Unit: Oncogenic Viruses - FRE2850 du CNRS
Director: YANIV Moshe
Our research unit studies the interplay between transcription factors, chromatin remodelling complexes and other chromosomal proteins in activating and repressing genes in mammalian cells. Our research examines the importance of several families of transcription factors in controlling 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 other diseases such as Type II diabetes, kidney polycystic disease or hepatic ductal plates malformation.
HNF1alpha and HNF1beta : Development and Disease
Group leader : Marco Pontoglio
Other members of the group : Olivier Bluteau, Anna d'Angelo, Antonia Doyen, Evelyne Fischer, Serge Garbay, Lionel Gresh and Andreas Reimann
Organ formation during development is a complex phenomenon whose molecular mechanisms are only partially understood. Hepatocyte Nuclear Factors 1 alpha and beta (HNF1α and HNF1β) are two homologous atypical 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. To gain more insight into the role of these genes during development, we have generated mouse models carrying null mutations in HNF1 genes. Mice lacking HNF1β die in utero at embryonic day 7.5 because of a defect in visceral endoderm differentiation. However, the conditional inactivation of HNF1β has shown that this factor plays a crucial role later during organ development. In the liver, HNF1β is essential for bile duct and hepatic artery formation, whereas in the kidney the lack of HNF1β leads to polycystic kidney disease (PKD). This renal phenotype is due to the defective expression of PKD2 and PKHD1, two genes whose mutations causes polycystic kidney disease with dominant and recessive inheritance, respectively. Interestingly, in humans, mutations in the HNF1β gene are associated with renal cysts and type 2 diabetes. PKD is characterized by a progressive tubular dilation leading to cyst formation. By studying tubular elongation during nephron maturation we showed that tubular cells division is specifically aligned with tubular axis. This coordination allows tubular lengthening at constant diameter. This coordination is lost in PKD animal models. Proliferating tubular cells, in these animals, have a random orientation of their spindles and give rise to tubular dilation (Fischer et al., Nature Genetics 2006, 38, 21-23). Mitotic HNF1α and HNF1β have complementary roles in the development of several organs. One of our major goals is to characterize the implication of these two transcription factors in the establishment of intestinal, hepatic, pancreatic and renal genetic programs.
The Proto-oncogenes Jun and Fos: transcription factors regulating cellular stress response
Group leader: Fatima Mechta-Grigoriou
Other members of the group : Vi Chiu, Damien Gerald, Gaëlle Laurent, Aurore Toullec.
The AP-1 transcription factor is central to the cell's ability to integrate multiple extracellular signals and initiate the appropriate genetic programme. AP-1 plays a critical role in regulating the cell cycle and the cellular response to stress. It 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 and Fos proteins using genetic and biochemical approaches. In contrast to c-Jun, overexpression of JunD partially blocks transformation by Ras by decreasing the proliferation rate of the cells and exerting an anti-angiogenic effect. Moreover, JunD protects cells against oxidative stress by regulating genes involved in anti-oxidant defence and H2O2 production. This study allowed us to decipher the mechanism linking oxidative stress to tumour angiogenesis. Taken together, these results indicate that the balance between different AP-1 components controls cell cycle progression and the process of oncogenic transformation. JunD-deficient mice are viable, but they exhibit premature aging and suffer from age-dependent diseases, including cachexia, kyphosis, cataracs, symptoms most probably related to constitutive oxidative stress. They also develop aggressive cancers that invariably lead to early death. These symptoms are exacerbated by the deletion of one copy of the c-jun gene, providing the first evidence for redundant functions between c-jun and junD in vivo. Finally, c-Jun and JunD display overlapping functions in heart and vascular development during embryogenesis. c-Jun and JunD regulates the expression of MEF2C, a major effector in the differentiation of cardiac and smooth muscle cell lineages.
Chromatin, transcription and diseases
Group leader : Christian Muchardt
Other members of the group : Eric Batsché, Yaïr Botbol, Brigitte Bourachot, Marc Lavigne, Bogdan Mateescu, Violaine Saint-André.
Gene expression in eukaryotes involves several consecutive steps including transcription factor recruitment and chromatin opening on the promoters, synthesis of the pre-messenger RNAs, excision of the intervening introns by the splicing machinery, and finally export of the messenger RNAs to the cytoplasm where they will be translated. Recent observations suggest that these different steps are linked and often, proteins involved interact both with the DNA template and the nascent RNA transcripts. The goal of our research is to get a better understanding of the interconnections between the transcription machineries and the transcripts that they generate. During the last year, we have demonstrated that the SWI/SNF complex involved in chromatin remodelling at the level of promoters also plays a role in the regulation of alternative splicing of messenger RNAs. This effect on splicing is dependent on the interaction of the SWI/SNF sub-unit Brm with several components of the spliceosome. SWI/SNF also modifies the elongation rate of the transcribing RNA polymerase II, and thereby facilitates usage of suboptimal splice donor sites (Batsché et al.,Nature Structural & Molecular Biology, 2006, 13, 22-29). In addition to the studies on splicing, we investigate the possible role of short transcript synthesized by non processive RNA polymerase II. Our data suggest that on some promoters these transcripts may be involved in the recruitment of transcriptional repressors like HP1. A third project in the groups aims at understanding how the state of the chromatin influences integration of the HIV1 retrovirus
Papillomavirus and cancer
Group leader : Françoise Thierry
Other members of the group : Caroline Demeret, Sébastien Teissier, Youcef Ben Khalifa, Aurélie Formey de Saint-Louvent.
Our research focuses on the mechanisms of malignant conversion of cervical carcinoma cells infected with Human Papillomavirus (HPV). Cervical cancer is the second cause of mortality among women from cancer worldwide, after breast cancer. It has been shown to be highly associated with HPV infection (more than 90%) and is one of the best examples of virally-induced cancer. The "high risk" HPV types that are associated with cervical carcinoma, mainly HPV16 or HPV18, specifically infect the genital tract, where they replicate in the upper layers of the epidermis. These viruses encode two oncogenic proteins E6 and E7, which alter the normal proliferative control of the host cell by interfering with two regulatory proteins of the cell cycle, p53 and pRB. Continuous expression of the viral oncogenes is required for maintaining the transformed phenotype. We have previously shown that the viral E2 protein represses transcription of the viral oncogenes. Recently, we have recently shown that, apart from its transcriptional activities, E2 could contribute to the early stages of carcinogenesis. E2 proteins of high-risk HPV types 18 and 16 could inactivate the mitotic ubiquitin ligase APC inducing a strong mitotic phenotype. More specifically, high-risk E2 proteins induce genomic instability of the host cell, which is recognized as a critical early event for tumorigenic progression in cancer. We have also shown that E2 can induce apoptosis by direct interaction and consequent activation of caspase 8. This interaction only occurs with proteins of the high-risk viruses and could play a decisive role in the selection of infected cells containing integrated viral DNA, one of the founding events in cervical malignant conversion.
Legend to Photo :
The amino terminal transactivation domains (TAD) of E2 proteins from high-risk HPV 16 and 18 induce centrosomal over duplication contrary to the low-risk HPV 6 and 11. Metaphasic plates are visualized by DAPI staining and the centrosomes by immunofluorescence with γ-tubulin antibodies coupled to Texas Red.
Keywords: oncogens, transcription, chromatin, development, cell cycle, diabetes, renal disease