Interaction of kindlin-2 with integrin ß3 promotes outside-in signaling responses by the αVß3 vitronectin receptor.

ABSTRACT

The bidirectional signaling and hemostatic functions of platelet αIIbß3 are regulated by kindlin-3 through interactions with the ß3 cytoplasmic tail. Little is known about kindlin regulation of the related "vitronectin receptor," αVß3. These relationships were investigated in endothelial cells, which express αVß3 and kindlin-2 endogenously. "ß3ΔRGT" knock-in mice lack the 3 C-terminal ß3 tail residues, whereas in "ß3/ß1(EGK)" mice, RGT is replaced by the corresponding residues of ß1. The wild-type ß3 tail pulled down kindlin-2 and c-Src in vitro, whereas ß3ΔRGT bound neither protein and ß3/ß1(EGK) bound kindlin-2, but not c-Src. ß3ΔRGT endothelial cells, but not ß3/ß1(EGK) endothelial cells, exhibited migration and spreading defects on vitronectin and reduced sprouting in 3-dimensional fibrin. Short hairpin RNA silencing of kindlin-2, but not c-Src, blocked sprouting by ß3 wild-type endothelial cells. Moreover, defective sprouting by ß3ΔRGT endothelial cells could be rescued by conditional, forced interaction of αVß3ΔRGT with kindlin-2. Stimulation of ß3ΔRGT endothelial cells led to normal extracellular ligand binding to αVß3, pin-pointing their defect to one of outside-in αVß3 signaling. ß3ΔRGT mice, but not ß3/ß1(EGK) mice, exhibited defects in both developmental and tumor angiogenesis, responses that require endothelial cell function. Thus, the ß3/kindlin-2 interaction promotes outside-in αVß3 signaling selectively, with biological consequences in vivo.