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Replication stress underlies genomic instability at CTCF/cohesin-binding sites in cancer

ABSTRACT: CCCTC-binding factor (CTCF) and cohesin play a significant role in the formation of chromatin loops and topologically associating domains (TADs), which influence gene expression and DNA replication. CTCF/cohesin-binding sites (CBSs) present at the loop anchors and TAD boundaries are frequently mutated in cancer; however, the molecular mechanisms underlying this remain unclear. Here, we investigate whether the binding of CTCF/cohesin on DNA imposes constraints on DNA replication, leading to replication stress and genomic instability. Our results reveal that CTCF and cohesin remain cobound to DNA during replication (S phase) in cancer cells (HeLa). Further, examination of replication stress through ChIP-seq of the DNA damage response/repair proteins (MRE11, STN1, FANCD2, γH2AX, RAD51 and ATM) showed high enrichment of these proteins at CBSs (as compared to their immediate flanking regions and control sites) and positively correlated with the binding strength of CTCF/cohesin at CBSs in the S phase. Moreover, analysis of somatic mutations from cancer genomes supports that the enrichment of mutations at CBSs is significantly higher in samples harbouring somatic copy number deletion in MRE11 and STN1 compared to wild-type samples. Together, these results demonstrate that the co-binding of CTCF/cohesin on the DNA during the S phase causes replication stress and DNA strand breaks, and this could lead to genome instability at CBSs observed in cancer.

ORGANISM(S): Homo sapiens

PROVIDER: GSE292153 | GEO | 2025/03/22

REPOSITORIES: GEO

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CTCF/cohesin-binding sites are frequently mutated in cancer

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Project description:The architectural protein CTCF binds to mammalian insulators genome wide with directionality and recruits cohesin to mediate oriented long-distance chromatin loops. In many cases, CTCF-binding sites (CBSs) are associated with distal enhancers and target promoters. It is generally thought that CTCF binding results in spatial contacts between distal enhancers and target promoters leading to activation of specific promoters. However, how CTCF orchestrates higher-order chromatin organization to regulate gene expression is not fully understood. Here we used CRISPR DNA-fragment editing to investigate the roles of CTCF in chromatin organization of the clustered protocadherin (Pcdh) genes, which is an ideal model system with repertoires of CBSs in variable promoters and super-enhancers. We found that the CBSs at chromatin domain boundary and even single CBSs could determine the orientation of long-distance chromatin looping. In addition, deletion or inversion of large regions containing tandem CBS arrays in mice demonstrated asymmetric influences on chromatin looping between super-enhancers and target promoters. These genetic data have important implications on the assembly mechanisms of higher-order chromatin structures.

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Project description:Gene amplification, copy-number increases of particular genes and surrounding genomic segments, promotes cancer progression and acquired therapy resistance. Thus, understanding genetic traits that confer gene amplification proficiency is important. The primary step for gene amplification is spontaneous DNA rearrangements initiated by DNA breaks. Here we show that mammalian cells became gene amplification-proficient when we knocked down Mre11/Rad50/Nbs1 (MRN) complex, a multifunctional complex that guards the genome from DNA breaks. Cells with reduced Mre11 experienced severe replication stress, with marked increases of single-stranded breaks followed by double-stranded breaks during DNA replication. Such breaks underlay for the increase in spontaneous gene amplification. Other traits associated with replication stress, such as impaired intra-S phase checkpoint and global transcriptional changes in DNA metabolism genes also contributed to gene amplification proficiency. Our results define Mre11 deficiency as a cause of replication stress and gene amplification proficiency and provide a candidate marker for aggressive cancer phenotypes. We sequenced four samples: 2 control, GFP-expressing samples and 2 Mre11 knockdown cells

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Transcription factor binding in human cells occurs in dense clusters formed around cohesin anchor sites

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CRISPR Inversion of CTCF Sites Alters Genome Topology and Enhancer/Promoter Function

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