Valdembri Donatella, Caswell Patrick T, Anderson Kurt I, Schwarz Juliane P, König Ireen, Astanina Elena, Caccavari Francesca, Norman Jim C, Humphries Martin J, Bussolino Federico, Serini Guido
Department of Oncological Sciences and Division of Molecular Angiogenesis, Institute for Cancer Research and Treatment, University of Torino School of Medicine, Candiolo, Italy.
PLoS Biol. 2009 Jan 27;7(1):e25. doi: 10.1371/journal.pbio.1000025.
Neuropilin 1 (Nrp1) is a coreceptor for vascular endothelial growth factor A165 (VEGF-A165, VEGF-A164 in mice) and semaphorin 3A (SEMA3A). Nevertheless, Nrp1 null embryos display vascular defects that differ from those of mice lacking either VEGF-A164 or Sema3A proteins. Furthermore, it has been recently reported that Nrp1 is required for endothelial cell (EC) response to both VEGF-A165 and VEGF-A121 isoforms, the latter being incapable of binding Nrp1 on the EC surface. Taken together, these data suggest that the vascular phenotype caused by the loss of Nrp1 could be due to a VEGF-A164/SEMA3A-independent function of Nrp1 in ECs, such as adhesion to the extracellular matrix. By using RNA interference and rescue with wild-type and mutant constructs, we show here that Nrp1 through its cytoplasmic SEA motif and independently of VEGF-A165 and SEMA3A specifically promotes alpha5beta1-integrin-mediated EC adhesion to fibronectin that is crucial for vascular development. We provide evidence that Nrp1, while not directly mediating cell spreading on fibronectin, interacts with alpha5beta1 at adhesion sites. Binding of the homomultimeric endocytic adaptor GAIP interacting protein C terminus, member 1 (GIPC1), to the SEA motif of Nrp1 selectively stimulates the internalization of active alpha5beta1 in Rab5-positive early endosomes. Accordingly, GIPC1, which also interacts with alpha5beta1, and the associated motor myosin VI (Myo6) support active alpha5beta1 endocytosis and EC adhesion to fibronectin. In conclusion, we propose that Nrp1, in addition to and independently of its role as coreceptor for VEGF-A165 and SEMA3A, stimulates through its cytoplasmic domain the spreading of ECs on fibronectin by increasing the Rab5/GIPC1/Myo6-dependent internalization of active alpha5beta1. Nrp1 modulation of alpha5beta1 integrin function can play a causal role in the generation of angiogenesis defects observed in Nrp1 null mice.
神经纤毛蛋白1（Nrp1）是血管内皮生长因子A165（小鼠中为VEGF - A164）和信号素3A（SEMA3A）的共受体。然而，Nrp1基因敲除胚胎表现出的血管缺陷与缺乏VEGF - A164或Sema3A蛋白的小鼠不同。此外，最近有报道称，Nrp1是内皮细胞（EC）对VEGF - A165和VEGF - A121亚型作出反应所必需的，而后者无法在内皮细胞表面结合Nrp1。综上所述，这些数据表明，Nrp1缺失导致的血管表型可能归因于Nrp1在内皮细胞中具有不依赖VEGF - A164/SEMA3A的功能，比如与细胞外基质的黏附。通过使用RNA干扰以及野生型和突变体构建体进行拯救实验，我们在此表明，Nrp1通过其胞质SEA基序，且独立于VEGF - A165和SEMA3A，特异性地促进α5β1整合素介导的内皮细胞与纤连蛋白的黏附，这对血管发育至关重要。我们提供的证据表明，Nrp1虽然不直接介导细胞在纤连蛋白上的铺展，但在黏附位点与α5β1相互作用。同多聚体内吞衔接蛋白GAIP相互作用蛋白C末端成员1（GIPC1）与Nrp1的SEA基序结合，选择性地刺激活性α5β1在Rab5阳性早期内体中的内化。因此，同样与α5β1相互作用的GIPC1以及相关的运动蛋白肌球蛋白VI（Myo6）支持活性α5β1的内吞作用以及内皮细胞与纤连蛋白的黏附。总之，我们提出，Nrp1除了作为VEGF - A165和SEMA3A的共受体发挥作用之外，还通过其胞质结构域，通过增加Rab5/GIPC1/Myo6依赖的活性α5β1的内化，刺激内皮细胞在纤连蛋白上的铺展。Nrp1对α5β1整合素功能的调节可能在Nrp1基因敲除小鼠中观察到的血管生成缺陷的产生中起因果作用。
