Roles of the SMUG1 DNA repair protein in active DNA demethylation and telomere maintenance; implications for stem cell function

The DNA base excision repair enzyme, SMUG1, is important for repair of oxidised thymine bases in DNA. If not repaired, these damages may give rise to mutations. One of the most important DNA lesions repaired by SMUG1 is also suggested to be an intermediate in active reprogramming of stem cells. Morevover, we have previously showed that SMUG1 also interacts with Dyskerin (DKC1), a protein that affects stem cells properties by being an important component of the telomerase holoenzyme. Thus, SMUG1 might affect stem cell properties both via its DNA repair function or via its interaction with DKC1. In this project we have made SMUG1-knockout mice and cell lines where we studied mechanisms by which SMUG1 activity affect stem cell properties by focusing on ints implication for telomere maintenance and identified a novel mechanism of telomere maintenance that involves SMUG1 and DKC1.

Reprogramming of somatic cells to induced pluripotent stem cells (iPSC) requires resetting of DNA epigenetic signatures to resemble that of the embryonic stem cell. Moreover, the efficiency and the quality of the resulting iPSC depend on reactivation of t elomerase to maintain or restore telomere length. This proposal addresses the role of the DNA repair enzyme SMUG1 that may affect both properties; in a recent paper in Molecular Cell, we demonstrated that SMUG1 processes modified RNA and has a function in RNA quality control in part by ensuring proper localisation of Dyskerin (DKC1) to Cajal bodies. In our paper we show data that demonstrate a function for SMUG1 in rRNA quality control and here we present preliminary evidence that SMUG1 associates with th e telomerase RNA component (TERC) and is required for maintaining telomerase function and telomere length. Aside from this new function on RNA quality control and DKC1 localisation, the classical DNA repair function of SMUG1 may contribute to reprogrammi ng fidelity or efficiency by potentially removing 5-hyroxymethyluracil (5-hmU) residues from DNA, which may be formed by deamination of 5-hydroxymethylcytosine (5-hmC) residues, a recently described epigenetic mark, by the AID/APOBEC enzymes. Hence, this project presents a new line of research in the front-line of basic research expected to make a significant contribution to our understanding of possible functions of SMUG1 in maintaining the quality and function of iPSC. We have prior experience demonstr ating potential for high impact publications, an existing network of national and international collaborators, and the competitive advantage of unique reagents (Smug1-knockout mice) and preliminary data that vouches for the feasibility of this project. Su pport for this project will offer new opportunities for international and national collaborations and promote the careers of two female scientists.