|Director : Israël Alain (firstname.lastname@example.org)|
The laboratory is involved in the study of two signalisation pathways characterized by inducible proteolysis events that lead to the nuclear translocation of transcription factors. The first project deals with the rel/NF-kB family of transcription factors, whose activity is controled by cytoplasmic retention through inhibitory molecules (IkBs) which get degraded in response to multiple signals. We have identified the first human genetic disease caused by mutations in a gene encoding a component of this signaling pathway (the NEMO protein), as well as a series of pathologies due to hypomorphic mutations in the same gene. We have also generated a series of transgenic mice where one or more of the IkB molecules have been inactivated, as well as mice where NF-kB activity has been inhibited in a tissue-specific manner.
A second project deals with the Notch receptor which transmits its signal following a series of three proteolytic steps which are followed by the nuclear translocation of the intracellular part of the receptor, which then behaves as a transcriptional co-activator : we have identified a mechanism of control of this activity which involves the degradation of the nuclear form of Notch.
Genetic and biochemical analysis of the NF-kB signaling pathway (G. Courtois, R. Weil, L. Arbibe, C. Bessia, K. Schwamborn)
In collaboration with an international consortium we have demonstrated that the human genetic disease known as Incontinentia pigmenti (IP) is the consequence of mutations in the gene encoding NEMO, the structural/regulatory subunit of the IKK complex, that plays a central role in the NF-kB signaling cascade. These mutations lead to a complete inactivation of this pathway. In collaboration with the group of JL Casanova (hopital Necker), we have shown that NEMO mutations that do not totally abolish the NF-kB pathway lead to a series of symptoms in male patients that associate a defect in innate immunity to a syndrom called EDA (anhydrotic ectodermal dysplasia). In collaboration with the group of K Rajewsky (Köln, Germany) we have generated mice carrying an inactivation of the Nemo gene, which represent a good animal model for IP.
We have finally characterized a molecule (called NRP/FIP2) which shows strong homologies with NEMO, which is associated with kinases in a high molecular weight complex, but which is not involved in the NF-kB cascade.
In vivo analysis of NF-kB activity (S. Mémet, A. Lilienbaum, V. Fridmacher, B. Goudeau)
Following the inactivation of the gene encoding the IkBe inhibitor, which allowed us to show that this molecule is involved in the differentiation of one of the T cell subpopulations and the transcriptional control of certain immunoglobulin and cytokine genes, we have constructed mice devoid of both IkBa et IkBe. The phenotype of these double KO mice is more severe than each individual KO : they die at birth and exhibit an increased NF-kB activity, correlated with an increased expression of some of its target genes. The analysis of lymphoid cells at E18.5 shows a deficiency in mature B cells, caused by a massive apoptosis of progenitor cells. Reconstitution experiments in host mice have revealed an unexpected role of NF-kB in the migration of B and T cells towards secondary lymphoid organs. These results confirm the central role played by NF-kB in homeostasis and survival of lymphocytes, and suggest that a decrease or an increase in NF-kB activity can lead to similar types of symptoms.
In parallel, an approach allowing to specifically express the IkBa inhibitor in a particular tissue has been undertaken. A particular effort has been made to target the brain, as previous experiments using NF-kB-lacZ reporter mice had indicated that several regions of the brain specifically exhibit a constitutive NF-kB activity. In this respect, the response of primary neurons to various NF-kB inducing signals has been evaluated.
The Notch signaling cascade (F. Logeat, C. Brou, N. Gupta, E. Six, O. LeBail)
We have proposed a model according to which the activation of the Notch receptor involves a series of three proteolytic steps. The first cleavage is due to a furin-like convertase, and is required for surface expression of a functional Notch receptor. A second cleavage, which takes place in the extracellular region of the receptor and is required for ligand-induced activation, has been characterized. The responsible enzyme has been purified and identified as TACE, a membrane metalloprotease already known to be involved in TNF shedding. The third and last cleavage is due to an activity called g-secretase and results in the liberation of the intracellular region of the receptor, which is then transported to the nucleus where it behaves as a transcriptional coactivator. We have recently shown that the activity of this molecule is controled by the ubiquitin-proteasome pathway : following a nuclear phosphorylation event, it is recognized by an ubiquitin-ligase called SEL-10, therefore leading to its degradation by the proteasome.
|Publications of the unit on Pasteur's references database|
|Office staff||Researchers||Scientific trainees||Other personnel|
BROU Christel, Institut Pasteur
COURTOIS Gilles, INSERM
LOGEAT Frédérique, CNRS
MÉMET Sylvie, INSERM
WEIL, Robert, CNRS
ARBIBE Laurence, post-doc
GUPTA Neetu, post-doc
SIX Emmanuelle, PhD student
LEBAIL Odile, engineer Institut Pasteur
BESSIA Christine, technician Institut Pasteur