Activator protein-1 transactivation of the major immediate early locus is a determinant of cytomegalovirus reactivation from latency
TL;DR: The findings reveal AP-1 binding to the major immediate early enhancer/promoter is critical for switching this locus from one that is repressed during latency toOne that is highly active following reactivation following reactivating.
Abstract: Human cytomegalovirus (HCMV) is a ubiquitous pathogen that latently infects hematopoietic cells and has the ability to reactivate when triggered by immunological stress. This reactivation causes significant morbidity and mortality in immune-deficient patients, who are unable to control viral dissemination. While a competent immune system helps retain HCMV in its latent form, a portrait of the factors that induce reactivation following the proper cues remains incomplete. Our understanding of the complex molecular mechanisms underlying latency and reactivation continue to evolve. We previously showed the HCMV-encoded G-protein coupled receptor US28 is expressed during latency and facilitates latent infection by attenuating the activator protein-1 (AP-1) transcription factor subunit, c-fos, expression and activity. We now show AP-1 is a critical component for HCMV reactivation. Pharmacological inhibition of c-fos significantly attenuates viral reactivation. In agreement, infection with a virus in which we disrupted the proximal AP-1 binding site in the major immediate early (MIE) enhancer results in inefficient reactivation compared to wild type. Concomitantly, AP-1 recruitment to the MIE enhancer is significantly decreased following reactivation of the mutant virus. Further, AP-1 is critical for de-repression of MIE-driven transcripts and downstream early and late genes, while immediate early genes from other loci remain unaffected. Our data also reveal MIE transcripts driven from the MIE promoter, the distal promoter, and the internal promoter, iP2, are dependent upon AP-1 recruitment, while iP1-driven transcripts are AP-1-independent. Collectively, our data demonstrate AP-1 binding to and activation of the MIE enhancer is a key molecular process controlling reactivation from latency. Significance StatementHuman cytomegalovirus (HCMV) is a common pathogen that infects the majority of the population for life. This infection poses little threat in immunologically healthy individuals, but can be fatal in people with compromised immune systems. Our understanding of the mechanisms underlying latency and reactivation remains incomplete. Here, we show the cellular transcription factor, AP-1, is a key to regulating HCMV reactivation. Our findings reveal AP-1 binding to the major immediate early enhancer/promoter is critical for switching this locus from one that is repressed during latency to one that is highly active following reactivation. Our work provides a novel mechanism HCMV exploits to reactivate, highlighting AP-1 as a potential target to prevent HCMV reactivation.
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TL;DR: Human cytomegalovirus is a ubiquitous herpesviral pathogen that results in life-long infection and one of the mechanisms controlling the balance between latency and reactivation/lytic replication is the regulation of the major immediate-early (MIE) locus.
Abstract: Human cytomegalovirus (HCMV) is a ubiquitous herpesviral pathogen that results in life-long infection. HCMV maintains a latent or quiescent infection in hematopoietic cells, which is broadly defined by transcriptional silencing and the absence of de novo virion production. However, upon cell differentiation coupled with immune dysfunction, the virus can reactivate, which leads to lytic replication in a variety of cell and tissue types. One of the mechanisms controlling the balance between latency and reactivation/lytic replication is the regulation of the major immediate-early (MIE) locus. This enhancer/promoter region is complex, and it is regulated by chromatinization and associated factors, as well as a variety of transcription factors. Herein, we discuss these factors and how they influence the MIE locus, which ultimately impacts the phase of HCMV infection.
21 citations
Cites background from "Activator protein-1 transactivation..."
...How AP-1 overcomes US28 upon reactivation is currently unknown, though this is likely an important facet in the switch between latency and reactivation....
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...As mentioned above, AP-1 is critical to the balance between latency and reactivation, as it is required for successful viral reactivation [83]....
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...Thus, US28-mediated downregulation of c-fos prevents AP-1 binding to the MIE enhancer, suppressing transcription from this region [272]....
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...Additionally, AP-1 recruitment to its consensus site in the MIE enhancer was necessary for the expression of MIEP-, iP2-, and dP-derived transcripts, while iP1-driven transcription was not altered with disruption of the AP-1 canonical binding site [83], suggesting the MIE canonical and alternative promoters differentially respond to transcription factor binding....
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...For example, the transcriptional repressors CUX1/CDP (cut like homeobox 1/CCAAT displacement protein) and Growth Factor Independent 1 (Gfi-1) are downregulated during myeloid differentiation, while transcriptional activators PU.1, CCAAT-enhancer-binding protein (C/EBP), activating transcription factor/cyclic AMP response element (CRE)-binding protein ATF/CREB, activator protein-1 (AP-1), and nuclear factor kappa B (NFκB) are upregulated [61]....
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TL;DR: The findings establish a mechanistic link by which infected cells sense environmental cues to regulate latency and reactivation, and emphasize the role of contextual activation of alternative MIE promoters as the primary drivers of reactivation.
Abstract: Human progenitor cells (HPCs) support human cytomegalovirus (HCMV) latency, and their differentiation along the myeloid lineage triggers cellular cues that drive reactivation. A key step during HCMV reactivation in latently infected HPCs is reexpression of viral major immediate early (MIE) genes. We recently determined that the major immediate early promoter (MIEP), which is primarily responsible for MIE gene expression during lytic replication, remains silent during reactivation. Instead, alternative promoters in the MIE locus are induced by reactivation stimuli. Here, we find that forkhead family (FOXO) transcription factors are critical for activation of alternative MIE promoters during HCMV reactivation, as mutating FOXO binding sites in alternative MIE promoters decreased HCMV IE gene expression upon reactivation and significantly decreased the production of infectious virus from latently infected primary CD34+ HPCs. These findings establish a mechanistic link by which infected cells sense environmental cues to regulate latency and reactivation, and emphasize the role of contextual activation of alternative MIE promoters as the primary drivers of reactivation.
9 citations
References
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TL;DR: Despite high seroprevalences in some populations, a substantial percentage of women of reproductive age are CMV seronegative and thus at risk of primary CMV infection during pregnancy, and future vaccine or educational campaigns to prevent primary infection in pregnant women may need to be tailored to suit the needs of different populations.
Abstract: Cytomegalovirus establishes a lifelong latent infection following primary infection that can periodically reactivate with shedding of infectious virus. Primary infection, reactivation and reinfection during pregnancy can all lead to in utero transmission to the developing fetus. Congenital CMV infections are a major cause of permanent hearing loss and neurological impairment. In this literature review, we found that CMV infection was relatively common among women of reproductive age, with seroprevalence ranging from 45 to 100%. CMV seroprevalence tended to be highest in South America, Africa and Asia and lowest in Western Europe and United States. Within the United States, CMV seroprevalence showed substantial geographic variation as well, differing by as much as 30 percentage points between states, though differences might be explained by variation in the types of populations sampled. Worldwide, seroprevalence among non-whites tended to be 20-30 percentage points higher than that of whites (summary prevalence ratio (PR) = 1.59, 95% confidence interval (CI) = 1.57-1.61). Females generally had higher seroprevalences than males, although in most studies the differences were small (summary PR = 1.13, 95% CI = 1.11-1.14). Persons of lower socioeconomic status were more likely to be CMV seropositive (summary PR = 1.33, 95% CI = 1.32-1.35). Despite high seroprevalences in some populations, a substantial percentage of women of reproductive age are CMV seronegative and thus at risk of primary CMV infection during pregnancy. Future vaccine or educational campaigns to prevent primary infection in pregnant women may need to be tailored to suit the needs of different populations.
1,207 citations
"Activator protein-1 transactivation..." refers background in this paper
...The betaherpesvirus human cytomegalovirus (HCMV) latently infects 50 - 75% of the healthy 62 US population (1)....
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TL;DR: In this article, the authors found that CD33+ cell populations were found to support latency and expression of viral latency-associated transcripts and to undergo reactivation of productive viral replication when differentiated in the presence of human fibroblasts.
Abstract: Hematopoietic cells and their progenitors play important roles in human cytomegalovirus latency and reactivation. Latent infection has been evaluated in defined populations of myeloid-lineage-committed progenitor cells coexpressing CD33 and CD15 or CD33 and CD14 along with the dendritic cell markers CD1a and CD10. These CD33+ cell populations were found to support latency and expression of viral latency-associated transcripts and to undergo reactivation of productive viral replication when differentiated in the presence of human fibroblasts. Reactivation was also observed when myeloid cells were carried in the presence of fibroblast-conditioned medium or medium supplemented with certain cytokines (interferon gamma, tumor necrosis factor alpha, interleukin 4, or granulocyte-macrophage colony-simulating factor), suggesting that cell differentiation pathways act as determinants of reactivation. More primitive CD34+ hematopoietic cells were also found to be susceptible to viral infection and latency was maintained as these cells differentiated into CD33+-lineage-committed populations. Between 0.01% and 0.001% of CD33+ CD14+ or CD33+ CD15+ bone marrow mononuclear cells isolated from naturally infected individuals were found to express latent transcripts. Thus, cytomegalovirus is carried within a small percentage of myeloid and dendritic cell progenitors in the healthy seropositive host. Virus reactivation may be triggered by factors associated with the inflammatory response.
513 citations
"Activator protein-1 transactivation..." refers background in this paper
...As such, the MIE 78 locus is significantly repressed during viral latency (9-12)....
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TL;DR: Ganciclovir-resistant cytomegalovirus is an important cause of late morbidity among D+/R- transplant recipients who have had lengthened exposure to gancic Lovir and have received highly potent immunosuppression and strategies to reduce this complication are warranted.
491 citations
"Activator protein-1 transactivation..." refers background in this paper
...Further, 68 these drugs target viral lytic replication, when disease is already primed to occur (6, 7)....
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TL;DR: The epidemiology and molecular and cellular pathology of this virus are summarized to provide an overarching model of pathogenesis, able to account for these varying clinical presentations of HCMV.
Abstract: Human cytomegalovirus (HCMV) is a recognized cause of disease in the fetus, the allograft recipient and AIDS patients. More recently, it has been recognized as a pathogen for those admitted to intensive care units, for the elderly and for the general population. The epidemiology and molecular and cellular pathology of this virus are summarized to provide an overarching model of pathogenesis, able to account for these varying clinical presentations. In brief, HCMV has the potential to spread in the bloodstream to all organs, but only produces overt disease if the viral load increases to high levels. This is normally prevented by a robust immune response, so that the infected individual usually remains asymptomatic. However, this benefit comes at the cost of committing more and more immunological resources to controlling HCMV with time, so that the overall function of the immune system is impaired. Fortunately, recent progress in developing novel antiviral drugs and vaccines suggests the possibility that the diverse effects of HCMV may soon become controllable at the individual and population level, respectively.
444 citations
"Activator protein-1 transactivation..." refers background in this paper
...While this infection is, for the most part, asymptomatic in healthy individuals, 58 reactivation from latency causes significant morbidity and mortality in immunocompromised and 59 immunosuppressed individuals (2, 3)....
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University of Alberta1, François Rabelais University2, University of California, San Francisco3, University of Pennsylvania4, University of Michigan5, University of Washington6, Université libre de Bruxelles7, University of Glasgow8, University of Hertfordshire9, Goethe University Frankfurt10, Ghent University11
TL;DR: It is demonstrated that extending valganciclovir prophylaxis (900 mg once daily) to 200 days significantly reduces the incidence of CMV disease and viremia through to 12 months compared with 100 days’ prophYLaxis, without significant additional safety concerns associated with longer treatment.
427 citations