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.
Ajithdoss
Dharani K
DK
Department of Poultry Science, College of Agriculture and Life Sciences, Texas A&M University, College Station, TX 77843, USA.
Reddy
Sanjay M
SM
Suchodolski
Paulette F
PF
Lee
Lucy F
LF
Kung
Hsing-Jien
HJ
Lupiani
Blanca
B
D000818:Animals; D002460:Cell Line; D002472:Cell Transformation, Viral; D002642:Chick Embryo; D002645:Chickens; D008381:Herpesvirus 2, Gallid / Q000235:genetics / Q000378:metabolism*; D008380:Marek Disease / Q000235:genetics / Q000378:metabolism / Q000821:virology*; D022501:Marek Disease Vaccines / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D009856:Oncogene Proteins, Viral / Q000235:genetics* / Q000378:metabolism*; D011201:Poultry Diseases / Q000235:genetics / Q000378:metabolism / Q000821:virology*; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D051381:Rats
C100369:Eco-Q protein, Gallid herpesvirus 2; D022501:Marek Disease Vaccines; D009856:Oncogene Proteins, Viral; D019253:Proto-Oncogene Proteins c-bcl-2