DDX21, a Host Restriction Factor of FMDV IRES-Dependent Translation and Replication

Abstract

In cells, the contributions of DEAD-box helicases (DDXs), without which cellular life is impossible, are of utmost importance. The extremely diverse roles of the nucleolar helicase DDX21, ranging from fundamental cellular processes such as cell growth, ribosome biogenesis, protein translation, protein–protein interaction, mediating and sensing transcription, and gene regulation to viral manipulation, drew our attention. We designed this project to study virus–host interactions and viral pathogenesis. A pulldown assay was used to investigate the association between foot-and-mouth disease virus (FMDV) and DDX21. Further insight into the DDX21–FMDV interaction was obtained through dual-luciferase, knockdown, overexpression, qPCR, and confocal microscopy assays. Our results highlight the antagonistic feature of DDX21 against FMDV, as it progressively inhibited FMDV internal ribosome entry site (IRES) -dependent translation through association with FMDV IRES domains 2, 3, and 4. To subvert this host helicase antagonism, FMDV degraded DDX21 through its non-structural proteins 2B, 2C, and 3C protease (3Cpro). Our results suggest that DDX21 is degraded during 2B and 2C overexpression and FMDV infection through the caspase pathway; however, DDX21 is degraded through the lysosomal pathway during 3Cpro overexpression. Further investigation showed that DDX21 enhanced interferon-beta and interleukin-8 production to restrict viral replication. Together, our results demonstrate that DDX21 is a novel FMDV IRES trans-acting factor, which negatively regulates FMDV IRES-dependent translation and replication.

DEAD-Box RNA Helicase 21 (DDX21) Positively Regulates the Replication of Porcine Reproductive and Respiratory Syndrome Virus via Multiple Mechanisms

“…DDX21 was first identified as a nucleolar RNA helicase involved in rRNA processing and RNA unwinding [ 42 , 58 ]. However, increasingly more evidence has shown that virus infection or treatment with stimulants, such as poly (I: C) and 3p-hpRNA, promote the translocation of DDX21 from the nucleus to the cytoplasm [ 28 , 41 , 61 ]. Although the exact mechanism of how pDDX21 translocation influences PRRSV replication is not clear, given that DDX21 possesses G-quadruplex-unwinding activity [ 25 ], we speculate that pDDX21 may unwind the viral genome.…”

Antiviral DExD/H-box helicase 60 selectively inhibits translation from type II internal ribosome entry sites

“…DDX60 is not the only DExD/H box RNA helicase observed to inhibit viral IRES-mediated translation. The DEAD box helicase DDX21 was recently shown to antagonize FMDV IRES, and the HCV like IRESs of classical swine fever virus and Seneca Valley virus (Abdullah et al, 2021). However, unlike DDX60, DDX21 is thought to inhibit these IRESs indirectly through upregulation of IFN-ß and IL-8 mRNAs (Abdullah et al, 2021).…”

“…The DEAD box helicase DDX21 was recently shown to antagonize FMDV IRES, and the HCV like IRESs of classical swine fever virus and Seneca Valley virus (Abdullah et al, 2021). However, unlike DDX60, DDX21 is thought to inhibit these IRESs indirectly through upregulation of IFN-ß and IL-8 mRNAs (Abdullah et al, 2021). Likewise, the ability for DDX21 to selectively inhibit IRES-mediated translation has not been tested.…”

The Intricacy of the Viral-Human Protein Interaction Networks: Resources, Data, and Analyses

“…All of them have RNA binding activity and some of them also take active part in immune regulation. For instance, DDX21, an RNA helicase, acts in innate immune response as positive regulator of NF-kB signaling ( Zhang et al, 2011 ; Chen et al, 2014 ; Abdullah et al, 2021 ) and as antiviral factor ( Chen et al, 2014 ). In addition, many RBPs commonly targeted by the three viruses are associated with ubiquitin mediated protein degradation pathways (e.g., RPS7, RPL11, RPS2, RPL5) and regulation of apoptotic processes (e.g., SERBP1, RSL1D1, RPS7), thus underlying the key role of RBPs in virus-host interactions.…”