Dynamic Chromatin Boundaries Delineate a Latency Control Region of Epstein-Barr Virus

Abstract

. We have used the chromatin immunoprecipitation assay to examine the chromatin architecture of the LCR in different types of EBV latency programs. We have found that histone H3 K4 methylation (H3mK4) was enriched throughout a large domain that extended from internal repeat 1 (IR1) to the terminal repeat in type III latency where EBNA2 and LMP1 genes are expressed. In type I latency where EBNA2 and LMP1 genes are transcriptionally silent, the H3mK4 domain contracts and does not enter the EBNA2 or LMP1 promoters. In contrast, histone H3 K9 methylation (H3mK9), associated with silent heterochromatin, was enriched in the EBNA2 EBNA2 and LMP1 are essential for EBV-induced cellular proliferation and immortalization of primary B lymphocytes (9, 25). However, their expression can be down-regulated during latency. At least four different gene expression patterns have been characterized for various forms of EBV latency found in different tumors or host cell types (5, 6, 53). For example, EBV immortalized lymphoblastoid cell lines (LCLs) express the full panoply of viral oncogenes in a transcription program referred to as type III latency (54). In contrast, viral latency in healthy donors or in most BL-derived cell lines expresses a more restricted transcription program referred to as type I, where EBNA2 and LMP1 transcription are repressed. EBNA2 is a transcriptional regulatory protein that binds to the LMP1 and EBNA2 promoters and enforces the type III latency program (1,17,20,22,71,78). The regulation of EBNA2 expression is, therefore, critical in determining the latency program and the proliferative capacity of EBV-infected cells.The transcriptional control of EBNA2 is complex (22,41,42,69,70,75,76). During the establishment of EBV latency, EBNA2 transcription initiates at a promoter in internal repeat 1 (IR1) referred to as Wp. Once EBNA2 protein levels reach a threshold, the protein activates a second promoter upstream of Wp, referred to as Cp. EBNA2 stimulates the Cp and LMP1 promoters through a cellular DNA binding protein called CSL (CBF1 or RBP-Jk) (20,22,35,77). CSL can also interact with cellular coactivators, like intracellular Notch, and corepressors, like CIR, that may regulate EBV latency transcripts in the absence of EBNA2 (11,23,24,77).Epigenetic events, like DNA methylation and histone modifications, constitute another level of regulatory mechanisms for EBNA2 and LMP1 expression (3,15,16,34,39,40,51,68,70). DNA methylation of proximal promoter elements correlates with the transcription repression of EBNA2 and LMP1 transcription in type I latency (3,16,58,66). Inhibitors of DNA methylation relieve this repression and induce a switch from type I to type III latency patterns of EBV gene expression (3,26). Histone modifications are also known to be important for EBNA2 regulation since transcription activation correlates with promoter-specific histone hyperacetylation and histone acetyltransferase association (2, 72). Moreover, the CSL corepressors CIR and EBNA3A/C are known to associate with

S-adenosylmethionine inhibits lipopolysaccharide-induced gene expression via modulation of histone methylation

“…MTA has been shown to block methylation of H3K4 in a number of systems. [23][24][25]27 In contrast to MTA, which is a very stable molecule, its precursor SAMe is highly unstable and can be converted to MTA spontaneously and also via the polyamine pathway 27,28 ; this suggests that the effect of exogenous SAMe may be mediated by MTA. It is also known that MTA inhibits SAH hydrolase, 32 the enzyme responsible for metabolizing SAH, and SAH itself is a strong inhibitor of almost all SAMe-dependent methyltransferases.…”

“…Although MTA has been shown to inhibit H3K4 methylation in various cell types, [23][24][25] whether it exerts a similar effect in vivo was unknown. Here we demonstrate that MTA completely recapitulated its effects in RAW cells in vivo by blocking LPS-induced hepatic expression of proinflammatory mediators and binding of trimethyl-H3K4 to these promoters.…”

“…Although MTA has been shown to inhibit H3K4 methylation, [23][24][25] none of the work investigated whether this could happen in vivo. We had previously shown that MTA could block LPS-induced lethality in mice.…”

“…23,24 In several studies, its ability to decrease the H3K4 methylation was correlated with attenuation of gene expression. 25,26 In contrast to MTA, which is a very stable molecule, its precursor SAMe is highly unstable and can be converted to MTA spontaneously and also via the polyamine pathway, 27,28 and this suggests that the effect of exogenous SAMe may be mediated by MTA.…”

Latency type-specific distribution of epigenetic marks at the alternative promoters Cp and Qp of Epstein–Barr virus

“…1f). However, a significant enrichment of H3K4me2 at Cp in the Mutu-I cells was not observed in another laboratory (Chau & Lieberman, 2004;Day et al, 2007). This discrepancy may be due to the different passage history of the cells used.…”