Herpes simplex virus (HSV) replicates in peripheral tissues and forms latent infections in neurons ofthe peripheral nervous system. It can be reactivated from latency by various stimuli to cause recurrent disease. During lytic infection in tissue culture cells, there is a well-described temporal pattern of (i) immediate-early, (ii) early, and (iii) late gene expression. However, latency is characterized by little if any expression of genes of the lytic cycle of infection. During reactivation, the pattern of gene expression is presumed to be similar to that during the lytic cycle in tissue culture, though recent work of W. P. Halford et al. (J. Virol. 70:5051-5060, 1996) and P. F. Nichol et al. (J. Virol. 70:5476-5486, 1996) suggests that it is modified in neuronal cell cultures. We have used the mouse trigeminal ganglion explant model and reverse transcription-PCR to determine the pattern of viral and cellular gene expression during reactivation. Surprisingly, the pattern of viral gene expression during lytic infection of cell cultures is not seen during reactivation. During reactivation, early viral transcripts were detected before immediate-early transcripts. The possibility that a cellular factor upregulates early genes during the initial reactivation stimulus is discussed.

No abstract

The detailed mechanism which governs the choice between herpes simplex virus (HSV) latency and reactivation remains to be elucidated. It is probable that altered expression of cellular factors in sensory neurons leads to induction of HSV gene expression resulting in reactivation. As an approach to identify novel cellular genes which are activated or repressed by stimuli that reactivate HSV from latency and hence may play a role in viral reactivation, RNA from explanted trigeminal ganglia (TG) was analyzed by differential display reverse transcription-PCR (DDRT-PCR). Nearly 50 cDNAs whose mRNA level was modified by the stress of explantation were isolated and sequenced. We present a listing of a spectrum of altered RNAs, including both known and unknown sequences. Five of those differentially displayed transcripts were identified as interferon-related murine TIS7 mRNA. These results were confirmed in both infected and uninfected ganglia by quantitative RNase protection assay and immunostaining. Alpha and beta interferons and interferon regulatory factor-1 (IRF-1) were also induced by explantation. In addition, we have identified sequences that correspond to IRF-1 consensus binding sites in both HSV type 1 origins of replication. Our findings suggest that physiological pathways that include these cellular factors may be involved in modulating HSV reactivation.

The earliest events within the peripheral mammalian nervous system that cause herpes simplex virus type 1 (HSV-1) to reactivate from latency are unknown but are highly likely to include altered regulation of cellular transcription factors. Using gene array analysis, we have examined the changes that occur in cellular mRNA levels in mouse trigeminal ganglia following explantation, a stimulus that results in HSV-1 reactivation from latency. We have detected both increased and decreased expression levels of particular cellular transcripts, which include RNAs encoding neuronal factors, transcription factors, and factors involved in the cell cycle. Among the transcription factors that are upregulated is Bcl-3, a coactivator for NFB. We have confirmed these increases in Bcl-3 transcription levels using reverse transcription-PCR and S1 nuclease protection assays. In addition, we have shown Bcl-3 upregulation at the protein level. Importantly, Bcl-3 RNA levels were found to increase specifically in neuronal cells within the trigeminal ganglia. We discuss a potential role for this factor in upregulating ICP0 transcription, which is an important viral event for initiation of HSV-1 reactivation.Following primary infection, herpes simplex virus (HSV) establishes a latent state within neurons of sensory ganglia. During latency, episomal HSV genomes are generally inactive, with viral transcription mainly from the latency-associated transcripts, although low levels of certain immediate-early (IE) and early (E) transcripts have been detected (18, 37). The virus can undergo periodic reactivation leading to recurrent disease in response to certain stimuli, such as stress, tissue damage, or the presence of immune system modulators, neurotransmitters, hormones, or growth factors (19,20,55). Similar to primary infection, the reactivation process includes several steps leading to the release of complete viral particles, including transcription of viral (IE and E) genes and replication of the viral DNA.The temporal pattern of HSV gene expression during primary infection in tissue culture is well documented (28, 29). The initial event is IE transcription, mediated by the cellular transcription factors Oct-1 and HCF functioning in a complex with the viral transactivator VP16 (a virion protein) through binding to TAATGARAT upstream sequences (52, 61). The IE gene products are transcription factors that promote E and late (L) gene expression. It has been shown that this cascade of viral gene expression is not seen during the reactivation process. Rather, IE and E transcripts are both detected at the earliest times of reactivation and the onset of their expression is simultaneous (63). Since VP16 is not expressed in latently infected neurons and moreover is not required for reactivation from ganglionic explants (60), it is likely that viral transcription is initiated during reactivation by endogenous factors expressed from these tissues. Candidates for this function are cellular factors that regulate the HSV type 1 (HSV-1) genome, either b...