In situ Fucosylation for Modulating Wnt Signaling in Live Cells

Wnt/{beta}-catenin signaling, also known as canonical Wnt signaling, regulates critical, context-dependent transcription in numerous (patho) physiological events. Amongst the well-documented mechanisms of canonical Wnt signaling, modification of N-glycans by L-fucose (Fuc) is the newest and the least understood. Using a combination of Chinese Hamster Ovary (CHO) cell mutants with different fucosylation levels and in situ cell-surface Fuc editing (ISF), we report that (1-3)-fucosylation of N-acetylglucosamine in the LacNAc (Gal{beta}(1-4)-GlcNAc) sequences of complex N-glycans modulates Wnt signaling by regulating the endocytosis of low density lipoprotein receptor-related protein 6 (LRP6). Pulse-chase experiments reveal that increasing N-glycan LacNAc fucosylation elevates endocytosis of lipid-raft-localized LRP6, leading to the suppression of Wnt-{beta}-catenin signaling. Inhibiting endocytosis by inhibiting dynamin 1, a GTPase responsible for endocytosis in eukaryotic cells, partially rescues Wnt signaling. Remarkably, inhibition of Wnt signaling by N-glycan LacNAc fucosylation is fully rescued by the addition of free Fuc to the medium, suggesting that endocytosis of N-glycan fucosylated LRP6 may be mediated by a receptor that recognizes the bound (1-3)-Fuc. This work provides the first evidence that in situ cell-surface fucosylation can be exploited to regulate a specific signaling pathway via endocytosis, revealing a novel regulatory mechanism linking glycosylation of a cell surface receptor with its intracellular signaling.