The HSV-1 Latency-Associated Transcript Functions to Repress Latent Phase Lytic Gene Expression and Suppress Virus Reactivation from Latently Infected Neurons.

Michael P Nicoll,João T Proença,Laura E R Harman,Heather M Coleman,Maitreyi Shivkumar,William Hann,Viv Connor,Stacey Efstathiou

doi:10.1371/journal.ppat.1005539

Abstract

Herpes simplex virus 1 (HSV-1) establishes life-long latent infection within sensory neurons, during which viral lytic gene expression is silenced. The only highly expressed viral gene product during latent infection is the latency-associated transcript (LAT), a non-protein coding RNA that has been strongly implicated in the epigenetic regulation of HSV-1 gene expression. We have investigated LAT-mediated control of latent gene expression using chromatin immunoprecipitation analyses and LAT-negative viruses engineered to express firefly luciferase or β-galactosidase from a heterologous lytic promoter. Whilst we were unable to determine a significant effect of LAT expression upon heterochromatin enrichment on latent HSV-1 genomes, we show that reporter gene expression from latent HSV-1 genomes occurs at a greater frequency in the absence of LAT. Furthermore, using luciferase reporter viruses we have observed that HSV-1 gene expression decreases during long-term latent infection, with a most marked effect during LAT-negative virus infection. Finally, using a fluorescent mouse model of infection to isolate and culture single latently infected neurons, we also show that reactivation occurs at a greater frequency from cultures harbouring LAT-negative HSV-1. Together, our data suggest that the HSV-1 LAT RNA represses HSV-1 gene expression in small populations of neurons within the mouse TG, a phenomenon that directly impacts upon the frequency of reactivation and the maintenance of the transcriptionally active latent reservoir.

Highlights

Herpes simplex viruses 1 (HSV-1) and 2 (HSV-2) are ancient human pathogens that are most commonly associated with sub-clinical and mild infections but can occasionally cause severe life threatening disease [1]
Whilst we were unable to determine a significant effect of latency-associated transcript (LAT) expression upon heterochromatin enrichment on latent HSV-1 genomes, we show that reporter gene expression from latent HSV-1 genomes occurs at a greater frequency in the absence of LAT
Herpes simplex virus 1 (HSV-1) persistently infects an individual for their entire life. This persistent—or latent—virus is maintained as silenced DNA within the nuclei of sensory neurons, from which only the virus latency-associated transcript

Summary

Introduction

Herpes simplex viruses 1 (HSV-1) and 2 (HSV-2) are ancient human pathogens that are most commonly associated with sub-clinical and mild infections but can occasionally cause severe life threatening disease [1]. HSV-1 is most commonly associated with infection of the oral mucosa, and following productive primary infection at this site the virus is able to access the sensory neurons of the trigeminal ganglia (TG). Within these cells, HSV is able to establish a latent infection, characterised by a global reduction of lytic gene expression and an absence of infectious virus production. The LAT intron has been strongly implicated in the global control of latent HSV gene expression in a number of studies describing the post-translational modification (PTM) of histones associated with viral promoters [7,8,9,10,11]

Methods

Results

Conclusion