Ribavirin Inhibits Parrot Bornavirus 4 Replication in Cell Culture.

Parrot bornavirus 4 is an etiological agent of proventricular dilatation disease, a fatal neurologic and gastrointestinal disease of psittacines and other birds. We tested the ability of ribavirin, an antiviral nucleoside analog with antiviral activity against a range of RNA and DNA viruses, to inhibit parrot bornavirus 4 replication in duck embryonic fibroblast cells. Two analytical methods that evaluate different products of viral replication, indirect immunocytochemistry for viral specific nucleoprotein and qRT-PCR for viral specific phosphoprotein gene mRNA, were used. Ribavirin at concentrations between 2.5 and 25 µg/mL inhibited parrot bornavirus 4 replication, decreasing viral mRNA and viral protein load, in infected duck embryonic fibroblast cells. The addition of guanosine diminished the antiviral activity of ribavirin suggesting that one possible mechanism of action against parrot bornavirus 4 may likely be through inosine monophosphate dehydrogenase inhibition. This study demonstrates parrot bornavirus 4 susceptibility to ribavirin in cell culture.

Both homo and heterodimers of Marek's disease virus encoded Meq protein contribute to transformation of lymphocytes in chickens.

Marek' disease virus serotype-1, also know as Gallid herpesvirus 2 (GaHV-2), elicits T-cell lymphomas in chickens. The GaHV-2 genome encodes an oncoprotein, Meq, with similarity to the Jun/Fos family of proteins. We have previously shown that Meq homodimers are not sufficient to induce lymphomas in chickens. In this study, we investigated the role of Meq heterodimers in the pathogenicity of GaHV-2 by generating a chimeric meq gene, which contains the leucine zipper region of Fos (meqFos). A recombinant virus containing the meqFos gene in place of parental meq, rMd5-MeqFos, was not capable of transforming chicken lymphocytes, indicating that heterodimerization of Meq alone is not sufficient for transformation. In addition, the recovery of the oncogenic phenotype by a recombinant virus encoding one copy each of MeqGCN (homodimer) and MeqFos (heterodimer) conclusively demonstrates that both homo and heterodimerization of Meq are required for oncogenesis.

In vitro characterization of the Meq proteins of Marek's disease virus vaccine strain CVI988.

Gallid herpesvirus 2 (GaHV-2), commonly known as Marek's disease virus serotype-1 (MDV-1), causes T cell lymphomas in chickens. Vaccines prepared from the attenuated CVI988/Rispens MDV-1 strain currently offer the best protection. Although attenuated CVI988/Rispens is non-oncogenic, it codes for at least two forms of the MDV oncoprotein Meq, and these proteins (CVI-Meq and CVI-LMeq) have not been fully characterized. Here, we report that both CVI-Meq proteins, like the Meq protein of Md5 (a very virulent oncogenic strain), were capable of transforming Rat-2 and NIH3T3 cells. Both CVI-Meq and CVI-LMeq proteins activated the meq promoter only in the presence of chicken c-Jun (CK-Jun) whereas Md5-Meq activated the same promoter irrespective of CK-Jun co-expression. However, Meq proteins of both Md5 and CVI988 bound the meq promoter in a ChIP assay regardless of whether CK-Jun was co-expressed. To understand the role of Meq DNA binding and transactivation/repression domains in transcription, we constructed three chimeric Meq proteins, namely, Md5-CVI-Meq, CVI-Md5-Meq, and Md5-CVI-L by exchanging domains between Md5 meq and CVI meq genes. Although these chimeric Meq proteins, unlike CVI-Meq proteins, transactivated the meq promoter, the activation was significantly less than Md5-Meq. To determine the role of individual amino acids, point mutations were introduced corresponding to the amino acid changes of CVI-Meq into Md5-Meq. Amino acid residues at positions 71 and 320 of the Md5-Meq protein were found to be important for transactivation of the meq promoter. All three Meq proteins activated the MDV gB, MMP-3 and Bcl-2 promoters and suppressed transcription from the MDV pp38/pp14 bidirectional promoter. Although no significant differences were observed, decreased transactivation activity was observed with CVI-Meq proteins when compared to Md5-Meq. Collectively, the data presented here indicate that CVI-Meq proteins are generally weak transactivators, which might contribute to the non-oncogenic phenotype of CVI988 virus in chickens.

Homodimerization of Marek's disease virus-encoded Meq protein is not sufficient for transformation of lymphocytes in chickens.

Marek's disease virus (MDV), the etiologic agent of Marek's disease, is a potent oncogenic herpesvirus. MDV is highly contagious and elicits a rapid onset of malignant T-cell lymphomas in chickens within several weeks after infection. MDV genome codes an oncoprotein, Meq, which shares resemblance with the Jun/Fos family of bZIP transcription factors. Similar to Jun, the leucine zipper region of Meq allows the formation of homo- and heterodimers. Meq homo- and heterodimers have different DNA binding affinities and transcriptional activity; therefore, they may differentially regulate transcription of viral and cellular genes. In this study we investigated the role of Meq homodimers in the pathogenicity of MDV by generating a chimeric meq gene, which contains the leucine zipper region of the yeast transcription factor GCN4 (meqGCN). A recombinant virus (rMd5-MeqGCN) containing the chimeric meqGCN gene in place of parental meq was generated with overlapping cosmid clones of Md5, a very virulent MDV strain. The rMd5-MeqGCN virus replicated in vitro and in vivo but was unable to transform T cells in infected chickens. These data provide the first in vivo evidence that Meq homodimers are not sufficient for MDV-induced transformation.