Receptor for Wnt proteins (PubMed:10097073). Most frizzled receptors are coupled to the beta-catenin (CTNNB1) canonical signaling pathway, which leads to the activation of disheveled proteins, inhibition of GSK-3 kinase, nuclear accumulation of beta-catenin (CTNNB1) and activation of Wnt target genes (PubMed:19837033). Plays a critical role in retinal vascularization by acting as a receptor for Wnt proteins and norrin (NDP) (PubMed:19837033). In retina, it can be activated by Wnt protein-binding and also by Wnt-independent signaling via binding of norrin (NDP), promoting in both cases beta-catenin (CTNNB1) accumulation and stimulation of LEF/TCF-mediated transcriptional programs (PubMed:19837033). A second signaling pathway involving PKC and calcium fluxes has been seen for some family members, but it is not yet clear if it represents a distinct pathway or if it can be integrated in the canonical pathway, as PKC seems to be required for Wnt-mediated inactivation of GSK-3 kinase. Both pathways seem to involve interactions with G-proteins. May be involved in transduction and intercellular transmission of polarity information during tissue morphogenesis and/or in differentiated tissues. Activation by Wnt5A stimulates PKC activity via a G-protein-dependent mechanism. Interacts with MAGI3 and NDP (PubMed:15035989, PubMed:15195140). Component of a complex, at least composed of TSPAN12, FZD4 and norrin (NDP) (PubMed:19837033). Interacts (via FZ domain) with TSKU; TSKU competes with WNT2B for binding to FZD4, inhibiting Wnt signaling and repressing peripheral eye development (PubMed:21856951). Interacts with glypican GPC3 (By similarity). Expressed in chondrocytes. Lys-Thr-X-X-X-Trp motif interacts with the PDZ domain of Dvl (Disheveled) family members and is involved in the activation of the Wnt/beta-catenin signaling pathway. The FZ domain is involved in binding with Wnt ligands. Ubiquitinated by ZNRF3, leading to its degradation by the proteasome. Defects in retinal vascularization. Belongs to the G-protein coupled receptor Fz/Smo family.