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

Dual antitumor immunomodulatory effects of PARP inhibitor on the tumor microenvironment: A counterbalance between anti-tumor and pro-tumor

Poly (ADP-ribose)-polymerases (PARPs) play an essential role in the maintenance of genome integrity, DNA repair, and apoptosis. PARP inhibitors (PARPi) exert antitumor effects via synthetic lethality and PARP trapping. PARPi impact the antitumor immune response by modulating the tumor microenvironment, and their effect has dual properties of promoting and inhibiting the antitumor immune response. PARPi promote M1 macrophage polarization, antigen presentation by dendritic cells, infiltration of B and T cells and their killing capacity and inhibit tumor angiogenesis. PARPi can also inhibit the activation and function of immune cells by upregulating PD-L1. In this review, we summarize the dual immunomodulatory effects and possible underlying mechanisms of PARPi, providing a basis for the design of combination regimens for clinical treatment and the identification of populations who may benefit from these therapies.

Ligusticum chuanxiong promotes the angiogenesis of preovulatory follicles (F1-F3) in late-phase laying hens

Ligusticum chuanxiong (CX) is a traditional Chinese medicine that is widely planted throughout the world. CX is one of the most important and commonly used drugs to enhance blood circulation. The preovulatory follicles in laying hens have a large number of blood arteries and meridians that feed the follicles' growth and maturation with nutrients, hormones, and cytokines. With the extension of laying time, preovulatory follicles angiogenesis decreased gradually. In this study, we studied the mechanism of CX on preovulatory follicles angiogenesis in late-phase laying hens. The results show that CX extract can increase the angiogenesis of preovulatory follicles (F1-F3) of late-phase laying hens. CX extract can promote vascular endothelial growth factor receptor 2 (VEGFR2) phosphorylation in preovulatory follicles theca layers, promote the proliferation, invasion and migration through PI3K/AKT and RAS/ERK signaling pathways in primary follicle microvascular endothelial-like cells (FMECs). In addition, CX extract can up-regulate the expression of hypoxia inducible factor α (HIF1α) in granulosa cells (GCs) and granulosa layers through PI3K/AKT and RAS/ERK signaling pathways, thereby promoting the secretion of vascular endothelial growth factor A (VEGFA). In conclusion, the current study confirmed the promoting effect of CX extract on the preovulatory follicles angiogenesis, which sets the stage for the design of functional animal feed for late-phase laying hens.

Extracellular vesicles as central regulators of blood vessel function in cancer

Blood vessels deliver oxygen and nutrients that sustain tumor growth and enable the dissemination of cancer cells to distant sites and the recruitment of intratumoral immune cells. In addition, the structural and functional abnormalities of the tumor vasculature foster the development of an aggressive tumor microenvironment and impair the efficacy of existing cancer therapies. Extracellular vesicles (EVs) have emerged as major players of tumor progression, and a growing body of evidence has demonstrated that EVs derived from cancer cells trigger multiple responses in endothelial cells that alter blood vessel function in tumors. EV-mediated signaling in endothelial cells can occur through the transfer of functional cargos such as miRNAs, lncRNAs, cirRNAs, and proteins. Moreover, membrane-bound proteins in EVs can elicit receptor-mediated signaling in endothelial cells. Together, these mechanisms reprogram endothelial cells and contribute to the sustained exacerbated angiogenic signaling typical of tumors, which, in turn, influences cancer progression. Targeting these angiogenesis-promoting EV-dependent mechanisms may offer additional strategies to normalize tumor vasculature. Here, we discuss the current knowledge pertaining to the contribution of cancer cell-derived EVs in mechanisms regulating blood vessel functions in tumors. Moreover, we discuss the translational opportunities in targeting the dysfunctional tumor vasculature using EVs and highlight the open questions in the field of EV biology that can be addressed using mass spectrometry-based proteomics analysis.

Src Homology 2 Domain Containing Protein Tyrosine Phosphatase-2 (SHP2) Combined with Dental Pulp Stem Cells Promote the Effect of Angiogenesis

Pulpitis is one of the most important dental diseases. How to improve the blood circulation in the infected and necrotic area of pulp is the current research hotspot in the treatment of pulpitis. Mesenchymal stem cells (MSCs) have similar regeneration and differentiation ability to the pluripotent stem cells, and can differentiate into various tissues under certain induced conditions. Dental pulp stem cells (DPSCs) extracted from dental pulp, which have stronger proliferation ability and stability, and are more ideal seed cells for the treatment of pulpitis. Research show that Src homology 2 domain containing SHP2 can promote blood vessel growth. In this subject, we studied the angiogenesis of SHP2 combined with dental pulp stem cells (DPSCs) transplantation. SHP2 and DPSCs were co cultured with human umbilical vein endothelial cells (HUVECs). The proliferation and migration of endothelial cells were detected by Wound Healing Assays. At the same time, the effect of SHP2+DPSC on endothelial cell angiogenesis was examined by tube formation test. The expression of angiogenesis related cytokines including vascular endothelial growth factor (VEGF), von willebrand factor (vWF), Angiopoietin-1 (Ang-1) and Cdc42/Rac1 signal pathway were also detected by Western blot. Our results demonstrated that SHP2 combined with DPSCs can advance endothelial cell angiogenesis. Meanwhile, SHP2+ DPSC obviously increased VEGF, Ang-1 and vWF expression. SHP2+DPSC significantly raise the Cdc42/Rac1 signal pathway in HUVECs. Our data illustrate that SHP2 combined with DPSCs can promote the effect of angiogenesis in pulpitis.

Apple polyphenol phloretin complexed with ruthenium is capable of reprogramming the breast cancer microenvironment through modulation of PI3K/Akt/mTOR/VEGF pathways

Our recent investigation directed to synthesize a novel ruthenium-phloretin complex accompanied by the study of antioxidant in addition to DNA binding capabilities, to determine the chemotherapeutic activity against breast carcinoma in vitro and in vivo. Ruthenium-phloretin complex was synthesized and characterized by different spectroscopic methods. The complex was further investigated to determine its efficacy in both MCF-7 and MDA-MB-231 human carcinoma cell lines and finally in an in vivo model of mammary carcinogenesis induced by DMBA in rats. Our studies confirm that the chelation of the metal and ligand was materialize by the 3-OH and 9-OH functional groups of the ligand and the complex is found crystalline and was capable of intercalating with CT-DNA. The complex was capable of reducing cellular propagation and initiate apoptotic events in MCF-7 and MDA-MB-231 breast carcinoma cell lines. Ruthenium-phloretin complex could modulate p53 intervene apoptosis in the breast carcinoma, initiated by the trail of intrinsic apoptosis facilitated through Bcl2 and Bax and at the same time down regulating the PI3K/Akt/mTOR pathway coupled with MMP9 regulated tumor invasive pathways. Ruthenium-phloretin chemotherapy could interrupt, revoke or suspend the succession of breast carcinoma by altering intrinsic apoptosis along with the anti-angiogenic pathway.

The role of microenvironment in tumor angiogenesis

Tumor angiogenesis is necessary for the continued survival and development of tumor cells, and plays an important role in their growth, invasion, and metastasis. The tumor microenvironment—composed of tumor cells, surrounding cells, and secreted cytokines—provides a conducive environment for the growth and survival of tumors. Different components of the tumor microenvironment can regulate tumor development. In this review, we have discussed the regulatory role of the microenvironment in tumor angiogenesis. High expression of angiogenic factors and inflammatory cytokines in the tumor microenvironment, as well as hypoxia, are presumed to be the reasons for poor therapeutic efficacy of current anti-angiogenic drugs. A combination of anti-angiogenic drugs and antitumor inflammatory drugs or hypoxia inhibitors might improve the therapeutic outcome.

Extracellular adenosine enhances pulmonary artery vasa vasorum endothelial cell barrier function via Gi/ELMO1/Rac1/PKA-dependent signaling mechanisms

The vasa vasorum (VV), the microvascular network around large vessels, has been recognized as an important contributor to the pathological vascular remodeling in cardiovascular diseases. In bovine and rat models of hypoxic pulmonary hypertension (PH), we have previously shown that chronic hypoxia profoundly increased pulmonary artery (PA) VV permeability, associated with infiltration of inflammatory and progenitor cells in the arterial wall, perivascular inflammation, and structural vascular remodeling. Extracellular adenosine was shown to exhibit a barrier-protective effect on VV endothelial cells (VVEC) via cAMP-independent mechanisms, which involved adenosine A1 receptor-mediated activation of Gi-phosphoinositide 3-kinase-Akt pathway and actin cytoskeleton remodeling. Using VVEC isolated from the adventitia of calf PA, in this study we investigated in more detail the mechanisms linking Gi activation to downstream barrier protection pathways. Using a small-interference RNA (siRNA) technique and transendothelial electrical resistance assay, we found that the adaptor protein, engulfment and cell motility 1 (ELMO1), the tyrosine phosphatase Src homology region 2 domain-containing phosphatase-2, and atypical Gi- and Rac1-mediated protein kinase A activation are implicated in VVEC barrier enhancement. In contrast, the actin-interacting GTP-binding protein, girdin, and the p21-activated kinase 1 downstream target, LIM kinase, are not involved in this response. In addition, adenosine-dependent cytoskeletal rearrangement involves activation of cofilin and inactivation of ezrin-radixin-moesin regulatory cytoskeletal proteins, consistent with a barrier-protective mechanism. Collectively, our data indicate that targeting adenosine receptors and downstream barrier-protective pathways in VVEC may have a potential translational significance in developing pharmacological approach for the VV barrier protection in PH.

Gαi1 and Gαi3mediate VEGF-induced VEGFR2 endocytosis, signaling and angiogenesis

VEGF binding to VEGFR2 leads to VEGFR2 endocytosis and downstream signaling activation to promote angiogenesis.

Methods: Using genetic strategies, we tested the requirement of α subunits of heterotrimeric G proteins (Gαi1/3) in the process.

Results: Gαi1/3 are located in the VEGFR2 endocytosis complex (VEGFR2-Ephrin-B2-Dab2-PAR-3), where they are required for VEGFR2 endocytosis and downstream signaling transduction. Gαi1/3 knockdown, knockout or dominant negative mutation inhibited VEGF-induced VEGFR2 endocytosis, and downstream Akt-mTOR and Erk-MAPK activation. Functional studies show that Gαi1/3 shRNA inhibited VEGF-induced proliferation, invasion, migration and vessel-like tube formation of HUVECs. In vivo, Gαi1/3 shRNA lentivirus inhibited alkali burn-induced neovascularization in mouse cornea. Further, oxygen-induced retinopathy (OIR)-induced retinal neovascularization was inhibited by intravitreal injection of Gαi1/3 shRNA lentivirus. Moreover, in vivo angiogenesis by alkali burn and OIR was significantly attenuated in Gαi1/3 double knockout mice. Significantly, Gαi1/3 proteins are upregulated in proliferative retinal tissues of proliferative diabetic retinopathy (PDR) patients.

Conclusion: These results provide mechanistic insights into the critical role played by Gαi1/3 proteins in VEGF-induced VEGFR2 endocytosis, signaling and angiogenesis.

Formyl Peptide Receptor 1 Modulates Endothelial Cell Functions by NADPH Oxidase-Dependent VEGFR2 Transactivation

In the vasculature, NADPH oxidase is the main contributor of reactive oxygen species (ROS) which play a key role in endothelial signalling and functions. We demonstrate that ECV304 cells express p47^phox, p67^phox, and p22^phox subunits of NADPH oxidase, as well as formyl peptide receptors 1 and 3 (FPR1/3), which are members of the GPCR family. By RT-PCR, we also detected Flt-1 and Flk-1/KDR in these cells. Stimulation of FPR1 by N-fMLP induces p47^phox phosphorylation, which is the crucial event for NADPH oxidase-dependent superoxide production. Transphosphorylation of RTKs by GPCRs is a biological mechanism through which the information exchange is amplified throughout the cell. ROS act as signalling intermediates in the transactivation mechanism. We show that N-fMLP stimulation induces the phosphorylation of cytosolic Y951, Y996, and Y1175 residues of VEGFR2, which constitute the anchoring sites for signalling molecules. These, in turn, activate PI3K/Akt and PLC-γ1/PKC intracellular pathways. FPR1-induced ROS production plays a critical role in this cross-talk mechanism. In fact, inhibition of FPR1 and/or NADPH oxidase functions prevents VEGFR2 transactivation and the triggering of the downstream signalling cascades. N-fMLP stimulation also ameliorates cellular migration and capillary-like network formation ability of ECV304 cells.

Recent advances of adapter proteins in the regulation of heart diseases

Heart diseases are major causes of mortality. Cardiac hypertrophy, myocardial infarction (MI), viral cardiomyopathy, ischemic and reperfusion (I/R) heart injury finally lead to heart failure and death. Insulin and IGF1 signal pathways play key roles in normal cardiomyocyte growth and physiological cardiac hypertrophy while inflammatory signal pathway is associated with pathological cardiac hypertrophy, MI, viral cardiomyopathy, I/R heart injury, and heart failure. Adapter proteins are the major family proteins, which transduce signals from insulin, IGF1, or cytokine receptors to the downstream pathways and have been shown to regulate variety of heart diseases. Here, we summarized the recent advances in understanding the physiological and pathological roles of adapter proteins in heart failure.

Glucocorticoids, genes and brain function

The identification of key genes in transcriptomic data constitutes a huge challenge. Our review of microarray reports revealed 88 genes whose transcription is consistently regulated by glucocorticoids (GCs), such as cortisol, corticosterone and dexamethasone, in the brain. Replicable transcriptomic data were combined with biochemical and physiological data to create an integrated view of the effects induced by GCs. The most frequently reported genes were Errfi1 and Ddit4. Their up-regulation was associated with the altered transcription of genes regulating growth factor and mTORC1 signaling (Gab1, Tsc22d3, Dusp1, Ndrg2, Ppp5c and Sesn1) and progression of the cell cycle (Ccnd1, Cdkn1a and Cables1). The GC-induced reprogramming of cell function involves changes in the mRNA level of genes responsible for the regulation of transcription (Klf9, Bcl6, Klf15, Tle3, Cxxc5, Litaf, Tle4, Jun, Sox4, Sox2, Sox9, Irf1, Sall2, Nfkbia and Id1) and the selective degradation of mRNA (Tob2). Other genes are involved in the regulation of metabolism (Gpd1, Aldoc and Pdk4), actin cytoskeleton (Myh2, Nedd9, Mical2, Rhou, Arl4d, Osbpl3, Arhgef3, Sdc4, Rdx, Wipf3, Chst1 and Hepacam), autophagy (Eva1a and Plekhf1), vesicular transport (Rhob, Ehd3, Vps37b and Scamp2), gap junctions (Gjb6), immune response (Tiparp, Mertk, Lyve1 and Il6r), signaling mediated by thyroid hormones (Thra and Sult1a1), calcium (Calm2), adrenaline/noradrenaline (Adcy9 and Adra1d), neuropeptide Y (Npy1r) and histamine (Hdc). GCs also affected genes involved in the synthesis of polyamines (Azin1) and taurine (Cdo1). The actions of GCs are restrained by feedback mechanisms depending on the transcription of Sgk1, Fkbp5 and Nr3c1. A side effect induced by GCs is increased production of reactive oxygen species. Available data show that the brain's response to GCs is part of an emergency mode characterized by inactivation of non-core activities, restrained inflammation, restriction of investments (growth), improved efficiency of energy production and the removal of unnecessary or malfunctioning cellular components to conserve energy and maintain nutrient supply during the stress response.

Ginsenoside Rh2 inhibits vascular endothelial growth factor-induced corneal neovascularization

VEGF-induced neovascularization plays a pivotal role in corneal neovascularization (CoNV). The current study investigated the potential effect of ginsenoside Rh2 (GRh2) on neovascularization. In HUVECs, pretreatment with GRh2 largely attenuated VEGF-induced cell proliferation, migration, and vessel-like tube formation in vitro. At the molecular level, GRh2 disrupted VEGF-induced VEGF receptor 2 (VEGFR2)-Grb-2-associated binder 1 (Gab1) association in HUVECs, causing inactivation of downstream AKT and ERK signaling. Gab1 knockdown (by targeted short hairpin RNA) similarly inhibited HUVEC proliferation and migration. Notably, GRh2 was ineffective against VEGF in Gab1-silenced HUVECs. In a mouse cornea alkali burn model, GRh2 eyedrops inhibited alkali-induced neovascularization and inflammatory cell infiltrations in the cornea. Furthermore, alkali-induced corneal expression of mRNAs/long noncoding RNAs in cornea were largely attenuated by GRh2. Overall, GRh2 inhibits VEGF-induced angiogenic effect via inhibiting VEGFR2-Gab1 signaling in vitro. It also alleviates angiogenic and inflammatory responses in alkali burn-treated mouse corneas.-Zhang, X.-P., Li, K.-R., Yu, Q., Yao, M.-D., Ge, H.-M., Li, X.-M., Jiang, Q., Yao, J., Cao, C. Ginsenoside Rh2 inhibits vascular endothelial growth factor-induced corneal neovascularization.

CdGAP/ARHGAP31, a Cdc42/Rac1 GTPase regulator, is critical for vascular development and VEGF-mediated angiogenesis

Mutations in the CdGAP/ARHGAP31 gene, which encodes a GTPase-activating protein for Rac1 and Cdc42, have been reported causative in the Adams-Oliver developmental syndrome often associated with vascular defects. However, despite its abundant expression in endothelial cells, CdGAP function in the vasculature remains unknown. Here, we show that vascular development is impaired in CdGAP-deficient mouse embryos at E15.5. This is associated with superficial vessel defects and subcutaneous edema, resulting in 44% embryonic/perinatal lethality. VEGF-driven angiogenesis is defective in CdGAP(-/-) mice, showing reduced capillary sprouting from aortic ring explants. Similarly, VEGF-dependent endothelial cell migration and capillary formation are inhibited upon CdGAP knockdown. Mechanistically, CdGAP associates with VEGF receptor-2 and controls VEGF-dependent signaling. Consequently, CdGAP depletion results in impaired VEGF-mediated Rac1 activation and reduced phosphorylation of critical intracellular mediators including Gab1, Akt, PLCγ and SHP2. These findings are the first to demonstrate the importance of CdGAP in embryonic vascular development and VEGF-induced signaling, and highlight CdGAP as a potential therapeutic target to treat pathological angiogenesis and vascular dysfunction.

VEGFR2 Signaling Prevents Colorectal Cancer Cell Senescence to Promote Tumorigenesis in Mice With Colitis

BACKGROUND & AIMS

Senescence prevents cellular transformation. We investigated whether vascular endothelial growth factor (VEGF) signaling via its receptor, VEGFR2, regulates senescence and proliferation of tumor cells in mice with colitis-associated cancer (CAC).

METHODS

CAC was induced in VEGFR2(ΔIEC) mice, which do not express VEGFR2 in the intestinal epithelium, and VEGFR2(fl/fl) mice (controls) by administration of azoxymethane followed by dextran sodium sulfate. Tumor development and inflammation were determined by endoscopy. Colorectal tissues were collected for immunoblot, immunohistochemical, and quantitative polymerase chain reaction analyses. Findings from mouse tissues were confirmed in human HCT116 colorectal cancer cells. We analyzed colorectal tumor samples from patients before and after treatment with bevacizumab.

RESULTS

After colitis induction, VEGFR2(ΔIEC) mice developed significantly fewer tumors than control mice. A greater number of intestinal tumor cells from VEGFR2(ΔIEC) mice were in senescence than tumor cells from control mice. We found VEGFR2 to activate phosphatidylinositol-4,5-bisphosphate-3-kinase and AKT, resulting in inactivation of p21 in HCT116 cells. Inhibitors of VEGFR2 and AKT induced senescence in HCT116 cells. Tumor cell senescence promoted an anti-tumor immune response by CD8(+) T cells in mice. Patients whose tumor samples showed an increase in the proportion of senescent cells after treatment with bevacizumab had longer progression-free survival than patients in which the proportion of senescent tumor cells did not change before and after treatment.

CONCLUSIONS

Inhibition of VEGFR2 signaling leads to senescence of human and mouse colorectal cancer cells. VEGFR2 interacts with phosphatidylinositol-4,5-bisphosphate-3-kinase and AKT to inactivate p21. Colorectal tumor senescence and p21 level correlate with patient survival during treatment with bevacizumab.

Gab1 regulates proliferation and migration through the PI3K/Akt signaling pathway in intrahepatic cholangiocarcinoma

Intrahepatic cholangiocarcinoma is the second most common primary malignant tumor of the liver, and it originates from the intrahepatic biliary duct epithelium. Prognosis is poor due to lack of effective comprehensive treatments. In this study, we assessed the expression of Gab1, VEGFR-2, and MMP-9 in intrahepatic cholangiocarcinoma solid tumors by immunohistochemistry and determined whether their expression was associated with clinical and pathological features. We found that expression of Gab1, VEGFR-2, and MMP-9 was highly and positively correlated with each other and with lymph node metastasis and TNM stage in intrahepatic cholangiocarcinoma tissues. Interference of Gab1 and VEGFR-2 expression via siRNA in the intrahepatic cholangiocarcinoma cell line RBE resulted in decreased PI3K/Akt pathway activity. Inhibition of Gab1 and VEGFR-2 expression also caused decreased cell proliferation, cell cycle arrested in G1 phase, increased apoptosis, and decreased invasion in RBE cells. These results suggest that Gab1, VEGFR-2, and MMP-9 contribute significantly to the highly malignant behavior of intrahepatic cholangiocarcinoma. The regulation of growth, apoptosis, and invasion by Gab1 through the VEGFR-2/Gab1/PI3K/Akt signaling pathway may represent potential targets for improving the treatment of intrahepatic cholangiocarcinoma.

Down-regulation of Gab1 inhibits cell proliferation and migration in hilar cholangiocarcinoma

Hilar cholangiocarcinoma is a highly aggressive malignancy originating from the hilar biliary duct epithelium. Due to few effective comprehensive treatments, the prognosis of hilar cholangiocarcinoma is poor. In this study, immunohistochemistry was first used to detect and analyze the expression of Gab1, VEGFR-2, and MMP-9 in hilar cholangiocarcinoma solid tumors and the relationships to the clinical pathological features. Furthermore, Gab1 and VEGFR-2 siRNA were used to interfere the hilar cholangiocarcinoma cell line ICBD-1 and then detect the PI3K/Akt signaling pathway, MMP-9 levels and malignant biological behaviors of tumor cells. The data showed that 1. Gab1, VEGFR-2, and MMP-9 were highly expressed and positively correlated with each other in hilar cholangiocarcinoma tissues, which were related to lymph node metastasis and differentiation. 2. After Gab1 or VEGFR-2 siRNA interference, PI3K/Akt pathway activity and MMP-9 levels were decreased in ICBD-1 cells. At the same time, cell proliferation decreased, cell cycle arrested in G1 phase, apoptosis increased and invasion decreased. These results suggest that the expression of Gab1, VEGFR-2, and MMP-9 are significantly related to the malignant biological behavior of hilar cholangiocarcinoma. Gab1 regulates growth, apoptosis and invasion through the VEGFR-2/Gab1/PI3K/Akt signaling pathway in hilar cholangiocarcinoma cells and influences the invasion of tumor cells via MMP-9.

Novel role for p21-activated kinase 2 in thrombin-induced monocyte migration

To understand the role of thrombin in inflammation, we tested its effects on migration of THP-1 cells, a human monocytic cell line. Thrombin induced THP-1 cell migration in a dose-dependent manner. Thrombin induced tyrosine phosphorylation of Pyk2, Gab1, and p115 RhoGEF, leading to Rac1- and RhoA-dependent Pak2 activation. Downstream to Pyk2, Gab1 formed a complex with p115 RhoGEF involving their pleckstrin homology domains. Furthermore, inhibition or depletion of Pyk2, Gab1, p115 RhoGEF, Rac1, RhoA, or Pak2 levels substantially attenuated thrombin-induced THP-1 cell F-actin cytoskeletal remodeling and migration. Inhibition or depletion of PAR1 also blocked thrombin-induced activation of Pyk2, Gab1, p115 RhoGEF, Rac1, RhoA, and Pak2, resulting in diminished THP-1 cell F-actin cytoskeletal remodeling and migration. Similarly, depletion of Gα12 negated thrombin-induced Pyk2, Gab1, p115 RhoGEF, Rac1, RhoA, and Pak2 activation, leading to attenuation of THP-1 cell F-actin cytoskeletal remodeling and migration. These novel observations reveal that thrombin induces monocyte/macrophage migration via PAR1-Gα12-dependent Pyk2-mediated Gab1 and p115 RhoGEF interactions, leading to Rac1- and RhoA-targeted Pak2 activation. Thus, these findings provide mechanistic evidence for the role of thrombin and its receptor PAR1 in inflammation.

Computational Model of Gab1/2-Dependent VEGFR2 Pathway to Akt Activation

Vascular endothelial growth factor (VEGF) signal transduction is central to angiogenesis in development and in pathological conditions such as cancer, retinopathy and ischemic diseases. However, no detailed mass-action models of VEGF receptor signaling have been developed. We constructed and validated the first computational model of VEGFR2 trafficking and signaling, to study the opposing roles of Gab1 and Gab2 in regulation of Akt phosphorylation in VEGF-stimulated endothelial cells. Trafficking parameters were optimized against 5 previously published in vitro experiments, and the model was validated against six independent published datasets. The model showed agreement at several key nodes, involving scaffolding proteins Gab1, Gab2 and their complexes with Shp2. VEGFR2 recruitment of Gab1 is greater in magnitude, slower, and more sustained than that of Gab2. As Gab2 binds VEGFR2 complexes more transiently than Gab1, VEGFR2 complexes can recycle and continue to participate in other signaling pathways. Correspondingly, the simulation results show a log-linear relationship between a decrease in Akt phosphorylation and Gab1 knockdown while a linear relationship was observed between an increase in Akt phosphorylation and Gab2 knockdown. Global sensitivity analysis demonstrated the importance of initial-concentration ratios of antagonistic molecular species (Gab1/Gab2 and PI3K/Shp2) in determining Akt phosphorylation profiles. It also showed that kinetic parameters responsible for transient Gab2 binding affect the system at specific nodes. This model can be expanded to study multiple signaling contexts and receptor crosstalk and can form a basis for investigation of therapeutic approaches, such as tyrosine kinase inhibitors (TKIs), overexpression of key signaling proteins or knockdown experiments.

T11TS impedes glioma angiogenesis by inhibiting VEGF signaling and pro-survival PI3K/Akt/eNOS pathway with concomitant upregulation of PTEN in brain endothelial cells

The crucial role of angiogenesis in malignant glioma progression makes it a potential target of therapeutic intervention in glioma. Previous studies from our lab showed that sheep erythrocyte membrane glycopeptide T11-target structure (T11TS) has potent anti-neoplastic and immune stimulatory effects in rodent glioma model. In the present study we investigated the anti-angiogenic potential of T11TS and deciphered the underlying molecular mechanism of its anti-angiogenic action in malignant glioma. Vascular endothelial growth factor (VEGF) signaling is crucial for initiating tumor angiogenic responses. The present preclinical study was designed to evaluate the effect of T11TS therapy on VEGF and VEGFR-2 expression in glioma associated brain endothelial cells and to determine the effects of in vivo T11TS administration on expression of PTEN and downstream pro-survival PI3K/Akt/eNOS pathway proteins in glioma associated brain endothelial cells. T11TS therapy in rodent glioma model significantly downregulated expression of VEGF along with its receptor VEGFR-2 and inhibited the expression of pro-survival PI3K/Akt/eNOS proteins in glioma associated brain endothelial cells. Furthermore, T11TS therapy in glioma induced rats significantly upregulated brain endothelial cell PTEN expression, inhibited eNOS phosphorylation and production of nitric oxide in glioma associated brain endothelial cells. Taken together our findings suggest that T11TS can be introduced as an effective angiogenesis inhibitor in human glioma as T11TS targets multiple levels of angiogenic signaling cascade impeding glioma neovascularisation.

VEGFA and tumour angiogenesis

In this review we summarize the current understanding of signal transduction downstream of vascular endothelial growth factor A (VEGFA) and its receptor VEGFR2, and the relationship between these signal transduction pathways and the hallmark responses of VEGFA, angiogenesis and vascular permeability. These physiological responses involve a number of effectors, including extracellular signal-regulated kinases (ERKs), Src, phosphoinositide 3 kinase (PI3K)/Akt, focal adhesion kinase (FAK), Rho family GTPases, endothelial NO and p38 mitogen-activated protein kinase (MAPK). Several of these factors are involved in the regulation of both angiogenesis and vascular permeability. Tumour angiogenesis primarily relies on VEGFA-driven responses, which to a large extent result in a dysfunctional vasculature. The reason for this remains unclear, although it appears that certain aspects of the VEGFA-stimulated angiogenic milieu (high level of microvascular density and permeability) promote tumour expansion. The high degree of redundancy and complexity of VEGFA-driven tumour angiogenesis may explain why tumours commonly develop resistance to anti-angiogenic therapy targeting VEGFA signal transduction.

Gab docking proteins in cardiovascular disease, cancer, and inflammation

The docking proteins of the Grb2-associated binder (Gab) family have emerged as crucial signaling compartments in metazoans. In mammals, the Gab proteins, consisting of Gab1, Gab2, and Gab3, are involved in the amplification and integration of signal transduction evoked by a variety of extracellular stimuli, including growth factors, cytokines, antigens, and other molecules. Gab proteins lack the enzymatic activity themselves; however, when phosphorylated on tyrosine residues, they provide binding sites for multiple Src homology-2 (SH2) domain-containing proteins, such as SH2-containing protein tyrosine phosphatase 2 (SHP2), phosphatidylinositol 3-kinase regulatory subunit p85, phospholipase Cγ, Crk, and GC-GAP. Through these interactions, the Gab proteins transduce signals from activated receptors into pathways with distinct biological functions, thereby contributing to signal diversification. They are known to play crucial roles in numerous physiological processes through their associations with SHP2 and p85. In addition, abnormal Gab protein signaling has been linked to human diseases including cancer, cardiovascular disease, and inflammatory disorders. In this paper, we provide an overview of the structure, effector functions, and regulation of the Gab docking proteins, with a special focus on their associations with cardiovascular disease, cancer, and inflammation.

Annexin-1-mediated endothelial cell migration and angiogenesis are regulated by vascular endothelial growth factor (VEGF)-induced inhibition of miR-196a expression

Endothelial cell migration induced in response to vascular endothelial growth factor (VEGF) is an essential step of angiogenesis. It depends in part on the activation of the p38/MAPKAP kinase-2/LIMK1/annexin-A1 (ANXA1) signaling axis. In the present study, we obtained evidence indicating that miR-196a specifically binds to the 3'-UTR region of ANXA1 mRNA to repress its expression. In accordance with the role of ANXA1 in cell migration and angiogenesis, the ectopic expression of miR-196a is associated with decreased cell migration in wound closure assays, and the inhibitory effect of miR-196a is rescued by overexpressing ANXA1. This finding highlights the fact that ANXA1 is a required mediator of VEGF-induced cell migration. miR-196a also reduces the formation of lamellipodia in response to VEGF suggesting that ANXA1 regulates cell migration by securing the formation of lamellipodia at the leading edge of the cell. Additionally, in line with the fact that cell migration is an essential step of angiogenesis, the ectopic expression of miR-196a impairs the formation of capillary-like structures in a tissue-engineered model of angiogenesis. Here again, the effect of miR-196a is rescued by overexpressing ANXA1. Moreover, the presence of miR-196a impairs the VEGF-induced in vivo neo-vascularization in the Matrigel Plug assay. Interestingly, VEGF reduces the expression of miR-196a, which is associated with an increased level of ANXA1. Similarly, the inhibition of miR-196a with an antagomir results in an increased level of ANXA1. We conclude that the VEGF-induced decrease of miR-196a expression may participate to the angiogenic switch by maintaining the expression of ANXA1 to levels required to enable p38-ANXA1-dependent endothelial cell migration and angiogenesis in response to VEGF.

Functions and regulation of circular dorsal ruffles

Cells construct a number of plasma membrane structures to meet a range of physiological demands. Driven by juxtamembrane actin machinery, these actin-based membrane protrusions are essential for the operation and maintenance of cellular life. They are required for diverse cellular functions, such as directed cell motility, cell spreading, adhesion, and substrate/matrix degradation. Circular dorsal ruffles (CDRs) are one class of such structures characterized as F-actin-rich membrane projections on the apical cell surface. CDRs commence their formation minutes after stimulation as flat, open, and immature ruffles and progressively develop into fully enclosed circular ruffles. These "rings" then mature and contract centrifugally before subsiding. Serving a critical function in receptor internalization and cell migration, CDRs are thus highly dynamic but transient formations. Here, we review the current state of knowledge concerning the regulation of circular dorsal ruffles. We focus specifically on the biochemical pathways leading to CDR formation in order to better define the roles and functions of these enigmatic structures.

GAB2 induces tumor angiogenesis in NRAS-driven melanoma

GAB2 is a scaffold protein with diverse upstream and downstream effectors. MAPK and PI3K signaling pathways are known effectors of GAB2. It is amplified and overexpressed in a variety of human tumors including melanoma. Here we show a previously undescribed role for GAB2 in NRAS-driven melanoma. Specifically, we found that GAB2 is co-expressed with mutant NRAS in melanoma cell lines and tumor samples and its expression correlated with metastatic potential. Co-expression of GAB2(WT) and NRAS(G12D) in melanocytes and in melanoma cells increased anchorage-independent growth by providing GAB2-expressing cells a survival advantage through upregulation of BCL-2 family of anti-apoptotic factors. Of note, collaboration of GAB2 with mutant NRAS enhanced tumorigenesis in vivo and led to an increased vessel density with strong CD34 and VEGFR2 activity. We found that GAB2 facilitiated an angiogenic switch by upregulating HIF-1α and VEGF levels. This angiogenic response was significantly suppressed with the MEK inhibitor PD325901. These data suggest that GAB2-mediated signaling cascades collaborate with NRAS-driven downstream activation for conferring an aggressive phenotype in melanoma. Second, we show that GAB2/NRAS signaling axis is non-linear and non-redundant in melanocytes and melanoma, and thus are acting independent of each other. Finally, we establish a link between GAB2 and angiogenesis in melanoma for the first time. In conclusion, our findings provide evidence that GAB2 is a novel regulator of tumor angiogenesis in NRAS-driven melanoma through regulation of HIF-1α and VEGF expressions mediated by RAS-RAF-MEK-ERK signaling.

Axl is essential for VEGF-A-dependent activation of PI3K/Akt

Herein, we report that vascular endothelial growth factor A (VEGF-A) engages the PI3K/Akt pathway by a previously unknown mechanism that involves three tyrosine kinases. Upon VEGF-A-dependent activation of VEGF receptor-2 (VEGFR-2), and subsequent TSAd-mediated activation of Src family kinases (SFKs), SFKs engage the receptor tyrosine kinase Axl via its juxtamembrane domain to trigger ligand-independent autophosphorylation at a pair of YXXM motifs that promotes association with PI3K and activation of Akt. Other VEGF-A-mediated signalling pathways are independent of Axl. Interfering with Axl expression or function impairs VEGF-A- but not bFGF-dependent migration of endothelial cells. Similarly, Axl null mice respond poorly to VEGF-A-induced vascular permeability or angiogenesis, whereas other agonists induce a normal response. These results elucidate the mechanism by which VEGF-A activates PI3K/Akt, and identify previously unappreciated potential therapeutic targets of VEGF-A-driven processes.

Docking Protein Gab1 Is an Essential Component of Postnatal Angiogenesis After Ischemia via HGF/c-Met Signaling

Rationale:

Grb2-associated binder (Gab) docking proteins, consisting of Gab1, Gab2, and Gab3, have crucial roles in growth factor–dependent signaling. Various proangiogenic growth factors regulate angiogenesis and endothelial function. However, the roles of Gab proteins in angiogenesis remain elusive.

Objective:

To elucidate the role of Gab proteins in postnatal angiogenesis.

Methods and Results:

Endothelium-specific Gab1 knockout (Gab1ECKO) mice were viable and showed no obvious defects in vascular development. Therefore, we analyzed a hindlimb ischemia (HLI) model of control, Gab1ECKO, or conventional Gab2 knockout (Gab2KO) mice. Intriguingly, impaired blood flow recovery and necrosis in the operated limb was observed in all of Gab1ECKO, but not in control or Gab2KO mice. Among several proangiogenic growth factors, hepatocyte growth factor (HGF) induced the most prominent tyrosine phosphorylation of Gab1 and subsequent complex formation of Gab1 with SHP2 (Src homology-2–containing protein tyrosine phosphatase 2) and phosphatidylinositol 3-kinase subunit p85 in human endothelial cells (ECs). Gab1-SHP2 complex was required for HGF-induced migration and proliferation of ECs via extracellular signal-regulated kinase (ERK)1/2 pathway and for HGF-induced stabilization of ECs via ERK5. In contrast, Gab1-p85 complex regulated activation of AKT and contributed partially to migration of ECs after HGF stimulation. Microarray analysis demonstrated that HGF upregulated angiogenesis-related genes such as KLF2 (Krüppel-like factor 2) and Egr1 (early growth response 1) via Gab1-SHP2 complex in human ECs. In Gab1ECKO mice, gene transfer of vascular endothelial growth factor, but not HGF, improved blood flow recovery and ameliorated limb necrosis after HLI.

Conclusion:

Gab1 is essential for postnatal angiogenesis after ischemia via HGF/c-Met signaling.

Grb-2-associated binder 1 (Gab1) regulates postnatal ischemic and VEGF-induced angiogenesis through the protein kinase A-endothelial NOS pathway

The intracellular signaling mechanisms underlying postnatal angiogenesis are incompletely understood. Herein we show that Grb-2-associated binder 1 (Gab1) plays a critical role in ischemic and VEGF-induced angiogenesis. Endothelium-specific Gab1 KO (EGKO) mice displayed impaired angiogenesis in the ischemic hindlimb despite normal induction of VEGF expression. Matrigel plugs with VEGF implanted in EGKO mice induced fewer capillaries than those in control mice. The vessels and endothelial cells (ECs) derived from EGKO mice were defective in vascular sprouting and tube formation induced by VEGF. Biochemical analyses revealed a substantial reduction of endothelial NOS (eNOS) activation in Gab1-deficient vessels and ECs following VEGF stimulation. Interestingly, the phosphorylation of Akt, an enzyme known to promote VEGF-induced eNOS activation, was increased in Gab1-deficient vessels and ECs whereas protein kinase A (PKA) activity was significantly decreased. Introduction of an active form of PKA rescued VEGF-induced eNOS activation and tube formation in EGKO ECs. Reexpression of WT or mutant Gab1 molecules in EGKO ECs revealed requirement of Gab1/Shp2 association for the activation of PKA and eNOS. Taken together, these results identify Gab1 as a critical upstream signaling component in VEGF-induced eNOS activation and tube formation, which is dependent on PKA. Of note, this pathway is conserved in primary human ECs for VEGF-induced eNOS activation and tube formation, suggesting considerable potential in treatment of human ischemic diseases.

The Gab1 scaffold regulates RTK-dependent dorsal ruffle formation through the adaptor Nck

The polarised distribution of signals downstream from receptor tyrosine kinases (RTKs) regulates fundamental cellular processes that control cell migration, growth and morphogenesis. It is poorly understood how RTKs are involved in the localised signalling and actin remodelling required for these processes. Here, we show that the Gab1 scaffold is essential for the formation of a class of polarised actin microdomain, namely dorsal ruffles, downstream from the Met, EGF and PDGF RTKs. Gab1 associates constitutively with the actin-nucleating factor N-WASP. Following RTK activation, Gab1 recruits Nck, an activator of N-WASP, into a signalling complex localised to dorsal ruffles. Formation of dorsal ruffles requires interaction between Gab1 and Nck, and also requires functional N-WASP. Epithelial cells expressing Gab1DeltaNck (Y407F) exhibit decreased Met-dependent Rac activation, fail to induce dorsal ruffles, and have impaired cell migration and epithelial remodelling. These data show that a Gab1-Nck signalling complex interacts with several RTKs to promote polarised actin remodelling and downstream biological responses.

Functional effects of PTPN11 (SHP2) mutations causing LEOPARD syndrome on epidermal growth factor-induced phosphoinositide 3-kinase/AKT/glycogen synthase kinase 3beta signaling

LEOPARD syndrome (LS), a disorder with multiple developmental abnormalities, is mainly due to mutations that impair the activity of the tyrosine phosphatase SHP2 (PTPN11). How these alterations cause the disease remains unknown. We report here that fibroblasts isolated from LS patients displayed stronger epidermal growth factor (EGF)-induced phosphorylation of both AKT and glycogen synthase kinase 3beta (GSK-3beta) than fibroblasts from control patients. Similar results were obtained in HEK293 cells expressing LS mutants of SHP2. We found that the GAB1/phosphoinositide 3-kinase (PI3K) complex was more abundant in fibroblasts from LS than control subjects and that both AKT and GSK-3beta hyperphosphorylation were prevented by reducing GAB1 expression or by overexpressing a GAB1 mutant unable to bind to PI3K. Consistently, purified recombinant LS mutants failed to dephosphorylate GAB1 PI3K-binding sites. These mutants induced PI3K-dependent increase in cell size in a model of chicken embryo cardiac explants and in transcriptional activity of the atrial natriuretic factor (ANF) gene in neonate rat cardiomyocytes. In conclusion, SHP2 mutations causing LS facilitate EGF-induced PI3K/AKT/GSK-3beta stimulation through impaired GAB1 dephosphorylation, resulting in deregulation of a novel signaling pathway that could be involved in LS pathology.

Activation of vascular endothelial growth factor receptor 2 in a cellular model of loricrin keratoderma

Loricrin is a major constituent of the epidermal cornified cell envelope. Recently, heterozygous loricrin gene mutations have been identified in two dominantly inherited skin diseases, Vohwinkel syndrome with ichthyosis and progressive symmetric erythrokeratoderma, collectively termed loricrin keratoderma. We generated stable HaCaT cell lines that express wild-type (WT) loricrin and a mutant form found in Vohwinkel syndrome with ichthyosis, using an ecdysone-inducible promoter system. The cells expressing the mutant loricrin grew more rapidly than those expressing WT loricrin after induction for 5 days. Confocal immunofluorescence microscopy revealed that phospho-Akt occurred in the nucleolus where the mutant loricrin was also located. The level of activity of Akt kinase was about nine times higher in cells with the mutant than in those with WT loricrin. ERK1/2, the epidermal growth factor receptor, vascular endothelial growth factor (VEGF) receptor 2 and Stat3 were all phosphorylated in cells with the mutant loricrin. The docking proteins, Gab1 and c-Cbl, were also tyrosine-phosphorylated in these cells. Furthermore, chromatin immunoprecipitation assays showed that Stat3 protein bound to the VEGF promoter in cells with the mutant. Thus, this study suggests that VEGF release and the subsequent activation of VEGF receptor 2 link loricrin gene mutations to rapid cell proliferation in a cellular model of loricrin keratoderma.

PI3K/PTEN signaling in angiogenesis and tumorigenesis

Phosphatidylinositol 3-kinase (PI3K) and phosphatase and tensin homolog deleted on chromosome 10 (PTEN) signaling pathway play an important role in multiple cellular functions such as cell metabolism, proliferation, cell-cycle progression, and survival. PI3K is activated by growth factors and angiogenesis inducers such as vascular endothelial growth factor (VEGF) and angiopoietins. The amplification and mutations of PI3K and the loss of the tumor suppressor PTEN are common in various kinds of human solid tumors. The genetic alterations of upstream and downstream of PI3K signaling molecules such as receptor tyrosine kinases and AKT, respectively, are also frequently altered in human cancer. PI3K signaling regulates tumor growth and angiogenesis by activating AKT and other targets, and by inducing HIF-1 and VEGF expression. Angiogenesis is required for tumor growth and metastasis. In this review, we highlight the recent studies on the roles and mechanisms of PI3K and PTEN in regulating tumorigenesis and angiogenesis, and the roles of the downstream targets of PI3K for transmitting the signals. We also discuss the crosstalk of these signaling molecules and cellular events during tumor growth, metastasis, and tumor angiogenesis. Finally, we summarize the potential applications of PI3K, AKT, and mTOR inhibitors and their outcome in clinical trials for cancer treatment.

Structure-function analysis of VEGF receptor activation and the role of coreceptors in angiogenic signaling

Vascular endothelial growth factors (VEGFs) constitute a family of six polypeptides, VEGF-A, -B, -C, -D, -E and PlGF, that regulate blood and lymphatic vessel development. VEGFs specifically bind to three type V receptor tyrosine kinases (RTKs), VEGFR-1, -2 and -3, and to coreceptors such as neuropilins and heparan sulfate proteoglycans (HSPG). VEGFRs are activated upon ligand-induced dimerization mediated by the extracellular domain (ECD). A study using receptor constructs carrying artificial dimerization-promoting transmembrane domains (TMDs) showed that receptor dimerization is necessary, but not sufficient, for receptor activation and demonstrates that distinct orientation of receptor monomers is required to instigate transmembrane signaling. Angiogenic signaling by VEGF receptors also depends on cooperation with specific coreceptors such as neuropilins and HSPG. A number of VEGF isoforms differ in binding to coreceptors, and ligand-specific signal output is apparently the result of the specific coreceptor complex assembled by a particular VEGF isoform. Here we discuss the structural features of VEGF family ligands and their receptors in relation to their distinct signal output and angiogenic potential.

Function, regulation and pathological roles of the Gab/DOS docking proteins

Since their discovery a little more than a decade ago, the docking proteins of the Gab/DOS family have emerged as important signalling elements in metazoans. Gab/DOS proteins integrate and amplify signals from a wide variety of sources including growth factor, cytokine and antigen receptors as well as cell adhesion molecules. They also contribute to signal diversification by channelling the information from activated receptors into signalling pathways with distinct biological functions. Recent approaches in protein biochemistry and systems biology have revealed that Gab proteins are subject to complex regulation by feed-forward and feedback phosphorylation events as well as protein-protein interactions. Thus, Gab/DOS docking proteins are at the centre of entire signalling subsystems and fulfil an important if not essential role in many physiological processes. Furthermore, aberrant signalling by Gab proteins has been increasingly linked to human diseases from various forms of neoplasia to Alzheimer's disease.

In this review, we provide a detailed overview of the structure, effector functions, regulation and evolution of the Gab/DOS family. We also summarize recent findings implicating Gab proteins, in particular the Gab2 isoform, in leukaemia, solid tumours and other human diseases.

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

BACKGROUND

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

METHODOLOGY/PRINCIPAL FINDINGS

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

CONCLUSIONS/SIGNIFICANCE

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

Non-redundant roles of the Gab1 and Gab2 scaffolding adapters in VEGF-mediated signalling, migration, and survival of endothelial cells

Gab1 was previously described as a positive modulator of Akt, Src, ERK1/2, endothelial cell migration, and capillary formation in response to vascular endothelial growth factor (VEGF). However, its involvement in endothelial cell survival, as well as the potential contribution of the other family member Gab2 to signalling and biological responses remained unknown. Here, we show that Gab2 is tyrosine phosphorylated in a Grb2-dependent manner downstream of activated VEGF receptor-2 (VEGFR2), and that it associates with signalling proteins including PI3K and SHP2, but apparently not with the receptor. Similarly to Gab1, over-expression of Gab2 induces endothelial cell migration in response to VEGF, whereas its depletion using siRNAs results in its reduction. Importantly, depletion of both Gab1 and Gab2 leads to an even greater inhibition of VEGF-induced cell migration. However, contrary to what has been reported for Gab1, the silencing of Gab2 results in increased Src, Akt and ERK1/2 activation, slightly reduced p38 phosphorylation, and up-regulation of Gab1 protein levels. Accordingly, re-expression of Gab2 in Gab2-/- fibroblasts leads to opposite results, suggesting that the modulation of both Gab2 and Gab1 expression in these conditions might contribute to the impaired signalling observed. Consistent with their opposite roles on Akt, the depletion of Gab1, but not of Gab2, results in reduced FOXO1 phosphorylation and VEGF-mediated endothelial cell survival. Mutation of VEGFR2 Y801 and Y1214, which abrogates the phosphorylation of Gab1, also correlates with inhibition of Akt. Altogether, these results underscore the non-redundant and essential roles of Gab1 and Gab2 in endothelial cells, and suggest major contributions of these proteins during in vivo angiogenesis.

New role for the protein tyrosine phosphatase DEP-1 in Akt activation and endothelial cell survival

Functional inactivation of the protein tyrosine phosphatase DEP-1 leads to increased endothelial cell proliferation and failure of vessels to remodel and branch. DEP-1 has also been proposed to contribute to the contact inhibition of endothelial cell growth via dephosphorylation of vascular endothelial growth factor receptor 2 (VEGFR2), a mediator of vascular development. However, how DEP-1 regulates VEGF-dependent signaling and biological responses remains ill-defined. We show here that DEP-1 targets tyrosine residues in the VEGFR2 kinase activation loop. Consequently, depletion of DEP-1 results in the increased phosphorylation of all major VEGFR2 autophosphorylation sites, but surprisingly, not in the overall stimulation of VEGF-dependent signaling. The increased phosphorylation of Src on Y529 under these conditions results in impaired Src and Akt activation. This inhibition is similarly observed upon expression of catalytically inactive DEP-1, and coexpression of an active Src-Y529F mutant rescues Akt activation. Reduced Src activity correlates with decreased phosphorylation of Gab1, an adapter protein involved in VEGF-dependent Akt activation. Hypophosphorylated Gab1 is unable to fully associate with phosphatidylinositol 3-kinase, VEGFR2, and VE-cadherin complexes, leading to suboptimal Akt activation and increased cell death. Overall, our results reveal that despite its negative role on global VEGFR2 phosphorylation, DEP-1 is a positive regulator of VEGF-mediated Src and Akt activation and endothelial cell survival.

Interaction of scaffolding adaptor protein Gab1 with tyrosine phosphatase SHP2 negatively regulates IGF-I-dependent myogenic differentiation via the ERK1/2 signaling pathway

Grb2-associated binder 1 (Gab1) coordinates various receptor tyrosine kinase signaling pathways. Although skeletal muscle differentiation is regulated by some growth factors, it remains elusive whether Gab1 coordinates myogenic signals. Here, we examined the molecular mechanism of insulin-like growth factor-I (IGF-I)-mediated myogenic differentiation, focusing on Gab1 and its downstream signaling. Gab1 underwent tyrosine phosphorylation and subsequent complex formation with protein-tyrosine phosphatase SHP2 upon IGF-I stimulation in C2C12 myoblasts. On the other hand, Gab1 constitutively associated with phosphatidylinositol 3-kinase regulatory subunit p85. To delineate the role of Gab1 in IGF-I-dependent signaling, we examined the effect of adenovirus-mediated forced expression of wild-type Gab1 (Gab1(WT)), mutated Gab1 that is unable to bind SHP2 (Gab1(DeltaSHP2)), or mutated Gab1 that is unable to bind p85 (Gab1(Deltap85)), on the differentiation of C2C12 myoblasts. IGF-I-induced myogenic differentiation was enhanced in myoblasts overexpressing Gab1(DeltaSHP2), but inhibited in those overexpressing either Gab1(WT) or Gab1(Deltap85). Conversely, IGF-I-induced extracellular signal-regulated kinase 1/2 (ERK1/2) activation was significantly repressed in myoblasts overexpressing Gab1(DeltaSHP2) but enhanced in those overexpressing either Gab1(WT) or Gab1(Deltap85). Furthermore, small interference RNA-mediated Gab1 knockdown enhanced myogenic differentiation. Overexpression of catalytic-inactive SHP2 modulated IGF-I-induced myogenic differentiation and ERK1/2 activation similarly to that of Gab1(DeltaSHP2), suggesting that Gab1-SHP2 complex inhibits IGF-I-dependent myogenesis through ERK1/2. Consistently, the blockade of ERK1/2 pathway reversed the inhibitory effect of Gab1(WT) overexpression on myogenic differentiation, and constitutive activation of the ERK1/2 pathway suppressed the enhanced myogenic differentiation by overexpression of Gab1(DeltaSHP2). Collectively, these data suggest that the Gab1-SHP2-ERK1/2 signaling pathway comprises an inhibitory axis for IGF-I-dependent myogenic differentiation.

Translational research in glioblastoma multiforme: molecular criteria for patient selection

In spite of the dismal outcome of glioblastoma multiforme (GBM), we are in a position to provide a ray of hope to patients and families. Methylation of MGMT in tumor occurs in approximately a third of patients and predicts meaningful response and survival to adjuvant radiotherapy plus temozolomide. Limited access to tumor tissue in some patients could be circumvented by examining MGMT methylation in circulating serum DNA, although this approach needs to be validated. Molecular signatures are also promising prognostic and predictive markers, and clinical trials should be carried out to validate their use in the selection of patients for specific targeted therapies. Gene expression by quantitative PCR of key components of these molecular signatures could pave the way for easy identification of different subgroups of patients. Translational clinical trials are warranted in order to detect the subgroups of patients resistant to radiotherapy who may derive benefit from novel therapies, including antiangiogenic drugs.

Up-regulation of multiple proteins and biological processes during maxillary expansion in rats

Background

Maxillary expansion (ME) is a common practice in orthodontics that aims to increase the constricted maxillary arch width. Relapse often occurs, however, and better treatment strategies are needed. In order to develop a more effective method, this study was designed to further examine the process of tissue remodeling during ME, to identify the changes in expression of several proteins of interest, and to clarify the molecular mechanism responsible for tissue remodeling.

Methods

Male Wistar rats were randomly divided into control and ME groups. The rats were euthanized at various intervals over 11 days, and the dissected palates were prepared for histological examination. The structure of the midpalatal sutures changed little during the first three days. Proteins from samples in the ground midpalatal tissues obtained on the third day were subjected to two-dimensional polyacrylamide gel electrophoresis (2-DE) and matrix assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) analysis. Validation of protein expression was performed by Western blot analyses.

Results

From day 5, chondrocytes in the inner layer of suture cartilage and osteoblasts at the end of the suture cartilage began to proliferate, and the skeletal matrix increased later adjacent to the cartilage in the ME group. Comparative proteomic analysis showed increases in 22 protein spots present in the ME group. The changes in three proteins closely related to osteogenesis (parathyroid hormone, osteoprotegerin and vimentin) were confirmed by Western blotting.

Conclusion

Many proteins are over-expressed during ME, and they may play an important role in the remodeling process.

Signal strength dictates phosphoinositide 3-kinase contribution to Ras/extracellular signal-regulated kinase 1 and 2 activation via differential Gab1/Shp2 recruitment: consequences for resistance to epidermal growth factor receptor inhibition

Phosphoinositide 3-kinase (PI3K) participates in extracellular signal-regulated kinase 1 and 2 (ERK1-2) activation according to signal strength, through unknown mechanisms. We report herein that Gab1/Shp2 constitutes a PI3K-dependent checkpoint of ERK1-2 activation regulated according to signal intensity. Indeed, by up- and down-regulation of signal strength in different cell lines and through different methods, we observed that Gab1/Shp2 and Ras/ERK1-2 in concert become independent of PI3K upon strong epidermal growth factor receptor (EGFR) stimulation and dependent on PI3K upon limited EGFR activation. Using Gab1 mutants, we observed that this conditional role of PI3K is dictated by the EGFR capability of recruiting Gab1 through Grb2 or through the PI3K lipid product PIP(3), according to a high or weak level of receptor stimulation, respectively. In agreement, Grb2 siRNA generates, in cells with maximal EGFR stimulation, a strong dependence on PI3K for both Gab1/Shp2 and ERK1-2 activation. Therefore, Ras/ERK1-2 depends on PI3K only when PIP(3) is required to recruit Gab1/Shp2, which occurs only under weak EGFR mobilization. Finally, we show that, in glioblastoma cells displaying residual EGFR activation, this compensatory mechanism becomes necessary to efficiently activate ERK1-2, which could probably contribute to tumor resistance to EGFR inhibitors.

Vascular endothelial growth factor receptor-2: structure, function, intracellular signalling and therapeutic inhibition

Vascular endothelial growth factors (VEGFs) regulate vascular development, angiogenesis and lymphangiogenesis by binding to a number of receptors. VEGFR-1 is required for the recruitment of haematopoietic stem cells and the migration of monocytes and macrophages, VEGFR-2 regulates vascular endothelial function and VEGFR-3 regulates lymphatic endothelial cell function. Over the last decade, considerable progress has been made in delineating the VEGFR-2 specific intracellular signalling cascades leading to proliferation, migration, survival and increased permeability, each of which contributes to the angiogenic response. Furthermore, therapeutic inhibition of VEGFR-2 action is now having an impact in the clinic for the treatment of a number of diseases.

Phosphorylation of tyrosine 801 of vascular endothelial growth factor receptor-2 is necessary for Akt-dependent endothelial nitric-oxide synthase activation and nitric oxide release from endothelial cells

Vascular endothelial growth factor (VEGF)-stimulated nitric oxide (NO) release from endothelial cells is mediated through the activation of VEGF receptor-2 (VEGFR-2). Herein, we have attempted to determine which autophosphorylated tyrosine residue on the VEGFR-2 is essential for VEGF-mediated endothelial nitric-oxide synthase (eNOS) activation and NO production from endothelial cells. Tyrosine residues 801, 1175, and 1214 of the VEGFR-2 were mutated to phenylalanine, and the mutated receptors were analyzed for their ability to stimulate NO production. We show, both in COS-7 cells cotransfected with the VEGFR-2 mutants and eNOS and in bovine aortic endothelial cells, that the Y801F-VEGFR-2 mutant is unable to stimulate NO synthesis and eNOS activation in contrast to the wild type, Y1175F-VEGFR-2, and Y1214F-VEGFR-2. However, the Y801F mutant retains the capacity to activate phospholipase C-gamma in contrast to the Y1175F-VEGFR-2. Interestingly, the Y801F-VEGFR-2, in contrast to the wild type receptor, does not fully activate phosphatidylinositol 3-kinase or recruit the p85 subunit upon receptor activation. This results in a complete incapacity of the Y801F-VEGFR-2 to stimulate Akt activation and eNOS phosphorylation on serine 1179 in endothelial cells. In addition, constitutive activation of Akt or a phosphomimetic mutant of eNOS (S1179D) fully rescues the inability of the Y801F-VEGFR-2 to induce NO release. Finally, we generated an antibody that specifically recognizes the phosphorylated form of tyrosine 801 of the VEGFR-2 and demonstrate that this residue is actively phosphorylated in response to VEGF stimulation of endothelial cells. We thus conclude that autophosphorylation of tyrosine residue 801 of the VEGFR-2 is essential for VEGF-stimulated NO production from endothelial cells, and this is primarily accomplished via the activation of phosphatidylinositol 3-kinase and Akt signaling to eNOS.

The scaffolding adapter Gab1 mediates vascular endothelial growth factor signaling and is required for endothelial cell migration and capillary formation

Vascular endothelial growth factor (VEGF) is involved in the promotion of endothelial cell proliferation, migration, and capillary formation. These activities are mainly mediated by the VEGFR2 receptor tyrosine kinase that upon stimulation, promotes the activation of numerous proteins including phospholipase Cgamma (PLCgamma), phosphatidylinositol 3-kinase (PI3K), Akt, Src, and ERK1/2. However, the VEGFR2-proximal signaling events leading to the activation of these targets remain ill defined. We have identified the Gab1 adapter as a novel tyrosine-phosphorylated protein in VEGF-stimulated cells. In bovine aortic endothelial cells, Gab1 associates with VEGFR2, Grb2, PI3K, SHP2, Shc, and PLCgamma, and its overexpression enhances VEGF-dependent cell migration. Importantly, silencing of Gab1 using small interfering RNAs leads to the impaired activation of PLCgamma, ERK1/2, Src, and Akt; blocks VEGF-induced endothelial cell migration; and perturbs actin reorganization and capillary formation. In addition, co-expression of VEGFR2 with Gab1 mutants unable to bind SHP2 or PI3K in human embryonic kidney 293 cells and bovine aortic endothelial cells mimics the defects observed in Gab1-depleted cells. Our work thus identifies Gab1 as a novel critical regulatory component of endothelial cell migration and capillary formation and reveals its key role in the activation of VEGF-evoked signaling pathways required for angiogenesis.