Transcription Machinery Anchors ecDNAs to Mitotic Chromosomes for Segregation

Extrachromosomal DNA (ecDNA) is a prevalent driver of cancer, whose random segregation promotes aggressive tumors. Acentric ecDNAs attach to chromosomes during mitosis for segregation. However, the molecular mechanism governing ecDNA-chromosome mitotic interactions remains poorly understood. This study shows that ecDNAs attach to histone 3 lysine 27 acetylation (H3K27ac)-marked chromatin during mitosis. H3K27ac depletion resulted in ecDNA detachment from mitotic chromosomes. Diverse bromodomain proteins, which are known readers of H3K27ac, stabilize ecDNAs’ mitotic interaction, exhibiting context-dependent and mutually complementary roles. Furthermore, disruptions of the Mediator complex and RNA polymerase II transcription activity both dissociate ecDNAs from mitotic chromosomes, suggesting that the transcription machinery mediates ecDNA segregation. Mis-segregated ecDNAs were expelled into the cytosol and degraded, leading to diminished oncogene expression and a reversal of therapy resistance. Our research provides new insights into the interplay between RNA transcription and acentric ecDNA inheritance in cancer, offering a novel avenue for disrupting ecDNA-driven oncogenesis.