Core Fucosylation Regulates Epidermal Growth Factor Receptor-mediated Intracellular Signaling*

α1,6-Fucosyltransferase (Fut8) catalyzes the transfer of a fucose residue to N-linked oligosaccharides on glycoproteins via an α1,6-linkage to form core fucosylation in mammals. We recently found that disruption of the Fut8 gene induces severe growth retardation and early postnatal death. To investigate the molecular mechanism involved, we have established embryonic fibroblasts of Fut8+/+ and Fut8–/–, derived from wild-type and Fut8-null mice, respectively. Interestingly, the epidermal growth factor (EGF)-induced phosphorylation levels of the EGF receptor (EGFR) were substantially blocked in Fut8–/– cells, compared with Fut8+/+ cells, while there are no significant changes in the total activities of tyrosine phosphatase for phosphorylated EGFR between two cells. The inhibition of EGFR phosphorylation was completely restored by re-introduction of the Fut8 gene to Fut8–/– cells. Consistent with this, EGFR-mediated JNK or ERK activation was significantly suppressed in Fut8–/– cells. Finally, we found that the core fucosylation of N-glycans is required for the binding of the EGF to its receptor, whereas no effect was observed for the expression levels of EGFR on the cell surface. Collectively, these results strongly suggest that core fucosylation is essential for EGF receptor-mediated biological functions.