Background: Wnt3a regulates a canonical signaling pathway in early development that controls the nuclear accumulation of beta-catenin and its activation of Lef/Tcf-sensitive transcription of developmentally important genes.
Results: Using totipotent mouse F9 teratocarcinoma cells expressing Frizzled-1 and biochemical analyses, we detail the influence of Wnt3a stimulation on the expression, complexation, and subcellular trafficking of key signaling elements of the canonical pathway, i.e., Dishevelled-2, Axin, glycogen synthase kinase-3beta, and beta-catenin. Cellular content of beta-catenin and Axin, and phospho-glycogen synthase kinase-3beta, but not Dishevelled-2, increases in response to Wnt3a. Subcellular localization of Axin in the absence of Wnt3a is symmetric, found evenly distributed among plasma membrane-, cytosol-, and nuclear-enriched fractions. Dishevelled-2, in contrast, is found predominately in the cytosol, whereas beta-catenin is localized to the plasma membrane-enriched fraction. Wnt3a stimulates trafficking of Dishevelled-2, Axin, and glycogen synthase kinase-3beta initially to the plasma membrane, later to the nucleus. Bioluminescence resonance energy transfer measurements reveal that complexes of Axin with Dishevelled-2, with glycogen synthase kinase-3beta, and with beta-catenin are demonstrable and they remain relatively stable in response to Wnt3a stimulation, although trafficking has occurred. Mammalian Dishevelled-1 and Dishevelled-2 display similar patterns of trafficking in response to Wnt3a, whereas that of Dishevelled-3 differs from the other two.
Conclusion: This study provides a detailed biochemical analysis of signaling elements key to Wnt3a regulation of the canonical pathway. We quantify, for the first time, the Wnt-dependent regulation of cellular abundance and intracellular trafficking of these signaling molecules. In contrast, we observe little effect of Wnt3a stimulation on the level of protein-protein interactions among these constituents of Axin-based complexes themselves.