The role of phosphatidylinositol 3-kinase in vascular endothelial growth factor signaling

Molecular diversity of VEGF-A as a regulator of its biological activity

The vascular endothelial growth factor (VEGF) family of proteins regulates blood flow, growth, and function in both normal physiology and disease processes. VEGF-A is alternatively spliced to form multiple isoforms, in two subfamilies, that have specific, novel functions. Alternative splicing of exons 5-7 of the VEGF gene generates forms with differing bioavailability and activities, whereas alternative splice-site selection in exon 8 generates proangiogenic, termed VEGF(xxx), or antiangiogenic proteins, termed VEGF(xxx)b. Despite its name, emerging roles for VEGF isoforms on cell types other than endothelium have now been identified. Although VEGF-A has conventionally been considered to be a family of proangiogenic, propermeability vasodilators, the identification of effects on nonendothelial cells, and the discovery of the antiangiogenic subfamily of splice isoforms, has added further complexity to their regulation of microvascular function. The distally spliced antiangiogenic isoforms are expressed in normal human tissue, but downregulated in angiogenic diseases, such as cancer and proliferative retinopathy, and in developmental pathologies, such as Denys Drash syndrome and preeclampsia. Here, we examine the molecular diversity of VEGF-A as a regulator of its biological activity and compare the role of the pro- and antiangiogenic VEGF-A splice isoforms in both normal and pathophysiological processes.

Antiangiogenic properties of silver nanoparticles

Angiogenesis is an important phenomenon involved in normal growth and wound healing processes. An imbalance of the growth factors involved in this process, however, causes the acceleration of several diseases including malignant, ocular, and inflammatory diseases. Inhibiting angiogenesis through interfering in its pathway is a promising methodology to hinder the progression of these diseases. The function and mechanism of silver nanoparticles (Ag-NPs) in angiogenesis have not been elucidated to date. PEDF is suggested to be a potent anti-angiogenic agent. In this study, we postulated that Ag-NPs might have the ability to inhibit angiogenesis, the pivotal step in tumor growth, invasiveness, and metastasis. We have demonstrated that Ag-NPs could also inhibit vascular endothelial growth factor (VEGF) induced cell proliferation, migration, and capillary-like tube formation of bovine retinal endothelial cells like PEDF. In addition, Ag-NPs effectively inhibited the formation of new blood microvessels induced by VEGF in the mouse Matrigel plug assay. To understand the underlying mechanism of Ag-NPs on the inhibitory effect of angiogenesis, we showed that Ag-NPs could inhibit the activation of PI3K/Akt. Together, our results indicate that Ag-NPs can act as an anti-angiogenic molecule by targeting the activation of PI3K/Akt signaling pathways.

PTEN regulates angiogenesis through PI3K/Akt/VEGF signaling pathway in human pancreatic cancer cells

Phosphoinositide 3-kinase (PI3K) pathway exerts its effects through Akt, its downstream target molecule, and thereby regulates various cell functions including cell proliferation, cell transformation, apoptosis, tumor growth, and angiogenesis. Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) has been implicated in regulating cell survival signaling through the PI3K/Akt pathway. However, the mechanism by PI3K/PTEN signaling regulates angiogenesis and tumor growth in vivo remains to be elucidated. Vascular endothelial growth factor (VEGF) plays a pivotal role in tumor angiogenesis. The effect of PTEN on VEGF-mediated signal in pancreatic cancer is unknown. This study aimed to determine the effect of PTEN on both the expression of VEGF and angiogenesis. Toward that end, we used the siRNA knockdown method to specifically define the role of PTEN in the expression of VEGF and angiogenesis. We found that siRNA-mediated inhibition of PTEN gene expression in pancreatic cancer cells increase their VEGF secretion, up-modulated the proliferation, and migration of co-cultured vascular endothelial cell and enhanced tubule formation by HUVEC. In addition, PTEN modulated VEGF-mediated signaling and affected tumor angiogenesis through PI3K/Akt/VEGF/eNOS pathway.

VEGFA upregulates FLJ10540 and modulates migration and invasion of lung cancer via PI3K/AKT pathway

BACKGROUND

Lung adenocarcinoma is the leading cause of cancer-related deaths among both men and women in the world. Despite recent advances in diagnosis and treatment, the mortality rates with an overall 5-year survival of only 15%. This high mortality is probably attributable to early metastasis. Although several well-known markers correlated with poor/metastasis prognosis in lung adenocarcinoma patients by immunohistochemistry was reported, the molecular mechanisms of lung adenocarcinoma development are still not clear. To explore novel molecular markers and their signaling pathways will be crucial for aiding in treatment of lung adenocarcinoma patients.

METHODOLOGY/PRINCIPAL FINDINGS

To identify novel lung adenocarcinoma-associated /metastasis genes and to clarify the underlying molecular mechanisms of these targets in lung cancer progression, we created a bioinformatics scheme consisting of integrating three gene expression profile datasets, including pairwise lung adenocarcinoma, secondary metastatic tumors vs. benign tumors, and a series of invasive cell lines. Among the novel targets identified, FLJ10540 was overexpressed in lung cancer tissues and is associated with cell migration and invasion. Furthermore, we employed two co-expression strategies to identify in which pathway FLJ10540 was involved. Lung adenocarcinoma array profiles and tissue microarray IHC staining data showed that FLJ10540 and VEGF-A, as well as FLJ10540 and phospho-AKT exhibit positive correlations, respectively. Stimulation of lung cancer cells with VEGF-A results in an increase in FLJ10540 protein expression and enhances complex formation with PI3K. Treatment with VEGFR2 and PI3K inhibitors affects cell migration and invasion by activating the PI3K/AKT pathway. Moreover, knockdown of FLJ10540 destabilizes formation of the P110-alpha/P85-alpha-(PI3K) complex, further supporting the participation of FLJ10540 in the VEGF-A/PI3K/AKT pathway.

CONCLUSIONS/SIGNIFICANCE

This finding set the stage for further testing of FLJ10540 as a new therapeutic target for treating lung cancer and may contribute to the development of new therapeutic strategies that are able to block the PI3K/AKT pathway in lung cancer cells.

TGF-beta effects on airway smooth muscle cell proliferation, VEGF release and signal transduction pathways

BACKGROUND AND OBJECTIVE

Airway smooth muscle (ASM) cell hyperplasia is a key feature of airway remodelling. Mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K) are key components in signal transduction associated with cell proliferation; MAPK consists of the extracellular signal-regulated kinase (ERK), p38MAPK and c-Jun NH(2)-terminal kinase (JNK). The effect of transforming growth factor (TGF)-beta on the proliferation of ASM cells, the release of vascular endothelial growth factor (VEGF) by ASM cells and relevant signal transduction pathways were investigated.

METHODS

ASM cells were growth-arrested for 48 h then stimulated with platelet-derived growth factor (PDGF), TGF-beta and dexamethasone. ASM cells were also treated with specific inhibitors of MAPK (PD98059), PI3K (wortmannin) and JNK (SP600125). Cell proliferation and VEGF concentrations were measured.

RESULTS

TGF-beta neither augmented ASM cell proliferation nor showed a synergistic effect on PDGF-mediated ASM cell proliferation. Dexamethasone did not suppress ASM cell proliferation. VEGF release was augmented by TGF-beta stimulation in a time-dependent manner, and was further enhanced by co-stimulation with PDGF and TGF-beta. Dexamethasone suppressed VEGF release significantly. TGF-beta enhanced PI3K phosphorylation, while PDGF augmented both ERK and PI3K phosphorylation. Wortmannin inhibited both TGF-beta- and PDGF-stimulated VEGF release.

CONCLUSIONS

TGF-beta may facilitate airway remodelling by promoting VEGF release through the PI3K pathway, rather than via ASM cell proliferation.

Cooperative effect of roscovitine and irradiation targets angiogenesis and induces vascular destabilization in human breast carcinoma

Angiogenesis is considered as an essential process for tumour development and invasion. Previously, we demonstrated that cyclin-dependent kinase inhibition by roscovitine induces a radiosensitization and a synergistic antitumoral effect in human carcinoma but its effect on the microenvironment and tumour angiogenesis remains unknown. Here, we investigated the effect of the combination roscovitine and ionizing radiation (IR) on normal cells in vitro and on tumour angiogenesis in MDA-MB 231 tumour xenografts. We observed that the combination roscovitine and IR induced a marked reduction of angiogenic hot spot and microvascular density in comparison with IR or roscovitine treatments alone. The Ang-2/Tie-2 ratio was increased in presence of reduced vascular endothelial growth factor level suggesting vessel destabilization. In vitro, no radiosensitization effect of roscovitine was found in endothelial, fibroblast, and keratinocyte cells. IR potentiated the antiproliferative effect of roscovitine without inducing apoptosis in endothelial cells. Roscovitine decreased IR-stimulated vascular endothelial growth factor secretion of MDA-MB 231 and endothelial cells. A reduction in the endothelial cells invasion and the capillary-like tube formation in Matrigel were observed following the combination roscovitine and IR. This combined treatment targets angiogenesis resulting in microvessel destabilization without inducing normal cell toxicity.

Neutrophil elastase cleaves VEGF to generate a VEGF fragment with altered activity

Excessive neutrophil elastase (NE) activity and altered vascular endothelial growth factor (VEGF) signaling have independently been implicated in the development and progression of pulmonary emphysema. In the present study, we investigated the potential link between NE and VEGF. We noted that VEGF(165) is a substrate for NE. Digestion of purified VEGF(165) with NE generated a partially degraded disulfide-linked fragment of VEGF. Mass spectrometric analysis revealed that NE likely cleaves VEGF(165) at both the NH(2) and COOH termini to produce VEGF fragment chains approximately 5 kDa reduced in size. NE treatment of VEGF-laden endothelial cell cultures and smooth muscle cells endogenously expressing VEGF generated VEGF fragments similar to those observed with purified VEGF(165). NE-generated VEGF fragment showed significantly reduced binding to VEGF receptor 2 and heparin yet retained the ability to bind to VEGF receptor 1. Interestingly, VEGF fragment showed altered signaling in pulmonary artery endothelial cells compared with intact VEGF(165). Specifically, treatment with VEGF fragment did not activate extracellular-regulated kinases 1 and 2 (ERK1/2), yet resulted in enhanced activation of protein kinase B (Akt). Treatment of monocyte/macrophage RAW 264.7 cells with VEGF fragment, on the other hand, led to both Akt and ERK1/2 activation, increased VEGFR1 expression, and stimulated chemotaxis. These findings suggest that the tissue response to NE-mediated injury might involve the generation of diffusible VEGF fragments that stimulate inflammatory cell recruitment and activation via VEGF receptor 1.

Mast cells can mediate vascular permeability through regulation of the PI3K-HIF-1alpha-VEGF axis

RATIONALE

Bronchial inflammation is usually accompanied by increased vascular permeability. Mast cells release a number of mediators that act directly on the vasculature, resulting in vasodilatation, increased permeability, and subsequent plasma protein extravasation. Vascular endothelial growth factor (VEGF) has been implicated to contribute to asthmatic tissue edema through its effect on vascular permeability. However, the effects of mast cells on VEGF-mediated signaling in allergic airway disease are not clearly understood.

OBJECTIVES

An aim of the present study was to investigate the role of mast cells on VEGF-mediated signal transduction in allergic airway disease.

METHODS

We used genetically mast cell-deficient WBB6F(1)-Kit(W)/Kit(W-v) (W/W(v)) mice and the congenic normal WBB6F(1)(+/+) mouse model for allergic airway disease to investigate the role of mast cells on VEGF-mediated signal transduction in allergic airway disease, more specifically in vascular permeability.

MEASUREMENTS AND MAIN RESULTS

Our present study, with ovalbumin (OVA)-sensitized without adjuvant and OVA-challenged mice, revealed the following typical pathophysiologic features of allergic airway diseases: increased inflammatory cells of the airways, airway hyperresponsiveness, increased vascular permeability, and increased levels of VEGF. However, levels of VEGF and plasma exudation in W/W(v) mice after OVA inhalation were significantly lower than levels in WBB6F(1)(+/+) mice. Moreover, mast cell-reconstituted W/W(v) mice restored vascular permeability and VEGF levels similar to those of the WBB6F(1)(+/+) mice. Our data also showed that VEGF expression was regulated by hypoxia-inducible factor-1alpha (HIF-1alpha) activation through the phosphatidylinositol 3-kinase (PI3K)-HIF-1alpha pathway in allergic airway disease.

CONCLUSIONS

These results suggest that mast cells modulate vascular permeability by the regulation of the PI3K-HIF-1alpha-VEGF axis.

Taspine downregulates VEGF expression and inhibits proliferation of vascular endothelial cells through PI3 kinase and MAP kinase signaling pathways

Taspine is an active component isolated from Radix et Rhizoma Leonticis with inhibiting tumor angiogenic properties. The molecular mechanism(s) of taspine on tumor angiogenic inhibition have not been well documented. The aim of this study was to elucidate in detail the effects of taspine on genetic expressions of VEGF in human umbilical vein endothelial cells, and on VEGFR2-mediated intracellular signaling of human umbilical vein endothelial cells. The genetic expression of vascular endothelial growth factor (VEGF) in the human umbilical vein endothelial cells (HUVECs) treated with taspine in vitro was measured by the ELISA and RT-PCR methods. The effects of taspine on cell proliferation of HUVECs and HUVECs induced by VEGF165 were considered by using MTT assay. And also, a western blot was used to detect Akt and Erk1/2 expressions and their phosphorylation levels in HUVECs treated with taspine. Our results show that VEGF protein and mRNA expressions in the cells treated with taspine were significantly decreased. Taspine also significantly inhibited cell proliferation of HUVECs induced by VEGF165. HUVECs treated with taspine showed decreased Akt and Erk1/2 activities.

ATL-1, an analogue of aspirin-triggered lipoxin A4, is a potent inhibitor of several steps in angiogenesis induced by vascular endothelial growth factor

BACKGROUND AND PURPOSE

Vascular endothelial growth factor (VEGF) is the most important proangiogenic protein. We have demonstrated that ATL-1, a synthetic analogue of aspirin-triggered lipoxin A(4), inhibits VEGF-induced endothelial cell (EC) migration. In the present study, we investigated the effects of ATL-1 in several other actions stimulated by VEGF.

METHODS

Human umbilical vein ECs were treated with ATL-1 for 30 min before stimulation with VEGF. Cell proliferation was measured by thymidine incorporation. Adherent cells were determined by fluorescence intensity using a Multilabel counter. Expression and activity of matrix metalloproteinases (MMP) were analysed by western blot and zymography.

KEY RESULTS

ATL-1 inhibited EC adhesion to fibronectin via interaction with its specific receptor. Furthermore, VEGF-induced MMP-9 activity and expression were reduced by pretreatment with ATL-1. Because the transcription factor NF-kappaB has been implicated in VEGF-mediated MMP expression and EC proliferation, we postulated that ATL-1 might modulate the NF-kappaB pathway and, indeed, ATL-1 inhibited NF-kappaB nuclear translocation. Pretreatment of EC with ATL-1 strongly decreased VEGF-dependent phosphorylation of phosphainositide 3-kinase (PI3-K) and extracellular signal-regulated kinase-2 (ERK-2), two signalling kinases involved in EC proliferation. Inhibition of VEGF-induced EC proliferation by ATL-1 was antagonized by sodium orthovanadate, suggesting that this inhibitory activity was mediated by a protein tyrosine phosphatase. This was confirmed by showing that ATL-1 inhibition of VEGF receptor-2 (VEGFR-2) phosphorylation correlates with SHP-1 association with VEGFR-2.

CONCLUSIONS AND IMPLICATIONS

The synthetic 15-epi-lipoxin analogue, ATL-1, is a highly potent molecule exerting its effects on multiple steps of the VEGF-induced angiogenesis.

Role of phosphatidylinositol signaling pathway in the development of cross-resistance of tumor cells to hormonal cytostatics and hypoxia

Long-term in vitro culturing of CaOv ovarian adenocarcinoma cells in the presence of a synthetic analogue of glucocorticoid hormone dexamethasone allowed us to obtain a subline of CaOv/D cells resistant to the antiproliferative effect of dexamethasone and characterized by high resistance to hypoxia. It was found that CaOv/D cells are characterized by constitutive increase in phosphatidylinositol 3-kinase expression and hypersecretion of vascular endothelial growth factor VEGF-A. Culturing of cells under hypoxic conditions was accompanied by a significant increase in phosphatidylinositol 3-kinase expression and VEGF-A synthesis. Experiments with cell transfection with phosphatidylinositol 3-kinase catalytic subunit proved its participation in the regulation of VEGF-A synthesis and maintenance of cell growth under condition of hypoxia. Our results indicate that coordinated activation of phosphatidylinositol 3-kinase and VEGF-A can be a factor determining the development of cross-resistance of tumor cells to hormonal cytostatics and hypoxia.

Inhibition of the tyrosine phosphatase SHP-2 suppresses angiogenesis in vitro and in vivo

Endothelial cell survival is indispensable to maintain endothelial integrity and initiate new vessel formation. We investigated the role of SHP-2 in endothelial cell survival and angiogenesis in vitro as well as in vivo. SHP-2 function in cultured human umbilical vein and human dermal microvascular endothelial cells was inhibited by either silencing the protein expression with antisense-oligodesoxynucleotides or treatment with a pharmacological inhibitor (PtpI IV). SHP-2 inhibition impaired capillary-like structure formation (p < 0.01; n = 8) in vitro as well as new vessel growth ex vivo(p < 0.05; n = 10) and in vivo in the chicken chorioallantoic membrane (p < 0.01, n = 4). Additionally, SHP-2 knock-down abrogated fibroblast growth factor 2 (FGF-2)-dependent endothelial proliferation measured by MTT reduction (p < 0.01; n = 12). The inhibitory effect of SHP-2 knock-down on vessel growth was mediated by increased endothelial apoptosis (annexin V staining, p < 0.05, n = 9), which was associated with reduced FGF-2-induced phosphorylation of phosphatidylinositol 3-kinase (PI3-K), Akt and extracellular regulated kinase 1/2 (ERK1/2) and involved diminished ERK1/2 phosphorylation after PI3-K inhibition (n = 3). These results suggest that SHP-2 regulates endothelial cell survival through PI3-K-Akt and mitogen-activated protein kinase pathways thereby strongly affecting new vessel formation. Thus, SHP-2 exhibits a pivotal role in angiogenesis and may represent an interesting target for therapeutic approaches controlling vessel growth.

Targeting neuropilin 1 as an antitumor strategy in lung cancer

PURPOSE

Neuropilin 1 (NRP1) is a mediator of lung branching and angiogenesis in embryonic development and angiogenesis in cancer. The role of NRP1 in cancer progression is not fully elucidated. We investigated the role of NRP1 in cancer invasion and tumor angiogenesis, its signaling pathways, prognostic significance, and therapeutic implications.

EXPERIMENTAL DESIGN

Sixty patients with non-small cell lung cancer (NSCLC) were studied. NRP1 mRNA expression was measured using real-time quantitative reverse-transcription PCR. NRP1 and cancer cell invasion, angiogenesis, and signaling pathways were studied using NRP1 stimulation by vascular endothelial growth factor 165 (VEGF(165)) and NRP1 inhibition by small interfering RNAs (siRNA), soluble NRP1 (sNRP1), and NRP1-inhibition peptides. The NRP1-inhibition peptides were identified using a phage display peptide library.

RESULTS

NSCLC patients with high expression of NRP1 had shorter disease-free (P = 0.0162) and overall survival (P = 0.0164; log-rank test). Multivariate analyses showed NRP1 is an independent prognostic factor in overall (HR, 2.37, 95% CI = 1.15 to 4.9, P = 0.0196) and disease-free survival [hazard ratio (HR), 2.38; 95% confidence interval (95% CI), 1.15-4.91; P = 0.0195] of NSCLC patients. Knockdown of NRP1 suppressed cancer cell migration, invasion, filopodia formation, tumorigenesis, angiogenesis, and in vivo metastasis. NRP1 signaling pathways involved VEGF receptor 2 and phosphoinositide-3-kinase (PI3K) and Akt activation. Two potent synthetic anti-NRP1 peptides, DG1 and DG2, which block NRP1 signaling pathways and suppress tumorigenesis, cancer invasion, and angiogenesis, were identified.

CONCLUSIONS

NRP1 is a cancer invasion and angiogenesis enhancer. NRP1 expression is an independent predictor of cancer relapse and poor survival in NSCLC patients. NRP1 plays a critical role in tumorigenesis, cancer invasion, and angiogenesis through VEGF, PI3K, and Akt pathways. NRP1 may have potential as a new therapeutic target in NSCLC.

A microarray analysis of the emergence of embryonic definitive hematopoiesis

OBJECTIVE

Human embryonic stem (ES) cells provide a unique model for studying the development and function of human tissues and have proven utility in a number of areas. However, results from ES cell-based studies have been limited by the paucity of information available about early human hematopoietic development.

METHODS

To better understand early development of the hematopoietic lineage, we use microarray analysis to examine the temporal patterns of gene expression in embryoid bodies derived from human ES cells, focusing around the time of the emergence of definitive hematopoiesis. We use an empirical Bayes hierarchical modeling approach, called EBarrays, to classify genes into each of the possible temporal patterns of gene expression for five different time points, and correlate those patterns with the emergence of hematopoiesis.

RESULTS

We find a distinct group of genes previously identified as important in adult hematopoietic self-renewal (such as PIK3R1, ABCB1/MDR-1, RGS18, IRS1, SENP6/SUMO-1, and Wnt5A, etc.) temporally correlates with the emergence of the definitive hematopoiesis. Microarray-based results are further supported via flow cytometry and reverse transcription-polymerase chain reaction studies.

CONCLUSION

The novel genes demonstrating the same expression pattern as this group could further facilitate the understanding of the molecular mechanisms of embryonic hematopoiesis.

Development of differential sensitivity of CaOv ovarian adenocarcinoma cells to antitumor agents under conditions of hypoxia

We studied the role of VEGF signal pathway in autocrine regulation of tumor cell growth and survival under conditions of hypoxia. Hypoxia-resistant CaOv/H substrain with high level of VEGF-A secretion was obtained by long-term culturing of CaOv ovarian adenocarcinoma cells with CoCl2 (hypoxia inductor). VEGF-A directly participates in autocrine regulation of CaOv cell growth, including the maintenance of cell growth under conditions of hypoxia or cytostatic treatment. On the other hand, CaOv/H cells retain high apoptotic potential and are characterized by high expression of p27Kip1 (cyclin-dependent kinase inhibitor), which attests to possible involvement of this inhibitor into the regulation of apoptotic response of cells under conditions of hypoxia.

Knock-down of Bcl-2 by antisense oligodeoxynucleotides induces radiosensitization and inhibition of angiogenesis in human PC-3 prostate tumor xenografts

Expression of the proto-oncogene Bcl-2 is associated with tumor progression. Bcl-2's broad expression in tumors, coupled with its role in resistance to chemotherapy and radiation therapy-induced apoptosis, makes it a rational target for anticancer therapy. Antisense Bcl-2 oligodeoxynucleotide (ODN) reagents have been shown to be effective in reducing Bcl-2 expression in a number of systems. We investigated whether treating human prostate cancer cells with antisense Bcl-2 ODN (G3139, oblimersen sodium, Genasense) before irradiation would render them more susceptible to radiation effects. Two prostate cancer cell lines expressing Bcl-2 at different levels (PC-3-Bcl-2 and PC-3-Neo) were subjected to antisense Bcl-2 ODN, reverse control (CTL), or mock treatment. Antisense Bcl-2 ODN alone produced no cytotoxic effects and was associated with G(1) cell cycle arrest. The combination of antisense Bcl-2 ODN with irradiation sensitized both cell lines to the killing effects of radiation. Both PC-3-Bcl-2 and PC-3-Neo xenografts in mice treated with the combination of antisense Bcl-2 ODN and irradiation were more than three times smaller by volume compared with xenografts in mice treated with reverse CTL alone, antisense Bcl-2 ODN alone, irradiation alone, or reverse CTL plus radiotherapy (P = 0.0001). Specifically, PC-3-Bcl-2 xenograft tumors treated with antisense Bcl-2 ODN and irradiation had increased rates of apoptosis and decreased rates of angiogenesis and proliferation. PC-3-Neo xenograft tumors had decreased proliferation only. This is the first study which shows that therapy directed at Bcl-2 affects tumor vasculature. Together, these findings warrant further study of this novel combination of Bcl-2 reduction and radiation therapy, as well as Bcl-2 reduction and angiogenic therapy.

Interleukin-6 upregulates expression of KDR and stimulates proliferation of human cerebrovascular smooth muscle cells

Interleukin-6 (IL-6) may play multiple roles in angiogenesis and vascular remodeling. Our previous study showed that a promoter polymorphism (174G>C) in IL-6 is associated with brain arteriovenous malformation hemorrhage; tissue expression is related to genotype. In this study, we investigated the effects of IL-6 on human cerebral smooth muscle cells (HCSMCs) and smooth muscle cells isolated from brain arteriovenous malformation surgical specimens (AVM SMCs) and surgical controls (control HCSMCs--from structurally normal temporal lobe taken during surgical treatment of epilepsy patients). We found that IL-6 (1.1+/-0.27 versus 0.37+/-0.04 pg/mL, n=5, P<0.05) and endogenous vascular endothelial growth factor (VEGF) receptor II (kinase domain-containing receptor (KDR), 15+/-3 versus 1.5+/-3 pg/mL, n=5, P<0.05) were increased in brain AVM SMCs compared with control HCSMCs. Further research revealed that IL-6 could stimulate SMC proliferation, VEGF release, and KDR activation in control HCSMCs. It could also stimulate KDR phosphorylation in control HCSMCs, further confirming a unique role of IL-6 in the triggering of KDR. Interleukin-6 could increase matrix metalloproteinase-9 (MMP-9) secretion through activating KDR in control HCSMCs (P<0.05 versus control). Inhibiting IL-6-induced KDR could reduce MMP-9 activity at least 50% compared with the control group (P<0.05). Increased MMP-9 activity was accompanied by increased control HCSMC proliferation, and blocking MMP-9 activity significantly reduced IL-6-induced control HCSMC proliferation (P<0.05). Collectively, our results show that IL-6 could activate, amplify, and maintain the angiogenic cascade in HCSMCs. A novel role of IL-6 during HCSMC proliferation is upregulating KDR expression and phosphorylation. The results may contribute to the angiogenic phenotype of human brain vascular diseases, such as brain AVM.

Inhibition of tumor endothelial ERK activation, angiogenesis, and tumor growth by sorafenib (BAY43-9006)

Activation of the Raf-MEK-ERK signal transduction pathway in endothelial cells is required for angiogenesis. Raf is the kinase most efficiently inhibited by the multikinase inhibitor sorafenib, which has shown activity against certain human cancers in clinical trials. To understand the mechanisms underlying this activity, we studied how it controlled growth of K1735 murine melanomas. Therapy caused massive regional tumor cell death accompanied by severe tumor hypoxia, decreased microvessel density, increased percentage of pericyte-covered vessels, and increased caliber and decreased arborization of vessels. These signs of K1735 angiogenesis inhibition, along with its ability to inhibit Matrigel neovascularization, showed that sorafenib is an effective anti-angiogenic agent. Extracellular signal-regulated kinase (ERK) activation in tumor endothelial cells, revealed by immunostaining for phospho-ERK and CD34, was inhibited, whereas AKT activation, revealed by phospho-AKT immunostaining, was not inhibited in K1735 and two other tumor types treated with sorafenib. Treatment decreased endothelial but not tumor cell proliferation and increased both endothelial cell and tumor cell apoptosis. These data indicate that sorafenib's anti-tumor efficacy may be primarily attributable to angiogenesis inhibition resulting from its inhibition of Raf-MEK-ERK signaling in endothelial cells. Assessing endothelial cell ERK activation in tumor bio-psies may provide mechanistic insights into and allow monitoring of sorafenib's activity in patients in clinical trials.

Beta2-microglobulin promotes the growth of human renal cell carcinoma through the activation of the protein kinase A, cyclic AMP-responsive element-binding protein, and vascular endothelial growth factor axis

PURPOSE

Beta(2)-microglobulin (beta2M), a soluble protein secreted by cancer and host inflammatory cells, has various biological functions, including antigen presentation. Because aberrant expression of beta2M has been reported in human renal cell carcinoma, we investigated the effects of beta2M overexpression on cancer cell growth and analyzed its molecular signaling pathway.

EXPERIMENTAL DESIGN

We established clonal cell lines that overexpressed beta2M in human renal cell carcinoma (SN12C) cells and then examined cell growth in vitro and in vivo and studied the beta2M-mediated downstream cell signaling pathway.

RESULTS

Our results showed that beta2M expression positively correlates with (a) in vitro growth on plastic dishes and as Matrigel colonies, (b) cell invasion and migration in Boyden chambers, and (c) vascular endothelial growth factor (VEGF) expression and secretion by cells. We found, in addition, that beta2M mediates its action through increased phosphorylation of cyclic AMP-responsive element-binding protein (CREB) via the protein kinase A-CREB axis, resulting in increased VEGF expression and secretion. In convergence with this signal axis, beta2M overexpression also activated both phosphatidylinositol 3-kinase/Akt and mitogen-activated protein kinase pathways. Beta2M overexpression induced accelerated growth of SN12C in mouse subcutis and bone. Interrupting the beta2M signaling pathway using small interfering RNA led to apoptosis with increased activation of caspase-3 and caspase-9 and cleaved poly(ADP-ribose) polymerase.

CONCLUSIONS

Our results showed for the first time that the beta2M-protein kinase A-CREB-VEGF signaling axis plays a crucial role in support of renal cell carcinoma growth and progression and reveals a novel therapeutic target.

Regulation of angiogenesis and tumor growth by p110 alpha and AKT1 via VEGF expression

Recent studies demonstrate that PI3K activation and PTEN mutation are frequently found in many human cancer cells and tissues. However, the mechanism of PI3K signaling in human cancer tumorigenesis remains to be elucidated. In this study we specifically downregulated p110alpha expression in ovarian cancer cells using siRNA interference. We found that p110alpha downregulation greatly decreased ovarian tumor growth and angiogenesis, and that p110alpha siRNA inhibited VEGF expression through decreasing hypoxia-inducible factor 1alpha expression in both ovarian cancer cells and tumor tissues. To determine the downstream targets of PI3K in regulating tumor growth and angiogenesis, we find that AKT1 is a major downstream mediator for regulating tumor growth, angiogenesis, and VEGF expression. These data show that p110alpha and AKT1 play an important role in tumor growth by inducing angiogenesis and by increasing HIF-1alpha and VEGF expression. This work provides a better understanding of the molecular mechanism of human cancer induced by the activation of PI3K signaling.

Activation of mitogenic pathways and sensitization to estrogen-induced apoptosis: two independent characteristics of tamoxifen-resistant breast cancer cells?

Paradoxical induction of apoptosis by estrogen has been described previously for estrogen-deprived and antiestrogen-resistant breast cancer cells. In this study we analyzed the possible interrelations between cell sensitization to estrogen apoptotic action and cell ability to (anti)estrogen-independent growth. Using tamoxifen-resistant sublines derived from the parent MCF-7 breast cancer cells by long-term tamoxifen treatment we demonstrated that resistant cells are characterized by increased level of EGF receptor and unexpected increase of VEGF receptor 2 (Flk-1/KDR) and its specific ligand, VEGF-A. The importance of the VEGF signaling in the autocrine regulation of cell growth was indicated by the ability of VEGF inhibitor, soluble fragment of Flt-1/Fc chimera, to suppress the phosphorylation of MAP kinases as well as to inhibit the estrogen-independent growth of MCF-7 cells. Sensitization of tamoxifen-resistant cells to estrogen-induced apoptosis required the additional continuous cultivation in steroid-depleted medium and did not depend on the activity of both EGF and VEGF pathways. Finally, we showed that treatment of the cells with 17beta-estradiol (10(-9) M) resulted in a marked increase in p53 level both in the resistant cells undergoing apoptosis and in the parent MCF-7 cells insensitive to apoptotic estrogen action. These data provide an important support for the existence of a disbalance between pro- and anti-apoptotic machinery in the resistant breast cancer cells that forms independently of the acquired ability to estrogen-independent growth.

Promising new treatments for neovascular age-related macular degeneration

Angiogenesis, the growth of new blood vessels from existing blood vessels, is responsible for vision loss in a variety of ophthalmic diseases. In neovascular age-related macular degeneration (AMD), the leading cause for legal blindness in many industrialised countries, abnormal blood vessels grow in the macula and cause blindness. There are a number of factors important in the angiogenic cascade but VEGF-A has been implicated in recent years as the major factor responsible for neovascular and exudative diseases of the eye. Numerous antiangiogenic drugs are in development but anti-VEGF drugs have shown great promise in treating neovascular AMD and other ocular diseases, and many of these drugs have been adopted from oncology where antiangiogenic therapy is gaining wide acceptance. For the first time in neovascular AMD, anti-VEGF drugs have brought the hope of vision improvement to a significant proportion of patients. This review provides an overview on angiogenic mechanisms, potential antiangiogenic treatment strategies and different antiangiogenic drugs with special focus on neovascular AMD.

Regulation of Ang2 release by PTEN/PI3-kinase/Akt in lung microvascular endothelial cells

Angiopoietin-2 (Ang2) is a Tie-2 ligand that destabilizes vascular structures, allowing for neovascularization or vessel regression depending on local vascular endothelial cell growth factor (VEGF) concentrations. Although various stimuli have been shown to affect Ang2 expression, information on the underlying mechanisms involved in Ang2 production in endothelial cells (EC) is just beginning to emerge. In the present study, we have used adenovirus-mediated gene transfer and pharmacological inhibitors to examine the role of the PTEN/PI3-K/Akt pathway on Ang2 release. Inhibition of PI3-kinase with wortmannin led to a stimulation of basal Ang2 release in EC, while overexpression of an active form of Akt reduced Ang2. In addition, adenovirus-mediated gene transfer of the phosphatase PTEN stimulated Ang2 release. Incubation of the cells with Ang1, an agent that activates the PI3-K/Akt pathway in EC, reduced Ang2 release. This effect of Ang1 could be prevented by wortmannin and LY-294002 pretreatment. Similarly, in VEGF-treated EC the increase in Ang2 production observed was greater in the presence of a PI3-K inhibitor. Our observations that PTEN acts as a positive modulator of Ang2 release, while activation of the PI3-K/Akt pathway downregulates Ang2, reveal an additional mechanism through which the PTEN/PI3-K/Akt pathway could affect the angiogenic process.

The adaptor protein Gab1 couples the stimulation of vascular endothelial growth factor receptor-2 to the activation of phosphoinositide 3-kinase

Phosphoinositide 3-kinase (PI3K) mediates essential functions of vascular endothelial growth factor (VEGF), including the stimulation of endothelial cell proliferation and migration. Nevertheless, the mechanisms coupling the receptor VEGFR-2 to PI3K remain obscure. We observed that the Grb2-bound adapter Gab1 is tyrosine-phosphorylated and relocated to membrane fractions upon VEGF stimulation of endothelial cells. We could detect the PI3K regulatory subunit p85 in immunoprecipitates of endogenous Gab1, and vice versa, and measure a Gab1-associated lipid kinase activity upon VEGF stimulation. Furthermore, transfection of the Gab1-YF3 mutant lacking all p85-binding sites strongly repressed PI3K activation measured in vitro. Moreover, Gab1-YF3 severely decreased the cellular amount of phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3) generated in response to VEGF. Furthermore, adenoviral expression of Gab1-YF3 suppressed both Akt phosphorylation and recovery of wounded human umbilical vein endothelial cell monolayers, a VEGF-dependent process involving cell migration and proliferation under PI3K control. Transfection of other Gab1 mutants, lacking Grb2-binding sites or the pleckstrin homology (PH) domain, also prevented Akt activation, further demonstrating Gab1 involvement in PI3K activation. These mutants were also used to show that interactions with both Grb2 and PtdIns(3,4,5)P3 mediate Gab1 recruitment by VEGFR-2. Importantly, Gab1 mobilization was impaired by (i) PI3K inhibitors, (ii) deletion of Gab1 PH domain, (iii) PTEN (phosphatase and tensin homolog deleted on chromosome 10) overexpression to repress PtdIns(3,4,5)P3 production, and (iv) overexpression of a competitor PH domain for PtdIns(3,4,5)P3 binding, which altogether demonstrated that PI3K is also an upstream regulator of Gab1. Gab1 thus appears as a primary actor in coupling VEGFR-2 to PI3K/Akt, recruited through an amplification loop involving PtdIns(3,4,5)P3 and its PH domain.

Vascular endothelial growth factor receptors: molecular mechanisms of activation and therapeutic potentials

Angiogenesis-associated eye diseases are among the most common cause of blindness in the United States and worldwide. Recent advances in the development of angiogenesis-based therapies for treatment of angiogenesis-associated diseases have provided new hope in a wide variety of human diseases ranging from eye diseases to cancer. One group of growth factor receptors critically implicated in angiogenesis is vascular endothelial growth factor receptors (VEGFR), a subfamily of receptor tyrosine kinases (RTKs). VEGFR-1 and VEGFR-2 are closely related receptor tyrosine kinases and have both common and specific ligands. VEGFR-1 is a kinase-impaired RTK and its kinase activity is suppressed by a single amino acid substitution in its kinase domain and by its carboxyl terminus. VEGFR-2 is highly active kinase, stimulates a variety of signaling pathways and broad biological responses in endothelial cells. The mechanisms that govern VEGFR-2 activation, its ability to recruit signaling proteins and to undergo downregulation are highly regulated by phosphorylation activation loop tyrosines and its carboxyl terminus. Despite their differential potentials to undergo tyrosine phosphorylation and kinase activation, both VEGFR-1 and VEGFR-2 are required for normal embryonic development and pathological angiogenesis. VEGFR-1 regulates angiogenesis by mechanisms that involve ligand trapping, receptor homodimerization and heterodimerization. This review highlights recent insights into the mechanism of activation of VEGFR-1 and VEGFR-2, and focuses on the signaling pathways employed by VEGFR-1 and VEGFR-2 that regulate angiogenesis and their therapeutic potentials in angiogenesis-associated diseases.

Signaling pathways mediating VEGF165-induced calcium transients and membrane depolarization in human endothelial cells

Cytosolic calcium and membrane potential were monitored simultaneously in quiescent human umbilical vein endothelial cells (HUVEC) exposed to vascular endothelial growth factor (VEGF)165 using the fluorescent indicators indo-1 AM and DiSBAC2(3), respectively. Application of VEGF165 to cells elicits a rapid rise in cytosolic calcium followed by a slower decline toward control values. Peak calcium is associated with a slight membrane hyperpolarization; however, as calcium falls toward control, a strong depolarization develops and is sustained throughout a 10-min period of VEGF165 stimulation. Both the VEGF165-mediated rise in cytosolic calcium and membrane depolarization are eliminated by inhibitors of VEGFR-2, tyrosine kinase, src kinase and inositol-1,4,5 triphosphate-operated calcium channels. Calcium entry, which is initially facilitated by transient hyperpolarization, is restricted by a substantial, sustained depolarization that developed during the downstroke of the calcium spike. Inhibition of plasmalemmal calcium channels diminished the magnitude and duration of the calcium spike, suggesting that extracellular calcium influx, secondary to stores release, is a significant component of the calcium transient. Inhibition of chloride channels substantially reduced membrane depolarization. In addition, the depolarization is modulated by PI3 kinase in a ras-independent manner. In summary, intracellular calcium and membrane potential are influenced by several key signaling cascades of VEGFR-2 activation in HUVEC.

Inhibition of endothelial cell proliferation by Notch1 signaling is mediated by repressing MAPK and PI3K/Akt pathways and requires MAML1

The requirement for Notch signaling in vasculogenesis and angiogenesis is well documented. In a previous study, we showed that activation of the Notch pathway in endothelial cells induces differentiation-associated growth arrest; however, the underlying mechanism remains to be elucidated. Here, we show that activation of the Notch pathway by either stimulation of cell surface Notch receptors with crosslinked soluble delta-like 4 (sDll4)/Jagged1 (sJag1) or constitutive expression of the Notch1 intracellular domain (N(IC)) suppresses endothelial cell proliferation. This suppression is mediated by the mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K)/Akt pathways. Following Notch1 activation, both pathways were suppressed in endothelial cells, and alterations in MAPK or PI3K/Akt pathway activity reversed Notch1-induced growth inhibition. Furthermore, we found the effect of Notch1 on endothelial cells to require Mastermind-like (MAML). Overexpression of a dominant-negative mutant of MAML1 antagonized the effects of activated Notch1 on the MAPK and PI3K/Akt pathways. Ectopic expression of Hairy/Enhancer of Split 1 (HES1) consistently reproduced the inhibitory effect of N(IC) on endothelial cell proliferation. Together, our data demonstrate that the Notch/MAML-HES signaling cascade can regulate both MAPK and PI3K/Akt pathways, which suggests a molecular mechanism for the inhibitory effect of Notch signaling on endothelial cell proliferation.

Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) reduces vascular endothelial growth factor expression in allergen-induced airway inflammation

Vascular endothelial growth factor (VEGF) plays a pivotal role in the pathogenesis of bronchial asthma. Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) has been implicated in regulating cell survival signaling through the phosphoinositide 3-kinase (PI3K)/Akt pathway. The key role of PI3K in VEGF-mediated signal transduction is established. However, the effects of PTEN on VEGF-mediated signaling in asthma are unknown. This study aimed to determine the effect of PI3K inhibitors and PTEN on VEGF expression in allergen-induced airway inflammation. We have used a female C57BL/6 mouse model for asthma to determine the role of PTEN in allergen-induced airway inflammation, specifically in the expression of VEGF. Allergen-induced airway inflammation leads to increased activity of PI3K in lung tissue. These mice develop the following typical pathophysiological features of asthma in the lungs: increased numbers of inflammatory cells of the airways; airway hyper-responsiveness; increased expression of interleukin (IL)-4, IL-5, IL-13, intercellular adhesion molecule 1, vascular cell adhesion molecule 1, regulated on activation normal T cell expressed and secreted (RANTES), and eotaxin; increased vascular permeability; and increased levels of VEGF. Administration of PI3K inhibitors or adenoviruses carrying PTEN cDNA reduced the symptoms of asthma and decreased the increased levels of plasma extravasation and VEGF in allergen-induced asthmatic lungs. These results indicate that PTEN reduces VEGF expression in allergen-induced airway inflammation.

Targeting tumor angiogenesis with histone deacetylase inhibitors: the hydroxamic acid derivative LBH589

PURPOSE

Angiogenesis is required for tumor progression and represents a rational target for therapeutic intervention. Histone deacetylase (HDAC) inhibitors have been shown to have activity against various tumor cell types by inhibiting proliferation and inducing apoptosis both in vitro and in vivo. HDAC inhibitors have also been reported to inhibit angiogenesis. The goal of this study was to characterize the antiangiogenic and antitumor activity of a recently developed HDAC inhibitor, the hydroxamic derivative LBH589.

MATERIALS AND METHODS

To evaluate the antiangiogenesis activity of LBH589, we did cell cycle analysis, cell proliferation, tube formation, invasion assays in vitro, and Matrigel plug assay in vivo. To determine the antitumor activity of LBH589, we established human prostate carcinoma cell PC-3 xenografts in vivo. To evaluate the effect of LBH589 on endothelial signaling pathways, gene expression, and protein acetylation, we did Western blots and reverse transcription-PCR in human umbilical vein endothelial cells (HUVEC). Immunohistochemical analysis was done to evaluate new blood vessel formation in vivo.

RESULTS

LBH589 induced acetylation of histone H3 and alpha-tubulin protein in HUVECs. Histone and nonhistone protein acetylation correlated with induction of G(2)-M cell cycle arrest, inhibition of HUVEC proliferation, and viability. Noncytotoxic concentrations of LBH589 inhibited endothelial tube formation, Matrigel invasion, AKT, extracellular signal-regulated kinase 1/2 phosphorylation, and chemokine receptor CXCR4 expression. In vivo dosing of mice with LBH589 (10 mg/kg/d) reduced angiogenesis and PC-3 tumor growth.

CONCLUSION

This study provides evidence that LBH589 induces a wide range of effects on endothelial cells that lead to inhibition of tumor angiogenesis. These results support the role of HDAC inhibitors as a therapeutic strategy to target both the tumor and endothelial compartment and warrant the clinical development of these agents in combination with angiogenesis inhibitors.

Vascular endothelial growth factor signalling in endothelial cell survival: a role for NFkappaB

Angiogenesis is the development of blood capillaries from pre-existing vessels. Vascular endothelial growth factor (VEGF) is a key regulator of vessel growth and regression, and acts as an endothelial survival factor by protecting endothelial cells from apoptosis. Many genes involved in cell proliferation and apoptosis are regulated by the nuclear factor kappa B (NFkappaB) transcription factor family. This study aimed to address the hypothesis that VEGF-mediated survival effects on endothelium involve NFkappaB. Using an NFkappaB-luciferase reporter adenovirus, we observed activation of NFkappaB following VEGF treatment of human umbilical vein endothelial cells. This was confirmed using electrophoretic mobility shift assay and found to involve nuclear translocation of NFkappaB sub-unit p65. However, NFkappaB activation occurred without degradation of inhibitory IkappaB proteins (IkappaBalpha, IkappaBbeta, and IkappaBepsilon). Instead, tyrosine phosphorylation of IkappaBalpha was observed following VEGF treatment, suggesting NFkappaB activation was mediated by degradation-independent dissociation of IkappaBalpha from NFkappaB. Adenovirus-mediated over-expression of either native IkappaBalpha, or of IkappaBalpha in which tyrosine residue 42 was mutated to phenylalanine, inhibited induction of NFkappaB-dependent luciferase activity in response to VEGF. Furthermore, VEGF-induced upregulation of mRNA for the anti-apoptotic protein Bcl-2 and cell survival following serum withdrawal was reduced following IkappaBalpha over-expression. This study highlights that different molecular mechanisms of NFkappaB activation may be involved downstream of stimuli which activate the endothelial lining of blood vessels.

Phosphatidylinostol 3-Kinase Mediates Angiogenesis and Vascular Permeability Associated with Ovarian Carcinoma

PURPOSE

To assess the role of phosphatidylinositol-3 kinase (PI3K) inhibition in vascular permeability, angiogenesis, and vascular remodeling in tumor vessels and peritoneal lining in an athymic mouse model of i.p. human ovarian carcinoma.

EXPERIMENTAL DESIGN

Mice were inoculated i.p. with cells from the human ovarian cancer cell line, OVCAR-3. Fourteen days after inoculation, mice were treated with or without the PI3K inhibitor LY294002, 3 days weekly for 4 weeks. At the end of the experiment, some mice were anesthetized and injected via the tail vein with FITC-labeled lycopersicon lectin and perfused through the aorta before sacrifice. The peritoneal wall and tumor from all mice were removed and embedded in 10% agarose. Tumor sections were visualized by fluorescence microscopy.

RESULTS

Ascites in the LY294002-treated group (0.69 +/- 0.27 mL) was reduced by 72.4% compared with the control group (2.5 +/- 1.2 mL). Tumor burden in the LY294002-treated group (0.62 +/- 0.32 g) was reduced by 47.3% compared with the control group (1.18 +/- 0.41 g). LY294002 inhibited peritoneal and tumor vascularization resulting in numerous leaky, irregular, tortuous vessels in scant, straight, relatively impermeable vessels.

CONCLUSIONS

The data indicate that LY294002 inhibits ascites formation in our mouse model of human ovarian cancer by inhibiting tumor and peritoneal neovascularization as well as vascular permeability. The data also show that LY294002 directly inhibits vascular endothelial growth factor (VEGF) protein expression and release from ovarian carcinoma and suggest that LY294002 blocks the VEGF signaling pathway involved in angiogenesis and vascular permeability.

PI3-kinase activation by GM-CSF in endothelium is upstream of Jak/Stat pathway: Role of αGMR

GM-CSF has been identified as a growth factor for endothelial cells. In this study, we investigated the role of PI3-kinase pathway in mediating GM-CSF induced angiogenesis. GM-CSF induced tube formation in human umbilical vein endothelial cells, as examined using Matrigel assay, was inhibited by specific inhibitors of PI3-kinase, wortmannin, and LY294002. The regulatory subunit of PI3-kinase (p85) interacted with alphaGMR via its C-SH2 domain in a GM-CSF-dependent fashion with concomitant phosphorylation of p85 and activation of PI3-kinase pathway. p85 binding site on the alphaGMR was essential to induce GM-CSF receptor-dependent Stat activation. Furthermore, inhibition of PI3-kinase activity also abrogated GM-CSF induced Stat activation. These studies underscore the significance of the GM-CSF mediated PI3-kinase activation and its role in angiogenesis.

Heat shock proteins and other components of cellular machinery for protein synthesis are up-regulated in vascular endothelial cell growth factor-activated human endothelial cells

Proteome analysis of human umbilical endothelial cells was performed to identify proteins that are modified during vascular endothelial cell growth factor (VEGF)-induced transition from the quiescent into the proliferating-migrative phenotype. Subtractive analysis of two-dimensional gel patterns of human endothelial cells, before and after stimulation with VEGF(165), revealed differences in 85 protein spots. All proteins were identified by peptide sequencing and peptide mass fingerprinting using an electrospray spectrometer. The proteins identified were members of specific families including Ca(2+)-binding proteins, fatty-acid binding proteins, structural proteins, and chaperones. Remarkably, there was a massive activation of cellular machinery for both protein synthesis and protein degradation. Thus, among up-regulated proteins there were members of all groups of heat shock proteins (HSPs; HSP 27, HSP 60, HSP 70p5, HSP 70p8, HSP 90, and HSP 96) and some other proteins showing either chaperone activity or which participate in assembly of multimolecular structures (TCP-1, desmoplakins, junction plakoglobin, GRP 94, thioredoxin related protein, and peptidylprolyl isomerase). The increased expression of HSPs was confirmed at the mRNA level at different stages of treatment with VEGF. Similarly, components of the proteolytic machinery for the degradation of misfolded proteins (ER-60, cathepsin D, proteasome subunits, and protease inhibitor 6) were also up-regulated. On the other hand, changes in the expression of structural proteins (T-plastin, vimentin, alpha tubulin, actin, and myosin) could account, at least in part, for the different morphologies displayed by migrating endothelial cells. In summary, our data show that VEGF levels similar to those during physiological stresses induce a number of genes and multiple endogenous pathways seem to be engaged in restoring cellular homeostasis. To ensure cell survival, the molecular chaperones (the heat shock family of stress proteins) are highly up-regulated providing protein-folding machinery to repair or degrade misfolded proteins.

Targeting angiogenesis: structural characterization and biological properties of a de novo engineered VEGF mimicking peptide

Modulating angiogenesis is an attractive goal because many pathological conditions depend on the growth of new vessels. Angiogenesis is mainly regulated by the VEGF, a mitogen specific for endothelial cells. In the last years, many efforts have been pursued to modulate the angiogenic response targeting VEGF and its receptors. Based on the x-ray structure of VEGF bound to the receptor, we designed a peptide, QK, reproducing a region of the VEGF binding interface: the helix region 17-25. NMR conformation analysis of QK revealed that it adopts a helical conformation in water, whereas the peptide corresponding to the alpha-helix region of VEGF, VEGF15, is unstructured. Biological assays in vitro and on bovine aorta endothelial cells suggested that QK binds to the VEGF receptors and competes with VEGF. VEGF15 did not bind to the receptors indicating that the helical structure is necessary for the biological activity. Furthermore, QK induced endothelial cells proliferation, activated cell signaling dependent on VEGF, and increased the VEGF biological response. QK promoted capillary formation and organization in an in vitro assay on matrigel. These results suggested that the helix region 17-25 of VEGF is involved in VEGF receptor activation. The peptide designed to resemble this region shares numerous biological properties of VEGF, thus suggesting that this region is of potential interest for biomedical applications, and molecules mimicking it could be attractive for therapeutic and diagnostic applications.

mTOR: a placental growth signaling sensor

The proliferation and differentiation of trophoblast cells is under the control of a variety of hormones and growth factors and is influenced by nutrient availability. The intracellular signaling pathways acting downstream of these mitogenic factors and nutrients to regulate trophoblast proliferation and placental development are poorly understood. Immortalized human trophoblast cells were used (HTR-8/SVneo) to investigate trophoblast proliferation in response to angiopoietin-2 (Ang-2), a major angiogenic factor and glucose (a major nutrient). Trophoblast cell proliferation was induced through activation of the phosphatidylinositol-3 (PI-3) kinase and the mammalian target of rapamycin (mTOR) signaling pathways, following Tie-2 receptor activation. Glucose also stimulated trophoblast cell proliferation through mTOR signaling. Ang-2 activated mTOR via PI-3 kinase-dependent signaling; whereas glucose-mediated mTOR activation was PI-3 kinase-independent and involved a novel nutrient sensor, glutamine fructose-6-phosphate amidotransferase (GFAT). Metabolites of the GFAT reaction acted upstream of mTOR and functioned as a nutrient sensor to regulate trophoblast cell proliferation in response to glucose. Overall, the results show that growth factor and nutrient signaling converge at tuberin, an upstream regulator of mTOR and that mTOR functions as an important placental growth signaling sensor. These results are the first to link mTOR with GFAT metabolites as nutrient sensors for trophoblast cell proliferation.

Mechanism of HIF-1alpha-dependent suppression of hypoxia-induced apoptosis in squamous cell carcinoma cells

The transcriptional factor hypoxia-inducible factor-1 (HIF-1) plays an important role in solid tumor cell growth and survival. Overexpression of HIF-1alpha has been demonstrated in many human tumors and predicts a poor response to chemoradiotherapy. We examined the HIF-1alpha-induced survival pathways in human oral squamous cell carcinoma cell (OSCC) lines. The results showed that forced expression of HIF-1alpha suppressed hypoxia-induced apoptosis of OSCC lines by inhibiting cytochrome c release from mitochondria. Overexpression of HIF-1alpha inhibited the generation of reactive oxygen species (ROS), elevation of intracellular Ca(2+) concentration, reduction of mitochondrial membrane potential, and cytosolic accumulation of cytochrome c, which resulted in the inactivation of caspase-9 and caspase-3. In addition, antiapoptotic Bcl-2 and Bcl-X(L) levels were increased and pro-apoptotic Bax and Bak levels were decreased in the HIF-1alpha-overexpressing OSCC line. Overexpression of HIF-1alpha also increased the levels of phosphorylation of Akt and extracellular signal-regulated kinases (ERK). These findings indicate that HIF-1alpha prevents apoptotic cell death through two mechanisms, including inhibition of cytochrome c release and activation of Akt and ERK.

Kinase domain insert containing receptor promotor controlled suicide gene system kills human umbilical vein endothelial cells

AIM: To evaluate the killing effect of double suicide gene mediated by adenovirus and regulated under kinase domain insert containing receptor (KDR) promoter on human umbilical vein endothelial cells.

METHODS: By PCR technology, human KDR promoter gene, Escherichia coli (E. coli) cytosine deaminase (CD) gene and the herpes simple virus-thymidine kinase (TK) gene were cloned. Plasmid pKDR-CDglyTK was constructed with them. Then, a recombinant adenoviral plasmid pAdKDR-CDglyTK was constructed in a “two-step transformation protocol”. The newly constructed plasmids were transfected to 293 packaging cells to grow adenoviruses, which were further propagated and purified. Human umbilical vein endothelial cells (HUVEC) were infected with a different multiplicity of infection (MOI) of resultant recombinant adenovirus, the infection rate was measured with the aid of (GFP) expression. Infected cells were cultured in culture media containing different concentrations of (GCV) and/or 5-(FC), and the killing effects were measured.

RESULTS: Recombinant adenoviruses AdKDR-CDglyTK were successfully constructed, and they infected HUVEC cells efficiently. Our data indicated that the infection rate was relevant to MOI of recombinant adenoviruses. HUVEC cells infected with AdKDR-CDglyTK were highly sensitive to the prodrugs, their survival rate correlated to both the concentration of the prodrugs and the MOI of recombinant adenoviruses. Our data also indicated that the two prodrugs used in combination were much more effective on killing transgeneic cells than GCV or 5-FC used alone.

CONCLUSION: Prodrug/KDR-CDglyTK system is effective on killing HUVEC cells, its killing effect correlates to the concentration of prodrugs and recombinant adenovirus’ MOI. Combined use of the two prodrugs confers better killing effects on transgeneic cells.

The vascular endothelial growth factor-induced disruption of gap junctions is relayed by an autocrine communication via ATP release in coronary capillary endothelium

Little is known concerning how the coordination of Ca(2+) signaling aids in capillary endothelial cell (CEC) functions, such as microvascular permeability and angiogenesis. Previous reports support the major involvement of gap junction (GJ) channels. However, the cell-to-cell communication may not be straightforward, especially if we consider the participation of active molecules released by CEC. In this study, short-term effects of vascular endothelial growth factor (VEGF-165) were compared with those of bradykinin (BK) on gap junction coupling (GJC) and remodeling of connexin-43 (Cx43) and then analyzed for intercellular Ca(2+) signal in primary cultures of coronary CEC. Dye-coupling experiments revealed that BK or VEGF completely blocked GJC. These effects correlated with the rapid internalization of Cx43 and its tyrosine phosphorylation in part via the phosphatidylinositol 3-kinase/Akt pathway. GJC slowly recovered with BK but not with VEGF in the following hour. In control conditions, mechanical stimulation of a single cell within a confluent monolayer triggered an intercellular Ca(2+) wave that was partially inhibited by GJC blockers or purinergic inhibitors. No wave propagation was observed after blockage of both GJC and purinergic receptors. Cell treatment with VEGF also reduced propagation of the Ca(2+) wave, which was totally prevented by applying a purinergic receptor antagonist but not with a GJC blocker. That excludes purine efflux through Cx hemichannels. We conclude that VEGF-induced disruption of GJC via Cx43 remodeling is relayed by an autocrine communication via secretion of ATP to preserve intercellular Ca(2+) signaling in capillary endothelium.

A protein tyrosine phosphatase inhibitor accelerates angiogenesis in a rat model of hindlimb ischemia

Vascular endothelial growth factor (VEGF) receptor-2 (KDR/flk-1) has a tyrosine kinase domain and, once activated, induces the autophosphorylation of the tyrosine residues. The phosphorylated KDR/flk-1 can be a substrate for intracellular protein tyrosine phosphatases (PTPs). In the present study, we have examined whether the PTP inhibitor sodium orthovanadate (SOV) activates KDR/flk-1 and accelerates angiogenesis in a rat model of hindlimb ischemia. The left femoral artery was exposed and excised to induce limb ischemia. The PTP activity in ischemic adductors increased, whereas SOV significantly suppressed the increase in the activity. Tyrosine phosphorylation of KDR/flk-1 and Akt phosphorylation significantly increased in the muscles injected with SOV compared with those injected with saline. The amount of VEGF increased in both the muscles injected with SOV and those injected with the saline but did not differ significantly. At 21 days after the induction of ischemia, immunohistochemical studies demonstrated that muscles injected with SOV showed significantly increased capillary density compared with those injected with saline. In a rat model of hindlimb ischemia, not only VEGF but also PTP, which might impair angiogenesis, increased. SOV activated KDR/flk-1 and accelerated angiogenesis. Thus, a PTP inhibitor can be a new drug for therapeutic angiogenesis in peripheral ischemic diseases.

A novel Src kinase inhibitor, M475271, inhibits VEGF-induced human umbilical vein endothelial cell proliferation and migration

Vascular endothelial growth factor (VEGF) was reported to be a potent proangiogenic factor that plays a pivotal role in both physiological and pathological angiogenesis. M475271, 4-quinazolinamine, N-(2-chloro-5-methoxyphenyl)-6-methoxy-7-[(1-methyl-4-piperidinyl) methoxy]-(9Cl), is a new anilinoquinazoline derivative that showed selective inhibition of Src kinase activity and tumor growth in vivo. Here, we examined the effect of M475271 on VEGF-induced human umbilical vein endothelial cell (HUVEC) proliferation and migration and their intracellular mechanisms. Our findings showed that M475271 pretreatment resulted in a significant inhibition of VEGF-induced HUVEC proliferation, [(3)H]thymidine incorporation, and migration. M475271 inhibited VEGF-induced Flk-1 and Src phosphorylation and their association. Confocal laser microscopic examination confirmed the inhibitory effect of M475271 on VEGF-induced Flk-1/Src association. M475271 inhibited VEGF-induced extracellular signal-regulated kinase1/2 (ERK1/2) and p38 but not Akt activation in a concentration-dependent manner. M475271, PI3-K inhibitor, and p38 inhibitor inhibited VEGF-induced HUVEC proliferation and migration. However, a MEK1/2 inhibitor inhibited VEGF-induced proliferation but not migration. These findings suggest that M475271 attenuates VEGF-induced HUVEC proliferation and migration through the inhibition of signaling pathways involving Src, ERK1/2, and/or p38. Taken together, these data indicate that M475271 may be a useful candidate for inhibition of endothelial cell proliferation and migration relevant to angiogenesis.

Chronic stress in the adult dentate gyrus reduces cell proliferation near the vasculature and VEGF and Flk-1 protein expression

Recent evidence has shown that cell proliferation in the adult hippocampal dentate gyrus occurs in tight clusters located near the vasculature. Also, changes in neurogenesis often appear parallel to changes in angiogenesis. Moreover, both these processes share similar modulating factors, like vascular endothelial growth factor (VEGF) and its receptor Flk-1. In an earlier study we found that chronic stress decreased new cell proliferation in the adult dentate gyrus. We here questioned whether these effects of chronic stress are mediated through the vasculature and whether they involve an angiogenic-signaling pathway. We therefore measured the surface area covered by the vasculature, the proportion of vascular-associated newborn cells, and analysed VEGF and Flk-1 protein expression in the hippocampus of a control, chronically stressed and recovery group of rats. Our results show that 32% of the proliferating cells in the rat hippocampus is vascular associated. Chronic stress affected this population of newborn cells to a significantly larger extent than the non-associated cells. Interestingly, after 3 weeks of recovery, the decreased proliferation not associated with the vasculature was more effectively restored than vascular-associated proportion of proliferating cells. VEGF protein was expressed in high densities in GFAP-positive astrocytes located in the hilus, with VEGF-positive end feet extending into and often contacting the granule cells. After chronic stress, both VEGF and Flk-1 protein levels were significantly decreased in the granular cell layer, and again recovered after 3 weeks. This demonstrates that changes in angiogenic factors are implicated in the decreased adult proliferation found after chronic stress.

Inhibition of endothelial cell migration by thrombospondin-1 type-1 repeats is mediated by beta1 integrins

The anti-angiogenic effect of thrombospondin-1 has been shown to be mediated through binding of the type-1 repeat (TSR) domain to the CD36 transmembrane receptor. We now report that the TSR domain can inhibit VEGF-induced migration in human umbilical vein endothelial cells (HUVEC), cells that lack CD36. Moreover, we identified β₁ integrins as a critical receptor in TSR-mediated inhibition of migration in HUVEC. Using pharmacological inhibitors of downstream VEGF receptor effectors, we found that phosphoinositide 3-kinase (PI3k) was essential for TSR-mediated inhibition of HUVEC migration, but that neither PLCγ nor Akt was necessary for this response. Furthermore, β₁ integrins were critical for TSR-mediated inhibition of microvascular endothelial cells, cells that express CD36. Together, our results indicate that β₁ integrins mediate the anti-migratory effects of TSR through a PI3k-dependent mechanism.

Inostamycin suppresses vascular endothelial growth factor-stimulated growth and migration of human umbilical vein endothelial cells

Angiogenesis involves multiple steps including proliferation and migration of endothelial cells. In the present study, we determined the effect of inostamycin (an inhibitor of phosphatidylinositol synthesis) on vascular endothelial growth factor (VEGF)-induced proliferation and migration of human umbilical vein endothelial cells (HUVECs). Inostamycin significantly attenuated both VEGF-induced proliferation and migration of HUVECs. Inostamycin inhibited activation of mitogen-activated kinases (ERK and p38) and elevation of cyclin D1 induced by VEGF. These data suggest that inostamycin reduced both proliferation and migration of HUVECs by targeting ERK-cyclin D1 and p38, respectively.

Blockade of Vascular Endothelial Growth Factor Receptor Signal Pathway and Antitumor Activity of ON-III (2′,4′-Dihydroxy-6′-methoxy-3′,5′-dimethylchalcone), a Component from Chinese Herbal Medicine

Antiangiogenesis is a promising strategy of cancer treatment. Vascular endothelial growth factor receptor [fetal liver kinase/kinase-inserting domain-containing receptor (KDR)] is a tyrosine kinase receptor and has been strongly implicated in tumor angiogenesis. In this study, we report that 2',4'-dihydroxy-6'-methoxy-3',5'-dimethylchalcone (ON-III), extracted from the dried flower Cleistocalyx operculatus, used in traditional Chinese medicine, reversibly inhibited KDR tyrosine kinase phosphorylation, but epidermal growth factor receptor tyrosine kinase phosphorylation was unaffected under the same concentrations of ON-III. ON-III also inhibited mitogen-activated protein kinase (MAPK) and AKT activation of KDR signal transduction in downstream molecules without reduced total MAPK and AKT. The results in vitro showed that ON-III inhibited growth of human vascular endothelial HDMEC cells in the presence of VEGF preferentially, compared with epidermal growth factor. Systemic administration of ON-III at nontoxic doses in nude mice resulted in inhibition of subcutaneous tumor growth of human hepatocarcinoma Bel7402 and lung cancer GLC-82 xenografts. The tumor vessel density decreased, as determined by immunohistochemical staining, for CD31 after ON-III treatment. These results indicated that ON-III inhibited KDR tyrosine kinase, shut down KDR-mediated signal transduction, and inhibited tumor growth of human xenografts in vivo.

Deficiency in the p110alpha subunit of PI3K results in diminished Tie2 expression and Tie2(-/-)-like vascular defects in mice

Phosphoinositide 3-kinase (PI3K) is activated by transmembrane tyrosine kinases such as vascular endothelial growth factor (VEGF) receptors and Tie2 (tunica intima endothelial kinase 2), both of which are key regulators of vascular development. However, the in vivo role of PI3K during developmental vascularization remains to be defined. Here we demonstrate that mice deficient in the p110alpha catalytic subunit of PI3K display multiple vascular defects, including dilated vessels in the head, reduced branching morphogenesis in the endocardium, lack of hierarchical order of large and small branches in the yolk sac, and impaired development of anterior cardinal veins. These vascular defects are strikingly similar to those in mice defective in the Tie2 signaling pathway. Indeed, Tie2 protein levels were significantly lower in p110alpha-deficient mice. Furthermore, RNA interference of p110alpha in cultured endothelial cells significantly reduced Tie2 protein levels. These findings raise the possibility that PI3K may function as an upstream regulator of Tie2 expression during mouse development.