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Activation of the herpes simplex virus immediate-early gene promoters by neuronally expressed POU family transcription factors.

ABSTRACT: Herpes simplex virus immediate-early (IE) promoters contain the TAATGARAT motif which acts as a target site for the cellular POU family transcription factors Oct-1 and Oct-2. Here we show that other members of the POU family that are expressed in sensory neurons can also affect IE promoter activity. In particular, two members of the Brn-3 family of POU proteins Brn-3a and Brn-3c can activate the IE-1 and IE-3 promoters when co-transfected into fibroblasts and neuronal cells whereas a third member Brn-3b represses IE promoter activity. In contrast, Brn-3 proteins cannot overcome the inhibitory effect of neuronal Oct-2 on IE promoter activity in co-transfections nor do they prevent transactivation of the IE promoters by the Oct-1-Vmw65 complex. The potential regulation of the IE promoters by several different neuronally expressed POU proteins during the initiation, maintenance and re-activation of latent infection in sensory neurons is discussed.

SUBMITTER: Lillycrop KA

PROVIDER: S-EPMC1136687 | biostudies-other | 1995 Apr

REPOSITORIES: biostudies-other

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Project description:Herpes simplex virus 1 (HSV-1) utilizes cellular RNA polymerase II (Pol) to transcribe its genes in one of two phases. In the latent phase, viral transcription is highly restricted, but during the productive lytic phase, more than 80 genes are expressed in a temporally coordinated cascade. In this study, we used Precision nuclear Run On followed by deep Sequencing (PRO-Seq) to characterize early viral transcriptional events using HSV-1 immediate early (IE) gene mutants, corresponding genetically repaired viruses, and wild-type virus. Unexpectedly, in the absence of the IE genes ICP4, ICP22, and ICP0 at 1.5 hours postinfection (hpi), we observed high levels of aberrant transcriptional activity across the mutant viral genomes but substantially less on either wild-type or the congenic repaired virus genomes. This feature was particularly prominent in the absence of ICP4 expression. Cycloheximide treatment during infection with both the ICP4 and ICP22 mutants and their respective genetic repairs did not alter the relative distribution of Pol activity, but it increased overall activity across both viral genomes, indicating that both virion components and at least some de novo protein synthesis were required for full repression. Overall, these data reveal that prior to their role in transcriptional activation, IE gene products and virion components first repress transcription and that the HSV-1 lytic transcriptional cascade is mediated through subsequent derepression steps. IMPORTANCE HSV-1 transcription during productive replication is believed to comprise a series of activation steps leading to a specific sequence of gene expression. Here, we show that virion components and IE gene products ICP0, ICP4, and ICP22 first repress viral gene transcription to various degrees before subsequently activating specific gene subsets. It follows that the entire HSV transcriptional program involves a series of steps to sequentially reverse this repression. This previously uncharacterized repressive activity of IE genes very early in infection may represent an important checkpoint allowing HSV-1 to orchestrate either the robust lytic transcriptional cascade or the more restricted transcriptional program during latency.

Project description:Herpes simplex virus 1 (HSV-1) transcription is tightly regulated in a temporal cascade, utilizing cellular RNA polymerase. We previously observed that infection with HSV-1 mutants lacking immediate early (IE) genes α0, α4, and α22 exhibited high levels of aberrant transcription across the viral genome at just 1.5 hpi. The strongest effect occurred in the absence of full-length ICP4 which is both an essential transcriptional activator and repressor. The goal of the current study was to define the mechanism of ICP4-mediated early transcriptional repression on the viral genome. Using PRO-Cap, PRO-Seq, GRO-Seq, and Nanopore direct RNA sequencing to analyze viral transcription, we found that initiation was elevated at viral promoters of all temporal classes in the absence of ICP4. Despite higher levels of initiation, transcription of non-IE genes was stalled within gene bodies and did not lead to production of mature mRNA. Thus, ICP4-independent mechanisms limit expression of viral genes that initiate prematurely. GRO-seq data also indicated rapid release from promoter proximal pausing, and rapid progression along HSV IE gene bodies, with termination as an important rate-limiting regulatory step. These findings highlight multiple mechanisms that HSV-1 employs to regulate early transcription and shows that ICP4's repressive role is to restrict initiation, thereby ensuring correct progression of the temporal cascade. IMPORTANCE Infection with herpes simplex virus 1 (HSV-1) leads to lifelong infection due to the virus's remarkable ability to control transcription of its own genome, resulting in two transcriptional programs: lytic (highly active) and latent (restricted). The lytic program requires immediate early (IE) proteins to first repress transcription of late viral genes, which then undergo sequential de-repression, leading to a specific sequence of gene expression. Here, we show that the IE ICP4 functions to regulate the cascade by limiting RNA polymerase initiation at immediate early times. However, late viral genes that initiate too early in the absence of ICP4 do not yield mRNA as transcription stalls within gene bodies. It follows that other regulatory steps intercede to prevent elongation of genes at the incorrect time, demonstrating the precise control HSV-1 exerts over its own transcription.

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Activation of the herpes simplex virus immediate-early gene promoters by neuronally expressed POU family transcription factors.

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