EphB1 in Endothelial Cells Regulates Caveolae Formation and Endocytosis

Caveolae, the cave-like structures abundant in endothelial cells (ECs), are important in regulating key functions such as caveolae-mediated endocytosis and generation of nitric oxide. Here we show that deletion of the receptor tyrosine kinase EphB1 ( EphB1 −/− ) in mice markedly reduced the caveolae number in ECs of heart and lung vessels and prevented caveolae-mediated endocytosis. EphB1 expressed in adult ECs was shown to bind the caveolin-1 (Cav-1) scaffold domain (CSD) via the CSD binding motif (CSDBM) on EphB1. We demonstrated that activation of EphB1 by the native ligand Ephrin B1 uncoupled EphB1 from Cav-1, and licensed Src- dependent Y-14 Cav-1 phosphorylation. Deletion of CSDBM on EphB1 prevented EphB1/Cav-1 interaction and the activation of Src and Src mediated Y-14 Cav-1 phosphorylation. These studies identify the central role of endothelium expressed EphB1 in regulating caveolae biogenesis and caveolae-mediated endocytosis.