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

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 in vitro 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 in vitro 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. IMPORTANCE 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.