However, the role of INO80 in cancer cell proliferation remains largely elusive. These observations suggest a critical function for INO80 in sustaining cancer development and progression. Depletion of INO80 in cancer cells decreases oncogenic transcription, compromises cell proliferation and subsequent tumour growth 21. Several INO80 subunits are overexpressed in different cancers such as breast 19, neuroendocrine prostate cancer 20 and melanoma 21, and their expression levels can correlate positively with bad prognosis 21, 22. Nevertheless, the role of INO80 in DNA replication remains unclear. Mammalian INO80 is required for replication fork stability and recovery following replication stress 17, whilst it also promotes DNA replication in unperturbed conditions 18. In yeast, INO80 has been shown to facilitate degradation of RNA Polymerase II during replication stress conditions in order to preserve genome stability 15, 16. The INO80 complex, which contains the INO80 ATPase, is a structurally and functionally evolutionary conserved chromatin remodelling complex 14. The chromatin landscape is shaped by the action of ATP-dependent chromatin remodelling enzymes that alter the structure, composition or position of nucleosomes 13. Importantly, whether the role of chromatin is that to solely suppress R-loop formation, or to also promote R-loop resolution, remains unknown. Nevertheless, our understanding of the role of chromatin regulation in R-loop modulation remains critically limited. The histone chaperone complex FACT, which promotes nucleosomal integrity 10 and facilitates transcription in the presence of chromatin 11, prevents R-loop accumulation and promotes resolution of transcription-replication conflicts 12. Mutations in the core nucleosomal histones H3 and H4 lead to accumulation of R-loops 9. However, the molecular pathways protecting forks from collisions with R-loops in cancer cells are poorly understood.Įmerging evidence indicates a role for chromatin structure in R-loop control. Several factors have been shown to prevent the formation or promote resolution of R-loops. This raises the question how cancer cells sustain sufficient DNA synthesis rates in the presence of increased transcription-replication conflicts. Recent studies indicate that R-loops are highly abundant and induce replication stress in cancer cells 6, 7. While R-loops play a regulatory role in transcription 1, encounters of forks with R-loops are a potent source of replication stress 2, 3, 4 and are particularly genotoxic when they occur in a head-on orientation 5. Mounting evidence indicates that co-transcriptional RNA:DNA hybrid structures known as R-loops 1 are a major obstacle to replication fork progression. Failure to resolve transcription-replication interference can lead to replication stress, which is characterized by stalling of the replication fork and induction of DNA breaks, with detrimental effects to cell proliferation and homeostasis. In proliferating cells, conflicts between DNA replication and transcription are one of the greatest threats to genome stability. Our work suggests that INO80-dependent resolution of R-loops promotes DNA replication in the presence of transcription, thus enabling unlimited proliferation in cancers. Finally, counteracting R-loops by INO80 promotes proliferation and averts DNA damage-induced death in cancer cells. Artificial tethering of INO80 to a LacO locus enabled turnover of R-loops in cis. R-loops co-localize with and promote recruitment of INO80 to chromatin. Overexpression of the RNA:DNA endonuclease RNAse H1 rescues the DNA synthesis defects and suppresses DNA damage caused by INO80 depletion. Depletion of INO80 in prostate cancer PC3 cells leads to increased R-loops. Here we show that the ATP-dependent chromatin remodelling INO80 complex promotes resolution of R-loops to prevent replication-associated DNA damage in cancer cells. How cancer cells deal with R-loops to proliferate is poorly understood. Collisions between the DNA replication machinery and co-transcriptional R-loops can impede DNA synthesis and are a major source of genomic instability in cancer cells.

S9.6 antibody cross reactivity