The cytoplasmic domain close to the transmembrane region of the glucagon-like peptide-1 receptor contains sequence elements that regulate agonist-dependent internalisation

Abstract

In order to gain better insight into the molecular events involved in the signal transduction generated through glucagon-like peptide-1 (GLP-1) receptors, we tested the effect of deletions and point mutations within the cytoplasmic tail of this receptor with a view to establishing relationships between signal transduction desensitisation and receptor internalisation. Wild-type and truncated (deletion of the last 27 amino acids (GLPR 4358) and deletion of 44 amino acids (GLPR 418R)) GLP-1 receptors bound the agonist with similar affinity. Deletion of the last 27 amino acids decreased the internalisation rate by 78%, while deletion of 44 amino acids containing all the phosphorylation sites hitherto described in this receptor decreased the internalisation rate by only 47%. Binding of the ligand to both receptors stimulated adenylyl cyclase. In contrast, deletion of the region containing amino acids 419 to 435 (GLPR 419Δ435) increased the internalisation rate by 268%, and the replacement of EVQ408-410 by alanine (GLPR A408-410) increased this process to 296%. In both receptors, the efficacy in stimulating adenylate cyclase was decreased. All the receptors studied were internalised by coated pits, except for the receptor with a deletion of the last 44 amino acids, which also had a faster resensitisation rate. Our findings indicate that the neighbouring transmembrane domain of the carboxyl-terminal tail of the GLP-1 receptor contains sequence elements that regulate agonist-dependent internalisation and transmembrane signalling. © 2005 Society for Endocrinology.