Etude de la signalisation P 13-kinase induite par le récepteur de costimulation ICOS au cours de l'activation lymphocytaire T

Il est maintenant communément admis qu une activation lymphocytaire T efficace requiert deux signaux indépendants. Le premier, qui détermine la spécificité de la réponse immunitaire, est délivré au travers de l interaction du récepteur à l antigène sur la cellule T (TcR) avec le complexe CMH-peptide antigénique à la surface des cellules présentatrices d antigène. Un signal additionnel (ou signal 2) aussi appelé costimulateur, est critique pour la régulation de l activation lymphocytaire T. La signalisation induite par le couple ICOS/ICOS-L fournit à la cellule un second signal positif qui contribue à l activation des lymphocytes T. La signalisation induite par l engagement du récepteur ICOS est actuellement peu référencée dans la littérature et ne semble engager que la voie PI3-kinase. Les résultats obtenus in vitro, nous ont montré que l engagement du récepteur ICOS par son ligand induit le recrutement de p50a au sein de sa partie intracellulaire via son motif consensus motif YxxM. L engagement du récepteur ICOS augmente également le recrutement intracellulaire de p85a, déjà présent au sein du récepteur à l état basal. De manière assez surprenante, nous avons constaté que la stimulation du récepteur ICOS semble renforcer la signalisation PI3K induite sous CD28 selon un mécanisme encore inconnu et a mit en évidence un "crosstalk" entre les deux molécules. Nous avons pu montré pour la première fois que le récepteur de costimulation ICOS se localise à la synapse immunologique, zone de la membrane où le récepteur semble influencer le recrutement de p50a. Enfin, dans notre système de stimulation de lymphocytes T primaires, ICOS est capable d activer la voie de signalisation PI3K beaucoup plus fortement que CD28 comme en témoigne les niveaux élevés de phosphorylation de la sérine/thréonine kinase Akt après engagement de ce récepteur.Inducible costimulator (ICOS) ligation in concert with TcR stimulation results in strong phosphoinositide 3-kinase (PI3K) activation in T lymphocytes. The ICOS cytoplasmic tail contains an YMFM motif that binds the p85a subunit of class IA PI3K, similar to the YMNM motif of CD28, suggesting a redundant function of the two receptors in PI3K signaling. However, ICOS costimulation shows greater PI3K activity than CD28 in T cells. We show in this report that ICOS expression in activated T cells triggers the participation of p50 , one of the regulatory subunits of class IA PI3Ks. Using different T-APC cell conjugate systems, we report that p50a accumulates at the immunological synapse in activated but not in resting T cells. Our results demonstrate that ICOS membrane expression is involved in this process and that p50a plasma membrane accumulation requires a functional YMFM SH2-binding motif in ICOS. We also show that ICOS triggering with its ligand, ICOSL, induces the recruitment of p50a at the synapse of T cell/APC conjugates. In association with the p110 catalytic subunit, p50 is known to carry a stronger lipid kinase activity compared to p85a. Accordingly, we observed that ICOS engagement results in a stronger activation of PI3K. Together, these findings provide evidence that p50a is likely a determining factor in ICOS mediated PI3K activity in T cells. These results also suggest that a differential recruitment and activity of class IA PI3K subunits represents a novel mechanism in the control of PI3K signaling by costimulatory molecules.AIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF

Dok-4 is a novel negative regulator of T cell activation.: Dok-4 and T cell activation

International audienceDok-4 (downstream of tyrosine kinase-4) is a recently identified member of the Dok family of adaptor proteins, which are characterized by an amino-terminal pleckstrin homology domain, a phosphotyrosine-binding domain, and a carboxyl-terminal region containing several tyrosines and poly-proline-rich motifs. Two members of the Dok family, Dok-1 and Dok-2, have already been described as negative regulators in T cells. However, the function of Dok-4, which is also expressed in T cells, remains unknown. In this study, we report that Dok-4 is phosphorylated after TCR engagement and shuttled within the cytoplasm of T cells before being recruited to the polarized microtubule organizing center after the formation of the immunological synapse. Loss-of-function experiments using RNA interference constructs show that Dok-4 is a negative regulator of ERK phosphorylation, IL-2 promoter activity, and T cell proliferation. Exogenous expression of wild-type Dok-4 induces a significant activation of Rap1, which is involved in the regulation of ERK. The pleckstrin homology domain of Dok-4 is required both for its cytoplasmic shuttling and relocalization as well as for its inhibitory properties on T cell activation. Thus, Dok-4 represents a novel negative regulator of T cells

ICOS Ligation Recruits the p50{alpha} PI3K Regulatory Subunit to the Immunological Synapse.: ICOS-p50α interactions

International audienceICOS ligation in concert with TCR stimulation results in strong PI3K activation in T lymphocytes. The ICOS cytoplasmic tail contains an YMFM motif that binds the p85alpha subunit of class IA PI3K, similar to the YMNM motif of CD28, suggesting a redundant function of the two receptors in PI3K signaling. However, ICOS costimulation shows greater PI3K activity than CD28 in T cells. We show in this report that ICOS expression in activated T cells triggers the participation of p50alpha, one of the regulatory subunits of class IA PI3Ks. Using different T-APC cell conjugate systems, we report that p50alpha accumulates at the immunological synapse in activated but not in resting T cells. Our results demonstrate that ICOS membrane expression is involved in this process and that p50alpha plasma membrane accumulation requires a functional YMFM Src homology 2 domain-binding motif in ICOS. We also show that ICOS triggering with its ligand, ICOSL, induces the recruitment of p50alpha at the synapse of T cell/APC conjugates. In association with the p110 catalytic subunit, p50alpha is known to carry a stronger lipid kinase activity compared with p85alpha. Accordingly, we observed that ICOS engagement results in a stronger activation of PI3K. Together, these findings provide evidence that p50alpha is likely a determining factor in ICOS-mediated PI3K activity in T cells. These results also suggest that a differential recruitment and activity of class IA PI3K subunits represents a novel mechanism in the control of PI3K signaling by costimulatory molecules

Le port dans la ville : donnees d'une osmose 4 : elements d'une geographie des paysages et des territoires portuaires a Marseille

Programme cite-projets : le port et la villeSIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : RP 13613 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Targeting phosphatase-dependent proteoglycan switch for rheumatoid arthritis therapy.

Despite the availability of several therapies for rheumatoid arthritis (RA) that target the immune system, a large number of RA patients fail to achieve remission. Joint-lining cells, called fibroblast-like synoviocytes (FLS), become activated during RA and mediate joint inflammation and destruction of cartilage and bone. We identify RPTPσ, a transmembrane tyrosine phosphatase, as a therapeutic target for FLS-directed therapy. RPTPσ is reciprocally regulated by interactions with chondroitin sulfate or heparan sulfate containing extracellular proteoglycans in a mechanism called the proteoglycan switch. We show that the proteoglycan switch regulates FLS function. Incubation of FLS with a proteoglycan-binding RPTPσ decoy protein inhibited cell invasiveness and attachment to cartilage by disrupting a constitutive interaction between RPTPσ and the heparan sulfate proteoglycan syndecan-4. RPTPσ mediated the effect of proteoglycans on FLS signaling by regulating the phosphorylation and cytoskeletal localization of ezrin. Furthermore, administration of the RPTPσ decoy protein ameliorated in vivo human FLS invasiveness and arthritis severity in the K/BxN serum transfer model of RA. Our data demonstrate that FLS are regulated by an RPTPσ-dependent proteoglycan switch in vivo, which can be targeted for RA therapy. We envision that therapies targeting the proteoglycan switch or its intracellular pathway in FLS could be effective as a monotherapy or in combination with currently available immune-targeted agents to improve control of disease activity in RA patients