Guanyl-nucleotide exchange factor that regulates small GTPases of the Rab family (PubMed:18559336, PubMed:20937701). Converts GDP-bound inactive form of RAB27A and RAB27B to the GTP-bound active forms (PubMed:18559336, PubMed:20937701). Converts GDP-bound inactive form of RAB3A, RAB3C and RAB3D to the GTP-bound active forms, GTPases involved in synaptic vesicle exocytosis and vesicle secretion (By similarity). Plays a role in synaptic vesicle formation and in vesicle trafficking at the neuromuscular junction (By similarity). Involved in up-regulating a post-docking step of synaptic exocytosis in central synapses (By similarity). Probably by binding to the motor proteins KIF1B and KIF1A, mediates motor-dependent transport of GTP-RAB3A-positive vesicles to the presynaptic nerve terminals (By similarity). Plays a role in TNFA-mediated activation of the MAPK pathway, including ERK1/2 (PubMed:32761064). May link TNFRSF1A with MAP kinase activation (PubMed:9115275). May be involved in the regulation of TNFA-induced apoptosis (PubMed:11577081, PubMed:32761064).
