p48 (ISGF-3gamma) is involved in interferon-alpha-induced suppression of hepatitis B virus enhancer-1 activity.
Interferon-alpha (IFN-alpha) suppresses hepatitis B virus (HBV) gene expression by reducing its enhancer-1 activity. IFN-alpha induces transcription factors, interferon-stimulated gene factor 3 (ISGF3), and interferon regulatory factor-1 (IRF-1), which activate interferon-inducible gene expression through binding to the interferon-stimulated regulatory element (ISRE) "AGTTTCNNTTTCNC" in the gene promoters. We found the ISRE-like sequence "AGGCTTTCACTTTCTC" in the HBV enhancer-1 region and elucidated the role of this sequence. Gel mobility shift assay showed binding of in vitro translated IRF-1 and in vitro translated p48 (ISGF3-gamma), which is a component of ISGF3 to this sequence. However, nuclear extracts binding to this sequence from human hepatoma cells (HuH-7) treated with IFN-alpha contained only the protein consisted of p48. In transfection experiments, IFN-alpha suppressed the HBV enhancer-1 activity, and overexpression of p48 enhanced this inhibitory effect. Both mutation and deletion of the ISRE-like sequence in the HBV enhancer-1 region reduced the suppressive effect of IFN-alpha. Our results suggest that the ISRE-like sequence in the HBV enhancer-1 can interact with the protein containing p48 and mediate the IFN-alpha-induced suppression of the enhancer activity.
Nakao
K
K
Health Research Center, Nagasaki University School of Medicine, 1-7-1, Sakamoto, Nagasaki 852-8501, Japan. kazuhiko@net.nagasaki-u.ac.jp
Nakata
K
K
Yamashita
M
M
Tamada
Y
Y
Hamasaki
K
K
Ishikawa
H
H
Kato
Y
Y
Eguchi
K
K
Ishii
N
N
D001483:Base Sequence; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000502:physiology*; D004742:Enhancer Elements, Genetic / Q000502:physiology*; D015967:Gene Expression Regulation, Viral / Q000502:physiology; D006515:Hepatitis B virus / Q000235:genetics*; D006801:Humans; D050832:Interferon-Stimulated Gene Factor 3; D050834:Interferon-Stimulated Gene Factor 3, gamma Subunit; D016898:Interferon-alpha / Q000502:physiology*; D014157:Transcription Factors / Q000502:physiology*; D014407:Tumor Cells, Cultured
D017931:DNA Primers; D004268:DNA-Binding Proteins; C494227:IRF9 protein, human; D050832:Interferon-Stimulated Gene Factor 3; D050834:Interferon-Stimulated Gene Factor 3, gamma Subunit; D016898:Interferon-alpha; D014157:Transcription Factors