FoxA proteins regulate H19 endoderm enhancer E1 and exhibit developmental changes in enhancer binding in vivo
FoxA proteins regulate H19 endoderm enhancer E1 and exhibit developmental changes in enhancer binding in vivo
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DOI：
10.1128/mcb.24.21.9601-9609.2004
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发表时间：
2004-11-01
影响因子：
5.3
通讯作者：
Spear, BT
中科院分区：
文献类型：
--
作者：
Long, LY;Spear, BT
多种增强子控制H19-Igf2位点的发育和组织特异性表达，但结合这些元件的因子尚未确定。利用染色质免疫沉淀法，我们在h19e1增强子中发现了两个FoxA结合位点。这些位点的突变会降低肝癌细胞中E1的活性。额外的染色质免疫沉淀表明，FoxA在胎儿肝脏中与E1结合，在胎儿肝脏中H19大量表达，但在成人肝脏中这种结合减少，在成人肝脏中H19不再转录，尽管FoxA蛋白在两个阶段都存在。FoxA蛋白在F9胚胎癌细胞分化为内脏内胚层（VE）和顶叶内胚层（PE）时被诱导表达。我们发现FoxA在表达H19的VIE细胞中与El结合，而在H19沉默的PE细胞中则不与El结合。FoxA结合与H19表达之间的相关性表明FoxA参与了H19的调控，包括卵黄囊和肝脏的发育激活以及出生后肝脏的抑制。这是首次证明组织特异性因子参与H19表达的发育控制。这些数据还表明FoxA蛋白的存在不足以结合，但必须有其他机制控制FoxA蛋白对H19 E1增强子内同源结合位点的可及性。
Multiple enhancers govern developmental and tissue-specific expression of the H19-Igf2 locus, but factors that bind these elements have not been identified. Using chromatin immunoprecipitation, we have found two FoxA binding sites in the H19 E1 enhancer. Mutating these sites diminishes E1 activity in hepatoma cells. Additional chromatin immunoprecipitations show that FoxA binds to E1 in fetal liver, where H19 is abundantly expressed, but that binding decreases in adult liver, where H19 is no longer transcribed, even though FoxA proteins are present at both times. FoxA proteins are induced when F9 embryonal carcinoma cells differentiate into visceral endoderm (VE) and parietal endoderm (PE). We show that FoxA binds El in VIE cells, where H19 is expressed, but not in PE cells, where H19 is silent. This correlation between FoxA binding and H19 expression indicates a role for FoxA in regulating H19, including developmental activation in the yolk sac and liver and postnatal repression in the liver. This is the first demonstration of a tissue-specific factor involved in developmental control of H19 expression. These data also indicate that the presence of FoxA proteins is not sufficient for binding but that additional mechanisms must govern the accessibility of FoxA proteins to their cognate binding sites within the H19 E1 enhancer.