The immediate-early protein 1 of human herpesvirus 6B interacts with NBS1 and inhibits ATM signaling.

Viral infection often trigger an ATM serine/threonine kinase (ATM)-dependent DNA damage response in host cells that suppresses viral replication. Viruses evolved different strategies to counteract this antiviral surveillance system. Here, we report that human herpesvirus 6B (HHV-6B) infection causes genomic instability by suppressing ATM signaling in host cells. Expression of immediate-early protein 1 (IE1) phenocopies this phenotype and blocks homology-directed double-strand break repair. Mechanistically, IE1 interacts with NBS1, and inhibits ATM signaling through two distinct domains. HHV-6B seems to efficiently inhibit ATM signaling as further depletion of either NBS1 or ATM do not significantly boost viral replication in infected cells. Interestingly, viral integration of HHV-6B into the host's telomeres is not strictly dependent on NBS1, challenging current models where integration occurs through homology-directed repair. Given that spontaneous IE1 expression has been detected in cells of subjects with inherited chromosomally-integrated form of HHV-6B (iciHHV-6B), a condition associated with several health conditions, our results raise the possibility of a link between genomic instability and the development of iciHHV-6-associated diseases.

Mapping the Human Herpesvirus 6B transcriptome.

The "omics" revolution of recent years has simplified the study of RNA transcripts produced during viral infection and under specific defined conditions. In the quest to find new and differentially expressed transcripts during the course of human Herpesvirus 6B (HHV-6B) infection, we made use of large-scale RNA sequencing to analyze the HHV-6B transcriptome during productive infection of human Molt-3 T-cells. Analyses were performed at different time points following infection and specific inhibitors were used to classify the kinetic class of each open reading frame (ORF) reported in the annotated genome of HHV-6B Z29 strain. The initial search focussed on HHV-6B-specific reads matching new HHV-6B transcripts. Differential expression of new HHV-6B transcripts were observed in all samples analyzed. The presence of many of these new HHV-6B transcripts were confirmed by RT-PCR and Sanger sequencing. Many of these transcripts represented new splice variants of previously reported ORFs, including some transcripts that have yet to be defined. Overall, our work demonstrates the diversity and the complexity of the HHV-6B transcriptome.IMPORTANCERNA sequencing (RNA-seq) is an important tool for studying RNA transcripts, particularly during active viral infection. We made use of RNA-seq to study human Herpesvirus 6B (HHV-6B) infection. Using six different time points, we were able to identify the presence of differentially spliced genes at 6, 9, 12, 24, 48 and 72 hours post-infection. Determination of the RNA profiles in the presence of cycloheximide (CHX) or phosphonoacetic acid (PAA) also permitted identification of the kinetic class of each ORF described in the annotated GenBank file. We also identified new spliced transcripts for certain genes and evaluated their relative expression over time. These data and next-generation sequencing (NGS) of the viral DNA have led us to propose a new version of the HHV-6B Z29 GenBank annotated file, without changing ORF names in order to facilitate trace back and correlate our work with previous studies on HHV-6B.

The Promyelocytic Leukemia Protein facilitates human herpesvirus 6B chromosomal integration, immediate-early 1 protein multiSUMOylation and its localization at telomeres.

Human herpesvirus 6B (HHV-6B) is a betaherpesvirus capable of integrating its genome into the telomeres of host chromosomes. Until now, the cellular and/or viral proteins facilitating HHV-6B integration have remained elusive. Here we show that a cellular protein, the promyelocytic leukemia protein (PML) that forms nuclear bodies (PML-NBs), associates with the HHV-6B immediate early 1 (IE1) protein at telomeres. We report enhanced levels of SUMOylated IE1 in the presence of PML and have identified a putative SUMO Interacting Motif (SIM) within IE1, essential for its nuclear distribution, overall SUMOylation and association with PML to nuclear bodies. Furthermore, using PML knockout cell lines we made the original observation that PML is required for efficient HHV-6B integration into host chromosomes. Taken together, we could demonstrate that PML-NBs are important for IE1 multiSUMOylation and that PML plays an important role in HHV-6B integration into chromosomes, a strategy developed by this virus to maintain its genome in its host over long periods of time.

Role for the shelterin protein TRF2 in human herpesvirus 6A/B chromosomal integration.

Human herpesviruses 6A and 6B (HHV-6A/B) are unique among human herpesviruses in their ability to integrate their genome into host chromosomes. Viral integration occurs at the ends of chromosomes within the host telomeres. The ends of the HHV-6A/B genomes contain telomeric repeats that facilitate the integration process. Here, we report that productive infections are associated with a massive increase in telomeric sequences of viral origin. The majority of the viral telomeric signals can be detected within viral replication compartments (VRC) that contain the viral DNA processivity factor p41 and the viral immediate-early 2 (IE2) protein. Components of the shelterin protein complex present at telomeres, including TRF1 and TRF2 are also recruited to VRC during infection. Biochemical, immunofluorescence coupled with in situ hybridization and chromatin immunoprecipitation demonstrated the binding of TRF2 to the HHV-6A/B telomeric repeats. In addition, approximately 60% of the viral IE2 protein localize at cellular telomeres during infection. Transient knockdown of TRF2 resulted in greatly reduced (13%) localization of IE2 at cellular telomeres (p<0.0001). Lastly, TRF2 knockdown reduced HHV-6A/B integration frequency (p<0.05), while no effect was observed on the infection efficiency. Overall, our study identified that HHV-6A/B IE2 localizes to telomeres during infection and highlight the role of TRF2 in HHV-6A/B infection and chromosomal integration.

rs73185306 C/T Is Not a Predisposing Risk Factor for Inherited Chromosomally Integrated Human Herpesvirus 6A/B.

Approximately 1% of people worldwide carry a copy of the human herpesvirus 6A or 6B (HHV-6A/B) in every cell of their body. This condition is referred to as inherited chromosomally integrated HHV-6A/B (iciHHV-6A/B). The mechanisms leading to iciHHV-6A/B chromosomal integration are yet to be identified. A recent report suggested that the rs73185306 C/T single-nucleotide polymorphism (SNP) represents a favorable predisposing factor leading to HHV-6A/B integration. After genotype analysis of an independent cohort (N = 11 967), we report no association between the rs73185306 C/T SNP and HHV-6A/B chromosomal integration (odds ratio, 0.90 [95% confidence interval, .54-1.51]; P = .69).

Inherited Chromosomally Integrated Human Herpesvirus 6 Demonstrates Tissue-Specific RNA Expression In Vivo That Correlates with an Increased Antibody Immune Response.

Human herpesviruses 6A and 6B (HHV-6A and HHV-6B) are human viruses capable of chromosomal integration. Approximately 1% of the human population carries one copy of HHV-6A/B integrated into every cell in their body, referred to as inherited chromosomally integrated human herpesvirus 6A/B (iciHHV-6A/B). Whether iciHHV-6A/B is transcriptionally active in vivo and how it shapes the immunological response are still unclear. In this study, we screened DNA sequencing (DNA-seq) and transcriptome sequencing (RNA-seq) data for 650 individuals available through the Genotype-Tissue Expression (GTEx) project and identified 2 iciHHV-6A- and 4 iciHHV-6B-positive candidates. When corresponding tissue-specific gene expression signatures were analyzed, low levels HHV-6A/B gene expression was found across multiple tissues, with the highest levels of gene expression in the brain (specifically for HHV-6A), testis, esophagus, and adrenal gland. U90 and U100 were the most highly expressed HHV-6 genes in both iciHHV-6A- and iciHHV-6B-positive individuals. To assess whether tissue-specific gene expression from iciHHV-6A/B influences the immune response, a cohort of 15,498 subjects was screened and 85 iciHHV-6A/B+ subjects were identified. Plasma samples from iciHHV-6A/B+ and age- and sex-matched controls were analyzed for antibodies to control antigens (cytomegalovirus [CMV], Epstein-Barr virus [EBV], and influenza virus [FLU]) or HHV-6A/B antigens. Our results indicate that iciHHV-6A/B+ subjects have significantly more antibodies against the U90 gene product (IE1) than do non-iciHHV-6-positive individuals. Antibody responses against EBV and FLU antigens or HHV-6A/B gene products either not expressed or expressed at low levels, such as U47, U57, and U72, were identical between controls and iciHHV-6A/B+ subjects. CMV-seropositive individuals with iciHHV-6A/B+ have more antibodies against CMV pp150 than do CMV-seropositive controls. These results argue that spontaneous gene expression from integrated HHV-6A/B leads to an increase in antigenic burden that translates into a more robust HHV-6A/B-specific antibody response.IMPORTANCE HHV-6A and -6B are human herpesviruses that have the unique property of being able to integrate into the telomeric regions of human chromosomes. Approximately 1% of the world's population carries integrated HHV-6A/B genome in every cell of their body. Whether viral genes are transcriptionally active in these individuals is unclear. By taking advantage of a unique tissue-specific gene expression data set, we showed that the majority of tissues from iciHHV-6 individuals do not show HHV-6 gene expression. Brain and testes showed the highest tissue-specific expression of HHV-6 genes in two separate data sets. Two HHV-6 genes, U90 (immediate early 1 protein) and U100 (glycoproteins Q1 and Q2), were found to be selectively and consistently expressed across several human tissues. Expression of U90 translates into an increase in antigen-specific antibody response in iciHHV-6A/B+ subjects relative to controls. Future studies will be needed to determine the mechanism of gene expression, the effects of these genes on human gene transcription networks, and the pathophysiological impact of having increased viral protein expression in tissue in conjunction with increased antigen-specific antibody production.

Stabilization of Telomere G-Quadruplexes Interferes with Human Herpesvirus 6A Chromosomal Integration.

Human herpesviruses 6A and 6B (HHV-6A/B) can integrate their genomes into the telomeres of human chromosomes using a mechanism that remains poorly understood. To achieve a better understanding of the HHV-6A/B integration mechanism, we made use of BRACO-19, a compound that stabilizes G-quadruplex secondary structures and prevents telomere elongation by the telomerase complex. First, we analyzed the folding of telomeric sequences into G-quadruplex structures and their binding to BRACO-19 using G-quadruplex-specific antibodies and surface plasmon resonance. Circular dichroism studies indicate that BRACO-19 modifies the conformation and greatly stabilizes the G-quadruplexes formed in G-rich telomeric DNA. Subsequently we assessed the effects of BRACO-19 on the HHV-6A initial phase of infection. Our results indicate that BRACO-19 does not affect entry of HHV-6A DNA into cells. We next investigated if stabilization of G-quadruplexes by BRACO-19 affected HHV-6A's ability to integrate its genome into host chromosomes. Incubation of telomerase-expressing cells with BRACO-19, such as HeLa and MCF-7, caused a significant reduction in the HHV-6A integration frequency (P < 0.002); in contrast, BRACO-19 had no effect on HHV-6 integration frequency in U2OS cells that lack telomerase activity and elongate their telomeres through alternative lengthening mechanisms. Our data suggest that the fluidity of telomeres is important for efficient chromosomal integration of HHV-6A and that interference with telomerase activity negatively affects the generation of cellular clones containing integrated HHV-6A.IMPORTANCE HHV-6A/B can integrate their genomes into the telomeres of infected cells. Telomeres consist of repeated hexanucleotides (TTAGGG) of various lengths (up to several kilobases) and end with a single-stranded 3' extension. To avoid recognition and induce a DNA damage response, the single-stranded overhang folds back on itself and forms a telomeric loop (T-loop) or adopts a tertiary structure, referred to as a G-quadruplex. In the current study, we have examined the effects of a G-quadruplex binding and stabilizing agent, BRACO-19, on HHV-6A chromosomal integration. By stabilizing G-quadruplex structures, BRACO-19 affects the ability of the telomerase complex to elongate telomeres. Our results indicate that BRACO-19 reduces the number of clones harboring integrated HHV-6A. This study is the first of its kind and suggests that telomerase activity is essential to restore a functional telomere of adequate length following HHV-6A integration.

Cell Culture Systems To Study Human Herpesvirus 6A/B Chromosomal Integration.

Human herpesviruses 6A/B (HHV-6A/B) can integrate their viral genomes in the telomeres of human chromosomes. The viral and cellular factors contributing to HHV-6A/B integration remain largely unknown, mostly due to the lack of efficient and reproducible cell culture models to study HHV-6A/B integration. In this study, we characterized the HHV-6A/B integration efficiencies in several human cell lines using two different approaches. First, after a short-term infection (5 h), cells were processed for single-cell cloning and analyzed for chromosomally integrated HHV-6A/B (ciHHV-6A/B). Second, cells were infected with HHV-6A/B and allowed to grow in bulk for 4 weeks or longer and then analyzed for the presence of ciHHV-6. Using quantitative PCR (qPCR), droplet digital PCR, and fluorescent in situ hybridization, we could demonstrate that HHV-6A/B integrated in most human cell lines tested, including telomerase-positive (HeLa, MCF-7, HCT-116, and HEK293T) and telomerase-negative cell lines (U2OS and GM847). Our results also indicate that inhibition of DNA replication, using phosphonoacetic acid, did not affect HHV-6A/B integration. Certain clones harboring ciHHV-6A/B spontaneously express viral genes and proteins. Treatment of cells with phorbol ester or histone deacetylase inhibitors triggered the expression of many viral genes, including U39, U90, and U100, without the production of infectious virus, suggesting that the tested stimuli were not sufficient to trigger full reactivation. In summary, both integration models yielded comparable results and should enable the identification of viral and cellular factors contributing to HHV-6A/B integration and the screening of drugs influencing viral gene expression, as well as the release of infectious HHV-6A/B from the integrated state.IMPORTANCE The analysis and understanding of HHV-6A/B genome integration into host DNA is currently limited due to the lack of reproducible and efficient viral integration systems. In the present study, we describe two quantitative cell culture viral integration systems. These systems can be used to define cellular and viral factors that play a role in HHV-6A/B integration. Furthermore, these systems will allow us to decipher the conditions resulting in virus gene expression and excision of the integrated viral genome resulting in reactivation.

The Telomeric Repeats of Human Herpesvirus 6A (HHV-6A) Are Required for Efficient Virus Integration.

Human herpesvirus 6A (HHV-6A) and 6B (HHV-6B) are ubiquitous betaherpesviruses that infects humans within the first years of life and establishes latency in various cell types. Both viruses can integrate their genomes into telomeres of host chromosomes in latently infected cells. The molecular mechanism of viral integration remains elusive. Intriguingly, HHV-6A, HHV-6B and several other herpesviruses harbor arrays of telomeric repeats (TMR) identical to human telomere sequences at the ends of their genomes. The HHV-6A and HHV-6B genomes harbor two TMR arrays, the perfect TMR (pTMR) and the imperfect TMR (impTMR). To determine if the TMR are involved in virus integration, we deleted both pTMR and impTMR in the HHV-6A genome. Upon reconstitution, the TMR mutant virus replicated comparable to wild type (wt) virus, indicating that the TMR are not essential for HHV-6A replication. To assess the integration properties of the recombinant viruses, we established an in vitro integration system that allows assessment of integration efficiency and genome maintenance in latently infected cells. Integration of HHV-6A was severely impaired in the absence of the TMR and the virus genome was lost rapidly, suggesting that integration is crucial for the maintenance of the virus genome. Individual deletion of the pTMR and impTMR revealed that the pTMR play the major role in HHV-6A integration, whereas the impTMR only make a minor contribution, allowing us to establish a model for HHV-6A integration. Taken together, our data shows that the HHV-6A TMR are dispensable for virus replication, but are crucial for integration and maintenance of the virus genome in latently infected cells.

Inherited chromosomally integrated human herpesvirus 6 as a predisposing risk factor for the development of angina pectoris.

Inherited chromosomally integrated human herpesvirus-6 (iciHHV-6) results in the germ-line transmission of the HHV-6 genome. Every somatic cell of iciHHV-6+ individuals contains the HHV-6 genome integrated in the telomere of chromosomes. Whether having iciHHV-6 predisposes humans to diseases remains undefined. DNA from 19,597 participants between 40 and 69 years of age were analyzed by quantitative PCR (qPCR) for the presence of iciHHV-6. Telomere lengths were determined by qPCR. Medical records, hematological, biochemical, and anthropometric measurements and telomere lengths were compared between iciHHV-6+ and iciHHV-6- subjects. The prevalence of iciHHV-6 was 0.58%. Two-way ANOVA with a Holm-Bonferroni correction was used to determine the effects of iciHHV6, sex, and their interaction on continuous outcomes. Two-way logistic regression with a Holm-Bonferroni correction was used to determine the effects of iciHHV6, sex, and their interaction on disease prevalence. Of 50 diseases monitored, a single one, angina pectoris, is significantly elevated (3.3×) in iciHHV-6+ individuals relative to iciHHV-6- subjects (P = 0.017; 95% CI, 1.73-6.35). When adjusted for potential confounding factors (age, body mass index, percent body fat, and systolic blood pressure), the prevalence of angina remained three times greater in iciHHV-6+ subjects (P = 0.015; 95%CI, 1.23-7.15). Analyses of telomere lengths between iciHHV-6- without angina, iciHHV-6- with angina, and iciHHV-6+ with angina indicate that iciHHV-6+ with angina have shorter telomeres than age-matched iciHHV-6- subjects (P = 0.006). Our study represents, to our knowledge, the first large-scale analysis of disease association with iciHHV-6. Our results are consistent with iciHHV-6 representing a risk factor for the development of angina.

Characterization of human herpesvirus 6A/B U94 as ATPase, helicase, exonuclease and DNA-binding proteins.

Human herpesvirus-6A (HHV-6A) and HHV-6B integrate their genomes into the telomeres of human chromosomes, however, the mechanisms leading to integration remain unknown. HHV-6A/B encode a protein that has been proposed to be involved in integration termed U94, an ortholog of adeno-associated virus type 2 (AAV-2) Rep68 integrase. In this report, we addressed whether purified recombinant maltose-binding protein (MBP)-U94 fusion proteins of HHV-6A/B possess biological functions compatible with viral integration. We could demonstrate that MBP-U94 efficiently binds both dsDNA and ssDNA containing telomeric repeats using gel shift assay and surface plasmon resonance. MBP-U94 is also able to hydrolyze adenosine triphosphate (ATP) to ADP, providing the energy for further catalytic activities. In addition, U94 displays a 3' to 5' exonuclease activity on dsDNA with a preference for 3'-recessed ends. Once the DNA strand reaches 8-10 nt in length, the enzyme dissociates it from the complementary strand. Lastly, MBP-U94 compromises the integrity of a synthetic telomeric D-loop through exonuclease attack at the 3' end of the invading strand. The preferential DNA binding of MBP-U94 to telomeric sequences, its ability to hydrolyze ATP and its exonuclease/helicase activities suggest that U94 possesses all functions required for HHV-6A/B chromosomal integration.

The putative U94 integrase is dispensable for human herpesvirus 6 (HHV-6) chromosomal integration.

Human herpesvirus 6 (HHV-6) can integrate its genome into the telomeres of host chromosomes and is present in the germline of about 1 % of the human population. HHV-6 encodes a putative integrase U94 that possesses all molecular functions required for recombination including DNA-binding, ATPase, helicase and nuclease activity, and was hypothesized by many researchers to facilitate integration ever since the discovery of HHV-6 integration. However, analysis of U94 in the virus context has been hampered by the lack of reverse-genetic systems and efficient integration assays. Here, we addressed the role of U94 and the cellular recombinase Rad51 in HHV-6 integration. Surprisingly, we could demonstrate that HHV-6 efficiently integrated in the absence of U94 using a new quantitative integration assay. Additional inhibition of the cellular recombinase Rad51 had only a minor impact on virus integration. Our results shed light on this complex integration mechanism that includes factors beyond U94 and Rad51.

Human herpesvirus 6B immediate-early I protein contains functional HLA-A*02, HLA-A*03, and HLA-B*07 class I restricted CD8(+) T-cell epitopes.

Human herpesvirus 6B (HHV-6B) is a ubiquitous pathogen with frequent reactivation observed in immunocompromised patients such as BM transplant (BMT) recipients. Adoptive immunotherapy is a promising therapeutic avenue for the treatment of opportunistic infections, including herpesviruses. While T-cell immunotherapy can successfully control CMV and EBV reactivations in BMT recipients, such therapy is not available for HHV-6 infections, in part due to a lack of identified protective CD8(+) T-cell epitopes. Our goal was to identify CD8(+) T-cell viral epitopes derived from the HHV-6B immediate-early protein I and presented by common human leukocyte Ag (HLA) class I alleles including HLA-A*02, HLA-A*03, and HLA-B*07. These epitopes were functionally tested for their ability to induce CD8(+) T-cell expansion and kill HHV-6-infected autologous cells. Cross-reactivity of specific HHV-6B-expanded T cells against HHV-6A-infected cells was also confirmed for a conserved epitope presented by HLA-A*02 molecule. Our findings will help push forward the field of adoptive immunotherapy for the treatment and/or the prevention of HHV-6 reactivation in BMT recipients.

Inhibition of breast cancer cell proliferation through disturbance of the calcineurin/NFAT pathway by human herpesvirus 6B U54 tegument protein.

Nuclear factor of activated T cell (NFAT) proteins are key regulators involved in multiple physiological mechanisms, such as immune response and cell growth. The capacity of selective calcineurin/NFAT inhibitors to decrease NFAT-dependent cancer cell progression, particularly in breast cancer, has already been demonstrated. In this study, we report a role for the human herpesvirus 6B (HHV-6B) U54 tegument protein in inhibiting MCF-7 breast cancer cell proliferation by inhibiting NFAT activation.

Inhibition of interleukin-2 gene expression by human herpesvirus 6B U54 tegument protein.

Human herpesvirus 6B (HHV-6B) is a ubiquitous pathogen causing lifelong infections in approximately 95% of humans worldwide. To persist within its host, HHV-6B has developed several immune evasion mechanisms, such as latency, during which minimal proteins are expressed, and the ability to disturb innate and adaptive immune responses. The primary cellular targets of HHV-6B are CD4(+) T cells. Previous studies by Flamand et al. (L. Flamand, J. Gosselin, I. Stefanescu, D. Ablashi, and J. Menezes, Blood 85:1263-1271, 1995) reported on the capacity of HHV-6A as well as UV-irradiated HHV-6A to inhibit interleukin-2 (IL-2) synthesis in CD4(+) lymphocytes, suggesting that viral structural components could be responsible for this effect. In the present study, we identified the HHV-6B U54 tegument protein (U54) as being capable of inhibiting IL-2 expression. U54 binds the calcineurin (CaN) phosphatase enzyme, causing improper dephosphorylation and nuclear translocation of NFAT (nuclear factor of activated T cells) proteins, resulting in suboptimal IL-2 gene transcription. The U54 GISIT motif (amino acids 293 to 297), analogous to the NFAT PXIXIT motif, contributed to the inhibition of NFAT activation. IMPORTANCE Human herpesvirus 6A (HHV-6A) and HHV-6B are associated with an increasing number of pathologies. These viruses have developed strategies to avoid the immune response allowing them to persist in the host. Several studies have illustrated mechanisms by which HHV-6A and HHV-6B are able to disrupt host defenses (reviewed in L. Dagna, J. C. Pritchett, and P. Lusso, Future Virol. 8:273-287, 2013, doi:10.2217/fvl.13.7). Previous work informed us that HHV-6A is able to suppress synthesis of interleukin-2 (IL-2), a key immune growth factor essential for adequate T lymphocyte proliferation and expansion. We obtained evidence that HHV-6B also inhibits IL-2 gene expression and identified the mechanisms by which it does so. Our work led us to the identification of U54, a virion-associated tegument protein, as being responsible for suppression of IL-2. Consequently, we have identified HHV-6B U54 protein as playing a role in immune evasion. These results further contribute to our understanding of HHV-6 interactions with its human host and the efforts deployed to ensure its long-term persistence.

Sequence analysis of transplacentally acquired human herpesvirus 6 DNA is consistent with transmission of a chromosomally integrated reactivated virus.

The majority of human herpesvirus 6 (HHV-6) congenital infections (86%) originate from germ line transmission of chromosomally integrated HHV-6 (ciHHV-6). To determine whether transplacentally acquired HHV-6 could derive from the transmission of reactivated maternal ciHHV-6, we identified mother-infant pairs in which infants had proven transplacentally acquired HHV-6 and mothers had documented ciHHV-6, and we sequenced and compared the HHV-6 gB gene sequences for each pair. Our data indicate that the gB gene sequence found in each cord blood specimen was identical to that of the corresponding mother but divergent from that of other known HHV-6 isolates. These results are consistent with transplacentally acquired HHV-6 originating from the transmission of reactivated ciHHV-6.

SARS-CoV-2 rapidly evolves lineage-specific phenotypic differences when passaged repeatedly in immune-naïve mice.

The persistence of SARS-CoV-2 despite the development of vaccines and a degree of herd immunity is partly due to viral evolution reducing vaccine and treatment efficacy. Serial infections of wild-type (WT) SARS-CoV-2 in Balb/c mice yield mouse-adapted strains with greater infectivity and mortality. We investigate if passaging unmodified B.1.351 (Beta) and B.1.617.2 (Delta) 20 times in K18-ACE2 mice, expressing the human ACE2 receptor, in a BSL-3 laboratory without selective pressures, drives human health-relevant evolution and if evolution is lineage-dependent. Late-passage virus causes more severe disease, at organism and lung tissue scales, with late-passage Delta demonstrating antibody resistance and interferon suppression. This resistance co-occurs with a de novo spike S371F mutation, linked with both traits. S371F, an Omicron-characteristic mutation, is co-inherited at times with spike E1182G per Nanopore sequencing, existing in different within-sample viral variants at others. Both S371F and E1182G are linked to mammalian GOLGA7 and ZDHHC5 interactions, which mediate viral-cell entry and antiviral response. This study demonstrates SARS-CoV-2's tendency to evolve with phenotypic consequences, its evolution varying by lineage, and suggests non-dominant quasi-species contribution.

Divergent susceptibilities of human herpesvirus 6 variants to type I interferons.

Two distinct human herpesvirus 6 (HHV-6) variants infect humans. HHV-6B is the etiologic agent of roseola and is associated with life-threatening neurological diseases, such as encephalitis, as well as organ transplant failure. The epidemiology and disease association for HHV-6A remain ill-defined. Specific anti-HHV-6 drugs do not exist and classic antiherpes drugs have secondary effects that are often problematic for transplant patients. Clinical trials using IFN were also performed with inconclusive results. We investigated the efficacy of type I IFN (alpha/beta) in controlling HHV-6 infection. We report that cells infected with laboratory strains and primary isolates of HHV-6B are resistant to IFN-alpha/beta antiviral actions as a result of improper IFN-stimulated gene (ISGs) expression. In contrast, HHV-6A-infected cells were responsive to IFN-alpha/beta with pronounced antiviral effects observed. Type II IFN (gamma)-signaling was unaltered in cells infected by either variant. The HHV-6B immediate-early 1 (IE1) physically interacts with STAT2 and sequestrates it to the nucleus. As a consequence, IE1B prevents the binding of ISGF3 to IFN-responsive gene promoters, resulting in ISG silencing. In comparison, HHV-6A and its associated IE1 protein displayed marginal ISG inhibitory activity relative to HHV-6B. The ISG inhibitory domain of IE1B mapped to a 41 amino acid region absent from IE1A. Transfer of this IE1B region resulted in a gain of function that conferred ISG inhibitory activity to IE1A. Our work is unique in demonstrating type I IFN signaling defects in HHV-6B-infected cells and highlights a major biological difference between HHV-6 variants.

SARS-CoV-2 Nsp2 Contributes to Inflammation by Activating NF-κB.

COVID-19 is associated with robust inflammation and partially impaired antiviral responses. The modulation of inflammatory gene expression by SARS-CoV-2 is not completely understood. In this study, we characterized the inflammatory and antiviral responses mounted during SARS-CoV-2 infection. K18-hACE2 mice were infected with a Wuhan-like strain of SARS-CoV-2, and the transcriptional and translational expression interferons (IFNs), cytokines, and chemokines were analyzed in mouse lung homogenates. Our results show that the infection of mice with SARS-CoV-2 induces the expression of several pro-inflammatory CC and CXC chemokines activated through NF-κB but weakly IL1ß and IL18 whose expression are more characteristic of inflammasome formation. We also observed the downregulation of several inflammasome effectors. The modulation of innate response, following expressions of non-structural protein 2 (Nsp2) and SARS-CoV-2 infection, was assessed by measuring IFNß expression and NF-κB modulation in human pulmonary cells. A robust activation of the NF-κB p65 subunit was induced following the infection of human cells with the corresponding NF-κB-driven inflammatory signature. We identified that Nsp2 expression induced the activation of the IFNß promoter through its NF-κB regulatory domain as well as activation of p65 subunit phosphorylation. The present studies suggest that SARS-CoV-2 skews the antiviral response in favor of an NF-κB-driven inflammatory response, a hallmark of acute COVID-19 and for which Nsp2 should be considered an important contributor.

Extra domain A of fibronectin primes leukotriene biosynthesis and stimulates neutrophil migration through activation of Toll-like receptor 4.

OBJECTIVE: There is increasing evidence of a role for Toll-like receptors (TLRs) in inflammatory arthritis. The extra domain A (ED-A)-containing isoform of fibronectin is generated under pathologic conditions such as rheumatoid arthritis, and ED-A has been identified as an endogenous TLR-4 ligand. Leukotriene B4 (LTB4) and polymorphonuclear neutrophils (PMNs) play a critical role in murine models of inflammatory arthritis. The aim of this study was therefore to investigate the putative effects of ED-A on leukotriene biosynthesis and PMN migration through TLR signaling. METHODS: The effect of recombinant human ED-A (rhED-A) on leukotriene biosynthesis was evaluated in isolated human blood PMNs and monocytes by high-performance liquid chromatography. The capacity of rhED-A to stimulate PMN migration was evaluated using a transendothelial/matrix migration assay in vitro and the mouse air-pouch model in vivo. RESULTS: Recombinant human ED-A efficiently primed the biosynthesis of LTB4 in PMN and monocyte suspensions. This priming effect was dependent on TLR-4 activation, since the TLR-4-signaling inhibitor CLI-095 completely blocked the effect of rhED-A but not that of other TLR ligands (R-848, Pam2 CSK4) or cytokines. Moreover, rhED-A stimulated transendothelial migration of PMNs in vitro, which was inhibited by 50-60% with the LTB4 receptor 1 (BLT1) antagonist CP105,696 or the cytosolic phospholipase A2 α inhibitor pyrrophenone. In vivo, rhED-A induced a significant PMN recruitment into the air pouch of C3H/HeOuJ mice (expressing functional TLR-4), but not in C3H/HeJ mice (expressing nonsignaling TLR-4). CONCLUSION: These results demonstrate the ability of rhED-A to promote LTB4 biosynthesis and PMN migration through TLR-4 activation, thus providing new insights on TLR-dependent mechanisms of regulation of LTB4 biosynthesis and PMN infiltration in inflammatory joint diseases.