Exposure to ionizing radiation from environmental sources is universal. In addition, most cancer patients receive radiation therapy. Ionizing radiation kills cells, in part, by inducing DNA double-strand breaks (DSBs). The DNA-dependent protein kinase (DNA-PK) is crucial to regulation of DSB repair. DNA-PK, which is activated by binding to broken DNA ends, phosphorylates itself, other repair proteins, and signaling molecules such as p53. The hypothesis to be tested is that DNA-PK has a decision-making, or """"""""checkpoint"""""""" function. It is proposed that DNA-PK binds initially to DNA ends to form an arrested complex. Synapsis of one DNA end with a compatible, opposing, DNA end leads to kinase activation and checkpoint release, probably via DNA-PK catalytic subunit autophosphorylation. It is proposed that DNA-PK also senses when a DSB cannot be repaired without further processing and responds by recruiting, and potentially phosphorylating, enzymes that are required to process the ends for ligation. Alternatively, if the complex remains unrepairable, DNA-PK may phosphorylate negative regulatory sites in the complex or in tumor suppressor p53.
Three specific aims are: (1) To characterize the initial complex formed when DNA-PK binds to an isolated DNA end. Points of DNA-protein crosslinking and the pattern of accessibility of protein and DNA to chemical and enzymatic probes will be characterized. (2) To characterize mechanisms involved in checkpoint release. Changes in protein-DNA contacts and protein conformation in the synaptic complex, relative to the initial complex, will be identified. Sites of DNA-PKcs phosphorylation in the synaptic complex will be identified and their function investigated. (3) To characterize the DNA-PK complex formed on a DNA end that requires processing prior to repair. Complexes will be formed on an oligonucleotide that has a hairpin terminus and is thus unrepairable without nucleolytic processing. The ability of this complex to recruit and phosphorylate the hairpin endonuclease, Artemis, will be characterized. The use of alternative substrates in the absence of Artemis, such as p53, will be investigated. An overall goal is to obtain basic insights into the regulation of DSB repair that will lead to new, mechanism-based strategies for increasing the efficacy of radiation therapy.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA098239-04
Application #
7239485
Study Section
Radiation Therapeutics and Biology Study Section (RTB)
Program Officer
Pelroy, Richard
Project Start
2004-07-26
Project End
2010-04-30
Budget Start
2007-05-01
Budget End
2010-04-30
Support Year
4
Fiscal Year
2007
Total Cost
$250,163
Indirect Cost
Name
Georgia Regents University
Department
Other Basic Sciences
Type
Schools of Medicine
DUNS #
966668691
City
Augusta
State
GA
Country
United States
Zip Code
30912
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Jaafar, Lahcen; Li, Zhentian; Li, Shuyi et al. (2017) SFPQ•NONO and XLF function separately and together to promote DNA double-strand break repair via canonical nonhomologous end joining. Nucleic Acids Res 45:1848-1859
Zhang, Hui; Head, PamelaSara E; Daddacha, Waaqo et al. (2016) ATRIP Deacetylation by SIRT2 Drives ATR Checkpoint Activation by Promoting Binding to RPA-ssDNA. Cell Rep 14:1435-1447
Udayakumar, Durga; Dynan, William S (2015) Characterization of DNA binding and pairing activities associated with the native SFPQ·NONO DNA repair protein complex. Biochem Biophys Res Commun 463:473-8
Li, Shuyi; Li, Zhentian; Shu, Feng-Jue et al. (2014) Double-strand break repair deficiency in NONO knockout murine embryonic fibroblasts and compensation by spontaneous upregulation of the PSPC1 paralog. Nucleic Acids Res 42:9771-80
Xiong, Hairong; Lee, Robert J; Haura, Eric B et al. (2012) Intranuclear delivery of a novel antibody-derived radiosensitizer targeting the DNA-dependent protein kinase catalytic subunit. Int J Radiat Oncol Biol Phys 83:1023-30
Ha, Kyungsoo; Takeda, Yoshihiko; Dynan, William S (2011) Sequences in PSF/SFPQ mediate radioresistance and recruitment of PSF/SFPQ-containing complexes to DNA damage sites in human cells. DNA Repair (Amst) 10:252-9
Li, Shuyi; Kuhne, Wendy W; Kulharya, Anita et al. (2009) Involvement of p54(nrb), a PSF partner protein, in DNA double-strand break repair and radioresistance. Nucleic Acids Res 37:6746-53
Xiong, Hairong; Li, Shuyi; Yang, Zhanqiu et al. (2009) E. coli expression of a soluble, active single-chain antibody variable fragment containing a nuclear localization signal. Protein Expr Purif 66:172-80
Dynan, William; Takeda, Yoshihiko; Roth, David et al. (2008) Understanding and re-engineering nucleoprotein machines to cure human disease. Nanomedicine (Lond) 3:93-105

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