Shapiro and colleagues and Rouha and colleagues were the first to independently describe recombinant cytoplasmic viruses that could successfully produce miRNAs from a pri-miRNA substrate, ...establishing that access to Drosha is not a limiting factor 9, 10. Since these initial discoveries, many other cytoplasmic viruses have been demonstrated to support miRNA production; these viruses include vesicular stomatitis virus (VSV), vaccinia virus (VacV), Semliki Forest virus (SFV), turnip crinkle virus (TCV), and Sendai virus (SeV) 11–13. When complements are not kind The last theoretical constraint that might explain the lack of miRNA production from cytoplasmic RNA viruses derives from the concept of self-targeting. Because RNA virus-produced miRNAs would be perfectly complementary to the antigenome, one would imagine that this could cause dramatic attenuation. ...it stands to reason that the only viruses generating miRNAs are those that persist within an infected cell, and these tend to be DNA viruses or RNA viruses with DNA phases (Fig 1). While it remains possible that an acute RNA virus could benefit from the modulation of a single host mRNA, this is likely not observed because such an activity can be achieved more broadly and efficiently through use of a protein-based antagonist. ...although initial efforts have failed to identify any obvious fitness cost from the inclusion of a single miRNA, more in-depth studies under greater selective pressures may reveal that the inclusion of a hairpin does consistently impact virus replication in a negative way.
More than one year after its inception, the coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) remains difficult to control despite ...the availability of several working vaccines. Progress in controlling the pandemic is slowed by the emergence of variants that appear to be more transmissible and more resistant to antibodies
. Here we report on a cohort of 63 individuals who have recovered from COVID-19 assessed at 1.3, 6.2 and 12 months after SARS-CoV-2 infection, 41% of whom also received mRNA vaccines
. In the absence of vaccination, antibody reactivity to the receptor binding domain (RBD) of SARS-CoV-2, neutralizing activity and the number of RBD-specific memory B cells remain relatively stable between 6 and 12 months after infection. Vaccination increases all components of the humoral response and, as expected, results in serum neutralizing activities against variants of concern similar to or greater than the neutralizing activity against the original Wuhan Hu-1 strain achieved by vaccination of naive individuals
. The mechanism underlying these broad-based responses involves ongoing antibody somatic mutation, memory B cell clonal turnover and development of monoclonal antibodies that are exceptionally resistant to SARS-CoV-2 RBD mutations, including those found in the variants of concern
. In addition, B cell clones expressing broad and potent antibodies are selectively retained in the repertoire over time and expand markedly after vaccination. The data suggest that immunity in convalescent individuals will be very long lasting and that convalescent individuals who receive available mRNA vaccines will produce antibodies and memory B cells that should be protective against circulating SARS-CoV-2 variants.
Antigenic diversity shapes immunity in distinct and unexpected ways. This is particularly true of the humoral response generated against influenza A viruses. Although it is known that immunological ...memory developed against previously encountered influenza A virus strains affects the outcome of subsequent infections, exactly how sequential exposures to antigenically variant viruses shape the humoral immune response in humans remains poorly understood. To address this important question, we performed a longitudinal analysis of antibody titers against various pandemic and seasonal strains of influenza virus spanning a 20-year period (1987 to 2008) with samples from 40 individuals (birth dates, 1917 to 1952) obtained from the Framingham Heart Study. Longitudinal increases in neutralizing antibody titers were observed against previously encountered pandemic H2N2, H3N2, and H1N1 influenza A virus strains. Antibody titers against seasonal strains encountered later in life also increased longitudinally at a rate similar to that against their pandemic predecessors. Titers of cross-reactive antibodies specific to the hemagglutinin stalk domain were also investigated because they are influenced by exposure to antigenically diverse influenza A viruses. These titers rose modestly over time, even in the absence of major antigenic shifts. No sustained increase in neutralizing antibody titers against an antigenically more stable virus (human cytomegalovirus) was observed. The results herein describe a role for antigenic variation in shaping the humoral immune compartment and provide a rational basis for the hierarchical nature of antibody titers against influenza A viruses in humans.
With the capacity to fine-tune protein expression via sequence-specific interactions, microRNAs (miRNAs) help regulate cell maintenance and differentiation. While some studies have also implicated ...miRNAs as regulators of the antiviral response, others have found that the RISC complex that facilitates miRNA-mediated silencing is rendered nonfunctional during cellular stress, including virus infection. To determine the global role of miRNAs in the cellular response to virus infection, we generated a vector that rapidly eliminates total cellular miRNA populations in terminally differentiated primary cultures. Loss of miRNAs has a negligible impact on both innate sensing of and immediate response to acute viral infection. In contrast, miRNA depletion specifically enhances cytokine expression, providing a posttranslational mechanism for immune cell activation during cellular stress. This work highlights the physiological role of miRNAs during the antiviral response and suggests their contribution is limited to chronic infections and the acute activation of the adaptive immune response.
Display omitted
•Vector-mediated miRNA ablation reveals biological impact during virus infection•Prolonged loss of miRNAs results in dramatic changes to the host transcriptome•miRNA-mediated activity requires kinetics that exceed the acute response to virus•miRNA function is generally limited to cytokine levels in response to RNA viruses
The role of microRNAs in antiviral immunity remains an ongoing question. Using vector-mediated ablation of microRNA expression, Aguado et al. demonstrate that microRNA posttranscriptional control selectively impacts proinflammatory cytokine expression during the acute response to virus. In contrast, microRNAs can dramatically influence the host during chronic infections.
Every living entity requires the capacity to defend against viruses in some form. From bacteria to plants to arthropods, cells retain the capacity to capture genetic material, process it in a variety ...of ways, and subsequently use it to generate pathogen‐specific small RNAs. These small RNAs can then be used to provide specificity to an otherwise non‐specific nuclease, generating a potent antiviral system. While small RNA‐based defenses in chordates are less utilized, the protein‐based antiviral invention in this phylum appears to have derived from components of the same ancestral small RNA machinery. Based on recent evidence, it would seem that RNase III nucleases have been reiteratively repurposed over billions of years to provide cells with the capacity to recognize and destroy unwanted genetic material. Here we describe an overview of what is known on this subject and provide a model for how these defenses may have evolved.
RNase III nuclease domains are widely used in an array of RNA metabolic functions as well as antiviral defenses. Here, we review their current usage as well as provide insight into how these domains may have shaped all major antiviral pathways over the course of evolution.
Drosha as an interferon-independent antiviral factor Shapiro, Jillian S.; Schmid, Sonja; Aguado, Lauren C. ...
Proceedings of the National Academy of Sciences,
05/2014, Letnik:
111, Številka:
19
Journal Article
Recenzirano
Odprti dostop
Utilization of antiviral small interfering RNAs is thought to be largely restricted to plants, nematodes, and arthropods. In an effort to determine whether a physiological interplay exists between ...the host small RNA machinery and the cellular response to virus infection in mammals, we evaluated antiviral activity in the presence and absence of Dicer or Drosha, the RNase III nucleases responsible for generating small RNAs. Although loss of Dicer did not compromise the cellular response to virus infection, Drosha deletion resulted in a significant increase in virus levels. Here, we demonstrate that diverse RNA viruses trigger exportin 1 (XPO1/CRM1)-dependent Drosha translocation into the cytoplasm in a manner independent of de novo protein synthesis or the canonical type I IFN system. Additionally, increased virus infection in the absence of Drosha was not due to a loss of viral small RNAs but, instead, correlated with cleavage of viral genomic RNA and modulation of the host transcriptome. Taken together, we propose that Drosha represents a unique and conserved arm of the cellular defenses used to combat virus infection.
Hepatitis B virus (HBV) is a small double-stranded DNA virus that chronically infects 296 million people. Over half of its compact genome encodes proteins in two overlapping reading frames, and ...during evolution, multiple selective pressures can act on shared nucleotides. This study combines an RNA-based HBV cell culture system with deep mutational scanning (DMS) to uncouple cis- and trans-acting sequence requirements in the HBV genome. The results support a leaky ribosome scanning model for polymerase translation, provide a fitness map of the HBV polymerase at single-nucleotide resolution, and identify conserved prolines adjacent to the HBV polymerase termination codon that stall ribosomes. Further experiments indicated that stalled ribosomes tether the nascent polymerase to its template RNA, ensuring cis-preferential RNA packaging and reverse transcription of the HBV genome.
Display omitted
•Deep mutational scanning (DMS) provides a high-resolution fitness map of HBV polymerase•Initiating HBV replication with RNA uncouples cis- and trans-acting protein functions•Ribosome pausing tethers HBV Pol to RNA, enforcing cis-preferential reverse transcription•DMS of the HBV genome supports a leaky ribosome scanning model for polymerase translation
Deep mutational scanning reveals that conserved proline codons at the 3′ end of the hepatitis B virus polymerase open reading frame stall ribosomes. As a result, the ribosome physically tethers the nascent polymerase to its encoding RNA, which enforces cis-preferential genome RNA packaging and reverse transcription.
In contrast to the DNA-based viruses in prokaryotes, the emergence of eukaryotes provided the necessary compartmentalization and membranous environment for RNA viruses to flourish, creating the need ...for an RNA-targeting antiviral system. Present day eukaryotes employ at least two main defence strategies that emerged as a result of this viral shift, namely antiviral RNA interference and the interferon system. Here we demonstrate that Drosha and related RNase III ribonucleases from all three domains of life also elicit a unique RNA-targeting antiviral activity. Systemic evolution of ligands by exponential enrichment of this class of proteins illustrates the recognition of unbranched RNA stem loops. Biochemical analyses reveal that, in this context, Drosha functions as an antiviral clamp, conferring steric hindrance on the RNA-dependent RNA polymerases of diverse positive-stranded RNA viruses. We present evidence for cytoplasmic translocation of RNase III nucleases in response to virus in diverse eukaryotes including plants, arthropods, fish, and mammals. These data implicate RNase III recognition of viral RNA as an antiviral defence that is independent of, and possibly predates, other known eukaryotic antiviral systems.
RNA interference (RNAi) is the major antiviral defense mechanism of plants and invertebrates, rendering the capacity to evade it a defining factor in shaping the viral landscape. Here we sought to ...determine whether different virus replication strategies provided any inherent capacity to evade RNAi in the absence of an antagonist. Through the exploitation of host microRNAs, we recreated an RNAi-like environment in vertebrates and directly compared the capacity of positive- and negative-stranded RNA viruses to cope with this selective pressure. Applying this defense against four distinct viral families revealed that the capacity to undergo homologous recombination was the defining attribute that enabled evasion of this defense. Independent of gene expression strategy, positive-stranded RNA viruses that could undergo strand switching rapidly excised genomic material, while negative-stranded viruses were effectively targeted and cleared upon RNAi-based selection. These data suggest a dynamic relationship between host antiviral defenses and the biology of virus replication in shaping pathogen prevalence.
Abstract
It is known that early exposures with influenza viruses impact the outcome of subsequent encounters. However, how sequential exposures to antigenically variant viruses shape the humoral ...immune response remains very poorly understood. To address this, a longitudinal analysis of antibody titers against pandemic (Japan/57 H2N2, Hong Kong/68 H3N2 and USSR/77 H1N1) and seasonal (Alabama/81 H3N2 and Texas/91 H1N1) strains of influenza virus was performed on matched serological samples collected over a 20 year period (1987-2008). These samples were obtained from the Framingham Heart Study Offspring Cohort. Sustained increases in neutralizing antibody titers were observed against both the pandemic and seasonal isolates. Hemagglutinin stalk-reactive antibody titers rose modestly over the 20 year study period, even in the absence of major antigenic shifts which are known to boost these antibodies most effectively. Neutralizing antibody titers against cytomegalovirus were also investigated. In contrast to influenza virus, no sustained increase in neutralizing antibody titers specific to cytomegalovirus was observed. These findings represent the first detailed longitudinal analysis of the humoral immune response against influenza virus in humans, and suggest a unique role for sequential exposures to antigenic variants in the maintenance of neutralizing antibodies.
PDF
