HBx Inhibits CYP2E1 Gene Expression via Downregulating HNF4α in Human Hepatoma Cells

HBx Inhibits CYP2E1 Gene Expression via Downregulating HNF4α in Human Hepatoma Cells

CYP2E1, one of the cytochrome P450 mixed-function oxidases located predominantly in liver, plays a key role in metabolism of xenobiotics including ethanol and procarcinogens. Recently, down-expression of CYP2E1 was found in hepatocellular carcinoma (HCC) with the majority to be chronic hepatitis B v...

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Main Authors: Liu, Hongming, Lou, Guiyu, Li, Chongyi, Wang, Xiaodong, Cederbaum, Arthur I., Gan, Lixia, Xie, Bin
Format: Online
Language:English
Published: Public Library of Science 2014
Online Access:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4169590/
id pubmed-4169590
recordtype oai_dc
spelling pubmed-41695902014-09-22 HBx Inhibits CYP2E1 Gene Expression via Downregulating HNF4α in Human Hepatoma Cells Liu, Hongming Lou, Guiyu Li, Chongyi Wang, Xiaodong Cederbaum, Arthur I. Gan, Lixia Xie, Bin Research Article CYP2E1, one of the cytochrome P450 mixed-function oxidases located predominantly in liver, plays a key role in metabolism of xenobiotics including ethanol and procarcinogens. Recently, down-expression of CYP2E1 was found in hepatocellular carcinoma (HCC) with the majority to be chronic hepatitis B virus (HBV) carriers. In this study, we tested a hypothesis that HBx may inhibit CYP2E1 gene expression via hepatocyte nuclear factor 4α (HNF4α). By enforced HBx gene expression in cultured HepG2 cells, we determined the effect of HBx on CYP2E1 mRNA and protein expression. With a bioinformatics analysis, we found a consensus HNF-4α binding sequence located on −318 to −294 bp upstream of human CYP2E1 promoter. Using reporter gene assay and site-directed mutagenesis, we have shown that mutation of this site dramatically decreased CYP2E1 promoter activity. By silencing endogenous HNF-4α, we have further validated knockdown of HNF-4α significantly decreased CYP2E1expression. Ectopic overexpression of HBx in HepG2 cells inhibits HNF-4α expression, and HNF-4α levels were inversely correlated with viral proteins both in HBV-infected HepG2215 cells and as well as HBV positive HCC liver tissues. Moreover, the HBx-induced CYP2E1 reduction could be rescued by ectopic supplement of HNF4α protein expression. Furthermore, human hepatoma cells C34, which do not express CYP2E1, shows enhanced cell growth rate compared to E47, which constitutively expresses CYP2E1. In addition, the significantly altered liver proteins in CYP2E1 knockout mice were detected with proteomics analysis. Together, HBx inhibits human CYP2E1 gene expression via downregulating HNF4α which contributes to promotion of human hepatoma cell growth. The elucidation of a HBx-HNF4α-CYP2E1 pathway provides novel insight into the molecular mechanism underlining chronic HBV infection associated hepatocarcinogenesis. Public Library of Science 2014-09-19 /pmc/articles/PMC4169590/ /pubmed/25238230 http://dx.doi.org/10.1371/journal.pone.0107913 Text en © 2014 Liu et al http://creativecommons.org/licenses/by/4.0/ This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are properly credited.
repository_type Open Access Journal
institution_category Foreign Institution
institution US National Center for Biotechnology Information
building NCBI PubMed
collection Online Access
language English
format Online
author Liu, Hongming
Lou, Guiyu
Li, Chongyi
Wang, Xiaodong
Cederbaum, Arthur I.
Gan, Lixia
Xie, Bin
spellingShingle Liu, Hongming
Lou, Guiyu
Li, Chongyi
Wang, Xiaodong
Cederbaum, Arthur I.
Gan, Lixia
Xie, Bin
HBx Inhibits CYP2E1 Gene Expression via Downregulating HNF4α in Human Hepatoma Cells
author_facet Liu, Hongming
Lou, Guiyu
Li, Chongyi
Wang, Xiaodong
Cederbaum, Arthur I.
Gan, Lixia
Xie, Bin
author_sort Liu, Hongming
title HBx Inhibits CYP2E1 Gene Expression via Downregulating HNF4α in Human Hepatoma Cells
title_short HBx Inhibits CYP2E1 Gene Expression via Downregulating HNF4α in Human Hepatoma Cells
title_full HBx Inhibits CYP2E1 Gene Expression via Downregulating HNF4α in Human Hepatoma Cells
title_fullStr HBx Inhibits CYP2E1 Gene Expression via Downregulating HNF4α in Human Hepatoma Cells
title_full_unstemmed HBx Inhibits CYP2E1 Gene Expression via Downregulating HNF4α in Human Hepatoma Cells
title_sort hbx inhibits cyp2e1 gene expression via downregulating hnf4α in human hepatoma cells
description CYP2E1, one of the cytochrome P450 mixed-function oxidases located predominantly in liver, plays a key role in metabolism of xenobiotics including ethanol and procarcinogens. Recently, down-expression of CYP2E1 was found in hepatocellular carcinoma (HCC) with the majority to be chronic hepatitis B virus (HBV) carriers. In this study, we tested a hypothesis that HBx may inhibit CYP2E1 gene expression via hepatocyte nuclear factor 4α (HNF4α). By enforced HBx gene expression in cultured HepG2 cells, we determined the effect of HBx on CYP2E1 mRNA and protein expression. With a bioinformatics analysis, we found a consensus HNF-4α binding sequence located on −318 to −294 bp upstream of human CYP2E1 promoter. Using reporter gene assay and site-directed mutagenesis, we have shown that mutation of this site dramatically decreased CYP2E1 promoter activity. By silencing endogenous HNF-4α, we have further validated knockdown of HNF-4α significantly decreased CYP2E1expression. Ectopic overexpression of HBx in HepG2 cells inhibits HNF-4α expression, and HNF-4α levels were inversely correlated with viral proteins both in HBV-infected HepG2215 cells and as well as HBV positive HCC liver tissues. Moreover, the HBx-induced CYP2E1 reduction could be rescued by ectopic supplement of HNF4α protein expression. Furthermore, human hepatoma cells C34, which do not express CYP2E1, shows enhanced cell growth rate compared to E47, which constitutively expresses CYP2E1. In addition, the significantly altered liver proteins in CYP2E1 knockout mice were detected with proteomics analysis. Together, HBx inhibits human CYP2E1 gene expression via downregulating HNF4α which contributes to promotion of human hepatoma cell growth. The elucidation of a HBx-HNF4α-CYP2E1 pathway provides novel insight into the molecular mechanism underlining chronic HBV infection associated hepatocarcinogenesis.
publisher Public Library of Science
publishDate 2014
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4169590/
_version_ 1613135665475616768

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