Required for activation of guanine nucleotide-binding proteins (G-proteins) during non-canonical Wnt signaling. Binds to ligand-activated Wnt receptor FZD7, displacing DVL1 from the FZD7 receptor and leading to inhibition of canonical Wnt signaling. Acts as a non-receptor guanine nucleotide exchange factor by also binding to guanine nucleotide-binding protein G(i) alpha (Gi-alpha) subunits, leading to their activation. Binding to Gi-alpha subunits displaces the beta and gamma subunits from the heterotrimeric G-protein complex, triggering non-canonical Wnt responses such as activation of RAC1 and PI3K-AKT signaling. Promotes apical constriction of cells via ARHGEF18. Homooligomer (PubMed:14750955). Interacts with DVL1 (via PDZ domain); dissociates following initiation of non-canonical Wnt signaling (PubMed:14750955). Interacts (via C-terminus) with ligand-activated Wnt receptor FZD7; competes with DVL1 for binding to FZD7 and displaces DVL1 from ligand-activated FZD7 (By similarity). Interacts (via GBA motif) with guanine nucleotide-binding protein G(i) alpha subunits GNAI1, GNAI2 and GNAI3 (inactive GDP-bound form); interacts with higher affinity with GNAI1 and GNAI3 than with GNAI2 and interaction leads to G(i) alpha subunit activation (By similarity). Does not interact with GNAO1 (By similarity). Enriched at apical cell junctions. The GBA (G-alpha binding and activating) motif mediates binding to the alpha subunits of guanine nucleotide-binding proteins (G proteins). The PDZ domain is required for localization to apical junctions. Belongs to the CCDC88 family.