Deletion of the NSm Virulence Gene of Rift Valley Fever Virus Inhibits Virus Replication in and Dissemination from the Midgut of Aedes aegypti Mosquitoes

Kading, Rebekah C.; Crabtree, Mary B.; Bird, Brian H.; Nichol, Stuart T.; Erickson, Bobbie R.; Horiuchi, Kalanthe; Biggerstaff, Brad J.; Miller, Barry R.

doi:10.1371/journal.pntd.0002670

Cited by 60 publications

(68 citation statements)

References 31 publications

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“…Work on BUNV NSm demonstrated that the protein can localize to the Golgi efficiently on its own (46) and may play a role in viral assembly (47). In Rift Valley fever virus (RVFV), the NSm protein is important for infection in mosquitoes by allowing the virus to cross the midgut barrier (48,49). Similarly, in tospoviruses, the NSm protein has been shown to be important for virus cell-to-cell spread (50)(51)(52).…”

Section: Discussionmentioning

confidence: 99%

Generation of Recombinant Oropouche Viruses Lacking the Nonstructural Protein NSm or NSs

Tilston-Lunel

Acrani

Randall

et al. 2016

J Virol

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Oropouche virus (OROV) is a midge-borne human pathogen with a geographic distribution in South America. OROV was first isolated in 1955, and since then, it has been known to cause recurring outbreaks of a dengue-like illness in the Amazonian regions of Brazil. OROV, however, remains one of the most poorly understood emerging viral zoonoses. Here we describe the successful recovery of infectious OROV entirely from cDNA copies of its genome and generation of OROV mutant viruses lacking either the NSm or the NSs coding region. Characterization of the recombinant viruses carried out in vitro demonstrated that the NSs protein of OROV is an interferon (IFN) antagonist as in other NSs-encoding bunyaviruses. Additionally, we demonstrate the importance of the nine C-terminal amino acids of OROV NSs in IFN antagonistic activity. OROV was also found to be sensitive to IFN-␣ when cells were pretreated; however, the virus was still capable of replicating at doses as high as 10,000 U/ml of IFN-␣, in contrast to the family prototype BUNV. We found that OROV lacking the NSm protein displayed characteristics similar to those of the wild-type virus, suggesting that the NSm protein is dispensable for virus replication in the mammalian and mosquito cell lines that were tested. IMPORTANCE Oropouche virus (OROV) is a public health threat in Central andSouth America, where it causes periodic outbreaks of denguelike illness. In Brazil, OROV is the second most frequent cause of arboviral febrile illness after dengue virus, and with the current rates of urban expansion, more cases of this emerging viral zoonosis could occur. To better understand the molecular biology of OROV, we have successfully rescued the virus along with mutants. We have established that the C terminus of the NSs protein is important in interferon antagonism and that the NSm protein is dispensable for virus replication in cell culture. The tools described in this paper are important in terms of understanding this important yet neglected human pathogen.

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Section: Discussionmentioning

confidence: 99%

Generation of Recombinant Oropouche Viruses Lacking the Nonstructural Protein NSm or NSs

Tilston-Lunel

Acrani

Randall

et al. 2016

J Virol

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“…A major virulence factor, NSs, is a nonstructural protein dispensable for viral replication (46,47) and plays a major role in counteracting the innate immunity of the host, e.g., by (i) shutting off of host cell transcription by interacting with TFIIH p44 (48) and by promoting the degradation of TFIIH p62 (49,50), (ii) specific inhibition of the beta interferon (IFN-␤) promoter (51,52), and (iii) posttranslational degradation of double-stranded RNA-dependent protein kinase (PKR) (53,54). Another nonstructural protein, NSm, has a role in delaying apoptosis in mammalian cells (55,56), while it is involved in the efficient transmission of virus in mosquitoes (57,58). The 78-kDa protein is a structural protein for virions derived from mosquito C6/36 cells but not for those derived from VeroE6 cells (3,59).…”

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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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“…The NSs protein, the major virulence factor, has been shown to inhibit host transcriptional immune response (Bouloy et al 2001) through generalized transcription downregulation, including repression of interferon-b (IFN-b) , Le May et al 2004, Le May et al 2008) and degradation of protein kinase R , Ikegami et al 2009). The NSm protein functions to suppress virus-induced apoptosis (Won et al 2007), and there is evidence that it plays a functional role in the vector competence of mosquitos for RVFV at the level of the midgut barrier (Kading et al 2014). The glycoproteins Gn and Gc are surface proteins that play a role in virus attachment to initiate infection and have been shown to carry epitopes that elicit the production of neutralizing antibodies, a correlate of protective immunity (Besselaar et al 1991, Besselaar and Blackburn 1992, Besselaar and Blackburn 1994.…”

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confidence: 99%

A Glycoprotein Subunit Vaccine Elicits a Strong Rift Valley Fever Virus Neutralizing Antibody Response in Sheep

Faburay

Lebedev²,

McVey³

et al. 2014

Vector-Borne and Zoonotic Diseases

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Rift Valley fever virus (RVFV), a member of the Bunyaviridae family, is a mosquito-borne zoonotic pathogen that causes serious morbidity and mortality in livestock and humans. The recent spread of the virus beyond its traditional endemic boundaries in Africa to the Arabian Peninsula coupled with the presence of susceptible vectors in nonendemic countries has created increased interest in RVF vaccines. Subunit vaccines composed of specific virus proteins expressed in eukaryotic or prokaryotic expression systems are shown to elicit neutralizing antibodies in susceptible hosts. RVFV structural proteins, amino-terminus glycoprotein (Gn), and carboxylterminus glycoprotein (Gc), were expressed using a recombinant baculovirus expression system. The recombinant proteins were reconstituted as a GnGc subunit vaccine formulation and evaluated for immunogenicity in a target species, sheep. Six sheep were each immunized with a primary dose of 50 lg of each vaccine immunogen with the adjuvant montanide ISA25; at day 21, postvaccination, each animal received a second dose of the same vaccine. The vaccine induced a strong antibody response in all animals as determined by indirect enzyme-linked immunosorbent assay (ELISA). A plaque reduction neutralization test (PRNT 80 ) showed the primary dose of the vaccine was sufficient to elicit potentially protective virus neutralizing antibody titers ranging from 40 to 160, and the second vaccine dose boosted the titer to more than 1280. Furthermore, all animals tested positive for neutralizing antibodies at day 328 postvaccination. ELISA analysis using the recombinant nucleocapsid protein as a negative marker antigen indicated that the vaccine candidate is DIVA (differentiating infected from vaccinated animals) compatible and represents a promising vaccine platform for RVFV infection in susceptible species.

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Deletion of the NSm Virulence Gene of Rift Valley Fever Virus Inhibits Virus Replication in and Dissemination from the Midgut of Aedes aegypti Mosquitoes

Cited by 60 publications

References 31 publications

Generation of Recombinant Oropouche Viruses Lacking the Nonstructural Protein NSm or NSs

Generation of Recombinant Oropouche Viruses Lacking the Nonstructural Protein NSm or NSs

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

A Glycoprotein Subunit Vaccine Elicits a Strong Rift Valley Fever Virus Neutralizing Antibody Response in Sheep

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