Comparative molecular characterization of gene segment 11-derived NSP6 from lamb rotavirus LLR strain used as a human vaccine in China

CRISPR/Cas9 screens identify key host factors that enhance rotavirus reverse genetics efficacy and vaccine production

Rotaviruses pose a significant threat to young children. To identify novel pro- and anti-rotavirus host factors, we performed genome-wide CRISPR/Cas9 screens using rhesus rotavirus and African green monkey cells. Genetic deletion of either SERPINB1 or TMEM236, the top two antiviral factors, in MA104 cells increased virus titers in a rotavirus strain independent manner. Using this information, we optimized the existing rotavirus reverse genetics systems by combining SERPINB1 knockout MA104 cells with a C3P3-G3 helper plasmid. We improved the recovery efficiency and rescued several low-titer rotavirus reporter and mutant strains that prove difficult to rescue otherwise. Furthermore, we demonstrate that TMEM236 knockout in Vero cells supported higher yields of two live-attenuated rotavirus vaccine strains than the parental cell line and represents a more robust vaccine-producing cell substrate. Collectively, we developed a third-generation optimized rotavirus reverse genetics system and generated gene-edited Vero cells as a new substrate for improving rotavirus vaccine production.

Rotavirus NSP6 localizes to mitochondria via a predicted N-terminal α-helix

Specific roles have been ascribed to each of the 12 known rotavirus proteins apart from the non-structural protein 6 (NSP6). However, NSP6 may be present at sites of viral replication within the cytoplasm. Here we report that NSP6 from diverse species of rotavirus A localizes to mitochondria via conserved sequences in a predicted N-terminal α-helix. This suggests that NSP6 may affect mitochondrial functions during rotavirus infection.

Defective rotavirus particle assembly in lovastatin-treated MA104 cells

Rotavirus is a non-enveloped virus that depends on cellular lipids for cell entry and associates with lipid rafts during assembly. However, the effects of cellular lipids on rotavirus assembly are still not fully understood. The present study analyzes the effects of lovastatin, an inhibitor of cholesterol biosynthesis, during rotavirus infection in MA104 cells with regard to viral growth and particle assembly. Following viral infection, a 2-log relative reduction of viral titers was observed in drug-treated cells, while viral mRNA levels in infected cells remained unaltered in both groups. Furthermore, the levels of some viral proteins in drug-treated cells were elevated. The observed discordance between the viral RNA and protein levels and the decrease in infectivity titers of viral progeny in the drug-treated cells suggested that the drug affects viral assembly, the viral proteins not being properly incorporated into virions. Transmission electron microscopic (TEM) analysis revealed that in drug-treated cells there was an increase in “empty-looking” rotavirus particles devoid of an electron-dense core as compared to the normal, electron-dense particles seen in untreated infected cells. The present study thus provides visual evidence of defective rotavirus particle assembly as a result of cholesterol depletion.

Group A human rotavirus genomics: evidence that gene constellations are influenced by viral protein interactions

Group A human rotaviruses (HRVs) are the major cause of severe viral gastroenteritis in infants and young children. To gain insight into the level of genetic variation among HRVs, we determined the genome sequences for 10 strains belonging to different VP7 serotypes (G types). The HRVs chosen for this study, D, DS-1, P, ST3, IAL28, Se584, 69M, WI61, A64, and L26, were isolated from infected persons and adapted to cell culture to use as serotype references. Our sequencing results revealed that most of the individual proteins from each HRV belong to one of three genotypes (1, 2, or 3) based on their similarities to proteins of genogroup strains (Wa, DS-1, or AU-1, respectively). Strains D, P, ST3, IAL28, and WI61 encode genotype 1 (Wa-like) proteins, whereas strains DS-1 and 69M encode genotype 2 (DS-1-like) proteins. Of the 10 HRVs sequenced, 3 of them (Se584, A64, and L26) encode proteins belonging to more than one genotype, indicating that they are intergenogroup reassortants. We used amino acid sequence alignments to identify residues that distinguish proteins belonging to HRV genotype 1, 2, or 3. These genotype-specific changes cluster in definitive regions within each viral protein, many of which are sites of known protein-protein interactions. For the intermediate viral capsid protein (VP6), the changes map onto the atomic structure at the VP2-VP6, VP4-VP6, and VP7-VP6 interfaces. The results of this study provide evidence that group A HRV gene constellations exist and may be influenced by interactions among viral proteins during replication.

Application of bioinformatics-coupled experimental analysis reveals a new transport-competent nuclear localization signal in the nucleoprotein of influenza A virus strain

Background

Two nuclear localization sequences (NLS) in influenza A virus nucleoprotein (NP) have been demonstrated to be critical for nuclear import of NP and viral ribonucleoprotein complexes. However, a deletion mutant lacking these two signals was still able to localize to the nucleus suggesting the presence of yet another (a third) potential NLS in the NP protein. In order to identify the nature of this potential NLS signal in the NP of a WS/33L influenza virus A strain, we utilized the tools of bioinformatics coupled with functional experimental analyses in the present study.

Results

Comparison of the deduced aa sequence of NP of WS/33L strain with the published WS/33 NP sequences revealed that a single amino acid (aa) change (Met to Arg) at position 105 results in converting the flanking regions (between aa position 90–121, a 32-residue stretch) into two classical overlapping bipartite NLS (obpNLS). GenBank search revealed that 9 out of 500 published NP sequences contain a similar Arg at position 105 (instead of Met) with a 100% homology to the obpNLS region. Various NP-green fluorescent protein (GFP) fusion constructs with and without the signal (obpNLS-Arg¹⁰⁵) were utilized to understand the functional nature of this signal. We analyzed the transport competency of the expressed chimeric proteins in terms of their cellular localization by confocal immunofluorescence assay. Our analysis revealed that all NP-GFP constructs containing the wild-type (R¹⁰⁵) sequence localized predominantly to the nucleus. Constructs lacking the obpNLS or constructs with reverse mutation (R¹⁰⁵ to M¹⁰⁵) on the other hand exhibited predominant cytoplasmic localization pattern. Interestingly, when the 32 aa obpNLS was fused with an unrelated viral protein (rotavirus NSP6) that has been known to be cytoplasmic protein, the chimeric protein (obpNLS-NSP6) was efficiently transported into the nucleus, indicating an efficient nuclear transport function of the 32-residue obpNLS in the NP of WS/33L strain of influenza A virus.

Conclusion

This report while not only establishing a new NLS in the influenza A virus strain, it also reinforces the idea that proper application of bioinformatics-coupled experimental analysis serves as a powerful tool in identifying new functional signals in proteins of interest.

Rotavirus vaccines in developed countries

PURPOSE OF REVIEW

Rotavirus is the most common cause of diarrhoea and dehydration in early childhood. The recent licensure in many nations of vaccines against rotavirus offers promise to significantly reduce this toll. The present review describes recent developments regarding rotavirus vaccines and the challenges they face.

RECENT FINDINGS

Rotavirus causes significant morbidity and impact upon healthcare systems, at both inpatient and outpatient levels. An earlier rotavirus vaccine, since withdrawn, was temporally associated with intussusception causing small bowel obstruction, especially in infants receiving their first dose at an older age. Large-scale safety and efficacy studies of two new live, oral, attenuated vaccines have shown excellent efficacy against severe rotavirus gastroenteritis. Importantly, both studies detected no association with intussusception with these new vaccines when administered at the scheduled ages. Developed using different rotavirus vaccinology philosophies, questions remain regarding their coverage against new rotavirus serotypes. Ongoing intussusception surveillance following introduction should answer whether they may be safely administered beyond scheduled ages.

SUMMARY

Safe, efficacious rotavirus vaccines are available in many developed countries, offering significant promise to reduce the burden of gastroenteritis and dehydration. The impact of these vaccines upon not only morbidity, but also circulating rotavirus serotypes, will be monitored with interest.