Receptor for Slit proteins, at least for SLIT2, and seems to be involved in angiogenesis and vascular patterning. May mediate the inhibition of primary endothelial cell migration by Slit proteins (By similarity). Involved in the maintenance of endothelial barrier organization and function (PubMed:30455415). {ECO:0000250, ECO:0000269|PubMed:30455415}. This is the function of ENSG00000154133 (ROBO4, roundabout guidance receptor 4).