Unit: Cytokine Signalling - CNRS URA 1961
Director: Pellegrini Sandra
Our projects point toward a better understanding of the complex signaling networks induced by type I interferons (IFN-α/β, particularly during the T lymphocyte immune response. We have studied the modulating effects of IFN-α/β, on human T lymphocytes at different times post-activation. We have progressed on the study of the receptor and the Jak tyrosine-kinases, as well as on the functional and biochemical characterization of novel proteins that associate with Jak kinases.
IFN-α/βin the control of human CD4+ T lymphocyte homeostasis
E. Dondi, in collaboration with the group of S. Susin (Groupe Apoptose et Système Immunitaire, I.P.)
Upon infection, IFN-α/βis rapidly secreted and participates in building up an early innate response. When produced by dendritic cells, IFN-α/βstimulate their maturation and their capacity to polarize T lymphocytes, thus linking innate and adaptive responses. To characterize the activities exerted by IFN-α/βdirectly on human T lymphocytes, we have compared IFN-α/βresponses in naïves T CD4+ T cells, purified from umbilical cord blood, before and after their in vitro activation. We found that upon TCR/CD28 stimulation of naïve cells there are significant changes in the proliferative and transcriptional responses to IFN-α/β Thus, the IFN signaling cascade is modulated according to the activation state of T cells (Dondi et al, 2003. J. Immunol. 170:749). In the same experimental model, we are presently studying the impact of IFN-α on cell death induced by TCR/CD28 engagement. By measuring death rates as well as morphological and molecular apopotic hallmarks, we conclude that, at 48 hr post-activation, an intrinsic mitochondrial apoptotic pathway is activated. IFN-α exerts a protective effect on the mitochondrial integrity, by modulating the Bcl-2/Bax ratio. Interestingly, at later times post-activation, IFN-α sensitizes cells to the extrinsic Fas/caspase8-dependent apoptotic pathway.
The tyrosine kinase Tyk2 and the traffic of the IFNAR1 receptor chain
J. Ragimbeau et Z. Marijanovic, in collaboration with A. Alcovèr (Unité de Biologie des Interactions Cellulaires, I. P.)
The four tyrosine kinases of the mammalian Jak family are non-covalently associated with cell surface receptors that bind four-helical bundled cytokines. In the type I IFN receptor complex, Tyk2, a member of the Jak family, associates with the IFNAR1 receptor subunit and positively influences ligand binding to the receptor complex. Tyk2 is essential for stable cell surface expression of IFNAR1. In the absence of Tyk2, mature IFNAR1 localizes into a perinuclear endosomal compartment. Conversely, co-expressed Tyk2, via its amino-terminal region, greatly enhances surface IFNAR1 expression, by reducing its basal internalization rate. Our results reveal a novel function of a Jak family member in the regulation of the surface level of cytokine receptor. We are presently interested in the fate of the IFN receptor components following ligand binding. In particular, we investigate the role of the Jak proteins in ligand-induced internalization and degradation of the receptor. Given the complexity of this four-component system (two receptor chains and two different Jaks), we initially restrain our analyses to two partners, using chimeric receptors.
Jamip, a novel family of proteins associated with microtubules and Jak tyrosine kinases
C. Steindler et Z. Li
Jamip1 (Jak and microtubule interacting protein) was identified for its ability to bind to the FERM homology domain of Tyk2. Jamip1 belongs to a novel family of three genes conserved in vertebrates and predominantly expressed in neural tissues and lymphoid organs. These proteins lack known domains and are extremely rich in predicted coiled coils that mediate dimerisation. In our initial characterisation of Jamip1, we found that it comprises a N-terminal region that targets the protein to microtubule polymers and, when overexpressed in fibroblasts, profoundly perturbs the microtubule network, inducing the formation of tight and stable bundles. The C-terminal domain of Jamip1 interacts with Jak kinases and can be target of multiple phosphorylation. The restricted expression of Jamip1 and its ability to associate to, and modify, microtubule polymers suggest a specialised function of these proteins in dynamic processes - cell polarisation, segregation of signaling complexes, vescicle traffic - some of which may involve Jak tyrosine kinases.
Keywords: immunology, signaling, cytokine, interferon-?/?, receptor, tyrosine kinase