The small GTPases Rab are key regulators of intracellular membrane trafficking, from the formation of transport vesicles to their fusion with membranes. Rabs cycle between an inactive GDP-bound form and an active GTP-bound form that is able to recruit to membranes different sets of downstream effectors directly responsible for vesicle formation, movement, tethering and fusion. That Rab is involved in endocytic recycling and regulates the transport to the plasma membrane of transmembrane proteins like the tight junction protein OCLN/occludin. Thereby, it regulates the assembly and the activity of tight junctions. Moreover, it may also regulate tight junction assembly by activating the PKA signaling pathway and by reorganizing the actin cytoskeleton through the activation of the downstream effectors PRKACA and MICALL2 respectively. Through its role in tight junction assembly, may play a role in the establishment of Sertoli cell barrier. Plays also a role in angiogenesis through regulation of endothelial cells chemotaxis. Also involved in neurite outgrowth. Has also been proposed to play a role in post-Golgi membrane trafficking from the TGN to the recycling endosome. Finally, it has been involved in insulin-induced transport to the plasma membrane of the glucose transporter GLUT4 and therefore may play a role in glucose homeostasis. Rab activation is generally mediated by a guanine exchange factor (GEF), while inactivation through hydrolysis of bound GTP is catalyzed by a GTPase activating protein (GAP). That Rab may be activated by DENND1C, a guanine exchange factor. Activated in response to insulin (By similarity). Interacts (GTP-bound form) with MICALL2; competes with RAB8A and is involved in tight junctions assembly. Interacts (GTP-bound form) with MICALL1. Interacts (GTP-bound form) with MICAL1, MICAL3, MICALCL, EHBP1 and EHBP1L1; ternary complexes of RAB8A, RAB13 and either MICAL1 or EHBP1L1 are possible. Interacts with PRKACA; downstream effector of RAB13 involved in tight junction assembly. Interacts with GRB2; may recruit RAB13 to the leading edge of migrating endothelial cells where it can activate RHOA. Interacts (isoprenylated form) with PDE6D; dissociates RAB13 from membranes. Interacts with BICDL2/BICDR2. Interacts with LEPROT and LEPROTL1. Tight junctions or associated with vesicles scattered throughout the cytoplasm in cells lacking tight junctions (By similarity). Relocalizes to the leading edge of lamellipodia in migrating endothelial cells (PubMed:21543326). Belongs to the small GTPase superfamily. Rab family.