Cellular Control of Extrachromosomal DNA: lessons from Ku heterodimer and the hepatitis B virus.

DNA viruses depend on host machinery for transcription and DNA maintenance, making host-virus interactions critical for viral persistence mechanisms. In this work, we identified the Ku70/Ku80 heterodimer, key components of the non-homologous end joining DNA repair pathways, as restriction factors for HBV infection and other DNA viral models. Silencing Ku proteins increased viral mRNA, protein levels and the amount of episomal genomes, revealing their negative role in the regulation of viral DNA homeostasis. Transcriptomic analyses showed that Ku70 depletion alters the expression of genes involved in nucleosome assembly and cccDNA regulation. These findings deepen our understanding on host factors that are determinant for viral replication and support the development of therapeutic strategies targeting HBV persistence or biotechnological improvement of other episomal viral genomes stability as in the case of recombinant adeno-associated vectors. Additionally, they provide new insights into the cellular mechanisms that could be involved into the regulation of extrachromosomal DNA.