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Journal of Virology, March 2001, p. 2946-2956, Vol. 75, No. 6
Department of Oncology1 and
Department of Pharmacology and Molecular
Sciences,3 Johns Hopkins School of
Medicine, Baltimore, Maryland, and Molecular Biology Institute,
University of California, Los Angeles,
California2
Received 16 October 2000/Accepted 22 December 2000
The Epstein-Barr virus (EBV) BamHI-A rightward
transcripts (BARTs) are expressed in all EBV-associated tumors as well
as in latently infected B cells in vivo and cultured B-cell lines. One of the BART family transcripts contains an open reading frame, RPMS1,
that encodes a nuclear protein termed RPMS. Reverse transcription-PCR analysis revealed that BART transcripts with the splicing pattern that
generates the RPMS1 open reading frame are commonly expressed in
EBV-positive lymphoblastoid cell lines and are also detected in
Hodgkin's disease tissues. Experiments undertaken to determine the
function of RPMS revealed that RPMS interacts with both CBF1 and
components of the CBF1-associated corepressor complex. RPMS interaction
with CBF1 was demonstrated in a glutathione S-transferase (GST) affinity assay and by the ability of RPMS to alter the
intracellular localization of a mutant CBF1. A Gal4-RPMS fusion protein
mediated transcriptional repression, suggesting an additional
interaction between RPMS and corepressor proteins. GST affinity assays
revealed interaction between RPMS and the corepressor Sin3A and CIR.
The RPMS-CIR interaction was further substantiated in mammalian
two-hybrid, coimmunoprecipitation, and colocalization experiments. RPMS
has been shown to interfere with NotchIC and EBNA2 activation of
CBF1-containing promoters in reporter assays. Consistent with this
function, immunofluorescence assays performed on cotransfected cells
showed that there was colocalization of RPMS with NotchIC and with
EBNA2 in intranuclear punctate speckles. The effect of RPMS on NotchIC
function was further examined in a muscle cell differentiation assay
where RPMS was found to partially reverse NotchIC-mediated inhibition of differentiation. The mechanism of RPMS action was examined in
cotransfection and mammalian two-hybrid assays. The results revealed
that RPMS blocked relief of CBF1-mediated repression and interfered
with SKIP-CIR interactions. We conclude that RPMS acts as a negative
regulator of EBNA2 and Notch activity through its interactions with the
CBF1-associated corepressor complex.
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.6.2946-2956.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Epstein-Barr Virus BamHI-A Rightward
Transcript-Encoded RPMS Protein Interacts with the CBF1-Associated
Corepressor CIR To Negatively Regulate the Activity of EBNA2 and
NotchIC
*
Corresponding author. Mailing address: Department of
Oncology, Johns Hopkins School of Medicine, 1650 Orleans St.,
Baltimore, MD 21231. Phone: (410) 614-0592. Fax: (410) 502-6802. E-mail: dhayward{at}jhmi.edu.
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