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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.

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.

Since the publication of the first report on fish nodaviruses in Korea in 1998, fish nodaviruses have caused widespread epizootic events among various fish species in Korea. However, the genotypes of fish nodaviruses in Korea have not yet been determined due to a lack of information about their nucleotide sequences. In this study, we isolated 5 fish nodaviruses from 4 fish species cultured in 4 different regions in Korea: rock bream Oplegnathus fasciatus, Japanese flounder Paralichthys olivaceus, sevenband grouper Epinephelus septemfasciatus, and grey mullet Mugil cophalus. The full open-reading frame (ORF) encoding the coat protein (1017 nt) was sequenced from each of the 5 fish nodaviruses and the nucleotide sequences were phylogenetically analyzed. Results showed that even though their sequences were not identical, all 5 Korean isolates were clustered in the RGNNV genotype. This is the first report on the phylogenetic analysis of fish nodaviruses from cultured fish in Korea.

Mass mortality occurred among Penaeus vannamei shrimp cultured in Korea in 2004. In an earlier study, we reported white spot syndrome virus (WSSV) as a causative agent of mass mortality of P. monodon shrimp in Korea (Moon et al. 2003; Dis Aquat Org 53:11-13). However, in the present study, we detected Taura syndrome virus (TSV) from the moribund 2004 P. vannamei shrimp by reverse transcription polymerase chain reaction (RT-PCR). In addition, during our regular screening for the TSV in stocks of P. vannamei imported from Hawaii, USA, we also detected TSV by RT-PCR. The nucleotide sequences of the partial capsid protein VP1 of 2 Korean isolates were 99% identical to each other and 96 to 99% identical to those of TSVs isolated from the Americas, Taiwan, and Thailand. Phylogenetic analysis revealed that the 2 Korean isolates were closely related to TSV types from Thailand. This is the first report on the detection of TSV during an epizootic among cultured P. vannamei in Korea, and our results suggests the possibility that TSV has been introduced via the imported stock of P. vannamei.

In 2003, 13 isolates of iridovirus were obtained from cultured flounders Paralichthys olivaceus during epizootics in Korea. The full open reading frames (ORFs) encoding the major capsid protein (MCP) (1362 bp) from the 13 flounder iridoviruses (FLIVs) were sequenced and the deduced amino acid sequences were phylogenetically analyzed. Phylogenetic analysis of the MCP revealed that all 13 FLIVs were the same species as rock bream iridovirus (RBIV), red sea bream iridovirus (RSIV), and infectious spleen and kidney necrosis virus (ISKNV), and were grouped into an unknown genus which was different from the 2 genera known to infect fish, Ranavirus and Lymphocystivirus. This is the first report on the isolation and phylogenetic analysis of the iridovirus of unknown genus from flounders during epizootics.

We report on a herpes-like virus, which was found to be associated with mass mortality of common carp Cyprinus carpio for the first time in Korea in 1998. The external signs of infection in moribund fish were darkened coloration and severe branchial necrosis in the gill. Transmission electron microscopy revealed the presence of herpes-like viruses in spleen tissue. Infected spleen cells showed hypertrophied nuclei and degeneration. Numerous nucleocapsids of about 82 nm in diameter were found within the nucleus and cytoplasm of infected cells, and extracellular enveloped particles were also observed. We conclude that this virus was a likely significant cause of the high mortality of common carp in Korea in 1998.

In Korea, mass mortality occurred among cultured shrimp with visible macroscopic white spots in 2000, and we confirmed the presence of white spot syndrome virus (WSSV) in the tissues of moribund shrimp by electron microscopy. In order to identify the characteristics of this Korean isolate of WSSV, we cloned and characterized its genomic DNA coding for VP24, VP26, and VP28. On the nucleotide level, VP24, VP26, and VP28 of the Korean isolate were found to be 100%, 100%, and 99% identical to those of Taiwan, Thailand and Chinese isolates, respectively. On the deduced amino-acid level, all 3 virion proteins showed 100% identity to those of the foreign isolates. The extent of sequence identity suggests that the Korean isolate originated from the same ancestor as the Taiwanese, Thai and Chinese isolates.