title: Phe27Cys polymorphism of the human delta opioid receptor predisposes cells to compromised calcium signaling.
abstract: A quarter of the human population with European background carries at least one allele of the OPRD1 gene that encodes the delta opioid receptor with cysteine at the amino acid position 27 (hδOR(Cys27)) instead of the evolutionary conserved phenylalanine (hδOR(Phe27)). The two variants have indistinguishable pharmacological properties but, importantly, hδOR(Cys27) differs from hδOR(Phe27) in having low maturation efficiency, lower stability at the cell surface and pronounced intracellular location. Both variants were previously shown to interact with the Sarco(endo)plasmic reticulum Ca²+ ATPase (SERCA) 2b in the early phase of their biosynthesis. We analyzed by pulse-chase assays, whether cellular signaling can affect hδOR(Cys27) maturation. Neither activation of the receptor by a δOR-specific agonist Leu-enkephalin, induction of intracellular calcium (Ca²+) release by ATP nor the direct stimulation of SERCA 2b by protein kinase C activation affected receptor maturation in HEK-293 cells. No signaling-mediated regulation of receptor maturation could therefore be demonstrated. Instead, we found by using single cell Ca²+ measurements that over-expression of hδOR(Cys27), but not hδOR(Phe27), compromised ATP-induced intracellular Ca²+-signaling. Furthermore, hδOR(Cys27) precursors showed slower dissociation from SERCA2b and hδOR(Cys27) expression caused down-regulation of the homocysteine-inducible endoplasmic reticulum-resident ubiquitin domain-like member 1 protein (HERP). We suggest that aging individuals with at least one hδOR(Cys27) encoding allele might have lowered threshold for Ca²+ dysregulation in neurons expressing hδOR.
authors.affiliation: Department of Anatomy and Cell Biology, Institute of Biomedicine, University of Oulu, P.O. Box 5000, FI-90014 Oulu, Finland. Jussi.Tuusa@oulu.fi
authors.forename: Jussi T
authors.initials: JT
authors.lastname: Tuusa
authors.forename: Ulla E
authors.initials: UE
authors.lastname: Petäjä-Repo
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D015153:Blotting, Western; D020013:Calcium Signaling / Q000235:genetics*; D002460:Cell Line; D003545:Cysteine / Q000235:genetics*; D004789:Enzyme Activation; D006801:Humans; D010649:Phenylalanine / Q000235:genetics*; D011110:Polymorphism, Genetic; D011493:Protein Kinase C / Q000378:metabolism; D017465:Receptors, Opioid, delta / Q000235:genetics*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism
chemical_list: D017465:Receptors, Opioid, delta; D010649:Phenylalanine; D000255:Adenosine Triphosphate; D011493:Protein Kinase C; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; C506946:ATP2A2 protein, human; D003545:Cysteine