Induces morphological reversion of a cell line transformed by a Ras oncogene. Counteracts the mitogenic function of Ras, at least partly because it can interact with Ras GAPs and RAF in a competitive manner. Together with ITGB1BP1, regulates KRIT1 localization to microtubules and membranes (By similarity). Plays a role in nerve growth factor (NGF)-induced neurite outgrowth. Plays a role in the regulation of embryonic blood vessel formation. Involved in the establishment of basal endothelial barrier function. May be involved in the regulation of the vascular endothelial growth factor receptor KDR expression at endothelial cell-cell junctions. GTP + H2O = GDP + H(+) + phosphate Activated by guanine nucleotide-exchange factors (GEF) EPAC and EPAC2 in a cAMP-dependent manner, and GFR. Found in a complex, at least composed of ITGB1BP1, KRIT1 and RAP1A. Interacts (active GTP-bound form preferentially) with KRIT1 (via C-terminus FERM domain); the interaction does not induce the opening conformation of KRIT1. In its GTP-bound form interacts with PLCE1 and RADIL. Interacts with SGSM1, SGSM2 and SGSM3. Interacts (via GTP-bound active form) with RAPGEF2 (via Ras-associating domain) (By similarity). Interacts with TBC1D21 (By similarity). Interacts with RAP1GDS1 (By similarity). Localized with RAPGEF2 at cell-cell junctions. Colocalized with RAPGEF2 in the perinuclear region (By similarity). Recruited from early endosome to late endosome compartment after nerve growth factor (NGF) stimulation. Belongs to the small GTPase superfamily. Ras family.