L’infection par le virus de l’herpès simplex de type 1 (HSV-1), un virus pathogène humain majeur, engendre la déstabilisation des centromères. Cette déstabilisation est induite par la protéine virale ICP0, et entraîne la dégradation par ICP0, via le protéasome, des protéines CENP-A, -B et CENP-C. Des résultats obtenus au laboratoire ont mis en évidence le phénomène iCDR (pour interphase Centromere Damage Response) qui implique la redistribution de la coïline, fibrillarine et SMN dans ces structures centromériques déstabilisées par ICP0 mais également par des drogues ou des siRNAs dirigés contre des constituants protéiques essentiels pour la stabilité des centromères. Il a été étudié leur interdépendance dans la réponse iCDR. Il a été ainsi démontré que la redistribution de SMN aux centromères déstabilisés est dépendante de : 1) la présence de la coïline aux centromères, et 2) de son interaction, via son domaine TUDOR, avec l’histone H3 méthylée sur la lysine K79 par l’enzyme Dot1L. L’équipe suggère donc l’hypothèse que ces protéines ont pour rôle de protéger l’ADN nu se trouvant aux centromères après dégradation des histones pour empêcher les cellules de rentrer en apoptose. Ces résultats ont mené à démontrer l’implication de certaines des protéines de l’iCDR et notamment la coïline, dans une réponse apoptotique générale suite à un stress UV. Ces protéines pourraient donc faire partie d’un mécanisme de contrôle qui serait défini comme un checkpoint centromérique / Infection by Herpes Simplex Virus type 1, a major pathogenic virus in human, has been shown to cause centromere destabilization. The infected cell protein 0 (ICP0) induces centromere destabilization and lead to proteasomal-dependent degradation of the proteins of the centromeres, CENP-A, -B and CENP-C. Recent data, obtained in our laboratory, highlights the interphase Centromere Damage Response (iCDR) phenomena. This phenomena involves centromeric accumulation and redistribution of the Cajal body-associated coilin and fibrillarin as well as the Survival Motor Neuron (SMN) proteins by ICP0 or by other drugs or siRNA targeting several constitutive centromere proteins known to play a major role in centromeres stabilization. Our data shows that SMN reditribution in the destabilized centromere is dependent of : 1) centromeric presence and accumulation of the coilin, 2) its interaction, via the TUDOR domain, with the methylated (Lys K79) histone H3. This methylation occurs in the presence of the Dot-1L enzyme. We hypothesize that these proteins play a critical role in safeguarding centromeric DNA to prevent the cells from apoptosis after Histone degradation. These observations, demonstrate the implication of certain iCDR proteins, more specifically the coilin, in the apoptotic response following a UV stress. In conclusion, these proteins could be part of a safeguard mechanism considered as a centromeric checkpoint

acase@tulane.edu

The epigenetic mechanisms that connect hormone signaling to chromatin remain largely unknown. Here we show that LSD1/KDM1A is a critical glucocorticoid receptor (GR) coactivator and report a previously unexplored mechanism where LSD1 activates gene transcription through H3K4me2 demethylation. We demonstrate that direct interaction of GR with LSD1 primarily inhibit its activity against H3K4me1 in vitro. While this interaction enables GR to recruit LSD1 in vivo and allows loss of H3K4me2, it impedes further demethylation. Thus resulting in conversion of H3K4me2 to H3K4me1 at enhancers and promotes H3K27 acetylation and gene activation. We also find that H3K4me2 is an early enhancer mark predicting GR and LSD1 recruitment. These findings differ from the reported mechanism for ER and AR-mediated gene activation, providing a novel mechanism for LSD1 coactivator function as well as shed light on the role of H3K4me2 and enhancers in hormone-mediated gene regulation. In addition we present evidence supporting never before characterized H3K79me3 demethylase activity by members of the JMJD2 family of proteins.

In Saccharomyces cerevisiae, telomeric and HM silencing requires the histone deacetylase Sir2 and the chromatin binding proteins Sir3 and Sir4, which interact to form the SIR complex. Silent chromatin formation begins with a nucleation step, followed by spreading of Sir proteins along chromatin. Overexpression of Sir3 extends silent chromatin domains, however the role of Sir protein interactions within silent chromatin extensions remains unknown. Here, we generated the Sir3 mutant, Sir3-4A, which cannot interact with Sir4 but is capable of forming silent chromatin extensions when overexpressed. Within extended silent domains, Sir2 and Sir4 enrichments are similar whether Sir3 or Sir3-4A is overexpressed, suggesting that silent chromatin extensions require Sir4 but not the interaction between Sir3 and Sir4. Tethering Sir3-4A at an HMR silencer cannot nucleate silencing in the absence of Sir3, suggesting that in addition to Sir3 recruitment, the Sir3-Sir4 interaction has at least one other function during silent chromatin nucleation.