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  Sigcyto


  Director : Pellegrini Sandra (pellegri@pasteur .fr)


  abstract

 

Type I IFNs (IFN-a/b) are critical players in the innate response to pathogens and important modulators of the adaptive immune response. Our work is on the molecular mechanisms underlying the immediate-early cellular responses to IFN-a/b. We study the biosynthesis, assembly and dynamics of activation of the IFN-a/b receptor complexed to the tyrosine kinases Tyk2 and Jak1. One project is aimed at the study of the interaction between Tyk2 and the IFNAR1 receptor subunit and the elucidation of the chaperon role of the kinase. A second project concerns the biochemical and functional characterisation of two Tyk2-binding partners (Pot-1 and Pot-2) identified as in a yeast-based two hybrid screen. A third project analyses the role of IFN-a/b in the development of human T lymphocytes.



  report

cale

Nuclear localisation of Tyk2 -Ragimbeau, J., E. Dondi, A. Vasserot, P. Romero, G. Uzé and S. Pellegrini. 2001. Receptor interaction region of Tyk2 contains a motif required for its nuclear localization. J. Biol. Chem. 276 : 30812

We have studied the subcellular distribution of the wild-type Tyk2 protein and of several mutants expressed in Tyk2-deficient human cells. Direct GFP-associated fluorescence and immunostaining showed a diffuse localization of Tyk2 throughout the cell, including the nuclear compartment. The nuclear localization of Tyk2 requires a NLS-like motif, rich in arginine residues, that maps within the region mediating interaction with cytokine receptors. Our studies demonstrate that Tyk2 can reside in the nucleus independently of receptor binding. The nuclear pool is dispensable for the transcriptional and antiviral responses induced by IFN-a/b and its function remains unknown.

Interference among cytokine receptors interacting with Tyk2 - Dondi, E., E. Pattyn, G. Lutfalla, X. Van Ostade, G. Uzé, S. Pellegrini, and J. Tavernier. 2001. Down-modulation of type I interferon responses by receptor cross-competition for a shared Jak kinase. J. Biol. Chem. 276 : 47004

In contrast to the large number of cytokine receptors, only four JAK proteins exists in mammalian cells, implying the shared use of these kinases by many different receptor complexes and the possibility of interference if receptor numbers exceed the amount of available JAK. In a collaborative effort, we have investigated whether cross-competition among Tyk2-interacting receptors can occur. Our results suggest that exogenously expressed Tyk2-interacting receptors can sequester and titer out the kinase away from the endogenous IFNAR1 receptor chain, leading to a reduced IFN-a/b response. This represents a novel mechanism of trans-modulation between cytokine responses based on competition for a shared receptor-associated tyrosine kinase.

Tyk2 is a regulator of surface expression of the IFNAR1 receptor chain (J. Ragimbeau)

We have recently initiated a study of the mecanism by which the tyrosine kinase Tyk2 is required for the expression of the IFNAR1 receptor chain. We demonstrate that overexpressed IFNAR1 is confined in the Golgi compartment, whereas co-expression of IFNAR1 with Tyk2 leads to cell surface targeting of the receptor. This novel result suggests that the formation of receptor/Jak complexes occurs early during the biosynthesis of the receptor.

Novel Tyk2 partners (C. Steindler)

The amino-terminal moiety of the Jak proteins carries the molecular determinants for binding to cytokine receptors. Sequence analysis of the amino-terminal region of JAKs has revealed the presence of a band 4.1-related domain, named FERM. This domain is present in cytoskeletal proteins of the ERM family (ezrin, radixin, moesin) where it mediates intramolecular interactions and membrane targeting. A yeast two-hybrid screen was performed using as bait the FERM domain of Tyk2. Functional and biochemical characterization of two partners is in progress. Pot-1 is a novel protein expressed in most tissues and localized in a vescicular compartment. Pot-2 is neuronal-specific, it associates to microtubules and belongs to a novel family of three members.

Study of the IFN-a/b response of human T lymphocytes (E. Dondi)

A critical aspect of the immune response to pathogens is mediated by the CD4+ and CD8+ T lymphocytes which, upon activation, differentiate and expand into functionally distinct subsets. IFN-a/b is produced in response to a viral or bacterial infection and performs multiple immunoregulatory functions, thus linking innate and adaptive immunity. We have recently found that the transcriptional response to IFN-a/b of human differentiated Th1 and Th2 subsets and of activated CD8+ cells is strongly compromised as compared to their naïve precursors. This downmodulation takes place at the time of cell cycle entry and is part of the complex genetic program of T cell development. The molecular mechanism and the physiological relevance of this phenomenon are under study.



  publications

puce Publications of the unit on Pasteur's references database


  personnel

  Office staff Researchers Scientific trainees Other personnel
 

Houssin Wendy, wendy.houssin@pasteur.fr

 

Dondi Elisabetta, Post-Doc, edondi@pasteur.fr

Steindler Corinna, Post-Doc, costei@pasteur.fr

Ragimbeau Josiane, Engineer, jragimbe@pasteur.fr


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