title: D(4) dopamine receptor differentially regulates Akt/nuclear factor-kappa b and extracellular signal-regulated kinase pathways in D(4)MN9D cells.
abstract: The present study was designed to investigate the role of D(4) dopamine receptors in regulating the Akt/nuclear factor-kappa B (NF-kappa B) and extracellular signal-regulated kinase (ERK) signaling pathways. The D(4) dopamine receptor agonist PD168077 induced time- and dose-dependent activation of Akt and ERK in D(4)MN9D cells that stably express D(4) dopamine receptors. Maximal Akt and ERK stimulation was achieved at 1 microM PD168077. The agonist-mediated stimulations of Akt and ERK were abolished when cells were preincubated with 50 ng/ml PTX or with 1 microM L745,870, a D(4) dopamine receptor antagonist, indicating that activation of the Akt or ERK pathways is mediated by D(4) dopamine receptors and require a pertussis toxin-sensitive G protein. We also detected a time- and dose-dependent activation of NF-kappa B. Activation of NF-kappa B by 1 microM PD168077 was attenuated in D(4)MN9D cells that were transfected with a kinase-deficient Akt but not in cells transfected with a dominant negative Ras (N17Ras), suggesting that NF-kappa B activation requires Akt but is independent of Ras. In contrast, the transfection of N17Ras into D(4)MN9D cells blunted D(4) dopamine receptor-mediated ERK activation, indicating a Ras-dependent mechanism. Moreover, PP2 (20 nM), an inhibitor of Src, blocked D(4) receptor-mediated SHC phosphorylation and ERK activation. In contrast, transfection of a kinase-dead Akt did not alter D(4) receptor-stimulated ERK. However, PP2 and the mitogen activated protein kinase kinase inhibitor PD98059 did not change D(4) receptor-mediated Akt/NF-kappa B activation. All these indicate that distinct mechanisms mediate ERK and Akt/NF-kappa B activation by D(4) dopamine receptor stimulation. We also demonstrated that D(4) receptor-stimulated cell proliferation is mediated by the Src/SHC/Ras/ERK pathway.
authors.affiliation: Laboratory of Molecular Pharmacology, Department of Pharmacology and Physiology, MCP Hahnemann School of Medicine, Philadelphia, Pennsylvania, USA.
authors.forename: X
authors.initials: X
authors.lastname: Zhen
authors.forename: J
authors.initials: J
authors.lastname: Zhang
authors.forename: G P
authors.initials: GP
authors.lastname: Johnson
authors.forename: E
authors.initials: E
authors.lastname: Friedman
mesh_terms: D000818:Animals; D016391:Genes, src / Q000502:physiology; D006822:Hybrid Cells; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D017448:Receptors, Dopamine D2 / Q000378:metabolism*; D050638:Receptors, Dopamine D4; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism; D018631:ras Proteins / Q000502:physiology; D018909:src Homology Domains / Q000502:physiology
chemical_list: C493600:Drd4 protein, mouse; D016328:NF-kappa B; D011518:Proto-Oncogene Proteins; D017448:Receptors, Dopamine D2; D050638:Receptors, Dopamine D4; D014443:Tyrosine; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases; D018631:ras Proteins