Murine gammaherpesvirus-68 (MHV68) is a rodent pathogen that offers a tractable system to study gammaherpesvirus lytic infection in primary cells. However, after entry into the infected cell nucleus, the HSV genome begins to associate with nucleosomes during the earliest stages of infection. The HCF-1 coactivator complex consists of a set of histone modification components, including the histone H3K9 demethylase LSD1 and the H3K4 methyltransferase Set1 or MLL. Mutated forms of the protein lacking this acidic domain lose the ability to activate transcription, and can dominantly interfere with the trans-activation function of native VP16 (ref. The usual site for HSV-1 infection is skin or mucous membranes, and it is the causative agent of cold sores. UL, unique long (L) region; US, unique short (S) region; open boxes, repeat regions. The major conclusions are as follows: (i) there is a threshold input multiplicity above which the mutant virus replicates normally; (ii) individual cells infected below the threshold multiplicity have a high probability of establishing a nonproductive infection; (iii) such nonproductively infected cells have a high probability of expressing IE products at 6 h postinfection; (iv) even at 24 h postinfection, IE protein-positive nonproductively infected human fibroblast cells exceed the number of cells that lead to plaque formation by up to 2 orders of magnitude; (v) expression of individual IE proteins in a proportion of the nonproductively infected cells is incompletely coordinated; (vi) the nonproductive cells can also express early gene products at low frequencies and in a stochastic manner; and (vii) significant numbers of human fibroblast cells infected at low multiplicity by an ICP0-deficient virus are lost through cell death.
Analysis of the significance of these potential functions and whether they are direct or indirect effects of ICP0 is complicated because HSV-1 mutants expressing mutant forms of ICP0 infect cells with widely differing efficiencies. In accordance with the guiding principles established by George Ellery Hale in 1914, PNAS publishes brief first announcements of Academy Members’ and Foreign Associates’ more important contributions to research and of work that appears to a Member to be of particular importance. Earlier studies have shown that ICP0 interacts with CoREST and displaces HDAC1 from the CoREST–REST–HDAC1/2 complex. However, the role(s) of H2AX phosphorylation in lytic infection remain unclear.Following infection of human foreskin fibroblasts by HSV-1 or HSV-2, we assayed the phosphorylation of H2AX in the presence of inhibitors of transcription, translation, or viral DNA replication, or in the presence of inhibitors of ATM and ATR kinases (KU-55933 and VE-821, respectively). Viral proteins promote reversal of the epigenetic silencing in epithelial cells while the viral latency-associated transcript promotes additional heterochromatin in neuronal cells. RPA is a ssDNA-binding protein that signals genotoxic stress through the ATR (ataxia telangiectasia-mutated and Rad3-related) pathway. Here we describe analysis of HSV-1 mutant viruses, providing strong genetic evidence that HSV-infected cell protein 0 (ICP0) is expressed during establishment and/or maintenance of latent infection in murine sensory neurons in vivo.
In lytically infected cells, in contrast, MCN releases HSV-1 DNA in primarily heterogeneously sized fragments. Understanding HSV latency may lead to new therapies or even a cure for this widespread pathogen. In addition however, the virus also establishes asymptomatic latent infections in sensory neurons which serve as a reservoir for further cycles of peripheral lytic infections. The soluble DNA-protein complexes were resolved on sucrose gradients. However, it is unclear how STAT3 regulates the innate immune response during the early phase of HSV-1 lytic infection. In reality, the genome of HSV-1 is prone to form shorter repeat sequences. However, the mechanisms that account for such low levels—how histone deposition on the viral genome is blocked or how histones are removed from the genome—are not yet defined.
These structures impart protection from damage and provide regulatory functions for genomic processes, including activity such as transcription and replication, as well as quiescence such as gene- specific repression and heterochromatic silencing (5). Triezenberg. A.D. The LAT gene has been shown to repress lytic-gene expression in sensory neurons. Analysis of the significance of these potential functions and whether they are direct or indirect effects of ICP0 is complicated because HSV-1 mutants expressing mutant forms of ICP0 infect cells with widely differing efficiencies. In heterologous expression systems, the VP16 activation domain (AD) can recruit various coactivators such as the p300/CBP histone acetyltransferases (HATs) and the Brm and Brg-1 chromatin remodeling complexes. The TAATGARAT elements are thought to mediate the trans-activation of IE RNA synthesis by a virion-associated protein(s)6–14, and the flanking G + C-rich sequences appear both to potentiate this induction and to direct IE promoter activity in vivo 9–14.
Infection of cells with alphaherpesviruses (herpes simplex virus [HSV] and varicella-zoster virus [VZV]) results in the deposition of nucleosomes bearing repressive histone H3K9 methylation on the viral genome. Analysis of the significance of these potential functions and whether they are direct or indirect effects of ICP0 is complicated because HSV-1 mutants expressing mutant forms of ICP0 infect cells with widely differing efficiencies.