Distinct modes of regulation of transcription of hepatitis B virus by the nuclear receptors HNF4alpha and COUP-TF1.
To study the effects of the nuclear receptors (NRs) HNF4alpha and COUP-TF1 on the life cycle of hepatitis B virus (HBV), the human hepatoma cell line Huh7 was transiently cotransfected with plasmids containing the HBV genome and encoding these two NRs. Overexpression of HNF4alpha and COUP-TF1 led to a 9-fold increase and a 7- to 10-fold decrease, respectively, in viral DNA synthesis. These two NRs also exhibited distinct modes of regulation of viral transcription. Overexpression of HNF4alpha led to a more-than-10-fold increase in synthesis of the pregenomic RNA but to only a 2- to 3-fold increase in synthesis of the pre-C and S RNAs. Moreover, the NR response element within the pre-C promoter, NRRE(preC,) played the major role in activation of pregenomic RNA synthesis by HNF4alpha. On the other hand, overexpression of COUP-TF1 led to an over-10-fold repression of synthesis of both pre-C and pregenomic RNAs mediated through either NRRE(preC) or NRRE(enhI). HNF4alpha and COUP-TF1 antagonized each other's effects on synthesis of pregenomic RNA and viral DNA when they were co-overexpressed. A naturally occurring HBV variant which allows for binding by HNF4alpha but not COUP-TF1 in its NRRE(preC) exhibited significantly higher levels of synthesis of pregenomic RNA and viral DNA than wild-type HBV in coexpression experiments. Last, deletion analysis revealed that non-NRRE sequences located within both the C and pre-S1 regions are also essential for maximum activation of the pregenomic promoter by HNF4alpha but not for repression by COUP-TF1. Thus, HNF4alpha and COUP-TF1 function through different mechanisms to regulate expression of the HBV genes.
Yu
Xianming
X
McArdle Laboratory for Cancer Research, University of Wisconsin Medical School, Madison, WI 53706-1599, USA.
Mertz
Janet E
JE
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D051838:COUP Transcription Factor I; D004279:DNA, Viral / Q000096:biosynthesis; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015967:Gene Expression Regulation, Viral; D006515:Hepatitis B virus / Q000235:genetics / Q000378:metabolism*; D051557:Hepatocyte Nuclear Factor 4; D006801:Humans; D009154:Mutation; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D012367:RNA, Viral / Q000096:biosynthesis; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism; D020218:Response Elements / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D051838:COUP Transcription Factor I; D004279:DNA, Viral; D004268:DNA-Binding Proteins; C496592:HNF4A protein, human; D051557:Hepatocyte Nuclear Factor 4; C403128:MLX protein, human; C497589:NR2F1 protein, human; D010750:Phosphoproteins; D012367:RNA, Viral; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors