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Final Report Summary - TLSCHECK (Regulation of pol-eta by phosphorylation, ubiquitination and SUMOylation)

Xeroderma pigmentosum variant (XP-V) is an autosomal recessive genetic disorder that results in a greatly enhanced predisposition to skin cancer. XP-V is caused by a defect in pol eta, a DNA polymerase used by the cells to replicate across damaged DNA. Pol eta belongs to a class of polymerases called Translesion synthesis polymerases (TLS) and is especially suited to bypass the adducts that are formed on DNA upon exposure to UV irradiation. It is important to remember that the sun is a major source of UV and we are constantly exposed to its light, thus the function of pol eta is crucial for cancer prevention. This polymerase can be modified by the addition of small peptides, called modifiers (Ubiquitin and SUMO) or by phosphate groups, in processes called respectively Ubiquitylation, SUMOylation and phosphorylation.
The aim of this proposal is to characterize the function of pol eta, and in its regulation by protein modifications, in the context of the cellular repair systems and the DNA damage surveillance mechanisms. During this project, we performed a screening for new interactors of polymerase in order to find and understand how the cells control its activity. We are currently focusing on a new protein that appears to control the recruitment of pol eta to the replication fork, where the DNA is being synthesized. This ensures that the polymerase is not engaged during unperturbed DNA replication. This is a crucial step for the cellular life as TLS polymerases, such as pol η can introduce mutations if they are not tightly regulated.
Protein phosphorylation is another post-translational modification that can control the DNA translesion synthesis response. Recent evidence shows that pol eta is activated by phosphorylation after DNA damage. We have now identified new sites where this modification occurs. This discovery provides an additional layer of control, ensuring the timely and correct use of damage avoidance systems.
This work will provide insights into the way pol eta assists in the maintenance of genome stability, potentially providing diagnostic biomarkers for atypical XP-V diagnosis and, in the long-term, hopefully contribute to the design of rational cancer therapies, such as synthetic lethality and drug combination strategies.
The CIG allowed the researcher to be employed by the National Research Council and to establish his own laboratory. He is now in charge of an independent line of research with the help of two recruited Post-doctoral fellows, one PhD student and two undergraduate students.

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