Inhibition of the Type I Interferon Response by the Nucleoprotein of the Prototypic Arenavirus Lymphocytic Choriomeningitis Virus

Abstract

The prototypic arenavirus lymphocytic choriomeningitis virus (LCMV) is a formidable battle horse for the study of viral immunology, as well as viral persistence and associated diseases. Investigations with LCMV have uncovered basic mechanisms by which viruses avoid elimination by the host adaptive immune response. In this study we show that LCMV also disables the host innate defense by interfering with beta interferon (IFN-␤) production in response to different stimuli, including infection with Sendai virus and liposome-mediated DNA transfection. Inhibition of IFN production in LCMV-infected cells was caused by an early block in the IFN regulatory factor 3 (IRF-3) activation pathway. This defect was restored in cells cured of LCMV, indicating that one or more LCMV products are responsible for the inhibition of IRF-3 activation. Using expression plasmids encoding individual LCMV proteins, we found that expression of the LCMV nucleoprotein (NP) was sufficient to inhibit both IFN production and nuclear translocation of IRF-3. To our knowledge, this is the first evidence of an IFN-counteracting viral protein in the Arenaviridae family. Inhibition of IFN production by the arenavirus NP is likely to be a determinant of virulence in vivo.Arenaviruses merit significant attention both as tractable model systems to study acute and persistent viral infections (28, 51) and as clinically important human pathogens, including several causative agents of severe hemorrhagic fever, chiefly Lassa fever virus (LFV) (8,14). In addition, the prototypic arenavirus lymphocytic choriomeningitis virus (LCMV) has proven to be a Rosetta stone in the fields of viral immunology and pathogenesis (28,51).LCMV is an enveloped virus with a bisegmented RNA genome (8,25). Each segment, designated L (ca 7.2 kb) and S (ca 3.4 kb), expresses two viral gene products using an ambisense coding strategy. The S RNA directs the synthesis of the nucleoprotein NP and the glycoprotein precursor GPC. The NP, the most abundant viral protein, encapsidates viral genomes and antigenomic replicative intermediates. GPC is posttranslationally cleaved by the cellular subtilase S1P into mature viral glycoproteins, GP-1 and GP-2 (5, 34). Noncovalently associated GP-1/GP-2 complexes make up the spikes on the virion envelope and mediate virus interaction with the host cell receptor (20). The L segment codes for the virus RNA-dependent RNA polymerase (L) and a small (11-kDa) RING finger protein called Z that functions as the arenavirus counterpart of the matrix protein found in many negative-strand RNA viruses (32, 42). Additional roles of Z in the arenavirus life cycle have been proposed on the basis of its interaction with several host cell proteins (8, 25) and its ability to inhibit RNA synthesis mediated by the virus polymerase (17, 25).The mechanisms underlying arenavirus hemorrhagic fever disease are not understood. Individuals succumbing to LF generate only minimal or no anti-LFV immune response, while those recovering from LF disease show evidence of both Tand B-ce...

Multiple Mechanisms Contribute to Impairment of Type 1 Interferon Production during Chronic Lymphocytic Choriomeningitis Virus Infection of Mice

“…Together, these results indicate that LCMV infection does not directly impair the ability of DCs to up-regulate type 1 IFN production in response to TLR ligation or infection with a DNA virus, HSV, but suggest that there could be an impairment in the response to stimuli that trigger type 1 IFN activation of cytoplasmic RNA helicases such as RIG-I. The latter observation is consistent with the recent finding that LCMV impairs nuclear translocation of IFN regulatory factor (IRF)-3 in the cells it infects to block the production of type 1 IFN that its own nucleic acids would otherwise elicit (50).…”

“…However, the reduction in DC numbers is probably not the only explanation for the low levels of type 1 IFN produced in chronically infected mice, as we also found that the remaining DCs in these animals exhibit a reduced capacity to up-regulate type 1 IFN production in response to TLR ligation. LCMV Cl13 is a DC-tropic LCMV isolate (50,62) and during chronic infection, may infect as many as a third of the DCs in the spleen. We thus addressed whether the impairment observed in TLR-stimulated type 1 IFN production by DCs from chronically infected mice may be a consequence of infection of these cells with LCMV.…”

Stimulation of Ebola virus production from persistent infection through activation of the Ras/MAPK pathway

“…Although the mechanisms of emergence from viral latency have been studied most thoroughly in viruses with nuclear replication strategies, a few RNA viruses with cytoplasmic replication, such as paramyxoviruses, hantaviruses, arenaviruses (24)(25)(26)(27)(28), and possibly filovirus (29), also may have longer-term persistence using similar strategies. We next tested to see whether latent ZEBOV infection, like other latent infections, such as herpesvirus or human immunodeficiency virus (HIV) (30)(31)(32), could be induced to replicate to higher titers through physiological treatments.…”

Structure of the Lassa Virus Nucleoprotein Revealed by X-ray Crystallography, Small-angle X-ray Scattering, and Electron Microscopy

“…Thus, RNA-free NP seems to exist exclusively as a trimer, which presumably has biological relevance. Besides being the building block of ribonucleoproteins, NP has additional functions during the life cycle of the virus, such as interaction with L and Z proteins and cellular proteins, budding of particles, suppression of the interferon response, exoribonuclease activity, and nucleotide binding (15)(16)(17)(18)(19)(20)(21)(22)(23). Some of these or other so far unknown functions of NP might be associated specifically with the trimeric configuration.…”

“…The association with Z protein and ALIX/AIP1, an ESCRT-associated host protein, is important for incorporation of NP into virus-like particles (15,(17)(18)(19). In addition, NP acts as an interferon antagonist (20,21). Recently published x-ray crystallographic data for full-length NP (22) and its C-terminal domain (23) of LASV strain Josiah revealed a nucleotidebinding site in the N terminus and a 3Ј-5Ј-exoribonuclease in the C terminus; the latter is critical for NP to function as an interferon antagonist.…”