TIRR/53BP1 complex regulates mitotic fidelity and immune-mediated radiation response

This proposal aims to investigate the mitotic function of 53BP1, a protein that plays an important role in the maintenance of genome stability by regulating the choice of double-strand break (DSB) repair pathway and p53 transactivation as well as its negative regulator TIRR. It brings together two investigators with expertise in DNA damage repair and genome stability (Dipanjan Chowdhury) and mitotic mechanisms of genome stability (Alexander Spektor) and builds upon our prior work on 53BP1 regulation in mitosis. While 53BP1 dissociates from DNA damage foci in mitosis to prevent genome instability, a subset of 53BP1 has been shown to localize to kinetochores and spindle poles and regulate various mitotic functions. Our preliminary results show that either loss or dysregulation of 53BP1 due to the loss of TIRR leads to mitotic abnormalities, including chromosome segregation defects and nuclear atypia. To understand the role of 53BP1 in mitosis, we identified 53BP1-interacting partners including several proteins with essential mitotic function including Plk1, Kif2a, Kif2c, and NuMA. We confirmed 53BP1 interaction with Plk1 and showed that dysregulation of 53BP1 alters dynamic spatial localization and function of Plk1 in mitosis. This leads us to hypothesize that 53BP1/TIRR complex regulates localization and function of Plk1 to ensure mitotic fidelity. In Aim 1, we will systemically test this hypothesis. In Aim 2, we will employ a combination of cytological and molecular approaches to dissect the mechanism of 53BP1 association with kinetochores and define the specific role that 53BP1 plays in mitosis. We will systemically define how 53BP1 regulates localization and function of its interacting partners and how this contributes to the observed mitotic abnormalities, including chromosome missegregation errors, spindle abnormalities and kinetochore assembly defects. Finally, we recently discovered that loss of 53BP1 leads to activation of innate immune pathways associated with anti-tumor immune response (Sun Y., Patterson-Fortin J, et al., Nature Communications 2024). In Aim 3, we will build upon this work to test the hypothesis that 53BP1 is an important regulator of immune-mediated radiation response in radioresistant tumors such as pancreatic adenocarcinoma using immunocompetent syngeneic mouse models. We will also test whether this response synergizes with immune checkpoint inhibitors (ICIs). Together, these experiments will define the role of 53BP1/TIRR complex during mitosis and in immune-mediated radiation response and pave the way for the development of novel therapeutic strategies including 53BP1 inhibitors. Project Number: 1R01CA301574-01A1 | Fiscal Year: 2026 | NIH Institute/Center: National Cancer Institute (NCI) | Principal Investigator: Alexander Spektor (+1 co-PI) | Institution: DANA-FARBER CANCER INST, BOSTON, MA | Award Amount: $683,075 | Activity Code: R01 | Study Section: Special Emphasis Panel[ZRG1 BTC-Y (02)] View on NIH RePORTER: https://reporter.nih.gov/project-details/11295720