Epidermal growth factor receptor transactivation is regulated by glucose in vascular smooth muscle cells

Abstract

We hypothesized that glucose-mediated alterations in vascular smooth muscle cell signal transduction contribute to diabetic complications. We found enhanced AngII activation of Akt and extracellular ERK1/2 in vascular smooth muscle cells incubated with high glucose (27.5 mM) compared with low glucose (5.5 mM). Because AngII-mediated transactivation of the epidermal growth factor receptor (EGFR) is important in Akt and ERK1/2 activation, we studied the effects of glucose on EGFR function. The EGFR in cells cultured for 48 h in low glucose was smaller (145 kDa) than the EGFR in cells cultured with high glucose (170 kDa). The shift from the 170-kDa isoform to the 145-kDa isoform was reversible and dependent upon glucose concentration with EC50 ∼1 mM. N-Glycosylation was responsible because peptide N-glycosidase F treatment of isolated 170-kDa EGFR yielded a single band at 145 kDa. Cell surface biotinylation showed that the 145-kDa EGFR was present on plasma membrane. AngII and other G-protein-coupled receptor ligands known to transactivate EGFR phosphorylated the 170-kDa EGFR but not the 145-kDa EGFR, whereas EGF, heparin-binding EGF-like growth factor, and transforming growth factor-α phosphorylated both receptors. Subcellular fractionation showed that the 145-kDa receptor localized to a different plasma membrane domain than the 170-kDa receptor. These results establish a novel mechanism by which glucose-dependent EGFR N-glycosylation modulates AngII signal transduction and suggest a potential mechanism for pathogenic effects of AngII in diabetic vasculopathy.