Herpes Simplex Virus Type 1 Latency-Associated Transcripts Suppress Viral Replication and Reduce Immediate-Early Gene mRNA Levels in a Neuronal Cell Line

Abstract

During herpes simplex virus type 1 (HSV-1) latent infection in human dorsal root ganglia, limited viral transcription, which has been linked to HSV-1 reactivation ability, takes place. To study the involvement of this transcription in HSV-1 replication in neuronal cells and consequently in viral latency, we constructed stably transfected neuronal cell lines containing (i) the entire HSV-1 latency transcriptionally active DNA fragment, (ii) the same DNA sequence with deletions of the latency-associated transcript (LAT) promoters, or (iii) the DNA coding sequence of the LAT domain. Replication of HSV-1 or a LAT-negative mutant was markedly repressed in the LAT-expressing cells, a phenomenon mediated by the LATs. To study the mechanism responsible for this effect, we examined LAT influence upon expression of HSV-1 immediate-early (IE) genes ICP0, ICP4, and ICP27, by Northern blot analysis. Following infection of a LAT-expressing neuronal cell line with a LAT-negative mutant, the steady-state levels of all three IE mRNAs were reduced compared to those for control cells. Transient transfections into a neuronal cell line indicated that the LAT suppressive effect upon ICP0 mRNA was mediated directly and was not due to the LAT effect upon the ICP0 promoter. We therefore propose that the LATs may repress viral replication in neuronal cells by reducing IE gene mRNA levels and thus facilitate the establishment of HSV-1 latency in nervous tissue.

Presence of HSV‐1 Immediate Early Genes and Clonally Expanded T‐cells with a Memory Effector Phenotype in Human Trigeminal Ganglia

“…One may speculate that the neurons with low levels of LAT express higher levels of IE genes. This hypothesis is in accordance with HSV‐1 in vitro experiments that clearly demonstrated that LAT can reduce the steady‐state mRNA levels of ICP0, ICP4 and ICP27 (26).…”

The Latency-Associated Transcript Inhibits Apoptosis via Downregulation of Components of the Type I Interferon Pathway during Latent Herpes Simplex Virus 1 Ocular Infection

“…Because ICP0 is still intact in the LAT null virus dLAT2903 used in this study, the effects seen in this study are not due to lack of ICP0 expression. However, LAT may repress expression of ICP0 during latency (58), although conflicting evidence has also been reported (59). Therefore, it is possible that continued expression of ICP0 in the absence of the LAT could contribute to downregulation of JAK-1 and JAK-2.…”

The molecular basis of herpes simplex virus latency

“…It is tempting to speculate that a LAT‐negative mutant could be at a greater propensity of spontaneous reactivation within murine TG, especially given the increased levels of TK mRNA, an early transcript dependent on the presence of ICP4 for expression (Chen et al ., ). Subsequently, the production of mouse neuronal cell lines expressing various forms of the LAT locus continued to provide evidence that LAT could exert a repressive effect on IE mRNA levels (Mador et al ., ). In the same study, the authors demonstrated that productive HSV replication was reduced in cell lines encoding the LAT locus during low multiplicity infection, but not in cell lines with a deletion in the promoter driving LAT transcription.…”