKC inhibitor bisindolylmaleimide (BIM) prevented this phenomenon. After 6-24 h, VEGF-treated monolayers displayed an HA- and BIM-sensitive reorganization of beta-catenin adherens junctions with fingerlike projections and the loss of beta-catenin at sites of small paracellular hole formation. HA and BIM prevented the VEGF-induced increase in EC growth. HA blocked the VEGF-induced rapid and prolonged (10 min-45 h) increases in the phosphotyrosine (PY) contents of VEGF receptor 2, phospholipase C-gamma1, paxillin, and beta-catenin as well as approximately 140- and 128- to 117-kDa proteins, whereas BIM inhibited only the tyrosine phosphorylation of beta-catenin. These data suggest that VEGF initiates increased EC growth and chronic, small-pore endothelial barrier dysfunction by PY signaling through beta-catenin that depends on PKC.

KDR/Flk-1 is a major regulator of vascular endothelial growth factor-induced tumor development and angiogenesis in murine hepatocellular carcinoma cells

Vascular endothelial growth factor (VEGF), which is one of the most potent angiogenic factors, has been shown to play a pivotal role in tumor angiogenesis, including hepatocellular carcinoma (HCC). The effects of VEGF are mediated mainly through two distinct receptors, flt-1 and KDR/Flk-1. It has been suggested that KDR/Flk-1 plays an important role in tumor development. However, the role of KDR/Flk-1 in HCC has not been examined. We previously reported that VEGF tightly regulated murine HCC development, based on the results of a study using a retroviral tetracycline-regulated (Retro-Tet) gene expression system. This system allows VEGF gene expression to be manipulated in vivo by providing tetracycline in the drinking water. In the present study, we combined the KDR/Flk-1-specific neutralizing monoclonal antibody (KDR/Flk-1mAb) and the Retro-Tet system to elucidate the role of KDR/Flk-1 in VEGF-induced tumor development and angiogenesis in a murine HCC experimental model. In a xenograft study, tumor augmentation induced by VEGF overexpression was almost abolished by means of KDR/Flk-1mAb treatment, with accompanying inhibition of angiogenesis, KDR/Flk-1 autophosphorylation, but not interference of flt-1 activation. This inhibitory effect was achieved even on established tumors and regardless of whether the tumor size was small or large. On the contrary, KDR/Flk-1mAb treatment significantly increased the apoptosis in the tumor. With orthotopic transplantation, KDR/Flk-1mAb also inhibited HCC development in the liver. These results suggest that KDR/Flk-1 is a major regulator of VEGF-mediated HCC development and angiogenesis not only at the initial stage, but also after the tumor has fully developed.

Spontaneous and thiazolidinedione-induced B6C3F1 mouse hemangiosarcomas exhibit low ras oncogene mutation frequencies

Hemangiosarcomasare uncommon malignant endothelial cell tumors in humans and experimental animal species. The mechanisms giving rise to these tumors are poorly understood even though the histotypes are comparable between humans and rodents. Activating mutations in cellular ras protooncogenes have been detected in sporadic and chemically induced human and rodent hemangiosarcomas. Ras activation significantly modulates tumor angiogenesis, suggesting that mutations in ras genes might be causally related to vascular tumorigenesis. To more clearly define the role of ras in experimental vascular tumorigenesis, mutations in the Ki- and Ha-ras genes were characterized in 63 hemangiosarcomas that arose unexpectedly in control and treated B6C3F1 mice during a two-year carcinogenicity study of the thiazolidinedione troglitazone. DNA was extracted from paraffin sections of mouse hemangiosarcomas, control liver, or positive control hepatocellular carcinomas with defined mutations in the Ki- or Ha-ras genes. Exons 1 and 2 of the Ki- and Ha-ras genes were independently amplified using primer extension preamplification/locus-specific heminested PCR, and PCR amplicons were directly sequenced to identify mutations in codons 12, 13, or 61. Activating mutations were detected in 3 of 63 hemangiosarcomas: a single G-->A transition in the second position of Ki-ras codon 13 in a tumor from a treated animal and two G-->T transversions in the second position of Ha-ras codon 13, one in a single tumor from a control animal and one in a tumor from a treated animal. These mutations are consistent with endogenous mutagenesis arising from oxidative DNA damage. The low frequency of mutation (<5%) indicates that ras mutations did not contribute significantly to hemangiosarcoma development and suggests that mutational ras activation may not be a necessary step in vascular tumorigenesis in mice.

Expression of vascular endothelial growth factor (VEGF) family members in breast cancer

Vascular endothelial growth factor (VEGF)-A is known to play an important role in tumor angiogenesis. Three additional members of the VEGF family, VEGF-B, -C and -D, have recently been discovered. VEGF-C and VEGF-D are ligands for VEGF receptor-3, which is expressed in the endothelium of lymphatic vessels. The expression of VEGF-C is known to be associated with the development of lymphatic vessels. Therefore, it is conceivable that VEGF-C and VEGF-D might play a role in the development of lymphatic vessels in solid tumors. To obtain some clue as to this role, we developed a semi-quantitative reverse transcription-polymerase chain reaction method to investigate the mRNA expression levels of each VEGF family member in breast cancer. All the VEGF family members were expressed at different levels in seven human breast cancer cell lines explored. Although VEGF-A and VEGF-B expressions were detected in both node-positive and node-negative breast tumors, VEGF-C expression was detected only in node-positive tumors. VEGF-D expression was detected only in an inflammatory breast cancer and a tumor which developed an inflammatory skin metastasis. These findings suggest a possible relationship between the expression level of VEGF-C and/or VEGF-D and the development of lymphatic tumor spread.

Vascular endothelial growth factor in ovarian cancer

Tumor growth requires nutrients and oxygen. Both nutrients and oxygen are provided via the vasculature. Thus, when a tumor increases in volume, new blood vessels must form and invade the expanding tumor. This process, called angiogenesis, has theoretical significance in the context of ovarian cancer for two reasons. First, the process of angiogenesis and vessel regression occurs in a tightly controlled way as part of normal ovarian function. This suggests that at least some ovarian cells are primed to produce the paracrine stimulus needed for new blood vessel growth and that, on transformation, this capability is present early in tumor development. Second, the characteristically large size of ovarian tumors indicates that angiogenesis is mandatory to sustain the tumor. In this article, we review the experimental and clinical correlative data that support the hypothesis that ovarian cancers are highly angiogenic. Because a critical component of angiogenesis is the paracrine and autocrine production of vascular endothelial cell growth factor, there is substantial focus on this topic.

Expression of the VEGF gene family during retinal vaso-obliteration and hypoxia

Vascular insufficiency and retinal ischaemia precede many proliferative retinopathies and stimulate secretion of vasoactive growth factors. Vascular endothelial growth factor (VEGF) plays a major role and we therefore investigated the other members of the VEGF family: Placental growth factor (PlGF), VEGF-B, -C, and -D, and platelet derived growth factors (PDGF) A and B. Neonatal mice were exposed to hyperoxia for 5 days and then returned to room air (resulting in acute retinal ischaemia). RT-PCR demonstrated that all the members of the VEGF family are expressed in the retina and in situ hybridization (ISH) located their mRNAs primarily in ganglion cells. Similarly to VEGF itself, VEGF-C, PDGF-A, and PDGF-B were upregulated during retinal ischaemia (P < 0.05). Only PlGF gene expression increased during hyperoxia (P < 0.01). The expression pattern of these growth factors suggests a role in the normal retina and during vaso-obliterative and ischaemic phases.

c-fos-induced growth factor/vascular endothelial growth factor D induces angiogenesis in vivo and in vitro

c-fos-induced growth factor/vascular endothelial growth factor D (Figf/Vegf-D) is a secreted factor of the VEGF family that binds to the vessel and lymphatic receptors VEGFR-2 and VEGFR-3. Here we report that Figf/Vegf-D is a potent angiogenic factor in rabbit cornea in vivo in a dose-dependent manner. In vitro Figf/Vegf-D induces tyrosine phosphorylation of VEGFR-2 and VEGFR-3 in primary human umbilical cord vein endothelial cells (HUVECs) and in an immortal cell line derived from Kaposi's sarcoma lesion (KS-IMM). The treatment of HUVECs with Figf/Vegf-D induces dose-dependent cell growth. Figf/VEGF-D also induces HUVEC elongation and branching to form an extensive network of capillary-like cords in three-dimensional matrix. In KS-IMM cells Figf/Vegf-D treatment results in dose-dependent mitogenic and motogenic activities. Taken together with the previous observations that Figf/Vegf-D expression is under the control of the nuclear oncogene c-fos, our data uncover a link between a nuclear oncogene and angiogenesis, suggesting that Figf/Vegf-D may play a critical role in tumor cell growth and invasion.

Clinical significance of angiogenic factors in breast cancer

Growth, progression, and metastasis of breast cancer, as well as of most of the other tumors, are angiogenesis-dependent processes. Several pro-angiogenic growth factors and endogenous inhibitors of angiogenesis have been identified and sequenced, and experimental studies suggest that angiogenic activity of a tumor may result from downregulation of inhibitors of angiogenesis or up-regulation of endothelial growth factors. The mechanisms leading to the alteration of the balance between positive and negative modulators of angiogenesis are only partially known. We are at the beginning of research to identify the more active angiogenic factors in human breast cancer, and little information is presently available on their clinical significance. Preliminary results suggest that among the known angiogenic peptides, both vascular endothelial growth factor (VEGF) and platelet-derived endothelial cell growth factor / thymidine phosphorylase (PD-ECGF/TP) have promising prognostic and, perhaps, predictive value. No data are available on the clinical value of co-determination of positive and negative regulators of angiogenesis to look at the angiogenic balance of each single tumor. Only a few studies have assessed the role of endogenous inhibitors of angiogenesis in human breast cancer, with results available only on thrombospondin-1 and -2 (TSP-1, -2). Finally, the determination of some integrins such as alpha6 and alphavbeta3 and of some other endothelial-adhesion molecules seems to be of potential prognostic value. Recognizing which are the more biologically active positive and negative angiogenic factors is the key for the identification not only of new prognostic markers but also of targets for antiangiogenic therapy in human breast cancer.

Endothelial cell integrin alpha5beta1 expression is modulated by cytokines and during migration in vitro

Alterations in endothelial cell-extracellular matrix interactions are central to the process of angiogenesis. We have investigated the effect of wound-induced two-dimensional migration, basic fibroblast growth factor (bFGF), transforming growth factor-beta1 (TGF-beta1) and leukemia inhibitory factor (LIF) on expression of the alpha5beta1 integrin in endothelial cells. In multiple-wounded monolayers of bovine microvascular endothelial (BME) cells, an increase in mRNA and total protein for both alpha5 and beta1 subunits was observed, and this could be correlated with a reduction in cell density but not proliferation, both of which are induced following wounding. Although as previously reported, the alpha5 subunit was increased when cells were exposed to TGF-beta1 alone, co-addition of bFGF and TGF-beta1 resulted in a striking synergistic induction of alpha5, with no significant changes in the expression of beta1. In contrast, the alpha5 subunit was decreased by LIF in bovine aortic endothelial but not in BME cells. These findings suggest that quantitative alterations in alpha5 and beta1 integrin subunit expression modulate the adhesive and migratory properties of endothelial cells during angiogenesis.

Vascular Endothelial Growth Factor (VEGF) Expression in Human Pituitary Adenomas and Carcinomas

Vascular endothelial growth factor (VEGF) is a key mediator of endothelial cell proliferation, angiogenesis, and vascular permeability. Little is known about its expression in human pituitary adenomas. We examined 148 human pituitary adenomas for VEGF protein expression by immunohistochemistry. The strongest immunoreactivity was present in GH adenomas, corticotroph, silent corticotroph. silent subtype 3, and nononcocytic null cell adenomas. GH adenomas treated with octreotide stained less intensely than did untreated tumors. Relatively weak staining was present in PRL, gonadotroph, thyrotroph, and oncocytic null cell adenomas in the same sections showed evidence of down-regulation of VEGE protein expression in adenomas. Pituitary carcinomas usually had stronger staining than adenomas. In situ hybridization studies with oligonucleotide probes showed positive staining in all groups with stronger staining in GH, ACTH, TSH, and gonadotroph adenomas and in pituitary carcinomas. These results indicate that VEGF expression is more prominent in certain adenoma subtypes, that decreased expression occurs in adenomas as compared to nontumorous pituitary and that carcinomas show increased VEGF expression relative to adenomas suggesting up-regulation of VEGF during pituitary tumor progression.