Effect of dexamethasone on the carbohydrate chains of the insulin receptor

Dexamethasone treatment of IM-9 lymphocytes and Fao hepatoma cells resulted in an increase in synthesis of the insulin receptor. The receptors synthesized after stimulation with the glucocorticoid had altered carbohydrate structure. The carbohydrate side chains of the insulin receptor were less branched on the dexamethasone-treated cells; i.e., the ratio of saccharides with three and four branches to those bearing only two branches was decreased. The predominant polymannose oligosaccharide after dexamethasone treatment was Man9GlcNAc (vs Man6GlcNAc in the control cell). Both of these changes are consistent with a less complete processing of the N-linked carbohydrate units and were not observed for the total cellular glycoproteins, whereas all glycoproteins manifested an increased sialylation in Fao cells after dexamethasone treatment. These data indicate that glucocorticoid treatment results in alterations in branching of carbohydrate side chains, in the size of polymannose chains and in sialylation of the insulin receptor.