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

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-beta) 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.