Role of PML-Nuclear Bodies in Human Herpesvirus 6A and 6B Genome Integration.

Abstract

Human herpesviruses 6A and 6B (HHV-6A/B) are two betaherpesviruses that readily integrate their genomes into the telomeres of human chromosomes. To date, the cellular or viral proteins that facilitate HHV-6A/B integration remain elusive. In the present study, we demonstrate that the immediate early protein 1 (IE1) of HHV-6A/B colocalizes with telomeres during infection. Moreover, IE1 associates with PML-NBs, a nuclear complex that regulates multiples cellular mechanism including DNA repair and antiviral responses. Furthermore, we could demonstrate that IE1 targets all PML isoforms and that both proteins colocalize at telomeres. To determine the role of PML in HHV-6A/B integration, we generated PML knockout cell lines using CRISPR/Cas9. Intriguingly, in the absence of PML, the IE1 protein could still localize to telomeres albeit less frequently. More importantly, HHV-6A/B integration was impaired in the absence of PML, indicating that it plays a role in the integration process. Taken together, we identified the first cellular protein that aids in the integration of HHV-6A/B and shed light on this targeted integration mechanism.\n\nAuthor summaryHuman herpesviruses type 6A and 6B are relatively common viruses whose infections can be life threatening in patients with a compromised immune system. A rather unique feature of these viruses is their ability to integrate their genome in human chromosomes. Integration takes place is a specialized region of the chromosomes known as telomeres, a region that controls cellular lifespan. To date, the mechanisms leading to HHV-6A and HHV-6B integration remain elusive. Our laboratory has identified that the IE1 protein of HHV-6A and HHV-6B target the telomeres. Moreover, we have shown that IE1 associates with a cellular protein, PML, that is responsible for the regulation of important cellular mechanisms such as the life span of cells and DNA repair. Hence, we studied the role of PML in HHV-6 integration. Our study demonstrates that in absence of PML, the HHV-6A and HHV-6B integrate 50-70% less frequently. Thus, our study unveils the first cellular protein involved in HHV-6A and HHV-6 chromosomal integration.