Human cytomegalovirus latency and reactivation is a major source of morbidity in immune-suppressed patient populations. Lifelong latent infections are established in CD34+progenitor cells in the bone marrow, which are hallmarked by a lack of major lytic gene expression, genome replication and virus production. A number of studies have shown that inhibition of the major immediate early promoter (MIEP) – the promoter that regulates immediate early (IE) gene expression – is important for the establishment of latency and that, by extension, reactivation requires reversal of this repression of the MIEP. The identification of novel promoters (termed ip1 and ip2) downstream of the MIEP that can drive IE gene expression has led to speculation over the precise role of the MIEP in reactivation. In this study we show that IE transcripts arise from both the MIEP and ip2 promoter in the THP1 cell macrophage cell line and also CD14+monocytes stimulated with phorbol ester. In contrast, we show that in in vitro generated dendritic cells or macrophages that support HCMV reactivation IE transcripts arise predominantly from the MIEP and not the intronic promoters. Furthermore, inhibition of histone modifying enzyme activity confirms the view that the MIEP is predominantly regulated by the activity of cellular chromatin. Finally, we observe that ip2-derived IE transcription is cycloheximide-sensitive in reactivating DCs, behaviour consistent with an early gene designation. Taken together, these data argue that MIEP activity is still important for HCMV reactivation but ip2 activity could play cell-type-specific roles in reactivation.

中文翻译：

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人类巨细胞病毒主要的早期早期转录本主要来自规范化的主要的早期早期启动子，可活化祖细胞衍生的树突状细胞。

人类巨细胞病毒潜伏期和重新激活是免疫抑制患者人群发病率的主要来源。终身潜伏感染建立在骨髓的CD34 +祖细胞中，其特征是缺乏主要的裂解基因表达，基因组复制和病毒产生。大量研究表明，抑制主要的立即早期启动子（MIEP）（即调节立即早期（IE）基因表达的启动子）对于建立潜伏期很重要，并且通过扩展，重新激活需要逆转这种抑制作用。 MIEP。在MIEP下游可以驱动IE基因表达的新型启动子（称为ip1和ip2）的鉴定导致人们对MIEP在再激活中的确切作用进行了推测。在这项研究中，我们显示IE转录本既来自THP1细胞巨噬细胞系中的MIEP和ip2启动子，也来自佛波醇酯刺激的CD14 +单核细胞。相反，我们表明体外产生的支持HCMV激活的树突状细胞或巨噬细胞IE转录本主要来自MIEP，而非内含子启动子。此外，抑制组蛋白修饰酶的活性证实了MIEP主要受细胞染色质活性调节的观点。最后，我们观察到ip2衍生的IE转录在激活DC时对环己酰亚胺敏感，其行为与早期基因指定一致。综上所述，这些数据表明MIEP活性对于HCMV激活仍然很重要，但是ip2活性可能在激活中起特定于细胞类型的作用。