title: Phosphoinositide 3-kinase cascade facilitates mu-opioid desensitization in sensory neurons by altering G-protein-effector interactions.
abstract: Signaling via G-protein-coupled receptors undergoes desensitization after prolonged agonist exposure. Here we investigated the role of phosphoinositide 3-kinase (PI3K) and its downstream pathways in desensitization of micro-opioid inhibition of neuronal Ca2+ channels. In cultured mouse dorsal root ganglion neurons, two mechanistically different forms of desensitization were observed after acute or chronic treatment with the micro agonist [D-Ala2, N-MePhe4, Gly-ol5]-enkephalin (DAMGO). Chronic DAMGO desensitization was heterologous in nature and significantly attenuated by blocking the activity of PI3K or mitogen-activated protein kinase (MAPK). A combined application of PI3K and MAPK inhibitors showed no additive effect, suggesting that these two kinases act in a common pathway to facilitate chronic desensitization. Acute DAMGO desensitization, however, was not affected by the inhibitors. Furthermore, upregulation of the PI3K-Akt pathway in mutant mice lacking phosphatase and tensin homolog, a lipid phosphatase counteracting PI3K, selectively enhanced chronic desensitization in a PI3K- and MAPK-dependent manner. Using the prepulse facilitation (PPF) test, we further examined changes in the voltage-dependent component of DAMGO action that requires direct interactions between betagamma subunits of G-proteins and Ca2+ channels. DAMGO-induced PPF was diminished after chronic treatment, suggesting disruption of G-protein-channel interactions. Such disruption could occur at the postreceptor level, because chronic DAMGO also reduced GTPgammaS-induced PPF that was independent of receptor activation. Again, inhibition of PI3K or MAPK reduced desensitization of PPF. Our data suggest that the PI3Kcascade involving MAPK and Akt enhances micro-opioid desensitization via postreceptor modifications that interfere with G-protein-effector interactions.
authors: Department of Psychiatry and Biobehavioral Sciences, Neuropsychiatric Institute, University of California, Los Angeles, Los Angeles, California 90024-1759, USA.
authors: Miao
authors: M
authors: Tan
authors: Matthias
authors: M
authors: Groszer
authors: Aiko M
authors: AM
authors: Tan
authors: Amy
authors: A
authors: Pandya
authors: Xin
authors: X
authors: Liu
authors: Cui-Wei
authors: CW
authors: Xie
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D005727:Ganglia, Spinal / Q000166:cytology; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D009475:Neurons, Afferent / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051059:PTEN Phosphohydrolase; D018408:Patch-Clamp Techniques; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010744:Phosphoric Monoester Hydrolases / Q000172:deficiency / Q000235:genetics; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D017450:Receptors, Opioid, mu / Q000819:agonists / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D025521:Tumor Suppressor Proteins / Q000172:deficiency / Q000235:genetics
chemical_list: D002118:Calcium; D015220:Calcium Channels; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D004791:Enzyme Inhibitors; D019204:GTP-Binding Proteins; D020928:Mitogen-Activated Protein Kinases; D051059:PTEN Phosphohydrolase; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010744:Phosphoric Monoester Hydrolases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D017450:Receptors, Opioid, mu; D025521:Tumor Suppressor Proteins