Vascular endothelial growth factor (VEGF)-driven actin-based motility is mediated by VEGFR2 and requires concerted activation of stress-activated protein kinase 2 (SAPK2/p38) and geldanamycin-sensitive phosphorylation of focal adhesion kinase

VEGF Enhances the Migration of MSCs in Neural Differentiation by Regulating Focal Adhesion Turnover

Mesenchymal stem cells (MSCs) hold great promise in neural regeneration, due to their intrinsic neuronal potential and migratory tropism to damaged nervous tissues. However, the chemotactic signals mediating the migration of MSCs remain poorly understood. Here, we investigated the regulatory roles for focal adhesion kinase (FAK) and Rac1 in vascular endothelial growth factor (VEGF)-stimulated migration of MSCs in neural differentiation. We found that MSCs in various differentiation states show significant different chemotactic responses to VEGF and cells in 24-h preinduction state possess the highest migration speed and efficiency. FAK, as the downstream signaling molecule, is involved in the VEGF-induced migration by regulating the assembly and distribution of focal adhesions (FAs) and reorganization of F-actin. The features of FAs and cytoskeletons and the ability of lamellipodia formation are closely related to the neural differentiation states of MSCs. VEGF promotes FA formation with an asymmetric distribution of FAs and induces the activation of Y397-FAK and Y31/118-paxillin of undifferentiated and 24-h preinduced MSCs in a time-dependent manner. Inhibition of FAK by PF-228 or expressing FAK-Y397F mutant impairs the dynamics of FAs in MSCs during VEGF-induced migration. Furthermore, Rac1 regulates FA formation in a FAK-dependent manner. Overexpression of constitutive activated mutants of Rac1 increases the number of FAs in undifferentiated and 24-h preinduced MSCs, while VEGF-induced increase of FA formation is decreased by inhibiting FAK by PF-228. Collectively, these results demonstrate that FAK and Rac1 signalings coordinately regulate the dynamics of FAs during VEGF-induced migration of MSCs in varying neural differentiation states.

The Emerging Regulation of VEGFR-2 in Triple-Negative Breast Cancer

Vascular endothelial growth factor-A (VEGF) signals vascular development and angiogenesis mainly by binding to VEGF receptor family member 2 (VEGFR-2). Adaptor proteins mediate many VEGFR-2's functions in the development of blood vessels. Cancer cells secrete VEGF to activate VEGFR-2 pathway in their neighboring endothelial cells in the process of cancer-related angiogenesis. Interestingly, activation of VEGFR-2 signaling is found in breast cancer cells, but its role and regulation are not clear. We highlighted research advances of VEGFR-2, with a focus on VEGFR-2's regulation by mutant p53 in breast cancer. In addition, we reviewed recent Food and Drug Administration-approved tyrosine kinase inhibitor drugs that can inhibit the function of VEGFR-2. Ongoing preclinical and clinical studies might prove that pharmaceutically targeting VEGFR-2 could be an effective therapeutic strategy in treating triple-negative breast cancer.

Kaempferol Identified by Zebrafish Assay and Fine Fractionations Strategy from Dysosma versipellis Inhibits Angiogenesis through VEGF and FGF Pathways

Natural products are a rich resource for the discovery of therapeutic substances. By directly using 504 fine fractions from isolated traditional Chinese medicine plants, we performed a transgenic zebrafish based screen for anti-angiogenesis substances. One fraction, DYVE-D3, was found to inhibit the growth of intersegmental vessels in the zebrafish vasculature. Bioassay-guided isolation of DYVE-D3 indicates that the flavonoid kaempferol was the active substance. Kaempferol also inhibited the proliferation and migration of HUVECs in vitro. Furthermore, we found that kaempferol suppressed angiogenesis through inhibiting VEGFR2 expression, which can be enhanced by FGF inhibition. In summary, this study shows that the construction of fine fraction libraries allows efficient identification of active substances from natural products.

Viral activation of stress-regulated Rho-GTPase signaling pathway disrupts sites of mRNA degradation to influence cellular gene expression

Viruses are useful tools that often reveal previously unrecognized levels of control within a cell. By studying the oncogenic Kaposi's sarcoma-associated herpesvirus (KSHV), we discovered a new signaling axis in endothelial cells (ECs) that links actin cytoskeleton dynamics to post-transcriptional control of gene expression. Translational repression and rapid decay of mRNAs containing AU-rich elements (AREs) occurs in cytoplasmic RNA granules known as processing bodies (PBs). Rho-GTPase activity influences PB dynamics but mechanistic details remain obscure. We have previously shown that the KSHV Kaposin B protein blocks the degradation of ARE-mRNAs that encode potent cytokines and angiogenic factors, at least in part by preventing PB formation. Moreover, Kaposin B is sufficient to cause marked alterations in endothelial cell physiology including the formation of long parallel actin stress fibers and accelerated migration and angiogenic phenotypes. All of these phenotypes depend on Kaposin B-mediated activation of a non-canonical signaling pathway comprising the stress-inducible kinase MK2, hsp27, p115RhoGEF and RhoA. Accelerated endothelial cell migration and angiogenesis depends on the subsequent activation of the RhoA-dependent kinase ROCK, but PB disruption is ROCK-independent. In this Commentary, we discuss implications of the activation of this signaling axis, and propose mechanistic links between RhoA activation and PB dynamics.

hMSC-Derived VEGF Release Triggers the Chemoattraction of Alveolar Osteoblasts

Human mesenchymal stem cells (hMSCs) are promising candidates for regenerative periodontal strategies, due to the broad spectrum of supportive effects on cells and tissues at the site of application. Although positive effects are visible, the understanding of their underlying mechanisms still requires further elucidation. Recently, we have shown that hMSCs are capable to prompt osteogenic differentiation of alveolar osteoblasts, thereby presumably contributing to alveolar bone regeneration. Another issue that is critical in this context is the attraction of hard tissue-forming cells to regeneration sites, but it is an open question whether hMSCs can afford this. In the present manuscript, we show by life cell imaging that in interactive cocultures, hMSCs successfully trigger osteoblast chemotaxis. Gene expression analysis for hMSC-innate chemoattractive biomolecules, orchestrating this process, revealed vascular endothelial growth factor (VEGF), PgE synthase, osteoprotegerin (OPG), monocyte colony-stimulating factor, and transforming growth factor β1, which was confirmed for VEGF and OPG on the protein level. Noteworthy, we showed that only corresponding levels of VEGF but not OPG attracted alveolar osteoblasts similar to hMSC coculture, while VEGF inhibitor abolished both the VEGF and the hMSC-triggered chemoattraction. In summary, we have identified secreted OPG and VEGF proteins as potential chemoattractants, of which further characterization yielded VEGF as a causative for hMSC-directed osteoblast chemotaxis. With respect to the better understanding of potential hMSC-based periodontal regeneration strategies, we propose hMSC-derived VEGF release as a mechanism in the recruitment of hard tissue-forming cells to alveolar bone sites in need of regeneration.

RhoC maintains vascular homeostasis by regulating VEGF-induced signaling in endothelial cells

Vasculogenesis and angiogenesis are controlled by vascular endothelial growth factor A (VEGF-A). Dysregulation of these physiological processes contributes to the pathologies of heart disease, cancer and stroke. Rho GTPase proteins play an integral role in VEGF-mediated formation and maintenance of blood vessels. The regulatory functions of RhoA and RhoB in vasculogenesis and angiogenesis are well defined, whereas the purpose of RhoC remains poorly understood. Here, we describe how RhoC promotes vascular homeostasis by modulating endothelial cell migration, proliferation and permeability. RhoC stimulates proliferation of human umbilical vein endothelial cells (HUVECs) by stabilizing nuclear β-catenin, which promotes transcription of cyclin D1 and subsequently drives cell cycle progression. RhoC negatively regulates endothelial cell migration through MAPKs and downstream MLC2 signaling, and decreases vascular permeability through downregulation of the phospholipase Cγ (PLCγ)-Ca(2+)-eNOS cascade in HUVECs. Using a VEGF-inducible zebrafish (Danio rerio) model, we observed significantly increased vascular permeability in RhoC morpholino (MO)-injected zebrafish compared with control MO-injected zebrafish. Taken together, our findings suggest that RhoC is a key regulator of vascular homeostasis in endothelial cells.

Viral activation of MK2-hsp27-p115RhoGEF-RhoA signaling axis causes cytoskeletal rearrangements, p-body disruption and ARE-mRNA stabilization

Kaposi's sarcoma-associated herpesvirus (KSHV) is the infectious cause of several AIDS-related cancers, including the endothelial cell (EC) neoplasm Kaposi's sarcoma (KS). KSHV-infected ECs secrete abundant host-derived pro-inflammatory molecules and angiogenic factors that contribute to tumorigenesis. The precise contributions of viral gene products to this secretory phenotype remain to be elucidated, but there is emerging evidence for post-transcriptional regulation. The Kaposin B (KapB) protein is thought to contribute to the secretory phenotype in infected cells by binding and activating the stress-responsive kinase MK2, thereby selectively blocking decay of AU-rich mRNAs (ARE-mRNAs) encoding pro-inflammatory cytokines and angiogenic factors. Processing bodies (PBs) are cytoplasmic ribonucleoprotein foci in which ARE-mRNAs normally undergo rapid 5′ to 3′ decay. Here, we demonstrate that PB dispersion is a feature of latent KSHV infection, which is dependent on kaposin protein expression. KapB is sufficient to disperse PBs, and KapB-mediated ARE-mRNA stabilization could be partially reversed by treatments that restore PBs. Using a combination of genetic and chemical approaches we provide evidence that KapB-mediated PB dispersion is dependent on activation of a non-canonical Rho-GTPase signaling axis involving MK2, hsp27, p115RhoGEF and RhoA. PB dispersion in latently infected cells is likewise dependent on p115RhoGEF. In addition to PB dispersion, KapB-mediated RhoA activation in primary ECs caused actin stress fiber formation, increased cell motility and angiogenesis; these effects were dependent on the activity of the RhoA substrate kinases ROCK1/2. By contrast, KapB-mediated PB dispersion occurred in a ROCK1/2-independent manner. Taken together, these observations position KapB as a key contributor to viral reprogramming of ECs, capable of eliciting many of the phenotypes characteristic of KS tumor cells, and strongly contributing to the post-transcriptional control of EC gene expression and secretion.

We have only scratched the surface in understanding how viruses control host gene expression. Several viruses disrupt important sites of post-transcriptional control of gene expression known as processing bodies (PBs), but underlying regulatory mechanisms and biological relevance remain poorly understood in most cases. Our study shows that the Kaposin B (KapB) protein of Kaposi's sarcoma (KS)-associated herpesvirus, known to block the degradation of a class of labile host mRNAs, does so by constitutively activating a signaling axis involving MK2, hsp27, p115RhoGEF and RhoA, thereby dispersing PBs. Thus, PB disruption may support the secretion of host pro-inflammatory cytokines and angiogenic factors that underlies KS tumor formation. Furthermore, by activating RhoA, KapB also causes cytoskeletal rearrangements, accelerated cell migration and angiogenesis in an endothelial cell model. Our findings position KapB as a key contributor to viral reprogramming of endothelial cells.

Endothelin-1 increases the expression of VEGF-R1/Flt-1 receptors in rat cultured astrocytes through ETB receptors

Expressions of vascular endothelial growth factor (VEGF) receptors in astrocytes are increased in damaged brains. To clarify the regulatory mechanisms of VEGF receptors, the effects of endothelin-1 (ET-1) were examined in rat cultured astrocytes. Expressions of VEGF-R1 and -R2 receptor mRNA were at similar levels, whereas the mRNA expressions of VEGF-R3 and Tie-2, a receptor for angiopoietins, were lower. Placenta growth factor, a selective agonist of the VEGF-R1 receptor, induced phosphorylation of focal adhesion kinase (FAK) and extracellular signal regulated kinase 1/2 (ERK1/2). Phosphorylations of FAK and ERK 1/2 were also stimulated by VEGF-E, a selective VEGF-R2 agonist. Increased phosphorylations of FAK and ERK1/2 by VEGF165 were reduced by selective antagonists for VEGF-R1 and -R2. Treatment with ET-1 increased VEGF-R1 mRNA and protein levels. The effects of ET-1 on VEGF-R1 mRNA were mimicked by Ala(1,3,11,15) -ET-1, a selective agonist for ETB receptors, and inhibited by BQ788, an ETB antagonist. ET-1 did not affect the mRNA levels of VEGF-R2, -R3, and Tie-2. Pre-treatment with ET-1 potentiated the effects of placenta growth factor on phosphorylations of FAK and ERK1/2. These findings suggest that ET-1 induces up-regulation of VEGF-R1 receptors in astrocytes, and potentiates VEGF signals in damaged nerve tissues. To clarify the regulatory mechanisms of vascular endothelial growth factor (VEGF) receptors, the effects of endothelin-1 (ET-1) were examined in rat cultured astrocytes. Effects of selective VEGF-R1 and R2 agonist showed that these receptors were linked to focal adhesion kinase (FAK) and extracellular signal regulated kinase 1/2 (ERK1/2). Treatment with ET-1 increased expression of VEGF-R1, which was mediated by ETB receptors. Pre-treatment with ET-1 potentiated the VEGF-R1-mediated activations of FAK and ERK1/2. These findings suggest that ET-1 induces up-regulation of VEGF-R1 receptors in astrocytes.

Heat shock protein 90β stabilizes focal adhesion kinase and enhances cell migration and invasion in breast cancer cells

Focal adhesion kinase (FAK) acts as a regulator of cellular signaling and may promote cell spreading, motility, invasion and survival in malignancy. Elevated expression and activity of FAK frequently correlate with tumor cell metastasis and poor prognosis in breast cancer. However, the mechanisms by which the turnover of FAK is regulated remain elusive. Here we report that heat shock protein 90β (HSP90β) interacts with FAK and the middle domain (amino acids 233-620) of HSP90β is mainly responsible for this interaction. Furthermore, we found that HSP90β regulates FAK stability since HSP90β inhibitor 17-AAG triggers FAK ubiquitylation and subsequent proteasome-dependent degradation. Moreover, disrupted FAK-HSP90β interaction induced by 17-AAG contributes to attenuation of tumor cell growth, migration, and invasion. Together, our results reveal how HSP90β regulates FAK stability and identifies a potential therapeutic strategy to breast cancer.

Isogambogenic acid inhibits tumour angiogenesis by suppressing Rho GTPases and vascular endothelial growth factor receptor 2 signalling pathway

Isogambogenic acid (iso-GNA) is a well-known herbal medicine extracted from Garcinia hanburyi. Although it is thought to have anti-tumour effects, its function is still unknown. This study carried out in vitro and in vivo evaluations of the anti-tumour and anti-angiogenic activity of iso-GNA and underlying mechanisms. A standard methyl thiazolyl tetrazolium assay showed that iso-GNA was more effective in inhibiting the proliferation of human umbilical vascular endothelial cells than A549 cancer cells. Iso-GNA demonstrated potent anti-angiogenic activity and low toxicity at appropriate concentrations in zebrafish embryos. In a xenograft nude mouse model of lung tumour, iso-GNA effectively inhibited tumour growth and tumour angiogenesis. Iso-GNA suppressed neovascularization of implanted matrigel plugs in vivo and inhibited vascular endothelial growth factor (VEGF)-induced microvessel sprouting from mouse aortic rings ex vivo. Iso-GNA inhibited VEGF-induced migration, invasion, and tube formation in vitro and affected cytoskeletal rearrangement in human umbilical vascular endothelial cells. The results show that iso-GNA suppressed angiogenesis-mediated tumour growth by targeting VEGFR2, Akt, mitogen-activated protein kinase, Rho GTPase, vascular endothelium-cadherin, and focal adhesion kinase signalling pathways. Together, these data suggest that iso-GNA inhibits angiogenesis and may be a viable drug candidate in anti-angiogenesis and anti-cancer therapies.

Heat shock response associated with hepatocarcinogenesis in a murine model of hereditary tyrosinemia type I

Hereditary Tyrosinemia type 1 (HT1) is a metabolic liver disease caused by genetic defects of fumarylacetoacetate hydrolase (FAH), an enzyme necessary to complete the breakdown of tyrosine. The severe hepatic dysfunction caused by the lack of this enzyme is prevented by the therapeutic use of NTBC (2-[2-nitro-4-(trifluoromethyl)benzoyl] cyclohexane-1,3-dione). However despite the treatment, chronic hepatopathy and development of hepatocellular carcinoma (HCC) are still observed in some HT1 patients. Growing evidence show the important role of heat shock proteins (HSPs) in many cellular processes and their involvement in pathological diseases including cancer. Their survival-promoting effect by modulation of the apoptotic machinery is often correlated with poor prognosis and resistance to therapy in a number of cancers. Here, we sought to gain insight into the pathophysiological mechanisms associated with liver dysfunction and tumor development in a murine model of HT1. Differential gene expression patterns in livers of mice under HT1 stress, induced by drug retrieval, have shown deregulation of stress and cell death resistance genes. Among them, genes coding for HSPB and HSPA members, and for anti-apoptotic BCL-2 related mitochondrial proteins were associated with the hepatocarcinogenetic process. Our data highlight the variation of stress pathways related to HT1 hepatocarcinogenesis suggesting the role of HSPs in rendering tyrosinemia-affected liver susceptible to the development of HCC.

Tryptanthrin inhibits angiogenesis by targeting the VEGFR2-mediated ERK1/2 signalling pathway

Angiogenesis is a key step for tumour growth and metastasis, and anti-angiogenesis has been proposed as an important strategy for cancer therapy. Tryptanthrin is a weakly basic alkaloid isolated from the dried roots of medicinal indigo plants and has been shown to possess anti-tumour activities on various cancer cell types. This study aims to investigate the in vitro and in vivo anti-angiogenic activities of tryptanthrin and to unravel its underlying molecular action mechanisms. Our results show that tryptanthrin inhibited the in vitro proliferation, migration, and tube formation of the human microvascular endothelial cells (HMEC-1) in a concentration-dependent manner and significantly suppressed angiogenesis in Matrigel plugs in mice. Mechanistic studies indicated that tryptanthrin reduced the expression of several pro-angiogenic factors (Ang-1, PDGFB and MMP2). Tryptanthrin was also found to suppress the VEGFR2-mediated ERK1/2 signalling pathway in HMEC-1 cells and molecular docking simulation indicated that tryptanthrin could bound to the ATP-binding site of VEGFR2. Collectively, the present study demonstrated that tryptanthrin exhibited both in vitro and in vivo anti-angiogenic activities by targeting the VEGFR2-mediated ERK1/2 signalling pathway and might have therapeutic potential for the treatment of angiogenesis-related diseases.

TRAIL negatively regulates VEGF-induced angiogenesis via caspase-8-mediated enzymatic and non-enzymatic functions

Solid tumors supply oxygen and nutrients required for angiogenesis by producing vascular endothelial growth factor (VEGF). Thus, inhibitors of VEGF signaling abrogate tumor angiogenesis, resulting in the suppression of tumor growth and metastasis. We here investigated the effects of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) on VEGF-induced angiogenesis. TRAIL inhibited VEGF-induced in vitro angiogenesis of human umbilical vein endothelial cells (HUVECs) and in vivo neovascularization in chicken embryos and mice. TRAIL blocked VEGF-induced angiogenic signaling by inhibiting ERK, Src, FAK, paxillin, Akt, and eNOS. Further, TRAIL blocked intracellular Ca(2+) elevation and actin reorganization in HUVECs stimulated with VEGF, without inhibiting VEGF receptor-2 tyrosine phosphorylation. TRAIL increased caspase-8 activity, without inducing caspase-9/-3 activation and apoptosis. Moreover, TRAIL resulted in cleavage of FAK into FAK-related non-kinase-like fragments in VEGF-stimulated HUVECs, which was blocked by a caspase-8 inhibitor and cellular caspase-8-like inhibitory protein. Biochemical and pharmacological inhibition of caspase-8 and FAK blocked the inhibitory effects of TRAIL on VEGF-stimulated anti-angiogenic signaling and events. In addition, caspase-8 knockdown also suppressed VEGF-mediated signaling and angiogenesis, suggesting that procaspase-8 plays a role of a non-apoptotic modulator in VEGF-induced angiogenic signaling. These results suggest that TRAIL inhibits VEGF-induced angiogenesis by increasing caspase-8 activity and subsequently decreasing non-apoptotic signaling functions of procaspase-8, without inducing caspase-3 activation and endothelial cell cytotoxicity. These data indicate that caspase-8 may be used as an anti-angiogenic drug for solid tumors resistant to TRAIL and anti-tumor drugs.

Cell stress promotes the association of phosphorylated HspB1 with F-actin

Previous studies have suggested that the small heat shock protein, HspB1, has a direct influence on the dynamics of cytoskeletal elements, in particular, filamentous actin (F-actin) polymerization. In this study we have assessed the influence of HspB1 phosphorylation on its interaction(s) with F-actin. We first determined the distribution of endogenous non-phosphorylated HspB1, phosphorylated HspB1 and F-actin in neuroendocrine PC12 cells by immunocytochemistry and confocal microscopy. We then investigated a potential direct interaction between HspB1 with F-actin by precipitating F-actin directly with biotinylated phalloidin followed by Western analyses; the reverse immunoprecipitation of HspB1 was also carried out. The phosphorylation influence of HspB1 in this interaction was investigated by using pharmacologic inhibition of p38 MAPK. In control cells, HspB1 interacts with F-actin as a predominantly non-phosphorylated protein, but subsequent to stress there is a redistribution of HspB1 to the cytoskeletal fraction and a significantly increased association of pHspB1 with F-actin. Our data demonstrate HspB1 is found in a complex with F-actin both in phosphorylated and non-phosphorylated forms, with an increased association of pHspB1 with F-actin after heat stress. Overall, our study combines both cellular and biochemical approaches to show cellular localization and direct demonstration of an interaction between endogenous HspB1 and F-actin using methodolgy that specifically isolates F-actin.

A heat-shock protein axis regulates VEGFR2 proteolysis, blood vessel development and repair

Vascular endothelial growth factor A (VEGF-A) binds to the VEGFR2 receptor tyrosine kinase, regulating endothelial function, vascular physiology and angiogenesis. However, the mechanism underlying VEGFR2 turnover and degradation in this response is unclear. Here, we tested a role for heat-shock proteins in regulating the presentation of VEGFR2 to a degradative pathway. Pharmacological inhibition of HSP90 stimulated VEGFR2 degradation in primary endothelial cells and blocked VEGF-A-stimulated intracellular signaling via VEGFR2. HSP90 inhibition stimulated the formation of a VEGFR2-HSP70 complex. Clathrin-mediated VEGFR2 endocytosis is required for this HSP-linked degradative pathway for targeting VEGFR2 to the endosome-lysosome system. HSP90 perturbation selectively inhibited VEGF-A-stimulated human endothelial cell migration in vitro. A mouse femoral artery model showed that HSP90 inhibition also blocked blood vessel repair in vivo consistent with decreased endothelial regeneration. Depletion of either HSP70 or HSP90 caused defects in blood vessel formation in a transgenic zebrafish model. We conclude that perturbation of the HSP70-HSP90 heat-shock protein axis stimulates degradation of endothelial VEGFR2 and modulates VEGF-A-stimulated intracellular signaling, endothelial cell migration, blood vessel development and repair.

Fast rearrangement of the neuronal growth cone's actin cytoskeleton following VEGF stimulation

The neuronal growth cone plays a crucial role in the development of the nervous system. This highly motile structure leads the axon to its final destination by translating guidance cues into cytoskeletal rearrangements. Recently, vascular endothelial growth factor (VEGF), which is essential for angiogenesis and vascular sprouting, has been found to exert a trophic activity also on neurons, leading to an increased axonal outgrowth, similar to the well-known nerve growth factor (NGF). The neurotrophic properties of VEGF are likely to be promoted via the VEGF receptor 2 (VEGFR-2) and neuropilin-1 (NRP-1). In the long term, VEGF attracts and influences the growth cone velocity and leads to growth cone enlargement. The present study focuses on immediate VEGF effects using RFP-actin and GFP-NF-M microinjected chicken dorsal root ganglia for live cell imaging of the neuronal growth cone. We analyzed actin and neurofilament dynamics following VEGF and NGF treatment and compared the effects. Furthermore, key signaling pathways of VEGF were investigated by specific blocking of VEGFR-2 or NRP-1. With the aid of confocal laser scanning microscopy and stimulated emission depletion microscopy, we show for the first time that VEGF has a quick effect on the actin-cytoskeleton, since actin rearrangements were identifiable within a few minutes, leading to a dramatically increased motion. Moreover, these effects were strongly enhanced by adding both VEGF and NGF. Most notably, the effects were inhibited by blocking VEGFR-2, therefore we propose that the immediate effects of VEGF on the actin-cytoskeleton are mediated through VEGFR-2.

HSP27 expression in primary colorectal cancers is dependent on mutation of KRAS and PI3K/AKT activation status and is independent of TP53

Colorectal adenomas display features of senescence, but these are often lost upon progression to carcinoma, indicating that oncogene induced senescence (OIS) could be a roadblock in colorectal cancer (CRC) development. Heat shock proteins (HSPs) have been implicated in the prognosis of CRC and HSP based therapy is a current interest for drug development. Recent cell culture studies have suggested that in the absence of a TP53 mutation, OIS mediated by PI3K/AKT activation can be circumvented by high expression of HSPs. Furthermore, while PI3K/AKT activation and KRAS mutations are independent inducers of OIS, PI3K/AKT activation can suppress KRAS-induced OIS when both are present in cultured cells. As KRAS mutations, PI3K/AKT activation and TP53 mutations are all common features of CRC, it is possible that the requirement for HSP to inhibit OIS in CRC is dependent on the mutation spectrum of a tumour. However, work on HSP that utilised mutation profiled human tumour tissues has been limited. Here, we characterised the expression of two major HSP proteins (HSP27 and 72) by immunohistochemistry (IHC), the mutation status of TP53, KRAS and PIK3CA genes by direct sequencing and the activation status of AKT by IHC in a cohort of unselected primary CRC (n=74). We compare our data with findings generated from cell-based studies. Expression of HSP27 and HSP72 was correlated to clinicopathological and survival data but no significant association was found. We also established the mutation status of TP53, KRAS and PIK3CA genes and the activation status of AKT in our CRC panel. We did not detect any associations between HSP27 or HSP72 expression with TP53 mutation status. However, HSP27 expression in CRCs was strongly associated with the co-presence of wildtype KRAS and activated PI3K/AKT (p=0.004), indicating a possible role of HSP27 in overcoming PI3K/AKT induced OIS in tumours. Our studies suggest a role for using archival tissues in validating hypotheses generated from cell culture based investigations.

CAPE suppresses VEGFR-2 activation, and tumor neovascularization and growth

The growth and metastasis of human solid tumors and the development of conditions such as diabetic retinopathy, rheumatoid arthritis, inflammatory psoriasis, and others are regulated by the balance between angiogenic stimulators and inhibitors released in the angiogenic-pathological microenvironment. Vascular endothelial growth factor (VEGF), an angiogenic factor, is a potent endothelial-specific mitogen that activates endothelial cells in pathological angiogenesis. Recently, we demonstrated that caffeic acid phenethyl ester (CAPE) inhibits tumor growth, invasion, and metastasis. However, the precise molecular mechanism underlying the inhibitory effect of CAPE on VEGF-mediated angiogenesis remains unknown. Here, we show that CAPE suppressed VEGF-induced proliferation, tube formation, migration, the formation of actin stress fibers and loss of VE-cadherin at cell-cell contacts in endothelial cells, indicating the inhibition of VEGF-mediated VEGF receptor-2 (VEGFR-2) and its downstream signal activation in vitro. CAPE blocked VEGF-stimulated neovascularization in the Matrigel plugs assay, and reduced vascular permeability in mouse skin capillaries in vivo. CAPE inhibited the growth and neovascularization of primary tumor cells in C57BL/6 and BALB/c mice inoculated with Lewis lung carcinoma, colon carcinoma, and melanoma cells. These results suggest that CAPE negatively modulates VEGF-induced angiogenesis by suppressing VEGFR-2 activation, and might be a therapeutic avenue for anti-angiogenesis.

Effect of cediranib, an inhibitor of vascular endothelial growth factor receptor tyrosine kinase, in a mouse model of choroidal neovascularization

BACKGROUND

This study was conducted to evaluate the effect of cediranib, an inhibitor of vascular endothelial growth factor receptor tyrosine kinase, in a mouse model of laser-induced choroidal neovascularization.

METHODS

Choroidal neovascularization was induced in C57BL/6 mice by rupturing Bruch's membrane using laser photocoagulation. Following laser injury, the mice were divided into three groups and administered either vehicle, 1 mg/kg or 5 mg/kg of cediranib daily by oral gavage for 2 weeks. Two weeks after laser injury, the area of choroidal neovascularization lesions was measured by choroidal flat mounts using fluorescein-labelled dextran. Immunofluorescence staining with isolectin IB4 was also used to quantify the choroidal neovascularization lesions.

RESULTS

Choroidal flat mount analysis revealed that orally administered cediranib reduced the extent of choroidal neovascularization. The groups treated with 1 and 5 mg/kg/day showed 57.2 and 66.0% reduction of choroidal neovascularization lesions, respectively, compared with the control group treated with vehicle alone (P = 0.012). The size of the fluorescently labelled choroidal neovascularization complex in cediranib-treated groups was much smaller than that from vehicle-treated group (P = 0.035).

CONCLUSIONS

Cediranib inhibited laser-induced choroidal neovascularization in mice and may have therapeutic potential for patients with neovascular age-related macular degeneration.

Fucoidan extract derived from Undaria pinnatifida inhibits angiogenesis by human umbilical vein endothelial cells

In recent years, anti-angiogenic therapy has become an effective strategy for inhibiting tumor growth. Fucoidan is a class of fucose-enriched sulfated polysaccharides found in brown algae, and it is known to have strong anti-tumor property. Using a human umbilical vein endothelial cells (HUVEC)-based cell culture model, the present study investigated the anti-angiogenic activity of fucoidan extracted from the brown seaweed Undaria pinnatifida. Treatment of HUVECs with various concentrations of fucoidan resulted in significant inhibition of cell proliferation, cell migration, tube formation and vascular network formation. However, significant inhibition of cell proliferation only occurred with longer treatment time (48 h instead of 24h or less). About 40% of cell proliferation and cell migration and 61% of tube formation by HUVECs were inhibited by 400 μg/ml fucoidan, the maximum concentration tested. These results appeared to suggest that modulation of angiogenesis by fucoidan might not occur through growth inhibition and apoptosis. Ex vivo angiogenesis assay demonstrated that at 100 μg/ml, fucoidan caused significant reduction in microvessel outgrowth. Western blot and RT-PCR analyses indicated that at 400 μg/ml, fucoidan significantly reduced the expression of the angiogenesis factor VEGF-A in the suppression of angiogenesis activity. Our results showed that fucoidan isolated from U. pinnatifida may have a new therapeutic potential in the prevention angiogenesis-related diseases.

miR-20a represses endothelial cell migration by targeting MKK3 and inhibiting p38 MAP kinase activation in response to VEGF

Endothelial cell migration induced in response to vascular endothelial growth factor (VEGF) is a crucial step of angiogenesis and it depends on the activation of the p38 MAP-kinase pathway downstream of VEGFR2. In this study, we investigated the role of microRNAs (miRNAs) in regulating these processes. We found that the VEGF-induced p38 activation and cell migration are modulated by overexpression of Argonaute 2, a key protein in the functioning of miRNAs. Thereafter, we found that miR-20a expression is increased by VEGF and that its ectopic expression inhibits VEGF-induced actin remodeling and cell migration. Moreover, the expression of miR-20a impairs the formation of branched capillaries in a tissue-engineered model of angiogenesis. In addition, the lentivirus-mediated expression of miR-20a precursor (pmiR-20a) is associated with a decrease in the VEGF-induced activation of p38. In contrast, these processes are increased by inhibiting miR-20a with a specific antagomir. Interestingly, miR-20a does not modulate VEGFR2 or p38 protein expression level. miR-20a does not affect either the expression of other known actors of the p38 MAP kinase pathway except MKK3. Indeed, by using quantitative PCR and Western Blot analysis, we found that pmiR-20a decreases the expression of MKK3 and we obtained evidence indicating that miR-20a specifically binds to the 3'UTR region of MKK3 mRNA. In accordance, the VEGF-induced activation of p38 and cell migration are impaired when the MKK3 expression is knocked down by siRNA. We conclude that miR-20a acts in a feedback loop to repress the expression of MKK3 and to negatively regulate the p38 pathway-mediated VEGF-induced endothelial cell migration and angiogenesis.

Plumbagin inhibits tumour angiogenesis and tumour growth through the Ras signalling pathway following activation of the VEGF receptor-2

BACKGROUND AND PURPOSE

Angiogenesis-based therapy is an effective anti-tumour strategy and previous reports have shown some beneficial effects of a naturally occurring bioactive compound plumbagin (5-hydroxy-2-methyl-1, 4-naphthoquinone). Here, we sought to determine the biological effects of plumbagin on signalling mechanisms during tumour angiogenesis.

EXPERIMENTAL APPROACH

The effects of plumbagin were evaluated in various in vitro assays which utilised human umbilical vein endothelial cells (HUVEC) proliferation, migration and tube formation. Plumbagin was also evaluated in vivo using chicken embryo chorioallantoic membrane (CAM) and mouse corneal micropocket models., Human colon carcinoma and prostate cancer xenograft mouse models were used to evaluate the effects of plumbagin on angiogenesis. Immunofluorescence, GST pull-down and Western blotting were employed to explore the underlying mechanisms of VEGF receptor (VEGFR)2-mediated Ras signalling pathways.

KEY RESULTS

Plumbagin not only inhibited endothelial cell proliferation, migration and tube formation but also suppressed chicken chorioallantoic membrane neovascularzation and VEGF-induced mouse corneal angiogenesis. Moreover, plumbagin suppressed tumour angiogenesis and tumour growth in human colon carcinoma and prostate cancer xenograft mouse models. At a molecular level, plumbagin blocked the Ras/Rac/cofilin and Ras/MEK signalling pathways mediated by VEGFR2 in HUVECs.

CONCLUSIONS AND IMPLICATIONS

Plumbagin inhibited tumour angiogenesis and tumour growth by interference with the VEGFR2-mediated Ras signalling pathway in endothelial cells. Our findings demonstrate a molecular basis for the effects of plumbagin and suggest that this compound might have therapeutic ant-tumour effects.

Low oxygen tension positively influences cardiomyocyte progenitor cell function

Previously we observed that cardiomyocyte progenitor cells (hCMPCs) isolated from the human heart differentiate spontaneously into cardiomyocytes and vascular cells when transplanted after myocardial infarction (MI) in the ischemic heart. After MI, deprivation of oxygen is the first major change in the cardiac environment. How cells handle hypoxia is highly cell type dependent. The effect of hypoxia on cardiac stem or progenitor cells remains to be elucidated. Here, we show for the first time that short- and long-term hypoxia have different effects on hCMPCs. Short-term hypoxia increased the migratory and invasive capacities of hCMPCs likely via mesenchymal transformation. Although long-term exposure to low oxygen levels did not induce differentiation of hCMPCs into mature cardiomyocytes or endothelial cells, it did increase their proliferation, stimulated the secretome of the cells which was shifted to a more anti-inflammatory profile and dampened the migration by altering matrix metalloproteinase (MMP) modulators. Interestingly, hypoxia greatly induced the expression of the extracellular matrix modulator thrombospondin-2 (TSP-2). Knockdown of TSP-2 resulted in increased proliferation, migration and MMP activity. In conclusion, short exposure to hypoxia increases migratory and invasive capacities of hCMPCs and prolonged exposure induces proliferation, an angiogenic secretion profile and dampens migration, likely controlled by TSP-2.

Brain-derived neurotrophic factor induces migration of endothelial cells through a TrkB-ERK-integrin αVβ3-FAK cascade

Brain-derived neurotrophic factor (BDNF) promotes the regeneration of periodontal tissue. Since angiogenesis is important for tissue regeneration, investigating effect of BDNF on endothelial cell function may help to reveal its mechanism, whereby, BDNF promotes periodontal tissue regeneration. In this study, we examined the influence of BDNF on migration in human microvascular endothelial cells (HMVECs), focusing on the effects on extracellular signal-regulated kinase (ERK), integrin α(V)β(3), and focal adhesion kinase (FAK). The migration of endothelial cells was assessed with a modified Boyden chamber and a wound healing assay. The expression of integrin α(V)β(3) and the phosphorylation of ERK and FAK were analyzed by immunoblotting and immunofluorescence microscopy. BDNF (25 ng/ml) induced cell migration. PD98059, an ERK inhibitor, K252a, a specific inhibitor for TrkB, a high affinity receptor of BDNF, and an anti-integrin α(V)β(3) antibody suppressed the BDNF-induced migration. BDNF increased the levels of integrin α(V)β(3) and phosphorylated ERK1/2 and FAK. The ERK inhibitor and TrkB inhibitor also reduced levels of integrin α(V)β(3) and phosphorylated FAK. We propose that BDNF stimulates endothelial cell migration by a process involving TrkB/ERK/integrin α(V)β(3)/FAK, and this may help to enhance the regeneration of periodontal tissue.

VEGF-induced growth cone enhancement is diminished by inhibiting tyrosine-residue 1214 of VEGFR-2

Axonal outgrowth is of paramount significance for establishing the intricate neuronal network both during embryogenesis and nerve regeneration. Vascular endothelial growth factor (VEGF), which is known for its essential role in vascular sprouting and its involvement in cancer, has recently been found to exert a trophic activity on neurons leading to an increased axonal outgrowth. Although two receptors, VEGFR-2 and neuropilin-1, were identified on neurons, the signaling pathways associated with them are not well understood. The aim of this study was to analyze the influence of VEGF on the growth cone morphology and motility of dorsal root ganglia (DRG) neurons. Moreover, we aimed for a deeper understanding of VEGFR-2 on growth cones that potentially mediates the stimulating and attractive effects. We cultivated chicken DRG in medium containing mouse VEGF and analyzed growth cone size. The data presented here show a positive effect of VEGF on growth cone size. Furthermore, we interrupted the activity of VEGFR-2 by either blocking the tyrosine residue 1214 (tyr1214) or by inhibiting the receptor phosphorylation with axitinib, a novel small molecule, which has recently entered phase III trials for cancer treatment. Disruption of the VEGFR-2 leads to a significantly diminished growth cone size. Based on these findings, we propose a positive effect of VEGF on peripheral nervous system growth cone size and show for the first time quantitative data to underline this hypothesis. Additionally, we propose that VEGFR-2 and especially the tyr1214-dependent pathway of VEGFR-2 are of importance in VEGF signaling in the growth cone of DRG neurons.

Signaling regulation of fetoplacental angiogenesis

During normal pregnancy, dramatically increased placental blood flow is critical for fetal growth and survival as well as neonatal birth weights and survivability. This increased blood flow results from angiogenesis, vasodilatation, and vascular remodeling. Locally produced growth factors including fibroblast growth factor 2 (FGF2) and vascular endothelial growth factor A (VEGFA) are key regulators of placental endothelial functions including cell proliferation, migration, and vasodilatation. However, the precise signaling mechanisms underlying such regulation in fetoplacental endothelium are less well defined, specifically with regard to the interactions amongst protein kinases (PKs), protein phosphatase, and nitric oxide (NO). Recently, we and other researchers have obtained solid evidence showing that different signaling mechanisms participate in FGF2- and VEGFA-regulated fetoplacental endothelial cell proliferation and migration as well as NO production. This review will briefly summarize currently available data on signaling mediating fetoplacental angiogenesis with a specific emphasis on PKs, ERK1/2, AKT1, and p38 MAPK and protein phosphatases, PPP2 and PPP3.

Quercetin-4'-O-β-D-glucopyranoside (QODG) inhibits angiogenesis by suppressing VEGFR2-mediated signaling in zebrafish and endothelial cells

BACKGROUND

Angiogenesis plays an important role in many physiological and pathological processes. Identification of small molecules that block angiogenesis and are safe and affordable has been a challenge in drug development. Hypericum attenuatum Choisy is a Chinese herb medicine commonly used for treating hemorrhagic diseases. The present study investigates the anti-angiogenic effects of quercetin-4'-O-β-D-glucopyranoside (QODG), a flavonoid isolated from Hypericum attenuatum Choisy, in vivo and in vitro, and clarifies the underlying mechanism of the activity.

METHODOLOGY/PRINCIPAL FINDINGS

Tg(fli1:EGFP) transgenic zebrafish embryos were treated with different concentrations of quercetin-4'-O-β-D-glucopyranoside (QODG) (20, 60, 180 µM) from 6 hours post fertilisation (hpf) to 72 hpf, and adult zebrafish were allowed to recover in different concentrations of QODG (20, 60, 180 µM) for 7 days post amputation (dpa) prior morphological observation and angiogenesis phenotypes assessment. Human umbilical vein endothelial cells (HUVECs) were treated with or without VEGF and different concentrations of QODG (5, 20, 60, 180 µM), then tested for cell viability, cell migration, tube formation and apoptosis. The role of VEGFR2-mediated signaling pathway in QODG-inhibited angiogenesis was evaluated using quantitative real-time PCR (qRT-PCR) and Western blotting.

CONCLUSION/SIGNIFICANCE

Quercetin-4'-O-β-D-glucopyranoside (QODG) was shown to inhibit angiogenesis in human umbilical vein endothelial cells (HUVECs) in vitro and zebrafish in vivo via suppressing VEGF-induced phosphorylation of VEGFR2. Our results further indicate that QODG inhibits angiogenesis via inhibition of VEGFR2-mediated signaling with the involvement of some key kinases such as c-Src, FAK, ERK, AKT, mTOR and S6K and induction of apoptosis. Together, this study reveals, for the first time, that QODG acts as a potent VEGFR2 kinase inhibitor, and exerts the anti-angiogenic activity at least in part through VEGFR2-mediated signaling pathway.

AAV5-mediated sFLT01 gene therapy arrests retinal lesions in Ccl2(-/-)/Cx3cr1(-/-) mice

To test the effects of adeno-associated virus encoding sFLT01 (AAV5.sFLT01) on the retinal lesions in Ccl2(-/-)/Cx3cr1(-/-) mice, a model for age-related macular degeneration (AMD), AAV5.sFLT01 was injected into the subretinal space of the right eyes and the left eyes served as controls. Histology found no retinal toxicity due to the treatment after 3 months. The treated eyes showed lesion arrest compared with lesion progression in the left eyes by fundus monitoring monthly and histological evaluation 3 months after treatment. Retinal ultrastructure showed fewer lipofuscin and better preserved photoreceptors after the treatment. A2E, a major component of lipofuscin, was lower in the treated eyes than in the control eyes. Molecular analysis showed that AAV5.sFLT01 lowered retinal extracellular signal-regulated kinase (ERK) phosphorylation and inducible nitric oxide synthetase expression, which suggested the involvement of reactive nitrogen species in the retinal lesions of Ccl2(-/-)/Cx3cr1(-/-). We concluded that local delivery of AAV5.sFLT01 can stabilize retinal lesions in Ccl2(-/-)/Cx3cr1(-/-) mice. The findings provide further support for the potential beneficial effects of sFLT01 gene therapy for age-related macular degeneration.

A novel function of p38-regulated/activated kinase in endothelial cell migration and tumor angiogenesis

The p38 mitogen-activated protein kinase (MAPK) pathway has been implicated in both suppression and promotion of tumorigenesis. It remains unclear how these 2 opposite functions of p38 operate in vivo to impact cancer development. We previously reported that a p38 downstream kinase, p38-regulated/activated kinase (PRAK), suppresses tumor initiation and promotion by mediating oncogene-induced senescence in a murine skin carcinogenesis model. Here, using the same model, we show that once the tumors are formed, PRAK promotes the growth and progression of skin tumors. Further studies identify PRAK as a novel host factor essential for tumor angiogenesis. In response to tumor-secreted proangiogenic factors, PRAK is activated by p38 via a vascular endothelial growth factor receptor 2 (VEGFR2)-dependent mechanism in host endothelial cells, where it mediates cell migration toward tumors and incorporation of these cells into tumor vasculature, at least partly by regulating the phosphorylation and activation of focal adhesion kinase (FAK) and cytoskeletal reorganization. These findings have uncovered a novel signaling circuit essential for endothelial cell motility and tumor angiogenesis. Moreover, we demonstrate that the tumor-suppressing and tumor-promoting functions of the p38-PRAK pathway are temporally and spatially separated during cancer development in vivo, relying on the stimulus, and the tissue type and the stage of cancer development in which it is activated.

The antitumor effect of a novel angiogenesis inhibitor (an octahydronaphthalene derivative) targeting both VEGF receptor and NF-κB pathway

Development of a novel type of angiogenesis inhibitor will be essential for further improvement of therapeutics against cancer patients. We examined whether an octahydronaphthalene derivative, AMF-26, which was screened as an inhibitor of intercellular adhesion molecule-1 (ICAM-1) production stimulated by inflammatory stimuli in vascular endothelial cells, could block angiogenesis in response to vascular endothelial growth factor (VEGF) and/or inflammatory cytokines. Low dose AMF-26 effectively inhibited the tumor necrosis factor-α (TNF-α)- or the interleukin-1β (IL-1β)-induced production of ICAM-1 in human umbilical vascular endothelial cells (HUVECs). We found that the TNF-α-induced phosphorylation of nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha (IκBα) and nuclear translocation of p65 were impaired by AMF-26 in both endothelial cells and cancer cells. AMF-26 was found to inhibit the phosphorylation of VEGF receptor 1 (VEGFR1), VEGFR2 and the downstream signaling molecules Akt, extracellular signal-regulated kinase (ERK)1/2 stimulated by VEGF in HUVECs. Therefore, the VEGF-induced proliferation, migration and tube formation of vascular endothelial cells was highly susceptible to inhibition by AMF-26. Oral administration of AMF-26 significantly blocked VEGF- or IL-1β-induced angiogenesis in the mouse cornea, and also tumor angiogenesis and growth. Together, our results indicate that AMF-26 inhibits angiogenesis through suppression of both VEGFR1/2 and nuclear factor-κB (NF-κB) signaling pathways when stimulated by VEGF or inflammatory cytokines. AMF-26 could be a promising novel candidate drug for cancer treatments.

VEGF binding to NRP1 is essential for VEGF stimulation of endothelial cell migration, complex formation between NRP1 and VEGFR2, and signaling via FAK Tyr407 phosphorylation

In endothelial cells, neuropilin-1 (NRP1) binds vascular endothelial growth factor (VEGF)-A and is thought to act as a coreceptor for kinase insert domain-containing receptor (KDR) by associating with KDR and enhancing VEGF signaling. Here we report mutations in the NRP1 b1 domain (Y297A and D320A), which result in complete loss of VEGF binding. Overexpression of Y297A and D320A NRP1 in human umbilical vein endothelial cells reduced high-affinity VEGF binding and migration toward a VEGF gradient, and markedly inhibited VEGF-induced angiogenesis in a coculture cell model. The Y297A NRP1 mutant also disrupted complexation between NRP1 and KDR and decreased VEGF-dependent phosphorylation of focal adhesion kinase at Tyr407, but had little effect on other signaling pathways. Y297A NRP1, however, heterodimerized with wild-type NRP1 and NRP2 indicating that nonbinding NRP1 mutants can act in a dominant-negative manner through formation of NRP1 dimers with reduced binding affinity for VEGF. These findings indicate that VEGF binding to NRP1 has specific effects on endothelial cell signaling and is important for endothelial cell migration and angiogenesis mediated via complex formation between NRP1 and KDR and increased signaling to focal adhesions. Identification of key residues essential for VEGF binding and biological functions provides the basis for a rational design of antagonists of VEGF binding to NRP1.

μ-Slide Chemotaxis: a new chamber for long-term chemotaxis studies

BACKGROUND

Effective tools for measurement of chemotaxis are desirable since cell migration towards given stimuli plays a crucial role in tumour metastasis, angiogenesis, inflammation, and wound healing. As for now, the Boyden chamber assay is the longstanding "gold-standard" for in vitro chemotaxis measurements. However, support for live cell microscopy is weak, concentration gradients are rather steep and poorly defined, and chemotaxis cannot be distinguished from migration in a single experiment.

RESULTS

Here, we describe a novel all-in-one chamber system for long-term analysis of chemotaxis in vitro that improves upon many of the shortcomings of the Boyden chamber assay. This chemotaxis chamber was developed to provide high quality microscopy, linear concentration gradients, support for long-term assays, and observation of slowly migrating cells via video microscopy. AlexaFluor 488 dye was used to demonstrate the establishment, shape and time development of linear chemical gradients. Human fibrosarcoma cell line HT1080 and freshly isolated human umbilical vein endothelial cells (HUVEC) were used to assess chemotaxis towards 10% fetal calf serum (FCS) and FaDu cells' supernatant. Time-lapse video microscopy was conducted for 48 hours, and cell tracking and analysis was performed using ImageJ plugins. The results disclosed a linear steady-state gradient that was reached after approximately 8 hours and remained stable for at least 48 hours. Both cell types were chemotactically active and cell movement as well as cell-to-cell interaction was assessable.

CONCLUSIONS

Compared to the Boyden chamber assay, this innovative system allows for the generation of a stable gradient for a much longer time period as well as for the tracking of cell locomotion along this gradient and over long distances. Finally, random migration can be distinguished from primed and directed migration along chemotactic gradients in the same experiment, a feature, which can be qualified via cell morphology imaging.

Anti-tumor effect of lentivirus-mediated gene transfer of alphastatin on human glioma

Alphastatin, an endogenous angiogenesis inhibitor, has recently been used as an anticancer agent in several tumor models. This study was to investigate whether local sustained long-term expression of alphastatin could serve to diminish tumor growth of a human xenograft glioma model. We found that the recombinant alphastatin lentiviruses were able to stably infect HUVECs, and infected HUVECs could sustainably secrete alphastatin, which exhibited potent inhibitory effects on HUVECs migration, differentiation but not proliferation induced by vascular endothelial growth factor (VEGF) or basic fibroblast growth factor(bFGF). And the expression of secreted protein alphastatin markedly decreased tumor vascularization and inhibited tumor growth. Additionally, alphastatin inhibited VEGF- or bFGF-induced initial stage of angiogenesis by reducing JNk and ERK phosphorylation in vitro. Taken together, these data demonstrate that secreted protein alphastatin inhibits VEGF- or bFGF-induced angiogenesis by suppressing JNK and ERK kinases activation pathways in HUVECs, and markedly inhibits tumor angiogenesis in vivo. Consequently lentivirus-mediated gene transfer might represent an effective strategy for expression of alphastatin to achieve inhibition of human malignant glioma proliferation and tumor progression.

Topical dihydroartemisinin inhibits suture-induced neovascularization in rat corneas through ERK1/2 and p38 pathways

AIM

To determine if topical instillation of dihydroartemisinin (DHA) inhibits corneal neovascularization (NV) in rats and to investigate the role of the extracellular regulated kinases (ERK) 1/2 and p38 pathways in this process.

METHODS

Suture-induced corneal NV was produced in rats and the eyes were topically treated with different concentrations of DHA (20mg/L, 10mg/L or 5mg/L) or normal saline 4 times a day for 7 days. The corneal NV was quantified as the proportion of NV area to the whole cornea. Western blot was used to determine the expressions of vascular endothelial growth factor (VEGF) and the phosphorylation status of VEGF receptor-2, ERK1/2 and p38 in the corneas. Immunofluorescent staining was used to determine the expressions of phospho-ERK1/2 and phospho-p38 in the corneal tissues from the eyes treated with 20 mg/L DHA (DHA group) or normal saline (control group).

RESULTS

The proportion of corneal NV area in the eyes treated with normal saline or DHA at dosages of 20mg/L, 10mg/L or 5mg/L was (23.74±3.00)%, (15.73±2.88)%, (19.53±2.42)%, and (23.38±2.79)%, respectively. In the eyes treated with 20mg/L or 10mg/L DHA, the corneal NV area was significantly reduced when compared to that in eyes with normal saline (P<0.05). Western blot analyses revealed that 20mg/L DHA significantly inhibited the expressions of VEGF and phospho-VEGFR-2. Both 20mg/L and 10mg/L DHA inhibited the expressions of phospho-ERK1/2 and phospho-p38. Immunofluorescent staining further demonstrated that 20mg/L DHA lowered the expression levels of phospho-ERK1/2 and phospho-p38 in the corneas with suture-induced NV.

CONCLUSION

Suture-induced NV in rat corneas was significantly inhibited by topical treatment with 20mg/L and 10mg/L DHA. The results suggest that the effects could be partially dependent on the DHA-mediated inhibitions of the ERK1/2 and p38 pathways.

Target inhibition in antiangiogenic therapy a wide spectrum of selectivity and specificity

Recent studies have revealed a previously unsuspected degree of vascular specialization within the host tissue and a tumor's microenvironment. The "vascular zip code" has been used to describe the unique expression of cell-surface molecules found in each vascular bed. Characterization of tumor blood vessels includes selective overexpression of a heterogenous group of proteins such as proteases, integrins, growth factor receptors, and proteoglycans. The process of angiogenesis consists of a "true cytokine storm," requiring many molecular events and biological steps. Antiangiogenic drugs may target a single critical kinase pathway or may interact with several nonspecific molecular targets via a process termed extended spectrum kinase inhibition. The latter strategy may lead to an absence of selectivity and specificity and may result in enhanced toxicities. In this review, we discuss recent developments in the pathogenesis of commonly observed adverse events and summarize new strategies that may ultimately improve efficacy and limit toxicity.

Bioluminescence imaging of angiogenesis in a murine orthotopic pancreatic cancer model

PURPOSE

Angiogenesis is essential for physiological processes as well as for carcinogenesis. New approaches to cancer therapy include targeting angiogenesis. One target is VEGF-A and its receptor VEGFR2. In this study, we sought to investigate pancreatic cancer angiogenesis in a genetically modified VEGFR2-luc-KI mouse.

PROCEDURES

Live in vivo bioluminescence imaging of angiogenesis was performed continuously until sacrifice in subcutaneous tumors as well as in orthotopically transplanted tumors. Tumor tissue was immunostained for CD-31 and VEGFR2.

RESULTS

Peritumoral angiogenesis measured by light emission was detected beginning at week 3 following subcutaneous injection. In the orthotopic model, light emission began at day 4, which likely corresponds to wound healing, and continued throughout the experimental period during tumor growth. Peritumoral CD-31 vessel- and VEGFR2-staining were positive.

CONCLUSIONS

The VEGFR2-luc-KI mouse is a valuable tool to demonstrate tumor angiogenesis and seems to be suitable to evaluate anti-angiogenic approaches in pancreatic cancer.

Murine rVEGF164b, an inhibitory VEGF reduces VEGF-A-dependent endothelial proliferation and barrier dysfunction

OBJECTIVE

To investigate the effects of the murine inhibitory vascular endothelial growth factor (VEGF, rVEGF164b), we generated an adenoviral vector encoding rVEGF164b, and examined its effects on endothelial barrier, growth, and structure.

METHOD

Mouse vascular endothelial cells (MVEC) proliferation was determined by an MTT assay. Barrier of MVEC monolayers was measured by trans-endothelial electrical resistance (TEER). Reorganization of actin and zonula occludens-1 (ZO-1) were determined by fluorescent microscopy.

RESULTS

Mouse venous endothelial cells treated with murine VEGF-A (VEGF-A) (50 ng/mL) increased proliferation (60.7 ± 0.1%) within 24 hours (p < 0.05) and rVEGF164b inhibited VEGF-A-induced proliferation. TEER was significantly decreased by VEGF-A (81.7 ± 6.2% of control). Treatment with rVEGF164b at 50 ng/mL transiently reduced MVEC barrier (p < 0.05) at 30 minutes post-treatment (87.9 ± 1.7% of control TEER), and returned to control levels by 40 minutes post-treatment. Treatment with rVEGF164b prevented barrier changes by subsequent exposure to VEGF-A. Treatment of MVECS with VEGF-A reorganized F-actin and ZO-1, which was attenuated by rVEGF164b.

CONCLUSIONS

VEGF-A may dysregulate endothelial barrier through junctional cytoskeleton processes, which can be attenuated by rVEGF164b. The VEGF-A stimulated MVEC proliferation, barrier dysregulation, and cytoskeletal rearrangement. However, rVEGF164b blocks these effects, therefore it may be useful for regulation studies of VEGF-A/VEGF-R signaling in many different models.

Role of the endothelium in inflammatory bowel diseases

Inflammatory bowel diseases (IBD) are a complex group of diseases involving alterations in mucosal immunity and gastrointestinal physiology during both initiation and progressive phases of the disease. At the core of these alterations are endothelial cells, whose continual adjustments in structure and function coordinate vascular supply, immune cell emigration, and regulation of the tissue environment. Expansion of the endothelium in IBD (angiogenesis), mediated by inflammatory growth factors, cytokines and chemokines, is a hallmark of active gut disease and is closely related to disease severity. The endothelium in newly formed or inflamed vessels differs from that in normal vessels in the production of and response to inflammatory cytokines, growth factors, and adhesion molecules, altering coagulant capacity, barrier function and blood cell recruitment in injury. This review examines the roles of the endothelium in the initiation and propagation of IBD pathology and distinctive features of the intestinal endothelium contributing to these conditions.

Anticancer and antiangiogenic activity of HPMA copolymer-aminohexylgeldanamycin-RGDfK conjugates for prostate cancer therapy

Tumor progression is dependent on neoangiogenesis for blood supply. Neovasculature over-express α(v)β(3) integrins which recognize the Arg-Gly-Asp (RGD) sequence in the extracellular matrix. N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers containing side chains terminated in cyclic RGD analogs such as RGDfK show increased accumulation in prostate tumors. Geldanamycin and their derivatives (e.g., aminohexylgeldanamycin (AH-GDM)) are benzoquinone ansamycins that have both antiangiogenic and antitumor activity. In this work the antiangiogenic and antitumor activities of targetable HPMA copolymer-RGDfK-AH-GDM conjugates were compared with non-targetable systems in vitro and in vivo. Copolymer-drug conjugates containing RGDfK in the side chains showed superior activity against endothelial and prostate cancer cell lines in vitro, as well as higher inhibition of angiogenesis in vivo. At equimolar doses of the drug, the RGDfK containing conjugates showed significantly higher antitumor activity in nude mice bearing DU-145 human prostate cancer xenografts. These findings suggest the utility of HPMA copolymer-RGDfK conjugates for targeted delivery of geldanamycin analogs with a dual mode of action.

Identification of VEGF receptor-2 tyrosine phosphorylation sites involved in VEGF-mediated endothelial platelet-activating factor synthesis

Vascular endothelial growth factor (VEGF)-mediated inflammation requires the synthesis of acute platelet-activating factor (PAF) by endothelial cells (ECs). We previously reported that VEGF-mediated PAF synthesis involves the activation of the homodimeric tyrosine kinase receptor VEGFR-2/R-2, leading to the recruitment of p38 and p42/p44 mitogen-activated protein kinases (MAPKs) and activation of secreted group V phospholipase A2 (sPLA2-V). We have also reported that VEGF-A165-mediated prostacyclin (PGI2) synthesis requires VEGFR-1/R-2 heterodimeric receptor activation. Selective activation of VEGF receptors can coordinate the synthesis of pro-PAF and anti-PGI2 inflammatory factors. It is unknown which VEGFR-2 tyrosine phosphorylation site(s) contribute(s) to PAF synthesis. Bovine aortic endothelial cells (BAECs) were transfected with pcDNA vectors encoding for native VEGF receptor-2 (VEGFR-2) cDNA or VEGFR-2 cDNA containing tyrosine phosphorylation sites mutated into phenylalanine residues (Y801F, Y1059F, Y1175F, Y1214F); an empty pcDNA vector was used as a negative control. Treatment of pcDNA-transfected BAECs with VEGF (10−9 mol/L) for 15 min increased PAF synthesis by 180%. In BAECs transfected with pcDNA vectors encoding mutated Y801F, Y1059F, Y1175F, or Y1214F VEGFR-2 cDNA, we observed a marked reduction of VEGF-mediated PAF synthesis by 38%, 46%, 69%, and 31%, respectively, compared with BAECs transfected with pcDNA vector encoding VEGFR-2 cDNA. Our data provide a novel insight as to the mechanisms by which VEGF promotes PAF synthesis.

HSP90 modulates actin dynamics: inhibition of HSP90 leads to decreased cell motility and impairs invasion

HSP90, a major molecular chaperone, plays an essential role in the maintenance of several signaling molecules. Inhibition of HSP90 by inhibitors such as 17-allylamino-demethoxy-geldanamycin (17AAG) is known to induce apoptosis in various cancer cells by decreasing the activation or expression of pro-survival molecules such as protein kinase B (Akt). While we did not observe either decrease in expression or activation of pro-survival signaling molecules in human breast cancer cells upon inhibiting HSP90 with 17AAG, we did observe a decrease in cell motility of transformed cells, and cell motility and invasion of cancer cells. We found a significant decrease in the number of filopodia and lamellipodia, and in the F-actin bundles upon HSP90 inhibition. Our results show no change in the active forms or total levels of FAK and Pax, or in the activation of Rac-1 and Cdc-42; however increased levels of HSP90, HSP90α and HSP70 were observed upon HSP90 inhibition. Co-immuno-precipitation of HSP90 reveals interaction of HSP90 with G-actin, which increases upon HSP90 inhibition. FRET results show a significant decrease in interaction between actin monomers, leading to decreased actin polymerization upon HSP90 inhibition. We observed a decrease in the invasion of human breast cancer cells in the matrigel assay upon HSP90 inhibition. Over-expression of αB-crystallin, known to be involved in actin dynamics, did not abrogate the effect of HSP90 inhibition. Our work provides the molecular mechanism by which HSP90 inhibition delays cell migration and should be useful in developing cancer treatment strategies with known anti-cancer drugs such as cisplatin in combination with HSP90 inhibitors.

Fluid flow-induced soluble vascular endothelial growth factor isoforms regulate actin adaptation in osteoblasts

Although load-induced mechanical signals play a key role in bone formation and maintenance of bone mass and structure, the cellular mechanisms involved in the translation of these signals are still not well understood. Recent identification of a novel flow-induced mechanosignaling pathway involving VEGF in osteoblasts and the known VEGF regulation of actin reorganization in various cell types has led us to hypothesize that fluid shear stress-induced Vegf up-regulation underlies the actin cytoskeleton adaptation observed in osteoblasts during mechanotransduction. Our results show that MC3T3-E1 cells secrete significant VEGF in response to 5 h of pulsatile fluid shear stress (PFSS; 5 dynes/cm(2) at 1 Hz), whereas expression of VEGF receptors (VEGFR-1, VEGFR-2, or NRP1) is unaffected. These receptors, in particular VEGFR-2, participate in PFSS-induced VEGF release. Exposure to flow-conditioned medium or exogenous VEGF significantly induces stress fiber formation in osteoblasts that is comparable with PFSS-induced stress fiber formation, whereas VEGF knockdown abrogates this response to PFSS, thereby providing evidence that flow-induced VEGF release plays a role in actin polymerization. Using neutralizing antibodies against the receptors and VEGF isoforms, we found that soluble VEGFs, in particular VEGF(164), play a crucial role in transient stress fiber formation during osteoblast mechanotransduction, most likely through VEGFR-2 and NRP1. Based on these data we conclude that flow-induced VEGF release from osteoblasts regulates osteoblast actin adaptation during mechanotransduction and that VEGF paracrine signaling may provide potent cross-talk among bone cells and endothelial cells that is essential for fracture healing, bone remodeling, and osteogenesis.

Angiostatic effects of Brazilian green propolis and its chemical constituents

Propolis, a resinous substance collected by honeybees from various plant sources, has several pharmacological actions, such as anti-tumor and anti-inflammatory effects. The aim of this study was to evaluate the anti-angiogenic effects of a water extract of Brazilian green propolis (WEP) and its constituents, caffeoylquinic acid derivatives, against angiogenic processes in human umbilical vein endothelial cells (HUVECs) in vitro. We also examined the anti-angiogenic effects of WEP against retinal neovascularization in a murine oxygen-induced retinopathy model in vivo. WEP and its constituents significantly suppressed vascular endothelial growth factor (VEGF)-induced HUVEC proliferation, migration, and tube formation in vitro. WEP and its caffeoylquinic acid derivatives suppressed VEGF-stimulated phosphorylation of mitogen-activated protein kinase in HUVECs (versus VEGF alone). Moreover, WEP (300 mg/kg/day, subcutaneously for 5 days) significantly suppressed retinal neovascularization in the murine oxygen-induced retinopathy model. These data indicate that (i) WEP has angiostatic effects against angiogenic processes in vitro and in an in vivo model of murine oxygen-induced retinopathy and (ii) the inhibitory effects of WEP against in vitro angiogenesis are chiefly derived from its caffeoylquinic acid derivatives. Judging from these findings, WEP and its caffeoylquinic acid derivatives may represent candidates for preventive or therapeutic agents against diseases caused by angiogenesis.

Increased expression of angiogenic genes in the brains of mouse meg3-null embryos

Maternally expressed gene 3 (MEG3) is a noncoding RNA highly expressed in the normal human brain and pituitary. Expression of MEG3 is lost in gonadotroph-derived clinically nonfunctioning pituitary adenomas. Meg3 knockout mice were generated to identify targets and potential functions of this gene in embryonic development and tumorigenesis. Gene expression profiles were compared in the brains of Meg3-null embryos and wild-type littermate controls using microarray analysis. Microarray data were analyzed with GeneSifter, which uses Kyoto Encyclopedia of Genes and Genomes pathways and Gene Ontology classifications to identify signaling cascades and functional categories of interest within the dataset. Differences were found in signaling pathways and ontologies related to angiogenesis between wild-type and knockout embryos. Quantitative RT-PCR and immunohistological staining showed increased expression of some Vascular Endothelial Growth Factor pathway genes and increased cortical microvessel density in the Meg3-null embryos. In conclusion, Meg3 may play an important role in control of vascularization in the brain and may function as a tumor suppressor in part by inhibiting angiogenesis.

Vascular endothelial growth factor C promotes cervical cancer metastasis via up-regulation and activation of RhoA/ROCK-2/moesin cascade

Background

The elevated expression of vascular endothelial growth factor C (VEGF-C) is correlated with clinical cervical cancer metastasis and patient survival, which is interpreted by VEGF-C functions to stimulate angiogenesis and lymphatic genesis. However, the direct impact of VEGF-C on cervical cancer cell motility remains largely unknown.

Methods

In this study, we investigated the effects of VEGF-C on actin cytoskeleton remodeling and on cervical cancer cell migration and invasion and how the actin-regulatory protein, moesin regulated these effects through RhoA/ROCK-2 signaling pathway.

Results

On cervical carcinoma cell line SiHa cells, exposure of VEGF-C triggered remodeling of the actin cytoskeleton and the formation of membrane ruffles, which was required for cell movement. VEGF-C significantly enhanced SiHa cells horizontal migration and three-dimensional invasion into matrices. These actions were dependent on increased expression and phosphorylation of the actin-regulatory protein moesin and specific moesin siRNA severely impaired VEGF-C stimulated-cell migration. The extracellular small GTPase RhoA/ROCK-2 cascade mediated the increased moesin expression and phosphorylation, which was discovered by the use of Y-27632, a specific inhibitor of Rho kinase and by transfected constitutively active, dominant-negative RhoA as well as ROCK-2 SiRNA. Furthermore, in the surgical cervical specimen from the patients with FIGO stage at cervical intra-epithelial neoplasia and I-II cervical squamous cell carcinoma, the expression levels of moesin were found to be significantly correlated with tumor malignancy and metastasis.

Conclusions

These results implied that VEGF-C promoted cervical cancer metastasis by upregulation and activation of moesin protein through RhoA/ROCK-2 pathway. Our findings offer new insight into the role of VEGF-C on cervical cancer progression and may provide potential targets for cervical cancer therapy.