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.
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.
|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|
|Lee, Younghyun; Sunada, Shigeaki; Hirakawa, Hirokazu et al. (2017) TAS-116, a Novel Hsp90 Inhibitor, Selectively Enhances Radiosensitivity of Human Cancer Cells to X-rays and Carbon Ion Radiation. Mol Cancer Ther 16:16-24|
|Lee, Younghyun; Li, Huizi Keiko; Masaoka, Aya et al. (2016) The purine scaffold Hsp90 inhibitor PU-H71 sensitizes cancer cells to heavy ion radiation by inhibiting DNA repair by homologous recombination and non-homologous end joining. Radiother Oncol 121:162-168|
|Chun, Changzoon; Wu, Yuehan; Lee, Suk-Hee et al. (2016) The homologous recombination component EEPD1 is required for genome stability in response to developmental stress of vertebrate embryogenesis. Cell Cycle 15:957-62|
|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|
|Nickoloff, Jac A (2015) Photon, light ion, and heavy ion cancer radiotherapy: paths from physics and biology to clinical practice. Ann Transl Med 3:336|
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