Role of Interferon Antagonist Activity of Rabies Virus Phosphoprotein in Viral Pathogenicity

Abstract

The fixed rabies virus (RV) strain Nishigahara kills adult mice after intracerebral inoculation, whereas the chicken embryo fibroblast cell-adapted strain Ni-CE causes nonlethal infection in adult mice. We previously reported that the chimeric CE(NiP) strain, which has the phosphoprotein (P protein) gene from the Nishigahara strain in the genetic background of the Ni-CE strain, causes lethal infection in adult mice, indicating that the P gene is responsible for the different pathogenicities of the Nishigahara and Ni-CE strains. Previous studies demonstrated that RV P protein binds to the interferon (IFN)-activated transcription factor STAT1 and blocks IFN signaling by preventing its translocation to the nucleus. In this study, we examine the molecular mechanism by which RV P protein determines viral pathogenicity by comparing the IFN antagonist activities of the Nishigahara and Ni-CE P proteins. The results, obtained from both RV-infected cells and cells transfected to express P protein only, show that Ni-CE P protein is significantly impaired for its capacity to block IFN-activated STAT1 nuclear translocation and, consequently, inhibits IFN signaling less efficiently than Nishigahara P protein. Further, it was demonstrated that a defect in the nuclear export of Ni-CE P protein correlates with a defect in its ability to cause the mislocalization of STAT1. These data provide the first evidence that the capacity of the RV P protein to inhibit STAT1 nuclear translocation and IFN signaling correlates with the viral pathogenicity.The host immune response to viral infection is a key factor in defining viral pathogenicity and the outcome of the infection. This depends not only on the capacity of the host to mount an innate and/or adaptive immune response against the virus but also on the ability of the virus to evade/subvert this response (22).The principal response of host cells to viral infection is the production of type I interferons (IFNs) (including alpha interferon [IFN-␣] and IFN-␤), which, on binding to IFN receptors on the cell surface, activate the JAK/STAT intracellular signaling pathway that culminates in the phosphorylation, heterodimerization, and nuclear translocation of the transcription factors signal transducer and activator of transcription 1 (STAT1) and STAT2. In the context of a complex called IFNstimulated gene factor 3 (ISGF3), the activated STATs bind to promoters in the DNA that contain an IFN-stimulated response element (ISRE) sequence, resulting in the transcription of a plethora of IFN-stimulated genes (ISGs) encoding antiviral proteins which act to establish the antiviral state in cells (reviewed in reference 22).To propagate efficiently in host cells, viruses have had to evolve multiple strategies to dampen the host IFN system, which appear to involve the expression of viral proteins with IFN antagonist functions. These IFN antagonists are reported to exert their effect by a variety of mechanisms, reflecting the diversity of host antiviral responses, but the STATs are known as common targ...

Roles of the Rabies Virus Phosphoprotein Isoforms in Pathogenesis

“…Specifically, this protein plays an essential role in viral RNA synthesis as a cofactor of viral RNA-dependent RNA polymerase (L protein) by bridging nucleoprotein (N protein), which directly binds to viral genomic RNA, and L protein in the ribonucleoprotein complex (reviewed in reference 3). In addition, P protein functions to antagonize the type I interferon (IFN)-mediated antiviral responses by inhibiting both signaling pathways for IFN induction and response (4)(5)(6)(7)(8)(9)(10)(11)(12). P protein suppresses activation of interferon regulatory factor 3 (IRF-3), which is an important transcription factor for IFN induction (5,8).…”

Involvement of the Rabies Virus Phosphoprotein Gene in Neuroinvasiveness

“…After transmission, RABV infects peripheral nerves and then spreads to the central nervous system (CNS) via retrograde axonal transport, followed by active viral replication and spread in the CNS, culminating in severe neurological symptoms and lethal outcome. To date, studies on pathogenesis of rabies have mainly focused on ability of the virus to spread in the CNS and to cause disease (neurovirulence), and results of those studies have revealed that the cell-to-cell infection and viral evasion of neuronal apoptosis and innate immunity contribute to the neurovirulence of RABV (3)(4)(5)(6).…”

“…The N protein enwraps the genomic RNA, whereas the P protein, in combination with the L protein, known as an RNA-dependent RNA polymerase, is involved in viral RNA synthesis. The P protein also functions as an interferon (IFN) antagonist by inhibiting both IFN induction and response (4,(15)(16)(17)(18)(19)(20)(21). The M protein, which interacts with both the RNP and G protein, participates in recruiting RNP to the host cell membrane and budding of enveloped virus particles.…”

Ambivalent Role of the Innate Immune Response in Rabies Virus Pathogenesis

“…RABV infection activates the innate immune sensor RIG-I, and likely also MDA-5 (15,22), and triggers classical type I IFN, chemoattractive, and inflammatory responses in infected cells, which could be responsible for setting up an antiviral environment and triggering an efficient immune response (3,9,15,25,39,41,58). Like most viruses, RABV has developed a strategy to counteract the antiviral effect of the type I IFN response (23,34,40,41,55,56). Despite these mechanisms, IFN, chemoattractive, and inflammatory responses in the RABV-infected NS are far from abrogated, and RABV successfully infects the NS (28,58).…”