ABSTRACT
Kaposi's sarcoma-associated herpesvirus (KSHV) belongs to the gamma-herpesvirus family and is a well-known human oncogenic virus. In infected cells, the viral genome of 165 kbp is circular DNA wrapped in chromatin. The tight control of gene expression is critical for latency, the transition into the lytic phase, and the development of viral-associated malignancies. Distal cis-regulatory elements, such as enhancers and silencers, can regulate gene expression in a position- and orientation-independent manner. Open chromatin is another characteristic feature of enhancers. To systematically search for enhancers, we cloned all the open chromatin regions in the KSHV genome downstream of the luciferase gene and tested their enhancer activity in infected and uninfected cells. A silencer was detected upstream of the latency-associated nuclear antigen promoter. Two constitutive enhancers were identified in the K12p-OriLyt-R and ORF29 Intron regions, where ORF29 Intron is a tissue-specific enhancer. The following promoters: OriLyt-L, PANp, ALTp, and the terminal repeats (TRs) acted as lytically induced enhancers. The expression of the replication and transcription activator (RTA), the master regulator of the lytic cycle, was sufficient to induce the activity of lytic enhancers in uninfected cells. We propose that the TRs that span about 24 kbp region serve as a "viral super-enhancer" that integrates the repressive effect of the latency-associated nuclear antigen (LANA) with the activating effect of RTA. Utilizing CRISPR activation and interference techniques, we determined the connections between these enhancers and their regulated genes. The silencer and enhancers described here provide an additional layer to the complex gene regulation of herpesviruses.IMPORTANCEIn this study, we performed a systematic functional assay to identify cis-regulatory elements within the genome of the oncogenic herpesvirus, Kaposi's sarcoma-associated herpesvirus (KSHV). Similar to other herpesviruses, KSHV presents both latent and lytic phases. Therefore, our assays were performed in uninfected cells, during latent infection, and under lytic conditions. We identified two constitutive enhancers, one of which seems to be a tissue-specific enhancer. In addition, four lytically induced enhancers, which are all responsive to the replication and transcription activator (RTA), were identified. Furthermore, a silencer was identified between the major latency promoter and the lytic gene locus. Utilizing CRISPR activation and interference techniques, we determined the connections between these enhancers and their regulated genes. The terminal repeats, spanning a region of about 24 kbp, seem like a "viral super-enhancer" that integrates the repressive effect of the latency-associated nuclear antigen (LANA) with the activating effect of RTA to regulate latency to lytic transition.
Subject(s)
Enhancer Elements, Genetic , Gene Expression Regulation, Viral , Genome, Viral , Herpesvirus 8, Human , Promoter Regions, Genetic , Virus Activation , Virus Latency , Humans , Antigens, Viral/genetics , Antigens, Viral/metabolism , Chromatin/metabolism , Chromatin/genetics , Enhancer Elements, Genetic/genetics , Gene Expression Regulation, Viral/genetics , Genome, Viral/genetics , HEK293 Cells , Herpesvirus 8, Human/genetics , Immediate-Early Proteins/metabolism , Nuclear Proteins/genetics , Nuclear Proteins/metabolism , Terminal Repeat Sequences/genetics , Trans-Activators/metabolism , Virus Activation/genetics , Virus Latency/geneticsABSTRACT
Bovine alphaherpesvirus 1 (BoHV-1) infection causes respiratory tract disorders and immune suppression and may induce bacterial pneumonia. BoHV-1 establishes lifelong latency in sensory neurons after acute infection. Reactivation from latency consistently occurs following stress or intravenous injection of the synthetic corticosteroid dexamethasone (DEX), which mimics stress. The immediate early transcription unit 1 (IEtu1) promoter drives expression of infected cell protein 0 (bICP0) and bICP4, two viral transcriptional regulators necessary for productive infection and reactivation from latency. The IEtu1 promoter contains two glucocorticoid receptor (GR) responsive elements (GREs) that are transactivated by activated GR. GC-rich motifs, including consensus binding sites for specificity protein 1 (Sp1), are in the IEtu1 promoter sequences. E2F family members bind a consensus sequence (TTTCCCGC) and certain specificity protein 1 (Sp1) sites. Consequently, we hypothesized that certain E2F family members activate IEtu1 promoter activity. DEX treatment of latently infected calves increased the number of E2F2+ TG neurons. GR and E2F2, but not E2F1, E2F3a, or E2F3b, cooperatively transactivate a 436-bp cis-regulatory module in the IEtu1 promoter that contains both GREs. A luciferase reporter construct containing a 222-bp fragment downstream of the GREs was transactivated by E2F2 unless two adjacent Sp1 binding sites were mutated. Chromatin immunoprecipitation studies revealed that E2F2 occupied IEtu1 promoter sequences when the BoHV-1 genome was transfected into mouse neuroblastoma (Neuro-2A) or monkey kidney (CV-1) cells. In summary, these findings revealed that GR and E2F2 cooperatively transactivate IEtu1 promoter activity, which is predicted to influence the early stages of BoHV-1 reactivation from latency. IMPORTANCE: Bovine alpha-herpesvirus 1 (BoHV-1) acute infection in cattle leads to establishment of latency in sensory neurons in the trigeminal ganglia (TG). A synthetic corticosteroid dexamethasone consistently initiates BoHV-1 reactivation in latently infected calves. The BoHV-1 immediate early transcription unit 1 (IEtu1) promoter regulates expression of infected cell protein 0 (bICP0) and bICP4, two viral transcriptional regulators. Hence, the IEtu1 promoter must be activated for the reactivation to occur. The number of TG neurons expressing E2F2, a transcription factor and cell cycle regulator, increased during early stages of reactivation from latency. The glucocorticoid receptor (GR) and E2F2, but not E2F1, E2F3a, or E2F3b, cooperatively transactivated a 436-bp cis-regulatory module (CRM) in the IEtu1 promoter that contains two GR responsive elements. Chromatin immunoprecipitation studies revealed that E2F2 occupies IEtu1 promoter sequences in cultured cells. GR and E2F2 mediate cooperative transactivation of IEtu1 promoter activity, which is predicted to stimulate viral replication following stressful stimuli.
Subject(s)
Cell Cycle , E2F2 Transcription Factor , Gene Expression Regulation, Viral , Herpesvirus 1, Bovine , Immediate-Early Proteins , Promoter Regions, Genetic , Receptors, Glucocorticoid , Transcriptional Activation , Animals , Cattle , Mice , Binding Sites , Cell Line , Dexamethasone/pharmacology , E2F2 Transcription Factor/metabolism , Gene Expression Regulation, Viral/drug effects , Gene Expression Regulation, Viral/genetics , Herpesviridae Infections/virology , Herpesviridae Infections/metabolism , Herpesviridae Infections/veterinary , Herpesviridae Infections/genetics , Herpesvirus 1, Bovine/genetics , Herpesvirus 1, Bovine/physiology , Immediate-Early Proteins/genetics , Neurons/virology , Receptors, Glucocorticoid/metabolism , Response Elements/genetics , Sp1 Transcription Factor/metabolism , Trans-Activators/metabolism , Trigeminal Ganglion/cytology , Trigeminal Ganglion/virology , Virus Activation , Virus LatencyABSTRACT
Recovery from COVID-19 depends on the ability of the host to effectively neutralize virions and infected cells, a process largely driven by antibody-mediated immunity. However, with the newly emerging variants that evade Spike-targeting antibodies, re-infections and breakthrough infections are increasingly common. A full characterization of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mechanisms counteracting antibody-mediated immunity is therefore needed. Here, we report that ORF8 is a virally encoded SARS-CoV-2 factor that controls cellular Spike antigen levels. We show that ORF8 limits the availability of mature Spike by inhibiting host protein synthesis and retaining Spike at the endoplasmic reticulum, reducing cell-surface Spike levels and recognition by anti-SARS-CoV-2 antibodies. In conditions of limited Spike availability, we found ORF8 restricts Spike incorporation during viral assembly, reducing Spike levels in virions. Cell entry of these virions then leaves fewer Spike molecules at the cell surface, limiting antibody recognition of infected cells. Based on these findings, we propose that SARS-CoV-2 variants may adopt an ORF8-dependent strategy that facilitates immune evasion of infected cells for extended viral production.
Subject(s)
COVID-19 , Gene Expression Regulation, Viral , Immune Evasion , SARS-CoV-2 , Spike Glycoprotein, Coronavirus , Humans , Antibodies, Viral , COVID-19/immunology , COVID-19/virology , Immune Evasion/genetics , SARS-CoV-2/genetics , Spike Glycoprotein, Coronavirus/genetics , Gene Expression Regulation, Viral/genetics , A549 Cells , HEK293 Cells , Endoplasmic Reticulum/virology , Host Microbial Interactions/genetics , Host Microbial Interactions/immunologyABSTRACT
Adeno-associated virus (AAV) vectors are one of the leading platforms for gene delivery for the treatment of human genetic diseases, but the antiviral cellular mechanisms that interfere with optimal transgene expression are incompletely understood. Here, we performed two genome-scale CRISPR screens to identify cellular factors that restrict transgene expression from recombinant AAV vectors. Our screens revealed several components linked to DNA damage response, chromatin remodeling, and transcriptional regulation. Inactivation of the Fanconi anemia gene FANCA; the human silencing hub (HUSH)-associated methyltransferase SETDB1; and the gyrase, Hsp90, histidine kinase, and MutL (GHKL)-type ATPase MORC3 led to increased transgene expression. Moreover, SETDB1 and MORC3 knockout improved transgene levels of several AAV serotypes as well as other viral vectors, such as lentivirus and adenovirus. Finally, we demonstrated that the inhibition of FANCA, SETDB1, or MORC3 also enhanced transgene expression in human primary cells, suggesting that they could be physiologically relevant pathways that restrict AAV transgene levels in therapeutic settings. IMPORTANCE Recombinant AAV (rAAV) vectors have been successfully developed for the treatment of genetic diseases. The therapeutic strategy often involves the replacement of a defective gene by the expression of a functional copy from the rAAV vector genome. However, cells possess antiviral mechanisms that recognize and silence foreign DNA elements thereby limiting transgene expression and its therapeutic effect. Here, we utilize a functional genomics approach to uncover a comprehensive set of cellular restriction factors that inhibit rAAV-based transgene expression. Genetic inactivation of selected restriction factors increased rAAV transgene expression. Hence, modulation of identified restriction factors has the potential to enhance AAV gene replacement therapies.
Subject(s)
Antiviral Restriction Factors , Dependovirus , Genetic Vectors , Genetic Vectors/genetics , Genetic Vectors/immunology , Dependovirus/genetics , Dependovirus/immunology , Antiviral Restriction Factors/genetics , Antiviral Restriction Factors/metabolism , Transgenes/genetics , Gene Expression Regulation, Viral/genetics , A549 Cells , K562 Cells , Gene Knockout Techniques , Cells, Cultured , Humans , Fanconi Anemia/geneticsABSTRACT
Kaposi's sarcoma-associated herpesvirus (KSHV) is an oncogenic gammaherpesvirus that can replicate in oral epithelial cells to promote viral transmission via saliva. To identify novel regulators of KSHV oral infection, we performed a transcriptome analysis of KSHV-infected primary human gingival epithelial (HGEP) cells, which identified the gene coding for the host transcription factor FOXQ1 as the top induced host gene. FOXQ1 is nearly undetectable in uninfected HGEP and telomerase-immortalized gingival keratinocytes (TIGK) cells but is highly expressed within hours of KSHV infection. We found that while the FOXQ1 promoter lacks activating histone acetylation marks in uninfected oral epithelial cells, these marks accumulate in the FOXQ1 promoter in infected cells, revealing a rapid epigenetic reprogramming event. To evaluate FOXQ1 function, we depleted FOXQ1 in KSHV-infected TIGK cells, which resulted in reduced accumulation of KSHV lytic proteins and viral DNA over the course of 4 days of infection, uncovering a novel lytic cycle-sustaining role of FOXQ1. A screen of KSHV lytic proteins demonstrated that the immediate early proteins ORF45 and replication and transcription activator (RTA) were both sufficient for FOXQ1 induction in oral epithelial cells, indicating active involvement of incoming and rapidly expressed factors in altering host gene expression. ORF45 is known to sustain extracellular signal-regulated kinase (ERK) p90 ribosomal s6 kinase (RSK) pathway activity to promote lytic infection. We found that an ORF45 mutant lacking RSK activation function failed to induce FOXQ1 in TIGK cells, revealing that ORF45 uses a shared mechanism to rapidly induce both host and viral genes to sustain lytic infection in oral epithelial cells. IMPORTANCE The oral cavity is a primary site of initial contact and entry for many viruses. Viral replication in the oral epithelium promotes viral shedding in saliva, allowing interpersonal transmission, as well as spread to other cell types, where chronic infection can be established. Understanding the regulation of KSHV infection in the oral epithelium would allow for the design of universal strategies to target the first stage of viral infection, thereby halting systemic viral pathogenesis. Overall, we uncover a novel positive feedback loop in which immediate early KSHV factors drive rapid host reprogramming of oral epithelial cells to sustain the lytic cycle in the oral cavity.
Subject(s)
Feedback, Physiological , Forkhead Transcription Factors , Gene Expression Regulation, Viral , Herpesvirus 8, Human , Immediate-Early Proteins , Humans , Epithelial Cells/metabolism , Forkhead Transcription Factors/genetics , Forkhead Transcription Factors/metabolism , Gene Expression Regulation, Viral/genetics , Herpesvirus 8, Human/physiology , Immediate-Early Proteins/genetics , Immediate-Early Proteins/metabolism , Virus Replication/physiology , Host Microbial Interactions , Cell Line , Promoter Regions, GeneticABSTRACT
Truncations of the cytoplasmic tail (CT) of entry proteins of enveloped viruses dramatically increase the infectivity of pseudoviruses (PVs) bearing these proteins. Several mechanisms have been proposed to explain this enhanced entry, including an increase in cell surface expression. However, alternative explanations have also been forwarded, and the underlying mechanisms for the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) S protein remain undetermined. Here, we show that the partial or complete deletion of the CT (residues 19 to 35) does not modify SARS-CoV-2 S protein expression on the cell surface when the S2 subunit is measured, whereas it is significantly increased when the S1 subunit is measured. We also show that the higher level of S1 in these CT-truncated S proteins reflects the decreased dissociation of the S1 subunit from the S2 subunit. In addition, we demonstrate that CT truncation further promotes S protein incorporation into PV particles, as indicated by biochemical analyses and cryo-electron microscopy. Thus, our data show that two distinct mechanisms contribute to the markedly increased infectivity of PVs carrying CT-truncated SARS-CoV-2 S proteins and help clarify the interpretation of the results of studies employing such PVs. IMPORTANCE Various forms of PVs have been used as tools to evaluate vaccine efficacy and study virus entry steps. When PV infectivity is inherently low, such as that of SARS-CoV-2, a CT-truncated version of the viral entry glycoprotein is widely used to enhance PV infectivity, but the mechanism underlying this enhanced PV infectivity has been unclear. Here, our study identified two mechanisms by which the CT truncation of the SARS-CoV-2 S protein dramatically increases PV infectivity: a reduction of S1 shedding and an increase in S protein incorporation into PV particles. An understanding of these mechanisms can clarify the mechanistic bases for the differences observed among various assays employing such PVs.
Subject(s)
SARS-CoV-2 , Spike Glycoprotein, Coronavirus , Virion , Humans , COVID-19/virology , Cryoelectron Microscopy , SARS-CoV-2/genetics , SARS-CoV-2/metabolism , SARS-CoV-2/pathogenicity , Spike Glycoprotein, Coronavirus/metabolism , Virion/genetics , Virion/pathogenicity , Gene Expression Regulation, Viral/geneticsABSTRACT
Viruses have evolved a multitude of mechanisms to combat barriers to productive infection in the host cell. Virally-encoded miRNAs are one such means to regulate host gene expression in ways that benefit the virus lifecycle. miRNAs are small non-coding RNAs that regulate protein expression but do not trigger the adaptive immune response, making them powerful tools encoded by viruses to regulate cellular processes. Diverse viruses encode for miRNAs but little sequence homology exists between miRNAs of different viral species. Despite this, common cellular pathways are targeted for regulation, including apoptosis, immune evasion, cell growth and differentiation. Herein we will highlight the viruses that encode miRNAs and provide mechanistic insight into how viral miRNAs aid in lytic and latent infection by targeting common cellular processes. We also highlight how viral miRNAs can mimic host cell miRNAs as well as how viral miRNAs have evolved to regulate host miRNA expression. These studies dispel the myth that viral miRNAs are subtle regulators of gene expression, and highlight the critical importance of viral miRNAs to the virus lifecycle.
Subject(s)
MicroRNAs , Viruses , MicroRNAs/genetics , MicroRNAs/metabolism , Viruses/genetics , Viruses/metabolism , Cell Differentiation , Protein Processing, Post-Translational , Gene Expression , Gene Expression Regulation, Viral/genetics , Gene Expression RegulationABSTRACT
All lentiviruses encode a post-transcriptional transactivator, Rev, which mediates the export of viral mRNA from the nucleus to the cytoplasm and which is required for viral gene expression and viral replication. In the current study, we demonstrate that equine infectious anemia virus (EIAV), an equine lentivirus, encodes a second post-transcriptional transactivator that we designate Grev. Grev is encoded by a novel transcript with a single splicing event that was identified using reverse transcription-PCR (RT-PCR) and RNA-seq in EIAV-infected horse tissues and cells. Grev is about 18 kDa in size, comprises the first 18 amino acids (aa) of Gag protein together with the last 82 aa of Rev, and was detected in EIAV-infected cells. Similar to Rev, Grev is localized to the nucleus, and both are able to mediate the expression of Mat (a recently identified viral protein of unknown function from EIAV), but Rev can mediate the expression of EIAV Gag/Pol, while Grev cannot. We also demonstrate that Grev, similar to Rev, specifically binds to rev-responsive element 2 (RRE-2, located in the first exon of mat mRNAs) to promote nuclear export of mat mRNA via the chromosome region maintenance 1 (CRM1) pathway. However, unlike Rev, whose function depends on its multimerization, we could not detect multimerization of Grev using coimmunoprecipitation (co-IP) or bimolecular fluorescence complementation (BiFC) assays. Together, these data suggest that EIAV encodes two post-transcriptional transactivators, Rev and Grev, with similar, but not identical, functions. IMPORTANCE Nuclear export of viral transcripts is a crucial step for viral gene expression and viral replication in lentiviruses, and this export is regulated by a post-transcriptional transactivator, Rev, that is shared by all lentiviruses. Here, we report that the equine infectious anemia virus (EIAV) encodes a novel viral protein, Grev, and demonstrated that Grev, like Rev, mediates the expression of the viral protein Mat by binding to the first exon of mat mRNAs via the chromosome region maintenance 1 (CRM1) pathway. Grev is encoded by a single-spliced transcript containing two exons, whereas Rev is encoded by a multiple-spliced transcript containing four exons. Moreover, Rev is able to mediate EIAV Gag/Pol expression by binding to rev-responsive element (RRE) located within the Env-coding region, while Grev cannot. Therefore, the present study demonstrates that EIAV encodes two post-transcriptional regulators, Grev and Rev, suggesting that post-transcriptional regulation patterns in lentivirus are diverse and complex.
Subject(s)
Equine Infectious Anemia , Infectious Anemia Virus, Equine , Trans-Activators , Animals , Equine Infectious Anemia/virology , Exons , Gene Products, rev/genetics , Horses/genetics , Infectious Anemia Virus, Equine/genetics , Infectious Anemia Virus, Equine/metabolism , RNA, Messenger/genetics , RNA, Messenger/metabolism , Trans-Activators/genetics , Trans-Activators/metabolism , Gene Expression Regulation, Viral/geneticsABSTRACT
Human papillomaviruses are DNA tumor viruses. A persistent infection with high-risk HPV types is the necessary risk factor for the development of anogenital carcinoma. The E6 protein is a viral oncoprotein that directly interacts with different cellular regulatory proteins mainly affecting the cell cycle, cellular differentiation and polarization of epithelial cells. In dependency of the phylogenetic classification of HPV different interaction partners of E6 have been described. The Notch pathway seems to be one common target of HPV, which can be up or down regulated by different E6 proteins. Our novel triple fluorescence flow-cytometry-based assay allows a semi-quantitative comparison of the E6 proteins´ effect on the Notch pathway using a Notch-responsive reporter plasmid. As a result, all E6 proteins of beta-HPV repressed the Notch reporter expression, of which HPV38 E6 showed the greatest repression potential. In contrast, alpha-HPV E6 of HPV16, activates the reporter expression most significantly, whereas E6 of HPV31 and low-risk HPV6b showed significant activation only in a p53-null cell line. Interestingly, HPV18 E6, with the second highest carcinogenic risk, shows no effect. This high divergence within different genus of HPV is important for targeting the Notch pathway regarding a potential HPV therapy.
Subject(s)
Flow Cytometry/methods , Fluorescence , Gene Expression Regulation, Viral/genetics , Oncogene Proteins, Viral/physiology , Papillomaviridae/genetics , Receptors, Notch/metabolism , Signal Transduction/genetics , Signal Transduction/physiology , DNA-Binding Proteins , Lymphocytes, Null , Papillomaviridae/classification , Phylogeny , Repressor ProteinsABSTRACT
The role of N6-methyladenosine (m6A) modifications has increasingly been associated with a diverse set of roles in modulating viruses and influencing the outcomes of viral infection. Here, we report that the landscape of m6A deposition is drastically shifted during Kaposi's sarcoma-associated herpesvirus (KSHV) lytic infection for both viral and host transcripts. In line with previous reports, we also saw an overall decrease in host methylation in favor of viral messenger RNA (mRNA), along with 5' hypomethylation and 3' hypermethylation. During KSHV lytic infection, a major shift in overall mRNA abundance is driven by the viral endoribonuclease SOX, which induces the decay of greater than 70% of transcripts. Here, we reveal that interlukin-6 (IL-6) mRNA, a well-characterized, SOX-resistant transcript, is m6A modified during lytic infection. Furthermore, we show that this modification falls within the IL-6 SOX resistance element, an RNA element in the IL-6 3' untranslated region (UTR) that was previously shown to be sufficient for protection from SOX cleavage. We show that the presence of this m6A modification is essential to confer SOX resistance to the IL-6 mRNA. We next show that this modification recruits the m6A reader YTHDC2 and found that YTHDC2 is necessary for the escape of the IL-6 transcript. These results shed light on how the host cell has evolved to use RNA modifications to circumvent viral manipulation of RNA fate during KSHV infection.
Subject(s)
Endoribonucleases/metabolism , RNA Helicases/metabolism , RNA Stability/physiology , Adenosine/analogs & derivatives , Adenosine/genetics , Adenosine/metabolism , Cell Line, Tumor , Endoribonucleases/genetics , Gene Expression/genetics , Gene Expression Regulation, Viral/genetics , HEK293 Cells , Herpesviridae Infections/genetics , Herpesviridae Infections/virology , Herpesvirus 8, Human/genetics , Herpesvirus 8, Human/pathogenicity , Humans , Interleukin-6/genetics , Interleukin-6/metabolism , Methylation , RNA Helicases/genetics , RNA Stability/genetics , RNA, Messenger/metabolism , RNA, Viral/genetics , Viral Proteins/metabolism , Virus Replication/geneticsABSTRACT
Many phage genes lack sequence similarity to any other open reading frame (ORF) in current databases. These enigmatic ORFan genes can have a tremendous impact on phage propagation and host interactions but often remain experimentally unexplored. We previously revealed a novel interaction between phage P22 and its Salmonella Typhimurium host, instigated by the ORFan gene pid (for phage P22 encoded instigator of dgo expression) and resulting in derepression of the host dgoRKAT operon. The pid gene is highly expressed in phage carrier cells that harbor a polarly located P22 episome that segregates asymmetrically among daughter cells. Here, we discovered that the pid locus is fitted with a weak promoter, has an exceptionally long 5' untranslated region that is instructive for a secondary pid mRNA species, and has a 3' Rho-independent termination loop that is responsible for stability of the pid transcript.
Subject(s)
Bacteriophage P22/genetics , Gene Expression Regulation, Viral/genetics , Bacteriophages/genetics , Gene Expression/genetics , Open Reading Frames/genetics , Operon , Promoter Regions, Genetic/genetics , Salmonella Phages/genetics , Salmonella typhimurium/genetics , Salmonella typhimurium/virologyABSTRACT
The presence of latent HIV-1 reservoirs in the periphery and brain represents a major obstacle to curing HIV-1 infection. As an essential protein for HIV-1 viral replication, HIV-1 Tat, mostly intracellular, has been implicated in latent HIV-1 infection. From HIV-1 infected cells, HIV-1 Tat is actively secreted and bystander cells uptake the released Tat whereupon it is endocytosed and internalized into endolysosomes. However, to activate the HIV-1 LTR promoter and increase HIV-1 replication, HIV-1 Tat must first escape from the endolysosomes and then enter the nucleus. Here, we tested the hypothesis that HIV-1 Tat can accumulate in endolysosomes and contribute to the activation of latent HIV-1 in astrocytes. Using U87MG astrocytoma cells expressing HIV-1 LTR-driven luciferase and primary human astrocytes we found that exogenous HIV-1 Tat enters endolysosomes, resides in endolysosomes for extended periods of time, and induces endolysosome de-acidification as well as enlargement. The weak base chloroquine promoted the release of HIV-1 Tat from endolysosomes and induced HIV-1 LTR transactivation. Similar results were observed by activating endolysosome Toll-like receptor 3 (TLR3) and TLR7/8. Conversely, pharmacological block of TLRs and knocking down expression levels of TLR3 and TLR7, but not TLR8, prevented endolysosome leakage and attenuated HIV-1 Tat-mediated HIV-1 LTR transactivation. Our findings suggest that HIV-1 Tat accumulation in endolysosomes may play an important role in controlling HIV-1 transactivation.
Subject(s)
Astrocytes/virology , Endocytosis/genetics , Endosomes/genetics , HIV Long Terminal Repeat/genetics , HIV-1/genetics , Lysosomes/genetics , Transcriptional Activation/genetics , tat Gene Products, Human Immunodeficiency Virus/genetics , Cell Line, Tumor , Gene Expression Regulation, Viral/genetics , HIV Infections/genetics , HIV Infections/virology , Humans , Promoter Regions, Genetic/genetics , Virus Latency/genetics , Virus Replication/geneticsABSTRACT
Microbes have been coevolving with their host for millions of years, exploiting host resources to their own benefit. We show that viral and bacterial pathogens convergently evolved to hijack cellular mitogen-activated protein kinase (MAPK) p90-ribosomal S6-kinases (RSKs). Theiler's virus leader (L) protein binds RSKs and prevents their dephosphorylation, thus maintaining the kinases active. Recruitment of RSKs enables L-protein-mediated inhibition of eukaryotic translation initiation factor 2 alpha kinase 2 (EIF2AK2 or PKR) and stress granule formation. Strikingly, ORF45 protein of Kaposi's sarcoma-associated herpesvirus (KSHV) and YopM protein of Yersinia use the same peptide motif as L to recruit and activate RSKs. All three proteins interact with a conserved surface-located loop of RSKs, likely acting as an allosteric regulation site. Some unrelated viruses and bacteria thus evolved to harness RSKs in a common fashion, yet to target distinct aspects of innate immunity. As documented for Varicella zoster virus ORF11, additional pathogens likely evolved to hijack RSKs, using a similar short linear motif.
Subject(s)
Host Microbial Interactions/physiology , Ribosomal Protein S6 Kinases, 90-kDa/genetics , Bacteria/pathogenicity , Bacterial Infections/genetics , Bacterial Infections/metabolism , Biological Evolution , Cell Line , Gene Expression Regulation, Viral/genetics , Host Microbial Interactions/genetics , Humans , Immediate-Early Proteins/genetics , MAP Kinase Signaling System/physiology , Mitogen-Activated Protein Kinase Kinases/metabolism , Ribosomal Protein S6 Kinases, 90-kDa/metabolism , Virus Diseases/genetics , Virus Diseases/metabolism , Virus Replication/physiology , Viruses/pathogenicityABSTRACT
In the last few years, microRNA-mediated regulation has been shown to be important in viral infections. In fact, viral microRNAs can alter cell physiology and act on the immune system; moreover, cellular microRNAs can regulate the virus cycle, influencing positively or negatively viral replication. Accordingly, microRNAs can represent diagnostic and prognostic biomarkers of infectious processes and a promising approach for designing targeted therapies. In the past 18 months, the COVID-19 infection from SARS-CoV-2 has engaged many researchers in the search for diagnostic and prognostic markers and the development of therapies. Although some research suggests that the SARS-CoV-2 genome can produce microRNAs and that host microRNAs may be involved in the cellular response to the virus, to date, not enough evidence has been provided. In this paper, using a focused bioinformatic approach exploring the SARS-CoV-2 genome, we propose that SARS-CoV-2 is able to produce microRNAs sharing a strong sequence homology with the human ones and also that human microRNAs may target viral RNA regulating the virus life cycle inside human cells. Interestingly, all viral miRNA sequences and some human miRNA target sites are conserved in more recent SARS-CoV-2 variants of concern (VOCs). Even if experimental evidence will be needed, in silico analysis represents a valuable source of information useful to understand the sophisticated molecular mechanisms of disease and to sustain biomedical applications.
Subject(s)
MicroRNAs/genetics , SARS-CoV-2/genetics , Virus Replication/genetics , COVID-19/genetics , Computational Biology/methods , DNA Viruses/genetics , Gene Expression/genetics , Gene Expression Regulation, Viral/genetics , Genome, Viral/genetics , Host-Pathogen Interactions/genetics , RNA, Viral/genetics , Sequence HomologyABSTRACT
Among CD4+ T cells, T helper 17 (Th17) cells are particularly susceptible to HIV-1 infection and are depleted from mucosal sites, which causes damage to the gut barrier, resulting in a microbial translocation-induced systemic inflammation, a hallmark of disease progression. Furthermore, a proportion of latently infected Th17 cells persist long term in the gastrointestinal lymphatic tract where a low-level HIV-1 transcription is observed. This residual viremia contributes to chronic immune activation. Thus, Th17 cells are key players in HIV pathogenesis and viral persistence. It is, however, unclear why these cells are highly susceptible to HIV-1 infection. Th17 cell differentiation depends on the expression of the master transcriptional regulator RORC2, a retinoic acid-related nuclear hormone receptor that regulates specific transcriptional programs by binding to promoter/enhancer DNA. Here, we report that RORC2 is a key host cofactor for HIV replication in Th17 cells. We found that specific inhibitors that bind to the RORC2 ligand-binding domain reduced HIV replication in CD4+ T cells. The depletion of RORC2 inhibited HIV-1 infection, whereas its overexpression enhanced it. RORC2 was also found to promote HIV-1 gene expression by binding to the nuclear receptor responsive element in the HIV-1 long terminal repeats (LTR). In treated HIV-1 patients, RORC2+ CD4 T cells contained more proviral DNA than RORC2- cells. Pharmacological inhibition of RORC2 potently reduced HIV-1 outgrowth in CD4+ T cells from antiretroviral-treated patients. Altogether, these results provide an explanation as to why Th17 cells are highly susceptible to HIV-1 infection and suggest that RORC2 may be a cell-specific target for HIV-1 therapy.
Subject(s)
Gene Expression Regulation, Viral/genetics , HIV-1/growth & development , Nuclear Receptor Subfamily 1, Group F, Member 3/metabolism , Adult , CD4-Positive T-Lymphocytes/immunology , Cell Differentiation/immunology , Cytokines/metabolism , Female , Gene Expression/genetics , HIV Infections/immunology , HIV-1/genetics , Humans , Lymphocyte Activation , Male , Middle Aged , Nuclear Receptor Subfamily 1, Group F, Member 3/genetics , Primary Cell Culture , T-Lymphocyte Subsets/immunology , T-Lymphocytes, Regulatory/immunology , Th17 Cells/metabolism , Th17 Cells/physiology , Transcription Factors/metabolism , Viremia/immunology , Viremia/virology , Virus Replication/physiologyABSTRACT
Influenza is a respiratory virus that alone or in combination with secondary bacterial pathogens can contribute to the development of acute pneumonia in persons >65 years of age. Host innate immune antiviral signaling early in response to influenza is essential to inhibit early viral replication and guide the initiation of adaptive immune responses. Using young adult (3 months) and aged adult mice infected with mouse adapted H1N1 or H3N2, the results of our study illustrate dysregulated and/or diminished activation of key signaling pathways in aged lung contribute to increased lung inflammation and morbidity. Specifically, within the first seven days of infection, there were significant changes in genes associated with TLR and RIG-I signaling detected in aged murine lung in response to H1N1 or H3N2. Taken together, the results of our study expand our current understanding of age-associated changes in antiviral signaling in the lung.
Subject(s)
Influenza A Virus, H1N1 Subtype/genetics , Influenza A Virus, H3N2 Subtype/genetics , Influenza, Human/genetics , Pneumonia/genetics , A549 Cells , Animals , DEAD Box Protein 58/genetics , Disease Models, Animal , Gene Expression Regulation, Viral/genetics , Humans , Immunity, Innate/genetics , Influenza A Virus, H1N1 Subtype/pathogenicity , Influenza A Virus, H3N2 Subtype/pathogenicity , Influenza, Human/microbiology , Influenza, Human/virology , Lung/metabolism , Lung/microbiology , Lung/pathology , Mice , Orthomyxoviridae Infections/genetics , Orthomyxoviridae Infections/microbiology , Orthomyxoviridae Infections/virology , Pneumonia/microbiology , Pneumonia/virology , Toll-Like Receptors/genetics , Virus Replication/geneticsABSTRACT
SARS-CoV-2, the etiologic agent at the root of the ongoing COVID-19 pandemic, harbors a large RNA genome from which a tiered ensemble of subgenomic RNAs (sgRNAs) is generated. Comprehensive definition and investigation of these RNA products are important for understanding SARS-CoV-2 pathogenesis. This review summarizes the recent progress on SARS-CoV-2 sgRNA identification, characterization, and application as a viral replication marker. The significance of these findings and potential future research areas of interest are discussed.
Subject(s)
COVID-19/genetics , Gene Expression Regulation, Viral/genetics , SARS-CoV-2/genetics , Animals , COVID-19/metabolism , Gene Expression/genetics , Genome, Viral/genetics , Genomics/methods , Humans , Pandemics , RNA, Viral/genetics , RNA, Viral/metabolism , SARS-CoV-2/pathogenicity , Virus ReplicationABSTRACT
Polyomavirus JC (JCPyV) causes the demyelinating disease progressive multifocal leukoencephalopathy (PML). JCPyV infection is very common in childhood and, under conditions of severe immunosuppression, JCPyV may reactivate to cause PML. JC viral proteins expression is regulated by the JCPyV non-coding control region (NCCR), which contains binding sites for cellular transcriptional factors which regulate JCPyV transcription. Our earlier studies suggest that JCPyV reactivation occurs within glial cells due to cytokines such as TNF-α which stimulate viral gene expression. In this study, we examined interferon-α (IFNα) or ß (IFNß) which have a negative effect on JCPyV transcriptional regulation. We also showed that these interferons induce the endogenous liver inhibitory protein (LIP), an isoform of CAAT/enhancer binding protein beta (C/EBPß). Treatment of glial cell line with interferons increases the endogenous level of C/EBPß-LIP. Furthermore, we showed that the negative regulatory role of the interferons in JCPyV early and late transcription and viral replication is more pronounced in the presence of C/EBPß-LIP. Knockdown of C/EBPß-LIP by shRNA reverse the inhibitory effect on JCPyV viral replication. Therefore, IFNα and IFNß negatively regulate JCPyV through induction of C/EBPß-LIP, which together with other cellular transcriptional factors may control the balance between JCPyV latency and activation.
Subject(s)
Interferon-alpha/metabolism , Interferon-beta/metabolism , JC Virus/metabolism , CCAAT-Enhancer-Binding Protein-beta/genetics , CCAAT-Enhancer-Binding Protein-beta/metabolism , Cell Line, Tumor , DNA, Viral/genetics , Gene Expression/genetics , Gene Expression Regulation, Viral/genetics , Humans , Interferon-alpha/immunology , Interferon-beta/immunology , JC Virus/genetics , JC Virus/immunology , JC Virus/pathogenicity , Leukoencephalopathy, Progressive Multifocal/virology , Neuroglia , Protein Isoforms , Virus Replication/geneticsABSTRACT
Wnt/ß-catenin signaling is a highly conserved pathway related to a variety of biological processes in different cells. The regulation of replication of various viruses by Wnt/ß-catenin signaling pathway has been reported. However, the interaction between the Wnt/ß-catenin pathway and avian leukosis virus is unknown. In the present study, we investigated the effect of modulating the Wnt/ß-catenin pathway during avian leukosis virus subgroup J (ALV-J) infection. The activation of the Wnt/ß-catenin pathway by GSK-3 inhibitor increased ALV-J mRNA, viral protein expression, and virus production in CEF cells. This increase was suppressed by iCRT14, one of the specific inhibitors of the Wnt/ß-catenin signaling pathway. Moreover, treatment with iCRT14 reduced virus titer and viral gene expression significantly in CEF and LMH cells in a dose-dependent manner. Inhibition Wnt/ß-catenin signaling pathway by knockdown of ß-catenin reduced virus proliferation in CEF cells also. Collectively, these results suggested that the status of Wnt/ß-catenin signaling pathway modulated ALV-J replication. These studies extend our understanding of the role of Wnt/ß-catenin signaling pathway in ALV-J replication and make a new contribution to understanding the virus-host interactions of avian leukosis virus.
Subject(s)
Avian Leukosis Virus/metabolism , Virus Replication/physiology , Wnt Signaling Pathway/physiology , Animals , Avian Leukosis/virology , Cell Line , Chick Embryo , Chickens/virology , China , Gene Expression/genetics , Gene Expression Regulation, Viral/genetics , Glycogen Synthase Kinase 3/metabolism , Poultry Diseases/virology , Pyridines/pharmacology , Pyrroles/pharmacology , RNA, Messenger , Thiazolidinediones/pharmacologyABSTRACT
Vaccinia virus (VACV) is an enveloped DNA virus from the Orthopoxvirus family, various strains of which were used in the successful eradication campaign against smallpox. Both original and newer VACV-based replicating vaccines reveal a risk of serious complications in atopic individuals. VACV encodes various factors interfering with host immune responses at multiple levels. In atopic skin, the production of type I interferon is compromised, while VACV specifically inhibits the phosphorylation of the Interferon Regulatory Factor 3 (IRF-3) and expression of interferons. To overcome this block, we generated a recombinant VACV-expressing murine IRF-3 (WR-IRF3) and characterized its effects on virus growth, cytokine expression and apoptosis in tissue cultures and in spontaneously atopic Nc/Nga and control Balb/c mice. Further, we explored the induction of protective immune responses against a lethal dose of wild-type WR, the surrogate of smallpox. We demonstrate that the overexpression of IRF-3 by WR-IRF3 increases the expression of type I interferon, modulates the expression of several cytokines and induces superior protective immune responses against a lethal poxvirus challenge in both Nc/Nga and Balb/c mice. Additionally, the results may be informative for design of other virus-based vaccines or for therapy of different viral infections.