Resumen de Ubiquitin and SUMO in DNA replication: from molecular studies to age-related pathologies
The correct regulation of the cell cycle requires the orchestration of fine-tuned molecular mechanisms, frequently regulated by post-translational modifications (PTMs). In this regard, there is still a significant lack of information on how DNA replication terminates, and how it is connected to mitotic entry. During my PhD, I have investigated how PTMs modulate DNA replication and its termination, and how alterations of these mechanisms might be behind certain age-related pathologies. First, I focused on a SUMO-specific deubiquitinase, USP7, which we previously identified as a key factor for DNA replication. The chemical blockade of USP7 leads to a severe impairment in DNA replication, which is accompanied by increases in SUMOylated and ubiquitinated factors on chromatin. Moreover, it also induces an accumulation of ubiquitinylated replication factors, such as MCM7, which are hallmarks for DNA replication termination. This work has contributed to better understand the metabolism of ubiquitinated replication factors, and how these are evicted from chromatin by the action of the VCP segregase. In the second part of this PhD thesis, I followed up upon our previous findings that identified the SUMO E3 ligase NSMCE2, as a suppressor of cancer and ageing in mammals. Part of the work indicated that the deficiency of NSMCE2 led to an accumulation of micronuclei. In this context, we speculated that part of the pathologies that are observed in Nsmce2-deficient mice, such as kidney fibrosis, could derive from the accumulation of cytoplasmic DNA that activates the cGAS-STING inflammatory signalling. The experiments performed confirmed this hypothesis, thereby providing one of the first examples of a disease that is triggered by the activation of the cGAS-STING pathway in response to genome instability. Collectively, this PhD has provided both a better molecular understanding of the role of ubiquitin and SUMO in DNA replication. Moreover, it has also deepened into the mechanisms that drive the onset of age-related pathologies upon deletion of the NSMCE2 SUMO ligase
