Kamiya Akihide, Inoue Yusuke, Gonzalez Frank J
Laboratory of Metabolism, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
Hepatology. 2003 Jun;37(6):1375-84. doi: 10.1053/jhep.2003.50212.
The fetal liver, the major site of hematopoiesis during embryonic development, acquires additional functions near birth. Among the important liver functions is the response to xenobiotic exposure due to expression of several cytochromes P450 (CYP) and drug efflux transporters. Expression of these genes is regulated by nuclear receptors such as the pregnane X receptor (PXR). In this study, regulation of xenobiotic responses during fetal liver development was analyzed using a fetal hepatocyte primary culture system derived from embryonic day 15 (E15) livers. Hepatocyte nuclear factor (HNF) 4alpha regulates the expression of many genes preferentially in the liver. Expression of several xenobiotic response genes as well as HNF4alpha was increased in fetal hepatocytes stimulated by the hepatic maturation factors oncostatin M (OSM) and Matrigel. To determine the contribution of HNF4alpha to xenobiotic responses in the fetal liver, fetal hepatocytes containing floxed HNF4alpha alleles were cultured and the HNF4alpha gene was inactivated by infection with an adenovirus containing the Cre gene. Expression of CYP3A11 and PXR was suppressed by inactivation of HNF4alpha. An HNF4alpha binding site was characterized in the PXR promoter and found to be required for activation of the PXR promoter in fetal hepatocytes. In conclusion, HNF4alpha is the key transcription factor regulating responses to xenobiotics through activation of the PXR gene during fetal liver development.
胎儿肝脏是胚胎发育过程中的主要造血部位，在临近出生时获得了额外的功能。肝脏的重要功能之一是由于几种细胞色素P450（CYP）和药物外排转运蛋白的表达而对外源物质暴露作出反应。这些基因的表达受核受体如孕烷X受体（PXR）的调控。在本研究中，使用源自胚胎第15天（E15）肝脏的胎儿肝细胞原代培养系统分析了胎儿肝脏发育过程中外源物质反应的调控。肝细胞核因子（HNF）4α优先调控肝脏中许多基因的表达。在受到肝成熟因子制瘤素M（OSM）和基质胶刺激的胎儿肝细胞中，几种外源物质反应基因以及HNF4α的表达均增加。为了确定HNF4α对胎儿肝脏中外源物质反应的作用，培养了含有floxed HNF4α等位基因的胎儿肝细胞，并通过感染含有Cre基因的腺病毒使HNF4α基因失活。HNF4α失活后，CYP3A11和PXR的表达受到抑制。在PXR启动子中鉴定出一个HNF4α结合位点，发现它是胎儿肝细胞中PXR启动子激活所必需的。总之，HNF4α是胎儿肝脏发育过程中通过激活PXR基因来调控对外源物质反应的关键转录因子。
