Cytokine Signalling - CNRS URA 1961  

  MEMBERSDr BROGARD Béatrice / BANG Gilles / CORRE Béatrice / DONG Shen / FRANCOIS Véronique / HUGOT Bérengère / Dr LI Zhi / Dr MANCEAU Hana / Dr MICHEL Frédérique / MORAGA GONZALEZ Ignacio

  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- From the description of the biochemical behaviour of the type I IFN receptor subunits, we moved to the study of the cellular determinants and the signaling events that govern the differential activities of IFN α2 and IFN β, two subtypes used in therapy for different diseases. Using a controlled cellular system we have questioned the relationship between ligand-receptor binding parameters and activation of intracellular effectors. We have shown that the α/β differential depends not only on ligand binding parameters but also on the density of receptor components. Moreover, we have excluded a linear correlation between activation of Stat proteins and antiproliferative activity and implicated non-Stat signaling effectors in the higher apoptotic potency of IFNβ.

To gain insights into receptor trafficking and its relation to IFN subtype specific signaling, we performed subcellular organelle fractionation from IFN-stimulated B lymphoma cells and identified biochemically an early endosomal compartment bearing the activated IFN receptor. The prolonged interaction of the Jak tyrosine kinases, still in an activated configuration, with the endocytosed receptors suggests that non-Stat signaling events can initiate or be regulated during vesicular trafficking.We have put forward a model of receptor activation by the two IFN subtypes and proposed that subtype-specific signaling may depend on endocytic routing.

II- We have continued addressing questions on the protein tyrosine kinase Tyk2. This member of the Janus kinase family is activated by several immune cytokines and may well represent an ideal target for therapeutical intervention in autoimmune diseases. Yet its regulation and precise role in immune cytokine signaling remain ill defined. The survey of sequence resources from International Consortia reveals a high number of single nucleotide polymorphisms (SNP) in the Tyk2 coding region. Family studies have shown the strong linkage of Tyk2 haplotypes or individual SNPs to risk of systemic and organ-specific autoimmune diseases (systemic lupus erythematosus, multiple sclerosis, Crohn’s disease). Thus, naturally occurring Tyk2 variants may underlie differential susceptibilities to complex immune diseases. We are exploring the biochemical and functional behaviour of some Tyk2 variants.

III- In collaboration with G. Uzé (CNRS, Montpellier II), we found that primary and transformed cells of different lineages that have been primed with IFNαβbecome refractory to a second stimulation with IFNα2 but retain sensitivity to IFNβ. This refractory state, designated differential desensitization, is targeted to all IFNα subtypes, is dependent of protein synthesis and is not consequent to receptor downregulation. We are presently investigating the molecular mechanism underlying this prolonged and specific inhibition of the IFNα response.

IV- The outcome of a naïve T cell activated by an antigen-presenting cell depends on the integration of distinct signals emanating from the T cell antigen receptor, costimulatory receptors and the cytokine environment. Our studies are focused on the understanding of the molecular mechanisms that regulate the early biochemical TCR signal and, consequently, T cell differentiation and effector functions. We have previously shown that the transmembrane scaffold protein LAT, Linker for activation of T cells, has an immunomodulatory role by recruiting negative regulators that attenuate TCR signaling (Dong, JEM, 2006). Our recent data indicate that the strength of TCR stimulation is critical in the establishment of positive and negative regulatory loops. We found a functional connection between the LAT and TCR/Src kinase modules and we propose that LAT promotes the maintenance of active Lck and Fyn close to their substrates at low strength of TCR engagement. In so doing, LAT may sustain not only the propagation of TCR signal but also the initiation. We also found that some intracellular signaling pathways are not impaired in LAT-depleted T cells. One goal is to decipher LAT-dependent and independent regulatory mechanisms of TCR signaling. Another aim is to understand how signals induced by the innate cytokines type I interferons integrate with TCR signaling.

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. 203:2509-2518. PMID: 17043143

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

Acuto, O., V. Di Bartolo, and F. Michel. 2008. Tailoring T-cell receptor signals by proximal negative feedback mechanisms. Nature Rev. Immunol. 8:699-712. PMID: 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. 181:5847-5856. PMID: 18941173

Moraga, M., D. Harari, G. Schreiber, G. Uzé, and S. Pellegrini. 2009. Receptor density is key to the interferon alpha2/beta differential activities. Mol. Cell. Biol. 29:4778-4787. PMID: 19564411

Activity Reports 2009 - Institut Pasteur
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