Roles of N-Acetylglucosaminyltransferase III in Epithelial-to-Mesenchymal Transition Induced by Transforming Growth Factor β1 (TGF-β1) in Epithelial Cell Lines

The epithelial-to-mesenchymal transition (EMT) plays crucial roles in embryonic development, wound healing, tissue repair, and cancer progression. Results of this study show how transforming growth factor beta 1 (TGF-beta 1) down-regulates expression of N-acetylglucosaminyltransferase III (GnT-III) during EMT-like changes. Treatment with TGF-beta 1 resulted in a decrease in E-cadherin expression and GnT-III expression, as well as its product, the bisected N-glycans, which was confirmed by erythro-agglutinating phytohemagglutinin lectin blot and HPLC analysis in human MCF-10A and mouse GE11 cells. In contrast with GnT-III, the expression of N-acetylglucosaminyltransferase V was slightly enhanced by TGF-beta 1 treatment. Changes in the N-glycan patterns on alpha 3 beta 1 integrin, one of the target proteins for GnT-III, were also confirmed by lectin blot analysis. To understand the roles of GnT-III expression in EMT-like changes, the MCF-10A cell was stably transfected with GnT-III. It is of particular interest that overexpression of GnT-III influenced EMT-like changes induced by TGF-beta 1, which was confirmed by cell morphological changes of phase contrast, immunochemical staining patterns of E-cadherin, and actin. In addition, GnT-III modified E-cadherin, which served to prolong E-cadherin turnover on the cell surface examined by biotinylation and pulse-chase experiments. GnT-III expression consistently inhibited beta-catenin translocation from cell-cell contact into the cytoplasm and nucleus. Furthermore, the transwell assay showed that GnT-III expression suppressed TGF-beta 1-induced cell motility. Taken together, these observations are the first to clearly demonstrate that GnT-III affects cell properties, which in turn influence EMT-like changes, and to explain a molecular mechanism for the inhibitory effects of GnT-III on cancer metastasis.