Abstract 6605: USP3 stabilizes STING to enhance radiosensitivity and antitumor immunity of NSCLC.

Abstract Purpose: Although radiotherapy (RT) is a predominant treatment for non-small cell lung cancer (NSCLC), radioresistance remains a major challenge and is strongly linked to dysregulated tumor immune microenvironments (TIME). Immunoradiotherapy has shown improved therapeutic activity by promoting antitumor immune responses and modifying the TIME. Recent studies positions STING activation as a potent catalyst of this immune reprogramming. Therefore, identifying upstream regulators capable of enhancing STING-mediated immune activation is critical for developing strategies to overcome radioresistance in NSCLC. Methods: Ubiquitin-specific protease3 (USP3) expression patterns, immune infiltration profiles, and pathway enrichment analyses were performed using public datasets and institutional sequencing data. Prognostic value was evaluated via TCGA datasets and validated in a clinical cohort of 105 NSCLC patients (Tianjin Medical University Cancer Institute & Hospital, 2013-2015). Subsequently, we investigated the interaction between USP3 and STING and the effects of USP3 on RT-induced STING/type I interferon (IFN-Is) signaling through co-immunoprecipitation and immunofluorescence. Finally, we evaluated the effects of USP3 on RT-induced T cell infiltration in tumor and sensitivity to RT and radioimmunotherapy. Results: USP3 expression was significantly downregulated in NSCLC specimens compared to normal tissues. High USP3 expression correlated with prolonged overall survival in public datasets and our independent clinical cohort. Functionally, USP3 overexpression enhanced the radiosensitivity of NSCLC cells and induced a pro-inflammatory phenotype. Mechanistically, USP3 physically interacted with STING, removed K48-linked polyubiquitin chains, and thereby prevented proteasomal degradation of STING. This stabilization amplified cGAS-STING signaling and downstream IFN-Is production. In vivo, USP3 overexpression remodeled the post-irradiation tumor immune microenvironment, as evidenced by increased infiltration of effector CD8+ T cells and enhanced systemic antitumor immunity. Conclusion: USP3 deubiquitinates STING and blocks its proteasomal degradation, thereby stabilizing the STING protein, potentiating the cGAS-STING axis and type I interferon signaling. These results highlight USP3 as a promising prognostic biomarker and a potential therapeutic target for overcoming radioresistance and improving radiotherapy-based treatment strategies. Citation Format: Zeyuan Cheng, Zhengkun Cai, Yihan Xu, jiazhuo yan, Zhiqiang Wu, Zhiyong Yuan. USP3 stabilizes STING to enhance radiosensitivity and antitumor immunity of NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 6605.