Rationale: The mechanistic foundation of vascular maturation is still largely unknown. Several human pathologies are characterized by deregulated angiogenesis and unstable blood vessels. Solid tumors, for instance, get their nourishment from newly formed structurally abnormal vessels which present wide and irregular interendothelial junctions. Expression and clustering of the main endothelial-specific adherens junction protein, VEC (vascular endothelial cadherin), upregulate genes with key roles in endothelial differentiation and stability.

Objective: We aim at understanding the molecular mechanisms through which VEC triggers the expression of a set of genes involved in endothelial differentiation and vascular stabilization.

Methods and Results: We compared a VEC-null cell line with the same line reconstituted with VEC wild-type cDNA. VEC expression and clustering upregulated endothelial-specific genes with key roles in vascular stabilization including claudin-5, vascular endothelial-protein tyrosine phosphatase (VE-PTP), and von Willebrand factor (vWf). Mechanistically, VEC exerts this effect by inhibiting polycomb protein activity on the specific gene promoters. This is achieved by preventing nuclear translocation of FoxO1 (Forkhead box protein O1) and β-catenin, which contribute to PRC2 (polycomb repressive complex-2) binding to promoter regions of claudin-5, VE-PTP, and vWf. VEC/β-catenin complex also sequesters a core subunit of PRC2 (Ezh2 [enhancer of zeste homolog 2]) at the cell membrane, preventing its nuclear translocation. Inhibition of Ezh2/VEC association increases Ezh2 recruitment to claudin-5, VE-PTP, and vWf promoters, causing gene downregulation. RNA sequencing comparison of VEC-null and VEC-positive cells suggested a more general role of VEC in activating endothelial genes and triggering a vascular stability-related gene expression program. In pathological angiogenesis of human ovarian carcinomas, reduced VEC expression paralleled decreased levels of claudin-5 and VE-PTP.

Conclusions: These data extend the knowledge of polycomb-mediated regulation of gene expression to endothelial cell differentiation and vessel maturation. The identified mechanism opens novel therapeutic opportunities to modulate endothelial gene expression and induce vascular normalization through pharmacological inhibition of the polycomb-mediated repression system.

理由：血管成熟的机制基础仍然很大程度上未知。几种人类疾病的特征是血管生成失调和血管不稳定。例如，实体瘤从新形成的结构异常血管中获取营养，这些血管呈现出宽而不规则的内皮间连接。主要内皮特异性粘附连接蛋白 VEC（血管内皮钙粘蛋白）的表达和聚集上调在内皮分化和稳定性中起关键作用的基因。

目的：我们旨在了解 VEC 触发一组参与内皮分化和血管稳定的基因表达的分子机制。

方法和结果：我们将 VEC 无效细胞系与用VEC野生型 cDNA 重组的相同细胞系进行了比较。VEC 表达和聚集上调了在血管稳定中起关键作用的内皮特异性基因，包括Claudin-5、血管内皮蛋白酪氨酸磷酸酶 ( VE-PTP ) 和血管性血友病因子 ( vWf )。从机制上讲，VEC 通过抑制特定基因启动子上的多梳蛋白活性来发挥这种作用。这是通过阻止 FoxO1（叉头盒蛋白 O1）和 β-连环蛋白的核转位来实现的，这有助于 PRC2（多梳抑制复合物 2）与Claudin-5、 VE-PTP和vWf的启动子区域结合. VEC/β-连环蛋白复合物还在细胞膜上隔离了 PRC2 的核心亚基（Ezh2 [zeste 同源物 2 的增强子]），防止其核转位。抑制 Ezh2/VEC 结合会增加 Ezh2 对claudin-5、VE-PTP和vWf启动子的募集，从而导致基因下调。VEC 无效和 VEC 阳性细胞的 RNA 测序比较表明，VEC 在激活内皮基因和触发血管稳定性相关基因表达程序方面具有更普遍的作用。在人类卵巢癌的病理性血管生成中，VEC 表达降低与 Claudin-5 和 VE-PTP 水平降低平行。

结论：这些数据将多梳介导的基因表达调控知识扩展到内皮细胞分化和血管成熟。已确定的机制为调节内皮基因表达和通过药理学抑制多梳介导的抑制系统诱导血管正常化开辟了新的治疗机会。