A Chemical and Systems Approach to Study the Wnt/beta-catenin Pathway

Abstract

Wnt/β‐catenin signaling plays a critical role in metazoan development, stem cell maintenance, and human disease. The multicomponent β‐catenin destruction complex maintains low cellular β‐catenin in the absence of a signal and becomes inhibited in the presence of a Wnt ligand, allowing β‐catenin levels to rise. We have identified an FDA-approved drug, pyrvinium, as a potent inhibitor of Wnt signaling. We show pyrvinium binds CK1α, enhances kinase activity and CK1α knockdown abrogates the effects of pyrvinium on the Wnt pathway. In addition to effects on Axin and β‐catenin levels, pyrvinium promotes degradation of Pygopus, a Wnt transcriptional component. Pyrvinium treatment of colon cancer cells with mutation of Adenomatous Polyposis Coli or β‐catenin inhibits both Wnt signaling and proliferation. These findings reveal allosteric activation of CK1α as an effective mechanism to inhibit Wnt signaling.

We also performed biochemical studies that identified positive feedback within the β‐catenin destruction complex between essential components, Axin and GSK3. Theoretical modeling of this positive feedback loop predicts bistability in the activity of the β‐catenin destruction complex. Through single cell studies, we generated experimental evidence for our theoretical predictions. These findings elucidate molecular design features that convert gradients into discrete binary cell fate decisions.

In conclusion, this work combines chemical studies and systems-level analysis to uncover novel mechanisms of regulating the Wnt/β‐catenin pathway. Our findings highlight new strategies for targeted therapeutics directed against the Wnt pathway.