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Journal of Virology, October 1999, p. 7943-7951, Vol. 73, No. 10
Program in Viral Oncogenesis and Tumor
Immunology, Department of Virology and Molecular Biology, St. Jude
Children's Research Hospital, Memphis, Tennessee
38105,1 and Department of Pathology,
University of Tennessee Health Sciences Center, Memphis, Tennessee
381632
Received 11 March 1999/Accepted 30 June 1999
During the restricted programs of Epstein-Barr virus (EBV) latency
in EBV-associated tumors and a subpopulation of latently infected B
cells in healthy EBV carriers, transcription of the EBV nuclear antigen
1 (EBNA-1) gene is mediated by the promoter Qp. Previously, two
noncanonical E2F binding sites were identified within Qp. The role of
E2F in the regulation of Qp, however, has been controversial and is
undefined. Here we demonstrate that an E2F factor(s) within Burkitt
lymphoma (BL) cells binds to a G/C-rich element [GGCG(C/G)]
within the previously identified binding sites in Qp and
prototypical E2F response elements. Furthermore, Qp-driven reporter
gene expression could be efficiently repressed through either E2F
binding site by the tumor suppressor pRb, a potent transcriptional
repressor targeted to promoters during G0 and the early
G1 phase of the cell cycle via its interaction with E2F; a
mutant pRb (pRb706) lacking E2F binding capability was
unable to repress Qp. However, we did not observe cell cycle variation
in the expression of either EBNA-1 mRNA or protein in exponentially
growing BL cells, consistent with previous predictions that Qp is
constitutively active in these cells and with the extremely long
t1/2 of EBNA-1. By contrast, within
G0/G1 in growth-arrested BL cells, EBNA-1 mRNA
levels were twofold lower than in S phase, similar to the two- to
eightfold differences in cell cycle expression of some cyclin mRNAs.
Thus, although regulation of Qp is coupled to the cell cycle, this
clearly has no impact on the level of EBNA-1 expressed in proliferating cells. We conclude, therefore, that the most important contribution of
E2F to the regulation of Qp is to direct the pRb-mediated suppression of EBNA-1 expression within resting B cells, the principal reservoir of
latent EBV. This would provide a means to restrict unneeded and
potentially deleterious expression of EBNA-1 in a nonproliferating cell
and to coordinate the activation of EBNA-1 expression necessary for EBV
genome replication and maintenance upon reentry of the cell cycle in
response to proliferative signals.
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Repression of Epstein-Barr Virus EBNA-1 Gene
Transcription by pRb during Restricted Latency
*
Corresponding author. Mailing address: Department of
Virology and Molecular Biology, St. Jude Children's Research Hospital, 332 N. Lauderdale, Memphis, TN 38105. Phone: (901) 495-3467. Fax: (901)
523-2622. E-mail: jeff.sample{at}stjude.org.
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