PhD PROPOSAL FOR THE PASTEUR-PARIS UNIVERSITY INTERNATIONAL PROGRAM

 

Deadline for full application: December 15th, 2013

 

Interviews: March, 2014

Start of the Ph.D.: October 1st, 2014

 

 

 

Department: Microbiology

Title of the PhD project:

 

Characterization of H. pylori factors responsible for mitochondria alteration and their consequences on gastric pathogenesis.

 

Name of the lab: Unité de Pathogenèse de Helicobacter

Head of the lab: H. DE REUSE

PhD advisor: E. TOUATI

Email address: etouati@pasteur.fr

Web site address of the lab:

http://www.pasteur.fr/ip/easysite/pasteur/en/research/scientific-departm...

Doctoral school affiliation and University:

Biochimie, Biothérapies, Biologie Moléculaire et Infectiologie-B3MI

Université Paris-Diderot, Paris 7

 

 

Presentation of the laboratory and its research topics:

 

Our group is composed of eight members and our research focuses on the pathogenesis of Helicobacter pylori by studying both bacterial virulence factors and the relation between H. pylori and its infected host.

We focus on the identification and characterization of H. pylori factors and mechanisms that make this bacterium a successful and persistent pathogen in its unique niche, the acidic stomach. Nickel is an essential element for H. pylori as it is the co-factor of the major virulence and acid-resistance factor, urease that produces large amounts of ammonia. We are characterizing original mechanisms for nickel uptake (TonB-dependent transporter), trafficking (protein complexes and chaperones) and regulation of its homeostasis by a multifaceted regulator, NikR. We also study the post-transcriptional gene regulation in H. pylori and the minimal RNA-degradosome associated to translating ribosomes that we have recently discovered.

In addition, we analyze the host response and genotoxicity associated with the infection by H. pylori, in relation with the gastric cancer development. The role of genetic instabilities and epigenetic alterations associated with H. pylori infection are investigated and their consequences for the host. Such events play a key role in the early steps of carcinogenesis. Another aspect of our studies concerns mitochondria which are important target in the host response to pathogens. We are investigating the consequences of H. pylori infection on these organelles and their impact on the gastric cancer process. We also search for host gene candidates as potential risk factors for the induction of gastric malignancies by H. pylori infection, focusing on pleiotropic regulators as transcription factors as preventive/diagnostic markers for gastric cancer.

 

 

 

 Description of the project:

(1 page, Arial font size 11 : 600 words in total with at least 50% dedicated specifically to the PhD project(s))

 

Although its incidence and mortality rates have gradually decreased in the last decades, gastric cancer remains the second cause of cancer-related death in developing countries and the fourth in industrialized countries. Helicobacter pylori (Hp) infection is a major risk factor for gastric cancer, associated with 60 to 80% of diagnosed cases. This bacterium is responsible for the most common infection among the human population worldwide. Hp induces a chronic gastritis in all infected-people that will evolve into peptic disease, MALT lymphoma or gastric adenocarcinoma. Hp is until now the unique bacteria recognized as related to cancer development. The mechanisms associated to the infection and responsible for the development of gastric cancer lesions are still unclear. The complex interplay between Hp strains, inflammation, host and environmental factors is thought to directly promote the gastric carcinogenesis. This bacterium possesses several virulence factors that allow its adaptation and resistance to stomach acidity as well as its escape from the host immune response. One important factor largely studied in the laboratory is urease that is responsible for the Hp resistance to the gastric acidity. The Cag pathogenicity island (CagPAI) coding for a type IV secretion system and the oncoprotein CagA is present in bacterial strains associated with more severe pathologies. Using a mouse model, our group showed that Hp induces a mutagenic effect associated to inflammation in the gastric mucosa. This mutagenic activity is related to an impairment of DNA repair activity of gastric epithelial cells including the inhibition of the expression mismatch repair and base excision repair genes. The mutator activity of H. pylori infection leads to alterations of key physiological regulatory processes, that certainly play a central role in the transformation of normal gastric cells into cancer cells.

Targeting mitochondria is a common strategy for pathogens to interfere with host cell physiology. One Hp factor, the pro-apoptotic cytotoxin VacA targets mitochondria forming anion-channels in the mitochondria inner-membrane leading to decreased ATP production and release of cytochrome C. Mitochondria dysfunction is also associated with human diseases and cancer. Moreover, mitochondrial DNA (mtDNA) mutations are present in most of the tumors analyzed including gastric adenocarcinoma. We have previously demonstrated that Hp infection induces mutations in the mitochondrial genome. This mutagenic effect is associated with mitochondrial alterations and deregulation of important functions involved in the maintenance of mtDNA integrity. The project aims i) to analyze the mechanisms induced by Hp infection and responsible for mitochondrial dysfunctions and mtDNA instabilities, ii) to characterize Hp factors responsible for mitochondrial alterations with a special focus on bacterial factors for which we have preliminary data indicating their involvement in the mitochondria damaging pathway. Several Hp mutants of the genes coding for these factors will be constructed and their consequences on mitochondria and mtDNA will be investigated on various types of gastric epithelial cells, and iii) to analyze the consequences of Hp factors on mitochondrial dysfunction and their impact on the gastric precancerous cascade initiated by Hp using a mouse model of gastric carcinogenesis currently in use in our laboratory.

This project is pluri-disciplinary involving different fields of biology as cellular biology, imaging, microbiology and bacterial genetics as well as animal model experimentation.

 

 

 

References:

 

- Machado AM, Figueiredo C, Touati E, Máximo V, Sousa S, Michel V, Carneiro F, Nielsen FC, Seruca R, Rasmussen LJ (2009) Helicobacter pylori infection influences genetic stability of nuclear and mitochondrial DNA. Clinical Cancer Research, 15 : 2995-3002.

 

- Bussière FI, Michel V, Mémet S, Avé P, Vivas JR, Huerre M, Touati E (2010) H. pylori-induced promoter hypermethylation downregulates USF1 and USF2 transcription factor gene expression. Cellular Microbiology, 12 : 1124-1133.

 

-Touati E. (2010) When bacteria are mutagenic and carcinogenic: lessons from H. pylori. Mutation Research. 703: 66-70.

 

- Muller C, Bahlawane C, Aubert S, Delay CM, Schauer K, Michaud-Soret I, De Reuse H (2011) Hierarchical regulation of the NikR-mediated nickel response in Helicobacter pylori. Nucleic Acids Res. 39 : 7564-7575

 

- Gomes J, Magalhaes A, Michel V, Amado I, Aranha P, Ovesen RG, Hansen HCB, Gartner F, Reis CA, Touati E (2012) Pteridium aquilinum and its ptaquiloside toxin induce DNA damage response in gastric epithelial cells, a link with gastric carcinogenesis. Toxicological Sciences, 126 : 60-71.

 

- Correia M, Michel V, Matos AP, Oliveira MJ, Ferreira R, Huerre M, Dillies MA, Seruca R., Figueiredo C, Machado JC, Touati E (2012) Docosahexaenoic acid (DHA) inhibits Helicobacter pylori growth in culture and mouse gastric colonization.  PLoS ONE, 7: e35072

 

- Redko Y, Aubert S, Stachowicz A, Lenormand P, Namane A, Darfeuille F, Thibonnier M, De Reuse H (2013) A minimal bacterial RNAse J-based degradosome is associated with translating ribosomes. Nucleic Acids Res. 41 : 288-301

 

- Correia M, Michel V, Osorio H, El Ghachi M, Bonis M, Boneca IG, De Reuse H, Matos AA, Lenormand P, Seruca R, Figueiredo C, Machado JC, Touati E (2013) Crosstalk between Helicobacter pylori and gastric epithelial cells is impaired by docosahexaenoic acid. PLoS ONE, 8 : e60657.

 

 

Keywords:

 

H. pylori infection, mitochondria, bacterial factors, mutation, gastric cancer

 

 

 

Expected profile of the candidate (optional):

 

Solid knowledge in cellular biology and microbiology is required

 

 

Contact: Eliette Touati: etouati@pasteur.fr

 

 

 

Mis à jour le 16/09/2013