H3.1Cys96 oxidation by mitochondrial ROS promotes chromatin remodeling, breast cancer progression to metastasis and multi-drug resistance

Transcription stability enforces cellular identity and is tightly controlled by restrictions imposed on both transcription factor function and target gene accessibility. Progression of cancer to metastasis and multi-drug resistance requires fluid transcriptional programs that can explore different genomic landscapes to enable clonal expansion of aggressive and treatment resistant phenotypes. Here, we show that increased levels of H2O2 produced in mitochondria leads to H3.1 oxidation at Cys96, a distinctive redox sensitive amino acid residue restricted to this histone variant, in the nucleus. The oxidation of Cys96 promotes the eviction of H3.1 from chromatin and its exchange with H3.3, thereby opening silenced portions of the chromatin. Mutation of Cys96 by an oxidation-resistant serine residue or quenching nuclear H2O2 reversed chemotherapy resistance and drove established metastatic disease into remission. Together, these results show that increased mitochondrial H2O2 production, characteristic of metabolic dysfunction, promotes transcriptional plasticity by removing structural chromatin restrictions imposed by the redox sensitive histone variant H3.1. We suggest that this new regulatory nexus between cancer metabolism and chromatin remodeling controls chromatin states that enable cancer progression and drug resistance acquisition.