The N-linked oligosaccharides of the Fcϵ receptors of rat basophilic leukemia cells

Abstract

This study was undertaken to investigate the nature and microheterogeneity of the carbohydrate moiety of the Fcϵ receptors of RBL-CA10 and RBL-CA10.7 cells. Treatment using the glycosylation processing inhibitors, castanospermine (CN), 1-deoxymannojirimycin (DMJ), and swainsonine (SW) resulted in a decrease of the relative molecular mass (M r) of both the α-chain of the high affinity receptor for IgE, FcϵRI(α), and the low affinity receptor for IgE, FcϵR L. Exposure to DMJ had the greatest effect on the M r, while CN seemed to lead to a decreased cell surface expression of FcϵRI. Both receptors are largely resistant to endoglycosidase H as their M r decreased only by approximately 2 kDa. These results suggest that both receptors are composed primarily of complex oligosaccharides with a single high mannose, N-glycosylated site. Both Fcϵ receptors become endoglycosidase H sensitive if first exposed to DMJ which indicates that the carbohydrate composition is indeed altered by this processing inhibitor presumably by blocking the formation of complex structures. When the Fcϵ receptors were reduced and hydrolyzed by N-glycanase, the M r values for FcϵRI(α) and FcϵR L decreased to approximately 28 and 34–38 kDa respectively. In the case of FcϵRI(α), this implies the presence of only a small amount of O-linked oligosaccharides.