Update on human herpesvirus 7 pathogenesis and clinical aspects as a roadmap for future research.

Human herpesvirus 7 (HHV-7) is a common virus that is associated with various human diseases including febrile syndromes, dermatological lesions, neurological defects, and transplant complications. Still, HHV-7 remains one of the least studied members of all human betaherpesviruses. In addition, HHV-7-related research is mostly confined to case reports, while in vitro or in vivo studies unraveling basic virology, transmission mechanisms, and viral pathogenesis are sparse. Here, we discuss HHV-7-related literature linking clinical syndromes to the viral life cycle, epidemiology, and viral immunopathogenesis. Based on our review, we propose a hypothetical model of HHV-7 pathogenesis inside its host. Furthermore, we identify important knowledge gaps and recommendations for future research to better understand HHV-7 diseases and improve therapeutic interventions.

Alzheimer's disease and herpes viruses: Current events and perspectives.

Alzheimer's disease (AD) is a real and current scientific and societal challenge. Alzheimer's disease is characterised by a neurodegenerative neuroinflammatory process, but the etiopathogenetic mechanisms are still unclear. The possible infectious aetiology and potential involvement of Herpes viruses as triggers for the formation of extracellular deposits of amyloid beta (Aß) peptide (amyloid plaques) and intraneuronal aggregates of hyperphosphorylated and misfold could be a possible explanation. In fact, the possible genetic interference of Herpes viruses with the genome of the host neuronal cell or the stimulation of the infection to a continuous immune response with a consequent chronic inflammation could constitute those mechanisms underlying the development of AD, with possible implications in the understanding and management of the disease. Herpes viruses could be significantly involved in the pathogenesis of AD and in particular, their ability to reactivate in particular conditions such as immunocompromise and immunosenescence, could explain the neurological damage characteristic of AD. Our review aims to evaluate the state of the art of knowledge and perspectives regarding the potential relationship between Herpes viruses and AD, in order to be able to identify the possible etiopathogenetic mechanisms and the possible therapeutic implications.

Characterization of the HHV-6B U20 Immunoevasin.

Roseoloviruses (human herpesvirus 6A [HHV-6A], -6B, and -7) infect >90% of the human population during early childhood and are thought to remain latent or persistent throughout the life of the host. As such, these viruses are among the most pervasive and stealthy of all viruses; they must necessarily excel at escaping immune detection throughout the life of the host, and yet, very little is known about how these viruses so successfully escape host defenses. Here, we characterize the expression, trafficking, and posttranslational modifications of the HHV6B U20 gene product, which is encoded within a block of genes unique to the roseoloviruses. HHV-6B U20 trafficked slowly through the secretory system, receiving several posttranslational modifications to its N-linked glycans, indicative of surface-expressed glycoproteins, and eventually reaching the cell surface before being internalized. Interestingly, U20 is also phosphorylated on at least one Ser, Thr, or Tyr residue. These results provide a framework to understand the role(s) of U20 in evading host defenses. IMPORTANCE The roseolovirus U20 proteins are virus-encoded integral membrane glycoproteins possessing class I major histocompatibility complex (MHC)-like folds. Surprisingly, although U20 proteins from HHV-6A and -6B share 92% identity, recent studies ascribe different functions to HHV6A U20 and HHV6B U20. HHV6A U20 was shown to downregulate NKG2D ligands, while HHV6B U20 was shown to inhibit tumor necrosis factor alpha (TNF-α)-induced apoptosis during nonproductive infection with HHV6B (E. Kofod-Olsen, K. Ross-Hansen, M. H. Schleimann, D. K. Jensen, et al., J Virol 86:11483-11492, 2012, https://doi.org/10.1128/jvi.00847-12; A. E. Chaouat, B. Seliger, O. Mandelboim, D. Schmiedel, Front Immunol 12:714799, 2021, https://doi.org/10.3389/fimmu.2021.714799). Here, we have performed cell biological and biochemical characterization of the trafficking, glycosylation, and posttranslational modifications occurring on HHV6B U20.

Hybrid capture shotgun sequencing detected unexpected viruses in the cerebrospinal fluid of children with acute meningitis and encephalitis.

PURPOSE: Investigation of undiagnosed cases of infectious neurological diseases, especially in the paediatric population, remains a challenge. This study aimed to enhance understanding of viruses in CSF from children with clinically diagnosed meningitis and/or encephalitis (M/ME) of unknown aetiology using shotgun sequencing enhanced by hybrid capture (HCSS). METHODS: A single-centre prospective study was conducted at Sant Joan de Déu University Hospital, Barcelona, involving 40 M/ME episodes of unknown aetiology, recruited from May 2021 to July 2022. All participants had previously tested negative with the FilmArray Meningitis/Encephalitis Panel. HCSS was used to detect viral nucleic acid in the patients' CSF. Sequencing was performed on Illumina NovaSeq platform. Raw sequence data were analysed using CZ ID metagenomics and PikaVirus bioinformatics pipelines. RESULTS: Forty episodes of M/ME of unknown aetiology in 39 children were analysed by HCSS. A significant viral detection in 30 CSF samples was obtained, including six parechovirus A, three enterovirus ACD, four polyomavirus 5, three HHV-7, two BKV, one HSV-1, one VZV, two CMV, one EBV, one influenza A virus, one rhinovirus, and 13 HERV-K113 detections. Of these, one sample with BKV, three with HHV-7, one with EBV, and all HERV-K113 were confirmed by specific PCR. The requirement for Intensive Care Unit admission was associated with HCSS detections. CONCLUSION: This study highlights HCSS as a powerful tool for the investigation of undiagnosed cases of M/ME. Data generated must be carefully analysed and reasonable precautions must be taken before establishing association of clinical features with unexpected or novel virus findings.

The persistent viral infections in the development and severity of myalgic encephalomyelitis/chronic fatigue syndrome.

BACKGROUND: Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a multifactorial disease with an unexplained aetiology in which viral infections are possible trigger factors. The aim of this study was to determine the involvement of human herpesvirus (HHV)-6A/B, HHV-7, and parvovirus B19 (B19V) in the etiopathogenesis of ME/CFS. METHODS: 200 patients with clinically diagnosed ME/CFS and 150 apparently healthy individuals were enrolled in this study. Single-round, nested, and quantitative real-time polymerase chain reactions (PCR) were used to detect the presence and load of HHV-6A/B, HHV-7, and B19V. HHV-6A and HHV-6B were distinguished by PCR and restriction analysis. Immunoenzymatic assays were applied to estimate the presence of virus-specific antibodies and the level of cytokines. RESULTS: HHV-6A/B, HHV-7, and B19V specific antibodies were detected among patients and healthy individuals in 92.1% and 76.7%, 84.6% and 93.8%, and 78% and 67.4% of cases. HHV-6B had 99% of HHV-6 positive patients. Latent HHV-6A/B, HHV-7, and B19V infection/co-infection was observed in 51.5% of the patients and 76.7% of the healthy individuals, whereas active-45% of the ME/CFS patients and 8.7% of healthy individuals. HHV-6A/B load in patients with a persistent infection/co-infection in a latent and active phase was 262 and 653.2 copies/106 cells, whereas HHV-7 load was 166.5 and 248.5 copies/106 cells, and B19V-96.8 and 250.8 copies/106 cells, respectively. ME/CFS patients with persistent infection in an active phase had a higher level of pro-inflammatory cytokines (interleukin(IL)-6, tumor necrosis factor-alpha(TNF-α) and IL-12) and anti-inflammatory (IL-10) than with a persistent infection in a latent phase. A significant difference was revealed in the levels of TNF-α, IL-12, and IL-10 among the patient groups without infection, with latent infection/co-infection, active single, double and triple co-infection. The levels of TNF-α, IL-12, and IL-10 are significantly higher in patients with severe compared with a moderate course of ME/CFS. CONCLUSIONS: Significantly more persistent HHV-6A/B, HHV-7, and B19V infection/co-infection in an active phase with a higher viral load and elevated levels of pro- and anti-inflammatory cytokines among patients with ME/CFS than healthy individuals indicate the importance of these infections/co-infections in ME/CFS development. The presence of these infections/co-infections influences the ME/CFS clinical course severity.

Frequency evaluation and molecular characterization of HHV-6 and HHV-7 among children under 5 years with fever and skin rash.

Skin rash is one of the most common complications during childhood. Viral agents play an essential role in the development of such symptoms. Present study aims to determine the prevalence and genetic variability of Human Herpesvirus 6 and 7 (HHV-6 and HHV-7) infections and their subtypes in children under 5 years of age with skin rash and negative for rubella and measles. We used serum and throat swap samples from 196 children with skin rash and fever. ELISA and IFA tests were performed to detect antibodies against HHV6/7. Sequencing was performed using Sanger sequencing, and BioEdit and MEGA10 software were used for sequence analysis. According to the results, 66% and 40% of cases were positive for HHV-6 IgM and HHV-7 IgM, respectively. According to the molecular analysis, HHV-6 Nested-PCR was positive in 18% of cases, however, HHV-7 Nested-PCR was positive in 7.7% of cases. On the other hand, HHV-6 IgG and HHV-7 IgG were positive in 91% and 55% of study cases, respectively. For HHV-6, we found some genetic variabilities resulting in antigenic changes compared to reference strains. HHV-7 isolates showed no genetic differentiation and had a stable gene sequence. Based on the results, the detection of some cases of HHV6/7 primary infection and the presence of specific symptoms of roseola in the study population needs continuous evaluation of HHV6/7 frequency and distribution, also genetic variabilities of HHV6. This can pave the way for investigating HHV6 immune evasion and vaccine research and studying the relationship between viral genetic variations and other factors like disease severity. Furthermore, it is necessary to determine the relation between HHV6 genetic changes and latent infection to be considered in possible future vaccines and antiviral drug development.

Meningitis associated with HHV-7 in an Iranian immunocompetent adolescent girl.

There is limited literature regarding meningitis associated with HHV-7. This article reports an immunocompetent adolescent girl who developed fever, headache, and meningism which CSF molecular analysis with PCR was positive only for HHV-7. Interestingly, persistent cavum septum pellucidum and cavum vergae were observed on brain magnetic resonance imaging. The patient received antibiotics, dexamethasone, and acyclovir and then she gained full recovery. HHV-7 is a rare and yet possible pathogen in patients with meningitis, and this is the first described case report from Iran.

Health impact of seven herpesviruses on (pre)diabetes incidence and HbA1c: results from the KORA cohort.

AIMS/HYPOTHESIS: The prevalence of type 2 diabetes is increasing worldwide, and previous studies have suggested that it is higher in individuals who are seropositive for herpesviruses. This study examines the prospective association of herpesviruses with (pre)diabetes to evaluate their potential role in diabetes aetiology. METHODS: Two follow-up examinations of the German population-based KORA cohort (F4 and FF4) were used to identify participants with normal glucose tolerance at baseline, thus being at risk for (pre)diabetes (n = 1257). All participants had repeated OGTTs and antibody measurements for herpes simplex virus (HSV) 1 and 2, varicella-zoster virus, Epstein-Barr virus, cytomegalovirus (CMV) and human herpesvirus 6 and 7. Regression models were used to evaluate the association between serostatus with (pre)diabetes incidence after a 7 year follow-up and HbA1c. RESULTS: HSV2 and CMV were associated with (pre)diabetes incidence after adjustment for sex, age, BMI, education, smoking, physical activity, parental diabetes, hypertension, lipid levels, insulin resistance and fasting glucose. Seropositivity of both viruses was also cross-sectionally associated with higher HbA1c at baseline, with the association of HSV2 being independent of confounders, including the prevalence of (pre)diabetes itself. While seropositivity for multiple herpesviruses was associated with a higher incidence of (pre)diabetes, this association was not independent of confounders. CONCLUSIONS/INTERPRETATION: The associations of HSV2 and CMV serostatus with (pre)diabetes incidence indicate that these herpesviruses may contribute to the development of impaired glucose metabolism. Our results highlight the link between viral infection and (pre)diabetes, and the need for more research evaluating viral prevention strategies.

The Roseoloviruses Downregulate the Protein Tyrosine Phosphatase PTPRC (CD45).

Like all herpesviruses, the roseoloviruses (HHV6A, -6B, and -7) establish lifelong infection within their host, requiring these viruses to evade host antiviral responses. One common host-evasion strategy is the downregulation of host-encoded, surface-expressed glycoproteins. Roseoloviruses have been shown to evade the host immune response by downregulating NK-activating ligands, class I MHC, and the TCR/CD3 complex. To more globally identify glycoproteins that are differentially expressed on the surface of HHV6A-infected cells, we performed cell surface capture of N-linked glycoproteins present on the surface of T cells infected with HHV6A, and compared these to proteins present on the surface of uninfected T cells. We found that the protein tyrosine phosphatase CD45 is downregulated in T cells infected with HHV6A. We also demonstrated that CD45 is similarly downregulated in cells infected with HHV7. CD45 is essential for signaling through the T cell receptor and, as such, is necessary for developing a fully functional immune response. Interestingly, the closely related betaherpesviruses human cytomegalovirus (HCMV) and murine cytomegalovirus (MCMV) have also separately evolved unique mechanisms to target CD45. While HCMV and MCMV target CD45 signaling and trafficking, HHV6A acts to downregulate CD45 transcripts. IMPORTANCE Human herpesviruses-6 and -7 infect essentially 100% of the world's population before the age of 5 and then remain latent or persistent in their host throughout life. As such, these viruses are among the most pervasive and stealthy of all viruses. Host immune cells rely on the presence of surface-expressed proteins to identify and target virus-infected cells. Here, we investigated the changes that occur to proteins expressed on the cell surface of T cells after infection with human herpesvirus-6A. We discovered that HHV-6A infection results in a reduction of CD45 on the surface of infected T cells and impaired activation in response to T cell receptor stimulation.

Α case of seronegative autoimmune encephalitis associated with human herpesvirus-7 (HHV-7).

In the last 10 years, an increased number of patients presenting with acute encephalitis is being observed, a finding that is attributed to autoimmune mechanisms. Despite the fact that autoantibodies usually target the neuronal cell surface or synaptic proteins in the central nervous system (CNS), in many cases these remain undetectable, constituting a future diagnostic and therapeutic challenge. Human herpesvirus-7 (HHV-7) is proven to be a neurotropic virus, causing various neurological complications mostly in the adult population. We present the case of a 10-year-old girl, with confirmed active HHV-7 infection of the CNS, who developed acute seronegative autoimmune encephalitis. To our best knowledge, there is no literature concerning pediatric cases of autoimmune encephalitis following HHV-7 infection.

Dynamics of salivary human herpesvirus-6 and -7 shedding in pregnant women.

Reactivation of Betaherpesvirinae (Human herpesvirus 6A: HHV-6A, -6B, HHV-7) may be associated with mental illness and host fatigue. This study aimed to determine whether viral reactivation, measured by monitoring salivary viral DNA load, can be used to monitor depression in pregnant and postpartum women. Saliva samples were collected from 64 pregnant women at five points of observation periods. The HHV-6- and HHV-7-specific qPCRs were carried out to measure viral DNA load. When HHV-6 DNA was detected in saliva, nested PCR was used to discriminate between HHV-6A and -6B. In both viruses, a significant correlation was observed between detection frequency and viral DNA load in saliva. In the low-shedding group, HHV-6 DNA was significantly higher in the third trimester (p < 0.0001), the time of delivery (p = 0.0003), 1 month after birth (p = 0.0023) compared with the first trimester, and HHV-7 was at the time of delivery (p = 0.0277) and 1 month after birth (p = 0.0235). Most of the detected HHV-6 DNAs in saliva were HHV-6B. Both viral DNA loads were significantly lower (HHV-6: p = 0.0101, HHV-7: p = 0.0044) in the subjects with abnormal Edinburgh Postnatal Depression Scale (EPDS) scores. The detection rate and viral DNA load of both viruses in saliva increased after the third trimester. Salivary virus DNA shedding was significantly lower in subjects with an abnormal EPDS score.

Human herpesvirus 7 encephalitis in an immunocompetent adult and a literature review.

BACKGROUND: Human herpesvirus 7 (HHV-7) is a common virus that infects children early and is accompanied by lifelong latency in cells, which is easy to reactivate in immunodeficient adults, but the underlying pathological mechanism is uncertain in immunocompetent adults without peculiar past medical history. Even though the clinical manifestation of the encephalitis caused by HHV-7 is uncommon in immunocompetent adults, the HHV-7 infection should not be neglected for encephalitis for unknown reasons. CASE PRESENTATION: We reported here a case of HHV-7 encephalitis with epileptic seizures. While the brain computer tomography was standard, electroencephalography displayed slow waves in the temporal and bilateral frontal areas, then HHV-7 DNA was detected in the metagenomic next-generation sequencing of cerebrospinal fluid. Fortunately, the patient recovered after treatment and was discharged 2 months later. We also collected the related cases and explored a better way to illuminate the underlying mechanism. CONCLUSION: The case indicates clinicians should memorize HHV-7 as an unusual etiology of encephalitis to make an early diagnosis and therapy.

Development of a PCR assay for the detection of human herpes virus type 7.

A PCR assay has been developed to identify the DNA of the human herpes virus type 7. The search and selection of conserved regions was carried out by comparing the whole genome nucleotide sequences of HHV-7. A fragment duplicated in the HHV-7 genomes was chosen as a target for amplification. The performance of the assay was tested on a synthetic matrix and clinical samples. The developed assay has high sensitivity and specificity and showed good efficiency in detecting HHV-7 DNA in clinical samples.

Evasion of the Host Immune Response by Betaherpesviruses.

The human immune system boasts a diverse array of strategies for recognizing and eradicating invading pathogens. Human betaherpesviruses, a highly prevalent subfamily of viruses, include human cytomegalovirus (HCMV), human herpesvirus (HHV) 6A, HHV-6B, and HHV-7. These viruses have evolved numerous mechanisms for evading the host response. In this review, we will highlight the complex interplay between betaherpesviruses and the human immune response, focusing on protein function. We will explore methods by which the immune system first responds to betaherpesvirus infection as well as mechanisms by which viruses subvert normal cellular functions to evade the immune system and facilitate viral latency, persistence, and reactivation. Lastly, we will briefly discuss recent advances in vaccine technology targeting betaherpesviruses. This review aims to further elucidate the dynamic interactions between betaherpesviruses and the human immune system.

Summary of the 11th International Conference on Human Herpesviruses-6A, -6B, and -7.

The 11th International Conference on Human Herpesviruses (HHV)-6A, -6B, and -7 was held in Quebec City, from 23 to 26 June 2019. It attracted 144 basic, translational, and clinical scientists from 20 countries. Important new information was presented regarding: the mechanisms of chromosomal integration for HHV-6A and -6B; the biology of inherited chromosomally integrated HHV-6A and -6B; animal models for, and animal viruses with similarities to, HHV-6A, -6B, and -7; established and possible disease associations, including provocative new information suggesting these viruses may be one trigger of Alzheimer's disease, and new treatment strategies. In this review, we summarize presentations that were of particular interest. The full text of the Abstracts cited in the manuscript is available in the online Supporting Information Materials.

Metagenomic next-generation sequencing of viruses, bacteria, and fungi in the epineurium of the facial nerve with Bell's palsy patients.

Bell's palsy (BP) represents a major cause leading to facial paralysis in the world. The etiology of BP is still unknown, and virology is the prevailing theory. The purpose of this study is to explore the pathogenic microorganisms that may be related to BP, and it is of great significance to study the pathogenesis and treatment of BP. Metagenomic next-generation sequencing (mNGS) detection was performed in the epineurium of the facial nerve of 30 BP patients who underwent facial nerve epineurium decompression. A total of 84 pathogenic microorganisms were detected in 30 clinical samples, including 4 viruses, 10 fungi, and 70 bacteria. The species with the highest detection frequency in virus was human betaherpesvirus 7 (HHV-7). The species with the highest detection frequency in Fungi was Malassezia restricta. The species with the highest detection frequency in Bacteria was Pseudomonas aeruginosa. In this study, mNGS method was firstly used to detect the pathogenic microorganisms in the epineurium of the facial nerve with BP patients. We have for the first time identified HHV-7 and aspergillus in the epineurium of the facial nerve of BP patients. These results suggest that these two pathogenic microorganisms should be considered in the pathogenesis of BP.

Inflammatory Cytokine-Producing Cells and Inflammation Markers in the Synovium of Osteoarthritis Patients Evidenced in Human Herpesvirus 7 Infection.

A direct association between joint inflammation and the progression of osteoarthritis (OA) has been proposed, and synovitis is considered a powerful driver of the disease. Among infections implicated in the development of joint disease, human herpesvirus 7 (HHV-7) infection remains poorly characterized. Therefore, we assessed synovitis in OA patients; determined the occurrence and distribution of the HHV-7 antigen within the synovial membrane of OA-affected subjects; and correlated plasma levels of the pro-inflammatory cytokines tumor necrosis factor (TNF), interleukin-6 (IL-6), and TNF expressed locally within lesioned synovial tissues with HHV-7 observations, suggesting differences in persistent latent and active infection. Synovial HHV-7, CD4, CD68, and TNF antigens were detected immunohistochemically. The plasma levels of TNF and IL-6 were measured by an enzyme-linked immunosorbent assay. Our findings confirm the presence of persistent HHV-7 infection in 81.5% and reactivation in 20.5% of patients. In 35.2% of patients, virus-specific DNA was extracted from synovial membrane tissue samples. We evidenced the absence of histopathologically detectable synovitis and low-grade changes in the majority of OA patients enrolled in the study, in both HHV-7 PCR+ and HHV-7 PCR‒ groups. The number of synovial CD4-positive cells in the HHV-7 polymerase chain reaction (PCR)+ group was significantly higher than that in the HHV-7 PCR‒ group. CD4- and CD68-positive cells were differently distributed in both HHV-7 PCR+ and HHV-7 PCR‒ groups, as well as in latent and active HHV-7 infection. The number of TNF+ and HHV-7+ lymphocytes, as well as HHV-7+ vascular endothelial cells, was strongly correlated. Vascular endothelial cells, especially in the case of infection reactivation, appeared vulnerable. The balance between virus latency and reactivation is a long-term relationship between the host and infectious agent, and the immune system appears to be involved in displaying overreaction when a shift in the established equilibrium develops.

The role of HHV-6 and HHV-7 infections in the development of fibromyalgia.

Human herpes virus-6 (HHV-6) and human herpes virus-7 (HHV-7) are immunomodulating viruses potentially affecting the nervous system. We evaluated the influence of HHV-6 and HHV-7 infections on fibromyalgia (FM) clinical course. Forty-three FM patients and 50 control group participants were enrolled. 39.50% (n = 17) FM patients had light A delta and C nerve fiber damage, 27.91% (n = 12) had severe A delta and C nerve fiber damage. 67.44% (n = 29) FM patients had loss of warm sensation in feet, loss of heat pain sensation, and increased cold pain sensation (34.90%, n = 15 in both findings). HHV-6 and HHV-7 genomic sequences in peripheral blood DNA in 23/43 (51.00%) and 34/43 (75.50%) of samples from FM patients and in 3/50 (6.00%) and 26/50 (52.00%) of samples from the control group individuals were detected. Active HHV-6 (plasma viremia) or HHV-7 infection was revealed only in FM patients (4/23, 17.40% and 4/34, 11.80%, respectively). A statistically significant moderate positive correlation was found between A delta and C nerve fiber damage severity and HHV-6 infection (p < 0.01, r = 0.410). 23/43 patients from the FM group and control group participants HHV-6 and 34/45 HHV-7 did have infection markers. A statistically significant moderate positive correlation was found between A delta and C nerve fiber damage severity and HHV-6 infection (p < 0.01, r = 0.410). No difference was found between detection frequency of persistent HHV-6 and HHV-7 infection between FM patients and the control group. Statistically significant correlation was observed between quantitation of changes in QST thermal modalities and HHV-6 infection. There was no correlation between A delta and C nerve fiber damage and HHV-7 infection.

Coevolution pays off: Herpesviruses have the license to escape the DNA sensing pathway.

Early detection of viral invasion by pattern recognition receptors (PRR) is crucial for the induction of a rapid and efficient immune response. Cytosolic DNA sensors are the most recently described class of PRR, and induce transcription of type I interferons (IFN) and proinflammatory cytokines via the key adaptor protein stimulator of interferon genes (STING). Herpesviruses are a family of large DNA viruses widely known for their immense arsenal of proteins dedicated to manipulating and evading host immune responses. Tantamount to the significant role played by DNA sensors and STING in innate immune responses, herpesviruses have in turn evolved a range of mechanisms targeting virtually every step of this key signaling pathway. Strikingly, some herpesviruses also take advantage of this pathway to promote their own replication. In this review, we will summarize the current understanding of DNA sensing and subsequent induction of signaling and transcription, and showcase the close adaptation of herpesviruses to their host reflected by the myriad of viral proteins dedicated to modulating this critical innate immune pathway.

Interactions of U24 from Roseolovirus with WW domains: canonical vs noncanonical.

U24 is a C-terminal membrane-anchored protein found in both human herpes virus type 6 and 7 (HHV-6 and HHV-7), with an N-terminal segment that is rich in prolines (PPxY motif in both HHV-6A and 7; PxxP motif in HHV-6A). Previous work has shown that U24 interacts strongly with Nedd4 WW domains, in particular, hNedd4L-WW3*. It was also shown that this interaction depends strongly on the nature of the amino acids that are upstream from the PY motif in U24. In this contribution, data was obtained from pull-downs, isothermal titration calorimetry, and NMR to further determine what modulates U24:WW domain interactions. Specifically, 3 non-canonical WW domains from human Smad ubiquitination regulatory factor (Smurf), namely hSmurf2-WW2, hSmurf2-WW3, and a tandem construct hSmurf2-WW2 + 3, were studied. Overall, the interactions between U24 and these Smurf WW domains were found to be weaker than those in U24:Nedd4 WW domain pairs, suggesting that U24 function is tightly linked to specific E3 ubiqitin ligases.