This item is under embargo and not available online per the author's request. For access information, please visit http://libanswers.wustl.edu/faq/5640.

ORCID

https://orcid.org/0000-0002-5250-3094

Date of Award

Winter 12-15-2016

Author's School

Graduate School of Arts and Sciences

Author's Department

Biology & Biomedical Sciences (Molecular Genetics & Genomics)

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

The nonsense mediated RNA decay (NMD) pathway maintains the integrity of cellular RNAs and controls gene expression. NMD is essential for vertebrate development and defects in NMD are associated with a variety of neurodevelopmental disorders and cancers. NMD activity is tightly regulated and is altered in response to environmental and developmental signals. To better study this dynamic pathway and to identify clinically relevant regulators of its activity, we developed a dual-color bioluminescent NMD reporter that rapidly and accurately quantifies NMD activity in mammalian cells. Using this reporter, we performed a chemical screen for small-molecule modulators of NMD activity and identified the cardiac glycosides (CGs) as potent repressors of NMD activity. Further studies on the mechanism of action of these drugs led to the finding that intracellular calcium, a key cellular signaling molecule, potently regulates NMD, with increases in intracellular calcium repressing NMD. The regulation of NMD by calcium may be exploited to treat certain genetic diseases and cancers. Regulation of NMD is particularly important to the cellular stress response. Stresses such as hypoxia, amino acid deprivation, and ER stress induce a reduction in NMD activity that promotes the expression of genes that help the cell to cope with these environmental insults. We investigated the regulation of NMD and its role in the cellular response to DNA damage and osmotic shock. We found that NMD is suppressed by persistent, but not transient, DNA damage. Conditions that constantly induce damage, such as excessive mitogenic signaling or the presence of genotoxic agents, or that prevent its swift repair, such as mutations in repair factors, generate persistent DNA lesions. Telomeres are another prominent source of persistent DNA damage because telomeric damage is difficult to repair, and telomere erosion from repeated cell divisions also elicits a protracted DNA damage response (DDR). The inhibition of NMD by persistent DNA damage is mediated in part by p38 MAP kinase signaling and augments the expression of ATF3, a stress-inducible transcription factor, by stabilizing its mRNAs. We found that osmotic shock also causes NMD inhibition but in a p38-independent manner. These results reveal a novel p38-dependent pathway that regulates NMD activity in response to persistent DNA damage which contributes to gene expression changes in damaged cells.

Language

English (en)

Chair and Committee

Zhongsheng You

Committee Members

Barry Sleckman, Jason Weber, Joseph Dougherty, Qin Liu

Comments

Permanent URL: https://doi.org/10.7936/K7TD9VRF

Available for download on Tuesday, December 15, 2116

Share

COinS