ABSTRACT
Dengue virus (DENV) nonstructural protein 5 (NS5), consisting of methyltransferase and RNA-dependent RNA polymerase (RdRp) domains, is critical for viral RNA synthesis within endoplasmic reticulum-derived replication complexes in the cytoplasm. However, a significant proportion of NS5 is localized to the nucleus of infected cells for DENV2, 3, and 4, whereas DENV1 NS5 is localized diffusely in the cytoplasm. We still have an incomplete understanding of how the DENV NS5 subcellular localization is regulated. Within NS5, two putative nuclear localization signal (NLS) sequences have been identified: NLSCentral residing in the palm of the RdRp domain as well as the recently discovered NLSC-term residing in the flexible region at the C-terminal of the RdRp domain. We have previously shown that DENV2 NS5 nuclear localization can be significantly reduced by single-point mutations to the NLSC-term. Here, we present biochemical, virological, and structural data demonstrating that the relative importance of either NLS in NS5 nuclear localization is unique to each of the four DENV serotypes. DENV1 NS5's cytoplasmic localization appears to be due to a functionally weak interaction between its NLSCentral and importin-α (IMPα), while DENV2 NS5 is almost exclusively nuclear through its NLSC-term's strong interaction with IMPα. Both NLSs of DENV3 NS5 appear to contribute to directing its nuclear localization. Lastly, in the case of DENV4, the regulation of its NS5 nuclear localization remains an enigma but appears to be associated with its NLSC-term.
Subject(s)
Cell Nucleus , Dengue Virus , Nuclear Localization Signals , Serogroup , Viral Nonstructural Proteins , Viral Nonstructural Proteins/metabolism , Viral Nonstructural Proteins/genetics , Viral Nonstructural Proteins/chemistry , Dengue Virus/genetics , Dengue Virus/physiology , Cell Nucleus/metabolism , Humans , Cytoplasm/metabolism , Virus Replication , RNA-Dependent RNA Polymerase/metabolism , RNA-Dependent RNA Polymerase/genetics , RNA-Dependent RNA Polymerase/chemistry , Animals , Dengue/virology , Protein TransportABSTRACT
The Zika virus (ZIKV) non-structural protein 5 (NS5) plays multiple viral and cellular roles during infection, with its primary role in virus RNA replication taking place in the cytoplasm. However, immunofluorescence assay studies have detected the presence of ZIKV NS5 in unique spherical shell-like structures in the nuclei of infected cells, suggesting potentially important cellular roles of ZIKV NS5 in the nucleus. Hence ZIKV NS5's subcellular distribution and localization must be tightly regulated during ZIKV infection. Both ZIKV NS5 expression or ZIKV infection antagonizes type I interferon signaling, and induces a pro-inflammatory transcriptional response in a cell type-specific manner, but the mechanisms involved and the role of nuclear ZIKV NS5 in these cellular functions has not been elucidated. Intriguingly, these cells originate from the brain and placenta, which are also organs that exhibit a pro-inflammatory signature and are known sites of pathogenesis during ZIKV infection in animal models and humans. Here, we discuss the regulation of the subcellular localization of the ZIKV NS5 protein, and its putative role in the induction of an inflammatory response and the occurrence of pathology in specific organs during ZIKV infection.
