Abstract 1411: ADAR1 enhances ribosome biogenesis and triggers oncogenic translation

Abstract Background: Ribosome biogenesis (RiBi) is a critical process underpinning cellular protein synthesis, meticulously regulated to maintain homeostasis. Dysregulated RiBi and translational control are integral to the uncontrolled proliferation of tumors, a hallmark of cancer, yet the molecular mechanisms remain poorly understood. Adenosine Deaminase Acting on RNA 1 (ADAR1), a key enzyme mediating RNA editing, has been linked to tumor transcriptomic heterogeneity and resistance to PD-1 immune checkpoint blockade. However, its precise role in tumor ribosome biogenesis and oncogenic translation remains unclear. Here, we uncover a novel connection between ADAR1 and RiBi, revealing its unrecognized role in driving tumorigenesis and therapeutic vulnerability. Methods: To identify ADAR1-regulated pathways, RNA sequencing (RNA-seq), ribosome profiling (Ribo-seq), and gene set enrichment analysis (GSEA) were performed in ADAR1-siRNA-treated tumor cells. The association between ADAR1 and RiBi was validated using single-sample GSEA (ssGSEA) in TCGA datasets and the RiBi Alu Editing Index (AEI) in the FUSCC TNBC cohort. Nucleolar morphology was evaluated using immunofluorescence and electron microscopy, while ribosome abundance and translational efficiency were assessed via sucrose density gradient centrifugation, rRNA quantification, and SUnSET assays. RNA pull-down and Sanger sequencing validated downstream targets. Functional and therapeutic potential of ADAR1 inhibition were assessed in mouse xenograft models and patient-derived organoids (PDOs) treated with CX-5461, an RNA polymerase I inhibitor. Results: ADAR1 was found to play a pivotal role in driving onco-RiBi, enhancing ribosome production and translation of oncogenic pathways such as MYC, mTOR, and DNA repair. Ribo-seq revealed that ADAR1 knockdown suppressed the translational efficiency of pro-tumorigenic genes, including MCM2 and CDC6. Mechanistically, ADAR1-mediated A-to-I RNA editing of Nucleolar Protein 14 (NOP14) stabilized fibrillarin (FBL), a key nucleolar marker, preserving nucleolar integrity and promoting ribosome assembly. High ADAR1 expression and elevated RiBi AEI scores correlated with poor prognosis in TCGA and FUSCC cohorts. CX-5461 disrupted RiBi, induced nucleolar stress, and suppressed tumor growth in preclinical models. PDOs with high ADAR1 expression demonstrated increased sensitivity to CX-5461, highlighting its therapeutic potential for targeting ADAR1-driven ribosomal dysregulation. Conclusions: Our study establishes a critical link between post-transcriptional RNA editing, tumor ribosome biogenesis, and oncogenic translation, addressing a key gap in the field. ADAR1 emerges as a pivotal regulator of onco-RiBi, and targeting ADAR1 in tumors with high expression using CX-5461 represents a promising therapeutic strategy. Citation Format: Xuliren Wang, Zhibo Shao, Qi Zhang, Han Zhu, Bingqiu Xiu, Yayun Chi, Jiong Wu. enhances ribosome biogenesis and triggers oncogenic translation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1411.