Deadline for full application: December 15th, 2013
Interviews: March, 2014
Start of the Ph.D.: October 1st, 2014
Department: Biologie cellulaire et infections
Title of the PhD project: Characterizing histone H3 deacetylation during infection with Listeria monocytogenes
Name of the lab: Unité interaction bactéries cellules
Head of the lab: Pascale Cossart
PhD advisor: Melanie Hamon
Email address: email@example.com
Web site address of the lab: http://www.pasteur.fr/recherche/unites/uibc/welcome.html
Doctoral school affiliation and University: University Paris 7, Diderot
Presentation of the laboratory and its research topics:
Our Unit investigates the molecular and cellular basis of the infection by Listeria monocytogenes, a model pathogen for the study of the intracellular parasitism. L. monocytogenes is responsible for severe foodborne infections. This bacterium is characterized by its ability to cross three host barriers -the intestinal, blood-brain or feto-placental barriers- and to invade several cell types in which it multiplies. L. monocytogenes moves in the cytosol of infected cells and spreads from cell to cell using an original propelling process; i.e. cell actin polymerization at one pole of the bacteria.
Our present activity focuses on: 1) the identification and characterization of new non-coding RNAs involved in virulence, as well as new RNA-mediated regulations; 2) the investigation of new molecular pathways involved in bacterial entry into host cells and cell-to-cell spread; 3) organelle dynamics during infection; 4) the systematic analysis of post-translational modifications of host molecules during infection, in particular SUMOylation; 5) chromatin remodeling upon infection; 6) the characterization of new bacterial virulence factors identified by post-genomic approaches or by their effect on cellular responses; and 7) in-depth understanding of the intestinal phase of the L. monocytogenes infection by analyzing the impact of commensals on L. monocytogenes growth and the bacterial effect on the intestinal tissue.
In many of these research themes, we try to generalize our findings to other bacterial models.
Description of the project:
(1 page, Arial font size 11 : 600 words in total with at least 50% dedicated specifically to the proposed PhD project(s))
Bacterial pathogens reprogram host cells during infection and studying how this is achieved is central to our understanding of infectious diseases. Very recently an emerging field of study has focused on the targeting of chromatin, and its associated regulatory factors, by bacterial pathogens. Indeed, infections have been shown to trigger histone modiﬁcations, thereby modulating the host’s transcriptional programs, especially those controlling immune responses. However, the molecular mechanisms involved in bacterial-induced chromatin remodelling remain largely unknown. Which host factors are involved in specific bacteria-induced chromatin modifications? What are the molecular mechanisms by which bacterial factors manipulate host chromatin? What are the targeted genes? These are some questions we aim to answer in order to understand the role of chromatin modifications in the establishment and/or persistence of infection.
More specifically, our work has uncovered a crucial role for Listeria monocytogenes induced deacetylation of histone H3 on lysine 18 during infection. While this discovery reveals a novel paradigm for manipulation of the host during infection, many questions remain regarding the molecular mechanisms at play and the genes affected by histone H3 deacetylation, which will be the focus of this thesis project.
In particular we plan to answer the following questions:
What is the molecular mechanism of SIRT2 translocation to nucleus and binding to chromatin?
Infection with L. monocytogenes is the first stimulus that has been identified which leads to translocation from the cytosol to the nucleus and chromatin association of SIRT2, a cellular deacetylase shown to be mainly cytoplasmic. We plan to study the molecular mechanisms of SIRT2 translocation. Preliminary data suggest that SIRT2 undergoes a novel dephosphorylation upon localization to the nuclear compartment. We will investigate the role of this posttranslational modification during infection and the mechanism by which it is imposed.
What is the genome-wide impact of H3K18 deacetylation and SIRT2 binding to chromatin?
Our data shows by western blot that H3K18 is globally deacetylated. However, by chromatin immunoprecipitation (ChIP), we observe deacetylation of H3K18 and SIRT2 binding at the transcription start site (TSS) of genes repressed during infection. Since TSS regions represent a small fraction of the genome, the results that we obtain by ChIP do not explain the global decrease in the levels of acetylated H3K18 observed by immunoblotting. We therefore aim to map the genome-wide distribution of H3K18 deacetylation and SIRT2 binding sites before and after infection with L. monocytogenes. A global map of SIRT2 binding will provide information regarding the genes targeted, the regions favored for binding, and could unveil a specific DNA binding motif to which a transcription factor acting to target SIRT2 would bind.
Eskandarian HA, Impens F, Nahori MA, Soubigou G, Coppée JY, Cossart P, Hamon M. A role for SIRT2-dependent histone H3K18 deacetylation in bacterial infection. Science. 2013. 341(6145):1238858
H. Bierne, M.A. Hamon, P. Cossart. Epigenetics and bacterial infections. Cold Spring Harb Perspect Med. 2, a010272 (Dec, 2012)
Hamon, M. A., and P. Cossart. Histone modifications and chromatin remodeling
during bacterial infections. Cell Host Microbe. 2008. 4:100-109
Bacteria, infection, host-pathogen interactions, chromatin remodeling, histone modifications, epigenetic regulation, histone deacetylase
Expected profile of the candidate (optional):
Contact: Mélanie Hamon, firstname.lastname@example.org