Laboratory of Developmental Genetics, Center for Experimental Medicine and Systems Biology, Institute of Medical Science, University of Tokyo, Minato-ku, Tokyo 108-8639, Japan.
Development. 2010 Mar;137(6):1003-13. doi: 10.1242/dev.043489.
Mammalian Ras, which is encoded by three independent genes, has been thought to be a versatile component of intracellular signalling. However, when, where and how Ras signalling plays essential roles in development and whether the three Ras genes have overlapping functions in particular cells remain unclear. Here, we show that the three Ras proteins dose-dependently regulate lymphatic vessel growth in mice. We find that lymphatic vessel hypoplasia is a common phenotype in Ras compound knockout mice and that overexpressed normal Ras in an endothelial cell lineage selectively causes lymphatic vessel hyperplasia in vivo. Overexpression of normal Ras in lymphatic endothelial cells leads to sustained MAPK activation, cellular viability and enhanced endothelial network formation under serum-depleted culture conditions in vitro, and knockdown of endogenous Ras in lymphatic endothelial cells impairs cell proliferation, MAPK activation, cell migration and endothelial network formation. Ras overexpression and knockdown result in up- and downregulation of vascular endothelial growth factor receptor (VEGFR) 3 expression, respectively, in lymphatic endothelial cells in vitro. The close link between Ras and VEGFR3 in vitro is consistent with the result that Ras knockout and transgenic alleles are genetic modifiers in lymphatic vessel hypoplasia caused by Vegfr3 haploinsufficiency. Our findings demonstrate a cooperative function of the three Ras proteins in normal development, and also provide a novel aspect of VEGFR3 signalling modulated by Ras in lymphangiogenesis.
哺乳动物 Ras 由三个独立的基因编码，被认为是细胞内信号转导的多功能组成部分。然而，Ras 信号在发育中何时、何地以及如何发挥重要作用，以及这三个 Ras 基因在特定细胞中是否具有重叠功能仍不清楚。在这里，我们展示了三种 Ras 蛋白在小鼠中剂量依赖性地调节淋巴管生长。我们发现淋巴管发育不良是 Ras 复合敲除小鼠的常见表型，而内皮细胞谱系中过表达的正常 Ras 选择性地导致体内淋巴管增生。正常 Ras 在淋巴管内皮细胞中的过表达导致 MAPK 激活持续、细胞存活和体外在血清耗尽培养条件下增强的内皮网络形成，而淋巴管内皮细胞中内源性 Ras 的敲低会损害细胞增殖、MAPK 激活、细胞迁移和内皮网络形成。Ras 过表达和敲低分别导致体外淋巴管内皮细胞中血管内皮生长因子受体 (VEGFR)3 表达的上调和下调。Ras 和 VEGFR3 之间在体外的紧密联系与 Ras 敲除和转基因等位基因是 Vegfr3 杂合不足引起的淋巴管发育不良的遗传修饰因子的结果一致。我们的研究结果表明，三种 Ras 蛋白在正常发育中具有协同功能，也为 Ras 在淋巴管生成中调节 VEGFR3 信号提供了一个新的方面。
