title: Involvement of cAMP response element-binding protein in the regulation of cell proliferation and the prolactin promoter of lactotrophs in primary culture.
abstract: Hypothalamic hormones, including dopamine, regulate critical functions of pituitary cells via the cAMP-protein kinase A (PKA) pathway. The PKA-downstream transcription factor cAMP response element (CRE)-binding protein (CREB) is an integrating molecule that is also activated by many other protein kinase pathways. We investigated the involvement of CREB in the regulation of cell proliferation and the PRL promoter of rat lactotrophs in primary cell culture. Recombinant adenoviruses were used for efficient gene delivery into pituitary cells. Bromocriptine, a dopaminergic agonist known to decrease intracellular cAMP concentrations, caused inhibition of PRL promoter activity and lactotroph proliferation, which was accompanied by decreases in CRE-mediated transcription and CREB phosphorylation in lactotrophs. Expression of a dominant-negative form of CREB (MCREB), which was effective in suppressing CRE-mediated transcription induced by the adenylate cyclase activator forskolin, inhibited basal and forskolin-induced PRL promoter activity and PRL mRNA expression. MCREB expression lowered basal proliferative levels and blocked forskolin-induced proliferation of lactotrophs. Insulin-like growth factor I (IGF-I), a potent mitogen in lactotrophs, did not affect intracellular cAMP concentrations but transiently increased lactotroph CREB phosphorylation. MCREB expression also inhibited IGF-I-induced lactotroph proliferation. These results suggest that CREB is involved in the regulation of cell proliferation and the PRL promoter in normal lactotrophs and that dopamine inhibition of these lactotroph functions is at least in part due to inhibition of the cAMP-PKA-CREB pathway.
authors.affiliation: Dept. of Physiology, Interdisciplinary Graduate School of Medicine and Engineering, Univ. of Yamanashi, 409-3898, Japan.
authors.forename: Maho
authors.initials: M
authors.lastname: Ishida
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Mitsui
authors.forename: Koji
authors.initials: K
authors.lastname: Yamakawa
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Sugiyama
authors.forename: Wakaba
authors.initials: W
authors.lastname: Takahashi
authors.forename: Hiroki
authors.initials: H
authors.lastname: Shimura
authors.forename: Toyoshi
authors.initials: T
authors.lastname: Endo
authors.forename: Tetsurou
authors.initials: T
authors.lastname: Kobayashi
authors.forename: Jun
authors.initials: J
authors.lastname: Arita
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D001971:Bromocriptine / Q000494:pharmacology; D049109:Cell Proliferation; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D017362:Cyclic AMP Response Element-Binding Protein / Q000502:physiology*; D018491:Dopamine Agonists / Q000494:pharmacology; D004318:Doxycycline / Q000494:pharmacology; D005260:Female; D015870:Gene Expression / Q000187:drug effects; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D052682:Lactotrophs / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011388:Prolactin / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics*; D051381:Rats; D017208:Rats, Wistar; D020218:Response Elements / Q000235:genetics; D014162:Transfection
chemical_list: D017362:Cyclic AMP Response Element-Binding Protein; D018491:Dopamine Agonists; D005576:Colforsin; D001971:Bromocriptine; D007334:Insulin-Like Growth Factor I; D011388:Prolactin; D000242:Cyclic AMP; D004318:Doxycycline