Two C-terminal amino acids, Ser(334) and Ser(335), are required for homologous desensitization and agonist-induced phosphorylation of opioid receptor-like 1 receptors.
Various cellular signaling pathways induced by nociceptin activation of ORL1 (opioid receptor-like 1 receptor) develop homologous desensitization. Multiple lines of evidence suggest that agonist-induced phosphorylation of serine (Ser)/threonine (Thr) residues at intracellular carboxyl tail leads to homologous desensitization of G protein-coupled receptors. In the present study, we investigated the functional role played by C-terminal Ser/Thr residues in agonist-induced desensitization and phosphorylation of ORL1. In HEK 293 cells expressing wild-type ORL1 and ORL1(CDelta21), which lacks C-terminal 21 amino acids, nociceptin inhibition of adenylate cyclase activity exhibited homologous desensitization after 1 h pretreatment of nociceptin. In contrast, ORL1(CDelta34), which differs with ORL1(CDelta21) by lacking C-terminal Ser(334), Ser(335) and Ser(343) residues, failed to develop agonist-induced desensitization. Point mutant (S343A) ORL1 underwent homologous desensitization after nociceptin pretreatment. Substituting Ser(334) or Ser(335) with alanine greatly impaired nociceptin-induced ORL1 desensitization. In HEK 293 cells expressing double mutant (S334A/S335A) ORL1, nociceptin pretreatment failed to significantly affect the efficacy and potency by which nociceptin inhibits forskolin-stimulated cAMP formation. Mutation of Ser(334) and Ser(335) also greatly reduced nociceptin-induced ORL1 phosphorylation. These results suggest that two C-terminal serine residues, Ser(334) and Ser(335), are required for homologous desensitization and agonist-induced phosphorylation of ORL1.
Wang
Hung-Li
HL
Department of Physiology, Chang Gung University School of Medicine; Kwei-San, Tao-Yuan, Taiwan, ROC. hlwns@mail.cgu.edu.tw
Kuo
Yo-Li
YL
Hsu
Chia-Yu
CY
Huang
Pei-Chen
PC
Li
Allen H
AH
Chou
An-Hsun
AH
Yeh
Tu-Hsueh
TH
Chen
Ying-Ling
YL
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D018847:Opioid Peptides / Q000378:metabolism*; D010766:Phosphorylation; D011869:Radioligand Assay; D051381:Rats; D011957:Receptors, Opioid / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D012694:Serine / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D000094942:Nociceptin Receptor; D000097629:Nociceptin
D018847:Opioid Peptides; D011957:Receptors, Opioid; D012694:Serine; D000094942:Nociceptin Receptor; D000097629:Nociceptin