Component of the Wnt-Fzd-LRP5-LRP6 complex that triggers beta-catenin signaling through inducing aggregation of receptor-ligand complexes into ribosome-sized signalsomes. Cell-surface coreceptor of Wnt/beta-catenin signaling, which plays a pivotal role in bone formation. The Wnt-induced Fzd/LRP6 coreceptor complex recruits DVL1 polymers to the plasma membrane which, in turn, recruits the AXIN1/GSK3B-complex to the cell surface promoting the formation of signalsomes and inhibiting AXIN1/GSK3-mediated phosphorylation and destruction of beta-catenin. Required for posterior patterning of the epiblast during gastrulation (By similarity). Homodimer; disulfide-linked (By similarity). Forms phosphorylated oligomer aggregates on Wnt-signaling (By similarity). Component of the Wnt-Fzd-LRP5-LRP6 complex. Interacts (via the extracellular domain) with WNT1; the interaction is enhanced by prior formation of the Wnt/Fzd complex. Interacts (via the beta-propeller regions 3 and 4) with WNT3A. Interacts (via the beta-propeller regions 1 and 2) with WNT9B. Interacts with FZD5; the interaction forms a coreceptor complex for Wnt signaling and is inhibited by DKK1 and DRAXIN. Interacts (via beta propeller region) with DKK1; the interaction inhibits FZD5/LRP6 complex formation. Interacts with DKK2. Interacts (via the phosphorylated PPPSP motifs) with AXIN1; the interaction recruits the AXIN1/GSK3B complex to cell surface LRP6 signalsomes. Interacts (via the extracellular domain) with RSPO1; the interaction activates Wnt/beta-catenin signaling. Interacts (via the extracellular domain) with RSPO3 (via the cysteine rich domain); the interaction activates Wnt/beta-catenin signaling. Interacts (via the beta-propeller regions 1 and 2) with SOST; the interaction competes with DKK1 for binding for inhibiting beta-catenin signaling. Interacts (via the cytoplasmic domain) with CSNKIE; the interaction phosphorylates LRP6, binds AXIN1 and inhibits AXIN1/GSK3B-mediated phosphorylation of beta-catenin (By similarity). Interacts with DRAXIN; the interaction inhibits Wnt signaling. Interacts with GRB10; the interaction prevents AXIN1 binding, thus negatively regulating the Wnt signaling pathway. Interacts with MESD; the interaction prevents the formation of LRP6 aggregates and targets LRP6 to the plasma membrane. Interacts with MACF1. Interacts with DAB2; the interaction involves LRP6 phosphorylation by CK2 and sequesters LRP6 towards clathrin-mediated endocytosis. Interacts with TMEM198 (By similarity). Interacts with CAPRIN2; the interaction promotes LRP6 phosphorylation at Ser-1490 (By similarity). Found in a complex with CAPRIN2, CCNY and CDK14 during G2/M stage; CAPRIN2 functions as a scaffold for the complex by binding to CCNY via its N terminus and to CDK14 via its C terminus. Interacts with LYPD6. Forms a ternary complex with DKK1 and KREM1 (By similarity). Interacts with KREM1 in a DKK1-dependent manner (By similarity). Interacts with MDK: this interaction is calcium dependent (PubMed:12573468). Interacts with LMBR1L (PubMed:31073040). On Wnt signaling, undergoes a cycle of caveolin- or clathrin-mediated endocytosis and plasma membrane location. Released from the endoplasmic reticulum on palmitoylation. Mono-ubiquitination retains it in the endoplasmic reticulum in the absence of palmitoylation. On Wnt signaling, phosphorylated, aggregates and colocalizes with AXIN1 and GSK3B at the plasma membrane in LRP6-signalsomes (By similarity). Chaperoned to the plasma membrane by MESD. Expressed in early embryo. Broadly expressed throughout the embryonic ectoderm and in nascent mesoderm, and in endoderm emerging from the primitive streak. The YWTD-EGF-like domains 1 and 2 are required for the interaction with Wnt-frizzled complex. The YWTD-EGF-like domains 3 and 4 are required for the interaction with DKK1 (By similarity). The PPPSP motifs play a central role in signal transduction by being phosphorylated, leading to activate the Wnt signaling pathway. Dual phosphorylation of cytoplasmic PPPSP motifs sequentially by GSK3 and CK1 is required for AXIN1-binding, and subsequent stabilization and activation of beta-catenin via preventing GSK3-mediated phosphorylation of beta-catenin. Phosphorylated, in vitro, by GRK5/6 within and outside the PPPSP motifs. Phosphorylation at Ser-1490 by CDK14 during G2/M phase leads to regulation of the Wnt signaling pathway during the cell cycle. Phosphorylation by GSK3B is induced by RPSO1 binding and inhibited by DKK1. Phosphorylated, in vitro, by casein kinase I on Thr-1479 (By similarity). Undergoes gamma-secretase-dependent regulated intramembrane proteolysis (RIP). The extracellular domain is first released by shedding, and then, through the action of gamma-secretase, the intracellular domain (ICD) is released into the cytoplasm where it is free to bind to GSK3B and to activate canonical Wnt signaling (By similarity). Palmitoylation on the two sites near the transmembrane domain leads to release of LRP6 from the endoplasmic reticulum. Mono-ubiquitinated which retains LRP6 in the endoplasmic reticulum. Ubiquitinated by ZNRF3, leading to its degradation by the proteasome (By similarity). N-glycosylation is required for cell surface location. Defects in Lrp6 are the cause of Ringelschwanz (rs) phenotype. Rs phenotype is a spontaneous mutation that is characterized by a combination of multiple Wnt-deficient phenotypes including dysmorphologies of the axial skeleton, digits and the neural tube. The establishment of the anteroposterior somite compartments, the epithelialization of nascent somites, and the formation of segment borders are disturbed in (rs) mutants. There is delayed ossification at birth and a low bone mass phenotype in adults. Functional analyses reveal impaired targeting to the plasma surface due to reduced interaction with MESD leading to inhibited Wnt/beta-catenin signaling. Belongs to the LDLR family.