Modulation of innate immune signaling by the secreted form of the West Nile virus NS1 glycoprotein

Abstract

West Nile virus (WNV) employs several different strategies to escape the innate immune response. We have previously demonstrated that the WNV NS1 protein interferes with signal transduction from Toll-like receptor 3 (TLR3). NS1 is a glycoprotein that can be found intracellularly or associated with the plasma membrane. In addition, NS1 is secreted to high levels during flavivirus infections. We investigated whether the secreted form of NS1 inhibits innate immune signaling pathways in uninfected cells. Secreted NS1 (sNS1) was purified from supernatants of cells engineered to express the protein. Purified sNS1 associated with and repressed TLR3-induced cytokine production by HeLa cells, and inhibited signaling from TLR3 and other TLRs in bone marrow-derived macrophages and dendritic cells. Footpad administration of sNS1 showed the protein associated predominantly with macrophages and dendritic cells in the draining lymph node. Additionally, sNS1 significantly reduced TLR3 signaling and WNV replicon particle-mediated cytokine transcription in popliteal lymph nodes.

An updated review of avian-origin Tembusu virus: a newly emerging avian Flavivirus

“…NS1 is believed to function as a co-factor in viral RNA replication [14], though reports regarding interaction of NS1 with TLR3 are contradictory [65]. Some studies have shown the increased presence of TLR3 in WNV infection in vivo [66]. Another study indicated that WNVNS1 inhibits TLR3 signal transduction [67,68], whereas the NS1 protein of several mosquito-borne flaviviruses cannot inhibit TLR3 signalling [69].…”

In vitro and in vivo characterization of chimeric duck Tembusu virus based on Japanese encephalitis live vaccine strain SA14-14-2

“…Similar to other known flaviviruses, DTMUV has an approximately 11 kb single-stranded positive-sense RNA genome, which contains a single ORF that encodes three structural proteins (C, prM, and E) and seven nonstructural proteins (NS1, NS2A, NS2B, NS3, NS4A, NS4B and NS5), flanked by the 5¢ and 3¢ untranslated regions (UTRs). The structural proteins are supposed to be involved in cellular attachment, membrane fusion and virion assembly, and the nonstructural proteins are responsible for genome replication and counteraction of host immunity, in similar mechanisms to other known pathogenic flaviviruses (Avirutnan et al, 2010;Best et al, 2005;Crook et al, 2014;Jones et al, 2005;Munoz-Jordan et al, 2003;Werme et al, 2008). DTMUV is highly pathogenic for ducks, and exhibited neurotropic effects in a mouse model Tang et al, 2013).…”

Last 20 aa of the West Nile virus NS1′ protein are responsible for its retention in cells and the formation of unique heat-stable dimers

“…Produced as a single polyprotein, it is cleaved by both host and viral proteases to give rise to the individual proteins (Lindenbach & Rice, 2003). NS1 is a multifunctional glycoprotein involved in the formation of the replication complex (Chu & Westaway, 1992;Khromykh et al, 1999Khromykh et al, , 2000Lindenbach & Rice, 1997;Westaway et al, 1997;Youn et al, 2012) and the modulation of the host immune response (Avirutnan et al, 2006(Avirutnan et al, , 2010Chung et al, 2006;Crook et al, 2014;Kurosu et al, 2007;Muller & Young, 2013;Schlesinger, 2006;Wilson et al, 2008). After cleavage from the polyprotein (Falgout & Markoff, 1995;Nowak et al, 1989), NS1 is glycosylated and forms a heat-labile dimer in the endoplasmic reticulum (ER) (Pryor & Wright, 1994;Winkler et al, 1988Winkler et al, , 1989.…”