Antagonism of Type I Interferon Responses by New World Hantaviruses

Pathogenic hantaviruses delay the type I interferon response during early stages of viral infection. However, the robust interferon response and induction of interferon-stimulated genes observed during later stages of hantavirus infection fail to combat the virus replication in infected cells. Protein kinase R (PKR), a classical interferon-stimulated gene product, phosphorylates the eukaryotic translation initiation factor eIF2␣ and causes translational shutdown to create roadblocks for the synthesis of viral proteins. The PKR-induced translational shutdown helps host cells to establish an antiviral state to interrupt virus replication. However, hantavirus-infected cells do not undergo translational shutdown and fail to establish an antiviral state during the course of viral infection. In this study, we showed for the first time that Andes virus infection induced PKR overexpression. However, the overexpressed PKR was not active due to a significant inhibition of autophosphorylation. Further studies revealed that Andes virus nucleocapsid protein inhibited PKR dimerization, a critical step required for PKR autophosphorylation to attain activity. The studies reported here establish a hantavirus nucleocapsid protein as a new PKR inhibitor. These studies provide mechanistic insights into hantavirus resistance to the host interferon response and solve the puzzle of the lack of translational shutdown observed in hantavirus-infected cells. The sensitivity of hantavirus replication to PKR has likely imposed a selective evolutionary pressure on hantaviruses to evade the PKR antiviral response for survival. We envision that evasion of the PKR antiviral response by NP has likely helped hantaviruses to exist during evolution and to survive in infected hosts with a multifaceted antiviral defense. IMPORTANCEProtein kinase R (PKR), a versatile antiviral host factor, shuts down the translation machinery upon activation in virus-infected cells to create hurdles for the manufacture of viral proteins. The studies reported here reveal that the hantavirus nucleocapsid protein counteracts the PKR antiviral response by inhibiting PKR dimerization, which is required for its activation. We report the discovery of a new PKR inhibitor whose expression in hantavirus-infected cells prevents the PKR-induced host translational shutdown to ensure the continuous synthesis of viral proteins required for efficient virus replication.

Section: Discussionmentioning

confidence: 99%

“…Pathogenic hantaviruses, such as ANDV and SNV, are well known to inhibit the early IFN response after infection (11,25,26). However, strong expression of both IFN and ISGs is observed in the later stages of infection.…”

Section: Andv Induces Pkr Overexpression But Fails To Shut Down the Hmentioning

confidence: 99%

Andes Virus Nucleocapsid Protein Interrupts Protein Kinase R Dimerization To Counteract Host Interference in Viral Protein Synthesis

Wang

Mir

2015

“…However, the Gn-T, but not the nucleocapsid protein, was reported to inhibit TBK1-and TRAF2/3-directed ISRE-, IFN-, and NF-B-directed transcriptional responses (1,2). Yet another report suggests that expressing the SNV glycoproteins Gn and Gc, but not the nucleocapsid protein, reduces Sendai virus-induced IFN-␤ promoter responses (29). In contrast, neither the ANDV Gn and Gc glycoproteins nor the nucleocapsid protein inhibited IFN-␤ promoter responses alone, but they were suggested to reduce transcription 45% when coexpressed (29).…”

Section: Vol 85 2011 Tulv Gn Cytoplasmic Tail Regulates Ifn Inductimentioning

confidence: 99%

“…Yet another report suggests that expressing the SNV glycoproteins Gn and Gc, but not the nucleocapsid protein, reduces Sendai virus-induced IFN-␤ promoter responses (29). In contrast, neither the ANDV Gn and Gc glycoproteins nor the nucleocapsid protein inhibited IFN-␤ promoter responses alone, but they were suggested to reduce transcription 45% when coexpressed (29). Thus, viral proteins that regulate IFN responses may differ between hantaviruses.…”

Section: Vol 85 2011 Tulv Gn Cytoplasmic Tail Regulates Ifn Inductimentioning

confidence: 99%

The C-Terminal 42 Residues of the Tula Virus Gn Protein Regulate Interferon Induction

Matthys¹,

Gorbunova

Gavrilovskaya

et al. 2011

In contrast, expressing the PHV Gn-T had no effect on TBK1-induced transcriptional responses. Analysis of Gn-T truncations demonstrated that the C-terminal 42 residues of the Gn-T (Gn-T-C42) from TULV, but not PHV, inhibited IFN induction >70%. These findings demonstrate that the TULV Gn-T inhibits IFN-and ISRE-directed responses upstream of IRF3 at the level of the TBK1 complex and further define a 42-residue domain of the TULV Gn-T that inhibits IFN induction. In contrast to pathogenic hantavirusGn-Ts, the TULV Gn-T lacks a C-terminal degron domain and failed to bind tumor necrosis factor (TNF) receptor-associated factor 3 (TRAF3), a TBK1 complex component required for IRF3 activation. These findings indicate that the nonpathogenic TULV Gn-T regulates IFN induction but accomplishes this via unique interactions with cellular TBK1 complexes. These findings fundamentally distinguish nonpathogenic hantaviruses, PHV and TULV, and demonstrate that IFN regulation alone is insufficient for hantaviruses to cause disease. Yet regulating the early IFN response is necessary for hantaviruses to replicate within human endothelial cells and to be pathogenic. Thus, in addition to IFN regulation, hantaviruses contain discrete virulence determinants which permit them to be human pathogens.

“…Furthermore, hantavirus NPs have been reported to regulate the functions of host eIFs (25) and ribosomal proteins (26,27) to enhance the translation of viral mRNA. In particular, hantavirus NP not only is a target for host innate immunity against infection via its association with MxA-mediated antiviral response (28) but also has been found to interfere with host innate immune responses by downregulating apoptosis (29), inhibiting interferon (IFN) signaling responses (30,31), and blocking tumor necrosis factor alpha (TNF-␣)-induced activation of NF-B (32,33).…”

mentioning

confidence: 99%

Crystal Structure of the Core Region of Hantavirus Nucleocapsid Protein Reveals the Mechanism for Ribonucleoprotein Complex Formation

Guo

Wang

Sun

et al. 2016

Hantaviruses, which belong to the genus Hantavirus in the family Bunyaviridae, infect mammals, including humans, causing either hemorrhagic fever with renal syndrome (HFRS) or hantavirus cardiopulmonary syndrome (HCPS) in humans with high mortality. Hantavirus encodes a nucleocapsid protein (NP) to encapsidate the genome and form a ribonucleoprotein complex (RNP) together with viral polymerase. Here, we report the crystal structure of the core domains of NP (NP core ) encoded by Sin Nombre virus (SNV) and Andes virus (ANDV), which are two representative members that cause HCPS in the New World. The constructs of SNV and ANDV NP core exclude the N-and C-terminal portions of full polypeptide to obtain stable proteins for crystallographic study. The structure features an N lobe and a C lobe to clamp RNA-binding crevice and exhibits two protruding extensions in both lobes. The positively charged residues located in the RNA-binding crevice play a key role in RNA binding and virus replication. We further demonstrated that the C-terminal helix and the linker region connecting the N-terminal coiled-coil domain and NP core are essential for hantavirus NP oligomerization through contacts made with two adjacent protomers. Moreover, electron microscopy (EM) visualization of native RNPs extracted from the virions revealed that a monomer-sized NP-RNA complex is the building block of viral RNP. This work provides insight into the formation of hantavirus RNP and provides an understanding of the evolutionary connections that exist among bunyaviruses. IMPORTANCEHantaviruses are distributed across a wide and increasing range of host reservoirs throughout the world. In particular, hantaviruses can be transmitted via aerosols of rodent excreta to humans or from human to human and cause HFRS and HCPS, with mortalities of 15% and 50%, respectively. Hantavirus is therefore listed as a category C pathogen. Hantavirus encodes an NP that plays essential roles both in RNP formation and in multiple biological functions. NP is also the exclusive target for the serological diagnoses. This work reveals the structure of hantavirus NP, furthering the knowledge of hantavirus RNP formation, revealing the relationship between hantavirus NP and serological specificity and raising the potential for the development of new diagnosis and therapeutics targeting hantavirus infection. Hantavirus causes severe infectious diseases in human and animals (1, 2). In addition to 24 representative species, increasing numbers of antigenically and genetically distinct hantaviruses have recently been registered as new members of the genus Hantavirus (3, 4). The reservoir hosts of hantaviruses in nature are primarily rodents, shrews, moles, and bats, and the transmission of hantaviruses via aerosols of rodent excreta to humans causes two human diseases: (i) hemorrhagic fever with renal syndrome (HFRS), which is primarily caused by Hantaan virus (HTNV) in Asia, by Puumala virus (PUUV) and Dobrava virus (DOBV) in Europe, and by Seoul virus (SEOV) worldwide, and ...