The recruitment of SOX/OCT complexes and the differential activity of HOXA1 and HOXB1 modulate the Hoxb1 auto-regulatory enhancer function
The recruitment of SOX/OCT complexes and the differential activity of HOXA1 and HOXB1 modulate the Hoxb1 auto-regulatory enhancer function
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DOI：
10.1074/jbc.m011175200
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发表时间：
2001-06-08
影响因子：
4.8
通讯作者：
Zappavigna, V
中科院分区：
文献类型：
--
作者：
Di Rocco, G;Gavalas, A;Zappavigna, V
在发育中的胚胎中，HOX基因的区域限制性表达模式依赖于自身、交叉和辅助调节转录元件。一个例子是Hoxb1自动调节元件(b1-ARE)，它驱动Hoxb1在后脑的第四个菱形粒中的表达，我们之前已经证明HOXB1和Pbx1激活从b1-ARE转录：通过与体内菱形核4中报告基因表达所需的序列结合，我们现在报道：在保留原始神经外胚层细胞特征的胚胎癌细胞中，b1-ARE显示出比其他细胞背景更高的基础和HOX/PBX诱导活性。我们已经在b1-ARE中确定了SOX/OCT异二聚体的两部分结合位点，这解释了其细胞上下文特异的活性，并且是胚胎癌细胞中HOX/PBX复合体最大转录活性所必需的。此外，我们发现在胚胎癌细胞背景下，HOXB1的转录活性显著高于其同源HOXA1。我们将这种差异活性的决定因素映射到HOXB1N末端转录激活结构域中。通过对转基因和HOXA1突变小鼠的分析，我们扩展了这些发现在体内HOXA1和HOXB1的差异活性，并证明了它们对于调节HOXB1在后脑的表达方面是重要的。我们发现，在转基因小鼠中，SOX/OCT位点的突变和HoxA1的靶向失活都会削弱b1-ARE对维甲酸的反应。我们的结果表明，HoxA1是体内b1-ARE对维甲酸反应的主要介质，这一功能依赖于SOX/OCT异二聚体与b1-ARE的结合。这些结果揭示了Hox类似物和它们的调节器之间新的功能差异。
Regionally restricted expression patterns of Hox genes in developing embryos rely on auto-, cross-, and para-regulatory transcriptional elements. One example is the Hoxb1 auto-regulatory element (b1-ARE), which drives expression of Hoxb1 in the fourth rhombomere of the hindbrain, We previously showed that HOXB1 and PBX1 activate transcription from the b1-ARE: by binding to sequences required for the expression of a reporter gene in rhombomere 4 in vivo, We now report: that in embryonal carcinoma cells, which retain characteristics of primitive neuroectodermal cells, the b1-ARE displays higher basal and HOX/PBX-induced activities than in other cell backgrounds. We have identified a bipartite-binding site for SOX/OCT heterodimers within the b1-ARE that accounts for its cell context-specific activity and is required for maximal transcriptional activity of HOX/PBX complexes in embryonal carcinoma cells. Furthermore, we found that in an embryonal carcinoma cell background, HOXB1 has a significantly higher transcriptional activity than its paralog HOXA1. We map the determinants for this differential activity within the HOXB1 N-terminal transcriptional activation domain. By using analysis in transgenic and HOXA1 mutant mice, we extended these findings on the differential activities of HOXA1 and HOXB1 in vivo, and we demonstrated that they are important for regulating aspects of HOXB1 expression in the hindbrain. We found that mutation of the SOX/OCT site and targeted inactivation of Hoxa1 both impair the response of the b1-ARE to retinoic acid in transgenic mice. Our results show that Hoxa1 is the primary mediator of the response of b1-ARE to retinoic acid in vivo and that this function is dependent on the binding of SOX/OCT heterodimers to the b1-ARE. These results uncover novel functional differences between Hox paralogs and their modulators.