Most cancer patients receive radio- and/or chemotherapy that causes DNA damage, which blocks DNA replication. Normal and tumor cells respond to DNA damage and associated replication stress by activating DNA repair, cell cycle arrest (checkpoint) systems, and when damage is severe, programmed death pathways, collectively termed the DNA damage response (DDR). DDR proteins play crucial roles in tumor suppression and genome stabilization (cancer etiology) as well as tumor response to radio- and chemotherapy (cancer treatment). DDR pathways determine cell fates in response to DNA damage, including cell survival, genome stability, and cell death/permanent growth arrest via apoptosis, autophagy, necrosis, senescence, or mitotic catastrophe. Cells are particularly vulnerable to DNA damage during S phase because most DNA lesions stall replication forks, causing replication stress. This proposal focuses on several proteins with roles in DNA repair, checkpoint activation, and recovery from replication stress. Metnase and DNA-PK were both initially characterized for their roles in DNA double-strand break (DSB) repair by non-homologous end joining (NHEJ). Recent studies demonstrate that Metnase and DNA-PK (along with replication protein A (RPA), ATM/ATR, Chk1, and others) also function in checkpoint activation and replication stress recovery. The replication checkpoint prevents new origin firing and stabilizes stalled replication forks to prevent fork collapse, allowing time for repair and for restart. Persistent replication stress can lead to fork collapse, producing one-ended DSBs marked by phosphorylated H2AX (?-H2AX). RPA accumulates on single-stranded DNA at stalled forks and the RPA32 subunit is phosphorylated at multiple sites by phosphoinositide 3-kinase-related protein kinases (PIKKs) DNA-PK, ATM and ATR, leading to Chk1 activation and replication arrest. Metnase also regulates Chk1 activation and replication arrest. Our central hypothesis is that Metnase, DNA-PK, and RPA operate within the DDR to influence cell fate after genotoxic stress, including cell survival, genome stability, and death pathway activation. We will determine roles of Metnase (Aim 1) and PIKK phosphorylation of RPA (Aim 2) in replication stress responses including replication arrest, fork restart, genome stability, cell survival and cell death by apoptosis.
In Aim 3 we will define epistatic relationships between Metnase and PIKK/RPA pathways, and test novel combinations of replication stress agents plus DDR inhibitors to enhance killing of breast, lung, pancreatic, colon, head and neck, and leukemic tumor cells. A better understanding of how DDR factors regulate cell fate decisions will drive the development of novel cancer therapies to improve local tumor control, and reduce the risk of therapy-induced tumor progression and secondary tumor induction.

Public Health Relevance

Most cancer patients receive radiotherapy and/or chemotherapy that damages DNA and blocks DNA replication. Normal and tumor cells respond to these threats by activating DNA repair pathways and arresting cell cycle progression, collectively called the DNA damage response network. This project is focused on understanding how DNA damage response proteins determine cell fate after chemotherapy. These studies will help us design more effective therapeutic strategies that increase local tumor control, and minimize therapy- induced tumor progression and secondary tumor induction.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Basic Mechanisms of Cancer Therapeutics Study Section (BMCT)
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Willis, Kristine Amalee
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Colorado State University-Fort Collins
Public Health & Prev Medicine
Schools of Veterinary Medicine
Fort Collins
United States
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Nickoloff, Jac A (2017) Paths from DNA damage and signaling to genome rearrangements via homologous recombination. Mutat Res 806:64-74
Allen, Christopher P; Hirakawa, Hirokazu; Nakajima, Nakako Izumi et al. (2017) Low- and High-LET Ionizing Radiation Induces Delayed Homologous Recombination that Persists for Two Weeks before Resolving. Radiat Res 188:82-93
Kim, Hyun-Suk; Nickoloff, Jac A; Wu, Yuehan et al. (2017) Endonuclease EEPD1 Is a Gatekeeper for Repair of Stressed Replication Forks. J Biol Chem 292:2795-2804
Kim, Hyun-Suk; Williamson, Elizabeth A; Nickoloff, Jac A et al. (2017) Metnase Mediates Loading of Exonuclease 1 onto Single Strand Overhang DNA for End Resection at Stalled Replication Forks. J Biol Chem 292:1414-1425
Nickoloff, Jac A; Boss, Mary-Keara; Allen, Christopher P et al. (2017) Translational research in radiation-induced DNA damage signaling and repair. Transl Cancer Res 6:S875-S891
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Wu, Yuehan; Lee, Suk-Hee; Williamson, Elizabeth A et al. (2015) EEPD1 Rescues Stressed Replication Forks and Maintains Genome Stability by Promoting End Resection and Homologous Recombination Repair. PLoS Genet 11:e1005675
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