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SH2 domains are a class of protein–protein interaction modules with the function to recognize and bind sequences characterized by the presence of a phosphorylated tyrosine. SHP2 is a protein phosphatase involved in the Ras‐ERK1/2 signaling pathway that possess two SH2 domains, namely, N‐SH2 and C‐SH2, that mediate the interaction of SHP2 with various partners and determine the regulation of its catalytic activity. One of the main interactors of the SH2 domains of SHP2 is Gab2, a scaffolding protein with critical role in determining cell differentiation. Despite their key biological role and the importance of a correct native fold to ensure it, the mechanism of binding of SH2 domains with their ligands and the determinants of their stability have been poorly characterized. In this article, we present a comprehensive kinetic study of the folding of the C‐SH2 domain and the binding mechanism with a peptide mimicking a region of Gab2. Our data, obtained at different pH and ionic strength conditions and supported by site‐directed mutagenesis, highlight the role of electrostatic interactions in the early events of recognition. Interestingly, our results suggest a key role of a highly conserved histidine residue among SH2 family in the interaction with negative charges carried by the phosphotyrosine of Gab2. Moreover, the analysis of the equilibrium and kinetic folding data of C‐SH2 describes a complex mechanism implying a change in rate‐limiting step at high denaturant concentrations. Our data are discussed under the light of previous works on N‐SH2 domain of SHP2 and other SH2 domains.

Grb2-associated-binding protein-2 (Gab2) is a member of the Gab/DOS family and functions as an adapter protein downstream of several growth factor signaling pathways. Gab2 is considered an Alzheimer's disease susceptibility gene. However, the role of Gab2 in the brain is still largely unknown. Herein, we report that Gab2 is involved in the postnatal development of microglia in mice. The Gab2 expression in the brain was detected at postnatal day 1 (P1) and increased until P14 but decreased thereafter. The tyrosine phosphorylation of Gab2 (pGab2) was also detected at P1 and increased until P14. Next, we focused on microglial development in Gab2 knockout and heterozygous mice. Although differences were not detected in the cytoplasmic area of Iba1-labeled microglia between Gab2(±) and Gab2(-/-) mice, the analysis of CD68 and cathepsin D (indicators of microglial lysosomal activation) immunolabeling within Iba1+ cells revealed significant underdevelopment of microglial lysosomes in Gab2(-/-) mice at P60. In addition to the developmental abnormality of microglia in Gab2(-/-) mice, lipopolysaccharide-induced lysosomal activation was selectively suppressed in Gab2(-/-) mice compared to that in Gab2(±) mice. Our findings suggest that Gab2 is involved not only in postnatal development but also in lysosomal activation of microglia, therefore Gab2 dysfunction in microglia might potentially contribute to the development of neurodegenerative diseases.

The incidence of liver cancer ranks seventh globally, with nearly half of all cases occurring in East Asia, but currently, there are very few drugs to treat it. Our previous studies demonstrated that the signal integration protein Gab2 is a potential drug target for the prevention and therapy of liver cancer. Here, we screened for and identified two miRNAs that target Gab2 to suppress the proliferation and migration of hepatocellular carcinoma (HCC) cells. First, we predicted Gab2-targeting miRNAs through biological websites, and we selected nine miRNAs that were reported in the literature as being abnormally expressed in liver cancer and fatty liver tissue. Then, we measured the expression of these miRNAs in the hepatic epithelial cell line HL-7702 and the HCC cell line HepG2. The expression levels of miR-9, miR-181a, miR-181c, miR-34a, and miR-134 were high in HL-7702 cells but low in HepG2 cells, and their expression patterns were the opposite of Gab2 in these cells. Furthermore, we transfected miR-9, miR-34a, miR-181a, and miR-181c mimics into HepG2 cells and found that only miR-9 and miR-181a reduced the level of Gab2 proteins. miR-9 also reduced the Gab2 mRNA level, but miR-181a did not affect the Gab2 mRNA levels. Using a miRNA-Gab2 3′UTR binding reporter, we confirmed that miR-9 and miR-181a bind to the Gab2 3′UTR region. Finally, we introduced miR-9 and miR-181a mimics into HepG2 cells and found that cell proliferation and migration were significantly inhibited. In conclusion, we identified two novel miRNAs targeting Gab2 and provided potential drug targets for the prevention and treatment of liver cancer.

Hepatic ischemia/reperfusion (I/R) injury (HIRI) often occurs following tissue resection, hemorrhagic shock or transplantation surgery. Previous investigations showed that sevoflurane (Sevo), an inhalation anesthetic, had protective properties against different organ damage in animal models including HIRI. This study is aimed to investigate the underlying mechanisms involved in the protective effects of Sevo on HIRI. The present study results showed that treatment with Sevo improved histologic damage, inflammatory response, oxidative stress and apoptosis after hepatic I/R, indicating the protective role of Sevo against liver I/R injury. Importantly, in order to determine the molecular mechanism of Sevo in HIRI, the focus of the study was on microRNA (miR) regulation. By retrieving the microarray data in the Gene Expression Omnibus dataset ({"type":"entrez-geo","attrs":{"text":"GSE72315","term_id":"72315"}}GSE72315), miR-218-5p was found to be significantly downregulated by Sevo. Moreover, miR-218-5p overexpression using agomiR-218-5p reversed the protective roles of Sevo against HIRI. Furthermore, GAB2, a positive regulator of PI3K/AKT signaling pathway, was found as a target gene of miR-218-5p. It was also found that the Sevo-mediated protective effects may be dependent on the activation of GAB2/PI3K/AKT. Collectively, these data revealed that Sevo alleviated HIRI in mice by restraining apoptosis, relieving oxidative stress and inflammatory response through the miR-218-5p/GAB2/PI3K/AKT pathway, which helps in understanding the novel mechanism of the hepatic-protection of Sevo.

This study is to investigate the effects of imperatorin (IMP) on allergic responses mediated by mast cells, both in vitro and in vivo. Passive cutaneous anaphylaxis (PCA) model was established. Histological detection was performed to assess the ear histology. ELISA and Western blot analysis were used to detect the levels of corresponding cytokines and signalling pathway proteins. IMP decreased the leakage of Evans blue and the ear thickness in the PCA models, in a dose-dependent manner, and alleviated the degranulation of mast cells. Moreover, IMP reduced the expression of TNF-α, IL-4, IL-1β, IL-8, and IL-13. Furthermore, IMP inhibited the phosphorylation levels of Syk, Lyn, PLC-γ1, and Gab2, as well as the downstream MAPK, PI3K/AKT, and NF-κB signaling pathways. In addition, IMP inhibited the mast cell-mediated allergic responses through the Nrf2/HO-1 pathway. IMP attenuates the allergic responses through inhibiting the degranulation and decreasing the expression levels of proinflammatory cytokines in the mast cells, involving the PI3K/Akt, MAPK, NF-κB, and Nrf2/HO-1 pathways.

Objective: To investigate whether miR-125a-5p can inhibit the proliferation and invasion of breast cancer cells and induce apoptosis by targeting GAB2. Methods: qRT-PCR was used to detect the expression of miR-125a-5p in normal mammary epithelial cells and breast cancer cell lines; The miR-125a-5p overexpression plasmid was transiently transfected into MDA-MB-157 cells, and the proliferation, invasion and apoptosis of breast cancer cells were detected by CCK8 kit, Transwell chamber and flow cytometry, respectively; Gene silencing was used to knock down GAB2 gene in MDA-MB-157 cells, and the changes of proliferation, invasion, apoptosis and apoptosis-related proteins in breast cancer cells were detected by CCK8 kit, Transwell chamber, flow cytometry and western blot, respectively; The direct interaction between miR-125a-5p and GAB2 was detected by dual-luciferase reporter assay. The miR-125a-5p overexpression plasmid was transiently transfected into MDA-MB-157 cells, and the expression levels of GAB2 and apoptosis-related proteins were detected by western blot. Results: The expression of miR-125a-5p in breast cancer cell lines, MDA-MB-157 cells, MDA-MB-361 cells and MDA-MB-415 cells, was significantly lower than that in normal breast epithelial cells, MCF-10A cells; The proliferation and invasion ability of MDA-MB-157 cells transfected with miR-125a-5p were significantly inhibited, and the apoptosis rate was significantly increased; Since GAB2 knocked down, the proliferation and invasion ability of MDA-MB-157 cells were significantly inhibited, while the apoptosis rate was significantly increased, the Bax protein expression was significantly down-regulated, and the Bcl-2 protein expression was significantly up-regulated; The dual-luciferase reporter assay demonstrated that miR-125a-5p can specifically target GAB2. Transfected with miR-125a-5p, the GAB2 protein expression and Bax protein expression were significantly down-regulated, but the Bcl-2 protein expression was significantly up-regulated. Conclusion: miR-125a-5p inhibits the proliferation and invasion of breast cancer cells and induces their apoptosis by negatively regulating GAB2.

Obesity is caused by a long-term imbalance between energy intake and consumption and is regulated by multiple signals. This study investigated the effect of signaling scaffolding protein Gab2 on obesity and its relevant regulation mechanism. Gab2 knockout (KO) and wild-type (WT) mice were fed with a standard diet (SD) or high-fat diet (HFD) for 12 weeks. The results showed that the a high-fat diet-induced Gab2 expression in adipose tissues, but deletion of Gab2 attenuated weight gain and improved glucose tolerance in mice fed with a high-fat diet. White adipose tissue and systemic inflammations were reduced in HFD-fed Gab2 deficiency mice. Gab2 deficiency increased the expression of Ucp1 and other thermogenic genes in brown adipose tissue. Furthermore, the regulation of Gab2 on the mature differentiation and function of adipocytes was investigated in vitro using primary or immortalized brown preadipocytes. The expression of brown fat-selective genes was found to be elevated in differentiated adipocytes without Gab2. The mechanism of Gab2 regulating Ucp1 expression in brown adipocytes involved with its downstream PI3K (p85)-Akt-FoxO1 signaling pathway. Our research suggests that deletion of Gab2 suppresses diet-induced obesity by multiple pathways and Gab2 may be a novel therapeutic target for the treatment of obesity and associated complications.

Protein functional interactions could explain the biological response of secoiridoids (SECs), main phenolic compounds in virgin olive oil (VOO). The aim was to assess protein¿protein interactions (PPIs) of the aorta gap junction alpha-1 (GJA1) and the heart peptidyl-prolyl cis-trans isomerase (FKBP1A), plus the phosphorylated heart proteome, to describe new molecular pathways in the cardiovascular system in rats using nanoliquid chromatography coupled with mass spectrometry. PPIs modified by SECs and associated with GJA1 in aorta rat tissue were calpain, TUBA1A, and HSPB1. Those associated with FKBP1A in rat heart tissue included SUCLG1, HSPE1, and TNNI3. In the heart, SECs modulated the phosphoproteome through the main canonical pathways PI3K/mTOR signaling (AKT1S1 and GAB2) and gap junction signaling (GAB2 and GJA1). PPIs associated with GJA1 and with FKBP1A, the phosphorylation of GAB2, and the dephosphorylation of GJA1 and AKT1S1 in rat tissues are promising protein targets promoting cardiovascular protection to explain the health benefits of VOO., The work summarized in this paper was supported in part by grants (grant nos. MEFOPC Project, AGL2012-40144-C03-02 and AGL2012-40144-C03-03, and AppleCOR Project, AGL2016-76943-C2-2-R) from the Ministerio de Economía, Industria y Competitividad, the Agencia Estatal de Investigación (AEI), and the European Regional Development Fund (ERDF). L.R. is supported by a Sara Borrell postdoctoral grant (CD14/00275; Spain), A.P. is supported by a postdoctoral grant (PTQ-15-08068; Spain), and Ú.C. is supported by a Pla Estratègic de Recerca i Innovació en Salut (PERIS) postdoctoral grant (SLT002/16/00239; Catalunya, Spain).

The present study investigates the anti-allergic activity of the marine algal bromophenol, 3-bromo-4,5-dihydroxybenzaldehyde (BDB), isolated from Polysiphonia morrowii Harvey in immunoglobulin (Ig)E/bovine serum albumin (BSA)-stimulated mouse bone marrow-derived cultured mast cells (BMCMCs) and a passive cutaneous anaphylaxis (PCA) mice ear model. BDB effectively inhibited β-hexosaminidase release (IC50 = 80.12 µM), in IgE/BSA-stimulated BMCMCs without a cytotoxic response. Also, BDB down-regulated the expression or secretion of cytokines, interleukin (IL)-1β, IL-4, IL-5, IL-6, IL-10, IL-13, interferon (IFN)-γ, and tumor necrosis factor (TNF)-α and the chemokine (thymus and activation-regulated chemokine (TARC). The above effects could be attributed to the dose-dependent decrease of FceRI expression on the surface of BMCMCs and its stable IgE binding. Moreover, BDB suppressed the nuclear factor (NF)-κB and spleen tyrosine kinase (SYK)-linker for T-cell activation (LAT)-GRB2 associated binding protein 2 (Gab2) signaling axis activated by IgE/BSA stimulation. Furthermore, oral administration of BDB to IgE-sensitized mice effectively attenuated IgE-triggered PCA reaction. Collectively, the anti-allergic effects of BDB suggest its potential applicability as a candidate for in-depth test trials.

Granulocyte colony-stimulating factor (G-CSF) stimulation of myeloid cells induced tyrosine-phosphorylation of cellular proteins. One of the tyrosine-phosphorylated proteins was found to be a scaffold protein, Grb2-associated binding protein 2 (Gab2). Another member of Gab family protein, Gab3, was exogenously overexpressed in neutrophil progenitor cells to make the Gab3 protein to compete with the endogenous Gab2 for the G-CSF-dependent signaling. In Gab3-overexpressed cells, the level of tyrosine phosphorylation of endogenous Gab2 by G-CSF stimulation was markedly downregulated, while the phosphorylation of Gab3 was significantly enhanced. The Gab3-overexpressed cells continuously proliferated in the medium containing G-CSF and lost the ability to differentiate to the mature neutrophil, characterized by the lobulated nucleus. The G-CSF stimulation-dependent tyrosine phosphorylation of Gab3, the association of SHP2 to Gab3 and the following mitogen-activated protein kinase (MAPK) activation were prolonged in the Gab3-overexpressed cells, compared to the parental cells, where the binding of SHP2 to Gab2 protein and thereby the activation of MAPK were not sustained after G-CSF stimulation. Inhibition of MAPK by pharmaceutical inhibitor restored the Gab3-overexpressed cells to the ability to differentiate to mature neutrophil. Therefore, G-CSF-dependent Gab2 phosphorylation and following its downregulation led the short-term MAPK activation. The downregulation of MAPK after transient Gab2 phosphorylation was necessary for the consequent neutrophil differentiation induced by G-CSF stimulation.

Thymol was identified as one of key compounds contributing to the aroma of thyme leaves. We investigated the effects of thymol on receptor activator NF-κB ligand (RANKL)-induced osteoclastogenesis in murine macrophage RAW264.7 cells and bone marrow derived macrophage (BMMs) cells and lipopolysaccharide (LPS)-induced bone loss in vivo. Thymol markedly reduced RANKL-stimulated osteoclast formation and differentiation in RAW264.7 cells and BMMs cells without any cytotoxic effects. The in vitro and in vivo osteoclastogenesis inhibitory effect of thymol was assessed by calculating the quantity of TRAP (+) multinucleated cells and its inhibitory effects on the resorbing capacity were examined on calcium phosphate-coated plates. Moreover, the inhibitory effects of thymol resulted in a reduction of RANK, cathepsin K, matrix metalloproteinase-9 (MMP-9), dendritic cell-specific transmembrane protein (DC-STAMP), c-terminal myc kinase (C-MYC), C-terminal Src kinase (C-SRC), GRB2-associated-binding protein 2 (GAB2), microphthalmia-associated transcription factor (MITF), and carbonic anhydrase II genes. Similarly, activities of ERK, JNK and AKT and protein expressions of NFATc1, C-FOS, MMP-9 and cathepsin K were downregulated by thymol. More importantly, the application of thymol significantly reduced LPS-induced inflammatory bone loss in mice. In conclusion, these findings identified that thymol could be a useful therapeutic agent for the prevention of bone destructive diseases.

Background The functionality of lncRNA snaR has only been characterized in breast cancer and colon cancer. The aim of the current study is to explore the involvement of lncRNA snaR in ovarian carcinoma (OC). Materials and methods Expression of lncRNA snaR and GRB2-associated binding protein 2 (GAB2) in plasma of both patients with OC and healthy females was detected by qRT-PCR. Application value of plasma lncRNA snaR in the diagnosis of OC was evaluated by ROC analysis. Correlation between plasma lncRNA snaR and GAB2 was analyzed by Pearson correlation coefficient. LncRNA snaR and GAB2 expression vectors as well as GAB2 siRNA were transfected into cells of human OC cell lines, and the effect on lncRNA snaR expression, GAB2 expression and cell proliferation was detected by qRT-PCR, western blot and CCK-8 assay. Results It was observed that plasma levels of lncRNA snaR and GAB2 were significantly higher in OC patients than those in healthy controls. In effect, high levels of plasma lncRNA snaR and GAB2 distinguished OC patients from healthy controls. Plasma lncRNA snaR and GAB2 were positively correlated in OC patients but not in healthy controls. LncRNA snaR overexpression promoted cancer cell proliferation and upregulated GAB2 expression. Conclusions GAB2 overexpression also promoted cancer cell proliferation but showed no significant effects on lncRNA snaR expression, while GAB2 siRNA silencing significantly attenuated the enhancing effects of lncRNA snaR overexpression on cancer cell proliferation. LncRNA snaR may promote proliferation of ovarian carcinoma cells by upregulating GAB2 expression.

The receptor activator of nuclear factor-κB (RANK) protein activates various protein kinase signaling cascades, including those involving NF-κB, mitogen-activated protein kinase (MAPK), and Bruton tyrosine kinase (Btk)/tyrosine-protein kinase Tec. However, the mechanism underlying the negative regulation of RANK by downstream signaling molecules remains unclear. Here, we report that Src homology 3 domain and cysteine-rich domain-containing protein 2 (STAC2) is a novel RANK ligand-inducible protein that negatively regulates RANK-mediated osteoclast formation. STAC2 physically interacts with RANK and inhibits the formation of the RANK signaling complex, which contains Grb-2-associated binder 2 (Gab2) and phospholipase Cγ2 (PLCγ2), thus leading to the suppression of RANK-mediated NF-κB and MAPK activation. Furthermore, STAC2 overexpression limits Btk/Tec-mediated PLCγ2 phosphorylation via the interaction between STAC2 and Btk/Tec. Taken together, our results reveal a novel mechanism whereby RANK signaling is restricted by its physical interaction with STAC2.

Background/Aims: HER2 has been implicated in mammary tumorigenesis as well as aggressive tumor growth and metastasis. Its overexpression is related to a poor prognosis and chemoresistance in breast cancer patients. Although Grb2-associated binding protein 2 (Gab2) is important in the development and progression of human cancer, its effects and mechanisms in HER2-overexpressing breast cancer are unclear. Methods: Clone formation and MTT assays were used to examine cell proliferation. To detect the effect of Gab2 on the stemness of breast cancer cells, we used flow cytometry, a sphere formation assay, real-time PCR, and western blot. An animal model was created to validate the effect of Gab2 on tumor growth in vivo. Tissue slides were analyzed by immunohistochemistry. Results: Knockdown of Gab2 suppressed PI3K/AKT and MAPK/ERK pathway activity. Gab2 ablation also reduced the stemness of HER2-overexpressing breast cancer cells. In vivo, knockdown of Gab2 inhibited tumor growth. Conclusion: This study unveils a potential function of Gab2 in HER2-overexpressing breast cancer cells. Gab2 might be a potential target in the clinical therapy of HER2-overexpressing breast carcinoma.

1,7-bis(4-hydroxy-3-methoxyphenyl)heptane-3,5-dione (tetrahydrocurcumin, THC) is a major bioactive metabolite of curcumin, demonstrating the potential anti-inflammatory, antioxidant and neuroprotective properties, etc. In this study, it was found that Aβ induced decreased cell viability, cell cycle arrest and apoptosis in BV-2 cells, which were ameliorated by THC. In vivo, THC administration rescued learning and memory, and reduced Aβ burden in the hippocampus of APP/PS1 mice. By proteomic analysis of the hippocampus of mice, 157 differentially expressed proteins were identified in APP/PS1 mice treated with THC (comparing with APP/PS1 mice), which also suggested that the effects of THC on the cell cycle and apoptosis were mostly related to the “Ras signaling pathway”, etc. In APP/PS1 mice, the down-regulation of Gab2 and K-Ras, and the up-regulation of caspase-3, TGF-β1 and TNF-ɑ were observed; THC attenuated the abnormal expression of Gab2, K-Ras, caspase-3 and TNF-ɑ, and up-regulated TGF-β1 and Bag1 expression. In BV-2 cells, Aβ induced the down-regulation of Gab2, K-Ras and TGF-β1, and the overexpression of caspase-3, PARP1, cleaved-PARP1 and TNF-ɑ, which were restored by THC. Moreover, THC up-regulated Bag1 expression in Aβ-treated BV-2 cells. The decreased transcriptional expression of Ccnd2 and Cdkn1a were also observed in Aβ-treated BV-2 cells, and THC alleviated the down-regulation of Ccnd2. For the first time, we identified that the action of THC in preventing AD was associated with inhibition of cell cycle arrest and apoptosis of microglia via the Ras/ERK signaling pathway, shedding new light on the role of THC in alleviating the progression of AD.

BCR-ABL1-targeting tyrosine kinase inhibitors (TKIs) have revolutionized treatment of Philadelphia chromosome-positive (Ph+) hematologic neoplasms. Nevertheless, acquired TKI resistance remains a major problem in chronic myeloid leukemia (CML), and TKIs are less effective against Ph+ B-cell acute lymphoblastic leukemia (B-ALL). GAB2, a scaffolding adaptor that binds and activates SHP2, is essential for leukemogenesis by BCR-ABL1, and a GAB2 mutant lacking SHP2 binding cannot mediate leukemogenesis. Using a genetic loss-of-function approach and bone marrow transplantation models for CML and BCR-ABL1+ B-ALL, we show that SHP2 is required for BCR-ABL1-evoked myeloid and lymphoid neoplasia. Ptpn11 deletion impairs initiation and maintenance of CML-like myeloproliferative neoplasm, and compromises induction of BCR-ABL1+ B-ALL. SHP2, and specifically, its SH2 domains, PTP activity and C-terminal tyrosines, are essential for BCR-ABL1+, but not WT, pre-B-cell proliferation. The mitogen-activated protein kinase kinase (MEK) / extracellular signal-regulated kinase (ERK) pathway is regulated by SHP2 in WT and BCR-ABL1+ pre-B cells, but is only required for the proliferation of BCR-ABL1+ cells. SHP2 is required for SRC family kinase (SFK) activation only in BCR-ABL1+ pre-B cells. RNAseq reveals distinct SHP2-dependent transcriptional programs in BCR-ABL1+ and WT pre-B cells. Our results suggest that SHP2, via SFKs and ERK, represses MXD3/4 to facilitate a MYC-dependent proliferation program in BCR-ABL1-transformed pre-B cells.

Uveal melanoma (UM) is characterized by high metastasis and poor prognosis. A more improved understanding of the metastatic mechanism in UM cells is essential for the design of molecular therapy. Grb2-associated binder 2 (Gab2) has been reported to serve important roles in the progression of various types of human cancer. However, the role of Gab2 in the migration and invasion of UM remains unclear. The present study sought to further assess the expression of Gab2 in UM and the role of Gab2 in the invasion of UM cells. Clinical UM tissue samples and UM cell lines were analyzed using western blot analysis for the expression of Gab2. RNA interference was used to investigate the effect of Gab2 on the migratory and invasive characteristics of UM cells in vitro. The expression levels of matrix metalloproteinase (MMP)2, MMP9 and fascin in Gab2-knockdown, and control cells were also detected using western blot analysis. A total of 20 clinical UM samples and a subset of UM cell lines were investigated with uniformly high Gab2 expression. In the in vitro experiment, reduction of Gab2 using small interfering RNA inhibited the migration and invasion of UM cells by mediating MMPs, and fascin expression. These data suggest that Gab2 is a useful prognostic marker for UM and a novel therapeutic target for UM metastasis intervention.

// Angelo Toto 1 , Daniela Bonetti 1 , Alfonso De Simone 2 and Stefano Gianni 1 1 Istituto Pasteur - Fondazione Cenci Bolognetti, Dipartimento di Scienze Biochimiche “A. Rossi Fanelli” and Istituto di Biologia e Patologia Molecolari del CNR, Sapienza Universita di Roma, 00185, Rome, Italy 2 Department of Life Sciences, Imperial College London, SW7 2AZ, London, UK Correspondence to: Stefano Gianni, email: stefano.gianni@uniroma1.it Keywords: binding kinetics, folding, induced fit, intrinsically disordered proteins, mutagenesis Received: May 10, 2017 Accepted: June 20, 2017 Published: July 18, 2017 ABSTRACT Gab2 is a large disordered protein that regulates several cellular signalling pathways and is overexpressed in different forms of cancer. Because of its disordered nature, a detailed characterization of the mechanisms of recognition between Gab2 and its physiological partners is particularly difficult. Here we provide a detailed kinetic characterization of the binding reaction between Gab2 and the C-terminal SH3 domain of the growth factor receptor-bound protein 2 (Grb2). We demonstrate that Gab2 folds upon binding following an induced fit type mechanism, whereby recognition is characterized by the formation of an intermediate, in which Gab2 is primarily disordered. In this scenario, folding of Gab2 into the bound conformation occurs only after binding. However, an alanine scanning of the proline residues of Gab2 suggests that the intermediate contains some degree of native-like structure, which might play a role for the recognition event to take place. The results, which represent a fundamental step forward in the understanding of this functional protein-protein interaction, are discussed on the light of previous structural works on these proteins.

Growing evidence suggests a major role for Src-homology-2-domain-containing phosphatase 2 (SHP2/PTPN11) in MYCN-driven high-risk neuroblastoma, although biologic confirmation and a plausible mechanism for this contribution are lacking. Using a zebrafish model of MYCN-overexpressing neuroblastoma, we demonstrate that mutant ptpn11 expression in the adrenal gland analog of MYCN transgenic fish promotes the proliferation of hyperplastic neuroblasts, accelerates neuroblastomagenesis, and increases tumor penetrance. We identify a similar mechanism in tumors with wild-type ptpn11 and dysregulated Gab2, which encodes a Shp2 activator that is overexpressed in human neuroblastomas. In MYCN transgenic fish, Gab2 overexpression activated the Shp2-Ras-Erk pathway, enhanced neuroblastoma induction, and increased tumor penetrance. We conclude that MYCN cooperates with either GAB2-activated or mutant SHP2 in human neuroblastomagenesis. Our findings further suggest that combined inhibition of MYCN and the SHP2-RAS-ERK pathway could provide effective targeted therapy for high-risk neuroblastoma patients with MYCN amplification and aberrant SHP2 activation.

Activating mutations, such as E76K and D61Y, in PTPN11 (SHP2), a protein tyrosine phosphatase implicated in multiple cell signaling processes, are associated with 35% of patients with juvenile myelomonocytic leukemia (JMML), an aggressive childhood myeloproliferative neoplasm (MPN). Effective therapeutic interventions for this malignancy are still lacking. Here we show that the interaction between leukemia-associated mutant Shp2 and Gab2, a scaffolding protein important for cytokine-induced PI3K/Akt signaling, was enhanced, and that the mTOR pathway was elevated in Ptpn11E76K/+ leukemic cells. Importantly, MPN induced by the Ptpn11E76K/+ mutation was markedly attenuated in Ptpn11E76K/+/Gab2−/− double mutant mice — Overproduction of myeloid cells was alleviated, splenomegaly was diminished, and myeloid cell infiltration in non-hematopoietic organs was decreased in these double mutants. Excessive myeloid differentiation of stem cells was also normalized by depletion of Gab2. Acute leukemia progression of MPN was reduced in the double mutant mice, and as such, their survival was much prolonged. Furthermore, treatment of Ptpn11E76K/+ mice with Rapamycin, a specific and potent mTOR inhibitor, mitigated MPN phenotypes. Collectively, this study reveals an important role of the Gab2/PI3K/mTOR pathway in mediating the pathogenic signaling of the PTPN11 gain-of-function mutations, and a therapeutic potential of Rapamycin for PTPN11 mutation-associated JMML.

High hyperdiploidy (HD) is the most common cytogenetic subtype of childhood acute lymphoblastic leukemia (ALL), and a higher incidence of HD has been reported in ALL patients with congenital cancer syndromes. We assessed the frequency of predisposing germline mutations in 57 HD-ALL patients from the California Childhood Leukemia Study via targeted sequencing of cancer-relevant genes. Three out of 57 patients (5.3%) harbored confirmed germline mutations that were likely causal, in NBN, ETV6, and FLT3, with an additional six patients (10.5%) harboring putative predisposing mutations that were rare in unselected individuals (

Copy number loss of PIK3R1 (p85α) most commonly occurs in ovarian cancer among all cancer types. Here we report that ovarian cancer cells manifest a spectrum of tumorigenic phenotypes upon knockdown of PIK3R1. PIK3R1 loss activates AKT and p110-independent JAK2/STAT3 signaling through inducing changes in the phosphorylation of the docking protein Gab2, thereby relieving the negative inhibition on AKT and promoting the assembly of JAK2/STAT3 signalosome, respectively. Additional mechanisms leading to AKT activation include enhanced p110α kinase activity and a decrease in PTEN level. PIK3R1 loss renders ovarian cancer cells vulnerable to inhibition of AKT or JAK2/STAT3. The combination of AKT and STAT3 inhibitors significantly increases the anti-tumor effect compared to single-agent treatments. Together, our findings provide a rationale for mechanism-based therapeutic approach that targets tumors with loss of PIK3R1., Loss of PIK3R1 in ovarian cancer is a common event, which provides opportunities for therapeutic intervention. Here, the authors show that the STAT3 and AKT signaling pathways are activated upon PIK3R1 loss and that, in mice, inhibitors of these pathways could block tumorigenesis.

Gab2 is essential for Bcr-Abl-mediated leukemic transformation and hydronephrosis in a chronic myeloid leukemia mouse model

Grb2-associated binding protein 2 (GAB2), a key member of the family of Gab scaffolding adaptors, is important in the phospoinositide3-kinase (PI3K) and extracellular signal-regulated kinase (ERK) signaling pathways, and is closely associated with cell proliferation, cell transformation, and tumor progression. But its role in hepatocellular carcinoma (HCC) is still unknown. In this study, we investigated the expression of GAB2 and its potential clinical and biological significances in HCC. Western bolt and immunohistochemistrical analyses revealed that GAB2 was obviously upregulated in HCC tissues. Meanwhile, GAB2 was significantly associated with histological grade, tumor size, and the proliferation marker Ki-67 through our further analysis. The Kaplan-Meier survival curves also showed that increased GAB2 expression was directly correlated with poor prognosis in HCC patients and served as an independent prognostic marker of overall survival. Moreover, serum starvation-refeeding, RNA interference, CCK-8, EDU, colony formation, and flow-cytometry analyses were all performed with the purpose of investigating GAB2's regulation of HCC cell proliferation. Our results indicated that GAB2 progressively accumulated when cells entered into S phase. Consistently, cell proliferation was distinctly hindered by small interfering RNA. More interestingly, we discovered that GAB2 promoted cell proliferation by enhancing ERK signaling and GAB2-induced cell proliferation was inhibited by the inhibition of ERK activation. Finally, GAB2 was verified to be able to confer doxorubicin resistance in HCC cells. In summary, these data demonstrated that GAB2 might promote HCC cell proliferation by enhancing ERK signaling, and all above findings provided a potential therapeutic strategy for the treatment of HCC.

Gab2 is a scaffold protein with a crucial role in colocalizing signaling proteins and it is involved in the regulation of several important molecular pathways. SHP2 is a protein phosphatase that binds, through its two SH2 domains, specific consensus sequences presenting a phosphorylated tyrosine located on the disordered tail of Gab2. To shed light on the details of such a fundamental interaction for the physiology of the cell, we present a complete mutational analysis of the kinetics of binding between the N-SH2 domain of SHP2 and a peptide mimicking a specific region of Gab2. By analyzing kinetic data, we determined structural features of the transition state of the N-SH2 domain binding to Gab2, highlighting a remarkable cooperativity of the binding reaction. Furthermore, comparison of these data with ones previously obtained for another SH2 domain suggests the presence of underlying general features characterizing the binding process of SH2 domains. Data are discussed under the light of previous works on SH2 domains.

The receptor tyrosine kinase FLT3 is expressed almost exclusively in the hematopoietic compartment. Binding of its ligand, FLT3 ligand (FL), induces dimerization and activation of its intrinsic tyrosine kinase activity. This leads to autophosphorylation of FLT3 on several tyrosine residues which constitute high affinity binding sites for signal transduction molecules. Recruitment of these signal transduction molecules to FLT3 leads to the activation of several signal transduction pathways that regulate cell survival, cell proliferation and differentiation. Oncogenic, constitutively active mutants of FLT3 are known to be expressed in acute myeloid leukemia and to correlate with poor prognosis. Activation of the receptor mediates cell survival, cell proliferation and differentiation of cells. Several of the signal transduction pathways downstream of FLT3 have been shown to include various members of the SRC family of kinases (SFKs). They are involved in regulating the activity of RAS/ERK pathways through the scaffolding protein GAB2 and the adaptor protein SHC. They are also involved in negative regulation of signaling through phosphorylation of the ubiquitin E3 ligase CBL. Initially studied as the SFKs, as if they were a homogenous group of kinases, recent data suggest that each SFK has its own specific signaling capabilities where some are involved in positive signaling, while others are involved in negative signaling. This review discusses some recent insights into how SFKs are involved in FLT3 signaling.

The signaling cascades triggered by the cross-linkage of immunoglobulin E (IgE) with its high-affinity receptor (FceRI) on mast cells contribute to multiple allergic disorders, such as asthma, rhinitis, and atopic dermatitis. Restraint of intracellular signals for mast cell activation is essential to restore homeostasis. In this study, we found that Raf kinase inhibitor protein (RKIP) negatively regulated mast cell activation. RKIP-deficient mast cells showed greater IgE−FceRI-mediated activation than wild-type mast cells. Consistently, RKIP deficiency in mast cells rendered mice more sensitive to IgE−FceRI-mediated allergic responses and ovalbumin-induced airway inflammation. Mechanistically, RKIP interacts with the p85 subunit of PI3K, prevents it from binding to GRB2-associated binding protein 2 (Gab2), and eventually inhibits the activation of the PI3K/Akt/NF-κB complex and its downstream signaling. Furthermore, the expression of RKIP was significantly down-regulated in the peripheral blood of asthma patients and in the IgE−FceRI-stimulated mast cells. Collectively, our findings not only suggest that RKIP plays an important role in controlling mast cell-mediated allergic responses but also provide insight into therapeutic targets for mast cell-related allergic diseases.

The cell-autonomous circadian clock regulates IgE- and IL-33-mediated mast cell activation, both of which are key events in the development of allergic diseases. Accordingly, clock modifiers could be used to treat allergic diseases, as well as many other circadian-related diseases, such as sleep and metabolic disorders. The nuclear receptors REV-ERB-&alpha, and -&beta, (REV-ERBs) are crucial components of the circadian clockwork. Efforts to pharmacologically target REV-ERBs using putatively specific synthetic agonists, particularly SR9009, have yielded beneficial effects on sleep and metabolism. Here, we sought to determine whether REV-ERBs are functional in the circadian clockwork in mast cells and, if so, whether SR9009 affects IgE- and IL-33-mediated mast cell activation. Bone marrow-derived mast cells (BMMCs) obtained from wild-type mice expressed REV-ERBs, and SR9009 or other synthetic REV-ERBs agonists affected the mast cell clockwork. SR9009 inhibited IgE- and IL-33-mediated mast cell activation in wild-type BMMCs in association with inhibition of Gab2/PI3K and NF-&kappa, B activation. Unexpectedly, these suppressive effects of SR9009 were observed in BMMCs following mutation of the core circadian gene Clock. These findings suggest that SR9009 inhibits IgE- and IL-33-mediated mast cell activation independently of the functional circadian clock activity. Thus, SR9009 or other synthetic REV-ERB agonists may have potential for anti-allergic agents.

FLT3-ITD is the most frequent tyrosine kinase mutation in acute myeloid leukemia (AML) associated with poor prognosis. We previously found that FLT3-ITD activates the mTORC1/S6K/4EBP1 pathway cooperatively through the STAT5/PIM and PI3K/AKT pathways to promote proliferation and survival by enhancing the eIF4F complex formation required for cap-dependent translation. Here, we show that, in contrast to BCR/ABL causing Ph-positive leukemias, FLT3-ITD distinctively activates the serine/threonine kinases RSK1/2 through activation of the MEK/ERK pathway and PDK1 to transduce signals required for FLT3-ITD-dependent, but not BCR/ABL-dependent, proliferation and survival of various cells, including MV4-11. Activation of the MEK/ERK pathway by FLT3-ITD and its negative feedback regulation by RSK were mediated by Gab2/SHP2 interaction. RSK1 phosphorylated S6RP on S235/S236, TSC2 on S1798, and eIF4B on S422 and, in cooperation with PIM, on S406, thus activating the mTORC1/S6K/4EBP1 pathway and eIF4B cooperatively with PIM. RSK1 also phosphorylated Bad on S75 and downregulated BIM-EL in cooperation with ERK. Furthermore, inhibition of RSK1 increased sensitivities to BH3 mimetics inhibiting Mcl-1 or Bcl-2 and induced activation of Bax, leading to apoptosis, as well as inhibition of proliferation synergistically with inhibition of PIM or PI3K. Thus, RSK1 represents a promising target, particularly in combination with PIM or PI3K, as well as anti-apoptotic Bcl-2 family members, for novel therapeutic strategies against therapy-resistant FLT3-ITD-positive AML.

Signal transduction pathways activated by receptor tyrosine kinases (RTK) play a critical role in many aspects of cell function. Adaptor proteins serve an important scaffolding function that facilitates key signaling transduction events downstream of RTKs. Recent work integrating both structural and functional genomic approaches has identified several adaptor proteins as new oncogenes. In this review, we focus on the discovery, structure and function, and therapeutic implication of three of these adaptor oncogenes, CRKL, GAB2, and FRS2. Each of the three genes is recurrently amplified in lung adenocarcinoma or ovarian cancer, and is essential to cancer cell lines that harbor such amplification. Overexpression of each gene is able to transform immortalized human cell lines in in vitro or in vivo models. These observations identify adaptor protein as a distinct class of oncogenes and potential therapeutic targets.

Poor prognosis of glioma is due to the characteristics of high invasiveness. Recently, it was demonstrated that Gab2 was over-expressed and related to cellular migration and invasion in glioma, however, the mechanisms of regulation are still unknown. A better understanding of molecular events key to the carcinogenesis and tumor progression may facilitate development of new therapeutic targets and anti-glioma strategies. This study is the first to focus on miR125a-5p, which was predicted to regulate Gab2 with directly targeting the 3' un-translated region (3'UTR) of Gab2 and could inhibit migration and invasion of glioma cells by mediating Gab2 to affect cytoskeleton rearrangement and matrix metalloproteinases expression. Interestingly, further evaluation revealed that the miR125a-5p promoter was hypermethylated and that attenuating promoter methylation was sufficient to up-regulate miR125a-5p expression in glioma cells. Additionally, we reported that miR125a-5p was down-regulated in glioma as well as statistical analysis suggested that its expression level correlated with the World Health Organization grades of glioma (P < 0.05) and that patients with a low miR125a-5p level exhibited shorter survival time (P < 0.05). Taken together, these results reveal that miR125a-5p represents potential therapeutic targets in glioma by modulating Gab2.

BCR-ABL1-targeting tyrosine kinase inhibitors (TKIs) have revolutionized treatment of Philadelphia chromosome-positive (Ph+) hematologic neoplasms. Nevertheless, acquired TKI resistance remains a major problem in chronic myeloid leukemia (CML), and TKIs are less effective against Ph+B-cell acute lymphoblastic leukemia (B-ALL). GAB2, a scaffolding adaptor that binds and activates SHP2, is essential for leukemogenesis by BCR-ABL1, and a GAB2 mutant lacking SHP2 binding cannot mediate leukemogenesis. Using a genetic loss-of-function approach and bone marrow transplantation (BMT) models for CML and BCR-ABL1+B-ALL, we show that SHP2 is required for BCR-ABL1-evoked myeloid and lymphoid neoplasia.Ptpn11deletion impairs initiation and maintenance of CML-like myeloproliferative neoplasm, and compromises induction of BCR-ABL1+B-ALL. SHP2, and specifically, its SH2 domains, PTP activity and C-terminal tyrosines, is essential for BCR-ABL1+, but not WT, pre-B cell proliferation. The MEK/ERK pathway is regulated by SHP2 in WT and BCR-ABL1+pre-B cells, but is only required for the proliferation of BCR-ABL1+cells. SHP2 is required for SRC family kinase (SFK) activation only in BCR-ABL1+pre-B cells. RNAseq reveals distinct SHP2-dependent transcriptional programs in BCR-ABL1+and WT pre-B cells. Our results suggest that SHP2, via SFKs and ERK, repressesMXD3/4to facilitate a MYC-dependent proliferation program in BCR-ABL1-transformed pre-B cells.

Recent studies indicated that the scaffolding adaptor protein GAB2 (GRB2-associated binding protein 2) plays a critical role in the proliferation and migration of various cancers. This study aimed to determine the role of aberrant GAB2 expression in human colorectal cancer (CRC). Quantitative real-time reverse transcription polymerase chain reaction was used to evaluate GAB2 mRNA expression in 152 CRC tissues samples to determine the clinicopathological significance of GAB2 expression. We also performed in vitro proliferation assays using siGAB2-transfected CRC cells. GAB2 expression in tumor colorectal tissues was significantly higher than in normal colorectal tissues (p = 0.0212). High GAB2 expression levels were associated with malignant clinicopathologic potential factors, including lymphatic invasion (p = 0.0003), venous invasion (p = 0.0170), and liver metastasis (p = 0.0144). The survival rate of patients with high GAB2 expression levels was significantly lower than that of patients with low GAB2 expression (p = 0.0074). Multivariate analysis indicated that GAB2 expression was a factor affecting lymph node metastasis. Cell proliferation was significantly suppressed by siGAB2 expression in CRC cells in vitro. GAB2 expression was associated with lymph node metastasis and may play a role in the growth and metastasis of CRC. These results suggest that GAB2 is a potential therapeutic target in CRC.

Erythroid homoeostasis is primarily controlled by Epo (erythropoietin) receptor signalling; however, the Lyn tyrosine kinase plays an important subsidiary role in regulating the erythroid compartment. Nonetheless, specific erythroid pathways that require Lyn activity and their biological significance remain unclear. To address this, we asked what consequence loss of Lyn had on the ex vivo expansion and maturation of splenic erythroid progenitors and Epo receptor signalling. Pharmacological inhibition of Lyn with PP2 inhibited the survival of terminally differentiated erythroblasts. Less committed erythroid progenitors expanded well, whereas early splenic Lyn−/− erythroblasts had attenuated ex vivo expansion, and late stage Lyn−/− erythroblasts were retarded in completing morphological maturation ex vivo. Furthermore, immortalized Lyn−/− erythroblasts were slower growing, less viable and inhibited in their differentiation. Signalling studies showed that Lyn was required for both positive GAB2/Akt/FoxO3 (forkhead box O3) survival signals as well as negative feedback of JAK2 (Janus kinase 2)/STAT5 (signal transducer and activator of transcription 5) and ERK1/2 (extracellular-signal-regulated kinase 1/2) signals via SHP-1 (Src homology 2 domain-containing protein tyrosine phosphatase 1). During differentiation, Lyn controls survival and cell cycle exit as demonstrated by reduced STAT5 and FoxO3/GSKα/β (glycogen synthase kinase α/β) phosphorylation and diminished p27Kip1 induction in Lyn-deficient erythroblasts. Lyn deficiency alters the balance of pro- and anti-apoptotic molecules (BAD and BclXL), thereby reducing survival and preventing cell cycle exit. Consequently, Lyn facilitates normal erythrocyte production by influencing different stages of erythroid progenitor expansion, and mature cell development and survival signalling.

Coxsackievirus type B3 (CV-B3), an enterovirus associated with the pathogenesis of several human diseases, subverts, or employs the host intracellular signaling pathways to support effective viral infection. We have previously demonstrated that Grb2-associated binding protein 1 (GAB1), a signaling adaptor protein that serves as a platform for intracellular signaling assembly and transduction, is cleaved upon CV-B3 infection, resulting in a gain-of-pro-viral-function via the modification of GAB1-mediated ERK1/2 pathway. GAB2 is a mammalian homolog of GAB1. In this study, we aim to address whether GAB2 plays a synergistic role with GAB1 in the regulation of CV-B3 replication. Here, we reported that GAB2 is also a target of CV-B3-encoded viral proteinase. We showed that GAB2 is cleaved at G238 during CV-B3 infection by viral proteinase 2A, generating two cleaved fragments of GAB2-N1−237 and GAB2-C238−676. Moreover, knockdown of GAB2 significantly inhibits the synthesis of viral protein and subsequent viral progeny production, accompanied by reduced levels of phosphorylated p38, suggesting a pro-viral function for GAB2 linked to p38 activation. Finally, we examined whether the cleavage of GAB2 can promote viral replication as observed for GAB1 cleavage. We showed that expression of neither GAB2-N1−237 nor GAB2-C238−676 results in enhanced viral infectivity, indicating a loss-of-function, rather than a gain-of-function of GAB2 cleavage in mediating virus replication. Taken together, our findings in this study suggest a novel host defense machinery through which CV-B3 infection is limited by the cleavage of a pro-viral protein.

Members of the metazoan Grb2-associated-binding (GAB) family of proteins are crucial regulatory elements of receptor tyrosine kinase (RTK) signaling pathways. These scaffold proteins link and amplify plasma membrane receptor signaling to downstream targets by staging protein-protein interactions. Aberrant GAB expression is associated with improper growth and development, and several members of the GAB family have been implicated as oncogenes. GAB1, GAB2, and GAB3 are overexpressed in various cancers including lung, breast, colorectal, nervous system, and ovarian cancers, along with certain leukemias and melanomas. Recent studies suggest a direct relationship between GAB expression levels and tumorigenesis, where induced or silenced expression respectively accelerated or inhibited tumor proliferation. Silencing of GAB1 in colorectal cancers and GAB2 in glioblastoma via miRNA, and GAB3 in gliomas via siRNA inhibits tumor proliferation indicating that GAB proteins can be potentially effective targets in cancer therapy. The most conserved structural moiety in all members of the GAB family is an N-terminally located pleckstrin homology (PH domain) that directs subcellular localization and is crucial for effective protein function. Given the challenges facing RNA-based cancer therapies, more practical therapeutic avenues may be found in disrupting or inhibiting proper PH domain function; however, the mechanism of membrane targeting of all GABs remains to be elucidated. To this end, we have performed a comprehensive computational analysis of the six known GAB family members - chordate GAB1, GAB2, GAB3, and GAB4; Caenorhabditis elegans Suppressor of Clear (SOC1); Drosophila melanogaster Daughter of Sevenless (DOS) and their respective homologs to establish intra-familiar relationships via sequence analysis. Furthermore, in silico homology-based and ab initio modeling techniques were employed to propose suitable structural models of the PH domains and confirm the structural conservation of the fold. The refined theoretical models were docked against phosphoinositide head-groups to establish binding affinities and the mechanism of GAB PH domain localization. Our results suggest that non-specific electrostatics may be a key component for membrane targeting of GAB PH domains acting in concert with interaction through specific conserved residues and reveal an alternative binding pocket in addition to the canonical binding site. Our study is the first step in rational design of potential therapies based on targeting GAB function via the PH domain. Citation Format: Antonio Lopez, Ezza Awan, Areeba Zaheer, Shaneen Singh. In silico analysis of the membrane targeting mechanism of the pleckstrin homology domains within the oncogenic Grb2-associated-binding protein family [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5098.

Phospholipase C γ2 (PLCγ2) is a critical regulator of innate immune cells and osteoclasts (OCs) during inflammatory arthritis. Both the catalytic domain and the adaptor motifs of PLCγ2 are required for OC formation and function. Due to the high homology between the catalytic domains of PLCγ2 and the ubiquitously expressed PLCγ1, molecules encompassing the adaptor motifs of PLCγ2 were designed to test the hypothesis that uncoupling the adaptor and catalytic functions of PLCγ2 could specifically inhibit osteoclastogenesis and bone erosion. Wild-type (WT) bone marrow macrophages (BMM) that overexpress the tandem Src homology 2 (SH2) domains of PLCγ2 (SH2(N+C)) failed to form mature OCs and resorb bone in vitro. Activation of the receptor activator of NF-κB (RANK) signaling pathway, which is critical for OC development, was impaired in cells expressing SH2(N+C). Arrest in OC differentiation was evidenced by a reduction of p38 and Iκ-Bα phosphorylation as well as decreased NFATc1 and c-Fos/c-Jun levels. Consistent with our hypothesis, SH2(N+C) abrogated formation of the RANK-Gab2 complex, which mediates NF-κB and AP-1 activation following RANK ligand (RANKL) stimulation. Furthermore, the ability of SH2(N+C) to prevent inflammatory osteolysis was examined in vivo following RANKL or LPS injections over the calvaria. Both models induced osteolysis in the control group, whereas the SH2(N+C)-treated cohort was largely protected from bone erosion. Collectively, these data indicate that inflammatory osteolysis can be abrogated by treatment with a molecule composed of the tandem SH2 domains of PLCγ2.

Recent studies using next-generation sequencing of selected individuals, such as those with familial leukemia or congenital syndromes, have identified rare and highly penetrant germline mutations that predispose to childhood acute lymphoblastic leukemia (ALL). High hyperdiploidy (HD), the most common cytogenetic subtype of childhood ALL, is enriched in children with RASopathies who develop ALL and, similarly, a high proportion of ALL patients with germline ETV6 or IKZF1 mutations presented with the HD subtype. Here, we aimed to identify novel predisposition genes in a selected group of HD-ALL patients. Targeted sequencing of 538 cancer-relevant genes was carried out using the UCSF500 Cancer Gene Panel in diagnostic bone marrow (i.e. tumor) DNA from 57 HD-ALL patients from the California Childhood Leukemia Study (CCLS). HD-ALL patients were selected based on absence of somatic KRAS or NRAS hotspot mutations detectable by Sanger sequencing, and absence of somatic copy number deletions from multiplex ligation-dependent probe amplification (MLPA) assays. After filtering out likely somatic mutations (mutant allele fraction Rare and predicted functional germline mutations in known (NBN, SH2B3, ETV6, CREBBP, MSH6) or suspected (MLL, ABL1, FLT3, MYH9) ALL predisposition genes were identified in nine out of 57 patients (15.8%). Three additional patients harbored germline mutations in the GRB2-associated binding protein 2 (GAB2), a known binding partner of PTPN11-encoded SHP2 and activator of the ERK/MAPK and PI3K/AKT pathways. Two GAB2 mutations, a missense mutation S592F and frameshift mutation P621fs, were predicted to be highly functional (CADD scores = 34 and 36 respectively) and absent in ExAC. Frequency of rare and damaging GAB2 mutations was significantly higher in our patient set (2.6%) than in ExAC (0.28%, P = 2.70 x 10-6). We replicated this finding in sequencing data from 309 ALL patients in the TARGET (Therapeutically Applicable Research to Generate Effective Treatments) project (0.81% vs. 0.28%, P = 0.015). Patient GAB2 mutations were cloned into HEK293 cells and, following EGF stimulation, we found that the P621fs mutation reduced SHP2 binding and ERK1/2 phosphorylation but increased AKT phosphorylation. This suggested possible Ras-independent leukemogenic effects, supported by a lack of somatic Ras pathway mutations in the three GAB2 mutant patients. Additional functional analyses and sequencing of larger patient cohorts will be required to elucidate the role of germline GAB2 mutations in childhood ALL. Disclosures No relevant conflicts of interest to declare.

Background: Many genetic drivers that are implicated in disease pathology and risk stratification have been identified for pediatric acute myeloid leukemia (pedi-AML). However, only a minority have been exploited for therapeutic interventions and most of the identified genetic events currently lack targeted therapy to address the mutations. The combined consequences of genetic and epigenetic events culminate in a net effect manifested at the protein level and most of the chemotherapies target proteins. Yet little is known about the proteomic landscape of pedi-AML. Methods: Reverse Phase Protein Array (RPPA) was performed with 291 strictly validated antibodies to determine the protein expression levels of bulk leukemic cells from 505 pedi-AML patient samples that were collected prior to therapy. All patients participated on the COG AAML1031 Phase 3 clinical trial, that compared standard therapy (ADE) to ADE plus bortezomib (ADE+B). Proteins were allocated into 31 protein functional groups (PFG) (e.g. cell cycle, apoptosis) to analyze proteins in relation to related proteins. Progeny clustering was performed to identify patients with correlated protein expression patterns within each PFG (protein cluster). Block clustering searched for protein clusters that recurrently co-occurred (protein constellation), and for subgroups of patients that expressed similar combinations of protein constellations (protein signatures). Protein signatures were correlated with known cytogenetics and mutational state. Results: For each PFG, cluster analysis identified an optimal number of protein clusters, resulting in a total of 120. From this we constructed 11 protein constellations (PRCON) and 10 protein signatures (SIG) (Fig. 1A). A training set (n=334) and test set (n=171) showed high reproducibility (Pearson's X2; p < 0.001). SIG were prognostic for event-free survival (EFS) (p = 0.029), with a favorable EFS for SIG 1, 2, 3, 5, 7 & 9, and an unfavorable EFS for SIG 4, 6, 8, 10. Notably, patients that formed SIG 3 had a significant better EFS after receiving ADE+B than patients that received ADE (p = 0.039) (Fig. 1B). This SIG was highly enriched for CEBPA mutated cases; 43% vs. 9% overall (p < 0.001). SIG were associated with cytogenetic aberrations (p < 0.001) and mutational state, as well as with the traditional risk groups (p < 0.001). For example, t(8;21) was overrepresented in SIG 9 (39% vs. 16% overall) and MLL-rearrangement in SIG 6 (61% vs. 19% overall). Multivariate analysis was performed using variables definable at time of diagnosis and known prognostic factors. This resulted in a final model including unfavorable protein SIG together with low risk cytogenetics and NPM1 mutation state as independent prognostic factors, suggesting that proteins add to known prognostic factors. Proteomics could also identify aberrantly expressed proteins within each SIG compared to normal CD34+ cells. This recognized 31 proteins as universally down regulated (e.g. CDKN1A, PPP2R2A) and 13 as universally up regulated (e.g. PIK3CA, NCL). Many other proteins were different between SIG, and thus potentially targetable in particular patient groups: high KIT (SIG 3, 4 & 5), high BCL2 (SIG 3, 4, 5, 6, 9 & 10) and high BRD4 (SIG 6). SIG 1 & 2 both had a very characteristic expression pattern and were most distinct from the others. IGFR1, IGFR1.pY1135, AKT3, SMAD5.pS463-7 and RICTOR.pT1135 were all high, whereas they were low in most other SIG. Conversely, STAT3 was normal in SIG 1&2, but changed in the other SIG. SIG 6, 7 & 8 also had relatively similar expression patterns, but had different outcomes. Compared to SIG 6 & 8, SIG 7 had higher GAB2 and MCL1 and lower RAD50, ERCC1. Conclusions: Pedi-AML is characterized by a finite number (n=10) of recurrent protein signatures. SIG were only partially correlated with cytogenetics and mutation state, indicating that protein expression could add to genetics in the process of risk stratification. We identified SIG that did well vs. SIG that did not, independent of known risk factors, and identified a group of patients that could potentially benefit from ADE+B. Recognition of differentially expressed proteins suggest potential targets for combinational treatment (Hoff et al. ASH HSF1 abstract). Figure 1. A. Identification of 11 PRCON (horizontally) and 10 SIG (vertically). B. SIG were prognostic for EFS. C. SIG 3 significantly benefitted from ADE+B (green) compared to ADE alone (blue). Disclosures Kolb: Roche- Genentech: Membership on an entity's Board of Directors or advisory committees; Servier: Membership on an entity's Board of Directors or advisory committees.

The aim of this study was to investigate the effect of saucerneol F (SF) on the productions of the pro-inflammatory cytokines, TNF-α and IL-6, in IgE/Ag-induced mouse bone marrow-derived mast cells (BMMCs). SF dose-dependently suppressed the transcriptions of these pro-inflammatory cytokines. To identify the molecular mechanisms responsible for these suppressions, we examined the effect of SF on three important transcription factors; activator protein-1 (AP-1), nuclear factor-κB (NF-κB), and STAT5. It was found that SF inhibited the nuclear translocation of the p65 subunit of NF-κB to the nucleus and its DNA-binding ability. SF also attenuated mitogen-activated protein kinase (MAPK)-mediated AP-1 activation and STAT5 activation. Biochemical analysis of FcεRI-mediated signaling pathways demonstrated that SF inhibited the phosphorylation of Fyn and multiple downstream signaling processes, including Syk, Gab2, and the Akt/IKK/IκB and MAPK pathways. Taken together, our results suggest that SF inhibits the production of pro-inflammatory cytokines by suppressing Fyn kinase-dependent signaling events.

Type III receptor tyrosine kinases (RTKs), FLT3 and c-Kit play important roles in a variety of cellular processes. A number of SH2-domain containing proteins interact with FLT3 and c-Kit and regulate downstream signaling. The SH2-domain containing non-receptor protein tyrosine kinase CSK is mainly studied in the context of regulating Src family kinases. Here we present an additional role of this kinase in RTK signaling. We show that CSK interacts with FLT3 and c-Kit in a phosphorylation dependent manner. This interaction is facilitated through the SH2-domain of CSK. Under basal conditions CSK is mainly localized throughout the cytosolic compartment but upon ligand stimulation it is recruited to the inner side of cell membrane. CSK association did not alter receptor ubiquitination or phosphorylation but disrupted downstream signaling. Selective depletion of CSK using siRNA, or inhibition with CSK inhibitor, led to increased phosphorylation of Akt and Erk, but not p38, upon FLT3 ligand (FL) stimulation. Stem cell factor (SCF)-mediated Akt and Erk activation was also elevated by CSK inhibition. However, siRNA mediated CSK knockdown increased SCF stimulated Akt phosphorylation but decreased Erk phosphorylation. CSK depletion also significantly increased both FL- and SCF-induced SHC, Gab2 and SHP2 phosphorylation. Furthermore, CSK depletion contributed to oncogenic FLT3- and c-Kit-mediated cell proliferation, but not to cell survival. Thus, the results indicate that CSK association with type III RTKs, FLT3 and c-Kit can have differential impact on receptor downstream signaling.

Mast cells are major players in allergic responses. IgE-dependent activation through Fc epsilon RI leads to degranulation and cytokine production, both of which require Gab2. To clarify how the signals diverge at Gab2, we established Gab2 knock-in mice that express Gab2 mutated at either the PI-3K- or SHP-2-binding sites. Examination of these mutants showed that both binding sites were required for the degranulation and anaphylaxis response, but not for cytokine production or contact hypersensitivity. Furthermore, the PI-3K- but not the SHP-2-binding site was important for granule translocation during degranulation. We also identified a small GTPase, ARF1, as the downstream target of PI-3K that regulates granule translocation. Fc epsilon RI-stimulation induced ARF1 activation, and this response was dependent on Fyn and the PI-3K-binding site of Gab2. ARF1 activity was required for the Fc epsilon RI-mediated granule translocation. These results indicate that Fyn/Gab2/PI-3K/ARF1-mediated signaling is specifically involved in granule translocation and the anaphylaxis response. In this review, I discussed how Gab2 controls biological events especially for mast cell degranulation and allergy response.

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.

Gliomas are characterized by high invasiveness and poor prognosis. Better understanding of the mechanism of invasion in glioma cells is essential to the design of effective therapy. Recently Grb2-associated binder 2 (Gab2), a member of the DOS/Gab family of scaffolding adapters, has been reported to play important roles in the development and progression of human cancers. However, it is not known whether Gab2 has any role in the migration and invasion of gliomas. This study attempts to investigate the association between Gab2 expression and progression of gliomas and the molecular mechanism of Gab2 in the glioma cell invasion. Methods. The expression of Gab2 in pairs of matched glioma tissues and their normal brain tissues was detected by Western blot. Immunohistochemistry was applied to evaluate the expression of Gab2 in 163 cases of histologically diagnosed gliomas. The invasive character of Gab2 decreased glioma cells and control glioma cells were investigated in vitro and in vivo in SCID mice brain. Results. Gab2 is found to be high expressed in gliomas and a subset of cancer cell lines. Statistical analysis suggested that the up-regulation of Gab2 correlated with the WHO grade of gliomas (p0.01) and that patients with high Gab2 expression levels exhibited shorter survival time (p0.01). In an animal experiment, knockdown of Gab2 through siRNA inhibited invasive ability of glioma cells into the brain of SCID mice. In cell research, reduction of Gab2 by siRNA inhibits the migration and invasion of glioma cells by mediating cytoskeleton rearrangement and MMPs expression. Additionally, IGF-1-induced pAkt and pmTOR phosphorylation was suppressed by the knockdown of Gab2. Conclusion. Gab2 may be a useful prognostic marker for gliomas and a novel therapeutic target for glioma invasion intervention.

Erythropoiesis is controlled principally through erythropoietin (Epo) receptor signaling, which involves Janus kinase 2 (JAK2) and Lyn tyrosine kinase, both of which are important for regulating red blood cell (RBC) development. Negative regulation of Lyn involves C-Src kinase (Csk)-mediated phosphorylation of its C-terminal tyrosine, which is facilitated by the transmembrane adaptor Csk-binding protein (Cbp). Although Cbp has significant functions in controlling Lyn levels and activity in erythroid cells in vitro, its importance to primary erythroid cell development and signaling has remained unclear. To address this, we assessed the consequence of loss of Cbp on the erythroid compartment in vivo and whether Epo-responsive cells isolated from Cbp-knockout mice exhibited altered signaling. Our data show that male Cbp−/− mice display a modest but significant alteration to late erythroid development in bone marrow with evidence of increased erythrocytes in the spleen, whereas female Cbp−/− mice exhibit a moderate elevation in early erythroid progenitors (not seen in male mice) that does not influence the later steps in RBC development. In isolated primary erythroid cells and cell lines generated from Cbp−/− mice, survival signaling through Lyn/Akt/FoxO3 was elevated, resulting in sustained viability during differentiation. The high Akt activity disrupted GAB2/SHP-2 feedback inhibition of Lyn; however, the elevated Lyn activity also increased inhibitory signaling via SHP-1 to restrict the Erk1/2 pathway. Interestingly, whereas loss of Cbp led to mild changes to late RBC development in male mice, this was not apparent in female Cbp−/− mice, possibly due to their elevated estrogen, which is known to facilitate early progenitor self-renewal.

Using a series of immunoprecipitation (IP) – tandem mass spectrometry (LC-MS/MS) experiments and reciprocal BLAST, we conducted a fly-human cross-species comparison of the phosphoinositide-3-kinase (PI3K) interactome in a drosophila S2R+ cell line and several NSCLC and human multiple myeloma cell lines to identify conserved interacting proteins to PI3K, a critical signaling regulator of the AKT pathway. Using H929 human cancer cells and drosophila S2R+ cells, our data revealed an unexpected direct binding of Corkscrew, the drosophila ortholog of the non-receptor protein tyrosine phosphatase type II (SHP2) to the Pi3k21B (p60) regulatory subunit of PI3K (p50/p85 human ortholog) but no association with Pi3k92e, the human ortholog of the p110 catalytic subunit. The p85-SHP2 association was validated in human cell lines and formed a ternary regulatory complex with GRB2-associated-binding protein 2 (GAB2). Validation experiments with knockdown of GAB2 and Far-Western blots proved the direct interaction of SHP2 with p85, independent of adaptor proteins and transfected FLAG-p85 provided evidence that SHP2 binding on p85 occurred on the SH2 domains. A disruption of the SHP2-p85 complex took place after insulin/IGF1 stimulation or imatinib treatment, suggesting that the direct SHP2-p85 interaction was both independent of AKT activation and positively regulates the ERK signaling pathway.

Background Grb2-associated binder 2 (Gab2), a scaffolding adaptor protein, has recently been implicated in cancer progression. However, the role of Gab2 in the progression and metastasis of colorectal cancer (CRC) remains unclear. Methods Gab2 expression was assessed in CRC patient specimens as well as in CRC cell lines. Recombinant lentivirus vector containing Gab2 gene and its small interfering RNAs were constructed and introduced into CRC cells. Cell migration and invasion ability were evaluated by transwell assays in vitro, and in vivo metastasis was performed on nude mice model. Moreover, the expression of Gab2 and epithelial-to-mesenchymal transition (EMT)-associated proteins (E-cadherin and vimentin) were assessed by western blot and qRT-PCR in CRC cells to evaluate the correlation between Gab2 and EMT. Finally, we evaluated the impact of Gab2 on the activation of its downstream signaling effectors, and furthermore the effects of these pathways on Gab2 induced-EMT were also detected. Results We confirmed that increased Gab2 expression correlated with higher tumor node metastasis stage and highly invasive CRC cell lines. Ectopic expression of Gab2 promoted metastasis of CRC cells, whereas silencing of Gab2 resulted in inhibited metastasis both in vitro and in vivo. Overexpression of Gab2 in CRC cells induced EMT, whereas knockdown of Gab2 had the opposite effect. Furthermore, upregulation of Gab2 expression obviously stimulated the activation of extracellular signal-regulated kinase-1/2 (ERK1/2), and increased the expression of matrix metalloproteinase-7 (MMP7) and matrix metalloproteinase-9 (MMP9) in CRC cells. Conversely, downregulation of Gab2 expression significantly decreased the activation of ERK1/2, and inhibited MMP7 and MMP9 expression. U0126, an inhibitor of mitogen-activated protein kinase (MEK), can reverse the effects of Gab2 on EMT. Conclusions Our work highlights that Gab2 induces EMT through the MEK/ERK/MMP pathway, which in turn promotes intestinal tumor metastasis. Electronic supplementary material The online version of this article (doi:10.1186/s13046-015-0280-0) contains supplementary material, which is available to authorized users.