Overexpression of DPAGT1 Leads to Aberrant N-glycosylation of E-cadherin and Cellular Discohesion in Oral Cancer

Cancer cells are frequently characterized by aberrant increases in protein N-glycosylation and by disruption of E-cadherin-mediated adherens junctions. The relationship between altered N-glycosylation and loss of E-cadherin adhesion in cancer, however, remains unclear. Previously, we reported that complex N-glycans on the extracellular domains of E-cadherin inhibited the formation of mature adherens junctions. Here, we examined whether dysregulated N-glycosylation was one of the underlying causes for cellular discohesion in oral cancer. We show that dense cultures of human salivary epidermoid carcinoma A253 cells exhibited elevated expression of DPAGT1, the gene that initiates protein N-glycosylation. Overexpression of DPAGT1 correlated with the production of E-cadherin-bearing complex N-glycans in nascent adherens junctions. Partial inhibition of DPAGT1 with small interfering RNA reduced the complex N-glycans of E-cadherin and increased the abundance of alpha-catenin and stabilizing proteins in adherens junctions. This was associated with the assembly of functional tight junctions. The inverse relationship between DPAGT1 expression and intercellular adhesion was a feature of oral squamous cell carcinoma. Oral squamous cell carcinomas displayed overexpression of DPAGT1 that correlated with diminished localization of E-cadherin and alpha-catenin at the sites of adherens junctions. Our studies show for the first time that DPAGT1 is an upstream regulator of E-cadherin N-glycosylation status and adherens junction composition and suggest that dysregulation of DPAGT1 causes disturbances in intercellular adhesion in oral cancer.