title: Agonist-specific transactivation of phosphoinositide 3-kinase signaling pathway mediated by the dopamine D2 receptor.
abstract: Bromocriptine, acting through the dopamine D2 receptor, provides robust protection against apoptosis induced by oxidative stress in PC12-D2R and immortalized nigral dopamine cells. We now report the characterization of the D2 receptor signaling pathways mediating the cytoprotection. Bromocriptine caused protein kinase B (Akt) activation in PC12-D2R cells and the inhibition of either phosphoinositide (PI) 3-kinase, epidermal growth factor receptor (EGFR), or c-Src eliminated the Akt activation and the cytoprotective effects of bromocriptine against oxidative stress. Co-immunoprecipitation studies showed that the D2 receptor forms a complex with the EGFR and c-Src that was augmented by bromocriptine, suggesting a cross-talk between these proteins in mediating the activation of Akt. EGFR repression by inhibitor or by RNA interference eliminated the activation of Akt by bromocriptine. D2 receptor stimulation by bromocriptine induced c-Src tyrosine 418 phosphorylation and EGFR phosphorylation specifically at tyrosine 845, a known substrate of Src kinase. Furthermore, Src tyrosine kinase inhibitor or dominant negative Src interfered with Akt translocation and phosphorylation. Thus, the predominant signaling cascade mediating cytoprotection by the D2 receptor involves c-Src/EGFR transactivation by D2 receptor, activating PI 3-kinase and Akt. We also found that the agonist pramipexole failed to stimulate activation of Akt in PC12-D2R cells, providing an explanation for our previous observations that, despite efficiently activating G-protein signaling, this agonist had little cytoprotective activity in this experimental system. These results support the hypothesis that specific dopamine agonists stabilize distinct conformations of the D2 receptor that differ in their coupling to G-proteins and to a cytoprotective c-Src/EGFR-mediated PI-3 kinase/Akt pathway.
authors.affiliation: Department of Neurology, Mount Sinai School of Medicine, One Gustave L. Levy Place, New York, NY 10029, USA.
authors.forename: Venugopalan D
authors.initials: VD
authors.lastname: Nair
authors.forename: Stuart C
authors.initials: SC
authors.lastname: Sealfon
mesh_terms: D000818:Animals; D001971:Bromocriptine / Q000494:pharmacology; D000081247:CSK Tyrosine-Protein Kinase; D002470:Cell Survival / Q000187:drug effects; D018491:Dopamine Agonists / Q000494:pharmacology; D004789:Enzyme Activation; D066246:ErbB Receptors / Q000096:biosynthesis / Q000378:metabolism; D006801:Humans; D018384:Oxidative Stress / Q000187:drug effects; D016716:PC12 Cells; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases / Q000096:biosynthesis / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D020239:Receptor Cross-Talk; D017448:Receptors, Dopamine D2 / Q000819:agonists* / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction; D015533:Transcriptional Activation; D014162:Transfection; D019061:src-Family Kinases
chemical_list: D001971:Bromocriptine; D000081247:CSK Tyrosine-Protein Kinase; D018491:Dopamine Agonists; D066246:ErbB Receptors; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D017448:Receptors, Dopamine D2; D019061:src-Family Kinases; C000631346:CSK protein, human; C494918:AKT1 protein, human; C494920:Akt1 protein, rat