Wnt target IQGAP3 promotes Wnt signaling via disrupting Axin1-CK1α interaction.

The scaffold protein IQGAP3 is highly upregulated in most epithelial cancers. While recent studies have highlighted its pivotal roles in cancer cell proliferation and metastasis, a deeper mechanistic understanding of IQGAP3 is currently lacking. We have here used TurboID to map IQGAP3 proximity partners and identified the Wnt signaling members Axin1 and CK1 as IQGAP3-interacting proteins. Our functional studies demonstrated that overexpression of IQGAP3 increases {beta}-catenin levels, while IQGAP3 depletion reduces {beta}-catenin levels in gastric cancer cells. Mechanistically, IQGAP3 disrupts Axin1-CK1 interaction, thereby inhibiting {beta}-catenin phosphorylation and ultimately leading to its accumulation. Importantly, we discovered that IQGAP3 itself is regulated by Wnt signaling, suggesting its involvement in a positive feedback loop in Wnt/{beta}-catenin signaling through interactions with Axin1 and CK1. These findings identify IQGAP3 as a novel mediator of {beta}-catenin stabilization and underscore its potential as a target for cancer therapy.