Abstract B009: BRCA1 regulates ZNFX1-induced mitochondrial dysfunction and STING activation in high grade serous ovarian cancer

Abstract Women harboring deleterious BRCA mutations are at greatly increased risk of developing high grade serous ovarian cancer (HGSC). BRCA1 and BRCA2 genes are crucial for repairing DNA double-strand breaks via homologous recombination, maintaining genomic stability. Recent findings suggest BRCA1 is also localized to the mitochondrial (mt) membrane, where it helps maintain mt metabolic stability. Mutations in BRCA1 and BRCA2 promote both genomic instability and mt dysfunction leading to an increase in cancer susceptibility. We recently reported that viral mimicry and therapeutic agents—poly (ADP-ribose) polymerase inhibitors (PARPis) and DNA methyltransferase inhibitors (DNMTis)—activate a cytosolic nucleic acid sensor, zinc finger NFX1-type containing 1 protein (ZNFX1) which is a master regulator of mt dysfunction and Stimulator of Interferon Genes (STING)-dependent interferon (IFN) and inflammasome signaling. However, the role of BRCA1/2 proteins in regulating ZNFX1-induced mt dysfunction and STING-dependent immune signaling remains unclear. To test whether BRCA1/2 proteins influence ZNFX1 expression, binding and STING activation, we used multiple isogenic mice and human HGSC cell lines with wild-type (WT) or CRISPR knock-out (KO) BRCA1. We showed for the first time that ZNFX1 colocalized with BRCA1 but had reduced binding to the mitochondrial antiviral-signaling protein (MAVS) in BRCA1 WT cells, using proximity ligation assays. In contrast, in BRCA1 KO cells, BRCA1–ZNFX1 binding was lost, and ZNFX1–MAVS colocalization was significantly increased, suggesting that BRCA1 may have acted as a negative regulator of ZNFX1 activity. Consistent with these findings, BRCA1 KO cells showed significantly increased ZNFX1 expression compared to WT controls, as measured by qPCR. As expected by its known role in genome stability, BRCA1 KO cells demonstrated increased nuclear and cytosolic double-stranded DNA, as well as R-loops, compared with WT cells. Mitochondrial reactive oxygen species (ROS) were also increased in BRCA1 KO vs WT cells, as measured by flow cytometry with MitoSOX dye. Notably, compared with WT cells, STING-dependent IFN signaling was also elevated in BRCA1 KO cells, indicated by increased TBK1, CXCL10, IFI27, TNFα, and IRF3. Treatment with PARPis and DNMTis further enhanced ZNFX1 binding to MAVS and mt ROS in both BRCA1 KO and WT cells, suggesting that these agents could have amplified immune signaling. Validation of above-described signaling is ongoing in HGSC cell lines with naturally occurring BRCA1 mutations (SNU-251) or with BRCA1 methylation (OVCAR8 and A1847). Further studies are evaluating these effects in syngeneic mouse models to assess changes in the tumor microenvironment and in vivo therapeutic responses. This study revealed novel mechanisms linking BRCA1 loss to ZNFX1 activation, viral mimicry, and immune modulation. It highlighted the therapeutic potential of targeting ZNFX1 pathways to enhance treatment efficacy in BRCA1-deficient HGSC. Citation Format: Zahra Gohari, Feyruz V. Rassool, Lora Stojanovic, Stephen B. Baylin, Kenneth P. Nephew. BRCA1 regulates ZNFX1-induced mitochondrial dysfunction and STING activation in high grade serous ovarian cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Ovarian Cancer Research; 2025 Sep 19-21; Denver, CO. Philadelphia (PA): AACR; Cancer Res 2025;85(18_Suppl):Abstract nr B009.