Targeting Membrane Trafficking as a Strategy for Cancer Treatment.

Membrane trafficking is emerging as an attractive therapeutic strategy for cancer. Recent reports have found a connection between Wnt signaling, receptor-mediated endocytosis, V-ATPase, lysosomal activity, and macropinocytosis through the canonical Wnt pathway. In macropinocytic cells, a massive internalization of the plasma membrane can lead to the loss of cell-surface cadherins, integrins, and other antigens that mediate cell-cell adhesion, favoring an invasive phenotype. V-ATPase is a key regulator in maintaining proper membrane trafficking, homeostasis, and the earliest developmental decisions in the Xenopus vertebrate development model system. Here, we review how the interference of membrane trafficking with membrane trafficking inhibitors might be clinically relevant in humans.

Canonical Wnt signaling induces focal adhesion and Integrin beta-1 endocytosis.

During canonical Wnt signaling, the Wnt receptor complex is sequestered together with glycogen synthase kinase 3 (GSK3) and Axin inside 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 link the cytoskeleton to the extracellular matrix. Wnt-induced endocytosis caused ITGß1 depletion from the plasma membrane 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 FA-associated proteins. An in vivo model using Xenopus embryos dorsalized by Wnt8 mRNA showed that ITGß1 depletion decreased Wnt signaling. The finding of a crosstalk between two major signaling pathways, canonical Wnt and focal adhesions, should be relevant to human cancer and cell biology.