Abstract
β-catenin plays multiple roles in the canonical Wnt signaling pathway and in cell-cell adhesion complexes. In addition, β-catenin is a proto-oncogene and activating β-catenin mutations are relevant in the genesis of colorectal, hepatocellular and other common cancers. Different functions of β-catenin as transcriptional co-activator or cell adhesion molecule are orchestrated by changes in concentration and phosphorylation as well as its ability to complex with proteins such as cadherins or transcription factors. Detailed quantitative and time-resolved analysis of β-catenin, based on the evaluation of the changes in the Wnt pathway, enable greater insights into health- and disease-related β-catenin function. The present paper describes a novel suspension bead array assay panel for β-catenin, which requires minimal amounts of sample and is able to relatively quantify total β-catenin, the extent of phosphorylation at multiple sites and the ratio of complexed and free β-catenin. This is the first study to combine three biochemical methods--sandwich immunoassay, co-immunoprecipitation, and protein-protein interaction assay--in one suspension bead assay panel. The assay was used to measure changes in the concentration of eight different β-catenin forms in HEK293 cells in a time-resolved manner. In contrast to the general consensus, our study demonstrates an increase in β-catenin phosphorylated at Ser-45 upon treatment of cells with rWnt3a or a GSK3 inhibition; we also link C-terminal phosphorylation of β-catenin on Ser-552 and Ser-675 with canonical Wnt signaling.