Department of Pathobiology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands.
PLoS One. 2013 Sep 12;8(9):e73693. doi: 10.1371/journal.pone.0073693. eCollection 2013.
Lymphatic vessels are derived from venous endothelial cells and their formation is governed by the Vascular endothelial growth factor C (VegfC)/Vegf receptor 3 (Vegfr3; Flt4) signaling pathway. Recent studies show that Collagen and Calcium Binding EGF domains 1 protein (Ccbe1) enhances VegfC-dependent lymphangiogenesis. Both Ccbe1 and Flt4 have been shown to be indispensable for lymphangiogenesis. However, how these essential players are transcriptionally regulated remains poorly understood. In the case of angiogenesis, atypical E2fs (E2f7 and E2f8) however have been recently shown to function as transcriptional activators for VegfA. Using a genome-wide approach we here identified both CCBE1 and FLT4 as direct targets of atypical E2Fs. E2F7/8 directly bind and stimulate the CCBE1 promoter, while recruitment of E2F7/8 inhibits the FLT4 promoter. Importantly, inactivation of e2f7/8 in zebrafish impaired venous sprouting and lymphangiogenesis with reduced ccbe1 expression and increased flt4 expression. Remarkably, over-expression of e2f7/8 rescued Ccbe1- and Flt4-dependent lymphangiogenesis phenotypes. Together these results identified E2f7/8 as novel in vivo transcriptional regulators of Ccbe1 and Flt4, both essential genes for venous sprouting and lymphangiogenesis.
淋巴管起源于静脉内皮细胞，其形成受血管内皮生长因子 C（VegfC）/血管内皮生长因子受体 3（Vegfr3；Flt4）信号通路的调控。最近的研究表明，胶原和钙结合 EGF 结构域 1 蛋白（Ccbe1）增强了 VegfC 依赖性淋巴管生成。Ccbe1 和 Flt4 都被证明对淋巴管生成是不可或缺的。然而，这些必需的分子如何被转录调控仍知之甚少。在血管生成的情况下，最近发现非典型 E2fs（E2f7 和 E2f8）作为 VegfA 的转录激活因子发挥作用。在这里，我们使用全基因组方法鉴定了 Ccbe1 和 Flt4 都是非典型 E2fs 的直接靶标。E2F7/8 直接结合并刺激 Ccbe1 启动子，而 E2F7/8 的募集抑制了 Flt4 启动子。重要的是，斑马鱼中 e2f7/8 的失活会导致静脉发芽和淋巴管生成受损，Ccbe1 表达降低，Flt4 表达增加。值得注意的是，E2f7/8 的过表达挽救了 Ccbe1 和 Flt4 依赖的淋巴管生成表型。这些结果共同确定了 E2f7/8 是 Ccbe1 和 Flt4 的新型体内转录调节剂，Ccbe1 和 Flt4 都是静脉发芽和淋巴管生成所必需的基因。
