CDB15:0001602 WNT5A — FZD2

ABSTRACT: The seven-transmembrane-spanning receptors of the FZD1-10 class are bound and activated by the WNT family of lipoglycoproteins, thereby inducing a complex network of signaling pathways. However, the specificity of the interaction between mammalian WNT and FZD proteins and the subsequent signaling cascade downstream of the different WNT-FZD pairs have not been systematically addressed to date. In this study, we determined the binding affinities of various WNTs for different members of the FZD family by using bio-layer interferometry and characterized their functional selectivity in a cell system. Using purified WNTs, we show that different FZD cysteine-rich domains prefer to bind to distinct WNTs with fast on-rates and slow off-rates. In a 32D cell-based system engineered to overexpress FZD2, FZD4, or FZD5, we found that WNT-3A (but not WNT-4, -5A, or -9B) activated the WNT-β-catenin pathway through FZD2/4/5 as measured by phosphorylation of LRP6 and β-catenin stabilization. Surprisingly, different WNT-FZD pairs showed differential effects on phosphorylation of DVL2 and DVL3, revealing a previously unappreciated DVL isoform selectivity by different WNT-FZD pairs in 32D cells. In summary, we present extensive mapping of WNT-FZD cysteine-rich domain interactions complemented by analysis of WNT-FZD pair functionality in a unique cell system expressing individual FZD isoforms. Differential WNT-FZD binding and selective functional readouts suggest that endogenous WNT ligands evolved with an intrinsic natural bias toward different downstream signaling pathways, a phenomenon that could be of great importance in the design of FZD-targeting drugs.

ABSTRACT: In Drosophila, members of the frizzled family of tissue-polarity genes encode proteins that are likely to function as cell-surface receptors of the type known as Wnt receptors, and to initiate signal transduction across the cell membrane, although how they do this is unclear. We show here that the rat protein Frizzled-2 causes an increase in the release of intracellular calcium which is enhanced by Xwnt-5a, a member of the Wnt family. This release of intracellular calcium is suppressed by an inhibitor of the enzyme inositol monophosphatase and hence of the phosphatidylinositol signalling pathway; this suppression can be rescued by injection of the compound myo-inositol, which overcomes the decrease in this intermediate caused by the inhibitor. Agents that inhibit specific G-protein subunits, pertussis toxin, GDP-beta-S and alpha-transducin also inhibit the calcium release triggered by Xwnt-5a and rat Frizzled-2. Our results indicate that some Wnt proteins work through specific Frizzled homologues to stimulate the phosphatidylinositol signalling pathway via heterotrimeric G-protein subunits.