title: A single amino acid in nonstructural protein NS4B confers virulence to dengue virus in AG129 mice through enhancement of viral RNA synthesis.
abstract: Dengue (DEN) is a mosquito-borne viral disease that has become an increasing economic and health burden for the tropical and subtropical world. The lack of an appropriate animal model of DEN has greatly impeded the study of its pathogenesis and the development of vaccines/antivirals. We recently reported a DEN virus 2 (DENV-2) strain (D2Y98P) that lethally infects immunocompromised AG129 mice, resulting in organ damage or dysfunction and increased vascular permeability, hallmarks of severe DEN in patients (G. K. Tan et al., PLoS Negl. Trop. Dis. 4:e672, 2010). Here we report the identification of one critical virulence determinant of strain D2Y98P. By mutagenesis, we showed that a Phe-to-Leu alteration at amino acid position 52 in nonstructural protein NS4B completely abolished the pathogenicity of the D2Y98P virus, as evidenced by a lack of lethality and the absence of histological signs of disease, which correlated with reduced viral titers and intact vascular permeability. Conversely, a Leu-to-Phe alteration at position 52 of NS4B in nonvirulent DENV-2 strain TSV01 led to 80% lethality and increased viremia. The NS4B(Phe52) viruses displayed enhanced RNA synthesis in mammalian cells but not in mosquito cells. The increased viral RNA synthesis was independent of the ability of NS4B to interfere with the host type I interferon response. Overall, our results demonstrate that Phe at position 52 in NS4B confers virulence in mice on two independent DENV-2 strains through enhancement of viral RNA synthesis. In addition to providing further insights into the functional role of NS4B protein, our findings further support a direct relationship between viral loads and DEN pathogenesis in vivo, consistent with observations in DEN patients.
authors.affiliation: Novartis Institute for Tropical Diseases, National University of Singapore, Singapore.
authors.forename: Dixon
authors.initials: D
authors.lastname: Grant
authors.forename: Grace K
authors.initials: GK
authors.lastname: Tan
authors.forename: Min
authors.initials: M
authors.lastname: Qing
authors.forename: Jowin K W
authors.initials: JK
authors.lastname: Ng
authors.forename: Andy
authors.initials: A
authors.lastname: Yip
authors.forename: Gang
authors.initials: G
authors.lastname: Zou
authors.forename: Xuping
authors.initials: X
authors.lastname: Xie
authors.forename: Zhiming
authors.initials: Z
authors.lastname: Yuan
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Schreiber
authors.forename: Wouter
authors.initials: W
authors.lastname: Schul
authors.forename: Pei-Yong
authors.initials: PY
authors.lastname: Shi
authors.forename: Sylvie
authors.initials: S
authors.lastname: Alonso
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D000818:Animals; D002460:Cell Line; D004279:DNA, Viral / Q000096:biosynthesis*; D003716:Dengue Virus / Q000235:genetics / Q000472:pathogenicity*; D005455:Fluorescent Antibody Technique; D006801:Humans; D051379:Mice; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017361:Viral Nonstructural Proteins / Q000737:chemistry / Q000502:physiology*; D014774:Virulence
chemical_list: D000596:Amino Acids; D004279:DNA, Viral; C080107:NS4B protein, flavivirus; D017361:Viral Nonstructural Proteins