Enterovirus 71 (EV71) has emerged as a major cause of neurological disease following the near eradication of poliovirus. Accumulating evidence suggests that mammalian microRNAs (miRNAs), a class of noncoding RNAs of 18 to 23 nucleotides (nt) with important regulatory roles in many cellular processes, participate in host antiviral defenses. However, the roles of miRNAs in EV71 infection and pathogenesis are still unclear. Here, hsa-miR-296-5p expression was significantly increased in EV71-infected human cells. As determined by virus titration, quantitative real-time PCR (qRT-PCR), and Western blotting, overexpression of hsa-miR-296-5p inhibited, while inhibition of endogenous hsa-miR-296-5p facilitated, EV71 infection. Additionally, two potential hsa-miR-296-5p targets (nt 2115 to 2135 and nt 2896 to 2920) located in the EV71 genome (strain BrCr) were bioinformatically predicted and validated by luciferase reporter assays and Western blotting. Genomic alignment of various EV71 strains revealed synonymous mutations in hsa-miR-296-5p target sequences. Furthermore, the introduction of synonymous mutations into the EV71 BrCr genome by site-directed mutagenesis impaired the viral inhibitory effects of hsa-miR-296-5p and facilitated mutant virus infection. Meanwhile, compensatory mutations in corresponding hsa-miR-296-5p target sequences of the EV71 HeN strain (GenBank accession number JN256064 ) restored the inhibitory effects of the miRNA. These results indicate that hsa-miR-296-5p inhibits EV71 replication by targeting the viral genome. Our findings support the notion that cellular miRNAs can inhibit virus infection and that the virus mutates to escape suppression by cellular miRNAs.

Many viruses depend on the extensive membranous network of the endoplasmic reticulum (ER) for their translation, replication, and packaging. Certain membrane modifications of the ER can be a trigger for ER stress, as well as the accumulation of viral protein in the ER by viral infection. Then, unfolded protein response (UPR) is activated to alleviate the stress. Zika virus (ZIKV) is a mosquito-borne flavivirus and its infection causes microcephaly in newborns and serious neurological complications in adults. Here, we investigated ER stress and the regulating model of UPR in ZIKV-infected neural cells in vitro and in vivo. Mice deficient in type I and II IFN receptors were infected with ZIKV via intraperitoneal injection and the nervous tissues of the mice were assayed at 5 days post-infection. The expression of phospho-IRE1, XBP1, and ATF6 which were the key markers of ER stress were analyzed by immunohistochemistry assay in vivo. Additionally, the nuclear localization of XBP1s and ATF6n were analyzed by immunohistofluorescence. Furthermore, two representative neural cells, neuroblastoma cell line (SK-N-SH) and astrocytoma cell line (CCF-STTG1), were selected to verify the ER stress in vitro. The expression of BIP, phospho-elF2α, phospho-IRE1, and ATF6 were analyzed through western blot and the nuclear localization of XBP1s was performed by confocal immunofluorescence microscopy. RT-qPCR was also used to quantify the mRNA level of the UPR downstream genes in vitro and in vivo. ZIKV infection significantly upregulated the expression of ER stress markers in vitro and in vivo. Phospho-IRE1 and XBP1 expression significantly increased in the cerebellum and mesocephalon, while ATF6 expression significantly increased in the mesocephalon. ATF6n and XBP1s were translocated into the cell nucleus. The levels of BIP, ATF6, phospho-elf2α, and spliced xbp1 also significantly increased in vitro. Furthermore, the downstream genes of UPR were detected to investigate the regulating model of the UPR during ZIKV infection in vitro and in vivo. The transcriptional levels of atf4, gadd34, chop, and edem-1 in vivo and that of gadd34 and chop in vitro significantly increased. Findings in this study demonstrated that ZIKV infection activates ER stress in neural cells. The results offer clues to further study the mechanism of neuropathogenesis caused by ZIKV infection.

Summary: Nasal administration has emerged as a promising and attractive route for vaccination, especially for the prophylaxis of respiratory diseases. Our previous studies have shown that severe acute respiratory syndrome coronavirus (SARS‐CoV) virus‐like particles (VLPs) can be assembled using a recombinant baculovirus (rBV) expression system and such VLPs induce specific humoral and cellular immune responses in mice after subcutaneous injection. Here, we investigated mucosal immune responses to SARS‐CoV VLPs in a mouse model. Mice were immunized in parallel, intraperitoneally or intranasally, with VLPs alone or with VLPs plus cytosine–phosphate–guanosine (CpG). Immune responses, including the production of SARS‐CoV‐specific serum immunoglobulin G (IgG) and secretory immunoglobulin A (sIgA), were determined in mucosal secretions and tissues. Both immunizations induced SARS‐CoV‐specific IgG, although the levels of IgG in groups immunized via the intraperitoneal (i.p.) route were higher. sIgA was detected in saliva in groups immunized intranasally but not in groups immunized intraperitoneally. CpG had an adjuvant effect on IgA production in genital tract washes when administered intranasally but only affected IgA production in faeces samples when administered intraperitoneally. In addition, IgA was also detected in mucosal tissues from the lung and intestine, while CpG induced an increased level of IgA in the intestine. Most importantly, neutralization antibodies were detected in sera after i.p. and intranasal (i.n.) immunizations. Secretions in genital tract washes from the i.n. group also showed neutralization activity. Furthermore, VLPs that were administered intraperitoneally elicited cellular immune responses as demonstrated by enzyme‐linked immunospot (ELISPOT) assay analyses. In summary, our study indicates that mucosal immunization with rBV SARS‐CoV VLPs represent an effective means for eliciting protective systemic and mucosal immune responses against SARS‐CoV, providing important information for vaccine design.

Zika virus (ZIKV) infection during the large epidemics in the Americas is related to congenital abnormities or fetal demise. To date, there is no vaccine, antiviral drug, or other modality available to prevent or treat Zika virus infection. Here we designed novel live attenuated ZIKV vaccine candidates using a codon pair deoptimization strategy. Three codon pair-deoptimized ZIKVs (Min E, Min NS1, and Min E+NS1) were de novo synthesized and recovered by reverse genetics and contained large amounts of underrepresented codon pairs in the E gene and/or NS1 gene. The amino acid sequence was 100% unchanged. The codon pair-deoptimized variants had decreased replication fitness in Vero cells (Min NS1 ≫ Min E > Min E+NS1), replicated more efficiently in insect cells than in mammalian cells, and demonstrated diminished virulence in a mouse model. In particular, Min E+NS1, the most restrictive variant, induced sterilizing immunity with a robust neutralizing antibody titer, and a single immunization achieved complete protection against lethal challenge and vertical ZIKV transmission during pregnancy. More importantly, due to the numerous synonymous substitutions in the codon pair-deoptimized strains, reversion to wild-type virulence through gradual nucleotide sequence mutations is unlikely. Our results collectively demonstrate that ZIKV can be effectively attenuated by codon pair deoptimization, highlighting the potential of Min E+NS1 as a safe vaccine candidate to prevent ZIKV infections. IMPORTANCE Due to unprecedented epidemics of Zika virus (ZIKV) across the Americas and the unexpected clinical symptoms, including Guillain-Barré syndrome, microcephaly, and other birth defects in humans, there is an urgent need for ZIKV vaccine development. Here we provided the first attenuated versions of ZIKV with two important genes (E and/or NS1) that were subjected to codon pair deoptimization. Compared to parental ZIKV, the codon pair-deoptimized ZIKVs were mammal attenuated and preferred insect to mammalian cells. Min E+NS1, the most restrictive variant, induced sterilizing immunity with a robust neutralizing antibody titer and achieved complete protection against lethal challenge and vertical virus transmission during pregnancy. More importantly, the massive synonymous mutational approach made it impossible for the variant to revert to wild-type virulence. Our results have proven the feasibility of codon pair deoptimization as a strategy to develop live attenuated vaccine candidates against flaviviruses such as ZIKV, Japanese encephalitis virus, and West Nile virus.

Human bocavirus (HBoV) mainly infects young children. Although many infected children suffer from respiratory or gastroenteric tract diseases, an association between HBoV and these diseases is not definite. Because modulation of type I IFN is crucial for viruses to establish efficient replication, in this study, we tested whether HBoV modulates type I IFN production. We observed that a nearly full-length HBoV clone significantly reduced both Sendai virus (SeV)- and poly(deoxyadenylic-thymidylic) acid-induced IFN-β production. Further study showed that NP1 blocked IFN-β activation in response to SeV, poly(deoxyadenylic-thymidylic) acid, and IFN-β pathway inducers, including retinoic acid-inducible protein I, mitochondrial antiviral signaling protein, inhibitor of κB kinase ε, and TANK-binding kinase 1. In addition, NP1 interfered with IRF-3–responsive PRD(III-I) promoter activated by SeV and a constitutively active mutant of IRF-3 (IRF-3/5D). Although NP1 suppressed the IRF-3 pathway, it did not affect IRF-3 activation processes, including phosphorylation, dimerization, and nuclear translocation. Coimmunoprecipitation assays confirmed the interaction between NP1 and IRF-3. Additional deletion mutagenesis and coimmunoprecipitation assays revealed that NP1 bound to the DNA-binding domain of IRF-3, resulting in the interruption of an association between IRF-3 and IFNB promoter. Altogether, our results indicate that HBoV NP1 blocks IFN production through a unique mechanism. To our knowledge, this is the first study to investigate the modulation of innate immunity by HBoV. Our findings suggest a potential immune-evasion mechanism used by HBoV and provide a basis for better understanding HBoV pathogenesis.