The role of the chromatin remodelling protein HELLS in maintaining genome stability

Abstract

ATP-dependent chromatin remodelling enzymes play an important role in maintaining genome integrity by modifying chromatin structure to alter nucleosome occupancy or composition and regulate essential genome maintenance pathways such as DNA double-strand break (DSB) repair and DNA replication. The HELLS subfamily of chromatin remodellers has been implicated in DSB repair and the response to replication stress, and human HELLS is mutated or aberrantly expressed in a number of cancers and mutated in a subset of ICF patients, a rare immune disorder characterised by chromosome instability. Previous work from our group has identified a novel role for HELLS in promoting the homologous recombination (HR) pathway of DSB repair within heterochromatin in G2 by facilitating DNA end resection. HR also plays an essential role in the response to replication stress in S-phase while alternative, inaccurate DSB repair pathways share a common end resection mechanism to HR. Consequently, my thesis investigates a role for human HELLS in the response to replication stress and in additional resection-dependent DSB repair pathways.

Using CRISPR-Cas9 to generate human immortalised fibroblast cell lines lacking HELLS, HELLS-deficient cells were confirmed to have a defect in HR and display signs of genomic instability. In addition, this thesis provides evidence that HELLS protects cells from replication stress by limiting replication-associated DNA damage and accumulation of stalled replication forks. HELLS is also shown to promote alternative resection-dependent DSB repair pathways in addition to HR, namely the mutagenic microhomology-mediated end-joining (MMEJ) and single-strand annealing (SSA) pathways. Furthermore, this work also identifies the potential to use PARP inhibitors as a synthetic lethal therapy for HELLS-defective tumours. The uncovered functions of HELLS in the response to replication stress and DSB repair pathway usage are important for maintenance of genome stability and are likely to contribute to HELLS role in disease.

Date of Award	27 Sept 2022
Original language	English
Awarding Institution	University of Bristol
Supervisor	Anna L Chambers (Supervisor) & Mark S Dillingham (Supervisor)