Nonstructural Protein NSs of Schmallenberg Virus Is Targeted to the Nucleolus and Induces Nucleolar Disorganization

Development of the nervous system is carried out by complex gene expression programs that are regulated at both transcriptional and translational level. In addition, quality control mechanisms such as the TP53-mediated apoptosis or neuronal activity-stimulated survival ensure successful neurogenesis and formation of functional circuitries. In the nucleolus, production of ribosomes is essential for protein synthesis. In addition, it participates in chromatin organization and regulates the TP53 pathway via the ribosomal stress response. Its tight regulation is required for maintenance of genomic integrity. Mutations in several ribosomal components and trans-acting ribosomal biogenesis factors result in neurodevelopmental syndromes that present with microcephaly, autism, intellectual deficits and/or progressive neurodegeneration. Furthermore, ribosomal biogenesis is perturbed by exogenous factors that disrupt neurodevelopment including alcohol or Zika virus. In this review, we present recent literature that argues for a role of dysregulated ribosomal biogenesis in pathogenesis of various neurodevelopmental syndromes. We also discuss potential mechanisms through which such dysregulation may lead to cellular pathologies of the developing nervous system including insufficient proliferation and/or loss of neuroprogenitors cells, apoptosis of immature neurons, altered neuronal morphogenesis, and neurodegeneration.

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“…The SBV non‐structural protein (NS) localizes to the nucleolus leading to ZIKV‐like nucleoplasmic translocation of NPM1 (Gouzil et al . ).…”

Section: Neuroteratogenic Factors That Target Ribosomal Biogenesismentioning

confidence: 97%

Ribosomal biogenesis as an emerging target of neurodevelopmental pathologies

Hetman

Słomnicki

2018

Journal of Neurochemistry

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“…Herpes simplex virus 1 (HSV-1) infection led to redistribution of nucleolin, B23, and fibrillarin, and viral DNA replication requires a high level of nucleolin expression (33). In Schmallenberg virus (SBV)-infected cells, B23 undergoes a nucleolus-to-nucleoplasm redistribution, which is important for SBV-induced inhibition of cellular transcription (13). Adenovirus infection results in the redistribution of fibrillarin and B23 from the nucleolus to the cytoplasm (34).…”

Section: Discussionmentioning

confidence: 99%

“…For example, the pseudorabies virus (PRV) early protein UL54 contains a nucleolar localization signal (NoLS), and the mutation or deletion of the nucleolar localization sequence resulted in severe defects in viral gene expression and DNA synthesis (12). Schmallenberg virus (SBV), a trisegmented negative-strand RNA virus, encoded a nonstructural major virulence factor, which is targeted to mainly the nucleolus through an NoLS, and B23 undergoes a nucleolus-to-nucleoplasm redistribution in SBV-infected cells (13). Assembly-activating protein (AAP) of adeno-associated virus serotype 2 (AAV2) is a nucleolus-localizing protein that plays a critical role in transporting viral capsid VP3 protein to the nucleoli of infected cells for assembly.…”

mentioning

confidence: 99%

Identification and Characterization of the Nucleolar Localization Signal of Autographa californica Multiple Nucleopolyhedrovirus LEF5

Chen

Yan

Wang

et al. 2020

J Virol

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Autographa californica multiple nucleopolyhedrovirus (AcMNPV) late expression factor 5 (LEF5) is highly conserved in all sequenced baculovirus genomes and plays an important role in production of infectious viral progeny. In this study, nucleolar localization of AcMNPV LEF5 was characterized. Through transcriptome analysis, we identified two putative nucleolar proteins, Spodoptera frugiperda nucleostemin (SfNS) and fibrillarin (SfFBL), from Sf9 cells. Immunofluorescence analysis demonstrated that SfNS and SfFBL were localized to the nucleolus. AcMNPV infection resulted in reorganization of the nucleoli of infected cells. Colocalization of LEF5 and SfNS showed that AcMNPV LEF5 was localized to the nucleolus in Sf9 cells. Bioinformatic analysis revealed that basic amino acids of LEF5 are enriched at residues 184 to 213 and may contain a nucleolar localization signal (NoLS). Green fluorescent protein (GFP) fused to NoLS of AcMNPV LEF5 localized to the nucleoli of transfected cells. Multiple-point mutation analysis demonstrated that amino acid residues 197 to 204 are important for nucleolar localization of LEF5. To identify whether the NoLS in AcMNPV LEF5 is important for production of viral progeny, a lef5-null AcMNPV bacmid was constructed; several NoLS-mutated LEF5 proteins were reinserted into the lef5-null AcMNPV bacmid with a GFP reporter. The constructs containing point mutations at residues 185 to 189 or 197 to 204 in AcMNPV LEF5 resulted in reduction in production of infectious viral progeny and occlusion body yield in bacmid-transfected cells. Together, these data suggested that AcMNPV LEF5 contains an NoLS, which is important for nucleolar localization of LEF5, progeny production, and occlusion body production. IMPORTANCE Many viruses, including human and plant viruses, target nucleolar functions as part of their infection strategy. However, nucleolar localization for baculovirus proteins has not yet been characterized. In this study, two nucleolar proteins, SfNS and SfFBL, were identified in Sf9 cells. Our results showed that Autographa californica multiple nucleopolyhedrovirus (AcMNPV) infection resulted in redistribution of the nucleoli of infected cells. We demonstrated that AcMNPV late expression factor 5 (LEF5) could localize to the nucleolus and contains a nucleolar localization signal (NoLS), which is important for nucleolar localization of AcMNPV LEF5 and for production of viral progeny and yield of occlusion bodies.

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“…While BUNV NSs on October 11, 2020 by guest http://jvi.asm.org/ Downloaded from --is reducing the mRNA elongation-relevant phosphorylation of the C-terminal serine 2 residue (part of the 52 times repeated heptapeptide motif in the C-terminal domain CTD) (44), LACV NSs additionally degrades the large subunit (RPB1) of RNAP II (28). An RPB1-degradative activity was also described for the NSs of SBV (43,45). Interestingly, the effect of LACV NSs on RPB1 has strong similarities with parts of the DNA damage response (DDR), not only in terms of RPB1 degradation, but also by activation of other DDR markers (28).…”

Section: Introductionmentioning

confidence: 97%

Elongin C Contributes to RNA Polymerase II Degradation by the Interferon Antagonist NSs of La Crosse Orthobunyavirus

Schoen

Lau

Verbruggen

et al. 2020

J Virol

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Mosquito-borne La Crosse virus (LACV; genus Orthobunyavirus, family Peribunyaviridae, order Bunyavirales) causes up to 100 annual cases of severe meningoencephalitis in children and young adults in the United States. A major virulence factor of LACV is the nonstructural protein NSs, which inhibits host cell mRNA synthesis to prevent the induction of antiviral type I interferons (IFN-α/β). To achieve this host transcriptional shutoff, LACV NSs drives the proteasomal degradation of RPB1, the large subunit of mammalian RNA polymerase II. Here, we show that NSs acts in a surprisingly rapid manner, as RPB1 degradation was commencing already at 1 h postinfection. The RPB1 degradation was partially dependent on the cellular E3 ubiquitin ligase subunit Elongin C. Consequently, removal of Elongin C, but also of the subunits Elongin A or B by siRNA transfection partially rescued general RNAP II transcription and IFN-beta mRNA synthesis from the blockade by NSs. In line with these results, LACV NSs was found to trigger the redistribution of Elongin C out of nucleolar speckles, which, however, is an epiphenomenon rather than part of the NSs mechanism. Our study also shows that the molecular phenotype of LACV NSs is different from RNA polymerase II inhibitors like α-amanitin or Rift Valley fever virus NSs, indicating that LACV is unique in involving the Elongin complex to shut off host transcription and IFN response. IMPORTANCE The mosquito-borne La Crosse virus (LACV; genus Orthobunyavirus, family Peribunyaviridae, order Bunyavirales) is prevalent in the United States and can cause severe childhood meningoencephalitis. Its main virulence factor, the nonstructural protein NSs, is a strong inhibitor of the antiviral type I interferon (IFN) system. NSs acts by imposing a global host mRNA synthesis shutoff, mediated by NSs-driven proteasomal degradation of the RPB1 subunit of RNA polymerase II. Here, we show that RPB1 degradation commences as early as 1 h postinfection, and identify the E3 ubiquitin ligase subunit Elongin C (and its binding partners Elongins A and B) as an NSs cofactor involved in RPB1 degradation and in suppression of global as well as IFN-related mRNA synthesis.

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Nonstructural Protein NSs of Schmallenberg Virus Is Targeted to the Nucleolus and Induces Nucleolar Disorganization

Cited by 25 publications

References 51 publications

Ribosomal biogenesis as an emerging target of neurodevelopmental pathologies

Ribosomal biogenesis as an emerging target of neurodevelopmental pathologies

Identification and Characterization of the Nucleolar Localization Signal of Autographa californica Multiple Nucleopolyhedrovirus LEF5

Elongin C Contributes to RNA Polymerase II Degradation by the Interferon Antagonist NSs of La Crosse Orthobunyavirus

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