title: Comparative studies of molecular mechanisms of dopamine D2 and D3 receptors for the activation of extracellular signal-regulated kinase.
abstract: Dopamine D(2) and D(3) receptors (D(2)R/D(3)R), which have similar structural architecture as well as functional similarities, are expressed in the same brain dopaminergic neurons. It is intriguing that two receptor proteins with virtually the same functional roles are expressed in the same neuron. Recently we have shown that D(2)R and D(3)R possess different regulatory processes including intracellular trafficking properties, which implies that they might employ different signaling mechanisms for regulation of the same cellular processes. Here we studied the signaling pathways of ERK activation mediated by D(2)R and D(3)R in HEK-293 cells and corroborated them with concomitant studies in COS-7 cells and C6 cells. Our results show that Src, phosphatidylinositol 3-kinase, and atypical protein kinase C were commonly involved in D(2)R-/D(3)R-mediated ERK activation. However, beta-arrestin and sequestration of D(2)R/D(3)R were found not to be involved. ERK activations mediated by D(3)R, but not D(2)R, were blocked by betaARK-CT, AG1478 epidermal growth factor receptor (EGFR) inhibitor, and by dominant negative mutants of Ras and Raf, suggesting the involvement of the Gbetagamma(i) pathway. The alpha-subunit of G(o) (Galpha(o)) was able to couple with D(3)R to mediate ERK activation. We conclude that D(3)R mainly utilizes the betagamma pathway of G(i) protein, which involves the transactivation of EGFR in HEK-293 cells. In contrast, the alpha-subunit of the G(i) protein plays a main role in D(2)R-mediated ERK activation. Our study suggests one example of intricate cellular regulations in the brain, that is, dopaminergic neurons could regulate ERK activity more flexibly through alternative usage of either the D(2)R or D(3)R pathway depending on the cellular situation.
authors.affiliation: Department of Pharmacology, College of Pharmacy, Chonnam National University, Kwang-Ju, 500-757 Korea.
authors.forename: SunRyeo
authors.initials: S
authors.lastname: Beom
authors.forename: Dawoon
authors.initials: D
authors.lastname: Cheong
authors.forename: Gonzalo
authors.initials: G
authors.lastname: Torres
authors.forename: Marc G
authors.initials: MG
authors.lastname: Caron
authors.forename: Kyeong-Man
authors.initials: KM
authors.lastname: Kim
mesh_terms: D000818:Animals; D019390:Arrestins / Q000378:metabolism; D001921:Brain / Q000378:metabolism; D019556:COS Cells; D002460:Cell Line; D004705:Endocytosis; D004789:Enzyme Activation; D066246:ErbB Receptors / Q000378:metabolism; D005799:Genes, Dominant; D049452:Green Fluorescent Proteins; D006801:Humans; D007150:Immunohistochemistry; D008164:Luminescent Proteins / Q000378:metabolism; D018613:Microscopy, Confocal; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D017434:Protein Structure, Tertiary; D017448:Receptors, Dopamine D2 / Q000737:chemistry / Q000378:metabolism*; D050637:Receptors, Dopamine D3; D015398:Signal Transduction; D013997:Time Factors; D015533:Transcriptional Activation; D014162:Transfection; D010738:Type C Phospholipases / Q000378:metabolism; D000071557:beta-Arrestins
chemical_list: D019390:Arrestins; C493593:DRD3 protein, human; D008164:Luminescent Proteins; D017448:Receptors, Dopamine D2; D050637:Receptors, Dopamine D3; D000071557:beta-Arrestins; D049452:Green Fluorescent Proteins; D019869:Phosphatidylinositol 3-Kinases; D066246:ErbB Receptors; D011493:Protein Kinase C; D020928:Mitogen-Activated Protein Kinases; D010738:Type C Phospholipases