Suppression of hepatitis B virus core promoter by the nuclear orphan receptor TR4.
The TR4 orphan receptor is a member of the nuclear receptor superfamily that modulates gene expression via binding to the AGGTCA direct repeat hormone response element. Here we report a functional study of TR4 interaction with the core promoter of the hepatitis B virus (HBV). The electrophoretic mobility shift assay shows that TR4 can bind to the direct repeat 1 sequence element (AGGTTAAAGGTCT, nucleotide coordinates 1757-1769, TR4RE-HBV) on the HBV core promoter. TR4 also can enhance the activity of a synthetic luciferase reporter linked with four copies of TR4RE-HBV in either liver HepG2 or non-liver H1299 cells in a dose-dependent manner. Surprisingly, TR4 represses the activity of a luciferase reporter containing the entire HBV genome sequences. Moreover, mutation of this TR4RE-HBV site in the HBV core promoter diminishes the TR4 suppression effect. This TR4-induced suppression of HBV core promoter activity is further confirmed by primer extension analysis of the HBV core RNAs, showing that TR4 represses both pre-core and core mRNAs. Further dissection of this repressive mechanism indicates that TR4 may suppress the HBV core promoter activity via repressing HNF4alpha-mediated transactivation by protein-protein interactions without inhibition of HNF4alpha DNA binding. Furthermore, our results indicate that the N- and C-terminal regions of TR4 protein are required for TR4-HNF4alpha interaction. It is possible that TR4-HNF4alpha interaction may block the HNF4alpha function that results in the suppression of HBV gene expression. Together, these results demonstrate that TR4 can serve as a negative modulator in the transcriptional regulation of HBV core gene expression.
Lin
Wen-Jye
WJ
George Whipple Lab for Cancer Research, Department of Pathology, University of Rochester Medical Center, Rochester, New York 14642, USA.
Li
Jie
J
Lee
Yi-Fen
YF
Yeh
Shauh-Der
SD
Altuwaijri
Saleh
S
Ou
Jing-Hsiung
JH
Chang
Chawnshang
C
D001665:Binding Sites; D002460:Cell Line; D005982:Glutathione Transferase / Q000378:metabolism; D006515:Hepatitis B virus / Q000235:genetics*; D006801:Humans; D008099:Liver / Q000378:metabolism; D008156:Luciferases / Q000378:metabolism; D008954:Models, Biological; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012313:RNA / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011987:Receptors, Steroid / Q000235:genetics / Q000378:metabolism*; D011988:Receptors, Thyroid Hormone / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection
C490515:NR2C2 protein, human; D012333:RNA, Messenger; D011987:Receptors, Steroid; D011988:Receptors, Thyroid Hormone; D012313:RNA; D008156:Luciferases; D005982:Glutathione Transferase