Senescence is a phenotypic state of stable proliferative arrest, typically occurring in lineagecommitted cells and triggered by various stimuli. It is generally accompanied by activation of a secretory program (senescence-associated secretory phenotype, SASP), which modulates 35 both local (tissue microenvironment) and systemic (ageing) homeostasis 1,2 . Enhancerpromoter interactions play a key role in gene regulation 3-5 , facilitated by chromatin loops, mostly formed via CCCTC binding factor (CTCF) and cohesin tethering 6-8 . The threedimensional chromatin structure of senescent cells has been characterised 9-11 mostly in terms of macro-domain structures, but its relevance in gene expression remains elusive.
40Here, we use Hi-C and capture 13 to show that oncogenic HRAS-induced senescence (RIS) in human diploid fibroblasts (HDFs) is accompanied by extensive enhancer-promoter rewiring, which is closely connected with dynamic cohesin binding to the genome. We find de novo cohesin peaks at the 3' end of a subset of active genes, reminiscent of the transcription-driven 'cohesin islands' recently discovered in mouse embryonic fibroblasts 45 deficient in both CTCF and the cohesin release factor Wings apart-like (Wapl) 14 . RIS de novo cohesin peaks are also transcription-dependent and enriched for SASP genes, as exemplified by IL1B, where de novo cohesin binding is involved in new loop formation. Cytokine induction is associated with similar cohesin islands appearance and enhancerpromoter rewiring during the terminal differentiation of monocytes to macrophages 15 , but not 50 upon acute TNFa treatment of HDFs 16 . These results suggest that RIS represents a fatedetermined process in which gene expression is regulated beyond the cell type specific 3D chromatin framework, in part through cohesin redistribution.
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MainOncogene-induced senescence (OIS) has been linked to dynamic alterations of the chromatin 60 landscape, through the formation of three-dimensional heterochromatic foci 17 , altered distributions of histone modifications and chromatin accessibility 2,18 or the appearance of new 'super-enhancers' 19 . While it has been shown that regulation of acute stress-responsive genes can be achieved through transcription factor (TF) recruitment to largely pre-existing enhancer-promoter (EP) contacts 16,20,21 , whether or not a similar mechanism is employed 65 during OIS (sustained oncogenic stress) is unknown. To study gene regulatory mechanisms in the 3D chromatin context at high resolution, we performed in situ Hi-C experiments as well as capture Hi-C (cHi-C) for 62 selected genomic regions of interest ( Supplementary Table 1) in normal growing and oncogenic HRAS-G12V-induced senescent (RIS) IMR90 human diploid fibroblasts (HDFs), using the 4-hydroxytamoxifen (4OHT)-inducible estrogen receptor 70 (ER) HRAS fusion system 22 (ER:HRAS G12V Fig. 1a). Growing (three replicates) and RIS (two replicates) Hi-C libraries yielded a total of 523 and 286 million valid reads respectively, after removal of artefacts and duplicate...