Activates Rho-GTPases by promoting the exchange of GDP for GTP. May be involved in epithelial barrier permeability, cell motility and polarization, dendritic spine morphology, antigen presentation, leukemic cell differentiation, cell cycle regulation, innate immune response, and cancer. Binds Rac-GTPases, but does not seem to promote nucleotide exchange activity toward Rac-GTPases. May stimulate instead the cortical activity of Rac. Inactive toward CDC42, TC10, or Ras-GTPases. Forms an intracellular sensing system along with NOD1 for the detection of microbial effectors during cell invasion by pathogens. Involved in innate immune signaling transduction pathway promoting cytokine IL6/interleukin-6 and TNF-alpha secretion in macrophage upon stimulation by bacterial peptidoglycans; acts as a signaling intermediate between NOD2 receptor and RIPK2 kinase. Contributes to the tyrosine phosphorylation of RIPK2 through Src tyrosine kinase leading to NF-kappaB activation by NOD2. Overexpression activates Rho-, but not Rac-GTPases, and increases paracellular permeability. Involved in neuronal progenitor cell division and differentiation. Involved in the migration of precerebellar neurons. Found in a complex composed at least of ARHGEF2, NOD2 and RIPK2. Interacts with RIPK2; the interaction mediates tyrosine phosphorylation of RIPK2 by Src kinase CSK. Interacts with RIPK1 and RIPK3. Interacts with YWHAZ/14-3-3 zeta; when phosphorylated at Ser-885. Interacts with the kinases PAK4, AURKA and MAPK1. Interacts with RHOA and RAC1. Interacts with NOD1 (By similarity). Interacts (via the N- terminal zinc finger) with CAPN6 (via domain II). Interacts with DYNLT1 (By similarity). Localizes to the tips of cortical microtubules of the mitotic spindle during cell division, and is further released upon microtubule depolymerization. Colocalized with NOD2 and RIPK2 in vesicles and with the cytoskeleton. The DH (DBL-homology) domain promotes tyrosine phosphorylation of RIPK2 (By similarity). The DH (DBL-homology) domain interacts with and promotes loading of GTP on RhoA. The PH domain has no affinity for phosphoinositides suggesting that it does not interact directly with membranes. The phorbol-ester/DAG-type zinc-finger and the C-terminal coiled-coil domains (606-986) are both important for association with microtubules. Phosphorylation of Ser-885 by PAK1 induces binding to protein YWHAZ, promoting its relocation to microtubules and the inhibition of its activity. Phosphorylated by AURKA and CDK1 during mitosis, which negatively regulates its activity. Phosphorylation by MAPK1 or MAPK3 increases nucleotide exchange activity. Phosphorylation by PAK4 releases GEF-H1 from the microtubules. Phosphorylated on serine, threonine and tyrosine residues in a RIPK2-dependent manner (By similarity).