RNF25 confers mRNA damage tolerance by curbing activation of the integrated stress response

Excessive RNA damage activates cellular stress responses, triggering cell death. However, pathways that negatively regulate RNA damage responses are largely uncharacterized. Using genetic screens, we find that the ubiquitin ligase RNF25 provides tolerance to RNA damage caused by the nucleoside analogue azacytidine, a chemotherapeutic agent used to treat acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). Mechanistically, we show that azacytidine is incorporated into mRNA, where it causes lesions that stall elongating ribosomes, leading to cytotoxic activation of the GCN2-dependent integrated stress response (ISR). Furthermore, we establish that RNF25 prevents ISR hyperactivation by ubiquitylation of ribosomal protein eS31, thereby suppressing cell death upon azacytidine treatment. Our study reveals an mRNA damage tolerance mechanism that determines cellular survival in response to azacytidine, highlighting RNA damage-induced stress response as a potentially critical component of chemosensitivity in AML and MDS.