Projet ANR-07-BLAN-0048 – YIN4F1YANG : The yin and the yang of E4F1, a key regulator of mammalian cell proliferation and survival.
Programme : Blanc (BLANC) 2007
Année de financement : 2007
Coordinateur du projet : Monsieur SARDET Claude (CNRS DELEGATION REGIONALE LANGUEDOC ROUSSILLON)
Partenaires : Centre national de la recherche scientifique; Centre national de la recherche scientifique; Université de Bordeaux
Montant : 350000.0 euros
Date de début : 2007
Durée : 36 mois
Résumé : "Since 10 years the research activity of our lab is focused on the transcriptional control of the mammalian cell cycle and survival machineries in normal and physio-pathological situations. Notably, our exploration of the protein networks involved in these processes led us to develop increasing interest for E4F1, a poorly studied, regulator of the proliferation/survival balance of mammalian cells. E4F1 is an ubiquitously expressed 120-kDa zinc-finger protein of the GLI/Kruppel family that was first identified, almost 20 years ago, as a cellular target of the adenoviral oncoprotein E1A13S, required for transcriptional regulation of the E4 and E1A adenoviral genes. -  Notably, in addition to their recruitment in adenoviral transcription, all the targets of E1A seem to have been selected because they also play essential functions in the reactivation of the cell cycle of quiescent infected cells. A reactivation required to push these cells to reinitiate their DNA replication machinery for the profit of the viral DNA replication. However, while most other cellular targets of E1A discovered at the same time than E4F1 (i.e. E2F/pRB, CBP/p300, pCAF etc...) became « famous », investigated in depth and recognized as central regulators of cell proliferation and cell survival, E4F1 remained, inexplicably, poorly studied until recently. Yet, like these other « stars » of the literature targeted by E1A, several recent observations indicate that E4F1 also plays important roles in cell proliferation and survival of somatic, stem and cancer cells, and during embryogenesis. These past five years, we have invested a lot of efforts in developing the molecular tools and animal models to explore the physiological function of E4F1. We have shown that E4F1-/- mouse embryos die at the peri-implantation stage and exhibit mitotic progression defects, chromosomal missegregation and increased apoptosis. Conversely, ectopic expression of E4F1 in various cell lines results in inhibition of the G1-S-phase progression and cytokinesis defects which correlate with altered levels of the cell cycle inhibitor p21Cip1of the cyclin A2 gene and of various other genes involved in cell cycle and cell survival (BclW, IGF2,PIM1, MCM7). Notably, the E4F1-mediated cell cycle arrest is reduced in cells deficient for either pRB or p53 and enhanced in presence of p14ARF and RASSF1A suggesting that E4F1 is involved in several essential oncogenic pathways. Importantly, E4F1 physically interacts with these four tumor suppressors: RASSF1A, pRB, p14ARF, and p53, as well as with 3 other regulators / effectors of these pathways: the proto-oncogene Bmi1, the histone deacetylase HDAC1 and FHL2 / DRAL . Finally, E4F1 activity was shown to be directly targeted by three viral oncoproteins, E1A, HBX and GAM1. Very recently, we moved ahead in our quest for E4F1 cellular functions by discovering that E4F1 is also an atypical E3-ligase for p53 that modulates its effector functions. E4F1 stimulates oligo-ubiquitylation in the hinge region of p53 on lysine residues previously described to be acetylated by the acetyltransferase PCAF but distinct from those targeted by the hiterho described E3-ligases of p53. Strikingly, E4F1-dependent Ub-p53 conjugates are not sent to degradation, are associated with chromatin, and their stimulation coincides with the induction of a p53-dependent transcriptional program involved in cell cycle arrest but not apoptosis. These data revealed that E4F1 is both a transcription factor and a novel key post-translational regulator of the p53 pathway that modulates its effector functions involved in alternative cell fates: growth arrest or apoptosis. -  Considering these published in vivo and in vitro data, we believe that E4F1 is becoming a hot topic. This conviction is reinforced by the unpublished results of our recent exploratory experiments (purification /Mass spec of E4F1 complexes, identification of other candidate substrates for the E4F1 E3 activity (p63), gene e