Suppression of Prolactin Expression by Cabergoline Requires Prolactin Regulatory Element-binding Protein (PREB) in GH3 Cells

Abstract

The prolactin regulatory element-binding protein (PREB) is a transcriptional factor that regulates prolactin (PRL) promoter activity in the anterior pituitary. Prolactinomas are the most common pituitary tumors. Administration of cabergoline, a selective dopamine D2-receptor agonist, has become the initial therapy of choice for most patients with prolactinomas. Although activation of the D2 receptor results in the inhibition of PRL synthesis, the details of the underlying mechanisms remain unknown. Samples of ten prolactinomas and ten nonfunctioning pituitary adenomas were analyzed by immunohistochemistry to detect the expression of PREB. The effect of cabergoline on PREB expression was assessed by western blotting and real-time polymerase chain reaction (PCR) analysis. Reporter gene analysis of PRL was employed to examine the role of PREB on cabergoline-induced suppression of PRL transcription. Immunohistochemical analysis revealed strong positive PREB expression in the prolactinoma tissue, but extremely weak or undetected expression in the nonfunctioning pituitary tumor tissue. Western blots probed with a PREB-specific antiserum revealed that the relative abundance of the PREB protein in the GH3 cells decreased in a dose-dependent manner in response to cabergoline treatment, as did the relative abundance of PREB mRNA. Although cabergoline inhibited the activity of the PRL promoter, mutation of PREB-binding site within the promoter abrogated the ability of cabergoline to inhibit the PRL promoter activity. We have demonstrated that PREB is expressed in prolactinomas and that the suppression of PRL expression by cabergoline requires the transcriptional factor PREB.

Key words

prolactinoma - PREB - cabergoline - transcription - pituitary

References

• 1 Colao A, Lombardi G. Growth-hormone and prolactin excess.  Lancet. 1998;  352 1455-1461
• 2 Molitch ME. Pharmacologic resistance in prolactinoma patients.  Pituitary. 2005;  8 43-52
• 3 Colao A, Di Sarno A, Cappabianca P, Di Somma C, Pivonello R, Lombardi G. Withdrawal of long-term cabergoline therapy for tumoral and nontumoral hyperprolactinemia.  N Engl J Med. 2003;  349 2023-2033
• 4 Di Sarno A, Landi ML, Cappabianca P, Di Salle F, Rossi FW, Pivonello R, Di Somma C, Faggiano A, Lombardi G, Colao A. Resistance to cabergoline as compared with bromocriptine in hyperprolactinemia: prevalence, clinical definition, and therapeutic strategy.  J Clin Endocrinol Metab. 2001;  86 5256-5261
• 5 Fliss MS, Hinkle PM, Bancroft C. Expression cloning and characterization of PREB (prolactin regulatory element binding), a novel WD motif DNA-binding protein with a capacity to regulate prolactin promoter activity.  Mol Endocrinol. 1999;  13 644-657
• 6 Taylor Clelland CL, Levy B, McKie JM, Duncan AM, Hirschhorn K, Bancroft C. Cloning and characterization of human PREB; a gene that maps to a genomic region associated with trisomy 2p syndrome.  Mamm Genome. 2000;  11 675-681
• 7 Neer EJ, Schmidt CJ, Nambudripad R, Smith TF. The ancient regulatory-protein family of WD-repeat proteins.  Nature. 1994;  371 297-300
• 8 Ohtsuka S, Murao K, Imachi H, Cao WM, Yu X, Li J, Iwama H, Wong NC, Bancroft C, Ishida T. Prolactin regulatory element binding protein as a potential transcriptional factor for the insulin gene in response to glucose stimulation.  Diabetologia. 2006;  49 1599-1607
• 9 Murao K, Imachi H, Yu X, Cao WM, Muraoka T, Dobashi H, Hosomi N, Haba R, Iwama H, Ishida T. The transcriptional factor prolactin regulatory element-binding protein mediates the gene transcription of adrenal scavenger receptor class B type I via 3′,5′-cyclic adenosine 5′-monophosphate.  Endocrinology. 2008;  149 6103-6112
• 10 Imachi H, Murao K, Cao WM, Muraoka T, Nishiuchi T, Dobashi H, Hosomi N, Iwama H, Ishida T. The prolactin regulatory element-binding regulates of the 11beta-hydroxylase gene.  Biochem Biophys Res Commun. 2008;  376 531-535
• 11 Murao K, Terpstra V, Green SR, Kondratenko N, Steinberg D, Quehenberger O. Characterization of CLA-1, a human homologue of rodent scavenger receptor BI, as a receptor for high density lipoprotein and apoptotic thymocytes.  J Biol Chem. 1997;  272 17551-17557
• 12 Murao K, Imachi H, Cao WM, Yu X, Tokumitsu H, Inuzuka H, Wong NC, Shupnik MA, Kobayashi R, Ishida T. Role of calcium-calmodulin-dependent protein kinase cascade in thyrotropin (TSH)-releasing hormone induction of TSH and prolactin gene expression.  Endocrinology. 2004;  145 4846-4852
• 13 Vallar L, Vicentini LM, Meldolesi J. Inhibition of inositol phosphate production is a late, Ca²⁺-dependent effect of D2 dopaminergic receptor activation in rat lactotroph cells.  J Biol Chem. 1988;  263 10127-10134
• 14 Liu JC, Baker RE, Sun C, Sundmark VC, Elsholtz HP. Activation of Go-coupled dopamine D2 receptors inhibits ERK1/ERK2 in pituitary cells. A key step in the transcriptional suppression of the prolactin gene.  J Biol Chem. 2002;  277 35819-35825
• 15 DeCamilli P, Macconi D, Spada A. Dopamine inhibits adenylate cyclase in human prolactin-secreting pituitary adenomas.  Nature. 1979;  278 252-254
• 16 Senogles SE. The D2 dopamine receptor isoforms signal through distinct Gia proteins to inhibit adenylyl cyclase.  J Biol Chem. 1994;  269 23120-23127
• 17 Ben-Jonathan N, Hnasko R. Dopamine as a prolactin (PRL) inhibitor.  Endocr Rev. 2001;  22 724-763
• 18 Kanasaki H, Fukunaga K, Takahashi K, Miyazaki K, Miyamoto E. Mitogen-activated protein kinase activation by stimulation with thyrotropin-releasing hormone in rat pituitary GH3 cells.  Biol Reprod. 1999;  61 319-325

Correspondence