Double-strand breaks in DNA (DSBs) are among the most lethal lesions in the genome if they are not repaired or if their repair is executed incorrectly. Most cancer therapies, including radiation therapy, induces multiple DSBs to kill cancer cells but concurrent induction of DSBs in non-tumor cells can result in chromosome rearrangements that might be a source of therapy related tumors in treated patients. DSB repair takes place through two main pathways, homology-directed repair (HDR) and non-homologous end-joining (NHEJ) that are carefully regulated to avoid the formation of chromosomal aberrations. DSB repair regulation is of great importance to human health since errors in the choice of DSB repair pathway can incite gene rearrangements that promote cancer and faulty DSB repair often generates aberrant chromosomal structures that kill cells. This proposal is focused on the regulation of DSB repair by 53BP1, a DNA damage response factor that affects the choice between HDR and NHEJ, promoting NHEJ and inhibiting HDR. 53BP1 has recently attracted attention because of its involvement in the treatment of BRCA-deficient breast and ovarian cancers with PARP inhibitors (PARPi) that generate DSBs in S/G2. Brca1-deficient cells are sensitive to PARPi treatment because they fail to repair PARPi-induced DSBs by homologous recombination (HR) and accumulate aberrantly linked lethal chromosomes formed by NHEJ. However, when 53BP1 is absent, inappropriate DSB repair by NHEJ is diminished, HR appears to be restored, and the PARPi treatment is no longer effective. This proposal aims to elucidate the mechanisms by which 53BP1 controls the balance between NHEJ and HDR. We propose to use unique aspects of a telomere-based assay system developed in our laboratory to determine the mechanism and consequences of three functional aspects of 53BP1.
In AIM 1, we will ask how the 53BP1-interacting factor Rif1 inhibits CtIP-dependent resection at DSBs and what the consequences are of this regulatory pathway for DSB repair, including in PARPi-treated Brca1-deficient cells.
In AIM 2, we will use a second, newly-developed telomere-based system to determine how 53BP1 inhibits a 5' resection pathway that is independent of CtIP. Finally, in AIM 3, we will focus on the ability of 53BP1 to increase the mobility of chromatin at/near sites of DNA damage, an attribute we discovered in the context of telomere dysfunction. The mechanism by which 53BP1 acts to change chromatin movement will be determined and we will address to what extent this pathway affects the repair of genome-wide DSBs. The experiments are designed to gain insights into fundamental aspects of the regulation of DSB repair by 53BP1 with the ultimate objective to provide information valuable to the use of PARP inhibitors for the treatment of breast and ovarian cancer and other cancer therapies, including radiation therapy in which DSB repair is central to the treatment outcome.

Public Health Relevance

This project is focused on understanding how cells repair breaks in their DNA, which is of great importance to human health because defective DNA repair is a cause of cancer. Conversely, cancer can be successfully treated with ionizing radiation or chemotherapeutic agents that introduce breaks in the DNA. The proposed experiments are focused on 53BP1, a key regulator of DNA break repair, and are designed to facilitate the development of better cancer therapies.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA181090-02
Application #
8782612
Study Section
Radiation Therapeutics and Biology Study Section (RTB)
Program Officer
Pelroy, Richard
Project Start
2013-12-15
Project End
2018-11-30
Budget Start
2014-12-01
Budget End
2015-11-30
Support Year
2
Fiscal Year
2015
Total Cost
Indirect Cost
Name
Rockefeller University
Department
Anatomy/Cell Biology
Type
Graduate Schools
DUNS #
071037113
City
New York
State
NY
Country
United States
Zip Code
10065
Gong, Yi; Handa, Naofumi; Kowalczykowski, Stephen C et al. (2017) PHF11 promotes DSB resection, ATR signaling, and HR. Genes Dev 31:46-58
Maciejowski, John; de Lange, Titia (2017) Telomeres in cancer: tumour suppression and genome instability. Nat Rev Mol Cell Biol 18:175-186
Takai, Hiroyuki; Jenkinson, Emma; Kabir, Shaheen et al. (2016) A POT1 mutation implicates defective telomere end fill-in and telomere truncations in Coats plus. Genes Dev 30:812-26
Kibe, Tatsuya; Zimmermann, Michal; de Lange, Titia (2016) TPP1 Blocks an ATR-Mediated Resection Mechanism at Telomeres. Mol Cell 61:236-46
Maciejowski, John; Li, Yilong; Bosco, Nazario et al. (2015) Chromothripsis and Kataegis Induced by Telomere Crisis. Cell 163:1641-54
Lottersberger, Francisca; Karssemeijer, Roos Anna; Dimitrova, Nadya et al. (2015) 53BP1 and the LINC Complex Promote Microtubule-Dependent DSB Mobility and DNA Repair. Cell 163:880-93