CHD5 dysregulation causes epigenetic changes that dictate DNA double-strand break repair pathway choice and vulnerability to KMT5B/C inhibition

The chromatin remodeler and helicase CHD5 is a tumor suppressor with broad relevance across several cancers. Here, we identify a role for CHD5 in the epigenetic control of DNA double-strand break (DSB) repair pathway choice. CHD5 is recruited to DSBs via PARP1/2-mediated chromatin relaxation where it acts to remodel the histone modification landscape to control repair pathway choice. We find that CHD5 promotes H3K36me3 deposition through the methyltransferase SETD2, enabling CtIP loading and homologous recombination (HR) repair of DSBs. CHD5 also suppresses KMT5B/C-dependent H4K20me2/3, which limits the recruitment of 53BP1 to DSBs and repair by non-homologous end joining (NHEJ). Therefore, our study illuminates how CHD5 loss disrupts histone distribution at DSBs to drive genomic instability and create a vulnerability to KMT5B/C inhibition. These findings define an epigenetic mechanism governed by the CHD5 tumor suppressor whereby its loss rewires DSB repair and exposes a therapeutic opportunity.