Abstract PR011: Novel role of glycogen synthase kinase-3β in determining cancer cell response to PARPi through regulation of 53BP1 function

Abstract

Abstract Glycogen synthase kinase-3β (GSK3β) is a multifunctional serine/threonine kinase involved in various cellular processes and signaling pathways. Accumulating evidence suggests GSK3β plays a role in cancer treatment with effects on tumorigenesis and treatment response. We have previously shown that inhibition of GSK3β protects neurons from ionizing radiation-induced apoptosis through regulation of the repair of double strand breaks (DSBs). Here, we investigate the molecular mechanism underlying GSK3β regulation of DSB repair. We illustrate that GSK3β directly interacts with 53BP1 and phosphorylates 53BP1 at threonine 334 amino acid (T334) within a region heavily phosphorylated by several stress kinases. Phosphorylation at T334 inhibits 53BP1’s function in recruitment to and retention at DSB sites as well as canonical NHEJ. In contrast, phosphorylation at Thr334 of 53BP1 enhances single strand DNA resection and promotes homologous recombination (HR) repair. Most importantly, genetic and pharmacologic inhibition of GSK3β-53BP1 signaling axis dramatically enhances the PARPi cytotoxic response of BRCA1 proficient cancer cells. The assessment of the effect of GSK3β-53BP1 axis on tumor cell response to radiation treatment is underway. In conclusion, this study establishes the connection between GSK3β kinase and DSB repair through its phosphorylation and regulation of 53BP1 property. Moreover, it demonstrates that GSK3β kinase activity uniquely results in inhibition of 53BP1 as opposed to other kinases that enhance 53BP1 function. Importantly, this novel signaling axis provides a strategy for targeting BRCA1-proficinet cancer cell resistance to PARPi. Citation Format: Fen Xia, Heba Allam, Scarlett Acklin, Mousumi Patra, Kirk West, Justin Leung. Novel role of glycogen synthase kinase-3β in determining cancer cell response to PARPi through regulation of 53BP1 function [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: DNA Damage Repair: From Basic Science to Future Clinical Application; 2024 Jan 9-11; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2024;84(1 Suppl):Abstract nr PR011.