Genomic instability is a hallmark of cancer. Cancer cells that are genetically unstable are often susceptible to radiation and chemotherapy. Radiation kills cancer cells by inflicting multiple types of DNA damage, including DNA double-stranded breaks (DSBs). Cancer cells defective for DSB repair, such as those carrying BRCA1/2 mutations, are highly sensitive to radiation. BRCA1/2-deficient cells are also sensitive to PARP inhibitors, presenting a new strategy to improve the efficacy of radiation therapy. However, BRCA1-deficient cancer cells often acquire resistance to radiation and PARP inhibitors due to the bypass of BRCA1 in homologous recombination (HR), hindering the treatment of BRCA1-deficient cancers. These findings raised important questions as to how BRCA1-independent HR differs from BRCA1-dependent HR, and whether the radiation and PARP inhibitor resistance of BRCA1-deficient cells can be overcome. Our recent studies on the master checkpoint kinase ATR have provided important clues to these questions. We found that in BRCA1-proficient cells, ATR phosphorylates BRCA1 and controls its downstream functions in HR. Surprisingly, even in BRCA1- deficient cells where the function of BRCA1 is bypassed, ATR is still critical for HR, suggesting a BRCA1- independent role for ATR in the radiation response. Based on these exciting findings, we hypothesize that ATR regulates HR via both BRCA1-dependent and -independent mechanisms. Furthermore, ATR inhibition may be an effective way to overcome the radiation and PARP inhibitor resistance of BRCA-deficient tumors. We propose to: 1) elucidate how ATR regulates HR by phosphorylating BRCA1; 2) reveal how ATR regulates BRCA1-independent HR; and 3) systematically test if ATR inhibitors can be broadly used to overcome the radiation and PARP inhibitor resistance of BRCA-deficient tumors.

Public Health Relevance

Genomic instability is a hallmark of cancer and an attractive target for therapy. We will investigate how ATR, a master DNA damage-signaling kinase in human cells, regulates the repair of radiation induced DNA breaks. Furthermore, we will explore how to attack specific vulnerabilities of cancer cells by inhibiting ATR.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA197779-04
Application #
9513494
Study Section
Radiation Therapeutics and Biology Study Section (RTB)
Program Officer
Pelroy, Richard
Project Start
2015-07-01
Project End
2020-06-30
Budget Start
2018-07-01
Budget End
2019-06-30
Support Year
4
Fiscal Year
2018
Total Cost
Indirect Cost
Name
Massachusetts General Hospital
Department
Type
DUNS #
073130411
City
Boston
State
MA
Country
United States
Zip Code
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Wu, Ching-Shyi; Zou, Lee (2016) The SUMO (Small Ubiquitin-like Modifier) Ligase PIAS3 Primes ATR for Checkpoint Activation. J Biol Chem 291:279-90