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  Director : YANIV Moshe (yaniv@pasteur.fr)


  abstract

 

Our research unit studies the interplay between transcription factors and chromatin remodeling in activating and repressing genes in mammalian cells. Our research examines the importance of several families of transcription factors in controling cell differentiation and organogenesis, cell growth or apoptosis. We use complete or conditional gene inactivation in mice , micro-array analysis and bioinformatics. Our work has implications for understanding viral and non-viral malignant cell transformation and for deciphering the mechanisms underlying diseases such as Type II diabetes, kidney or liver disorders.



  report

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HNF1alpha and HNF1beta : development and disease Head of the group : Marco Pontoglio. Members of the group: Olivier Bluteau, Claire Chéret, Antonia Doyen, Evelyne Fischer, Lionel Gresh and Andreas Reimann

Hepatocyte Nuclear Factors 1 alpha and beta (HNF1a and HNF1b) are two homologous atypical dimeric homeoproteins that appeared during evolution with the first vertebrates. They are expressed in the polarized epithelia of different organs, including liver, kidney, pancreas and intestine, where they control the expression of numerous tissue-specific genes. Mice lacking HNF1b die in utero at embryonic day 7.5 because of a defect in visceral endoderm differentiation. In contrast, the conditional inactivation of HNF1 b in the liver leads to defective differentiation in the intrahepatic bile duct and hepatic artery. Inactivation of HNF1 a leads to postnatal dysfunctions of the liver, kidney and pancreas. These mice suffer from hypercholesterolemia, hyperphenylalaninemia, renal Fanconi syndrome and a drastic defect in insulin secretion. Mutations in both HNF1 a and b are associated with familial type II diabetes in humans (MODY3 and MODY5). We have used DNA oligonucleotide microarray hybridisation technology (Affymetrix) to identify several hundred genes whose expression is downregulated in the absence of one of these two transcription factors in the liver. We are currently studying the correlation between the transcriptional effect of these target genes and the enrichment for HNF1 binding sites detected in the nearby genomic regions using an in silico approach.

Proto-oncogenes Jun and Fos : a family of transcription factors Heads of the group : Fatima Mechta-Grigoriou and Jonathan Weitzman. Members of the group : Maya Ameyar-Zazoua, Damien Gérald, Chaouki Miled, Marta Wisniewska.

The AP-1 transcription factor is central to the cell's ability to integrate multiple extracellular signals and initiate the appropriate genetic response. AP-1 plays a critical role in regulating the cell cycle and the cellular response to stress. AP-1 is composed of dimers of Jun (c-Jun, JunB or JunD) and Fos (c-Fos, FosB, Fra1 and Fra2) proto-oncoproteins. Our laboratory focuses on unravelling the functions of the different Jun proteins using genetic and biochemical approaches. We have demonstrated that the balance between different AP-1 dimers controls progression through the cell cycle. The different Jun proteins also determine cellular transformation by the RAS oncogene. We have shown that AP-1 activates target genes such as cyclin D1 that drive cell cycle progression, as well as genes encoding inhibitors of cell proliferation such as p14ARF. We found that JunD protects cells from p53-dependent senescence and stress-induced apoptosis. These observations place AP-1 at a key position linking the RAS/pRb and p53 regulatory pathways. We are currently using genomic approaches to decipher the transcriptional programs that link AP-1 and p53 pathways in the cellular response to stress. We have found evidence for genetic redundancy and cooperation between the c-jun and junD genes. Mice lacking both jun genes display cardio-vascular and angiogenic defects during embryonic development. These mutants also exhibit an abnormal response to hypoxic stress, suggesting a potential role for AP-1 in the appearance of hypoxia-linked pathologies, such as myocardial ischemia or tumour progression. We are currently investigating the gene programs that underlie these cellular and developmental phenotypes.

Chromatin remodelling and cell growth control Head of the group : Christian Muchardt. Members of the group: Brigitte Bourachot, Bogdan Mateescu.

In eukaryotes, genomic DNA associates with histones to form chromatin. This environment renders the DNA partially inaccessible to other proteins. To overcome the chromatin barrier, the cell contains large multi-subunit machineries that use the energy of ATP hydrolysis to locally modify the histone-DNA interactions. One of these machineries is known as the SWI/SNF complex. This complex is specifically involved in transcription and facilitates the recruitment of transcriptional regulators to a limited number of promoters. We have shown that this complex is essential for early development of mice. In addition, several lines of evidence suggest that the SWI/SNF complex is generally associated with the control of cell growth. We have shown that overexpression of Brm, the catalytic subunit of the complex, slows down the growth of cancer cells. Conversely, inactivation of the Brm gene in mice causes increased cell proliferation. Another subunit of the complex, known as SNF5/INI1, is encoded by a "tumor suppressor" gene inactivated in rhabdoid tumors, a very aggressive form of cancer of young children. We have shown that inactivation of both copies of this gene in mice leads to the formation of tumors with many similarities to the human rhabdoid tumors. The use of conditional inactivation and microarrays RNA hybridization will help to unravel how inactivation of the SWI/SNF complex deregulates cell proliferation. Another protein that regulates the accessibility of the chromatin is HP1 (Heterochromatin Protein 1). We have shown that HP1 interaction with the pericentromeric chromatin depends both on its capacity to recognize methylated H3 histone, as well as on RNA recognition.

Control of human papillomavirus type 18 carcinogenesis . Head of the group : Françoise Thierry. Members of the group : Sophie Bellanger, Stéphanie Blachon, Caroline Demeret, Sébastien Teissier.

Our research focuses on the mechanisms of malignant conversion of cervical cells infected with the Human Papillomavirus type 18 (HPV18). Cervical cancer is the second cause of mortality in women from cancer, after breast cancer. The HPV virus infects specifically the genital tract, where it replicates in the upper layers of the epidermis. The virus encodes two oncogenic proteins E6 and E7, which alter the normal proliferative control of cells by interfering with two regulatory proteins of the cell cycle, p53 and pRB. During carcinogenic progression, the viral genome integrates into the cellular genome from which transcription of the two viral oncogenes is strongly activated by a high-order transcriptional control element called an "enhanceosome". This viral enhanceosome is specific for cervical carcinoma cells and is exclusively composed of cellular proteins. We are currently searching for the proteins involved in its activity and for the basis of its cell specificity using chromatin immunoprecipitation experiments. In contrast, transcription of the viral oncogenes is repressed by the viral protein E2, which is specifically inactivated upon integration of the viral DNA into the cellular genome in cervical carcinomas. Reintroduction of the viral E2 protein into these cells induces a strong anti-proliferative effect that is due to both cell cycle arrest and cell death by apoptosis. We are currently studying this anti-proliferative effect of E2 using specific molecular approaches, as well as global strategies involving microarray analysis.

Photo: Hepatic gene expression pattern in HNF1alpha and HNF1beta mutant mice

Hierarchical clustering of gene expression pattern of livers carrying different genotypes as indicated just above each group of three columns. HNF1a, WT and HNF1b stand for HNF1a-/-, wild-type and HNF1b -/- animals at 8 days after birth. The last group of 3 columns, at the right and labelled "E18.5", represents the expression of the same set of genes just immediately before birth in wild-type animals. Each column represents an independent hybridization (3 replica for each group). The expression level of each gene is represented with different colors as indicated below (blue = downregulated; red = upregulated).

Keywords: oncogens, transcription, chromatin, development, cell cycle, diabetes



  publications

puce Publications of the unit on Pasteur's references database


  personnel

  Office staff Researchers Scientific trainees Other personnel
  OLLIVIER Edith, Institut Pasteur, secretary DEMERET Caroline, Institut Pasteur, Assistant de Recherche (cdemeret@pasteur.fr)

LAVIGNE Marc, Institut Pasteur, Chargé de Recherche (mlavigne@pasteur.fr)

MECHTA-GRIGORIOU Fatima, Institut Pasteur, Chargé de Recherche (fmechta@pasteur.fr)

MUCHARDT Christian, CNRS, CR1 (muchardt@pasteur.fr)

PONTOGLIO Marco, CNRS, DR2 (marcop@pasteur.fr)

THIERRY Françoise, Institut Pasteur, Chef de laboratoire (fthierry@pasteur.fr)

WEITZMAN Jonathan, Institut Pasteur, Chargé de Recherche (jonnyw@pasteur.fr

AMEYAR-ZAZOUA Maya, Postdoc (maya@pasteur.fr)

BELLANGER Sophie, PhD student (bellange@pasteur.fr)

BLACHON Stéphanie, PhD student (sblachon@pasteur.fr)

BLUTEAU Olivier, Postdoc (obluteau@pasteur.fr)

CHERET Claire, PhD student (ccheret@pasteur.fr)

FISCHER Evelyne, Postdoc (efischer@pasteur.fr)

GERALD Damien, PhD student (dgerald@pasteur.fr)

GRESH Lionel, PhD student (gresh@pasteur.fr)

MATEESCU Bogdan, PhD student

MILED Chaouki, Postdoc (miled@pasteur.fr)

REIMANN Andreas, PhD student (areimann@pasteur.fr)

TEISSIER Sébastien, PhD student (teissier@pasteur.fr)

WISNIEWSKA Marta, Postdoc (mwisniew@pasteur.fr)

BOURACHOT Brigitte, CNRS, Ingénieur d’Etudes (bboura@pasteur.fr)

DOYEN Antonia, Institut Pasteur, Technicienne Supérieure (adoyen@pasteur.fr)

GARBAY Serge, CNRS, Ingénieur de Recherche (garbay@pasteur.fr)


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