Involvement of the E3 ubiquitin ligase TRIP12 in chromatin organization ; Implication de l'E3 ubiquitine ligase TRIP12 dans l'organisation de la chromatine

TRIP12 is a nuclear HECT-type E3 ubiquitin ligase that is overexpressed in numerous cancers. TRIP12 is involved in several nuclear functions via its catalytic domain HECT. Indeed, TRIP12 is implicated in pancreatic carcinogenesis by controlling the stability of PTF1a, an essential transcription factor for pancreatic homeostasis. TRIP12 regulates the chromatin remodeling complexes SWI/SNF and PRC1 by inducing the degradation of BAF57 and ASXL1, respectively. It is also involved in DNA damage repair by targeting RNF168 and parPARP1. Recently, we identified in the N-terminal extremity of TRIP12 an intrinsically disordered region (IDR) that is responsible for TRIP12 interaction with the chromatin. However, the consequences of TRIP12 overexpression observed in cancers on chromatin homeostasis and the involvement of its IDR in this process remain largely unknown. Thus, my PhD objectives were to characterize TRIP12 role on chromatin organization and to determine the consequences of TRIP12/chromatin interaction on nuclear processes such as DNA damage repair. To this aim, I established TRIP12 proxisome in which I identified 327 statistically enriched proteins, among them, already known substrates such ASXL1 or BAF57. Functional network analysis revealed that TRIP12 partners are massively involved in chromatin organization and histone modifications which are in favor of a TRIP12 role on these functions. Using high-resolution microscopy, I demonstrated that TRIP12 overexpression modifies chromatin organization by inducing heterochromatin condensates through its IDR and independently of its catalytic activity. These condensates are dynamic, reversible and governed by polymer-polymer phase separation. In parallel, I measured the functional consequences of TRIP12 induced-chromatin condensates on biological processes such as genome accessibility and DNA damage response. I highlighted an important decrease in genome accessibility after TRIP12 overexpression. Besides, it is well known that chromatin compaction is an important ...