Jeong Wan Do

Sequence variation in the gene encoding the major capsid protein of Korean fish iridoviruses

Summary.Ten iridoviruses were isolated from cultured fish from various regions in Korea; 7 from rock bream, 1 from red sea bream, 1 from sea bass, and 1 from rockfish. The full open-reading frame (ORF) encoding the major capsid protein (MCP) (1362 bp) from ten iridoviruses were sequenced and the nucleotide sequences were phylogenetically analyzed. Phylogenetic analysis revealed that the ten Korean isolates were classified into one cluster. However, their sequences were not identical and, based on the nucleotide sequence variation, they could be further divided into two subgroups. While nine Korean isolates were similar to the Japanese isolate red sea bream iridovirus (RSIV), one isolate was distinct from other iridovirus isolates. These results suggest that a diversity of iridoviruses exist in Korea and that a new variant strain has emerged.

A nuclear localization of the infectious haematopoietic necrosis virus NV protein is necessary for optimal viral growth.

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.

Comparison of the immunogenicity of recombinant VP2 and VP3 of infectious pancreatic necrosis virus and marine birnavirus

Summary.Recombinant proteins of truncated viral protein-2 (VP2) (aa 79-359) and VP3 of infectious pancreatic necrosis virus (IPNV) and marine birnavirus (MABV) were expressed in E. coli and their immunogenicities in fish were investigated. The recombinant proteins from IPNV were used to immunize rainbow trout and those from MABV to immunize flounder. The sera from the immunized fishes were assayed for antibody by ELISA and a neutralization test. Both the recombinant VP2 and VP3 produced antibodies in fish but the VP3 antibody titers were higher than that of the VP2 of IPNV and MABV. These results indicate that the recombinant VP3 is more immunogenic than the re-combinant VP2.

Genetically similar VHSV isolates are differentially virulent in olive flounder Paralichthys olivaceus

Two viral hemorrhagic septicemia virus (VHSV) isolates, VHSV-KR-CJA and VHSV-KR-YGH, were isolated from viral hemorrhagic septicemia disease outbreaks in flounder farms in South Korea. The VHSV-KR-CJA isolate was isolated from a flounder farm with high mortality (80%), while the VHSV-KR-YGH isolate was isolated from a flounder farm with low mortality (15%), suggesting that these isolates differ in virulence. The virulence of these isolates was evaluated in juvenile flounder via intraperitoneal injection. Consistent with their virulence in the field, mortality data revealed that the VHSV-KR-CJA isolate was highly pathogenic (cumulative mortality of 80%), while the VHSV-KR-YGH isolate was less pathogenic in flounder (cumulative mortality of 20%). To characterize the genotypes of these viruses, the full open reading frames (ORFs) encoding nucleoprotein N, phosphoprotein P, matrix protein M, glycoprotein G, nonstructural viral protein NV, and polymerase L of these viruses were sequenced and analyzed. Sequence analysis revealed that both isolates are genetically very similar (identical amino acid sequences for P, M, NV, and L and >99.7 and 99.8% amino acid sequence identity for N and G, respectively). Phylogenetic analysis indicated that both of these viruses belong to the Genotype IVa group, suggesting that they originated from a common ancestral virus. The low pathogenicity VHSV strain may potentially evolve to become a more pathogenic strain through only a few nucleotide substitutions. Further functional analyses of mutations in VHSV genes are necessary to identify factors that determine VHSV pathogenicity in flounder.

TTP mediates cisplatin-induced apoptosis of head and neck cancer cells by down-regulating the expression of Bcl-2

Abstract The chemotherapeutic agent cisplatin is widely used for treatment of head and neck squamous cell carcinoma (HNSCC). B-cell lymphoma 2 (Bcl-2) is an anti-apoptotic protein that is overexpressed in cancer cells and confers resistance to cisplatin. Thus, inhibition of Bcl-2 expression may enhance the cisplatin sensitivity of cancer cells. In this study, we report that the AU-rich element (ARE) binding protein tristetraprolin (TTP) inhibits the expression of Bcl-2 and enhances cisplatin sensitivity of HNSCC cells. Cisplatin-sensitive HNSCC cells express high levels of TTP and low levels of Bcl-2, while cisplatin-resistant HNSCC cells have low levels of TTP and high levels of Bcl-2. Inhibition of TTP expression using siRNA increases levels of Bcl-2 and decreases cisplatin sensitivity in HNSCC cells. On the contrary, overexpression of TTP decreases Bcl-2 expression and increases sensitivity to cisplatin. Together, the results of the present study suggest that TTP expression enhances cisplatin sensitivity in HNSCC cells by reducing levels of Bcl-2.