Regulation of Histone H4-K20 Methylation

University Of Illinois At Urbana-Champaign, Urbana IL

Investigators

Abstract

Project Summmary: If the DNA from all of the chromosomes in a single human cell were joined end to end, the genome would span approximately 2 meters. In eukaryotic cells, the DNA is tightly associated with proteins called histones that allow it to be extensively folded upon itself to form a polymer called chromatin. The compaction of DNA afforded by wrapping around a complex of histones allows the entire genome to be packed into the microscopic confines of the nucleus of each cell. However, for individual genes to be expressed, for damaged DNA to be repaired, and for the genome to be replicated prior to cell division, regions of chromatin must be unfolded so that the relevant cellular machinery can gain access to the DNA. Conversely, chromatin must be condensed to form chromosomes during cell division to ensure that daughter cells each receive a complete copy of the genome. The addition and removal of small chemical groups or "modifications" to histones are central to both chromatin folding and unfolding. A wide variety of histone modifications have been described, but little is known about the molecular mechanisms involved in mediating their function or how the levels of individual modifications are controlled. This project will investigate how the levels and genomic localization of histone H4-lysine 20 methylation are regulated. Lysine 20 can be unmodified or modified by the addition of one, two or three methyl groups. The enzyme PR-Set7 mediates monomethylation, whereas Suv4-20 mediates both di- and trimethylation. Decreased levels of PR-Set7 are associated with increased DNA damage and defective cell division, whereas depletion of Suv4-20 alters cellular responses to DNA damage and increases genomic instability. Both enzymes are activated during cell division and it is likely that their activities are coordinately regulated by dynamic modifications or interactions with other proteins. State-of-the-art approaches will be used to identify proteins associated with PR-Set7 and Suv4-20, characterize the modifications affecting the activities of these enzymes and associated proteins, and ascertain the significance of the PI's findings in human and Drosophila cells. Understanding the molecular regulation of these enzymes will impact our understanding of the roles of chromatin structure in cell cycle progression, detection and repair of damaged DNA, mitosis, and other processes that are critical for normal cell function. Broader Impacts: This work will enhance our understanding of an epigenetic pathway involved in aspects of chromatin function that are fundamental to normal cell biology and the development of multicellular organisms. The cell lines, antisera and other reagents created during this project will be useful to labs investigating other aspects of chromatin function and will be made readily available. In addition, this work demonstrates how proteomic methodologies can be used in conjunction with cell biology and molecular biology approaches to make paradigm-shifting discoveries in the life sciences. The unique training that graduate and undergraduate students receive in this project will enable them to apply these powerful strategies in their own careers.