HUMAN MUTS HOMOLOGUE HMSH4: CHARACTERIZATION OF PROTEIN INTERACTION AND POST-TRANSLATIONAL MODIFICATION
Genomic stability is essential for the faithful transmission of genetic information during cell division. Although genomic integrity is constantly challenged by endogenous and exogenous factors that cause DNA damage, cells have evolved to utilize multiple surveillance mechanisms through which DNA lesions can be detected and repaired. Collectively, the fate of these cells is determined by the outcomes of cellular DNA damage response - a dynamic interplay between DNA damage signaling and DNA repair. Emerging evidence suggests that post-translational acetylation/deacetylation is an important regulatory mechanism which contributes to both DNA damage signaling and DNA repair. Among various DNA repair mechanisms, the DNA mismatch repair (MMR) and double-strand break (DSB) repair pathways play unique roles to intertwine cell cycle regulation with respect to DNA repair activities. Of note, MMR deficiency is often associated with decreased cellular sensitivity to anti-cancer treatment. In order to gain a better understanding of the roles individual MMR proteins play, here we have focused on the biochemical properties and biological functions of one of the MMR proteins - the human MutS homologue 4 (hMSH4). The work presented in this dissertation describes our effort to identify the roles of hMSH4 through characterizing its interacting protein partners and DNA damage-induced post-translational modification, with a specific emphasis on acetylation and deacetylation. Together, the results demonstrate that DNA damage-induced post-translational acetylation of hMSH4 is controlled by the acetyl-transferase hMof (human males absent on the first) and, possibly, also by hGCN5 (human general control nonderepressible 5), whereas the deacetylation of hMSH4 is mediated by HDAC3 (histone deacetylase 3). In addition, our effort also leads to the identification of eIF3f (eukaryotic translation initiation factor 3 subunit f) as another novel hMSH4 interacting partner, in which this interaction is mediated through the N-termini of both proteins. Further functional analysis indicated that the interplay between hMSH4 and eIF3f is involved in the regulation of DNA damage-induced cell cycle arrest, cell survival, and DSB repair. In short, our current work directs a new avenue and has better positioned us to address new challenges that will arise amid the continuum of research into the mechanisms involved with hMSH4 in DNA damage repair.