Role of tyrosine residues and protein interaction domains of SHC adaptor in VEGF receptor 3 signaling

Estrogen-receptor status determines differential regulation of α1- and α2-adrenoceptor-mediated cell survival, angiogenesis, and intracellular signaling responses in breast cancer cell lines

Psychosocial stress promotes cancer pathogenesis involving angiogenesis through alterations in neuroendocrine-immune functions that may involve adrenoceptor (AR)-dependent signaling mechanisms in the brain, lymphoid organs, and cancerous cells. Various concentrations of α1- and α2- AR-specific agonists and antagonists were incubated in vitro with estrogen receptor-positive (ER +) MCF-7, and ER (-) MDA MB-231 cells to examine the secretions of VEGF-A, VEGF-C, and nitric oxide (NO), and expression of signaling molecules- p-ERK, p-CREB, and p-Akt on the proliferation of breast cancer cell lines. Cellular proliferation, VEGF-A and NO secretion, expression of p-ERK, p-CREB, and p-Akt were enhanced in MCF-7 cells treated with α1-AR agonist while VEGF-C secretion alone was enhanced in MDA MB-231 cells. Treatment of MCF-7 and MDA MB-231 cells with α2- AR agonist similarly enhanced proliferation and decreased NO production and p-CREB expression while VEGF-C secretion was decreased in MCF-7 cells and p-Akt expression was decreased in MDA MB-231 cells. α1-AR inhibition reversed cellular proliferation and VEGF-A secretion by MCF-7 cells while α2-AR inhibition reversed the proliferation of MCF-7 and MDA MB-231 cells and VEGF-C secretion by MCF-7 cells. Taken together, breast cancer pathogenesis may be influenced by distinct α-AR-mediated signaling mechanisms on angiogenesis and lymphangiogenesis that are dependent on estrogen receptor status.

CCM3 Loss-Induced Lymphatic Defect Is Mediated by the Augmented VEGFR3-ERK1/2 Signaling

OBJECTIVE

Cerebral cavernous malformations (CCMs) can happen anywhere in the body, although they most commonly produce symptoms in the brain. The role of CCM genes in other vascular beds outside the brain and retina is not well-examined, although the 3 CCM-associated genes (CCM1, CCM2, and CCM3) are ubiquitously expressed in all tissues. We aimed to determine the role of CCM gene in lymphatics. Approach and Results: Mice with an inducible pan-endothelial cell (EC) or lymphatic EC deletion of Ccm3 (Pdcd10ECKO or Pdcd10LECKO) exhibit dilated lymphatic capillaries and collecting vessels with abnormal valve structure. Morphological alterations were correlated with lymphatic dysfunction in Pdcd10LECKO mice as determined by Evans blue dye and fluorescein isothiocyanate(FITC)-dextran transport assays. Pdcd10LECKO lymphatics had increased VEGFR3 (vascular endothelial growth factor receptor-3)-ERK1/2 (extracellular signal-regulated kinase 1/2) signaling with lymphatic hyperplasia. Mechanistic studies suggested that VEGFR3 is primarily regulated at a transcriptional level in Ccm3-deficient lymphatic ECs, in an NF-κB (nuclear factor κB)-dependent manner. CCM3 binds to importin alpha 2/KPNA2 (karyopherin subunit alpha 2), and a CCM3 deletion releases KPNA2 to activate NF-κB P65 by facilitating its nuclear translocation and P65-dependent VEGFR3 transcription. Moreover, increased VEGFR3 in lymphatic EC preferentially activates ERK1/2 signaling, which is critical for lymphatic EC proliferation. Importantly, inhibition of VEGFR3 or ERK1/2 rescued the lymphatic defects in structure and function.

CONCLUSIONS

Our data demonstrate that CCM3 deletion augments the VEGFR3-ERK1/2 signaling in lymphatic EC that drives lymphatic hyperplasia and malformation and warrant further investigation on the potential clinical relevance of lymphatic dysfunction in patients with CCM.

AIP1 mediates vascular endothelial cell growth factor receptor-3-dependent angiogenic and lymphangiogenic responses

OBJECTIVE

To investigate the novel function of ASK1-interacting protein-1 (AIP1) in vascular endothelial cell growth factor receptor (VEGFR)-3 signaling, and VEGFR-3-dependent angiogenesis and lymphangiogenesis.

APPROACH AND RESULTS

AIP1, a signaling scaffold protein, is highly expressed in the vascular endothelium. We have previously reported that AIP1 functions as an endogenous inhibitor in pathological angiogenesis by blocking VEGFR-2 activity. Surprisingly, here we observe that mice with a global deletion of AIP1-knockout mice (AIP1-KO) exhibit reduced retinal angiogenesis with less sprouting and fewer branches. Vascular endothelial cell (but not neuronal)-specific deletion of AIP1 causes similar defects in retinal angiogenesis. The reduced retinal angiogenesis correlates with reduced expression in VEGFR-3 despite increased VEGFR-2 levels in AIP1-KO retinas. Consistent with the reduced expression of VEGFR-3, AIP1-KO show delayed developmental lymphangiogenesis in neonatal skin and mesentery, and mount weaker VEGF-C-induced cornea lymphangiogenesis. In vitro, human lymphatic endothelial cells with AIP1 small interfering RNA knockdown, retinal endothelial cells, and lymphatic endothelial cells isolated from AIP1-KO all show attenuated VEGF-C-induced VEGFR-3 signaling. Mechanistically, we demonstrate that AIP1 via vegfr-3-specific miR-1236 increases VEGFR-3 protein expression and that, by directly binding to VEGFR-3, it enhances VEGFR-3 endocytosis and stability.

CONCLUSION

Our in vivo and in vitro results provide the first insight into the mechanism by which AIP1 mediates VEGFR-3-dependent angiogenic and lymphangiogenic signaling.

Vascular endothelial growth factor C enhances cervical cancer migration and invasion via activation of focal adhesion kinase

Vascular endothelial growth factor C (VEGF-C) is correlated positively with clinical cervical cancer metastasis and survival. Previously we showed that VEGF-C directly activated actin-binding protein moesin, leading to the formation of membrane protrusions. However, whether VEGF-C alters cervical cancer cell adhesion to the extra-cellular matrix is currently unknown. In this study, we investigated the effects of VEGF-C on the formation of focal adhesion complexes, which provide anchoring sites for cell attachment to the extracellular matrix. On cultured cervical carcinoma cell line SiHa cells, VEGF-C enhanced focal adhesion kinase (FAK) phosphorylation. As a result, VEGF-C led to increased formation of focal adhesion complexes and enhanced migration and invasion, which was reversed by siRNA abrogating FAK. VEGF-C resulted in increased interaction of its receptor Flt-4 with non-receptor tyrosine kinase c-Src, leading to c-Src phosphorylation. The specific inhibitor of c-Src kinase, PP2, or the transfection with specific c-Src siRNA largely impaired VEGF-C-enhanced FAK phosphorylation, suggesting that Flt-4/c-Src cascade plays a central role in these processes. These results implied that VEGF-C promotes cervical cancer metastasis by activation of FAK protein through Flt-4/c-Src pathway.

The fungicide ciclopirox inhibits lymphatic endothelial cell tube formation by suppressing VEGFR-3-mediated ERK signaling pathway

Ciclopirox olamine (CPX), an off-patent antifungal agent used to treat mycoses of skin and nails, has recently been demonstrated to be a potential anticancer agent. However, the underlying mechanism is not well understood. Here for the first time we show that CPX inhibited lymphangiogenesis in an in vitro model (tube formation). This effect was in part associated with inhibition of vascular endothelial growth factor receptor 3 (VEGFR-3) expression, as overexpression of VEGFR-3 conferred partial resistance to CPX inhibitory effect on tube formation in lymphatic endothelial cells (LECs), whereas downregulation of VEGFR-3 mimicked the effect of CPX, blocking the tube formation. Further study revealed that CPX did not alter mRNA level, but inhibited protein synthesis and promoted protein degradation of VEGFR-3. In addition, we found that CPX inhibited phosphorylation of the extracellular signal-related kinase 1/2 (ERK1/2), a downstream effector of VEGFR-3. Overexpression of VEGFR-3 attenuated CPX inhibition of ERK1/2 phosphorylation, whereas downregulation of VEGFR-3 inhibited extracellular signal-related kinase 1/2 (ERK1/2) phosphorylation in LECs. Ectopic expression of constitutively active mitogen -activated protein kinase kinase 1 (MKK1) resulted in activation of ERK1/2, and partially prevented CPX inhibition of LEC tube formation. The results suggest that CPX inhibits LEC tube formation at least in part through inhibiting VEGFR-3-mediated ERK signaling pathway.

Functional analyses of the bone marrow kinase in the X chromosome in vascular endothelial growth factor-induced lymphangiogenesis

OBJECTIVE

The goal of this study was to investigate the novel hypothesis that bone marrow kinase in the X chromosome (Bmx), an established inflammatory mediator of pathological angiogenesis, promotes lymphangiogenesis.

METHODS AND RESULTS

We have recently demonstrated a critical role for Bmx in inflammatory angiogenesis. However, the role of Bmx in lymphangiogenesis has not been investigated. Here, we show that in wild-type mice, Bmx is upregulated in lymphatic vessels in response to vascular endothelial growth factor (VEGF). In comparison with wild-type mice, Bmx-deficient mice mount weaker lymphangiogenic responses to VEGF-A and VEGF-C in 2 mouse models. In vitro, Bmx is expressed in cultured human dermal microvascular lymphatic endothelial cells. Furthermore, pharmacological inhibition and short interfering RNA mediated silencing of Bmx reduces VEGF-A and VEGF-C-induced signaling and lymphatic endothelial cell tube formation. Mechanistically, we demonstrated that Bmx differentially regulates VEGFR-2 and VEGFR-3 receptor signaling pathways: Bmx associates with and directly regulates VEGFR-2 activation, whereas Bmx associates with VEGFR-3 and regulates downstream signaling without an effect on the receptor autophosphorylation.

CONCLUSIONS

Our in vivo and in vitro results provide the first insight into the mechanism by which Bmx mediates VEGF-dependent lymphangiogenic signaling.

Novel aspects of corneal angiogenic and lymphangiogenic privilege

In this article, we provide the results of experimental studies demonstrating that corneal avascularity is an active process involving the production of anti-angiogenic factors, which counterbalance the pro-angiogenic/lymphangiogenic factors that are upregulated during wound healing. We also summarize pertinent published reports regarding corneal neovascularization (NV), corneal lymphangiogenesis and corneal angiogenic/lymphangiogenic privilege. We outline the clinical causes of corneal NV, and discuss the angiogenic proteins (VEGF and bFGF) and angiogenesis regulatory proteins. We also describe the role of matrix metalloproteinases MMP-2, -7, and MT1-MMP, anti-angiogenic factors, and lymphangiogenic regulatory proteins during corneal wound healing. Established and potential new therapies for the treatment of corneal neovascularization are also discussed.

IL-20 activates human lymphatic endothelial cells causing cell signalling and tube formation

IL-20 is an arteriogenic cytokine that remodels collateral networks in vivo, and plays a role in cellular organization. Here, we investigate its role in lymphangiogenesis using a lymphatic endothelial cell line, hTERT-HDLEC, which expresses the lymphatic markers LYVE-1 and podoplanin. Upon stimulation of hTERT-HDLEC with IL-20, we found an increase in the intracellular free calcium concentration, in Akt and eNOS phosphorylations as well as in perinuclear NO production. We found that eNOS phosphorylation and NO synthesis are highly dependent on the PI3K/Akt signalling pathway. We also found an IL-20 induced phosphorylation of Erk1/2 and mTOR, and using the MEK inhibitor PD98059 and mTOR complex inhibitor rapamycin we demonstrated the importance of these signalling pathways in IL-20-mediated proliferation. IL-20 triggered actin polymerization and morphological changes resulting in elongated cell structures, and in matrigels, IL-20 caused tube formations of hTERT-HDLEC in a PI3K- and mTOR dependent way. In a sprouting assay we found that IL-20 caused cell migration within 24 h at a rate comparable to VEGF-C, and this migration could be inhibited by wortmannin and rapamycin. These data show that IL-20 activates cell signalling resulting in lymphangiogenic processes including migration, proliferation and tube formation. Thus, IL-20 is a cytokine that has the potential of activating or modulating the formation of lymphatic vessels.

Grb2 signaling in cell motility and cancer

BACKGROUND

Metastasis is the primary cause of death in most human cancers, and understanding the molecular mechanisms underpinning this multistep process is fundamental to identifying novel molecular targets and developing more effective therapies.

OBJECTIVE/METHODS

Here we review the role of growth factor receptor-bound protein 2 (Grb2) in cancer and specifically in metastasis-related processes, and summarize the development of anticancer therapeutics selectively targeting this adapter protein.

RESULTS/CONCLUSION

Grb2 is a key molecule in intracellular signal transduction, linking activated cell surface receptors to downstream targets by binding to specific phosphotyrosine-containing and proline-rich sequence motifs. Grb2 signaling is critical for cell cycle progression and actin-based cell motility, and, consequently, more complex processes such as epithelial morphogenesis, angiogenesis and vasculogenesis. These functions make Grb2 a therapeutic target for strategies designed to prevent the spread of solid tumors through local invasion and metastasis.

Pathways targeting tumor lymphangiogenesis

Tumor metastasis to sentinel lymph nodes represents the first step of tumor dissemination in most human cancers and serves as a major prognostic indicator for disease progression. Recent studies have revealed that tumors can actively induce the formation of lymphatic vessels, and that tumor lymphangiogenesis is correlated with lymph node metastasis in experimental cancer models and in several types of human cancers. Metastatic tumor cells may continue to promote lymphatic vessel growth even after their metastasis to sentinel lymph nodes, likely promoting further cancer spread. Vascular endothelial growth factor-C (VEGF-C) and VEGF-D were the first specific lymphangiogenesis factors identified, acting predominantly via VEGF receptor-3 (VEGFR-3) that is expressed by lymphatic endothelial cells, and a large number of clinical studies have shown a correlation between tumor expression of VEGF-C or VEGF-D and lymph node metastasis. VEGFR-3 activation promotes lymphatic endothelial cell proliferation, migration, and survival via the extracellular signal-regulated kinase 1/2, the phosphatidylinositol 3-kinase/AKT, and the c-Jun NH(2)-terminal kinase 1/2 pathways. Additional tumor lymphangiogenesis factors have been recently identified, including VEGF-A. Importantly, blockade of the VEGFR-3 pathway by specific antibodies, by soluble receptor constructs, and by small molecule kinase inhibitors efficiently inhibits experimental tumor lymphangiogenesis and metastasis and might also represent a novel therapeutic avenue for the treatment of human cancers.

Genes critical to vasculogenesis as defined by systematic analysis of vascular defects in knockout mice

To identify genes important to the process of vasculogenesis, we evaluated embryonic vascular anomalies from 100 mouse knockout studies using a novel meta-analysis approach. By applying this method, termed approach for ranking of embryonic vascular anomalies (AREVA), rank scores were calculated for each knockout based on the occurrence of vascular defects during periods of vasculogenesis in specific embryonic regions. As a result, 12 genes (fibronectin, VEGFR-1/Flt-1, VEGFR-2/Flk-1, alpha 5 integrin, Tek/Tie2, VE-cadherin, VEGFA, connexin 45, ShcA, cytochrome P450 reductase, CD148/DEP-1, and EphrinB2) were determined to play critical roles in vasculogenesis. Functional categorization of these genes revealed the fundamental importance of VEGF signaling since 10 of the 12 genes (fibronectin, VEGFR-1/Flt-1, VEGFR-2/Flk-1, alpha 5 integrin, VE-cadherin, VEGFA, ShcA, cytochrome P450 reductase, CD148/DEP-1, and EphrinB2) relate to this pathway. Furthermore, the findings highlight a potential network for regulating VEGF signaling involving integration of fibronectin, EphrinB2, Tie2, and connexin 45 signaling pathways via the ShcA/Ras/Raf/Mek/Erk cascade. In addition to retrospective application of AREVA as done herein, AREVA can be used prospectively to determine the relevancy to vasculogenesis of newly inactivated genes.

Direct recruitment of CRK and GRB2 to VEGFR-3 induces proliferation, migration, and survival of endothelial cells through the activation of ERK, AKT, and JNK pathways

Vascular endothelial growth factor receptor-3 (VEGFR-3) plays a key role for the remodeling of the primary capillary plexus in the embryo and contributes to angiogenesis and lymphangiogenesis in the adult. However, VEGFR-3 signal transduction pathways remain to be elucidated. Here we investigated VEGFR-3 signaling in primary human umbilical vein endothelial cells (HUVECs) by the systematic mutation of the tyrosine residues potentially involved in VEGFR-3 signaling and identified the tyrosines critical for its function. Y1068 was shown to be essential for the kinase activity of the receptor. Y1063 signals the receptor-mediated survival by recruiting CRKI/II to the activated receptor, inducing a signaling cascade that, via mitogen-activated protein kinase kinase-4 (MKK4), activates c-Jun N-terminal kinase-1/2 (JNK1/2). Inhibition of JNK1/2 function either by specific peptide inhibitor JNKI1 or by RNA interference (RNAi) demonstrated that activation of JNK1/2 is required for a VEGFR-3–dependent prosurvival signaling. Y1230/Y1231 contributes, together with Y1337, to proliferation, migration, and survival of endothelial cells. Phospho-Y1230/Y1231 directly recruits growth factor receptor–bonus protein (GRB2) to the receptor, inducing the activation of both AKT and extracellular signal–related kinase 1/2 (ERK1/2) signaling. Finally, we observed that Y1063 and Y1230/Y1231 signaling converge to induce c-JUN expression, and RNAi experiments demonstrated that c-JUN is required for growth factor–induced prosurvival signaling in primary endothelial cells.

Heterodimerization with vascular endothelial growth factor receptor-2 (VEGFR-2) is necessary for VEGFR-3 activity

VEGFR-3 is essential for vascular development and maintenance of lymphatic vessel's integrity. Little is known about its cooperative effect with other receptors of the same family. Contrary to VEGFR-2, stimulation of VEGFR-3 by VEGF-C and -D failed to enhance its phosphorylation either in HEK293T or in PAE cells. These ligands were unable to induce angiogenesis of PAEC expressing VEGFR-3 alone. In the presence of VEGFR-2, VEGF-C and -D induced heterodimerization of VEGFR-3 with VEGFR-2. This heterodimerization was associated with enhanced VEGFR-3 phosphorylation and subsequent cellular responses as evidenced by the formation of capillary-like structures in PAE cells and proliferation of primary human endothelial cells expressing both receptors. Taken together, these results show for the first time that VEGFR-3 needs to be associated to VEGFR-2 to induce ligand-dependent cellular responses.

Inhibition of angiogenesis by growth factor receptor bound protein 2-Src homology 2 domain bound antagonists

Growth factor receptor bound protein 2 (Grb2) is an intracellular adaptor protein that participates in the signal transduction cascades of several angiogenic factors, including hepatocyte growth factor, basic fibroblast growth factor, and vascular endothelial growth factor. We described previously the potent blockade of hepatocyte growth factor–stimulated cell motility, matrix invasion, and epithelial tubulogenesis by synthetic Grb2-Src homology 2 (SH2) domain binding antagonists. Here, we show that these binding antagonists block basic morphogenetic events required for angiogenesis, including hepatocyte growth factor–, vascular endothelial growth factor–, and basic fibroblast growth factor–stimulated endothelial cell proliferation and migration, as well as phorbol 12-myristate 13-acetate–stimulated endothelial cell migration and matrix invasion. The Grb2-SH2 domain binding antagonists also impair angiogenesis in vitro, as shown by the inhibition of cord formation by macrovascular endothelial cells on Matrigel. We further show that a representative compound inhibits angiogenesis in vivo as measured using a chick chorioallantoic membrane assay. These results suggest that Grb2 is an important mediator of key proangiogenic events, with potential application to pathologic conditions where neovascularization contributes to disease progression. In particular, the well-characterized role of Grb2 in signaling cell cycle progression together with our present findings suggests that Grb2-SH2 domain binding antagonists have the potential to act as anticancer drugs that target both tumor and vascular cell compartments.

Vascular endothelial growth factor and its receptors in multiple myeloma

Multiple myeloma (MM) progresses from an avascular to a vascular phase (active MM) accompanied by a significant increase in microvessel density in the bone marrow. This article summarizes the literature concerning the specific role played by vascular endothelial growth factor (VEGF) in this process. Recent applications of antiangiogenic agents that interfere with VEGF signaling and block MM progression are also described.

Biological activity of the thyroid TRK-T3 oncogene requires signalling through Shc

The thyroid TRK-T3 oncogene, produced by a chromosomal translocation, is a chimeric, constitutively activated version of the NTRK1/NGF receptor and it is able to transform NIH3T3 cells and differentiate PC12 cells. TRK-T3 oncoprotein triggers multiple signal transduction pathways. Among others, TRK-T3 binds and phosphorylates the Shc and SNT1/FRS2 adaptor proteins both involved in coupling the receptor tyrosine kinase to the mitogen-activated protein kinase pathway by recruiting Grb2/SOS. We were interested in defining the role of Shc in the oncogenesis by TRK-T3. The mutation of TRK-T3 tyrosine 291, docking site for both Shc and FRS2, abrogates the oncogene biological activity. To directly explore the role of Shc we used the ShcY317F mutant, which carries the mutation of a tyrosine residue involved in Grb2 recruitment. We demonstrated that the ShcY317F mutant exerts an inhibitory effect on TRK-T3 transforming activity. Such effect can be modulated by the amount of ShcY317F protein and affects the viability of cells expressing TRK-T3 by means of a mechanism involving apoptosis. Our results indicate a definitive role of the adaptor protein Shc in TRK-T3 transforming activity.

Vascular endothelial growth factor receptors in the regulation of angiogenesis and lymphangiogenesis

VEGFR-1 (Flt-1), VEGFR-2 (KDR) and VEGFR-3 (Flt4) are endothelial specific receptor tyrosine kinases, regulated by members of the vascular endothelial growth factor family. VEGFRs are indispensable for embryonic vascular development, and are involved in the regulation of many aspects of physiological and pathological angiogenesis. VEGF-C and VEGF-D, as ligands for VEGFR-3 are also capable of stimulating lymphangiogenesis and at least VEGF-C can enhance lymphatic metastasis. Recent studies have shown that missense mutations within the VEGFR-3 tyrosine kinase domain are associated with human hereditary lymphedema, suggesting an important role for this receptor in the development of the lymphatic vasculature.

Signaling via vascular endothelial growth factor receptors

Angiogenesis, or development of blood vessels from preexisting vasculature, has important functions under both normal and pathophysiological conditions. Vascular endothelial growth factor receptors 1-3, also known as flt-1, KDR, and flt-4, are endothelial cell-specific receptor tyrosine kinases which serve as key mediators of the angiogenic responses. The review focuses on the signaling pathways that are initiated from these receptors and the recently identified VEGF coreceptor neuroplilin-1.