Overexpression of N-acetylglucosaminyltransferase III enhances the epidermal growth factor-induced phosphorylation of ERK in HeLaS3 cells by up-regulation of the internalization rate of the receptors

N-Acetylglucosaminyltransferase III (GnT-III) is a key enzyme that inhibits the extension of N-glycans by introducing a bisecting N-acetylglucosamine residue. In this study we investigated the effect of GnT-III on epidermal g rowth factor (EGF) signaling in HeLaS3 cells. Although the binding of EGF t o the epidermal growth factor receptor (EGFR) was decreased in GnT-III tran sfectants to a level of about 60% of control cells, the EGF-induced activat ion of extracellular signal-regulated kinase (ERR) in GnT-III transfectants was enhanced to similar to1.4-fold that of the control cells. A binding an alysis revealed that only low affinity binding of EGF was decreased in the GnT-III transfectants, whereas high affinity binding, which is considered t o be responsible for the downstream signaling, was not altered, EGF-induced autophosphorylation and dimerization of the EGFR in the GnT-III transfecta nts were the same levels as found in the controls. The internalization rate of EGFR was, however, enhanced in the GnT-III transfectants as judged by t he uptake of I-125-EGF and Oregon Green-labeled EGF. Then the EGFR internal ization was delayed by dansylcadaverine, the up-regulation of ERK phosphory lation in GnT-III transfectants was completely suppressed to the same level as control cells. These results suggest that GnT-III overexpression in HeL aS3 cells resulted in an enhancement of EGF-induced ERR phosphorylation at least in part by the upregulation of the endocytosis of EGFR.