The p.Arg63Trp polymorphism controls Vav1 functions and Foxp3 regulatory T cell development

A single nucleotide polymorphism causing constitutive activation of Vav1 results in increased natural Treg generation and is responsible for the imbalance between Vav1 GEF and adaptor functions

Rôle du phosphatidylinositol 5-phosphate dans la survie et la migration cellulaires (implication dans la dynamique des membranes et du cytosquelette)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Rôle des GTPases de la famille Rho et de leurs régulateurs dans les propriétés transformantes des lymphomes anaplasiques NPM-ALK positifs

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Regulation of the DH-PH tandem of guanine nucleotide exchange factor for Rho GTPases by phosphoinositides.

International audienceRho GTPases act as molecular switches central in cellular processes such as cytoskeleton dynamics, migration, cell proliferation, growth or survival. Their activation is tightly regulated downstream of cell surface receptors by Guanine nucleotide Exchange Factors (GEFs), that are responsible for the specificity, the accuracy, and the spatial restriction of Rho GTPases response to extracellular cues. Because there is about four time more RhoGEFs that Rho GTPases, and GEFs do not always show a strict specificity for GTPases, it is clear that their regulation depends on specific interactions with the subcellular environment. RhoGEFs bear a peculiar structure, highly conserved though evolution, consisting of a DH-PH tandem, the DH (Dbl homology) domain being responsible for the exchange activity. The function of the PH (Pleckstrin homology) domain known to bind phosphoinositides, however, remains elusive, and reports are in many cases rather confusing. This review summarizes data on the regulation of RhoGEFs activity through interaction of the PH-associated DH domain with phosphoinositides which are considered as critical players in the spatial organization of major signaling pathways

Phosphoinositides and cellular pathogens.

International audiencePhosphoinositides are considered as highly dynamic players in the spatiotemporal organization of key signaling pathways, actin cytoskeleton rearrangements, establishment of cell polarity and intracellular vesicle trafficking. Their metabolism is accurately controlled and mutations in several phosphoinositide metabolizing enzymes take part in the development of human pathologies. Interestingly, evidence is accumulating that modulation of the phosphoinositide metabolism is critical for pathogenicity and virulence of many human pathogens. Given the importance of phosphoinositides, which link membrane and cytoskeleton dynamics to cell responses, it is not surprising that many invasive pathogens hijack their metabolism as part of their strategies to establish infection. In fact, according to their lifestyle, cellular pathogens use the phosphoinositide metabolism in order to trigger their uptake in nonphagocytic cells and/or modulate the maturation of the pathogen-containing vacuole to establish their replicative niche or escape in the cytosol and promote host cell survival. The last two decades have been marked by the discovery of different tactics used by cellular pathogens to modulate the phosphoinositide metabolism as part of their strategies to survive, proliferate and disseminate in a hostile environment

A novel mass assay to quantify the bioactive lipid PtdIns3P in various biological samples.

International audiencePtdIns3P is recognized as an important player in the control of the endocytotic pathway and in autophagy. Recent data also suggest that PtdIns3P contributes to molecular mechanisms taking place at the plasma membrane and at the midbody during cytokinesis. This lipid is present in low amounts in mammalian cells and remains difficult to quantify either by traditional techniques based on radiolabelling followed by HPLC to separate the different phosphatidylinositol monophosphates, or by high-sensitive liquid chromatography coupled to MS, which is still under development. In the present study, we describe a mass assay to quantify this lipid from various biological samples using the recombinant PtdIns3P 5-kinase, PIKfyve. Using this assay, we show an increase in the mass level of PtdIns3P in mouse and human platelets following stimulation, loss of this lipid in Vps34-deficient yeasts and its relative enrichment in early endosomes isolated from BHK cells

Profilin 1-mediated cytoskeletal rearrangements regulate integrin function in mouse platelets

Platelet adhesion and aggregation at sites of vascular injury is essential for hemostasis but may also cause thrombosis.1 Firm platelet adhesion is mediated by heterodimeric receptors of the β1- and β3-integrin families, which upon activation reversibly shift to a high-affinity state and efficiently bind their ligands, most notably components of the extracellular matrix and other receptors.2⇓-4 Binding of talin-1 (Tln1) and kindlins to the intracellular tail of the integrin β-subunit triggers the switch to the high-affinity state, whereas their dissociation results in integrin closure, the switch back to the low-affinity state.5⇓⇓-8 Tln1 and kindlins connect integrins to the actin cytoskeleton, thereby enabling the sensing and exertion of mechanical forces as well as regulating adhesion formation and turnover.9⇓⇓-12 Consistently, defects in actin-regulating proteins result in altered platelet and megakaryocyte integrin function.13⇓⇓⇓⇓⇓-19 Furthermore, we have recently shown a critical role of twinfilin 2a (Twf2a) and the cortical cytoskeleton in regulating platelet integrin turnover in a profilin 1 (Pfn1)–dependent manner.10 The small actin-binding protein Pfn1 is central for actin dynamics by mediating the nucleotide exchange on G-actin monomers, thereby promoting filament assembly with implications for platelet biogenesis.13,20 Megakaryocyte-specific Pfn1 deficiency resulted in microthrombocytopenia because of cytoskeletal alterations and accelerated platelet clearance (supplemental Figure 1).13 However, the precise role of Pfn1 for platelet function is unknown. Here, we report that the lack of Pfn1 in platelets (Pfn1fl/fl-Pf4Cre) perturbs the organization of the adhesion-dependent circumferential actin network and thereby results in accelerated integrin inactivation and hence impaired platelet function in vitro and in vivo

The importance of blood platelet lipid signaling in thrombosis and in sepsis

International audienceBlood platelets are the first line of defense against hemorrhages and are also strongly involved in the processes of arterial thrombosis, a leading cause of death worldwide. Besides their well-established roles in hemostasis, vascular wall repair and thrombosis, platelets are now recognized as important players in other processes such as inflammation, healing, lymphangiogenesis, neoangiogenesis or cancer. Evidence is accumulating they are key effector cells in immune and inflammatory responses to host infection. To perform their different functions platelets express a wide variety of membrane receptors triggering specific intracellular signaling pathways and largely use lipid signaling systems. Lipid metabolism is highly active in stimulated platelets including the phosphoinositide metabolism with the phospholipase C (PLC) and the phosphoinositide 3-kinase (PI3K) pathways but also other enzymatic systems producing phosphatidic acid, lysophosphatidic acid, platelet activating factor, sphingosine 1-phosphate and a number of eicosanoids. While several of these bioactive lipids regulate intracellular platelet signaling mechanisms others are released by activated platelets acting as autocrine and/or paracrine factors modulating neighboring cells such as endothelial and immune cells. These bioactive lipids have been shown to play important roles in hemostasis and thrombosis but also in vessel integrity and dynamics, inflammation, tissue remodeling and wound healing. In this review, we will discuss some important aspects of platelet lipid signaling in thrombosis and during sepsis that is an important cause of death in intensive care unit. We will particularly focus on the implication of the different isoforms of PI3Ks and on the generation of eicosanoids released by activated platelets