Bruhl Thomas, Urbich Carmen, Aicher Diana, Acker-Palmer Amparo, Zeiher Andreas M, Dimmeler Stefanie
Molecular Cardiology, Department of Internal Medicine IV, University of Frankfurt, Frankfurt, Germany.
Circ Res. 2004 Apr 2;94(6):743-51. doi: 10.1161/01.RES.0000120861.27064.09. Epub 2004 Feb 5.
Homeobox genes (Hox) encode for transcription factors, which regulate cell proliferation and migration and play an important role in the development of the cardiovascular system during embryogenesis. In this study, we investigated the role of HoxA9 for endothelial cell migration and angiogenesis in vitro and identified a novel target gene, the EphB4 receptor. Inhibition of HoxA9 expression decreased endothelial cell tube formation and inhibited endothelial cell migration, suggesting that HoxA9 regulates angiogenesis. Because Eph receptor tyrosine kinases importantly contribute to angiogenesis, we examined whether HoxA9 may transcriptionally regulate the expression of EphB4. Downregulation of HoxA9 reduced the expression of EphB4. Chromatin-immunoprecipitation revealed that HoxA9 interacted with the EphB4 promoter, whereas a deletion construct of HoxA9 without DNA-binding motif (Delta(aa) 206-272) did not bind. Consistently, HoxA9 wild-type overexpression activated the EphB4 promoter as determined by reporter gene expression. HoxA9 binds to the EphB4 promoter and stimulates its expression resulting in an increase of endothelial cell migration and tube forming activity. Thus, modulation of EphB4 expression may contribute to the proangiogenic effect of HoxA9 in endothelial cells.
同源框基因（Hox）编码转录因子，这些转录因子调节细胞增殖和迁移，并在胚胎发生过程中的心血管系统发育中发挥重要作用。在本研究中，我们调查了HoxA9在体外对内皮细胞迁移和血管生成的作用，并鉴定了一个新的靶基因，即EphB4受体。抑制HoxA9表达可减少内皮细胞管形成并抑制内皮细胞迁移，提示HoxA9调节血管生成。由于Eph受体酪氨酸激酶对血管生成有重要作用，我们研究了HoxA9是否可能转录调节EphB4的表达。HoxA9的下调降低了EphB4的表达。染色质免疫沉淀显示HoxA9与EphB4启动子相互作用，而没有DNA结合基序的HoxA9缺失构建体（Delta(aa) 206-272）不结合。一致地，如报告基因表达所确定的，HoxA9野生型过表达激活了EphB4启动子。HoxA9与EphB4启动子结合并刺激其表达，导致内皮细胞迁移和管形成活性增加。因此，EphB4表达的调节可能有助于HoxA9在内皮细胞中的促血管生成作用。
