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

Abstract

18 Human herpesviruses 6A and 6B (HHV-6A/B) are two betaherpesviruses that readily 19 integrate their genomes into the telomeres of human chromosomes. To date, the cellular 20 or viral proteins that facilitate HHV-6A/B integration remain elusive. In the present study, 21 we demonstrate that the immediate early protein 1 (IE1) of HHV-6A/B colocalizes with 22 telomeres during infection. Moreover, IE1 associates with PML-NBs, a nuclear complex 23 that regulates multiples cellular mechanism including DNA repair and antiviral responses.24 Furthermore, we could demonstrate that IE1 targets all PML isoforms and that both 25 proteins colocalize at telomeres. To determine the role of PML in HHV-6A/B integration, 26 we generated PML knockout cell lines using CRISPR/Cas9. Intriguingly, in the absence of 27 PML, the IE1 protein could still localize to telomeres albeit less frequently. More 28 importantly, HHV-6A/B integration was impaired in the absence of PML, indicating that 29 it plays a role in the integration process. Taken together, we identified the first cellular 30 protein that aids in the integration of HHV-6A/B and shed light on this targeted integration 31 mechanism. 32 33 Author summary 34 Human herpesviruses type 6A and 6B are relatively common viruses whose infections can 35 be life threatening in patients with a compromised immune system. A rather unique feature 36 of these viruses is their ability to integrate their genome in human chromosomes.37 Integration takes place is a specialized region of the chromosomes known as telomeres, a 38 region that controls cellular lifespan. To date, the mechanisms leading to HHV-6A and 39 HHV-6B integration remain elusive. Our laboratory has identified that the IE1 protein of 3 40 HHV-6A and HHV-6B target the telomeres. Moreover, we have shown that IE1 associates 41 with a cellular protein, PML, that is responsible for the regulation of important cellular 42 mechanisms such as the life span of cells and DNA repair. Hence, we studied the role of 43 PML in HHV-6 integration. Our study demonstrates that in absence of PML, the HHV-6A 44 and HHV-6B integrate 50-70% less frequently. Thus, our study unveils the first cellular 45 protein involved in HHV-6A and HHV-6 chromosomal integration. 46 47 4 49 Human herpesviruses type 6A and 6B (HHV-6A/B) are members of the betaherpesvirinae 50 that were isolated in the 1980's. In 2013, the International Committee on Taxonomy of 51 Viruses recognized HHV-6A and HHV-6B as distinct viral species (1). HHV-6B is known 52 as the etiologic agent of exanthem subitum, a childhood disease whose symptoms include, 53 fever, occasional skin rash and respiratory distress (2). HHV-6A is much less characterized 54 than HHV-6B. Considering that many HHV-6A/B proteins share 90-95% homology, the

Impact of Host Telomere Length on HHV-6 Integration

“…HHV-6A/B encode a putative integrase termed U94 that was considered as a likely candidate for HHV-6A/B integration based on its biological properties; however, U94 was found to be dispensable for integration, at least in vitro [47,48]. We and others have also looked at other factors, both viral and cellular, without establishing a key set of proteins responsible for the integration mechanism, suggesting that HHV-6A/B likely exploit several different pathways to achieve integration [40,46,49,50]. Thus, any information regarding the HHV-6-telomere interaction is vital to provide a better understanding of this process and its biological consequences.…”