title: Signaling pathways mediating phosphorylation and inactivation of glycogen synthase kinase-3β by the recombinant human δ-opioid receptor stably expressed in Chinese hamster ovary cells.
abstract: Besides being involved in analgesia, δ-opioid receptors have recently been shown to exert antidepressant-like and neuroprotective effects. Glycogen synthase kinase-3β (GSK-3β), a key enzyme involved in cellular apoptosis and in mood disorders, may constitute a molecular target of δ-opioid receptors. However, relatively little is known on how δ-opioid receptors affect the multiple signaling pathways regulating GSK-3β. In the present study, we show that activation of human δ-opioid receptors stably expressed in Chinese hamster ovary (CHO) cells induced a rapid GSK-3β phosphorylation on Ser9 and a significant inhibition of the kinase activity. This effect was dependent on G proteins Gi/Go, unaffected by cell transfection with the Gβγ scavenger transducin, required the Src non-receptor tyrosine kinase and the specific involvement of the α isoform of phosphatidylinositol 3-kinase. δ-Opioid agonists activated the protein kinase Akt in a Src-dependent manner and chemical inhibition of Akt or stable expression of a dominant negative Akt1 mutant reduced the stimulation of GSK-3β phosphorylation. Moreover, δ-opioid receptor regulation of Akt and GSK-3β was dependent on transphosphorylation and transactivation of platelet-derived growth factor and insulin-like growth factor-1 receptor tyrosine kinases. AMP-activated protein kinase (AMPK) activity was also required, as δ-opioid effects on Akt and GSK-3β were mimicked by the AMPK activator A-769662 and reduced by the AMPK inhibitor Compound C. Conversely, inhibition of protein kinase C isoforms, extracellular signal-regulated protein kinases 1/2 and mammalian target of rapamycin was without effect, although the latter two kinases were activated by δ-opioid agonists. The results identify Src-dependent transactivation of receptor tyrosine kinases as a key process in δ-opioid receptor inhibitory control of GSK-3β and reveal a novel δ-opioid regulatory mechanism mediated by AMPK. This article is part of a Special Issue entitled 'Trends in neuropharmacology: in memory of Erminio Costa'.
authors.affiliation: Section of Biochemical Pharmacology, Department of Neuroscience, University of Cagliari, 09042 Cagliari, Italy. onali@unica.it
authors.forename: Maria C
authors.initials: MC
authors.lastname: Olianas
authors.forename: Simona
authors.initials: S
authors.lastname: Dedoni
authors.forename: Pierluigi
authors.initials: P
authors.lastname: Onali
mesh_terms: D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D005260:Female; D044387:GTP-Binding Protein beta Subunits / Q000378:metabolism; D005822:Genetic Vectors / Q000235:genetics; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D051058:Oncogene Protein v-akt / Q000378:metabolism; D037342:Pertussis Toxin / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation / Q000502:physiology; D017465:Receptors, Opioid, delta / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D014162:Transfection; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: D044387:GTP-Binding Protein beta Subunits; D017465:Receptors, Opioid, delta; D037342:Pertussis Toxin; D019869:Phosphatidylinositol 3-Kinases; D019061:src-Family Kinases; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D051058:Oncogene Protein v-akt; D038362:Glycogen Synthase Kinase 3