Secreted NS1 Protects Dengue Virus from Mannose-Binding Lectin–Mediated Neutralization

Abstract

Flavivirus nonstructural protein 1 (NS1) is a unique secreted non-structural glycoprotein. Although it is absent from the flavivirus virion, intracellular and extracellular forms of NS1 have essential roles in viral replication and the pathogenesis of infection. The fate of NS1 in insect cells has been more controversial, with some reports suggesting it is exclusively cell-associated. Here, we confirm NS1 secretion from cells of insect origin and characterize its physical, biochemical, and functional properties in the context of dengue virus (DENV) infection. Unlike mammalian cell-derived NS1, which displays both high mannose and complex type N-linked glycans, soluble NS1 secreted from DENV-infected insect cells contains only high mannose glycans. Insect cell-derived secreted NS1 also has different physical properties including smaller and more heterogeneous sizes, and the formation of less stable NS1 hexamers. Both mammalian and insect cell-derived NS1 bind to complement proteins C1s, C4 and C4 binding protein as well as to a novel partner, mannose-binding lectin (MBL). Binding of NS1 to MBL protects DENV virus against MBL-mediated neutralization by the lectin pathway of complement activation. As we detected secreted NS1 and DENV virus together in the saliva of infected Aedes aegypti mosquitoes, these findings suggest a mechanism of viral immune evasion at the very earliest phase of infection.

Complement Evasion Strategies of Viruses: An Overview

“…HSV-1 (Heineman, 1967;Friedman et al, 2000;Hook et al, 2006) HSV-2 (Heineman, 1967;Hook et al, 2006) EBV (Mold et al, 1988) HSV-2 (Gadjeva et al, 2004) Flaviviridae YFV (Schlesinger et al, 1985) -DENV (Avirutnan et al, 2010;Fuchs et al, 2010;Thiemmeca et al, 2016) WNV (Avirutnan et al, 2010;Fuchs et al, 2010) YFV (Avirutnan et al, 2010) HCV (Ishii et al, 2001) Retroviridae HIV-1 (Ebenbichler et al, 1991;Susal et al, 1994;Stoiber et al, 1996) HIV-2 (Ozkaya et al, 2013) HTLV-1 (Ikeda et al, 1998) -HIV-1 (Ezekowitz et al, 1989;Saifuddin et al, 2000) Togaviridae Venezuelan equine encephalitis virus (Brooke et al, 2012) Sindbis virus (Hirsch et al, 1980b) - (Reading et al, 1995) Paramyxoviridae Parainfluenza type 3 (Vasantha et al, 1988) Newcastle disease virus (Welsh, 1977) Measles (Sissons et al, 1979(Sissons et al, , 1980Devaux et al, 2004) Mumps (Hirsch et al, 1986;Johnson et al, 2008) NiV (Johnson et al, 2011) PIV (Vasantha et al, 1988) Sendai virus (Okada et al, 1979) Simian virus 5 (McSharry et al, 1981;Johnson et al, 2009) Mumps (Johnson et al, 2008) DENV (Avirutnan et al, 2011a),...…”

Non-Canonical Roles of Dengue Virus Non-Structural Proteins

“…NS1 also interacts with C1q, but the effects of this interaction on inactivation of complement cascade have not been explored so far [5]. Regarding the lectin pathway, MBL has been identified as an NS1 target both in mammalian and mosquito cells [64], protecting infected cells from immune recognition and impairing virus neutralization by complement activation. …”

Role of NS1 antibodies in the pathogenesis of acute dengue infection

“…In addition, in vitro data show that some antibodies against NS1 cross-react with endothelial cells and induces apoptosis, which is suggested to contribute to endothelial dysfunction and vascular leak 9 . Interestingly, NS1 is important for viral evasion of complement activation by binding mannose-binding lectin and preventing neutralization of DENV via the lectin pathway 10 .…”