GLUCAGON INDUCES A RAPID AND SUSTAINED PHOSPHORYLATION OF THE HUMAN GLUCAGON RECEPTOR IN CHINESE-HAMSTER OVARY CELLS

The glucagon receptor is a member of the G protein-coupled receptor su perfamily. Since several G protein-coupled receptors undergo phosphory lation in response to agonist, we investigated the phosphorylation of the glucagon receptor following the addition of glucagon to a Chinese hamster ovary cell line expressing the human glucagon receptor (CHO/hG R). Glucagon induced a rapid, time and concentration-dependent phospho rylation of its receptor on serine residues. Neither forskolin nor pho rbol ester increased receptor phosphorylation, suggesting that cAMP-de pendent protein kinase and protein kinase C do not catalyze this phosp horylation event. Furthermore, two mutant cell lines expressing glucag on receptors with successively truncated receptor cytoplasmic tails we re tested. A strong correlation between the number of potential phosph orylation sites, receptor phosphorylation and receptor internalization was observed, suggesting that phosphorylation of the glucagon recepto r in CHO/hGR cells is functionally linked to its internalization. (C) 1996 Academic Press, Inc.