Biology subjects

Silverman, R. H.

Publications and source records attributed to Silverman, R. H..

3 recordsLinked to original sources

bioRxiv2021

Specificity and Mechanism of Coronavirus, Rotavirus and Mammalian Two-Histidine-Phosphoesterases That Antagonize Antiviral Innate Immunity

2,5-oligoadenylate(2-5A)-dependent endoribonuclease, RNase L, is a principal mediator of the interferon (IFN) antiviral response. Therefore, regulation of cellular levels of 2-5A is a key point of control in antiviral innate immunity. Cellular 2-5A levels are determined by IFN-inducible 2,5-oligoadenylate synthetases (OASs) and by enzymes that degrade 2-5A. Importantly, many coronaviruses and rotaviruses encode 2-5A degrading enzymes thereby antagonizing RNase L and its antiviral effects. A-kinase anchoring protein 7 (AKAP7), a mammalian counterpart, could possibly limit tissue damage from excessive or prolonged RNase L activation during viral infections or from self double-stranded-RNAs that activate OAS. We show these enzymes, members of the two-histidine-phosphoesterase (2H-PE) superfamily, constitute a sub-family referred here as 2,5-PEs. 2,5-PEs from mouse coronavirus (CoV) MHV (NS2), MERS-CoV (NS4b), group A rotavirus (VP3), and mouse (AKAP7) were investigated for their evolutionary relationships and activities. While there was no activity against 3,5-oligoribonucleotides, all cleaved 2,5-oligoadenylates efficiently, but with variable activity against other 2,5-oligonucleotides. The 2,5-PEs are shown to be metal ion-independent enzymes that cleave trimer 2-5A (2,5-p3A3) producing mono- or di- adenylates with 2,3-cyclic phosphate termini. Our results suggest that elimination of 2-5A might be the sole function of viral 2,5-PEs, thereby promoting viral escape from innate immunity by preventing or limiting the activation of RNase L. IMPORTANCEViruses often encode accessory proteins that antagonize the host antiviral immune response. Here we probed the evolutionary relationships and biochemical activities of two-histidine-phosphoesterases (2H-PEs) that allow some coronaviruses and rotaviruses to counteract antiviral innate immunity. In addition, we investigated the mammalian enzyme, AKAP7, which has homology and shared activities with the viral enzymes and might reduce self-injury. These viral and host enzymes, that we refer to as 2,5-PEs, specifically degrade 2,5-oligoadenylate activators of the antiviral enzyme RNase L. We show that the host and viral enzymes are metal ion independent and exclusively cleave 2,5- and not 3,5-phosphodiester bonds, producing cleavage products with cyclic 2,3-phosphate termini. Our study defines 2,5-PEs as enzymes that share characteristic conserved features with the 2H-PE superfamily but which have specific and distinct biochemical cleavage activities. These findings may eventually lead to pharmacologic strategies for developing antiviral drugs against coronaviruses, rotaviruses, and other viruses.

microbiology↗

bioRxiv2020

SARS-CoV-2 induces double-stranded RNA-mediated innate immune responses in respiratory epithelial derived cells and cardiomyocytes

Coronaviruses are adept at evading host antiviral pathways induced by viral double-stranded RNA, including interferon (IFN) signaling, oligoadenylate synthetase-ribonuclease L (OAS-RNase L), and protein kinase R (PKR). While dysregulated or inadequate IFN responses have been associated with severe coronavirus infection, the extent to which the recently emerged SARS-CoV-2 activates or antagonizes these pathways is relatively unknown. We found that SARS-CoV-2 infects patient-derived nasal epithelial cells, present at the initial site of infection, induced pluripotent stem cell-derived alveolar type 2 cells (iAT2), the major cell type infected in the lung, and cardiomyocytes (iCM), consistent with cardiovascular consequences of COVID-19 disease. Robust activation of IFN or OAS-RNase L is not observed in these cell types, while PKR activation is evident in iAT2 and iCM. In SARS-CoV-2 infected Calu-3 and A549ACE2 lung-derived cell lines, IFN induction remains relatively weak; however activation of OAS-RNase L and PKR is observed. This is in contrast to MERS-CoV, which effectively inhibits IFN signaling as well as OAS-RNase L and PKR pathways, but similar to mutant MERS-CoV lacking innate immune antagonists. Remarkably, both OAS-RNase L and PKR are activated in MAVS knockout A549ACE2 cells, demonstrating that SARS-CoV-2 can induce these host antiviral pathways despite minimal IFN production. Moreover, increased replication and cytopathic effect in RNASEL knockout A549ACE2 cells implicates OAS-RNase L in restricting SARS-CoV-2. Finally, while SARS-CoV-2 fails to antagonize these host defense pathways, which contrasts with other coronaviruses, the IFN signaling response is generally weak. These host-virus interactions may contribute to the unique pathogenesis of SARS-CoV-2. SignificanceSARS-CoV-2 emergence in late 2019 led to the COVID-19 pandemic that has had devastating effects on human health and the economy. Early innate immune responses are essential for protection against virus invasion. While inadequate innate immune responses are associated with severe COVID-19 diseases, understanding of the interaction of SARS-CoV-2 with host antiviral pathways is minimal. We have characterized the innate immune response to SARS-CoV-2 infections in relevant respiratory tract derived cells and cardiomyocytes and found that SARS-CoV-2 activates two antiviral pathways, oligoadenylate synthetase-ribonuclease L (OAS-RNase L), and protein kinase R (PKR), while inducing minimal levels of interferon. This in contrast to MERS-CoV which inhibits all three pathways. Activation of these pathways may contribute to the distinctive pathogenesis of SARS-CoV-2.

microbiology↗

bioRxiv2019

The host antiviral ribonuclease L protein supports Zika virus replication factory formation to enhance infectious virus production

The flavivirus Zika virus (ZIKV) activates ribonuclease L (RNase L) catalytic antiviral function during infection, yet deletion of RNase L decreases ZIKV production, suggesting a proviral role of RNase L. In this study, we reveal that latent RNase L supports ZIKV replication factory (RF) assembly. Deletion of RNase L induced broader cellular distribution of ZIKV dsRNA and NS3 compared with densely concentrated RFs detected in WT cells. An inactive form of RNase L was sufficient to contain ZIKV genome and dsRNA within a smaller area, which increased levels of viral RNA within RFs as well as infectious ZIKV released from the cell. We used a microtubule stabilization drug to demonstrate that RNase L deletion impaired the cytoskeleton rearrangements that are required for proper generation of RFs. During infection with dengue or West Nile Kunjin viruses, RNase L decreased virus production, suggesting that RNase L proviral function is specific to ZIKV.

microbiology↗