Year of Publication

2020

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Medicine

Department

Molecular and Cellular Biochemistry

First Advisor

Dr. Yvonne Fondufe-Mittendorf

Abstract

Chronic, low dose exposure to inorganic arsenic (iAs) is a public health concern throughout the world, contributing to the development of many diseases, including lung cancer. Several mechanisms for iAs-mediated carcinogenesis have been proposed, of which the production of reactive oxygen species and formation of chromosomal aberrations are the most studied. Another equally important, yet less studied mechanism is dysregulation of epigenetic marks. “Epigenetics” refers to changes that occur on the DNA and chromatin that do not alter base pair identity, but alter compaction, expression, and regulation of specific DNA sequences. There are several types of epigenetic marks including histone post-translational modifications, DNA methylation, and histone variants. Understanding the role of these epigenetic regulators in iAs-mediated carcinogenesis is, therefore, important because these aberrant changes influence the disease phenotype. Specifically, these epigenetic changes have been implicated in a process called the epithelial-to-mesenchymal transition, which allows cancer cells to metastasize. First, this study used high-resolution microarray analysis to measure the changes in DNA methylation in cells undergoing inorganic arsenic-induced epithelial-to-mesenchymal transition, and on the reversal of this process, after removal of the inorganic arsenic exposure. Inorganic arsenic exposure not only influences DNA methylation, but we also identified for the first time that differential expression of specific histone H2B variants occurs in iAs-exposed cells. The histone H2B variants, which have point amino acid changes compared to the canonical sequence, exhibit dysregulated expression patterns that are responding to iAs-induced changes in stem loop binding protein (SLBP), which is responsible for regulating histone variant transcripts. While the H2B variants have only a few small amino acid changes, some are located at histone:DNA interfaces, while others are at histone:histone interfaces. These small amino acid changes could cause steric and electrostatic changes which influence nucleosome dynamics. Therefore, this study also sought to reveal how histone H2B variants influence octamer and nucleosome stability. We found that histone H2B variants confer unique stability and dynamic properties to both the histone octamer and the nucleosome. Therefore, histone H2B variants are playing a unique role in chromatin dynamics, both in iAs-induced carcinogenesis and normal chromatin functioning. In whole, this study identified multiple epigenetic marks that are disrupted by iAs treatment and identified how those epigenetic marks may be influencing chromatin compaction to promote the epithelial-to-mesenchymal transition.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.299

Funding Information

National Science Foundation (MCB 1517986-YFM) 2015-2016, National Institute of Environmental Health Sciences (R01-ES024478-YFN with supplement 02S1) 2016-2020

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