The Meq oncoprotein of Marek's disease virus interacts with p53 and inhibits its transcriptional and apoptotic activities.
BACKGROUND
Marek's disease virus (MDV) is an oncogenic herpesvirus, which causes malignant lymphoma in chickens. The Meq protein of MDV, which is expressed abundantly in MDV-infected cells and in Marek's disease (MD) tumor cells, functions as a transcriptional activator and has been proposed to play an important role in oncogenic transformation. Preliminary studies demonstrated that Meq is able to bind p53 in vitro, as demonstrated using a protein-binding assay. This observation prompted us to examine whether the interaction between Meq and p53 occurs in cells, and to investigate the biological significance of this interaction.


RESULTS
We confirmed first that Meq interacted directly with p53 using a yeast two-hybrid assay and an immunoprecipitation assay, and we investigated the biological significance of this interaction subsequently. Exogenous expression of Meq resulted in the inhibition of p53-mediated transcriptional activity and apoptosis, as analyzed using a p53 luciferase reporter assay and a TUNEL assay. The inhibitory effect of Meq on transcriptional activity mediated by p53 was dependent on the physical interaction between these two proteins, because a Meq deletion mutant that lacked the p53-binding region lost the ability to inhibit p53-mediated transcriptional activity and apoptosis. The Meq variants L-Meq and S-Meq, but not VS-Meq and ∆Meq, which were expressed in MD tumor cells and MDV-infected cells, exerted an inhibitory effect on p53 transcriptional activity. In addition, ∆Meq was found to act as a negative regulator of Meq.


CONCLUSIONS
The Meq oncoprotein interacts directly with p53 and inhibits p53-mediated transcriptional activity and apoptosis. These findings provide valuable insight into the molecular basis for the function of Meq in MDV oncogenesis.
Shanghai Veterinary Research Institute, Chinese Academy of Agricultural Science, Shanghai 200241, PR China.
Xufang
X
Deng
Xiangdong
X
Li
Yang
Y
Shen
Yafeng
Y
Qiu
Zixue
Z
Shi
Donghua
D
Shao
Yamei
Y
Jin
Hongjun
H
Chen
Chan
C
Ding
Li
L
Li
Puyan
P
Chen
Zhiyong
Z
Ma
D000818:Animals; D017209:Apoptosis; D001665:Binding Sites; D002478:Cells, Cultured; D002645:Chickens; D017353:Gene Deletion; D017930:Genes, Reporter; D006801:Humans; D047468:Immunoprecipitation; D020287:In Situ Nick-End Labeling; D008156:Luciferases / Q000096:biosynthesis; D025922:Mardivirus / Q000472:pathogenicity*; D015513:Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D025941:Protein Interaction Mapping; D017384:Sequence Deletion; D014158:Transcription, Genetic; D016159:Tumor Suppressor Protein p53 / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D020798:Two-Hybrid System Techniques; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*
D015513:Oncogene Proteins; D016159:Tumor Suppressor Protein p53; D014764:Viral Proteins; D008156:Luciferases