PMID- 11238850 OWN - NLM STAT- MEDLINE DCOM- 20010405 LR - 20220311 IS - 0022-538X (Print) IS - 1098-5514 (Electronic) IS - 0022-538X (Linking) VI - 75 IP - 7 DP - 2001 Apr TI - ICP0 is required for efficient reactivation of herpes simplex virus type 1 from neuronal latency. PG - 3240-9 AB - Relative to wild-type herpes simplex virus type 1 (HSV-1), ICP0-null mutant viruses reactivate inefficiently from explanted, latently infected mouse trigeminal ganglia (TG), indicating that ICP0 is not essential for reactivation but plays a central role in enhancing the efficiency of reactivation. The validity of these findings has been questioned, however, because the replication of ICP0-null mutants is impaired in animal models during the establishment of latency, such that fewer mutant genomes than wild-type genomes are present in latently infected mouse TG. Therefore, the reduced number of mutant viral genomes available to reactivate, rather than mutations in the ICP0 gene per se, may be responsible for the reduced reactivation efficiency of ICP0-null mutants. We have recently demonstrated that optimization of the size of the ICP0 mutant virus inoculum and transient immunosuppression of mutant-infected mice with cyclophosphamide can be used to establish wild-type levels of ICP0-null mutant genomes in latently infected TG (W. P. Halford and P. A. Schaffer, J. Virol. 74:5957-5967, 2000). Using this procedure to equalize mutant and wild-type genome numbers, the goal of the present study was to determine if, relative to wild-type virus, the absence of ICP0 function in two ICP0-null mutants, n212 and 7134, affects reactivation efficiency from (i) explants of latently infected TG and (ii) primary cultures of latently infected TG cells. Although equivalent numbers of viral genomes were present in TG of mice latently infected with either wild-type or mutant viruses, reactivation of n212 and 7134 from heat-stressed TG explants was inefficient (31 and 37% reactivation, respectively) relative to reactivation of wild-type virus (KOS) (95%). Similarly, n212 and 7134 reactivated inefficiently from primary cultures of dissociated TG cells plated directly after removal from the mouse (7 and 4% reactivation, respectively), relative to KOS (60% reactivation). The efficiency and kinetics of reactivation of KOS, n212, and 7134 from cultured TG cells (treated with acyclovir to facilitate the establishment of latency) in response to heat stress or superinfection with a nonreplicating HSV-1 ICP4(-) mutant, n12, were compared. Whereas heat stress induced reactivation of KOS from 69% of latently infected TG cell cultures, reactivation of n212 and 7134 was detected in only 1 and 7% of cultures, respectively. In contrast, superinfection with the ICP4(-) virus, which expresses high levels of ICP0, resulted in the production of infectious virus in nearly 100% of cultures latently infected with KOS, n212, or 7134 within 72 h. Thus, although latent mutant viral genome loads were equivalent to that of wild-type virus, in the absence of ICP0, n212 and 7134 reactivated inefficiently from latently infected TG cells during culture establishment and following heat stress. Collectively, these findings demonstrate that ICP0 is required to induce efficient reactivation of HSV-1 from neuronal latency. FAU - Halford, W P AU - Halford WP AD - Department of Microbiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6076, USA. FAU - Schaffer, P A AU - Schaffer PA LA - eng GR - F32 AI010147/AI/NIAID NIH HHS/United States GR - P01 NS035138/NS/NINDS NIH HHS/United States GR - F32 AI 10147/AI/NIAID NIH HHS/United States GR - P01 NS 35138/NS/NINDS NIH HHS/United States PT - Journal Article PT - Research Support, U.S. Gov't, P.H.S. PL - United States TA - J Virol JT - Journal of virology JID - 0113724 RN - 0 (Antigens, Viral) RN - 0 (Immediate-Early Proteins) RN - 0 (herpes simplex virus, type 1 protein ICP4) RN - 8N3DW7272P (Cyclophosphamide) RN - EC 2.3.2.27 (Ubiquitin-Protein Ligases) RN - EC 2.3.2.27 (Vmw110 protein, Human herpesvirus 1) RN - X4HES1O11F (Acyclovir) SB - IM MH - Acyclovir/pharmacology MH - Animals MH - Antigens, Viral/analysis MH - Cells, Cultured MH - Chlorocebus aethiops MH - Cyclophosphamide/pharmacology MH - Herpesvirus 1, Human/immunology/*physiology MH - Hot Temperature MH - Immediate-Early Proteins/*physiology MH - Male MH - Mice MH - Mice, Inbred ICR MH - Trigeminal Ganglion/virology MH - Ubiquitin-Protein Ligases MH - Vero Cells MH - *Virus Activation MH - *Virus Latency PMC - PMC114117 EDAT- 2001/03/10 10:00 MHDA- 2001/04/06 10:01 PMCR- 2001/04/01 CRDT- 2001/03/10 10:00 PHST- 2001/03/10 10:00 [pubmed] PHST- 2001/04/06 10:01 [medline] PHST- 2001/03/10 10:00 [entrez] PHST- 2001/04/01 00:00 [pmc-release] AID - 1720 [pii] AID - 10.1128/JVI.75.7.3240-3249.2001 [doi] PST - ppublish SO - J Virol. 2001 Apr;75(7):3240-9. doi: 10.1128/JVI.75.7.3240-3249.2001.