Epigenetic Regulation of the Latency-Associated Region of Marek's Disease Virus in Tumor-Derived T-Cell Lines and Primary Lymphoma

Abstract

Meq is the major Marek's disease virus (MDV)-encoded oncoprotein and is essential for T-cell lymphomagenesis. Meq and several noncoding RNAs, including three microRNA (MiR) clusters, are expressed from the repeats of the MDV genome during latent infection of T cells. To investigate the state of the chromatin in this and flanking regions, we carried out chromatin immunoprecipitation (ChIP) analysis of covalent histone modifications and associated bound proteins. T-cell lines and a lymphoma were compared. The chromatin around the promoters for Meq and the noncoding RNAs in both cell lines and the lymphoma were associated with H3K9 acetylation and H3K4 trimethylation, which are marks of transcriptionally active chromatin. These correlated with bound Meq-c-Jun heterodimers. The only binding site for Meq homodimers is located at the lytic origin of replication (OriLyt), next to the lytic gene pp38. This region lacked active marks and was associated with repressive histone modifications (H3K27 and H3K9 trimethylation). DNA CpG methylation was investigated using methylated DNA precipitation (MeDP). In cell lines, DNA methylation was abundant across the repeats but noticeably reduced or absent around the active promoters. In primary tumors, CpG methylation occurred less than 2 months after infection, focused within the ICP4 gene. These data suggest that nonrandom de novo DNA methylation occurs early in lymphomagenesis. In addition, the histone data indicate a role for Meq in the epigenetic regulation of the MDV genome repeats in transformed T cells and suggest that the OriLyt region and the Meq/MiR region might be separated by chromatin boundary elements, and preliminary data on CTCF binding are consistent with this.

Role of Virus-Encoded microRNAs in Avian Viral Diseases

“…A recent report has shown that the transcription of cluster 1 and 2 miRNAs is driven by a single promoter, prmiRM9M4, corresponding to the 1300-bp immediately upstream from mdv1-miR-M9, under two distinct transcriptional models during different infection phases [39]. Indeed, this promoter has been shown to be active by both active histone marks and DNA hypomethylation during MDV-1 latency [42], confirming its transcriptional activity. A p53-dependent promoter, which has no consensus core promoter element but contains at least two 60-bp tandem repeats harboring a p53-response element, has been found to drive the transcription of LAT-clustered miRNAs [43].…”

Kinetic expression analysis of the cluster mdv1-mir-M9–M4, genes meq and vIL-8 differs between the lytic and latent phases of Marek’s disease virus infection

“…No splicing events involving R-LORF4 were detected, suggesting the probable use of another promoter to generate splicing variants encoding R-LORF4 (Jarosinski et al, 2003(Jarosinski et al, , 2005. The low level of vIL-8 promoter use in MSB-1 cells is consistent with the weak transcription activity of the corresponding chromatin region in different GaHV-2 cell lines, contrasting with the strong transcription activity of the region encompassing the prmiRM9M4 promoter (Brown et al, 2012). Our data are also consistent with the large increase in vIL-8 transcript levels detected on Northern blots following treatment with n-butyrate (Parcells et al, 2001).…”

Role of Virus-Encoded microRNAs in Avian Viral Diseases

“…The promoter prmiRM9M4, corresponding to the 1300-bp immediately upstream from the first Meq-cluster miRNA mdv1-miR-M9, has been shown to drive the transcription of both Meqcluster and Mid-cluster miRNAs with two distinct transcriptional models during different infection phases [33]. Indeed, this promoter has been shown to be active during MDV-1 latency by both DNA hypomethylation and active histone marks [36], confirming its transcriptional activity. In contrast, the transcription of LATclustered miRNAs is driven by a p53-dependent promoter, which contains at least two 60-bp tandem repeats harboring a p53-response element but has no consensus core promoter element [37].…”