Publication Date
2025
Document Type
Thesis
Committee Members
Michael G. Kemp, Ph.D. (Advisor); Ravi P. Sahu, Ph.D. (Committee Member); Yong-jie Xu, M.D., Ph.D. (Committee Member)
Degree Name
Master of Science (MS)
Abstract
Ultraviolet (UV) radiation from the sun is the most prominent source of exogenous UV damage to DNA. UV directly causes damage by forming UV photoproducts, including pyrimidine-pyrimidone (6-4) photoproducts ((6-4) PPs), which significantly distort the helical structure of DNA and interfere with transcription and replication processes. The only known repair process of these photoproducts in human cells is nucleotide excision repair (NER). However, a recent study reported an APE1-dependent base excision repair (BER) of a subset of UV photoproducts. The study showed that deletion or inhibition of APE1, PARP1, NTH1, XRCC1, and FEN1 led to a 2-fold increase in sensitivity to UVC and a decrease in the early rate of removal of (6-4) PPs. To validate and extend the results of this study, we pharmacologically or genetically disrupted the functions of these proteins in proliferating or quiescent human keratinocytes exposed to solar-simulating UV light (SSL) and then monitored cell viability, UV photoproduct removal, and the activation of DNA damage response kinase signaling. We observed that though PARP1 inhibition produced a modest increase in sensitivity of proliferating but not quiescent cells to UV radiation, the rate of repair of (6-4) PPs is similar in the two types of cells. Whereas SSL-induced phospho-CHK1 levels were not impacted by PARP1 inhibition, H2AX phosphorylation was decreased, and KAP1 phosphorylation was increased following SSL exposure and PARP1 inhibition. The inhibition of APE1 with a small molecule inhibitor did not increase the sensitivity to UV radiation, however, deletion of APE1 modestly increased the sensitivity following SSL exposure. Experiments to examine the impact of the loss of APE1 on the rate of removal of (6-4) PP from DNA indicate that APE1 loss may indeed reduce the rate of removal of this photoproduct from DNA. In summary, these results show that disruption of PARP1 and APE1 function impacts how proliferating and quiescent keratinocytes respond to SSL exposure, which has important implications for understanding the origins of mutations and cancers in sun-exposed skin.
Page Count
60
Department or Program
Department of Pharmacology and Toxicology
Year Degree Awarded
2025
Copyright
Copyright 2025, all rights reserved. My ETD will be available under the "Fair Use" terms of copyright law.
