Methylation-Dependent Binding of the Epstein-Barr Virus BZLF1 Protein to Viral Promoters

The switch between latent and lytic Epstein-Barr virus (EBV) infection is mediated by the viral immediate-early (IE) protein, BZLF1 (Z). Z, a homologue of c-jun that binds to AP1-like motifs (ZREs), induces expression of the BRLF1 (R) and BRRF1 (Na) viral proteins, which cooperatively activate transcription of the Z promoter and thereby establish a positive autoregulatory loop. A unique feature of Z is its ability to preferentially bind to, and activate, the methylated form of the BRLF1 promoter (Rp). To date, however, Rp is the only EBV promoter known to be regulated in this unusual manner. We now demonstrate that the promoter driving transcription of the early BRRF1 gene (Nap) has two CpG-containing ZREs (ACGCTCA and TCGCCCG) that are only bound by Z in the methylated state. Both Nap ZREs are highly methylated in cells with latent EBV infection. Z efficiently activates the methylated, but not unmethylated, form of Nap in reporter gene assays, and both ZREs are required. Z serine residue 186, which was previously shown to be required for Z binding to methylated ZREs in Rp, but not for Z binding to the AP1 site, is required for Z binding to methylated Nap ZREs. The Z(S186A) mutant cannot activate methylated Nap in reporter gene assays and does not induce Na expression in cells with latent EBV infection. Molecular modeling studies of Z bound to the methylated Nap ZREs help to explain why methylation is required for Z binding, and the role of the Z Ser186 residue. Methylation-dependent Z binding to critical viral promoters may enhance lytic reactivation in latently infected cells, where the viral genome is heavily methylated. Conversely, since the incoming viral genome is initially unmethylated, methylation-dependent Z activation may also help the virus to establish latency following infection

Sequencing of DC-SIGN promoter indicates an association between promoter variation and risk of nasopharyngeal carcinoma in cantonese

<p>Abstract</p> <p>Background</p> <p>The dendritic cell-specific intercellular adhesion molecule 3 grabbing non-integrin (<it>DC-SIGN</it>) is an important pathogen recognition receptor of the innate immune system. <it>DC-SIGN </it>promoter variants play important role in the susceptibility to various infectious diseases. Nasopharyngeal carcinoma (NPC) is a malignancy that is common in southern China and whether <it>DC-SIGN </it>promoter variants have effects on susceptibility to NPC is still unknown. The aim of this study is to ascertain the potential involvement of <it>DC-SIGN </it>promoter single nucleotide polymorphisms (SNPs) in NPC susceptibility.</p> <p>Methods</p> <p>We conducted a case control study based on Cantonese population including 444 NPC patients and 464 controls matched on age and sex. The 1041 bp of <it>DC-SIGN </it>promoter region was directly sequenced for all samples. Sequence alignment and SNP search were inspected using DNAStar analysis programs and haplotype frequencies were estimated in Haploview V 4.0. The associations between the SNPs and the risk of NPC were analyzed using chi-square test and non-conditional logistic regression analysis with SPSS 13.0 software.</p> <p>Results</p> <p>A total of six variants were observed in the <it>DC-SIGN </it>promoter region and <it>DC-SIGN </it>-139 GG and -939 AA were significantly associated with NPC risk with adjusted Odds Ratios (ORs) of 2.10 (95% confidence interval [CI] = 1.23-3.59; <it>P </it>= 0.006) and 2.52 (1.29-4.93; <it>P </it>= 0.007) respectively and subjects carrying the risk allele <it>DC-SIGN </it>-871 G had 1.47-fold (95% CI = 1.14-1.90) increased risks of developing NPC (<it>P </it>= 0.003). Haplotype analysis revealed that h1 'AAAG' was significantly associated with protection against NPC (OR = 0.69; <it>P </it>= 0.0002) and the association was still significant when using 1000 permutation test runs (<it>P </it>= 0.001).</p> <p>Conclusions</p> <p>Our study indicated that <it>DC-SIGN </it>promoter variants appear to be involved in the susceptibility to NPC and the detailed mechanism of this effect need further studies.</p