Department of Molecular, Cellular, and Developmental Biology, University of California, Los Angeles, Los Angeles, CA 90095, USA.
J Cell Biol. 2010 Feb 22;188(4):595-609. doi: 10.1083/jcb.200906044.
VEGF can be secreted in multiple isoforms with variable affinity for extracellular proteins and different abilities to induce vascular morphogenesis, but the molecular mechanisms behind these effects remain unclear. Here, we show molecular distinctions between signaling initiated from soluble versus matrix-bound VEGF, which mediates a sustained level of VEGFR2 internalization and clustering. Exposure of endothelial cells to matrix-bound VEGF elicits prolonged activation of VEGFR2 with differential phosphorylation of Y1214, and extended activation kinetics of p38. These events require association of VEGFR2 with beta1 integrins. Matrix-bound VEGF also promotes reciprocal responses on beta1 integrin by inducing its association with focal adhesions; a response that is absent upon exposure to soluble VEGF. Inactivation of beta1 integrin blocks the prolonged phosphorylation of Y1214 and consequent activation of p38. Combined, these results indicate that when in the context of extracellular matrix, activation of VEGFR2 is distinct from that of soluble VEGF in terms of recruitment of receptor partners, phosphorylation kinetics, and activation of downstream effectors.
VEGF 可以以多种同种型分泌，这些同种型对细胞外蛋白具有不同的亲和力，并具有不同的诱导血管形态发生的能力，但这些作用背后的分子机制仍不清楚。在这里，我们展示了由可溶性 VEGF 与基质结合的 VEGF 引发的信号之间的分子区别，这介导了 VEGFR2 内化和聚集的持续水平。内皮细胞暴露于基质结合的 VEGF 会引发 VEGFR2 的持续激活，导致 Y1214 的差异化磷酸化，并延长 p38 的激活动力学。这些事件需要 VEGFR2 与β1 整合素的关联。基质结合的 VEGF 还通过诱导其与焦点粘连的关联来促进β1 整合素的相互反应；而当暴露于可溶性 VEGF 时，则不存在这种反应。β1 整合素的失活会阻止 Y1214 的持续磷酸化和随后的 p38 激活。综上所述，这些结果表明，当处于细胞外基质的情况下，VEGFR2 的激活与可溶性 VEGF 的激活在受体伙伴的募集、磷酸化动力学和下游效应物的激活方面是不同的。
