title: A dopamine-responsive domain in the N-terminal sequence of Pit-1. Transcriptional inhibition in endocrine cell types.
abstract: The POU transcription factor Pit-1 activates the prolactin gene in pituitary lactotrophs and may integrate responses of the gene to external signals. To study the role of Pit-1 in dopaminergic inhibition of the prolactin gene, we transiently transfected Pit-1 and dopamine D2 receptor vectors into a series of heterologous cell lines and examined dopamine regulation of the prolactin gene promoter. Regulation was Pit-1-dependent in all cell lines tested. Moreover, dopamine responsiveness was cell type-specific: stimulatory in fibroblasts (COS-7) and muscle-type cells (P19/Me2SO-induced) and inhibitory in pancreatic endocrine (RIN, InR1-G9) and neural-like (P19/retinoic acid-induced) cells. Because dopaminergic responses in Pit-1-transfected RIN cells paralleled those in pituitary GH4 cells, the islet cell line was used to test for sequences in Pit-1 that mediate negative hormone signals. Dopamine responsiveness of the Pit-1 transactivation domain (residues 8-80) was examined using a chimeric LexA construct. LxPit-1, LxSp1, and Lx-glucocorticoid receptor fusions all activated basal transcription, but only LxPit-1 was regulated by dopamine. Regulatory responses of LxPit-1 and full-length Pit-1 were quantitatively similar. In addition, gain-of-function G alpha mutants that inhibit Pit-1-dependent promoters in GH4 cells also suppressed selectively Pit-1- or LxPit-1-dependent promoters in RIN cells. This demonstrates that Pit-1 can function as a specific target for distinct inhibitory G protein signals. Interestingly, Pit-1 sequences N-terminal to the DNA-binding POU domain appear to be sufficient in mediating regulation by these pathways.
authors.affiliation: Department of Clinical Biochemistry, University of Toronto, Ontario, Canada.
authors.forename: A M
authors.initials: AM
authors.lastname: Lew
authors.forename: H P
authors.initials: HP
authors.lastname: Elsholtz
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000378:metabolism; D002460:Cell Line; D002522:Chlorocebus aethiops; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D004298:Dopamine / Q000494:pharmacology*; D005347:Fibroblasts; D007515:Islets of Langerhans; D007668:Kidney; D008156:Luciferases / Q000096:biosynthesis; D009132:Muscles; D010902:Pituitary Gland; D011388:Prolactin / Q000096:biosynthesis*; D011401:Promoter Regions, Genetic / Q000187:drug effects; D051381:Rats; D017448:Receptors, Dopamine D2 / Q000096:biosynthesis / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000378:metabolism; D012697:Serine Endopeptidases; D050817:Transcription Factor Pit-1; D014157:Transcription Factors / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection; D000099160:LexA Repressor Protein
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D004298:Dopamine; D008156:Luciferases; D011388:Prolactin; D017448:Receptors, Dopamine D2; D011993:Recombinant Fusion Proteins; D012697:Serine Endopeptidases; D050817:Transcription Factor Pit-1; D014157:Transcription Factors; D000099160:LexA Repressor Protein; C494186:Pou1f1 protein, rat