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Involvement of cAMP response element-binding protein in the regulation of cell proliferation and the prolactin promoter of lactotrophs in primary culture

Departments of Physiology and Internal Medicine, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Yamanashi, Japan

Submitted 13 January 2007 ; accepted in final form 27 September 2007

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.

adenosine 3',5'-cyclic monophosphate; dopamine; insulin-like growth factor I

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				Z. Wang, T. Mitsui, M. Ishida, and J. Arita Adenovirus vectors differentially modulate proliferation of pituitary lactotrophs in primary culture in a mitogen and infection time-dependent manner J. Endocrinol., July 1, 2008; 198(1): 209 - 217. [Abstract] [Full Text] [PDF]