Summary Many viruses shut off host gene expression to inhibit antiviral responses. Viral proteins and host proteins required for viral replication are typically spared in this process, but the mechanisms of target selectivity during host shutoff remain poorly understood. Using transcriptome-wide and targeted reporter experiments, we demonstrate that the influenza A virus endoribonuclease PA-X usurps RNA splicing to selectively target host RNAs for destruction. Proximity-labeling proteomics reveals that PA-X interacts with cellular RNA processing proteins, some of which are partially required for host shutoff. Thus, PA-X taps into host nuclear pre-mRNA processing mechanisms to destroy nascent mRNAs shortly after their synthesis. This mechanism sets PA-X apart from other viral host shutoff proteins that target actively translating mRNAs in the cytoplasm. Our study reveals a unique mechanism of host shutoff that helps us understand how influenza viruses suppress host gene expression.

This study confirms the hypotensive effect of exercise on intraocular pressure and shows that exercise significantly increases pulsatile ocular blood flow.

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Influenza A virus (IAV) increases the presentation of class I human leukocyte antigen (HLA) proteins that limit antiviral responses mediated by natural killer (NK) cells, but molecular mechanisms for these processes have not yet been fully elucidated. We observed that infection with A/Fort Monmouth/1/1947(H1N1) IAV significantly increased the presentation of HLA-B, -C, and -E on lung epithelial cells. Virus entry was not sufficient to induce HLA upregulation because UV-inactivated virus had no effect. Aberrant internally deleted viral RNAs (vRNAs) known as mini viral RNAs (mvRNAs) and defective interfering RNAs (DI RNAs) expressed from an IAV minireplicon were sufficient for inducing HLA upregulation. These defective RNAs bind to retinoic acid-inducible gene I (RIG-I) and initiate mitochondrial antiviral signaling (MAVS) protein-dependent antiviral interferon (IFN) responses. Indeed, MAVS was required for HLA upregulation in response to IAV infection or ectopic mvRNA/DI RNA expression. The effect was partially due to paracrine signaling, as we observed that IAV infection or mvRNA/DI RNA-expression stimulated production of IFN-β and IFN-λ1 and conditioned media from these cells elicited a modest increase in HLA surface levels in naive epithelial cells. HLA upregulation in response to aberrant viral RNAs could be prevented by the Janus kinase (JAK) inhibitor ruxolitinib. While HLA upregulation would seem to be advantageous to the virus, it is kept in check by the viral nonstructural 1 (NS1) protein; we determined that NS1 limits cell-intrinsic and paracrine mechanisms of HLA upregulation. Taken together, our findings indicate that aberrant IAV RNAs stimulate HLA presentation, which may aid viral evasion of innate immunity. IMPORTANCE Human leukocyte antigens (HLAs) are cell surface proteins that regulate innate and adaptive immune responses to viral infection by engaging with receptors on immune cells. Many viruses have evolved ways to evade host immune responses by modulating HLA expression and/or processing. Here, we provide evidence that aberrant RNA products of influenza virus genome replication can trigger retinoic acid-inducible gene I (RIG-I)/mitochondrial antiviral signaling (MAVS)-dependent remodeling of the cell surface, increasing surface presentation of HLA proteins known to inhibit the activation of an immune cell known as a natural killer (NK) cell. While this HLA upregulation would seem to be advantageous to the virus, it is kept in check by the viral nonstructural 1 (NS1) protein, which limits RIG-I activation and interferon production by the infected cell.

Background: Punctate palmoplantar keratoderma type 1 (PPPK1) presents in late childhood to adulthood with multiple small discrete hyperkeratotic papules on palms and soles. PPPK1 is an autosomal dominant skin disease caused by AAGAB mutations. It has been suggested that PPPK1 may be associated with an increased predisposition to systemic malignancies. Objectives: To evaluate the presence of AAGAB mutations in Canadian families with PPPK1 and the possible increased predisposition to systemic malignancies. Methods: Eighteen unrelated Canadian families with PPPK1 were recruited for this study. Genomic DNA was extracted from saliva and PCR amplification was performed for all AAGAB exons and exon/intron junctions. PCR products were sequenced and analyzed for mutations. A family history of malignancy was obtained from the index case and, when possible, from other family members. Results: We have identified 5 heterozygous AAGAB loss of function mutations in 11 families. The mutation c.370 C>T, p.Arg124* was the most prevalent and was identified in 6 families. A splice site mutation, c.451+3delAAGT, was identified in 2 families. The other mutations c.473delG, p.Gly158Glufs*0; c.550-551insAAT, p.Gly183*; and c.505-506 dupAA, p.Asn169Lysfs*6 were each identified in 1 family. Different cancers were reported in 11 families (Table 1 and Supplemental Figure S1). Conclusions: AAGAB mutations were found in 11 of 18 families with PPPK1. In some families there appears to be an association with cancer.

Background: The COVID-19 pandemic caused significant morbidity and mortality in people who inject drugs (PWID). Upper extremity soft tissue infections are frequently associated with intravenous drug use (IVDU) due to poor compliance with aseptic technique. In Canada, multiple safe injection sites providing clean injection supplies closed, leaving many PWID with no alternatives to inject safely. It was hypothesized that these closures will correspond with increased morbidity and mortality among PWID. The main objective of this study was to determine the effect of the COVID-19 pandemic on the incidence of upper extremity infections in PWID. Methods: This was a retrospective chart review study. The primary outcome of interest was the frequency of upper extremity infections in PWID. Data were filtered to include only those patients presenting to the emergency department between March to June of 2019 and 2020. Chi-squared analysis was used to compare the number of IVDU patients among patients with upper extremity skin infections between these time periods. Results: The number of IVDU patients treated for upper extremity infections in Hamilton significantly increased during the pandemic, relative risk = 2.0 (95% confidence interval [CI]: 1.3-2.9, P = .0012,) while total upper extremity infections numbers have decreased overall. During the pandemic, PWID made up a larger proportion of upper extremity infections ( χ2 = 10.444, P = .00123). Demographic data such as age and sex of IVDU patients presenting with upper extremity infection was not significantly affected by the pandemic. Conclusions: The effect of the pandemic on accessing harm reduction services has led to evident increases in morbidity as described by this study. Further research on the impact of closures in PWID is needed to quantify these harms and work toward mitigation strategies.

ABSTRACTInfluenza A virus (IAV) increases presentation of class I human leukocyte antigen (HLA) proteins that limit antiviral responses mediated by natural killer (NK) cells, but molecular mechanisms have not yet been fully elucidated. We observed that infection with A/Fort Monmouth/1/1947 (H1N1) IAV significantly increased presentation of HLA-B, -C and -E on lung epithelial cells. Virus entry was not sufficient to induce HLA upregulation, because UV-inactivated virus had no effect. We found that HLA upregulation was elicited by aberrant internally-deleted viral RNAs (vRNAs) known as mini viral RNAs (mvRNAs) and defective interfering RNAs (DI RNAs), which bind to retinoic acid-inducible gene-I (RIG-I) and initiate mitochondrial antiviral signaling (MAVS) protein-dependent antiviral interferon (IFN) responses. Indeed, MAVS was required for HLA upregulation in response to IAV infection or ectopic mvRNA/DI RNA expression. The effect was partially due to paracrine signalling, as we observed that IAV infection or mvRNA/DI RNA-expression stimulated production of IFN-β and IFN-λ1, and conditioned media from these cells elicited a modest increase in HLA surface levels in naïve epithelial cells. HLA upregulation in response to aberrant viral RNAs could be prevented by chemical blockade of IFN receptor signal transduction. While HLA upregulation would seem to be advantageous to the virus, it is kept in check by the viral non-structural 1 (NS1) protein; we determined that NS1 limits cell-intrinsic and paracrine mechanisms of HLA upregulation. Taken together, our findings indicate that aberrant IAV RNAs stimulate HLA presentation, which may aid viral evasion of innate immunity.IMPORTANCEHuman leukocyte antigens (HLA) are cell surface proteins that regulate innate and adaptive immune responses to viral infection by engaging with receptors on immune cells. Many viruses have evolved ways to evade host immune responses by modulating HLA expression and/or processing. Here, we provide evidence that aberrant RNA products of influenza virus genome replication can trigger RIG-I/MAVS-dependent remodeling of the cell surface, increasing surface presentation of HLA proteins known to inhibit the activation of an immune cell known as a natural killer (NK) cell. While this HLA upregulation would seem to be advantageous to the virus, it is kept in check by the viral non-structural 1 (NS1) protein, which limits RIG-I activation and interferon production by the infected cell.