TIP60-chromatin remodeling complex roles in chromosome break repair

Ohio State University, Columbus OH

Investigators

Abstract

PROJECT SUMMARY/ABSTRACT Homologous recombination (HR) is the primary mechanism for repair of DNA double strand breaks (DSBs) arising during DNA replication. Chromosomes can break when the replication machinery collides with the transcription machinery, navigates repetitive DNA sequences, or runs into other impediments. These types of DSBs are called endogenous because they are caused by normal cellular transactions. They are district from exogenous breaks which are caused by chemicals or radiation. Central to HR are the breast cancer susceptibility genes, BRCA1 and BRCA2 which load the RAD51 recombinase onto the broken end to engage homology search and repair. Mutations in BRCA1 or BRCA2 severely cripple HR and cause chromosomal re-arrangements. RAD52 is an accessory gene that can substitute for the BRCA1&2, but it is not as proficient and can cause chromosomal instability. Importantly, most cancers harbor mutations in these four genes underscoring the HR machinery role in maintaining genome stability. Chromatin remodeling also plays a major role in HR repair. Accurate removal or reposition of histones is essential to access the broken ends and initiate strand invasion. The KAT5 histone acetyltransferase is one enzyme that is required for both activation of the DNA damage checkpoint and recruitment of HR machinery at the break. We have identified previously unreported physical and genetic interactions between KAT5 and RAD52 in the yeast model system. We also published data showing that KAT5 recruits RAD52 to the break and that KAT5 mutations affect DSB end resection and repair pathway choice. KAT5 is a subunit of the TIP60-complex which also functions in transcription dependent chromatin remodeling. However, the role of the other TIP60 subunits in DSB repair is less understood. In this grant we want to place all TIP60 complex subunits with the DNA damage response epistatic group. We hypothesize that KAT5 and members of the TIP60-complex promote error-free DSB repair by modulating the role of RAD52. In Aim 1 we propose to test combinations of mutations between the HR repair machinery components and the TIP60-complex subunits. We will use in vivo recombination assays to directly delineate their role within the several HR sub pathways. In Aim 2 we will use in silico protein structure techniques to model the HAT module of TIP60, which is currently unknown. We will then model the overall TIP60 complex including the HAT module. Additionally, we will query cancer genomes to identify high frequency and driver mutations in TIP60-complex components and investigate how they affect interaction with other members of the complex and HR repair.