Psychological Stress Compromises CD8+ T Cell Control of Latent Herpes Simplex Virus Type 1 Infections

Persisting latent herpes simplex virus genomes are to some degree found in a heterochromatic state, and this contributes to reduced gene expression resulting in quiescence. We used a relatively long-term quiescent infection model in human fibroblasts, followed by provision of ICP0 in trans, to determine the effects of ICP0 on the viral chromatin state as gene expression is reactivated. Expression of ICP0, even at low levels, results in a reduction of higher-order chromatin structure and heterochromatin on quiescent viral genomes, and this effect precedes an increase in transcription. Concurrent with transcriptional activation, high levels of ICP0 expression result in the reduction of the heterochromatin mark trimethylated H3K9, removal of histones H3 and H4 from the quiescent genome, and hyperacetylation of the remaining histones. In contrast, low levels of ICP0 did not appreciably change the levels of histones on the viral genome. These results indicate that ICP0 activity ultimately affects chromatin structure of quiescent genomes at multiple levels, including higher-order chromatin structure, histone modifications, and histone association. Additionally, the level of ICP0 expression affected its ability to change chromatin structure but not to reactivate gene expression. While these observations suggest that some of the effects on chromatin structure are possibly not direct, they also suggest that ICP0 exerts its effects through multiple mechanisms.Herpes simplex virus type 1 (HSV-1) latency is characterized by significantly reduced transcription of the viral genome relative to that seen in productive infection. One gene that appears to be selectively transcribed is that for the latency-associated transcript (LAT) (54,56). This general repression of gene expression suggests that latent gene expression is controlled by epigenetic mechanisms. Since viral DNA is not extensively methylated (33), expression is probably repressed by chromatin structure on the viral genome. During latency, the viral genome is found in an endless, possibly circular, episomal structure, bound by nucleosomes (12, 30) and heterochromatin (12).Periodically in vivo, HSV-1 reactivates, replicates, and can cause recurrent disease. Cellular stress (10,11,39,49,60) and decrease in immune function can both contribute to reactivation (19). Upon reactivation, the full repertoire of viral genes is eventually expressed. The exact order of gene expression upon reactivation is unclear, but latently infected explanted mouse trigeminal ganglia (TG) were shown to express genes in a temporal pattern different from that seen in productive infection (57), while there is also a decrease in LAT expression prior to, or concurrent with, lytic gene expression (55, 60). The relative contributions of viral activators of gene expression to different aspects of the reactivation process are unclear. However, one activator, the immediate-early (IE) protein ICP0, is required for efficient reactivation from latency in vivo (4-6, 26, 27, 31).ICP0 is a promiscuous activa...

“…Cellular stress (10,11,39,49,60) and decrease in immune function can both contribute to reactivation (19). Upon reactivation, the full repertoire of viral genes is eventually expressed.…”

mentioning

confidence: 99%

Reversal of Heterochromatic Silencing of Quiescent Herpes Simplex Virus Type 1 by ICP0

Ferenczy

DeLuca

2011

“…However, the vast majority of these individuals do not experience recurrent herpetic disease and are designated asymptomatic patients (32,52,80). In contrast, for some individuals (symptomatic patients), the reactivation of latent virus leads to the induction of ineffective or "symptomatic" HSV-specific CD4 ϩ and CD8 ϩ T cells (25,32,80). While some people have frequent recurrences of herpes disease (i.e., symptomatic patients, with 1 to 5 episodes of recurrent disease/year), others have less frequent recurrent disease to no history of recurrent disease (i.e., asymptomatic patients, with 0 to 1 episodes of recurrent disease/year).…”

mentioning

confidence: 99%

Immunodominant “Asymptomatic” Herpes Simplex Virus 1 and 2 Protein Antigens Identified by Probing Whole-ORFome Microarrays with Serum Antibodies from Seropositive Asymptomatic versus Symptomatic Individuals

Dasgupta

Chentoufi

Kalantari

et al. 2012

cHerpes simplex virus 1 (HSV-1) and HSV-2 are medically significant pathogens. The development of an effective HSV vaccine remains a global public health priority. HSV-1 and HSV-2 immunodominant "asymptomatic" antigens (ID-A-Ags), which are strongly recognized by B and T cells from seropositive healthy asymptomatic individuals, may be critical to be included in an effective immunotherapeutic HSV vaccine. In contrast, immunodominant "symptomatic" antigens (ID-S-Ags) may exacerbate herpetic disease and therefore must be excluded from any HSV vaccine. In the present study, proteome microarrays of 88 HSV-1 and 84 HSV-2 open reading frames(ORFs) (ORFomes) were constructed and probed with sera from 32 HSV-1-, 6 HSV-2-, and 5 HSV-1/HSV-2-seropositive individuals and 47 seronegative healthy individuals (negative controls). The proteins detected in both HSV-1 and HSV-2 proteome microarrays were further classified according to their recognition by sera from HSV-seropositive clinically defined symptomatic (n ‫؍‬ 10) and asymptomatic (n ‫؍‬ 10) individuals. We found that (i) serum antibodies recognized an average of 6 ORFs per seropositive individual; (ii) the antibody responses to HSV antigens were diverse among HSV-1-and HSV-2-seropositive individuals; (iii) panels of 21 and 30 immunodominant antigens (ID-Ags) were identified from the HSV-1 and HSV-2 ORFomes, respectively, as being highly and frequently recognized by serum antibodies from seropositive individuals; and (iv) interestingly, four HSV-1 and HSV-2 cross-reactive asymptomatic ID-A-Ags, US4, US11, UL30, and UL42, were strongly and frequently recognized by sera from 10 of 10 asymptomatic patients but not by sera from 10 of 10 symptomatic patients (P < 0.001). In contrast, sera from symptomatic patients preferentially recognized the US10 ID-S-Ag (P < 0.001). We have identified previously unreported immunodominant HSV antigens, among which were 4 ID-A-Ags and 1 ID-S-Ag. These newly identified ID-A-Ags could lead to the development of an efficient "asymptomatic" vaccine against ocular, orofacial, and genital herpes.

“…Reactivation stimuli include various forms of cellular stress (12,13,56,69,89) and diminished immune function (34). The IE protein ICP0 is required for efficient reactivation from latency in vivo (5-7, 44, 45, 50).…”

mentioning

confidence: 99%

Activities of ICP0 Involved in the Reversal of Silencing of Quiescent Herpes Simplex Virus 1

Ferenczy

Ranayhossaini

DeLuca

2011

ICP0 is a transcriptional activating protein required for the efficient replication and reactivation of latent herpes simplex virus 1 (HSV-1). Multiple regions of ICP0 contribute its activity, the most prominent of which appears to be the RING finger, which confers E3 ubiquitin ligase activity. A region in the C terminus of ICP0 has also been implicated in several activities, including the disruption of a cellular repressor complex, REST/CoREST/HDAC1/2/LSD1. We used quiescent infection of MRC-5 cells with a virus that does not express immediate-early proteins, followed by superinfection with various viral mutants to quantify the ability of ICP0 variants to reactivate gene expression and alter chromatin structure. Superinfection with wild-type virus resulted in a 400-fold increase in expression from the previously quiescent d109 genome, the removal of heterochromatin and histones from the viral genome, and an increase in histone marks associated with activated transcription. RING finger mutants were unable to reactivate transcription or remove heterochromatin from d109, while mutants that are unable to bind CoREST activate gene expression from quiescent d109, albeit to a lesser degree than the wild-type virus. One such mutant, R8507, resulted in the partial removal of heterochromatin. Infection with R8507 did not result in the hyperacetylation of H3 and H4. The results demonstrate that (i) consistent with previous findings, the RING finger domain of ICP0 is required for the activation of quiescent genomes, (ii) the RF domain is also crucial for the ultimate removal of repressive chromatin, (iii) activities or interactions specified by the carboxy-terminal region of ICP0 significantly contribute to activation, and (iv) while the effects of the R8507 on chromatin are consistent with a role for REST/CoREST/HDAC1/2/LSD1 in the repression of quiescent genomes, the mutation may also affect other activities involved in derepression.Lytic replication of herpes simplex 1 (HSV-1) occurs in epithelial cells, followed by viral infection of the sensory neurons enervating the site of initial infection. The virus can establish latency in neurons, a state characterized by an almost complete lack of virus gene expression, with the exception of the latency-associated transcript (80, 81). Since latent HSV-1 DNA is not extensively methylated (53) and is found to be packaged in nucleosomes (12), it is likely that chromatin structure participates in repression of the genome and helps to control gene expression. Chromatin can modulate gene expression on a number of levels. Histones can physically impede the access of the transcriptional machinery to the DNA. Certain modifications of the histone tails can recruit repressive or activating proteins to promoters. For example, the repressive chromatin mark trimethylation of histone H3 lysine 9 (H3K9me3) has been shown to form a binding site for, and recruit, heterochromatin protein 1␥ (HP1␥) (1, 54, 64).As in latency in animal models, viral DNA was shown to be in a chromatin structure in a ...