Abstract Background: DNA damage plays a critical role in breast cancer, induced by both endogenous and exogenous factors. Abnormal repair mechanisms, such as homologous recombination repair (HRR) and non-homologous end joining (NHEJ), result in genomic instability and the accumulation of mutations, thereby driving cellular malignant transformation. DNA damage also promotes tumor progression by activating inflammatory pathways and modulating the immune microenvironment, serving as a key basis for breast cancer development and treatment resistance. Core Findings: PRAK (p38-regulated/activated protein kinase) is highly expressed in breast cancer and significantly correlates with poor patient prognosis and reduced survival rates. In vitro and in vivo experiments demonstrate that PRAK deficiency sensitizes tumor cells to PARP inhibitors and impairs DNA double-strand break (DSB) repair capacity, leading to defects in the homologous recombination (HR) pathway. Molecular Mechanism: Through affinity chromatography, mass spectrometry, and co-immunoprecipitation, PRAK was confirmed to directly interact with FOXO3 in vitro and in vivo. DNA-damaging agents (PARP inhibitors) induce nuclear accumulation of FOXO3, promoting the interaction between PRAK and FOXO3 within the nucleus. RNA-seq analysis revealed that BRCA1 is a key target of PRAK. PRAK deficiency reduces FOXO3 nuclear localization and inhibits its binding to the BRCA1 promoter, thereby downregulating BRCA1 expression. In vivo validation demonstrated that PRAK deficiency enhances the sensitivity of mouse xenografts to DNA-damaging agents. Conclusions: PRAK is upregulated in multiple human tumor tissues. PRAK deficiency inhibits tumor cell proliferation and sensitizes cells to DNA-damaging agents. PRAK participates in HR-mediated DNA damage repair in an enzyme activity-independent manner. PRAK interacts with FOXO3, influences FOXO3 nuclear localization to regulate DNA damage responses, and affects FOXO3 binding to the BRCA1 promoter to modulate BRCA1 transcriptional activation. PRAK deficiency enhances tumor sensitivity to DNA-damaging drugs. Collectively, this study reveals that PRAK promotes DNA damage repair by transcriptionally regulating BRCA1 expression through FOXO3, representing a novel regulatory mechanism by which PRAK maintains genomic stability via DNA damage repair. Targeting the PRAK/FOXO3/BRCA1 axis may serve as a potential therapeutic strategy to enhance the efficacy of DNA-damaging agents in cancer treatment. Our findings uncover the functions and molecular mechanisms of PRAK in cell proliferation and DNA damage responses, with potential clinical implications for breast cancer therapy. Citation Format: L. Jingjing. The Molecular Mechanism of PRAK Regulating DNA Damage Repair and Its Role in Breast Cancer abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS2-12-22.
Lin Jingjing (Tue,) studied this question.