The function of RAPGEF3 (Rap guanine nucleotide exchange factor 3, ENSG00000079337) is as follows. Guanine nucleotide exchange factor (GEF) for RAP1A and RAP2A small GTPases that is activated by binding cAMP. Through simultaneous binding of PDE3B to RAPGEF3 and PIK3R6 is assembled in a signaling complex in which it activates the PI3K gamma complex and which is involved in angiogenesis. Plays a role in the modulation of the cAMP- induced dynamic control of endothelial barrier function through a pathway that is independent on Rho-mediated signaling. Required for the actin rearrangement at cell-cell junctions, such as stress fibers and junctional actin. {ECO:0000269|PubMed:10777494, ECO:0000269|PubMed:21840392, ECO:0000269|PubMed:9853756}.