Functional Consequences of Histone H2B Variants in Driving Oncogenic Phenotypes

Emory University, Atlanta GA

Investigators

Abstract

Project Summary Histone proteins are the basic packaging unit of DNA. They comprise a hetero-octamer protein complex around which DNA is wound, and are compacted into chromatin. Histone proteins also play a critical role in regulating gene expression; however, missense mutations in genes encoding histone proteins, referred to as oncohistones, drive cancers. Although the majority of characterized oncohistones occur in histone H3, mutations in other histone genes can also drive cancer. Histone residues that support post-translational modification have also been shown to regulate DNA damage repair. Missense mutations to these residues could disrupt these pathways and potentially impact how cancer cells respond to DNA-damaging therapeutics, such as radiation. Through the analysis of publicly available tumor genomic data, I have identified five histone H2B variants that recur in patient tumors. Like the most extensively characterized H2B oncohistone, H2BE76K, these variants occur in various cancer types, including solid cancers and hematological malignancies such as Non-Hodgkin Lymphoma (NHL), making human mammary epithelial cells and Ramos cells, a transformed cell line modeling NHL, relevant models in which to characterize the functional impact of these mutations. I hypothesize that novel cancer-associated histone H2B variants can drive oncogenic phenotypes and alter cellular responses to DNA damage. To examine the oncogenic potential of cancer-associated H2B variants, I have engineered human cell lines expressing these H2B variants and have designed a research strategy implementing several interdisciplinary approaches that will characterize H2B variants as putative oncohistones, and elucidate their functional impact in the DNA damage response. The overarching goal is to test whether cancer-associated H2B variants may contribute to oncogenic processes and explore how these H2B variants may impact cellular DNA damage response, gene expression, and chromatin accessibility in response to DNA damage. These goals will be accomplished though two Specific Aims. In Aim 1, I will characterize H2B variants’ impact on cancer hallmarks in vitro by assessing cell proliferation, colony formation, migration and invasion comparing cells expressing wildtype H2B to cells expressing the variants I have defined. I will then examine the ability of H2B variants to drive tumorigenesis using in vivo murine xenografts. In Aim 2, I will examine how H2B variants influence cell viability after exposure to DNA damaging agents such as irradiation and characterize DNA damage repair. I will then examine gene expression and chromatin accessibility changes in cell lines that score in in vitro assays in the presence and absence of DNA damage. My exciting preliminary data reveal that several of these potential oncohistone mutants can drive pro-invasive phenotypes, providing proof of principle that the potential oncohistone mutations I have identified confer oncogenic phenotypes. Completion of these studies will test the model that additional H2B variants function as oncogenic drivers and provide mechanistic insight into their cancer-driving properties, which may unmask possible therapeutic targets for H2B oncohistone-driven cancers.