Mechanisms and effects of DNA damage-induced sumoylation in double-strand break repair

• Applicant: Dr. Inn Chung
• Subject Area: Cell Biology
• Term: from 2012 to 2014
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 228992793

Proper repair of DNA double-strand breaks (DSBs) is critical for genome stability. One well-conserved mechanism of DSB repair is homologous recombination (HR). Recently, the important role of the post-translational modification by the small-ubiquitin like modifier (SUMO) in HR has become evident, as many HR proteins are sumoylated and sumoylation enzymes are required for efficient HR. However, the mechanisms by which HR factors are sumoylated at DSB sites have not yet been studied. In addition, knowledge about the detailed mechanisms by which sumoylation regulates HR is still lacking. The proposed project aims to elucidate these mechanisms using the model system S. cerevisiae.First, the mechanisms by which the sumoylation of HR proteins is induced by DSBs will be addressed. Two non-mutually exclusive models will be tested. The first one is the “enzyme recruitment model”, which hypothesizes that the accumulation of sumoylated HR proteins at DSB sites is a result of enrichment of sumoylation enzymes at DSB sites. The other model is the “substrate-priming model”, which proposes that binding to DNA or other recombination proteins by the substrates upon recombination reaction can induce their property changes in favor of sumoylation. I will use a combination of in vivo and in vitro approaches to test these models. I will examine the mechanisms and importance of the recruitment of sumoylation enzymes at a defined DSB and how the interactions between HR factors and with DNA contribute to HR protein sumoylation. Another goal of this proposal is to address how sumoylation regulates the first step of HR, namely the nucleolytic processing of the ends of DSBs. Previous work has revealed that two nucleases responsible for this step are subjected to sumoylation. However, how this modification influences their DSB processing functions is not understood. I will use several approaches to address how lack of sumoylation of these enzymes affects DSB resection. In summary, the project aims to gain mechanistic insight into how sumoylation is regulated upon the occurrence of DSBs and how sumoylation influences the first step of HR-mediated DSB repair. Results from these studies will provide new understanding of how cells repair DSBs to ensure genomic stability, which is particularly important for understanding and treatment of genomic instability diseases like cancer.

• DFG Programme: Research Fellowships
• International Connection: USA
• Host: Dr. Xiaolan Zhao