Chromatin dynamics during T lymphocyte activation: role of HP1 – chromaTin

Chromatin immunoprecipitation approach allowed monitoring epigenetic modifications at precise genomic locations and therefore defining the mechanisms of the off-lineage gene silencing during TH2 development. Allergic asthma model in mice allowed to follow the development of this pathology under deficiency in epigenetic silencers of interest and under the treatment with epigenetic drug.

It has been shown that the epigenetic pathway Suv39h1/HP1? plays an important role in the stability of TH2 cells by directly silencing TH1 genes. Without each of these proteins, TH2 cells remain plastic and can be reprogrammed into TH1 under TH1-skewing conditions. Suv39h1/HP1a deficiencies or chemical inhibition of Suv39h1 were beneficial to the outcome of allergic asthma in mice and were associated with changes in the TH2/TH1 ratio.

The obtained results establish a link between Suv39h1/ HP1? pathway and the stability of TH2 cells and help to identify potential targets for therapeutic intervention during TH2-mediated inflammatory diseases.

Patent: Methods and Pharmaceutical compositions for the treatment of TH2 mediadted diseases n° de depot 113062723 du 03/10/2011

Publication:
An epigenetic silencing pathway controlling T helper 2 cell lineage commitment.
Allan RS, Zueva E, Cammas F, Schreiber HA, Masson V, Belz GT, Roche D, Maison C, Quivy JP, Almouzni G, Amigorena S. Nature. 2012 Jul 12;487(7406):249-53.

Efficient T cell responses require a precise orchestration of T cell activation and proliferation (for the clonal selection of antigen specific cells), differentiation (into effectors or memory cells) and death (during the contraction phase). Although immunologists have analyzed all these different phases of T cells responses in great details, the nuclear organization and chromatin dynamics implicated received little attention so far. Activation, proliferation, differentiation and cell death have all been analyzed in great details in other cell types, and the results show that epigenetic marks and chromatin dynamics play critical roles in the control of all these processes. It is therefore most likely, but has not yet been addressed in details, that this is also the case in T lymphocytes.

The present project will investigate the function HP1 in T lymphocytes. In other cell types, HP1 inhibits transcription through heterochromatin propagation, an effect that requires the histone methyltransferase Suv39h. HP1 and Suv39h can be recruited by negative regulators of gene transcription to the promoters of genes found in specific regions of the heterochromatin involved in gene silencing. Importantly, it was shown (and our preliminary results confirmed it) that upon T cell activation, HP1 is recruited to dense heterochromatin domains in a Suv39h-dependent manner. In addition, one of the main phenotypes of Suv39h-deficient mice is immunological (splenomegaly, strong lymphoproliferation).

The main objective of this project is therefore to investigate the function of HP1 and its associated proteins (including Suv39h and CAF1) in T lymphocytes. We will analyze the dynamics of chromatin re-arrangements during T cell activation, using both morphological (immunofluorescence and dynamic imaging) and biochemical (co-immunoprecipitation and Tandem-Affinty-Purification (TAP)) approaches. We will also identify the genes targeted by these histone marks (using Chipseq) and the genes regulated by through this pathway (using RNAseq) in T lymphocytes knocked down or knock out for Suv39h, HP1 or CAF1. Finally, the same deficient T cells will be used to analyze the functions of the corresponding proteins in T cell activation, proliferation, differentiation (into effector or memory cells) and death.

The lab of the coordinator of this project (Partner 1), S. Amigorena, has been interested in T cell-dendritic cell biology for many years. His lab made important contributions to the analysis of T cell activation, analysing the dynamics of T cell interactions with dendritic cells, both in vitro and in vivo. The lab of G. Almouzni and C. Maison (Partner 2), made critical contributions and developped numerous dedicated experimental tools for the functional analysis of HP1 and CAF1-related chromatin dynamics. The lab of J-C Andrau and P. Ferrier (partner 3) has established different technological approaches for the systemic analysis of epigenetic marks or gene expression. Together, the 3 labs involved have all the conceptual and technological expertise required for the success of this project. Although the present project will focus on H3K9me3 and HP1, the collaboration of the 3 labs will establish a solid ground for the future analysis of other epigenetic marks and their associated factors in T lymphocytes.