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Journal of Virology, June 2000, p. 5032-5039, Vol. 74, No. 11
Le Centre de Recherche en Cancérologie
de l'Université Laval, L'Hôtel-Dieu de Québec,
Département de Biologie Médicale, Faculté de
Médecine, Québec G1R 2J6, Canada
Received 29 November 1999/Accepted 13 March 2000
Orphan nuclear receptor fetoprotein transcription factor (FTF) was
previously identified as a specific regulator of the
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Copyright © 2000, American Society for Microbiology. All rights reserved.
The Hepatitis B Virus Core Promoter Is Strongly Activated by
the Liver Nuclear Receptor Fetoprotein Transcription Factor or
by Ectopically Expressed Steroidogenic Factor 1
1-fetoprotein gene during early liver development and in
response to hormonal signals (L. Galarneau, J.-F. Paré, D. Allard, D. Hamel, L. Lévesque, J. D. Tugwood, S. Green, and
L. Bélanger, Mol. Cell. Biol. 16:3853-3865, 1996). Here we
report a functional analysis of FTF interactions with the hepatitis B
virus (HBV) nucleocapsid promoter. DNA-protein-binding assays show that
the HBV core promoter contains two high-affinity FTF-binding sites and
a third, lower-affinity site shared with other receptors. Transfections
in HepG2, Hep3B, and PLC/PRF/5 hepatoma cells using chloramphenicol
acetyltransferase reporter genes with the nucleocapsid promoter linked
or not linked to enhancer I indicate that FTF is a potent activator of
the HBV core promoter, more efficient than HNF4
, HNF3
, HNF3
,
or C/EBP
. Steroidogenic factor 1, a close FTF homolog which binds to
the same DNA motif and is expressed ectopically in HepG2 cells, seems
to be an even stronger inducer than FTF. Point mutations of the
FTF-binding sites indicate direct FTF activatory effects on the core
promoter and the use of both high-affinity sites for productive
interaction between the core promoter and enhancer I. Coexpression
assays further indicate that FTF and HNF4
are the most efficient
partners for coactivation of the pregenomic core promoter, which may
largely account for the hepatic tropism and the early amplification of HBV infection. Carboxy terminus-truncated FTF behaves as a dominant negative mutant to compete all three FTF sites and strongly deactivate core promoter interactions with enhancer I; this suggests possible new
ways to interfere with HBV infection.
*
Corresponding author. Mailing address: Cancer Research
Centre, L'Hôtel-Dieu de Québec, Québec G1R 2J6,
Canada. Phone: (418) 691-5543. Fax: (418) 691-5489. E-mail:
luc.belanger{at}crhdq.ulaval.ca.
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