Role of chromatin and the DNA damage response in transcription-associated genome instability

Resumen del trabajo presentado a la Conferencia Dynamic DNA Structure in Biology, celebrada en Saxtons River, Vermont (US) del 10 al 15 de julio de 2016.Coordination of DNA replication with DNA-damage sensing, repair and cell cycle progression ensures with high probability genome integrity during cell divisions, thus preventing mutations and DNA rearrangements. Such events may be harmful for the cell and the organism, and are usually associated with pathological disorders. One important type of genome instability is that associated with transcription. R-loops are transcriptional by-products that can be formed naturally as key intermediates in specific cellular processes, but they are also a major source of genome instability. Specific RNA processing factors have been shown to play a role in preventing R-loop and transcription-associated genome instability. The first one identified with this role was the yeast THO complex, a conserved factor working at the interface between transcription and RNA export. However, other proteins directly or indirectly related with a function in RNA processing, such as human SRSF2 and AQR or yeast Trf4 or Npl3 among others, also prevent RNA-DNA hybrids. The working hypothesis suggests that in cells defective in such factors a suboptimal nascent mRNA-protein particle is formed, enhancing the probability that the nascent RNA interacts with the DNA. However, it is unclear how this mechanism occurs. To explore further the mechanism by which RNA processing factors control genome integrity, we have screened a human library for proteins that physically interact with components of the human THO complex using the yeast two-hybrid system. Further confirmation of this interaction via co-immunoprecipitation and Proximity Ligation Assay, has permitted us to identify a chromatin remodeling complex. Functional analyses of this interaction and of the effect of depleting cells from these factors has permitted us to propose a new model to explain how cells prevent co-transcriptional RNA-DNA hybrid formation and transcription-associated genome instability. Our work open news perspectives to understand the different mechanisms used by the cells to prevent the accumulation of DNA structures that compromises genome integrity.Peer Reviewe