Mao Changhui, Tai Wei-Cheng, Bai Yan, Poizat Coralie, Lee Amy S
Department of Biochemistry and Molecular Biology, University of Southern California/Norris Comprehensive Cancer Center, Los Angeles, CA 90089-9176, USA.
J Biol Chem. 2006 Mar 31;281(13):8877-87. doi: 10.1074/jbc.M505784200. Epub 2006 Feb 1.
The transcriptional activation of GRP78, which controls multiple signaling pathways of the unfolded protein response, has been used extensively as an indicator for the onset of endoplasmic reticulum stress in tissue culture systems. Here we investigate the mechanism of Grp78 induction during mouse embryonic development. Our results reveal that in transgenic mouse models, reporter gene activity driven by the Grp78 promoter is strongly activated during early embryonic heart development but subsides in later stages. This activation is strictly dependent on a 100-base pair region of the Grp78 promoter containing the endoplasmic reticulum stress response elements (ERSEs). Previous studies establish that endoplasmic reticulum stress induces in vivo binding of YY1 and the nuclear form of ATF6 to the ERSE. Since the expression of YY1 as well as ATF6 is ubiquitous in the mouse embryo, activation of the Grp78 promoter in the early embryonic heart may involve a specific mechanism. Here we report that GATA-4, a transcription factor essential for heart development, binds to the Grp78 promoter in vivo and activates the ERSE, which does not contain a consensus GATA binding site. GATA-4 cooperatively activates the Grp78 promoter with YY1, and the DNA binding domain of YY1 is necessary and sufficient for this cooperation. In addition, GATA-4 activation of the Grp78 promoter is enhanced by the nuclear form of ATF6, and this synergy is further potentiated by YY1. These results suggest that during early heart organogenesis, Grp78 can be activated through cooperation between the cell type-specific transcription factors and ERSE-binding factors.
GRP78可控制未折叠蛋白反应的多种信号通路，其转录激活已在组织培养系统中被广泛用作内质网应激发生的指标。在此，我们研究小鼠胚胎发育过程中Grp78诱导的机制。我们的结果显示，在转基因小鼠模型中，由Grp78启动子驱动的报告基因活性在胚胎心脏发育早期被强烈激活，但在后期减弱。这种激活严格依赖于Grp78启动子中包含内质网应激反应元件（ERSEs）的100个碱基对区域。先前的研究表明，内质网应激可诱导YY1和核形式的ATF6在体内与ERSE结合。由于YY1和ATF6在小鼠胚胎中普遍表达，早期胚胎心脏中Grp78启动子的激活可能涉及一种特定机制。在此我们报告，GATA-4是心脏发育所必需的转录因子，它在体内与Grp78启动子结合并激活ERSE，而该ERSE不包含共有GATA结合位点。GATA-4与YY1协同激活Grp78启动子，YY1的DNA结合结构域对于这种协同作用是必需且充分的。此外，核形式的ATF6增强了GATA-4对Grp78启动子的激活，并且YY1进一步增强了这种协同作用。这些结果表明，在早期心脏器官发生过程中，Grp78可通过细胞类型特异性转录因子与ERSE结合因子之间的协同作用而被激活。
