title: Carboxyl-terminal multi-site phosphorylation regulates internalization and desensitization of the human sst2 somatostatin receptor.
abstract: The somatostatin receptor 2 (sst2) is the pharmacological target of somatostatin analogs that are widely used in the diagnosis and treatment of human neuroendocrine tumors. We have recently shown that the stable somatostatin analogs octreotide and pasireotide (SOM230) stimulate distinct patterns of sst2 receptor phosphorylation and internalization. Like somatostatin, octreotide promotes the phosphorylation of at least six carboxyl-terminal serine and threonine residues namely S341, S343, T353, T354, T356 and T359, which in turn leads to a robust receptor endocytosis. Unlike somatostatin, pasireotide stimulates a selective phosphorylation of S341 and S343 of the human sst2 receptor followed by a partial receptor internalization. Here, we show that exchange of S341 and S343 by alanine is sufficient to block pasireotide-driven internalization, whereas mutation of T353, T354, T356 and T359 to alanine is required to strongly inhibited both octreotide- and somatostatin-induced internalization. Yet, combined mutation of T353, T354, T356 and T359 is not sufficient to prevent somatostatin-driven β-arrestin mobilization and receptor desensitization. Replacement of all fourteen carboxyl-terminal serine and threonine residues by alanine completely abrogates sst2 receptor internalization and β-arrestin mobilization in HEK293 cells. Together, our findings demonstrate for the first time that agonist-selective sst2 receptor internalization is regulated by multi-site phosphorylation of its carboxyl-terminal tail.
authors.affiliation: Institute of Pharmacology and Toxicology, Jena University Hospital, Friedrich-Schiller-University, 07747 Jena, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Lehmann
authors.affiliation: Institute of Pharmacology and Toxicology, Jena University Hospital, Friedrich-Schiller-University, 07747 Jena, Germany.
authors.forename: Andrea
authors.initials: A
authors.lastname: Kliewer
authors.affiliation: Institute of Pharmacology and Toxicology, Jena University Hospital, Friedrich-Schiller-University, 07747 Jena, Germany.
authors.forename: Dagmar
authors.initials: D
authors.lastname: Schütz
authors.affiliation: Institute of Pharmacology and Toxicology, Jena University Hospital, Friedrich-Schiller-University, 07747 Jena, Germany.
authors.forename: Falko
authors.initials: F
authors.lastname: Nagel
authors.affiliation: Institute of Pharmacology and Toxicology, Jena University Hospital, Friedrich-Schiller-University, 07747 Jena, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Stumm
authors.affiliation: Institute of Pharmacology and Toxicology, Jena University Hospital, Friedrich-Schiller-University, 07747 Jena, Germany. Electronic address: Stefan.Schulz@med.uni-jena.de.
authors.forename: Stefan
authors.initials: S
authors.lastname: Schulz
mesh_terms: D000595:Amino Acid Sequence; D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology; D019390:Arrestins / Q000378:metabolism; D002460:Cell Line; D004705:Endocytosis / Q000187:drug effects*; D057809:HEK293 Cells; D006801:Humans; D008969:Molecular Sequence Data; D018358:Neuroendocrine Tumors / Q000188:drug therapy; D015282:Octreotide / Q000494:pharmacology*; D010766:Phosphorylation; D021381:Protein Transport / Q000187:drug effects; D017481:Receptors, Somatostatin / Q000235:genetics* / Q000378:metabolism*; D013004:Somatostatin / Q000031:analogs & derivatives* / Q000494:pharmacology; D000071557:beta-Arrestins
chemical_list: D018931:Antineoplastic Agents, Hormonal; D019390:Arrestins; D017481:Receptors, Somatostatin; D000071557:beta-Arrestins; D013004:Somatostatin; C517782:pasireotide; C093733:somatostatin receptor 2; D015282:Octreotide
keywords: Desensitization; Internalization; Octreotide; Pasireotide; Somatostatin; Somatostatin receptor