NSs Protein of Rift Valley Fever Virus Promotes Posttranslational Downregulation of the TFIIH Subunit p62

Abstract

Rift Valley fever virus (RVFV; family Bunyaviridae, genus Phlebovirus) is an important emerging pathogen of humans and ruminants. Its NSs protein has previously been identified as a major virulence factor that suppresses host defense through three distinct mechanisms: it directly inhibits beta interferon (IFN-␤) promoter activity, it promotes the degradation of double-stranded RNA-dependent protein kinase (PKR), and it suppresses host transcription by disrupting the assembly of the basal transcription factor TFIIH through sequestration of its p44 subunit. Here, we report that in addition to PKR, NSs also promotes the degradation of the TFIIH subunit p62. Infection of cells with the RVFV MP-12 vaccine strain reduced p62 protein levels to below the detection limit early in the course of infection. This NSs-mediated downregulation of p62 was posttranslational, as it was unaffected by pharmacological inhibition of transcription or translation and MP-12 infection had no effect on p62 mRNA levels. Treatment of cells with proteasome inhibitors but not inhibition of lysosomal acidification or nuclear export resulted in a stabilization of p62 in the presence of NSs. Furthermore, p62 could be coprecipitated with NSs from lysates of infected cells. These data suggest that the RVFV NSs protein is able to interact with the TFIIH subunit p62 inside infected cells and promotes its degradation, which can occur directly in the nucleus.

Curcumin Inhibits Rift Valley Fever Virus Replication in Human Cells

“…The S (small) segment encodes the N protein and a second nonstructural protein, NSs. NSs, a viral virulence factor, is a transcriptional repressor critical to the down-regulation of the host interferon response (7)(8)(9)(10)(11)(12)(13)(14)(15)(16).…”

Rift Valley fever virus MP-12 vaccine encoding Toscana virus NSs retains neuroinvasiveness in mice

“…Therefore, we aim to develop second-generation MP-12 vaccines that encode DIVA markers while retaining strong immunogenicity. MP-12 NSs is fully functional (Billecocq et al, 2008;Ikegami et al, 2006Ikegami et al, , 2009Kalveram et al, 2011a) and is dispensable for vaccine efficacy in mice (Lihoradova et al, 2012). Potential disadvantages of MP-12 lacking NSs is a slightly lower level of neutralizing antibody in vaccinated ruminants (Morrill et al, 2013) and inefficient replication in MRC-5 cells, which have been used for MP-12 amplification for vaccine manufacturing (Ikegami et al, 2006;Lokugamage et al, 2012).…”

“…Both NSs and NSm proteins are non-structural, and the former is a major virulence factor for RVF (Bouloy et al, 2001). The NSs protein inhibits host transcription by sequestering transcription factor (TF) IIH p44 subunits (Le May et al, 2004) and by promoting post-translational degradation of TFIIH p62 subunits (Kalveram et al, 2011a). In addition, NSs specifically interacts with Sin3A-associated protein (SAP30) on the interferon (IFN)-b promoter, and inhibits the activation of the IFN-b promoter at the transcriptional level during viral replication (Le May et al, 2008).…”

Using Reverse Genetics to Manipulate the NSs Gene of the Rift Valley Fever Virus MP-12 Strain to Improve Vaccine Safety and Efficacy

“…However, NSs inhibit the release of repressor complex from the IFN-beta promoter even after the binding of those transcription factors, thus suppressing the synthesis of IFN-beta mRNA 26 . Furthermore, NSs sequesters TFIIH p44 subunits8 and also promotes degradation of TFIIH p62 subunits 27 , thus inducing a general host transcription suppression including IFN-alpha gene and genes under the ISRE promoter. C13type or other NSs mutants lacking IFN-beta suppression function induce IFN-beta synthesis, which in turn activates the IFN-alpha promoter and the interferon-sensitive response element (ISRE) promoter.…”