Toscana Virus NSs Protein Promotes Degradation of Double-Stranded RNA-Dependent Protein Kinase

Kalveram, Birte; Ikegami, Tetsuro

doi:10.1128/jvi.02506-12

Cited by 40 publications

(48 citation statements)

References 35 publications

(51 reference statements)

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“…We previously reported that rMP-12 carrying the Toscana virus (TOSV) NSs increases the neuroinvasion of rMP-12 in mice (death rate, ϳ36%) (68). TOSV NSs inhibits the IFN-␤ promoter and promotes the degradation of PKR, yet it does not suppress host general transcription (75). This indicates that the quality of the host antiviral response in target cells influences the neuroinvasion of RVFV.…”

Section: Discussionmentioning

confidence: 99%

Rift Valley Fever Virus MP-12 Vaccine Is Fully Attenuated by a Combination of Partial Attenuations in the S, M, and L Segments

Ikegami

Hill

Smith

et al. 2015

J Virol

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Rift Valley fever (RVF) is a mosquito-borne zoonotic disease endemic to Africa and characterized by a high rate of abortion in ruminants and hemorrhagic fever, encephalitis, or blindness in humans. RVF is caused by Rift Valley fever virus (RVFV; family Bunyaviridae, genus Phlebovirus), which has a tripartite negative-stranded RNA genome (consisting of the S, M, and L segments). Further spread of RVF into countries where the disease is not endemic may affect the economy and public health, and vaccination is an effective approach to prevent the spread of RVFV. A live-attenuated MP-12 vaccine is one of the best-characterized RVF vaccines for safety and efficacy and is currently conditionally licensed for use for veterinary purposes in the United States. Meanwhile, as of 2015, no other RVF vaccine has been conditionally or fully licensed for use in the United States. The MP-12 strain is derived from wild-type pathogenic strain ZH548, and its genome encodes 23 mutations in the three genome segments. However, the mechanism of MP-12 attenuation remains unknown. We characterized the attenuation of wild-type pathogenic strain ZH501 carrying a mutation(s) of the MP-12 S, M, or L segment in a mouse model. Our results indicated that MP-12 is attenuated by the mutations in the S, M, and L segments, while the mutations in the M and L segments confer stronger attenuation than those in the S segment. We identified a combination of 3 amino acid changes, Y259H (Gn), R1182G (Gc), and R1029K (L), that was sufficient to attenuate ZH501. However, strain MP-12 with reversion mutations at those 3 sites was still highly attenuated. Our results indicate that MP-12 attenuation is supported by a combination of multiple partial attenuation mutations and a single reversion mutation is less likely to cause a reversion to virulence of the MP-12 vaccine. IMPORTANCERift Valley fever (RVF) is a mosquito-transmitted viral disease that is endemic to Africa and that has the potential to spread into other countries. Vaccination is considered an effective way to prevent the disease, and the only available veterinary RVF vaccine in the United States is a live-attenuated MP-12 vaccine, which is conditionally licensed. Strain MP-12 is different from its parental pathogenic RVFV strain, strain ZH548, because of the presence of 23 mutations. This study determined the role of individual mutations in the attenuation of the MP-12 strain. We found that full attenuation of MP-12 occurs by a combination of multiple mutations. Our findings indicate that a single reversion mutation will less likely cause a major reversion to virulence of the MP-12 vaccine.

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Section: Discussionmentioning

confidence: 99%

Rift Valley Fever Virus MP-12 Vaccine Is Fully Attenuated by a Combination of Partial Attenuations in the S, M, and L Segments

Ikegami

Hill

Smith

et al. 2015

J Virol

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“…TOSV NSs has been shown to possess two distinct functions: (i) to limit IFN-␤ upregulation (Gori Savellini et al, 2001) and (ii) to promote RNA-dependent protein kinase degradation (Kalveram and Ikegami, 2013). Further studies will be necessary to understand if and how these phosphorylation sites are involved in these functions.…”

Section: Resultsmentioning

confidence: 98%

Genetic variability of the S segment of Toscana virus

et al. 2015

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“…28,29,32 We assume that RVFV NSs functions, such as general transcription suppression, PKR degradation, or IFN-b suppression, coordinately support efficient RVFV replication and spread in liver tissues, and thus, the spreads of rZH501-TOSNSs and rZH501-SFSNSs were more restricted than parental rZH501 in mouse livers.…”

Section: Discussionmentioning

confidence: 99%

“…The NSs gene of ZH501 S-segment in the pProT7-wS(C) plasmid were replaced with NSs open-reading frame (ORF) of TOSV (ISS. Phl.3), SFSV (Sabin), PTA (TVP10208), PTB (TVP13993), or PKRDE7, as described previously 13,30,32,33 to rescue rZH501-TOSNSs, rZH501-SFSNSs, rZH501-PTANSs, rZH501-PTBNSs, or rZH501-PKRDE7, respectively. To generate rZH501-DNSs16/198 or rZH501-DNSm21/384, corresponding regions in the S-, or M-segment were deleted by site-directed mutagenesis using pProT7-wS(C) or pProT7-wM(C) plasmids, respectively.…”

Section: Methodsmentioning

confidence: 99%

“…[28][29][30][31] In addition, TOSV NSs also promotes the degradation of PKR. 32 The MP-12 encoding TOSV NSs (rMP12-TOSNSs), however, showed increased viral encephalitis in vaccinated mice (30% or more), compared to parental MP-12, which causes encephalitis in up to 5% of mice. 33 The MP-12 encoding SFSV NSs (rMP12-SFSNSs) or PTA NSs (rMP12-PTANSs) displayed strong immunogenicity similar to that of the parental MP-12 strain, while no increased virulence has been detected in vaccinated mice.…”

Section: Introductionmentioning

confidence: 99%

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Attenuation of pathogenic Rift Valley fever virus strain through the chimeric S-segment encoding sandfly fever phlebovirus NSs or a dominant-negative PKR

et al. 2016

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Rift Valley fever is a mosquito-borne zoonotic disease affecting ruminants and humans. Rift Valley fever virus (RVFV: family Bunyaviridae, genus Phlebovirus) causes abortions and fetal malformations in ruminants, and hemorrhagic fever, encephalitis, or retinitis in humans. The live-attenuated MP-12 vaccine is conditionally licensed for veterinary use in the US. However, this vaccine lacks a marker for the differentiation of vaccinated from infected animals (DIVA). NSs gene is dispensable for RVFV replication, and thus, rMP-12 strains lacking NSs gene is applicable to monitor vaccinated animals. However, the immunogenicity of MP-12 lacking NSs was not as high as parental MP-12. Thus, chimeric MP-12 strains encoding NSs from either Toscana virus (TOSV), sandfly fever Sicilian virus (SFSV) or Punta Toro virus Adames strain (PTA) were characterized previously. Although chimeric MP-12 strains are highly immunogenic, the attenuation through the S-segment remains unknown. Using pathogenic ZH501 strain, we aimed to demonstrate the attenuation of ZH501 strain through chimeric S-segment encoding either the NSs of TOSV, SFSV, PTA, or Punta Toro virus Balliet strain (PTB). In addition, we characterized rZH501 encoding a human dominant-negative PKR (PKRDE7), which also enhances the immunogenicity of MP-12. Study done on mice revealed that attenuation of rZH501 occurred through the S-segment encoding either PKRDE7 or SFSV NSs. However, rZH501 encoding either TOSV, PTA, or PTB NSs in the S-segment uniformly caused lethal encephalitis. Our results indicated that the S-segments encoding PKRDE7 or SFSV NSs are attenuated and thus applicable toward next generation MP-12 vaccine candidates that encode a DIVA marker.

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Toscana Virus NSs Protein Promotes Degradation of Double-Stranded RNA-Dependent Protein Kinase

Cited by 40 publications

References 35 publications

Rift Valley Fever Virus MP-12 Vaccine Is Fully Attenuated by a Combination of Partial Attenuations in the S, M, and L Segments

Rift Valley Fever Virus MP-12 Vaccine Is Fully Attenuated by a Combination of Partial Attenuations in the S, M, and L Segments

Genetic variability of the S segment of Toscana virus

Attenuation of pathogenic Rift Valley fever virus strain through the chimeric S-segment encoding sandfly fever phlebovirus NSs or a dominant-negative PKR

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