Plays a central role in tight junction maintenance via the complex formed with ARHGAP17; which acts by regulating the uptake of polarity proteins at tight junctions. Appears to regulate endothelial cell migration and tube formation. May also play a role in the assembly of endothelial cell-cell junctions. {ECO:0000269|PubMed:11257124; ECO:0000269|PubMed:16678097}.