delta-Opioid receptor-stimulated Akt signaling in neuroblastoma x glioma (NG108-15) hybrid cells involves receptor tyrosine kinase-mediated PI3K activation.
delta-Opioid receptor (DOR) agonists possess cytoprotective properties, an effect associated with activation of the "pro-survival" kinase Akt. Here we delineate the signal transduction pathway by which opioids induce Akt activation in neuroblastomaxglioma (NG108-15) hybrid cells. Exposure of the cells to both [D-Pen(2,5)]enkephalin and etorphine resulted in a time- and dose-dependent increase in Akt activity, as measured by means of an activation-specific antibody recognizing phosphoserine-473. DOR-mediated Akt signaling is blocked by the opioid antagonist naloxone and involves inhibitory G(i/o) proteins, because pre-treatment with pertussis toxin, but not over-expression of the G(q/11) scavengers EBP50 and GRK2-K220R, prevented this effect. Further studies with Wortmannin and LY294002 revealed that phophoinositol-3-kinase (PI3K) plays a central role in opioid-induced Akt activation. Opioids stimulate Akt activity through transactivation of receptor tyrosine kinases (RTK), because pre-treatment of the cells with inhibitors for neurotrophin receptor tyrosine kinases (AG879) and the insulin-like growth factor receptor IGF-1 (AG1024), but not over-expression of the Gbetagamma scavenger phosducin, abolished this effect. Activated Akt translocates to the nuclear membrane, where it promotes GSK3 phosphorylation and prevents caspase-3 cleavage, two key events mediating inhibition of cell apoptosis and enhancement of cell survival. Taken together, these results demonstrate that in NG108-15 hybrid cells DOR agonists possess cytoprotective properties mediated by activation of the RTK/PI3K/Akt signaling pathway.
Institute of Pharmacology, Toxicology and Pharmacy Ludwig-Maximilians-University of Munich Koeniginstrasse 16, 80539 Muenchen, Federal Republic of Germany.
Anika
A
Heiss
Hermann
H
Ammer
Daniela A
DA
Eisinger
D045744:Cell Line, Tumor; D002470:Cell Survival; D019610:Cytoprotection; D004745:Enkephalins / Q000494:pharmacology; D004789:Enzyme Activation; D005048:Etorphine / Q000494:pharmacology; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000502:physiology; D044387:GTP-Binding Protein beta Subunits / Q000502:physiology; D044388:GTP-Binding Protein gamma Subunits / Q000502:physiology; D005910:Glioma; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D006801:Humans; D006822:Hybrid Cells / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000037:antagonists & inhibitors / Q000378:metabolism; D009447:Neuroblastoma; D009685:Nuclear Envelope / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D021381:Protein Transport; D051057:Proto-Oncogene Proteins c-akt / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology*; D020794:Receptor Protein-Tyrosine Kinases / Q000502:physiology*; D017475:Receptors, Nerve Growth Factor / Q000037:antagonists & inhibitors / Q000378:metabolism; D017465:Receptors, Opioid, delta / Q000819:agonists* / Q000037:antagonists & inhibitors / Q000502:physiology; D015398:Signal Transduction; D015533:Transcriptional Activation
D004745:Enkephalins; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D017475:Receptors, Nerve Growth Factor; D017465:Receptors, Opioid, delta; D005048:Etorphine; D007334:Insulin-Like Growth Factor I; D019869:Phosphatidylinositol 3-Kinases; D020794:Receptor Protein-Tyrosine Kinases; D051057:Proto-Oncogene Proteins c-akt; D038362:Glycogen Synthase Kinase 3; D019206:GTP-Binding Protein alpha Subunits, Gi-Go