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See detailThe Ras/Rap GTPase activating protein RASA3 : from gene structure to in vivo functions
Schurmans, Stéphane ULg; Polizzi, Séléna; Scoumanne, Ariane ULg et al

in Advances in Biological Regulation (2015), 57

RASA3 (or GTPase Activating Protein III, R-Ras GTPase-activating protein, GAP1IP4BP) is a GTPase activating protein of the GAP1 subfamily which targets Ras and Rap1. RASA3 was originally purified from pig ... [more ▼]

RASA3 (or GTPase Activating Protein III, R-Ras GTPase-activating protein, GAP1IP4BP) is a GTPase activating protein of the GAP1 subfamily which targets Ras and Rap1. RASA3 was originally purified from pig platelet membranes through its intrinsic ability to bind inositol 1,3,4,5-tetrakisphosphate (I(1,3,4,5)P4) with high affinity, hence its first name GAP1IP4BP (for GAP1 subfamily member which binds I(1,3,4,5)P4). RASA3 was thus the first I(1,3,4,5)P4 receptor identified and cloned. The in vitro and in vivo functions of RASA3 remained somewhat elusive for a long time. However, recently, using genetically-modified mice and cells derived from these mice, the function of RASA3 during megakaryopoiesis, megakaryocyte adhesion and migration as well as integrin signaling has been reported. The goal of this review is thus to summarize and comment recent and less recent data in the literature on RASA3, in particular on the in vivo function of this specific GAP1 subfamily member. [less ▲]

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See detailSHIP2 signaling in normal and pathological situations: Its impact on cell proliferation.
Elong Edimo, W; Schurmans, Stéphane ULg; Roger, PP et al

in Advances in Biological Regulation (2014), 54

Phosphoinositide 5-phosphatases are critical enzymes in modulating the concentrations of PI(3,4,5)P3, PI(4,5)P2 and PI(3,5)P2. The SH2 domain containing inositol 5-phosphatases SHIP1 and SHIP2 belong to ... [more ▼]

Phosphoinositide 5-phosphatases are critical enzymes in modulating the concentrations of PI(3,4,5)P3, PI(4,5)P2 and PI(3,5)P2. The SH2 domain containing inositol 5-phosphatases SHIP1 and SHIP2 belong to this family of enzymes that dephosphorylate the 5 position of PI(3,4,5)P3 to produce PI(3,4)P2. Data obtained in zebrafish and in mice have shown that SHIP2 is critical in development and growth. Exome sequencing identifies mutations in the coding region of SHIP2 as a cause of opsismodysplasia, a severe but rare chondrodysplasia in human. SHIP2 has been reported to have both protumorigenic and tumor suppressor function in human cancer very much depending on the cell model. This could be linked to the relative importance of PI(3,4)P2 (a product of SHIP2 phosphatase activity) which is also controlled by the PI 4-phosphatase and tumor suppressor INPP4B. In the glioblastoma cell line 1321 N1, that do not express PTEN, lowering SHIP2 expression has an impact on the levels of PI(3,4,5)P3, cell morphology and cell proliferation. It positively stimulates cell proliferation by decreasing the expression of key regulatory proteins of the cell cycle such as p27. Together the data point out to a role of SHIP2 in development in normal cells and at least in cell proliferation in some cancer derived cells. [less ▲]

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See detailInositol 1,4,5-trisphosphate 3-kinase B (Itpkb) controls survival, proliferation and cytokine production in mouse peripheral T cells
Pouillon, Valérie; Maréchal, Yoann; Frippiat, Christophe et al

in Advances in Biological Regulation (2013), 53(1), 39-50

Mice genetically-deficient for the B isoform of the inositol 1,4,5-trisphosphate 3-kinase (or Itpkb) have a severe defect in thymocytes differentiation and thus lack peripheral T cells. In order to study ... [more ▼]

Mice genetically-deficient for the B isoform of the inositol 1,4,5-trisphosphate 3-kinase (or Itpkb) have a severe defect in thymocytes differentiation and thus lack peripheral T cells. In order to study the functional role of Itpkb in peripheral T cells, we constructed a new mouse where a transgene encoding mouse Itpkb is specifically and transiently expressed in thymocytes of Itpkb-/- mice. This allows a partial rescue of mature thymocyte/T cell differentiation and thus the functional characterization of peripheral T cells lacking Itpkb. We show here that Itpkb-/- CD4+ and CD8+ peripheral T cells present important functional alterations. Indeed, an increased activated/memory phenotype as well as a decreased proliferative capacity and survival were detected in these T cells. These Itpkb-deficient peripheral T cells have also an increased capacity to secrete cytokines upon stimulation. Together, our present results define the important role of Itpkb in peripheral mature T cell fate and function in mouse, suggesting a potential role for Itpkb in autoimmunity. [less ▲]

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