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

Virus Res. 2009 Jun;142(1-2):57-67. doi: 10.1016/j.virusres.2009.01.008. Epub 2009 Feb 2.

Abstract

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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Cell Line
  • Cell Transformation, Viral
  • Chick Embryo
  • Chickens
  • Herpesvirus 2, Gallid / genetics
  • Herpesvirus 2, Gallid / metabolism*
  • Marek Disease / genetics
  • Marek Disease / metabolism
  • Marek Disease / virology*
  • Marek Disease Vaccines / genetics
  • Marek Disease Vaccines / metabolism*
  • Mice
  • Oncogene Proteins, Viral / genetics*
  • Oncogene Proteins, Viral / metabolism*
  • Poultry Diseases / genetics
  • Poultry Diseases / metabolism
  • Poultry Diseases / virology*
  • Promoter Regions, Genetic
  • Protein Binding
  • Proto-Oncogene Proteins c-bcl-2 / genetics
  • Proto-Oncogene Proteins c-bcl-2 / metabolism
  • Rats

Substances

  • Eco-Q protein, Gallid herpesvirus 2
  • Marek Disease Vaccines
  • Oncogene Proteins, Viral
  • Proto-Oncogene Proteins c-bcl-2