Dissecting Herpes Simplex Virus 1-Induced Host Shutoff at the RNA Level

Abstract

Herpes simplex virus 1 (HSV-1) induces a profound host shutoff during lytic infection. The virion host shutoff (vhs) protein plays a key role in this process by efficiently cleaving host and viral mRNAs. Furthermore, the onset of viral DNA replication is accompanied by a rapid decline in host transcriptional activity. To dissect relative contributions of both mechanisms and elucidate gene-specific host transcriptional responses throughout the first 8 h of lytic HSV-1 infection, we used transcriptome sequencing of total, newly transcribed (4sU-labeled) and chromatin-associated RNA in wild-type (WT) and Δvhs mutant infection of primary human fibroblasts. Following virus entry, vhs activity rapidly plateaued at an elimination rate of around 30% of cellular mRNAs per hour until 8 h postinfection (p.i.). In parallel, host transcriptional activity dropped to 10 to 20%. While the combined effects of both phenomena dominated infection-induced changes in total RNA, extensive gene-specific transcriptional regulation was observable in chromatin-associated RNA and was surprisingly concordant between WT and Δvhs infections. Both induced strong transcriptional upregulation of a small subset of genes that were poorly expressed prior to infection but already primed by H3K4me3 histone marks at their promoters. Most interestingly, analysis of chromatin-associated RNA revealed vhs-nuclease-activity-dependent transcriptional downregulation of at least 150 cellular genes, in particular of many integrin adhesome and extracellular matrix components. This was accompanied by a vhs-dependent reduction in protein levels by 8 h p.i. for many of these genes. In summary, our study provides a comprehensive picture of the molecular mechanisms that govern cellular RNA metabolism during the first 8 h of lytic HSV-1 infection.IMPORTANCE The HSV-1 virion host shutoff (vhs) protein efficiently cleaves both host and viral mRNAs in a translation-dependent manner. In this study, we model and quantify changes in vhs activity, as well as virus-induced global loss of host transcriptional activity, during productive HSV-1 infection. In general, HSV-1-induced alterations in total RNA levels were dominated by these two global effects. In contrast, chromatin-associated RNA depicted gene-specific transcriptional changes. This revealed highly concordant transcriptional changes in WT and Δvhs infections, confirmed DUX4 as a key transcriptional regulator in HSV-1 infection, and identified vhs-dependent transcriptional downregulation of the integrin adhesome and extracellular matrix components. The latter explained seemingly gene-specific effects previously attributed to vhs-mediated mRNA degradation and resulted in a concordant loss in protein levels by 8 h p.i. for many of the respective genes.

Keywords: 4sU-seq; RNA degradation; RNA-seq; chromatin-associated RNA; herpes simplex virus 1; proteomics; transcriptional regulation; virion host shutoff protein.