Abstract
The nonvirion (NV) protein of infectious hematopoietic necrosis virus (IHNV) has been previously reported to be essential for efficient growth and pathogenicity of IHNV. However, little is known about the mechanism by which the NV supports the viral growth. In this study, cellular localization of NV and its role in IHNV growth in host cells was investigated. Through transient transfection in RTG-2 cells of NV fused to green fluorescent protein (GFP), a nuclear localization of NV was demonstrated. Deletion analyses showed that the 32EGDL35 residues were essential for nuclear localization of NV protein, and fusion of these 4 amino acids to GFP directed its transport to the nucleus. We generated a recombinant IHNV, rIHNV-NV-ΔEGDL in which the 32EGDL35 was deleted from the NV. rIHNVs with wild-type NV (rIHNV-NV) or with the NV gene replaced with GFP (rIHNV-ΔNV-GFP) were used as controls. RTG-2 cells infected with rIHNV-ΔNV-GFP and rIHNV-NV-ΔEGDL yielded 12- and 5-fold less infectious virion, respectively, than wild type rIHNV-infected cells at 48 h post-infection (p.i.). While treatment with poly I∶C at 24 h p.i. did not inhibit replication of wild-type rIHNVs, replication rates of rIHNV-ΔNV-GFP and rIHNV-NV-ΔEGDL were inhibited by poly I∶C. In addition, both rIHNV-ΔNV and rIHNV-NV-ΔEGDL induced higher levels of expressions of both IFN1 and Mx1 than wild-type rIHNV. These data suggest that the IHNV NV may support the growth of IHNV through inhibition of the INF system and the amino acid residues of 32EGDL35 responsible for nuclear localization are important for the inhibitory activity of NV.
Highlights
Infectious hematopoietic necrosis virus (IHNV) is a rhabdovirus belonging to the genus Novirhabdovirus of the Rhabdoviridae family
We showed that the 111-amino acid NV protein of IHNV can localize to the nucleus, and identified amino acid residues, 32EGDL35, within the NV protein that are responsible for the nuclear localization of the NV protein
NV is known to be required for the efficient growth of IHNV in rainbow trout [6], the exact role of the NV in IHNV infection is still unclear
Summary
Infectious hematopoietic necrosis virus (IHNV) is a rhabdovirus belonging to the genus Novirhabdovirus of the Rhabdoviridae family. IHNV causes an acute disease in wild and hatchery-reared salmonid fish in North America, Europe, and Asia [1,2]. The IHNV genome encodes five structural proteins that make up the virions: a nucleoproetin (N), a polymerase-associated phosphoprotein (P), a matrix protein (M), a unique glycoprotein (G), and a RNA polymerase protein (L) [3,4]. The Novirhabdovirus genome possesses an additional non-virion (NV) gene located between the viral glycoprotein (G) and the polymerase (L) genes [3]. While the functions of most IHNV proteins are known, that of the NV protein remains unclear. The molecular basis for the role of NV is not known
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