Canonical Wnt Induces Focal Adhesion and Integrin Beta-1 Endocytosis

Activation of the Wnt pathway is at the core of many human cancers. During canonical Wnt signaling, the Lrp6 and Frizzled receptors bind to the Wnt growth factor, which leads to the complex being endocytosed. Glycogen Synthase Kinase 3 (GSK3), Dishevelled (Dvl), and Axin are sequestered inside the intraluminal vesicles of late endosomes, known as multivesicular bodies (MVBs). Here we present experiments showing that Wnt causes the endocytosis of focal adhesion (FA) proteins and depletion of Integrin ß 1 (ITGß1) from the cell surface. FAs and integrins provide link the cytoskeleton to the extracellular matrix. Wnt-induced macropinocytosis of the plasma membrane caused ITGß1 depletion and was accompanied by striking changes in the actin cytoskeleton. In situ protease protection assays in cultured cells showed that ITGß1 was sequestered within membrane-bounded organelles that corresponded to Wnt-induced MVBs containing GSK3 and focal adhesion-associated proteins. An in vivo model using Xenopus embryos dorsalized by Wnt8 mRNA showed that ITGß1 depletion decreased Wnt signaling. The cross-talk between Wnt signaling, membrane trafficking, and focal adhesions should be relevant to human cancer and cell biology. Overall design: RNA sequencing of Alexander1 ± Axin1 cells (Hepatocellular Carcinoma cell line). This HCC cell line has a deletion of the GSK3-binding region of the tumor suppressor Axin1 that results in constitutive activation of the Wnt pathway, and a stable cell line derivative that restores full-length Axin1 at physiological levels. See Albrecht et al., PNAS (2020): 115:E5317–25. DOI: 10.1073/pnas.1804091115, PMID: 29773710