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The BCR/ABL oncogene causes chronic myelogenous leukemia (CML) in humans and a CML-like disease, as well as lymphoid leukemia, in mice. p210 BCR/ABL is an activated tyrosine kinase that phosphorylates itself and several cellular signaling proteins. The autophosphorylation site tyrosine 177 binds the adaptor Grb2 and helps determine the lineage and severity of BCR/ABL disease: Tyr177 mutation (BCR/ABL-Y177F) dramatically impairs myeloid leukemogenesis, while diminishing lymphoid leukemogenesis. The critical signal(s) from Tyr177 has remained unclear. We report that Tyr177 recruits the scaffolding adaptor Gab2 via a Grb2/Gab2 complex. Compared to BCR/ABL-expressing Ba/F3 cells, BCR/ABL-Y177F cells exhibit markedly reduced Gab2 tyrosine phosphorylation and association of phosphatidylinositol-3 kinase (PI3K) and Shp2 with Gab2 and BCR/ABL, and decreased PI3K/Akt and Ras/Erk activation, cell proliferation, and spontaneous migration. Remarkably, bone marrow myeloid progenitors from Gab2 (-/-) mice are resistant to transformation by BCR/ABL, whereas lymphoid transformation is diminished as a consequence of markedly increased apoptosis. BCR/ABL-evoked PI3K/Akt and Ras/Erk activation also are impaired in Gab2 (-/-) primary myeloid and lymphoid cells. Our results identify Gab2 and its associated proteins as key determinants of the lineage and severity of BCR/ABL transformation.

Background: Human immunodeficiency virus (HIV) infected patients are at increased risk for the development of pulmonary arterial hypertension (PAH). Recent reports have demonstrated that HIV associated viral proteins induce reactive oxygen species (ROS) with resultant endothelial cell dysfunction and related vascular injury. In this study, we explored the impact of HIV protein induced oxidative stress on production of hypoxia inducible factor (HIF)-1α and platelet-derived growth factor (PDGF), critical mediators implicated in the pathogenesis of HIV-PAH.Methods: The lungs from 4-5 months old HIV-1 transgenic (Tg) rats were assessed for the presence of pulmonary vascular remodeling and HIF-1α/PDGF-BB expression in comparison with wild type controls. Human primary pulmonary arterial endothelial cells (HPAEC) were treated with HIV-associated proteins in the presence or absence of pretreatment with antioxidants, for 24 hrs followed by estimation of ROS levels and western blot analysis of HIF-1α or PDGF-BB.Results: HIV-Tg rats, a model with marked viral protein induced vascular oxidative stress in the absence of active HIV-1 replication demonstrated significant medial thickening of pulmonary vessels and increased right ventricular mass compared to wild-type controls, with increased expression of HIF-1α and PDGF-BB in HIV-Tg rats. The up-regulation of both HIF-1α and PDGF-B chain mRNA in each HIV-Tg rat was directly correlated with an increase in right ventricular/left ventricular+septum ratio. Supporting our in-vivo findings, HPAECs treated with HIV-proteins: Tat and gp120, demonstrated increased ROS and parallel increase of PDGF-BB expression with the maximum induction observed on treatment with R5 type gp-120CM. Pre-treatment of endothelial cells with antioxidants or transfection of cells with HIF-1α small interfering RNA resulted in abrogation of gp-120CM mediated induction of PDGF-BB, therefore, confirming that ROS generation and activation of HIF-1α plays critical role in gp120 mediated up-regulation of PDGF-BB.Conclusion: In summary, these findings indicate that viral protein induced oxidative stress results in HIF-1α dependent up-regulation of PDGF-BB and suggests the possible involvement of this pathway in the development of HIV-PAH. [ABSTRACT FROM AUTHOR]

Transformation of fibroblasts by V-SEA involves activation of the ERK and phosphatidylinositol 3-kinase (PI3K) pathways. Effector proteins that are key mediators of the ERK and PI3K pathways, namely Grb2, the tyrosine phosphatase, SHP2 and PI3K, interact with the two phosphotyrosines found in the bidentate motif in the carboxy-terminal region of V-SEA. Genetic analysis demonstrated that while Y557 was a primary binding site and thus activator of the PI3K-Akt pathway, Y564 also contributed to the activation of this pathway. Y564 was located within a Grb2-binding motif, this raised the possibility that a protein that associated with Grb2 might be important for this PI3K activation. The scaffolding proteins Gab1 and/or Gab2 were candidates for this role. In this report, we demonstrate that V-SEA preferentially interacts with Gab2. Furthermore by using Gab2 null fibroblasts, we demonstrate that Gab2 is essential for fibroblast transformation by V-SEA. Using mutant forms of Gab2, we show that activation of the PI3K-Akt pathway via Gab2 is required for V-SEA-induced transformation. However, efficient fibroblast transformation also requires the SHP2 interaction site on Gab2.Oncogene (2003) 22, 6311-6318. doi:10.1038/sj.onc.1206742 [ABSTRACT FROM AUTHOR]

Provides information on a study which examined the role for Gab2 in the allergic response experimentally. Composition of the Gab2; Function of Gab2 in signaling; Results; How the study was conducted.

Abstract: 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. [Copyright &y& Elsevier]