N-Glycosylation Modification of Fzd4 Is Essential for the Fzd4-Wnt-β-Catenin Signalling Axis.

Wnt signalling is a highly conserved signalling pathway that plays an important role in a variety of biological processes. Frizzled (Fzd) family proteins are receptors for Wnt ligands. The physiological processes involved in mature trafficking of Fzd proteins remain elusive. Here, we identified asparagine residues 59 and 144 as the N-glycosylation modification sites of Fzd4. Sequence analysis of Fzd4 in different species showed that the two asparagine residues were highly conserved. N-glycosylation modification of Fzd4 is indispensable for its maturation and transport to the plasma membrane. N-glycosylation modification enhances the stability of Fzd4 and is also necessary for Fzd4 activity, which promotes Fzd4 interaction with Wnt ligands and co-receptor Norrin. Knockout of Fzd4 in the non-small cell lung cancer (NSCLC) cell line A549 followed by replenishment of Fzd4 glycosylation site mutants inhibited the growth and migration ability of A549 cells in vitro and in vivo. In summary, we identified N-glycosylation modification sites of Fzd4. N-glycosylation modification of Fzd4 is necessary for its stability and activity. When N-glycosylation modification is absent, Fzd4 cannot mediate the Wnt/β-catenin signalling pathway, which can inhibit the proliferation and migration of NSCLC and provide new targets and strategies for the treatment of NSCLC.