Vascular endothelial cadherin controls VEGFR-2 internalization and signaling from intracellular compartments

Receptor endocytosis is a fundamental step in controllingthe magnitude, duration, and nature of cellsignaling events. Confl uent endothelial cells are contactinhibited in their growth and respond poorly to theproliferative signals of vascular endothelial growth factor(VEGF). In a previous study, we found that the associationof vascular endothelial cadherin (VEC) with VEGF receptor(VEGFR) type 2 contributes to density- dependent growthinhibition (Lampugnani, G.M., A. Zanetti, M. Corada,T. Takahashi, G. Balconi, F. Breviario, F. Orsenigo,A. Cattelino, R. Kemler, T.O. Daniel, and E. Dejana.2003. J. Cell Biol. 161:793–804). In the present study,we describe the mechanism through which VEC reducesVEGFR-2 signaling. We found that VEGF induces theclathrin- dependent internalization of VEGFR-2. WhenVEC is absent or not engaged at junctions, VEGFR-2 isinternalized more rapidly and remains in endosomalcompartments for a longer time. Internalization does notterminate its signaling; instead, the internalized receptoris phosphorylated, codistributes with active phospholipaseC–γ, and activates p44/42 mitogen- activated proteinkinase phosphorylation and cell proliferation. Inhibition ofVEGFR-2 internalization reestablishes the contact inhibitionof cell growth, whereas silencing the junction-associateddensity-enhanced phosphatase-1/CD148 phosphataserestores VEGFR-2 internalization and signaling. Thus,VEC limits cell proliferation by retaining VEGFR-2 atthe membrane and preventing its internalization intosignaling compartments.