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 alpha 3 beta 1, alpha 6 beta 1, and alpha 6 beta 4) in nonendothelial cells. Objective: We tested whether integrins are Netrin-4 receptors in the endothelium. Methods and Results: The alpha 6 beta 1 integrin is expressed by endothelial cells, and binds Netrin-4 in a dose-dependent manner. Inhibition of alpha 6 or beta 1 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 alpha 6 or beta 1 inhibition. Finally, Netrin-4 and alpha 6 beta 1 integrin expression colocalize in mouse embryonic, intestine, and tumor vasculature. Conclusions: The alpha 6 beta 1 integrin is a Netrin-4 receptor in lymphatic endothelium and consequently represents a potential target to inhibit Netrin-4-0induced metastatic dissemination. (Circ Res. 2011; 109: 770-0774.)