Evolutionarily related small viral fusogens hijack distinct but modular actin nucleation pathways to drive cell-cell fusion

Fusion-associated small transmembrane (FAST) proteins are a diverse family of nonstructural viral proteins. Once expressed on the plasma membrane of infected cells, they drive fusion with neighboring cells, increasing viral spread and pathogenicity. Unlike viral fusogens with tall ectodomains that pull two membranes together through conformational changes, FAST proteins have short fusogenic ectodomains that cannot bridge the intermembrane gap between neighboring cells. One orthoreovirus FAST protein, p14, has been shown to hijack the actin cytoskeleton to drive cell-cell fusion, but the actin adaptor-binding motif identified in p14 is not found in any other FAST protein. Here, we report that an evolutionarily divergent FAST protein, p22 from aquareovirus, also hijacks the actin cytoskeleton but does so through different adaptor proteins, Intersectin-1 and Cdc42, that trigger N-WASP–mediated branched actin assembly. We show that despite using different pathways, the cytoplasmic tail of p22 can replace that of p14 to create a potent chimeric fusogen, suggesting they are modular and play similar functional roles. When we directly couple p22 with the parallel filament nucleator formin instead of the branched actin nucleation promoting factor N-WASP, its ability to drive fusion is maintained, suggesting that localized mechanical pressure on the plasma membrane coupled to a membrane-disruptive ectodomain is sufficient to drive cell-cell fusion. This work points to a common biophysical strategy used by FAST proteins to push rather than pull membranes together to drive fusion, one that may be harnessed by other short fusogens responsible for physiological cell-cell fusion.

Aquareovirus and orthoreovirus are two genera of the Reoviridae family of segmented double-stranded RNA viruses that form multinucleated syncytia after infection, which can increase viral spread and pathogenicity (1–4). To drive cell-cell fusion, both aquareovirus and orthoreovirus express a nonstructural, fusion-associated small transmembrane (FAST) protein on the plasma membrane of infected cells. The FAST protein is not required for viral entry, and expression of FAST protein alone is sufficient to cause cells to fuse with naïve neighboring cells, forming large multinucleated syncytium (1, 2, 5–12), confirming they are bona fide cell-cell fusogens. Although they have similar function and topology in the membrane, FAST proteins from aquareovirus and orthoreovirus share minimal sequence identity (13). Based on phylogenetic analysis, they are hypothesized to have evolved from a common, likely nonfusogenic, ancestor 510 million years ago (4, 13, 14). Separate gain-of-function events are believed to have produced fusogenic proteins in both aquareovirus and orthoreovirus, with further divergence or acquisition events resulting in the diversity of FAST proteins found in reoviruses today (13).Aquareovirus and orthoreovirus FAST proteins are single-pass membrane proteins of fewer than 200 residues comprised of a mostly disordered cytoplasmic tail, a transmembrane domain, and a small ectodomain of fewer than 40 residues (1, 2). The membrane-disruptive ectodomains of FAST proteins typically have solvent-exposed hydrophobic residues and/or myristoylation motifs that are necessary for cell-cell fusion (5, 15–17). In contrast to other cell-cell fusogens that fuse membranes by pulling them together using conformational changes in their ∼10 nm-tall ectodomains, the ectodomains of FAST proteins have minimal predicted secondary structure, are unlikely to undergo conformational changes to drive membrane fusion (1, 2), and extend only ∼1 nm above the bilayer (5, 18). How such short fusogens can overcome the ∼2 nm repulsive hydration barrier and larger barrier presented by cell surface proteins to reach and fuse with an opposing membrane (5, 18) has been a long-standing question for FAST proteins and other short cell-cell fusogens, such as myomixer and myomaker that are involved in myoblast fusion (19–22).Recently, we found that the FAST protein from reptilian orthoreovirus, p14, hijacks the host cell actin cytoskeleton to drive cell-cell fusion by forming localized branched actin networks (23). This is accomplished through a c-src phosphorylated tyrosine motif, YVNI, in p14’s disordered cytoplasmic tail that binds to a host adaptor protein, Grb2, which then binds to N-WASP and nucleates branched actin assembly. We hypothesize that this directly couples local actin-generated forces to push p14’s short, fusogenic ectodomain into the opposing cell’s plasma membrane (23). While all FAST family proteins have similarly short ectodomains, it is unclear if this is a general strategy used by other FAST proteins to drive cell-cell fusion.Here, we report that a FAST protein from the divergent aquareovirus, p22, also hijacks the host actin cytoskeleton but does so using a molecular strategy distinct from that of the orthoreovirus FAST protein p14. Instead of binding to Grb2, we find that p22 binds to Intersectin-1 through an SH3 binding motif in its cytoplasmic tail, which binds Cdc42 to activate N-WASP–mediated branched actin assembly. We show that despite minimal sequence identity, the p22 cytoplasmic tail can be functionally swapped with that of p14, suggesting that while the cytoplasmic tails of the two FAST proteins evolved independently, they serve a similar function. By directly coupling the ectodomain to a different actin nucleator, we suggest that actin’s functional role is applying mechanical pressure to a fusogenic ectodomain at the plasma membrane. This biophysical role may be shared across other members of the FAST protein family and could be more generally employed by other cell-cell fusogens.     

Lumbar Epidural Varix Causing Radicular Pain: A Case Report and Differential Diagnosis of Lumbar Cystic Lesions

Lumbar epidural varices are a rare cause of radicular pain mimicking lumbar disc herniation or other cyst-like masses including sequestrated disc herniation, facet joint synovial cyst, or perineural cyst. We report a case of a 36-year-old woman presenting with lumbar radicular pain caused by a lumbar epidural varix. Lumbar magnetic resonance imaging (MRI) revealed a cystic lesion in the ventral epidural space posterior to the right L4 body. Surgery was conducted and histopathology confirmed the diagnosis of an epidural varix. Lumbar epidural varices and other lumbar cystic lesions can commonly cause radicular pain. Physicians will benefit from increased awareness of epidural varices as a cause of lumbosacral radicular pain and the associated radiologic findings supporting differential diagnosis. In particular, careful interpretation of MRI scans may help ensure proper diagnosis of an epidural varix versus other cystic lesions.

Paclitaxel-coated balloon treatment for functionally nonsignificant residual coronary lesions after balloon angioplasty

There is limited data on the efficacy of paclitaxel-coated balloon (PCB) compared to stents for de novo coronary lesions. The purpose of this study was to compare the efficacy of PCB treatment with stent implantation for de novo coronary lesions after successful plain old balloon angioplasty (POBA) guided by fractional flow reserve (FFR). In 200 patients scheduled for elective percutaneous coronary intervention (PCI) for de novo lesions, FFR was measured after POBA (POBA–FFR). If POBA–FFR was ≥?0.75, patients were treated with PCB (PCB group, n?=?78) or stent (Stent group, n?=?73). If POBA–FFR was <?0.75, stent was implanted as planned (Reference group, n?=?42). The primary endpoint was late lumen loss at 9 months and the secondary endpoint was adverse cardiac events (cardiac death, myocardial infarction, target lesion thrombosis, or repeat revascularization) at 12 months follow-up. There was no between-group differences in the POBA–FFR (0.87?±?0.05 in PCB, 0.89?±?0.06 in stent, p?=?0.101). At 9 months, late lumen loss was significantly lower in the PCB group compared to the Stent group (0.05?±?0.33 vs. 0.59?±?0.76 mm, p?<?0.001). Adverse cardiac events were not different between the PCB, Stent and Reference groups (2.6, 5.5, and 9.5% respectively; p?=?0.430 for PCB vs. Stent group; p?=?0.229 for the reference vs. both other groups). PCB treatment guided by POBA–FFR showed excellent 9 months angiographic and functional results, as well as comparable 12 months clinical outcomes, compared with stent implantation for de novo coronary lesions.     

Risk factors for latent tuberculosis infection in children in South Korea

Objectives: In South Korea, latent tuberculosis infection (LTBI) screening is a critical strategy associated with efforts to reduce the incidence of tuberculosis (TB). Currently, only children with a known history of TB contact are considered as pediatric high-risk groups for LTBI, and consequently, LTBI screening is only provided to these children. However, to reduce the incidence of TB, the high-risk groups that undergo LTBI screening should be expanded. This study aimed to assess the risk factors for LTBI among children living in South Korea with no known history of TB contact for the identification of additional high-risk groups. We investigated the risk factors for LTBI among US visa applicant children, who undergo LTBI screening regardless of their TB contact history.

Methods: We obtained data on demographic characteristics, medical history, Bacillus Calmette–Guerin (BCG) vaccination history, and results of LTBI screening for children aged 2–14 years. A tuberculin skin test was used for the diagnosis of LTBI, and an induration of 10 mm or greater was used to define a positive test. Adjusted odds ratios and 95% confidence intervals were calculated to determine the association between clinical and demographic variables and LTBI.

Results: Of the 1,664 study participants, 91 (5.5%) had LTBI. The binary logistic regression analysis showed that children born in high TB burden foreign countries had the highest odds of LTBI when considering all the risk factors investigated. Increasing age, absence of BCG vaccination, and a previous diagnosis of asthma were also significant risk factors for LTBI.

Conclusion: These results indicate that children born in high TB burden foreign countries should be considered a high-risk group for LTBI in South Korea; the inclusion of these children in LTBI screening should be considered.     

Serum interleukin-6 levels as an indicator of aseptic meningitis among children with enterovirus 71-induced hand,foot and mouth disease

Objectives: The enterovirus EV71 is a major pathogen of hand, foot, and mouth disease (HFMD) in children. Aseptic meningitis is the most common neurologic complication of EV71-induced HFMD. Lumbar puncture is a crucial procedure in the diagnosis of aseptic meningitis. It is often performed based on physicians’ clinical suspicion. A diagnostic method that can aid in deciding whether this procedure should be performed is necessary. Cytokines are speculated to be associated with neurologic complications. In this study, we aimed to find an indicator of the presence of aseptic meningitis in children with EV71-induced HFMD.

Methods: This cross-sectional study included children with EV71-induced HFMD. The children underwent lumbar puncture due to suspected aseptic meningitis. They were categorized into an aseptic meningitis complicated group (n = 54) and uncomplicated group (n = 47) based on the results of cerebrospinal fluid examination. Healthy children were included as controls (n = 51). The sample serum levels of tumor necrosis factor-α, interferon-γ, interleukin (IL)-1β, IL-2, IL-6, IL-8, IL-10, and IL-13 were detected using multiplexed fluorescent bead-based immunoassays.

Results: The levels of all cytokines were significantly higher in children with EV71-induced HFMD complicated with aseptic meningitis than in children with uncomplicated EV71-induced HFMD and controls (p < 0.001). Binary logistic regression analysis demonstrated that IL-6 had the strongest association with aseptic meningitis of all cytokines examined. According to receiver operating characteristic analysis, the optimal cutoff value for IL-6 was 66 pg/mL with maximum sensitivity and specificity.

Conclusions: The results of this study suggest the association between higher production of cytokine and aseptic meningitis among children with EV71-induced HFMD. IL-6 was also suggested as an indicator of aseptic meningitis. Rapid measurement of IL-6 could be useful in deciding whether physicians should perform lumbar puncture on children.     

Correlations Between the Incidence of National Notifiable Infectious Diseases and Public Open Data,Including Meteorological Factors and Medical Facility Resources

Objectives:

This study was performed to investigate the relationship between the incidence of national notifiable infectious diseases (NNIDs) and meteorological factors, air pollution levels, and hospital resources in Korea.

Methods:

We collected and stored 660 000 pieces of publicly available data associated with infectious diseases from public data portals and the Diseases Web Statistics System of Korea. We analyzed correlations between the monthly incidence of these diseases and monthly average temperatures and monthly average relative humidity, as well as vaccination rates, number of hospitals, and number of hospital beds by district in Seoul.

Results:

Of the 34 NNIDs, malaria showed the most significant correlation with temperature (r=0.949, p<0.01) and concentration of nitrogen dioxide (r=-0.884, p<0.01). We also found a strong correlation between the incidence of NNIDs and the number of hospital beds in 25 districts in Seoul (r=0.606, p<0.01). In particular, Geumcheon-gu was found to have the lowest incidence rate of NNIDs and the highest number of hospital beds per patient.

Conclusions:

In this study, we conducted a correlational analysis of public data from Korean government portals that can be used as parameters to forecast the spread of outbreaks.