The Role of CHD6 in the DNA Damage Response
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2024-04-26
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Cells can often experience oxidative stress from events or processes such as dysfunctional metabolism, acute or chronic inflammation, hyper proliferation, and/or exposure to oxidizing or ionizing agents. Oxidative damage to DNA is one of the most common forms of DNA damage, thus cells have evolved mechanisms to cope with and repair lesions to prevent mutation accumulation and promote cell survival. One of the earliest responses to oxidative DNA damage is the activation of poly(ADP-ribose) (PAR) polymerase, resulting in the formation of negatively charged polymers on proteins, chromatin, and DNA, thereby recruiting repair factors and chromatin remodeling enzymes to reshape chromatin at damage sites. Remodeling of chromatin is critical for cellular resilience to oxidative stress, due to the refractory effect that nucleosome arrays can have on DNA damage signalling and repair. The Chromodomain Helicase DNA-binding (CHD) 6 (CHD6) chromatin remodeling enzyme is recruited to sites of oxidative DNA damage in a PAR-dependent manner and is known to be important for preserving cell health during oxidative stress conditions; however, its exact role in repair and DNA repair outcomes is not fully understood. To discover the molecular mechanism by which CHD6 is regulated by and functions within the oxidative DNA damage response, I carried out biochemical, molecular, and cellular studies investigating how individual protein domains of CHD6 contribute to its recruitment and retention at DNA damage sites induced by laser micro-irradiation, and what happens to cells when CHD6 function is lost. I identified CHD6 as capable of directly binding PAR, and that both a functional PAR interacting motif and previously undescribed DNA binding domain are required for effective localization and retention of CHD6 at DNA damage sites. Investigating the biological outcomes of CHD6 loss, I discovered that CHD6-/- normal human tissue-derived cells are sensitive to PARP-trapping small molecule inhibitors and other causes of DNA replication stress, identifying a mechanism of synthetic lethality between CHD6 function and PARP-trapping drugs that does not depend on defective homologous recombination repair. Through molecular biology and mass spectrometry-based techniques, I have identified CHD6 as a base excision repair accessory factor, whose loss causes the accumulation of abasic sites in the genome. Consequently, treatment with PARP-trapping inhibitors results in overwhelming replication stress in CHD6-/- cells that proves lethal to cells. My work has compelling implications for cancer therapy development, where identification of novel ways to increase the effectiveness of PARP inhibitors or overcome acquired resistance to these drugs can positively impact patient outcomes.
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Provencher, L. (2024). The role of CHD6 in the DNA damage response (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.