Eukaryotic organisms utilize post-translational modifications of highly conserved histone proteins to control gene expression programs. Methylation of lysine 4 on histone H3 (H3K4me) in particular, is thought to be associated with actively transcribed DNA. Paradoxically, recent evidence has suggested that H3K4me has a repressive function as well. Pho23, a member of the highly conserved ING family of tumour suppressor proteins, binds H3K4me and is a component of the gene repressive complex, Rpd3L. My genetic analysis suggests that Pho23 controls transcriptional repression via H3K4me and that Pho23 is itself regulated by the sequence-specific DNA-binding protein Ume6. Moreover, this Ume6-regulated function appears to be governed by Ume6 phosphorylation by Mck1, an evolutionarily conserved kinase. Finally, while Ume6/Pho23 are known to function together with the histone deacteylase Rpd3, my findings suggest the existence of an Rpd3-independent function for Pho23.

Eukaryotic organisms utilize post-translational modifications of highly conserved histone proteins to control gene expression programs. Methylation of lysine 4 on histone H3 (H3K4me) in particular, is thought to be associated with actively transcribed DNA. Paradoxically, recent evidence has suggested that H3K4me has a repressive function as well. Pho23, a member of the highly conserved ING family of tumour suppressor proteins, binds H3K4me and is a component of the gene repressive complex, Rpd3L. My genetic analysis suggests that Pho23 controls transcriptional repression via H3K4me and that Pho23 is itself regulated by the sequence-specific DNA-binding protein Ume6. Moreover, this Ume6-regulated function appears to be governed by Ume6 phosphorylation by Mck1, an evolutionarily conserved kinase. Finally, while Ume6/Pho23 are known to function together with the histone deacteylase Rpd3, my findings suggest the existence of an Rpd3-independent function for Pho23.

Les gènes ING (Inhibitor of Growth) sont des gènes candidats suppresseurs de tumeurs conservés de la Levure à l'Homme. Les protéines ING ont des fonctions suppressives de tumeurs de type I ou « caretaker » car elles participent aux processus de maintien de la stabilité du génome en régulant la réplication et la réparation de l'ADN. Elles ont aussi des fonctions suppressives de tumeurs de type II ou « gatekeeper » puisqu'elles sont impliquées dans la régulation de la prolifération cellulaire de façon dépendante et indépendante de p53 et car elles contrôlent la transcription génique en participant au remodelage de la chromatine. L'objectif de ma thèse est de mieux comprendre l'implication de ING1, ING2 et ING3 dans les voies de suppression des tumeurs. Nos travaux montrent que ING1 est sumoylée sur la lysine 193 principalement par l'E3 SUMO ligase PIAS4, afin de réguler l'ancrage de ING1 sur le promoteur de gènes cibles pour réguler leur transcription. Nous avons aussi décrit pour la première fois l'implication de ING2 et de ING3 dans la réponse aux cassures double brin de l'ADN. Nous montrons que cette fonction est conservée entre ING2, ING3 et leur orthologues, respectivement, Pho23 et Yng2 chez la Levure Saccharomyces cerevisiae. ING2 contrôle l'accumulation de PIAS4 au niveau des sites de dommages et régule la sumoylation de l'E3 ubquitine ligase RNF168, afin de permettre la signalisation et la réparation des cassures double brin de l'ADN. ING3 est nécessaire à l'accumulation de 53BP1 et contrôle la réparation de ces dommages. Ces travaux contribuent donc à une meilleure connaissance du rôle des ING dans les voies de suppression des tumeurs. Ils permettent de mieux comprendre comment ING1 régule la transcription génique et décrivent une nouvelle fonction suppressive de tumeur de type I ou « caretaker » pour ING2 et ING3 dans le maintien de la stabilité du génome. / ING (Inhibitor of Growth) genes are tumor suppressor gene candidates conserved from Yeast to Humans. ING proteins have type I tumor suppressive functions or "caretaker" because they participate in the maintenance of genome stability by regulating DNA replication and repair processes. They have also tumor suppressive functions of type II or "gatekeeper" because they are involved in the regulation of cell proliferation in p53 dependent and independent manners. They also participate in the regulation of gene transcription by regulating chromatin remodeling. The aim of my thesis was to better understand how ING1, ING2 and ING3 are involved in tumor suppressive pathways. Our work shows that ING1 is sumoylated on lysine 193 mainly by the SUMO E3 ligase PIAS4 to regulate ING1 anchoring on target gene promoters to control gene transcription. We have also described the involvement of ING2 and ING3 in the DNA double strand breaks response. We show the conservation of this function between ING2, ING3 and their orthologs, respectively, Pho23 and Yng2 in Yeast Saccharomyces cerevisiae. ING2 controls the accumulation of PIAS4 at DNA damage sites and regulates the sumoylation of the E3 ubiquitin ligase RNF168, to regulate DNA double strand break signaling and repair. ING3 is necessary for the accumulation of 53BP1 and promotes DNA damage repair. This work contributes to a better understanding of the role of ING proteins in tumor suppression. It thus provides new insights of how ING1 regulates gene transcription and emphasizes a new tumor suppressive function of type I or "caretaker" for ING2 and ING3 in the genome stability maintenance.