Activation of Go-coupled dopamine D2 receptors inhibits ERK1/ERK2 in pituitary cells. A key step in the transcriptional suppression of the prolactin gene.
In pituitary lactotrophs the prolactin gene is stimulated by neuropeptides and estrogen and is suppressed by dopamine via D2-type receptors. Stimulatory signals converge on activation of the mitogen-activated protein kinases ERK1/2, but dopamine regulation of this pathway is not well defined. Paradoxically, D2 agonists activate ERK1/2 in many cell types. Here we show that in prolactin-secreting GH4ZR7 cells and primary pituitary cells, dopamine treatment leads to a rapid, pronounced, and specific decrease in activated ERK1/2. The response is blocked by D2-specific antagonists and pertussis toxin. Interestingly, in stable lines expressing specific pertussis toxin-resistant Galpha subunits, toxin treatment blocks dopamine suppression of MAPK in Galpha(i2)- but not Galphao-expressing cells, demonstrating that G(o)-dependent pathways can effect the inhibitory MAPK response. At the nuclear level, the MEK1 inhibitor U0126 mimics the D2-agonist bromocryptine in suppressing levels of endogenous prolactin transcripts. Moreover, a good correlation is seen between the IC(50) values for inhibition of MEK1 and suppression of prolactin promoter function (PD184352 > U0126 > U0125). Both dopamine and U0126 enhance the nuclear localization of ERF, a MAPK-sensitive ETS repressor that inhibits prolactin promoter activity. In addition, U0126 suppression is transferred by tandem copies of the Pit-1-binding site, consistent with mapping experiments for dopamine responsiveness. Our data suggest that ERK1/2 suppression is an obligatory step in the dopaminergic control of prolactin gene transcription and that bidirectional control of ERK1/2 function in the pituitary may provide a key mechanism for endocrine gene control.
Liu
Jeffrey C
JC
Department of Laboratory Medicine and Pathobiology, Banting and Best Diabetes Centre, University of Toronto and the University Health Network, Toronto, Ontario M5G 1L5.
Baker
Ross E
RE
Sun
Clement
C
Sundmark
Valdine C
VC
Elsholtz
Harry P
HP
D000818:Animals; D001665:Binding Sites; D001971:Bromocriptine / Q000494:pharmacology; D002070:Butadienes / Q000494:pharmacology; D002478:Cells, Cultured; D003001:Cloning, Molecular; D018491:Dopamine Agonists / Q000494:pharmacology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation; D049452:Green Fluorescent Proteins; D015151:Immunoblotting; D020128:Inhibitory Concentration 50; D008164:Luminescent Proteins / Q000378:metabolism; D020935:MAP Kinase Signaling System; D018613:Microscopy, Confocal; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008956:Models, Chemical; D016297:Mutagenesis, Site-Directed; D009570:Nitriles / Q000494:pharmacology; D037342:Pertussis Toxin / Q000494:pharmacology; D010766:Phosphorylation; D010902:Pituitary Gland / Q000166:cytology*; D010957:Plasmids / Q000378:metabolism; D011388:Prolactin / Q000096:biosynthesis* / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012313:RNA / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017448:Receptors, Dopamine D2 / Q000378:metabolism*; D013997:Time Factors; D014158:Transcription, Genetic
D002070:Butadienes; D018491:Dopamine Agonists; D004791:Enzyme Inhibitors; D008164:Luminescent Proteins; D009570:Nitriles; D017448:Receptors, Dopamine D2; C113580:U 0126; D049452:Green Fluorescent Proteins; D001971:Bromocriptine; D012313:RNA; D011388:Prolactin; D037342:Pertussis Toxin; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases