Date of Award

Spring 1-16-2024

Embargo Period

1-16-2029

Document Type

Dissertation - MUSC Only

Degree Name

Doctor of Philosophy (PhD)

Department

Biochemistry and Molecular Biology

College

College of Graduate Studies

First Advisor

David Long

Second Advisor

Stephen Duncan

Third Advisor

Joe Delaney

Fourth Advisor

Wenjian Gan

Fifth Advisor

John O’Bryan

Abstract

The DNA damage response (DDR) is crucial for maintaining genomic stability and integrity. The epigenetic reader BRD4 acts as a molecular scaffold and is a key regulator of both transcription and DNA repair. In response to DNA double-strand break (DSB), BRD4’s interaction with chromatin undergoes dynamic changes. However, the detailed mechanisms that govern BRD4 binding to chromatin remain elusive. This study aims to investigate the regulatory mechanism of BRD4 binding to chromatin, focusing on its displacement from regions of damaged chromatin. I show the significance of ATM in mediating the displacement of BRD4 from chromatin utilizing Xenopus egg extracts and multiple in vitro assays. I show that BRD4 is a direct ATM substrate that is phosphorylated at Ser345. Surprisingly, ATM does not displace BRD4 from chromatin by phosphorylation, but instead through direct protein-protein binding. ATM-mediated phosphorylation reduces BRD4’s affinity for ATM, allowing it to be released. In addition, I reveal the role of PRMT4 in DSB repair through BRD4 methylation at the 3R region, which is required for retention of BRD4 on chromatin. This methylation is also stimulated by DSB induction and acts downstream of ATM-mediated displacement of BRD4. In this study, I further explore TIP60 revealing a role in BRD4 regulation that is distinct from its established role in activating ATM upstream of BRD4 displacement from chromatin. Overall, this research highlights multiple ways that post-translational modifications can modulate BRD4 activity, leading to new mechanistic insights that can be exploited in cancer therapeutics.

Rights

Copyright is held by the author. All rights reserved.

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Available for download on Tuesday, January 16, 2029

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