Please use this identifier to cite or link to this item: http://scholarbank.nus.edu.sg/handle/10635/23281
Title: THE ROLE OF DENGUE VIRUS NON-STRUCTURAL (NS) PROTEINS IN THE PATHOGENESIS OF DENGUE VIRUS INFECTION
Authors: LIU WEI YANG EDWIN
Keywords: dengue, non-structural proteins, flavivirus
Issue Date: 21-Jan-2011
Source: LIU WEI YANG EDWIN (2011-01-21). THE ROLE OF DENGUE VIRUS NON-STRUCTURAL (NS) PROTEINS IN THE PATHOGENESIS OF DENGUE VIRUS INFECTION. ScholarBank@NUS Repository.
Abstract: Viral pathogenesis involves the intricate interactions between multitudes of viral and host factors. Emerging evidences showed that dengue virus non-structural proteins can contribute to the pathogenesis of dengue virus infection by regulating key signalling pathways in the host. To date, the underlying molecular mechanisms by which dengue virus non-structural proteins modulate host signalling pathways are still not clearly defined. Hence, this study aims to dissect the molecular basis of signalling pathway regulation by dengue virus non-structural proteins. Profiling of signal transduction pathways modulated during dengue virus infection was first performed using a customized phospho-protein detection assay. Dengue virus non-structural proteins were next screened for their ability to regulate these pathways. In depth analyses using yeast-two-hybrid interaction domain screening, co-immunoprecipitation, immunofluorescence, Western Blot and interferon-ß (IFNß) promoter reporter assays were then performed to identify the mechanisms of action of dengue virus non-structural proteins on these pathways. Dengue virus infection resulted in the modulation of nuclear factor kappa of activated B cells (NF-kB), janus kinase/signal transducers and activators of transcription (Jak/STAT), phosphoinositide 3-kinase/Akt (PI3K/Akt) and mitogen-activated protein kinase (MAPK) signalling pathways. Dengue virus non-structural 1 protein exhibited significant inhibitory effect on Jak/STAT signalling. The coiled-coil domain of STAT3ß was identified as the interaction domain between dengue virus non-structural 1 and STAT3ß proteins in yeast-two-hybrid system. Interaction studies in mammalian cells, however, revealed that dengue virus non-structural 1 protein did not block Jak/STAT signalling through direct interaction with STAT3a/ß protein. Dengue virus non-structural 1 protein also did not inhibit IFNa- and IL6-mediated STAT3 activation. Analysis of upstream IFNß promoter activity showed that dengue virus as well as its non-structural 1 protein down-regulated polyinosine-polycytidylic acid (pIC)-induced IFNß gene induction. This attenuation of IFNß promoter activation was found not to be attributed to the modulation of NF-kB signalling. Instead, dengue non-structural 1 protein hampered pIC-stimulated IFNß promoter induction by antagonising upstream interferon regulatory factor 3 (IRF3) activation. Reduced IRF3 nuclear localization was observed in dengue virus non-structural 1 protein-expressing cells. Impairment of IRF3 activation by dengue virus non-structural 1 protein also led to transcriptional inhibition of downstream interferon-stimulated genes (ISGs) such as chemokine (C-C motif) ligand 5 (CCL5), (IRF1), (IRF7), interferon-stimulated gene 56 (ISG56), myxovirus resistance protein 1 (Mx1), 2'-5'-oligoadenylate synthetase 1 (OAS1) and viperin. Lastly, viperin protein expression was also blocked by dengue virus non-structural 1 protein. The findings of this study offered novel insights into the suppression of innate immune responses by dengue virus through its non-structural 1 protein which could lead to increased virus replication. This could impact clinical outcomes as elevated virus production was shown to be associated with greater disease severity. This implicates targeting dengue virus non-structural 1 protein as an innovative strategy for anti-viral therapeutic intervention and development of vaccines.
URI: http://scholarbank.nus.edu.sg/handle/10635/23281
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