NS5 of Dengue Virus Mediates STAT2 Binding and Degradation

Abstract

The mammalian interferon (IFN) signaling pathway is a primary component of the innate antiviral response. As such, viral pathogens have devised multiple mechanisms to antagonize this pathway and thus facilitate infection. Dengue virus (DENV) encodes several proteins (NS2a, NS4a, and NS4b) that have been shown individually to inhibit the IFN response. In addition, DENV infection results in reduced levels of expression of STAT2, which is required for IFN signaling (M. Jones, A. Davidson, L. Hibbert, P. Gruenwald, J. Schlaak, S. Ball, G. R. Foster, and M. Jacobs, J. Virol. 79:5414-5420, 2005). Translation of the DENV genome results in a single polypeptide, which is processed by viral and host proteases into at least 10 separate proteins. To date, no single DENV protein has been implicated in the targeting of STAT2 for decreased levels of expression. We demonstrate here that the polymerase of the virus, NS5, binds to STAT2 and is necessary and sufficient for its reduced level of expression. The decrease in protein level observed requires ubiquitination and proteasome activity, strongly suggesting an active degradation process. Furthermore, we show that the degradation of but not binding to STAT2 is dependent on the expression of the polymerase in the context of a polyprotein that undergoes proteolytic processing for NS5 maturation. Thus, the mature form of NS5, when not expressed as a precursor, was able to bind to STAT2 but was unable to target it for degradation, establishing a unique role for viral polyprotein processing in providing an additional function to a viral polypeptide. Therefore, we have identified both a novel mechanism by which DENV evades the innate immune response and a potential target for antiviral therapeutics.Dengue virus (DENV) is the causative agent of dengue fever, dengue hemorrhagic fever, and dengue shock syndrome (2). The virus and its arthropod vector, Aedes aegypti (21), are endemic to over 100 countries around the world including the United States. It is responsible for an estimated 50 million to 100 million infections annually, with over 24,000 deaths resulting, predominantly in children under 14 years of age (25). The virus exists in four serotypes (DEN1 to DEN4) and is grouped into the flavivirus genus along with a number of additional human pathogens including West Nile virus (WNV), Japanese encephalitis virus (JEV), and tick-borne encephalitis virus (TBEV). These viruses have a positive-strand, nonsegmented genome of ϳ11 kb (5, 55), the organization of which is highly conserved, encoding, in order, three structural proteins (C, M, and E), followed by seven nonstructural proteins (NS1, NS2a, NS2b, NS3, NS4a, NS4b, and NS5). The genome is translated as a single endoplasmic reticulum (ER)-bound polyprotein, which is co-and posttranslationally processed by both viral (NS2b and NS3) and cellular proteases (8,44).A critical component of the human antiviral response is the type 1 interferon (IFN) pathway, which acts to delay virus replication and to stimulate the activation of antiviral ...

Dengue reporter viruses reveal viral dynamics in interferon receptor-deficient mice and sensitivity to interferon effectors in vitro

“…Gene expression studies indicated that STAT2 overexpression is not driving antiviral signaling like IRF1. Previous studies have shown that the DENV NS5 polymerase potently antagonizes IFN signaling by mediating STAT2 degradation (35,36). Our data fit this mechanism and suggest that STAT2 overexpression may be sufficient to squelch DENV replication by stoichiometrically overcoming the viral NS5 polymerase.…”

A Physical Interaction Network of Dengue Virus and Human Proteins

“…1A, supplemental Table S5). Of the 20 DENV-human protein interactions identified in the literature, only the interaction between NS5 and STAT2 was also detected in this study (85,86). Other proteins in our data set (UBE2I, CALR, and PTBP1) were reported to interact with DENV proteins, though the interacting viral proteins differ from those identified here (87)(88)(89)(90)(91); these host factors may bind to multiple DENV proteins, as has previously been observed for other viruses (21), or may represent false-positives.…”

Development of viable TAP-tagged dengue virus for investigation of host–virus interactions in viral replication

“…NS5 recruits at least NS3 and a subset of host cellular proteins to form the replication complex or 'replicase' in virus-induced membranous compartments for productive viral RNA synthesis (Bidet & Garcia-Blanco, 2014). NS5 also plays important roles as an immune suppressor by downregulating type I IFN responses through interacting with STAT2 (Ashour et al, 2009). Moreover, both NS3 and NS5 were implicated in DHF as they were found to be the immunodominant T-cell antigens compared to other viral proteins (Duangchinda et al, 2010).…”