Inhibition of herpes simplex virus replication by methyl daunosamine

Expression of herpes simplex virus type 1 (HSV-1) latency-associated transcripts and transcripts affected by the deletion in avirulent mutant HFEM: evidence for a new class of HSV-1 genes

During latent herpes simplex virus type 1 (HSV-1) infection in the trigeminal ganglia of mice, three virus-specific transcripts, 2.0, 1.5, and 1.45 kilobases (kb), are detectable by Northern (RNA) blot analysis, but only the 2.0-kb transcript can be detected in HSV-1-infected tissue culture cells (J.G. Spivack and N. W. Fraser, J. Virol. 61:3842-3847, 1987). Since these latency-associated genes map to a diploid region of the genome, transcription from the deletion mutant HFEM, which contains only one complete copy of these genes, was investigated to determine the effect of gene dosage. The 4.1-kb HFEM deletion is located between the alpha genes ICP0 and ICP27. ICP0 mRNA and the 2.0-kb latency-associated transcript were present at normal levels during HFEM infection, but ICP27 mRNA and 0.9- and 1.1-kb transcripts that map near the deletion were not readily detectable. The levels of expression of one or more of these genes might be an important determinant of HSV-1 virulence in animal hosts. ICP27 mRNA accumulated when protein synthesis was inhibited before HFEM infection, implying that the deletion may affect ICP27 regulatory rather than coding elements. Expression of the 2.0-kb latency-associated transcript was characterized in infected CV-1 cells with metabolic inhibitors and strand-specific probes. On the basis of metabolic inhibitor studies, the gene encoding the 2.0-kb latency-associated transcript is not an alpha gene. During HSV-1 replication in infected tissue culture cells, the beta and gamma genes require the prior expression of alpha gene products. However, the latency-associated RNAs are expressed in the absence of detectable levels of alpha transcripts in latently infected mice. Thus, this latency-associated gene family appear to be regulated quite differently than alpha, beta, or gamma genes. For these reasons, and because the latency-associated genes may perform latent rather than replicative functions, we propose that they should be considered members of a new HSV-1 gene class, the lambda genes.

Expression of herpes simplex virus type 1 latency-associated transcripts in the trigeminal ganglia of mice during acute infection and reactivation of latent infection

Herpes simplex virus type 1 (HSV-1) establishes a latent infection in the trigeminal ganglia of mice infected via the eye. In these ganglia three viral transcripts, of 2.0, 1.5, and 1.45 kilobases (kb), which are at least partially colinear, have been identified by Northern (RNA) blot analysis. These RNAs partially overlap ICPO, but are transcribed in the opposite direction (J. G. Spivack and N. W. Fraser, J. Virol. 61:3841-3847, 1987). The accumulation of these latency-associated transcripts, as well as other viral RNAs, was studied during an acute infection and the reactivation of a latent HSV-1 infection in mice. The 2.0-kb latency-associated transcript was detected in trigeminal ganglia of mice as early as 4 days postinfection, and the 1.45- and 1.5-kb RNA doublet was detected at 14 days postinfection. The levels of these latency-associated transcripts increased steadily over a 60-day period. In contrast, other HSV-1 transcripts were detected at 2 to 3 days postinfection, reached a peak on day 4, and rapidly declined below detectable levels by day 7. The data indicate that the temporal expression of the latency-associated genes during acute infection in the trigeminal ganglia of mice is different from the temporal expression of genes involved in HSV-1 replication. During the reactivation of latent HSV-1 from explanted trigeminal ganglia, the latency-associated RNAs decreased about twofold, but were present at significant levels even after HSV-1 DNA increased and infectious virus was recovered. The decrease of the latency-associated transcripts occurred when reactivation was blocked by phosphonoacetic acid or novobiocin, which suggests that this decrease may be an early event in the entry of latent HSV-1 into the viral replication cycle.

Detection of herpes simplex virus type 1 transcripts during latent infection in mice

A latent infection can be established in the trigeminal ganglia of mice after corneal inoculation of herpes simplex virus type 1 (HSV-1). With a virion DNA probe, three transcripts (2.0, 1.5, and 1.45 kilobases [kb]) were detected by Northern blot (RNA blot) analysis of RNAs isolated from the ganglia of latently infected mice. All three transcripts hybridized to a nick-translated HSV-1 DNA probe from BamHI restriction fragment B (strain F). These RNAs were mapped with subfragments of BamHI-B and with strand-specific probes. They are at least partially colinear with each other, map to a 3.0-kb PstI-MluI subfragment of BamHI-B, and are transcribed from left to right. The latent HSV-1 RNAs partially overlap the 3' end of ICP0 mRNA but are transcribed in the opposite direction. The latent RNAs were not as extensively poly(A)+ as actin mRNA. The HSV-1 transcripts detected in latently infected trigeminal ganglia did not correspond with any that have been previously identified in permissively infected cells in tissue culture. However, the 2.0-kb HSV-1 RNA present during latency was detectable at reduced levels in the trigeminal ganglia of acutely infected mice and in infected tissue culture cells. The data indicate that the pattern of viral gene expression during HSV-1 latency in the trigeminal ganglia of mice does not represent restriction of the genes actively transcribed during the lytic replication cycle in tissue culture.

New antiviral compounds

Several potent and selective antiviral agents against herpes virus infections have been developed. However, the majority of compounds against other viral diseases has not yet reached such high standard. Based on progress in molecular virology it can, however, be anticipated that similar concepts of selective inhibition will also be developed for other virus groups. In addition to virus-induced enzymes, viral proteins other than enzymes with specific activities will be identified. The identification of active sites will lead to the design of new and specific inhibitors. Moreover, studies on the mode of action of the huge number of known antiviral compounds may provide the basis for new and potent approaches to specific virus chemotherapy. New inhibitors of viral replication may also be derived from 2'-5'A and other mediators of the interferon induced antiviral state. However, since 2'-5'A does not enter cells, is rapidly degraded by phosphodiesterases, and affects viral and cellular protein synthesis, only analogs which do not have these disadvantages may qualify as antiviral drugs. In addition to refinements at the molecular level quantitative assays for a better evaluation of antiviral agents for clinical use are required. For clinical trials, rapid diagnosis, early initiation of treatment, and quantitative evaluation of the antiviral effects of a drug need to be developed. Moreover, new methods of drug delivery and/or drug targeting will improve potency and selectivity of antiviral compounds. Drug carriers have already successfully been used in cancer therapy (Poste and Fidler, 1981) they should be also applicable to virus chemotherapy. Finally, a better understanding of the pathogenesis and the natural course of viral diseases will contribute to the development of more effective and safe antiviral agents.