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Journal of Virology, November 2001, p. 10383-10392, Vol. 75, No. 21
Department of Biochemistry and Molecular
Biology1 and Department of Molecular
Genetics,2 University of Illinois at Chicago,
Chicago, Illinois 60612, and Department of Molecular Virology
and Microbiology, Baylor College of Medicine, Houston, Texas
770303
Received 1 May 2001/Accepted 30 July 2001
The hepatitis B virus (HBV) X protein (HBx) is critical for the
life cycle of the virus. HBx associates with several host cell proteins
including the DDB1 subunit of the damaged-DNA binding protein DDB.
Recent studies on the X protein encoded by the woodchuck hepadnavirus
have provided correlative evidence indicating that the interaction with
DDB1 is important for establishment of infection by the virus. In
addition, the interaction with DDB1 has been implicated in the nuclear
localization of HBx. Because the DDB2 subunit of DDB is required for
the nuclear accumulation of DDB1, we investigated the role of DDB2 in
the nuclear accumulation of HBx. Here we show that expression of DDB2
increases the nuclear levels of HBx. Several C-terminal deletion
mutants of DDB2 that fail to bind DDB1 are able to associate with HBx,
suggesting that DDB2 may associate with HBx independently of binding to
DDB1. We also show that DDB2 enhances the nuclear accumulation of HBx independently of binding to DDB1, since a mutant that does not bind
DDB1 is able to enhance the nuclear accumulation of HBx. HBV infection
is associated with liver pathogenesis. We show that the nuclear levels
of DDB1 and DDB2 are tightly regulated in hepatocytes. Studies with
regenerating mouse liver indicate that during late G1 phase
the nuclear levels of both subunits of DDB are transiently increased,
followed by a sharp decrease in S phase. Taken together, these results
suggest that DDB1 and DDB2 would participate in the nuclear functions
of HBx effectively only during the late-G1 phase of the
cell cycle.
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.21.10383-10392.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
DDB2 Induces Nuclear Accumulation of the Hepatitis
B Virus X Protein Independently of Binding to DDB1
*
Corresponding author. Mailing address: Department of
Biochemistry and Molecular Biology (M/C 536), University of Illinois at
Chicago, 1819 W. Polk St., Chicago, IL 60612-7334. Phone: (312) 413-0255. Fax: (312) 413-0364. E-mail: Pradip{at}uic.edu.
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