Institut de Génétique Moléculaire de Montpellier UMR 5535 CNRS, Montpellier, France.
PLoS One. 2012;7(7):e40484. doi: 10.1371/journal.pone.0040484. Epub 2012 Jul 6.
The two related basic helix-loop-helix, TAL1 and LYL1, and their cofactor LIM-only-2 protein (LMO2) are present in blood and endothelial cells. While their crucial role in early hematopoiesis is well established, their function in endothelial cells and especially in angiogenesis is less understood. Here, we identified ANGIOPOIETIN-2 (ANG-2), which encodes a major regulator of angiogenesis, as a direct transcriptional target of TAL1, LYL1 and LMO2. Knockdown of any of the three transcription factors in human blood and lymphatic endothelial cells caused ANG-2 mRNA and protein down-regulation. Transient transfections showed that the full activity of the ANG-2 promoter required the integrity of a highly conserved Ebox-GATA composite element. Accordingly, chromatin immunoprecipitation assays demonstrated that TAL1, LYL1, LMO2 and GATA2 occupied this region of ANG-2 promoter in human endothelial cells. Furthermore, we showed that LMO2 played a central role in assembling TAL1-E47, LYL1-LYL1 or/and LYL1-TAL1 dimers with GATA2. The resulting complexes were able to activate endogenous ANG-2 expression in endothelial cells as well as in non-endothelial cells. Finally, we showed that ANG-2 gene activation during angiogenesis concurred with the up-regulation of TAL1 and LMO2. Altogether, we identified ANG-2 as a bona fide target gene of LMO2-complexes with TAL1 and/or LYL1, highlighting a new function of the three hematopoietic factors in the endothelial lineage.
两个相关的基本螺旋-环-螺旋（basic helix-loop-helix）转录因子 TAL1 和 LYL1，以及它们的协同因子 LIM 仅含 2 个结构域蛋白（LIM-only-2 protein，LMO2）存在于血液和血管内皮细胞中。虽然它们在早期造血中的关键作用已得到充分证实，但它们在血管内皮细胞中的功能，尤其是在血管生成中的功能，还了解甚少。在这里，我们确定了编码血管生成主要调节因子的血管生成素 2（angiopoietin-2，ANG-2）是 TAL1、LYL1 和 LMO2 的直接转录靶标。在人血液和淋巴内皮细胞中敲低任何三种转录因子都会导致 ANG-2 mRNA 和蛋白下调。瞬时转染表明，ANG-2 启动子的全部活性需要高度保守的 Ebox-GATA 复合元件的完整性。因此，染色质免疫沉淀分析表明，TAL1、LYL1、LMO2 和 GATA2 占据了人内皮细胞 ANG-2 启动子的这一区域。此外，我们还表明，LMO2 在组装 TAL1-E47、LYL1-LYL1 或/和 LYL1-TAL1 二聚体与 GATA2 方面发挥核心作用。由此产生的复合物能够在血管内皮细胞以及非内皮细胞中激活内源性 ANG-2 表达。最后，我们表明在血管生成过程中 ANG-2 基因的激活与 TAL1 和 LMO2 的上调一致。总之，我们确定 ANG-2 是 LMO2 与 TAL1 和/或 LYL1 复合物的真正靶基因，强调了这三个造血因子在血管内皮谱系中的新功能。
