Human Herpesvirus 6B Induces Hypomethylation on Chromosome 17p13.3, Correlating with Increased Gene Expression and Virus Integration

Abstract

Human herpesvirus 6B (HHV-6B) is a neurotropic betaherpesvirus that achieves latency by integrating its genome into host cell chromosomes. Several viruses can induce epigenetic modifications in their host cells, but no study has investigated the epigenetic modifications induced by HHV-6B. This study analyzed methylation with an Illumina 450K array, comparing HHV-6B-infected and uninfected Molt-3 T cells 3 days postinfection. Bisulfite pyrosequencing was used to validate the Illumina results and to investigate methylation over time Expression of genes was investigated using quantitative PCR (qPCR), and virus integration was investigated with PCR. A total of 406 CpG sites showed a significant HHV-6B-induced change in methylation Remarkably, 86% (351/406) of these CpGs were located <1 Mb from chromosomal ends and were all hypomethylated in virus-infected cells. This was most evident at chromosome 17p13.3, where HHV-6B had induced CpG hypomethylation after 2 days of infection, possibly through TET2, which was found to be upregulated by the virus. In addition, virus-induced cytosine hydroxymethylation was observed. Genes located in the hypomethylated region at 17p13.3 showed significantly upregulated expression in HHV-6B-infected cells. A temporal experiment revealed HHV-6B integration in Molt-3 cell DNA 3 days after infection. The telomere at 17p has repeatedly been described as an integration site for HHV-6B, and we show for the first time that HHV-6B induces hypomethylation in this region during acute infection, which may play a role in the integration process, possibly by making the DNA more accessible. The ability to establish latency in the host is a hallmark of herpesviruses, but the mechanisms differ. Human herpesvirus 6B (HHV-6B) is known to establish latency through integration of its genome into the telomeric regions of host cells, with the ability to reactivate. Our study is the first to show that HHV-6B specifically induces hypomethylated regions close to the telomeres and that integrating viruses may use the host methylation machinery to facilitate their integration process. The results from this study contribute to knowledge of HHV-6B biology and virus-host interaction. This in turn will lead to further progress in our understanding of the underlying mechanisms by which HHV-6B contributes to pathological processes and may have important implications in both disease prevention and treatment.

MCPyV Large T Antigen-Induced Atonal Homolog 1 Is a Lineage-Dependency Oncogene in Merkel Cell Carcinoma

“…herpesvirus 6B infection leads to hypomethylation in telomere regions, which serve as human herpesvirus 6B integration sites as they are more accessible by hypomethylation (Engdahl et al, 2017). In MCPyV þ MCC cells, LT of MCPyV might induce demethylation of the ATOH1 and miR-375 promoters, resulting in increased transcription of both ATOH1 and miR-375.…”

ALV Integration-Associated Hypomethylation at the TERT Promoter Locus

“…Concurrently, investigations into the effects of human integrating viruses on methylation in tumors were performed. Human herpesvirus 6B has been shown to integrate into subtelomeric regions and induce hypomethylation in these regions [ 53 ]. Notably, the human TERT gene is located in the subtelomeric region of chromosome 5.…”

Outcomes of hematopoietic cell transplantation using donors or recipients with inherited chromosomally integrated HHV-6

“…HHV-6 integration into human chromosomes may drive human disease via mechanisms such as chromosomal instability or epigenetic effects. 24 Telomeres carrying integrated HHV-6 may be unstable, leading to deletions, 25 and telomere length has important implications for chromosomal stability and cell viability. 26 Indeed, disruption in telomeres is associated with conditions ranging from pulmonary to hematologic diseases.…”