Cohesin reorganizes stressed DNA replication sites to protect genome stability

An experimental study by researchers at the University of Zurich and the Spanish National Cancer Research Centre has identified a protective role for cohesin during DNA replication. The chromosome-organising protein is rapidly recruited to sites where DNA copying is disrupted, where it reshapes contacts involving newly replicated DNA and helps prevent potentially harmful DNA breaks and mutations. The findings, published in Nature, show that cohesin protects genome stability through two complementary actions: stabilising DNA at stressed replication sites and preventing activation of an emergency pathway that can introduce numerous genetic errors.

The work focuses on replication forks, the moving structures at which molecular machinery copies DNA while a chromosome is duplicated. Replication can encounter obstacles or proceed slowly when a cell lacks enough molecular building blocks to complete the new DNA copy. These interruptions, described as replication stress, can leave the genome vulnerable to damage if they are not properly managed. The researchers found that cohesin accumulates near newly replicated DNA under such conditions and promotes a protective DNA organisation that helps preserve genome integrity.

Cohesin was already known for two important roles in cell division. First, it holds together the two copies of each chromosome produced before division, helping ensure their correct distribution into daughter cells. Second, it helps newly replicated DNA adopt an appropriate three-dimensional organisation inside the nucleus. That organisational task is demanding because a DNA molecule is several metres long when fully extended but must fit inside a microscopic nucleus. By bringing genomic regions that may be far apart along the DNA sequence into proximity, cohesin-mediated folding allows distant genes to coordinate their responses, a function highlighted by Ana Losada, head of the Chromosome Dynamics Group at CNIO and a senior co-author of the study.

The new experiments extend that view of genome organisation from chromosome structure and gene response to a direct role in protecting DNA during replication. Microscopy experiments showed that cohesin accumulates near newly replicated DNA when cells experience replication stress. Its rapid arrival at affected regions supports the local DNA structure and promotes an arrangement associated with reduced genome instability. The study therefore indicates that cohesin’s folding activity is not simply a way of packaging DNA within the nucleus: it also participates in managing the local consequences of interrupted DNA synthesis.

To examine this process in three dimensions, Daniel González of the University of Zurich’s Institute of Molecular Cancer Research and Daniel Giménez of CNIO developed a genomic approach that maps the three-dimensional organisation of newly replicated DNA. This analysis was complemented by microscopy experiments, while the researchers also studied partially defective cohesin variants to identify which functions of the protein are required to protect DNA. Together, these methods connected the recruitment of cohesin, its accumulation near newly replicated DNA and the reshaping of replication-associated DNA contacts with the maintenance of genome stability during stress.

Cohesin also prevented the activation of Primpol, a factor that can restart DNA replication as an emergency response. The source release describes this restart mechanism as potentially error-prone because it can introduce a high number of genetic errors. By suppressing Primpol alongside its direct effects on DNA organisation, cohesin limits two complementary routes to genome instability: harmful changes in the structure of stressed DNA and an emergency restart response that may generate errors. The experiments support these effects in the cellular system studied; they do not establish how widely the mechanism operates across every human cell type or how changes in cohesin affect disease in patients.

The project brought together research groups led by Massimo Lopes at the Institute of Molecular Cancer Research, which specialises in replication stress, and Losada at CNIO, which investigates cohesin biology. González led the conception and much of the experimental work and is the corresponding author of the Nature paper; Giménez and González are co-first authors. Proteomics expertise was provided by Javier Muñoz’s group at the Biobizkaia Health Research Institute. The publication is a peer-reviewed experimental study of cells, using genomic analysis, microscopy and functional examination of cohesin variants to investigate a cellular mechanism rather than a treatment in patients.

The discovery may have implications for precision oncology because many cancer therapies work by inducing replication stress in tumour cells, ultimately producing DNA damage that can lead to cell death. If cohesin helps such cells withstand this pressure, selectively interfering with its protective function could potentially enhance treatment effects. Giménez said understanding how cohesin protects replication forks could support combination therapies designed to disrupt the mechanism specifically in tumour cells while preserving healthy cells, with the aim of improving effectiveness and reducing toxicity. This remains a therapeutic hypothesis arising from cellular research, not a demonstrated clinical benefit or a clinical recommendation, and further testing would be required before its clinical relevance could be assessed.

Cohesin is mutated in several cancer types, including Ewing sarcoma, bladder cancer and some myeloid leukaemias. The new results provide a mechanism that researchers could examine when studying whether particular cohesin alterations influence how cancer cells respond to treatments that damage or impede DNA replication. For now, the study establishes a mechanistic connection in cells between cohesin’s reshaping of replication-fork contacts, its regulation of fork slowing and reversal, and its suppression of harmful DNA damage. By showing that a protein already central to chromosome cohesion and genome organisation also helps coordinate a cell’s response to replication stress, the work identifies a potential point of control for future studies of genome stability and cancer therapy.

Subject of Research: Cohesin-mediated protection of DNA replication forks during replication stress in cells

Article Title: A new mechanism discovered that helps cells prevent errors during DNA replication

Article References: A new mechanism discovered that helps cells prevent errors during DNA replication. Original publication (Bibliographic details unavailable.)

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Keywords: DNA replication, cohesin, replication stress, replication forks, genome stability, chromosome organisation, DNA damage, cancer biology, precision oncology, cell division, mechanism, discovered