Coordinate regulation of N-glycosylation gene DPAGT1, canonical Wnt signaling and E-cadherin adhesion

Abstract

The metabolic pathway of protein N-glycosylation influences intercellular adhesion by affecting the composition and cytoskeletal association of E-cadherin protein complexes, or adherens junctions (AJs). In sparse cells, E-cadherin is modified extensively with complex N-glycans and forms nascent AJs, while in dense cultures, hypoglycosylated E-cadherin drives the assembly of mature AJs with increased levels of γ- and α-catenins. N-glycosylation of E-cadherin is controlled by the DPAGT1 gene, a key regulator of the N-glycosylation pathway. DPAGT1 is a target of the canonical Wnt signaling pathway, with both β- and γ-catenins binding to Tcf at its promoter. We now report that DPAGT1 senses cell density through canonical Wnt signaling. In dense cells, depletion of β-catenin from the DPAGT1 promoter correlated with downregulation of its cellular abundance, while loss of nuclear γ-catenin reflected its greater recruitment to AJs. DPAGT1 itself affected canonical Wnt signaling, with forced changes in its expression resulting in corresponding changes in transcriptionally active β-catenin and canonical Wnt activity. Remarkably, a 2.4-fold increase in the DPAGT1 mRNA level resulted in increased N-glycosylation and reduced membrane localization of E-cadherin, coincident with dramatic changes in cell morphology. Lastly, we present evidence that N-glycosylation status of E-cadherin controls its antagonism of canonical Wnt signaling. Transfection of hypoglycosylated E-cadherin mutant, V13, but not fully N-glycosylated E-cadherin, into sparse cells inhibited canonical Wnt activity by depleting nuclear β- and γ-catenins. Collectively, our studies show that cells coordinate DPAGT1 expression and protein N-glycosylation with canonical Wnt signaling and E-cadherin adhesion via positive and negative feedback mechanisms.