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Journal of Virology, September 1998, p. 7075-7083, Vol. 72, No. 9
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

The Epstein-Barr Virus Major Latent Promoter Qp Is Constitutively Active, Hypomethylated, and Methylation Sensitive

Qian Tao,1 Keith D. Robertson,1 Angela Manns,2 Allan Hildesheim,2 and Richard F. Ambinder1,*

Oncology Center, Johns Hopkins School of Medicine, Baltimore,1 and Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Rockville,2 Maryland

Received 26 March 1998/Accepted 27 May 1998

Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA1) is indispensable for viral DNA replication and episome maintenance in latency. Four promoters, Cp, Wp, Qp, and Fp, are known to drive EBNA1 expression. Here we show that the TATA-less Qp is constitutively active in a variety of EBV-positive [EBV(+)] tumors and cell lines, irrespective of the activities of other EBNA1 promoters, the type of viral latency, and the cell type. The transcription of highly regulated promoters such as the EBV Cp is known to be directly regulated by CpG methylation. To characterize the role of CpG methylation in the regulation of the constitutively active Qp, we performed bisulfite genomic sequencing and functional analyses using a methylation cassette transcriptional reporter assay. Twenty consecutive CpG sites (16 proximal to the Qp initiation site and 4 upstream of the adjacent Fp initiation site) were studied by bisulfite sequencing of DNA extracted from EBV(+) tumors and cell lines. Eighteen EBV(+) tumors of lymphoid (B, T, and NK cell) or epithelial origin and five Burkitt's lymphoma cell lines were studied. The 16 CpG sites proximal to Qp were virtually all unmethylated, but the 4 CpG sites upstream of the Fp initiation site were variably methylated. The methylation cassette assay showed that in vitro methylation of the Qp cassette (-172 to +32) resulted in strong repression of Qp activity in transient transfection. Thus, Qp is susceptible to repression by methylation but was found to be consistently hypomethylated and expressed in all tumors and tumor-derived cell lines studied.

* Corresponding author. Mailing address: 418 N. Bond St., Johns Hopkins Oncology Center, Baltimore, MD 21231. Phone: (410) 955-5617. Fax: (410) 955-0961. E-mail: rambind{at}welchlink.welch.jhu.edu.

Journal of Virology, September 1998, p. 7075-7083, Vol. 72, No. 9
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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