Figure 5.

Schematic representation of the interactions between the Gq and Wnt/β-catenin signaling pathways. As shown in the model, APC promotes β-catenin nuclear export and facilitates proteasome-mediated degradation of β-catenin after sequential phosphorylation by CKIα and GSK-3β on the Axin-based complex. Wnt binding to coreceptors LRP and Frizzled blocks proteasome-mediated degradation, which further leads to nuclear localization of β-catenin, gene expression, and cell proliferation. As an alternative degradation pathway, Ca²⁺ activation by Gq signaling pathway promotes nuclear export of β-catenin into cytoplasm, where it is further degraded by calpain in a Ca²⁺-dependent manner. Consequently, β-catenin–TCF/LEF-dependent cell proliferation is inhibited. LRP, low-density-lipoprotein receptor-related protein; UPS, ubiquitin-proteasome system; PLCβ, phospholipase C β; PIP₂, phosphatidylinositol 4,5-bisphosphate; IP₃R, IP₃ receptor.