Netrin-4 Activates Endothelial Integrin α6β1

Rationale: Netrin-4 regulates vascular development. Identity of netrin-4 endothelial receptor and its subsequent cell functions is controversial. We previously demonstrated that the inhibition of netrin-1 canonical receptors, Unc5B and neogenin, expressed by lymphatic endothelial cells, do not suppress netrin-4-induced cell signaling and functions. Netrin family members were shown to signal through a range of receptors, including integrins (such as α3β1, α6β1, and α6β4) in nonendothelial cells. Objective: We tested whether integrins are netrin-4 receptors in the endothelium. Methods and Results: The α6β1 integrin is expressed by endothelial cells, and binds netrin-4 in a dose-dependent manner. Inhibition of α6 or β1 integrin subunits suppresses netrin-4-induced endothelial cell migration, adhesion, and focal adhesion contact. Netrin-4-stimulated phosphorylation of Src kinase family, effectors of endothelial cell migration, is also abolished by α6 or β1 inhibition. Finally, netrin-4 and α6β1 integrin expression colocalize in mouse embryonic, intestine, and tumor vasculature. Conclusions: The α6β1 integrin is a netrin-4 receptor in lymphatic endothelium and consequently represents a potential target to inhibit netrin-4-induced metastatic dissemination.