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Journal of Virology, December 2003, p. 12841-12851, Vol. 77, No. 23
0022-538X/03/$08.00+0 DOI: 10.1128/JVI.77.23.12841-12851.2003
Copyright © 2003, American
Society for
Microbiology. All Rights Reserved.
Characterization of the Chromosomal Binding Sites and Dimerization Partners of the Viral Oncoprotein Meq in Marek's Disease Virus-Transformed T Cells
Alon M. Levy,1,2 Yoshihiro Izumiya,1,2 Peter Brunovskis,1,2 Liang Xia,1,2 Mark S. Parcells,3 Sanjay M. Reddy,4 Lucy Lee,4 Hong-Wu Chen,1,2 and Hsing-Jien Kung1,2*
Departmentof Biological Chemistry, School of Medicine, University of California,
Davis, Davis, California 95616,1
UC Davis Cancer Center,
Sacramento, California 95817,2
Center of Excellence for
Poultry Science, Department of Poultry Science, University of
Arkansas, Fayetteville, Arkansas 72701,3
Avian Disease and Oncology
Laboratory, USDA-ARS, East Lansing, Michigan
488234
Received 18 June 2003/
Accepted 11 August 2003
Marek's
disease virus (MDV) is an acute transforming alphaherpesvirus that
causes T-cell lymphomas in chickens. We previously reported
the identification of a putative oncogene, meq, that is
encoded only by the oncogenic serotype of MDV. The gene product, Meq,
is a latent protein that is consistently expressed in MDV-transformed
lymphoblastoid cells and tumor cells. Meq has a bZIP (basic leucine
zipper) structure resembling the family of Jun/Fos. The mechanism
whereby Meq transforms T cells remains poorly understood. In this
study, we explored the properties of Meq as a transcriptional factor.
We analyzed Meq's dimerization partners and its target genes in
MSB-1, an MDV-transformed T-cell line. By using in vitro assays, we
first demonstrated Meq's potential to dimerize with a variety of
bZIP proteins. We then identified c-Jun as the primary dimerization
partner of Meq. Both are found to be colocalized in the nucleus and
corecruited to promoters with AP-1 sequences. By using chromatin
immunoprecipitation (ChIP), we scanned the entire MDV genome for Meq
binding sites and found three regions that were enriched with Meq
binding: the MDV lytic replication origin, the promoter for Meq, and
the promoter for ICP4. Transactivation assays using the above promoters
showed that Meq/Meq homodimers exhibited repression activity, whereas
Meq/Jun heterodimers showed activation. Finally, we were able to show
by ChIP that Meq is recruited to the interleukin-2 promoter in a region
encompassing an AP-1 site. Thus, in addition to providing general
knowledge about the transcriptional properties of Meq, our studies
revealed for the first time the ability of Meq to interact with the
latent MDV and host genomes. Our data suggest, therefore, a role for
Meq in viral genome regulation during latency, in addition to its
putative causal role in T-cell
transformation.
* Corresponding
author. Mailing address: UC Davis Cancer Center, Research Building III,
Room 2400B, 4645 2nd Ave., Sacramento, CA 95817. Phone: (916) 734-1538.
Fax: (916) 734-2589. E-mail:
hkung{at}ucdavis.edu.
Journal of Virology, December 2003, p. 12841-12851, Vol. 77, No. 23
0022-538X/03/$08.00+0 DOI: 10.1128/JVI.77.23.12841-12851.2003
Copyright © 2003, American
Society for
Microbiology. All Rights Reserved.
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