title: Structural determinants of agonist-selective signaling at the sst(2A) somatostatin receptor.
abstract: The clinically used somatostatin (SS-14) analogs octreotide and pasireotide (SOM230) stimulate distinct species-specific patterns of sst(2A) somatostatin receptor phosphorylation and internalization. Like SS-14, 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 endocytosis of both rat and human sst(2A) receptors. Unlike SS-14, pasireotide fails to induce any substantial phosphorylation or internalization of the rat sst(2A) receptor. Nevertheless, pasireotide is able to stimulate a selective phosphorylation of S341 and S343 of the human sst(2A) receptor followed by a clearly detectable receptor sequestration. Here, we show that transplantation of amino acids 1-180 of the human sst(2A) receptor to the rat sst(2A) receptor facilitates pasireotide-induced internalization. Conversely, construction of a rat-human sst(2A) chimera conferred resistance to pasireotide-induced internalization. We then created a series of site-directed mutants leading to the identification of amino acids 27, 30, 163, and 164 that when exchanged to their human counterparts facilitated pasireotide-driven S341/S343 phosphorylation and internalization of the rat sst(2A) receptor. Exchange of these amino acids to their rat counterparts completely blocked the pasireotide-mediated internalization of the human sst(2A) receptor. Notably, octreotide and SS-14 stimulated a full phosphorylation and internalization of all mutant sst(2A) receptors tested. Together, these findings suggest that pasireotide activates the sst(2A) receptor via a molecular switch that is structurally and functionally distinct from that turned on during octreotide-driven sst(2A) activation.
authors.affiliation: Department of Pharmacology and Toxicology, University Hospital Jena, Friedrich Schiller University, Drackendorfer Strasse 1, D-07747 Jena, Germany.
authors.forename: Falko
authors.initials: F
authors.lastname: Nagel
authors.forename: Christian
authors.initials: C
authors.lastname: Doll
authors.forename: Florian
authors.initials: F
authors.lastname: Pöll
authors.forename: Andrea
authors.initials: A
authors.lastname: Kliewer
authors.forename: Helmut
authors.initials: H
authors.lastname: Schröder
authors.forename: Stefan
authors.initials: S
authors.lastname: Schulz
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D054768:G-Protein-Coupled Receptor Kinases / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D015282:Octreotide / Q000494:pharmacology; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D051381:Rats; D017481:Receptors, Somatostatin / Q000819:agonists / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D013004:Somatostatin / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D017481:Receptors, Somatostatin; C106140:somatostatin receptor sst2A; D013004:Somatostatin; C517782:pasireotide; D054768:G-Protein-Coupled Receptor Kinases; D015282:Octreotide