MSH2-MSH3 MEDIATED REPLICATION DEFECTS PROMOTE GENOME INSTABILITY

High fidelity DNA replication is vital for the maintenance of a stable genome and efficient cell functioning. DNA replication fidelity is governed by numerous mechanisms within the cell with a major factor being the DNA mismatch repair pathway (MMR). The indispensability of MMR for accurate DNA replication and genomic stability is evident in multiple genetic disorders including several cancers associated with MMR deficiency. Paradoxically, the mismatch binding protein, Msh2-Msh3 has been implicated in the promotion of trinucleotide repeat (TNR) expansion events which are the leading cause of several neurological disorders. Research into underlying mechanisms reveal that Msh2-Msh3 may interfere with the Okazaki fragment maturation (OFM) process, specifically FEN1 and Lig I to enhance TNR expansions. In addition to TNR expansions, this finding also exposes a path to genomic instability through interference with DNA replication. In the current study, we explore Msh2-Msh3 mediated OFM interference with a focus on mechanistically understanding the nature of this interference. It is important to note that Msh2-Msh3’s accurate repair function is crucial for the maintenance of genomic stability and the overall efficiency of MMR suggests that pathogenic functioning by Msh2-Msh3 only occurs under specific conditions. Hence, we also aim to study specific factors that trigger aberrant repair by Msh2-Msh3 including various DNA structures, Msh2-Msh3’s ability to bind and hydrolyze ATP, protein-protein interactions, and the lysine acetylation status of Msh2-Msh3. So far, our findings suggest that Msh2-Msh3 has a detrimental effect on OFM proteins, which opens a path for genomic instability. We also establish that binding to various DNA structures and the conformational shift within Msh2-Msh3 as a consequence of ATP binding are important factors underlying this effect. This study additionally reveals that Msh2-Msh3 physically interacts with DNA polymerase (Pol δ) and that its transactions with Pol δ are conserved between S. cerevisiae and humans. Finally, we elucidate the role of lysine acetylation in Msh2-Msh3’s interaction with OFM proteins and suggest that lysine acetylation may be a means by which Msh2-Msh3 abundance is regulated within the nucleus. Understanding the factors responsible for abnormal repair by Msh2-Msh3 brings us one step closer to therapeutics targeting pathogenic repair by Msh2-Msh3 specifically and preserving accurate repair.