G-Protein-Coupled Receptor-2-Interacting Protein-1 Controls Stalk Cell Fate by Inhibiting Delta-like 4-Notch1 Signaling.

The spatiotemporal localization and expression of Dll4 are critical for sprouting angiogenesis. However, the related mechanisms are poorly understood. Here, we show that G-protein-coupled receptor-kinase interacting protein-1 (GIT1) is a robust endogenous inhibitor of Dll4-Notch1 signaling that specifically controls stalk cell fate. GIT1 is highly expressed in stalk cells but not in tip cells. GIT1 deficiency remarkably enhances Dll4 expression and Notch1 signaling, resulting in impaired retinal sprouting angiogenesis, which can be rescued by treatment with the Notch inhibitor or Dll4 neutralizing antibody. Notch1 regulates Dll4 expression by binding to recombining binding protein suppressor of hairless (RBP-J, a transcriptional regulator of Notch) via a highly conserved ankyrin (ANK) repeat domain. We show that GIT1, which also contains an ANK domain, inhibits the Notch1-Dll4 signaling pathway by competing with Notch1 ANK domain for binding to RBP-J in stalk cells.