Cytokine Signalling - CNRS URA 1961  

  MEMBERSDr BROGARD Béatrice / BANG Gilles / CORRE Béatrice / DONG Shen / FRANCOIS Véronique / HUGOT Bérengère / MORAGA GONZALEZ Ignacio / Dr MICHEL Frédérique / Dr RAGIMBEAU Josiane

  Annual Report

Type I interferons (IFN) contribute to immediate defense against pathogens, development of an adaptive immunity and protective antitumor responses. Several IFN subtypes participate vigorously in the cytokine network that regulates differentiation, function and homeostasis of a variety of cell lineages. IFN are pathogenic factors in a number of systemic and organ-specific autoimmune and inflammatory diseases but they are also among the most widely used therapeutic agents. An important aspect of our research centers on the molecular mechanisms of type I IFN action, with particular attention to receptor and Jak tyrosine kinases functioning, differential activities of IFNα2 and IFNβ, engagement of non-Stat signaling cascades and mechanisms leading to cellular desensitization.

I- Our studies have established new concepts regarding the role of Jaks and receptor traffic. We found that the catalytic activity of Tyk2 is required for ligand-induced modification and lysosomal proteolysis of the IFNAR1 receptor chain. The intracellular route of the other receptor chain, IFNAR2, is influenced by the IFN subtype bound. To gain insights into receptor trafficking and its relation to subtype-specific signaling, we performed subcellular organelle fractionation from IFN-stimulated Daudi cells and defined biochemically an early endosomal compartment bearing the activated IFN receptor. Altogether, our data strongly point to the prolonged interaction of the Jak tyrosine kinases, still in an activated configuration, with the receptors and suggest that trafficking of the complex through endosomes may regulate signaling pathways.

II- We have analyzed the behaviour of a Tyk2 mutant bearing the V678F substitution in the kinase-like domain. Importantly, in Jak2 the same mutation (V617F) has been implicated in a wide range of myeloproliferative diseases. We found that Tyk2V678F has high basal catalytic potential and phosphorylates constitutively Stat3, but, surprisingly, has no effect on the canonical IFN-induced signaling. Only if anchored to a homodimeric EpoR/R1 chimeric receptor Tyk2V678F confers increased sensitivity to ligand. Thus, despite a catalytic gain of function of Tyk2V678F, an effect on ligand-induced signaling is manifest only when two mutant enzymes are juxtaposed via the homodimeric receptor. This result suggests that Jak1, which faces Tyk2 in the type I IFN receptor, prevails over the deregulated Tyk2 mutant and points to the existence of a hierarchy of Jak function in the IFN receptor and perhaps in other cytokine receptors.

III- Jakmip1 ( Jak and microtubule interacting protein) was identified in a screen for Tyk2 interactors. Jakmip1 associates to microtubules in both neuronal cells and lymphocytes. We have analyzed expression and function of Jakmip1 in distinct subsets of human primary T lymphocytes. Jakmip1 is transcriptionally induced upon T cell priming, with maximal expression in the terminally differentiated CD8+ effector subset with highest cytotoxic potential. Functional analysis by lentiviral mediated silencing in primary CD8+ T cells showed that Jakmip1 negatively regulates the killing potential of cytotoxic T lymphocytes.

IV- We are interested in understanding the molecular mechanisms that regulate T cell activation in response to T cell receptor (TCR) stimulation. TCR-mediated signal form, characterized by its intensity and duration, is thought to depend on the strength of stimulation, the latter correlating with the half-life of TCR interaction with its ligand, the peptide-MHC complex. New models propose that negative and positive feedback loops also influence signal form and, consequently, T cell biological outcomes such as cell survival, differentiation and death. Our aim is to better understand regulatory mechanisms of TCR signaling that depend on the transmembrane scaffold protein LAT (Linker for activation of T cells). We have previously shown that TCR engagement leads to the recruitment of the inhibitory adaptors Dok-1 and Dok-2 into a multimolecular complex that interacts with LAT and attenuates the activation of the protein tyrosine kinase ZAP-70. Our recent data point to a new layer of control on TCR signal initiation by LAT. This control operates within a restricted window of TCR stimulation. Another goal to understand how T cell activation is influenced in the presence of type 1 interferons, one of the earliest cytokines produced in a pathogenic viral or bacterial environment. We focus on the direct effect of IFN on T cells and explore potential crosstalks at the level of early biochemical signals that may affect T helper cell differentiation.

Throughout these studies we hope to gain new insights into the molecular mechanisms of IFN action, understand how individual IFN subtypes act differentially and unravel the nature of the cooperative crosstalk between IFN and stimulation of the TCR.

Keywords: signaling, tyrosine kinase, innate immune response, inflammation, T cell activation, T cell receptor


Dong S, B. Corre, E. Foulon, E. Dufour, A. Veillette, O. Acuto, and F. Michel. 2006. T cell receptor for antigen induces linker for activation of T cell-dependent activation of a negative signaling complex involving Dok-2, SHIP-1, and Grb-2. J. Exp. Med. 203 : 2509-2518PMID: 17043143

Marijanovic, Z., J. Ragimbeau, J. Van der Heyden, G. Uzé, and S. Pellegrini. 2007. Comparable potency of IFNα and IFNβon immediate Jak/Stat activation but differential down-regulation of IFNAR2.Biochem. J., 407 : 141-151PMID: 17627610

Gakovic M., J. Ragimbeau, V. Francois, S.N. Constantinescu, and S. Pellegrini. 2008. The Stat3 activating Tyk2V678F mutant does not upregulate signaling through the type I IFN receptor but confers ligand hypersensitivity to a homodimeric receptor. J. Biol. Chem. 283:18522-18529PMID: 18456658

Acuto, O., Di Bartolo, V.,and F. Michel. 2008. Tailoring T-cell receptor signals by proximal negative feedback mechanisms. Nature Rev. Immunol. 8:699-712PMID: 18728635

Libri V., D. Schulte, A. van Stijn, J. Ragimbeau, L. Rogge, and S. Pellegrini. 2008. Jakmip1 is expressed upon T cell differentiation and has an inhibitory function in cytotoxic T lymphocytes. J Immunol. 181:5847-5856PMID: 18941173

Activity Reports 2009 - Institut Pasteur
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