ADAR1 Regulates Alternative Splicing Through an RNA Editing-Independent Mechanism.

Dysregulation of the RNA-editing enzyme ADAR1 is associated with human diseases, including cancer, but its RNA-editing-independent roles in alternative splicing remain largely unexplored. Comprehending these molecular mechanisms is paramount, as they may unveil novel therapeutic targets. This study elucidates how the ADAR1p110 isoform influences alternative splicing independently of its canonical editing activity. Employing RNA-sequencing, proteomic analysis of ADAR1p110 interactors, and functional assays with wild-type and mutant ADAR1 in diverse human cell lines (including cancer models), we investigated its impact on the splicing landscape. Our findings indicate that ADAR1p110 interacts with pivotal spliceosome components and auxiliary splicing regulators. Notably, ADAR1 extensively modulates alternative-splicing events, with most of these alterations occurring independently of its RNA-editing activity and often its RNA-binding capacity. Furthermore, ADAR1 alters the isoform expression of other splicing factors (e.g., ACIN1), suggesting an indirect regulatory mechanism. Importantly, this splicing reprogramming affects genes that govern therapeutic response, positioning the ADAR-splicing axis as a potential driver of drug resistance. By revealing this predominantly editing-independent mechanism, we expand the understanding of ADAR1's non-canonical functions and identify a new avenue for therapeutic intervention in cancer.