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Kucka M, Bjelobaba I, Tomić M, Stojilkovic SS. The role of cyclic nucleotides in pituitary lactotroph functions. Front Endocrinol (Lausanne) 2013; 4:122. [PMID: 24062725 PMCID: PMC3772395 DOI: 10.3389/fendo.2013.00122] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/30/2013] [Accepted: 08/30/2013] [Indexed: 11/13/2022] Open
Abstract
Lactotrophs are one of the five secretory anterior pituitary cell types specialized to synthesize and release prolactin. In vitro, these cells fire action potentials (APs) spontaneously and the accompanied Ca(2+) transients are of sufficient amplitude to keep the exocytotic pathway, the transcription of prolactin gene, and de novo hormone synthesis continuously active. Basal cyclic nucleotide production is also substantial in cultured cells but not critical for the APs secretion/transcription coupling in lactotrophs. However, elevated intracellular cAMP levels enhance the excitability of lactotrophs by stimulating the depolarizing non-selective cationic hyperpolarization-activated cyclic nucleotide-regulated and background channels, whereas cGMP inhibits it by activating Ca(2+)-controlled K(+) channels. Elevated cAMP also modulates prolactin release downstream of Ca(2+) influx by changing the kinetic of secretory pores: stimulate at low and inhibit at high concentrations. Induction of prolactin gene and lactotroph proliferation is also stimulated by elevated cAMP through protein kinase A. Together, these observations suggest that in lactotrophs cAMP exhibits complex regulatory effects on voltage-gated Ca(2+) influx and Ca(2+)-dependent cellular processes.
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Affiliation(s)
- Marek Kucka
- Section on Cellular Signaling, Program in Developmental Neuroscience, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
- *Correspondence: Marek Kucka, Section on Cellular Signaling, Program in Developmental Neuroscience, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Building 49, Room 6A-36, 49 Convent Drive, Bethesda, MD 20892-4510, USA e-mail:
| | - Ivana Bjelobaba
- Section on Cellular Signaling, Program in Developmental Neuroscience, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - Melanija Tomić
- Section on Cellular Signaling, Program in Developmental Neuroscience, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - Stanko S. Stojilkovic
- Section on Cellular Signaling, Program in Developmental Neuroscience, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
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Stanley FM. Insulin-increased prolactin gene expression requires actin treadmilling: potential role for p21 activated kinase. Endocrinology 2007; 148:5874-83. [PMID: 17884942 DOI: 10.1210/en.2007-0127] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Insulin-increased prolactin gene transcription in GH4 cells was enhanced by binding on fibronectin. This was mediated by receptor-like protein tyrosine phosphatase alpha, which activated Src, Rho, and phosphatidylinositol 3-kinase. It suggested that insulin signaling to gene transcription was partly dependent on actin rearrangement. This was confirmed through studies using inhibitors of actin treadmilling. Cytochalasin D, jasplakinolide, latrunculin B, and swinholide A altered the actin cytoskeleton of GH4 cells, as assessed by Alexa Fluor phalloidin staining, and inhibited insulin-increased prolactin gene transcription. These reagents did not affect the controls. Nor was it due to a gross defect of insulin signaling because activation/translocation of glycogen synthase kinase 3beta and mammalian target of rapamycin were not affected. Expression of wild-type and mutant actin treadmilling agents, Cdc42, TC10, neuronal Wiskott-Aldrich syndrome protein, and Nck, indicated that they were essential to insulin-increased prolactin gene expression, and suggested that activation of p21 associated kinase (PAK) might also be essential to this process. PAK expression also increased and PAK mutants decreased prolactin promoter activity in insulin-treated cells. The activation of PAK in the presence of inhibitors was also consistent with a role in activation of insulin-increased prolactin gene expression. Finally, small interfering RNA-mediated reduction of PAK decreased the effect of insulin on prolactin gene expression. Thus, it is likely that insulin activation of actin treadmilling through Cdc42/TC10 and neuronal Wiskott-Aldrich syndrome protein activates PAK and prolactin gene transcription.
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Affiliation(s)
- Frederick M Stanley
- Department of Pharmacology, New York University Medical Center, 550 First Avenue, New York, NY 10016, USA.
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Al Kahtane A, Kannan M, Kang SW, El Halawani ME. Regulation of prolactin gene expression by vasoactive intestinal peptide and dopamine in the turkey: role of Ca signalling. J Neuroendocrinol 2005; 17:649-55. [PMID: 16159377 DOI: 10.1111/j.1365-2826.2005.01352.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Our recent work has demonstrated that dopamine, acting through D2 dopamine receptors on pituitary cells, inhibits the stimulatory effects of vasoactive intestinal peptide (VIP) on prolactin release and prolactin gene transcription. It is hypothesised that the stimulatory and inhibitory roles of VIP and dopamine, respectively, on prolactin synthesis and release are mediated by their opposite effects on intracellular Ca2+ concentration ([Ca2+]i) in lactotrophs. The present study aimed: (i) to investigate the effect of VIP and dopamine on [Ca2+]i of cultured turkey anterior pituitary cells and (ii) to examine the role of Ca2+ signalling in mediating the regulatory effects of VIP and dopamine on prolactin mRNA levels and prolactin release. Changes in [Ca2+]i were measured spectrofluorometrically using Fura-2/AM as a fluorescent Ca2+ indicator. Semi-quantitative reverse transcription-polymerase chain reaction and radioimmunoassay were used to determine prolactin mRNA levels and prolactin release, respectively. VIP or the L-type Ca2+ channel activator, Bay K8644 (Bay) increased [Ca2+]i in a concentration- and time-dependent fashion, an effect abolished by preincubating the cells with R(-)-propylnorapomorphine HCl, a D2 dopamine receptor agonist (D2AG) or Verapamil (VR), a specific L-type Ca2+ channel blocker. Similarly, either VR or D2Ag diminished the VIP/Bay stimulatory effect on prolactin expression and release. On the other hand, pretreatment of pituitary cells with thapsigargin (TG) or neomycin (NEO), to deplete the intracellular Ca2+ stores, showed no effect on basal or VIP-stimulated prolactin mRNA levels; although VIP-induced prolactin release was partially inhibited by NEO but not TG. These results suggest that intracellular Ca2+ represents a common signal transduction pathway through which VIP and dopamine can exert antagonistic control on prolactin synthesis and release in avian lactotrophs.
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Affiliation(s)
- A Al Kahtane
- Department of Animal Science, University of Minnesota, St Paul, MN, USA
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Leclerc GM, Leclerc GJ, Shorte SL, Stephen Frawley L, Boockfor FR. Cloning and mRNA expression of the Ca2+-binding DREAM protein in the pituitary. Gen Comp Endocrinol 2002; 129:45-55. [PMID: 12409095 DOI: 10.1016/s0016-6480(02)00509-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
It is well recognized that the level of intracellular calcium governs several cellular processes such as gene expression and secretion in the pituitary. Recently, a novel gene has been identified in neuroendocrine cells that encodes DREAM, a calcium-binding protein that acts as a transcriptional repressor by binding specific downstream regulatory elements (DRE) on DNA. To explore the possibility that DREAM may be expressed in the rat pituitary and may function in endocrine activity, we analyzed its mRNA expression by RT-PCR. Using oligonucleotide primers derived from the mouse DREAM cDNA, we amplified, cloned, and characterized a 852-bp RT-PCR product from rat pituitary tissue. Two splice variants of the rat DREAM gene differing by four nucleotides (tetramer ACAG) were identified. The ACAG(+) variant (ORF1) consisted of 768bp encoding a protein of 256 residues with an estimated molecular weight of 29.5kDa. Amino acid sequence analysis of ORF1 indicated 92.6% and 98.1% identity to the DREAM gene product from human and mouse, respectively. The second variant, ACAG(-) (ORF2), was 567-bp long and was predicted to encode a peptide of 189 residues with a molecular mass of about 20.8kDa. To determine which endocrine pituitary cells were expressing DREAM, we evaluated several different clonal populations containing cells that expressed specific pituitary hormones. We found that both DREAM splice variants were expressed in each pituitary cell types examined, which included the mammotropes (MMQ cells), somatotropes (GC cells), mammosomatotropes (GH(3) cells), gonadotropes (LbetaT2 cells), thyrotropes (TalphaT1 cells), and corticotropes (AtT-20 cells). Interestingly, the levels of the two variants differed between the cell types tested with the ACAG(+) variant comprising about two-thirds of the DREAM expression for the mammotropes, somatotropes, mammosomatotropes, and corticotropes as compared to less than one-half for the thyrotropes and the gonadotropes. Our initial attempts to identify pituitary-specific genes regulated by DREAM revealed that prolactin gene expression was not influenced by DREAM suggesting that an action of DREAM may involve other pituitary hormones or be mediated by other cell processes. When taken together, our findings of DREAM expression in the pituitary in a manner specific to pituitary endocrine cell type raises the possibility that this protein may play a role in determining specific pituitary cell function.
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Affiliation(s)
- Gilles M Leclerc
- Laboratory of Molecular Dynamics, Department of Cell Biology and Anatomy, Medical University of South Carolina, Charleston 29425, USA
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Gore AC, Villalobos C, Frawley LS. Differential influences of gender and physiological status on calcium dynamics and prolactin gene expression in rat mammotropes. Endocrine 1999; 11:131-6. [PMID: 10709759 DOI: 10.1385/endo:11:2:131] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/26/1999] [Revised: 07/07/1999] [Accepted: 07/07/1999] [Indexed: 11/11/2022]
Abstract
The rate of prolactin (PRL) secretion is influenced by the gender and physiological state of an animal, but little is known about the mechanisms involved. In the present study, we assessed possible contributions of Ca2+ dynamics and PRL gene expression to these differences. This was accomplished by monitoring spontaneous [Ca2+]i changes and PRL promotor-driven reporter activity in pituitary cultures derived from rats comprising a broad spectrum of PRL secretory capacities: male, cycling female, and lactating rats. We found that Ca2+ oscillatory activity exhibited a rank order of lactating > cycling females > males, consistent with the reported secretory capacities of mammotropes from these sources. Interestingly, we observed that the basal level of PRL promotor-driven reporter activity was the same for all three models, but that mammotropes from males were the most responsive to stimulation of PRL gene expression by elevation of [Ca2+]i. Collectively, our findings reveal gender- and state-specific differences in Ca2+ dynamics and induction of PRL gene expression. These likely contribute to reported differences in secretory capacity.
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Affiliation(s)
- A C Gore
- Department of Cell Biology and Anatomy, Medical University of South Carolina, Charleston 29425, USA
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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; 13:644-57. [PMID: 10194769 DOI: 10.1210/mend.13.4.0260] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Previous studies have implied that a transcription factor(s) other than Pit-1 is involved in homeostatic regulation of PRL promoter activity via Pit-1-binding elements. One such element, 1P, was employed to clone from a rat pituitary cDNA expression library a novel 417-amino acid WD protein, designated PREB (PRL regulatory element binding) protein. PREB contains two PQ-rich potential transactivation domains, but no apparent DNA-binding motif, and exhibits sequence-specific binding to site 1P, to a site nonidentical to that for Pit-1. The PREB gene (or a related gene) is conserved, as an apparently single copy, in rat, human, fly, and yeast. A single approximately 1.9-kb PREB transcript accumulates in GH3 rat pituitary cells, to levels similar to Pit-1 mRNA. PREB transcripts were detected in all human tissues examined, but the observation of tissue-specific multiple transcript patterns suggests the possibility of tissue-specific alternative splicing. RT-PCR analysis of human brain tumor RNA samples suggested region-specific expression of PREB transcripts in brain. Western and immunocytochemical analysis implied that PREB accumulates specifically in GH3 cell nuclei. Transient transfection employing PREB-negative C6 rat glial cells showed that PREB is as active as, and additive with, Pit-1 in transactivation of a PRL promoter construct, and that PREB, but not Pit-1, can mediate transcriptional activation by protein kinase A (PKA). Expression in GH3 cells of a GAL4-PREB fusion protein both strongly transactivated a 5XGAL indicator construct and yielded a further stimulation of expression of this construct by coexpressed PKA, implying that PREB can mediate both basal and PKA-stimulated transcriptional responses in pituitary cells. These observations imply that PREB will prove to play a significant transcriptional regulatory role, both in the pituitary and in other organs in which transcripts of its gene are expressed.
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Affiliation(s)
- M S Fliss
- Department of Physiology and Biophysics, Mount Sinai School of Medicine, New York, New York 10029, USA
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Nowakowski BE, Okimura Y, Maurer RA. Characterization of DNA regions mediating the ability of Ca2+/calmodulin dependent protein kinase II to stimulate prolactin promoter activity. Mol Cell Endocrinol 1997; 132:109-16. [PMID: 9324052 DOI: 10.1016/s0303-7207(97)00127-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The ability of Ca2+/calmodulin-dependent protein kinases (CaMKs) to regulate transcription of the rat prolactin (PRL) gene has been examined. We found that KN-62, a potent inhibitor of CaM kinases, blunted the ability of TRH to activate the prolactin promoter. Transfection experiments using expression plasmids for constitutively active forms of CaMKI, CaMKII, or CaMKIV show that CaMKII is the most effective activator of prolactin promoter expression. Deletion studies demonstrated that the upstream boundary of sequences necessary to respond to CaMKII is located within the distal enhancer of the prolactin gene. Neither the distal enhancer alone nor the proximal region of the prolactin gene are sufficient to mediate a response to CaMKII. Mutational analysis suggests that several Pit-1 binding sites contribute to CaMKII responsiveness. These findings suggest that CaMKII responsiveness of the prolactin promoter requires multiple factor binding sites in both the distal and proximal regions of the gene.
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Affiliation(s)
- B E Nowakowski
- Department of Cell and Developmental Biology, Oregon Health Sciences University, Portland 97201, USA
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Lail-Trecker MR, Hanrahan CJ, White BA. Role of cell-cell adhesion in the regulation of prolactin gene expression by extracellular CaCl(2). Endocrine 1996; 5:341-9. [PMID: 21153086 DOI: 10.1007/bf02739069] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/02/1996] [Revised: 09/18/1996] [Accepted: 09/18/1996] [Indexed: 11/26/2022]
Abstract
We have investigated a role for calcium-dependent cell-cell adhesion in the regulation of prolactin gene expression in rat pituitary GH(3) cells. Cells cultured in a calcium-free, serum-free medium (SFM) express low levels of prolactin and growth hormone mRNA. As expected, addition of 0.5 mM CaCl(2) to GH(3) cells in SFM produced a specific, severalfold increase in prolactin mRNA levels. CaCl(2) also promoted intercellular adhesion, during which cells assembled end-to-end in to cords. Prolactin mRNA increased after a delay of several hours. This latency period ranged from 4-12 h among different experiments, but always occurred after the onset of cell-cell adhesion. The voltage-sensitive calcium channel (VSCC) blocker, nitrendipine, inhibited the CaCl(2)-induced increase in prolactin mRNA without affecting cord formation. However, the VSCC agonist, BAY K-8644, was unable to induce prolactin gene expression prior to the onset of intercellular adhesion at 8 h, even though it produced a cellular response (tyrosine phosphorylation of a ca. 130-kDa protein) within 30 min. Blocking cell-cell adhesion inhibited the calcium-dependent induction of prolactin gene expression. Low levels (0.0025-0.02%) of trypsin blocked cell-cell adhesion and the prolactin mRNA induction by CaCl(2) without affecting the levels of other mRNAs or cell-matrix adhesion. Heparin also specifically blocked the induction of both cell-cell adhesion and prolactin gene expression. Based on these data, we propose a role for both VSCCs and calcium-dependent cell-cell adhesion in the induction of prolactin gene expression by extracellular CaCl(2).
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Affiliation(s)
- M R Lail-Trecker
- Graduate Program in Developmental Biology, Department of Anatomy, University of Connecticut Health Center, 06030, Farmington, CT
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Abstract
We have employed the GH3 rat pituitary cell line to investigate whether nicotine can regulate prolactin (PRL) gene expression. Nicotine strongly inhibited (45%) transient expression of a construct containing the first 187 base-pairs of the rat PRL promoter cloned upstream of the chloramphenicol acetyl transferase (CAT) gene. This implies that nicotine acts directly on the GH3 cells to inhibit transcription directed by the PRL promoter. Expression of a control reporter construct containing the CAT gene under the control of the RSV promoter was not affected by exposure of the cells to nicotine, demonstrating that the effect of nicotine is promoter-specific. The inhibition by nicotine of PRL promoter activity was not blocked by hexamethonium, suggesting that this effect of nicotine may be mediated by a novel type of nicotine receptor previously described in frog pituitary cells. Nicotine was also observed to yield a concentration-dependent inhibition of the stimulation by thyrotrophin-releasing hormone (TRH) of PRL promoter activity, implying that nicotine can also interfere with hormonal regulation of the PRL gene. These results suggest that the reduced serum PRL levels that result from smoking may originate in part from decreased transcription of the PRL gene resulting from a direct effect of nicotine on pituitary PRL-secreting cells.
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Affiliation(s)
- D T Coleman
- Department of Physiology & Biophysics, Mount Sinai School of Medicine, New York, NY 10029, USA
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Tian J, Ma HW, Bancroft C. Constitutively active Gq-alpha stimulates prolactin promoter activity via a pathway involving Raf activity. Mol Cell Endocrinol 1995; 112:249-56. [PMID: 7489829 DOI: 10.1016/0303-7207(95)03614-d] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
We have investigated the ability of a constitutively active Gq-alpha mutant, Q209L-alpha q, to regulate target gene expression. Transient expression in GH3 pituitary cells of a rat proximal prolactin promoter-chloramphenicol acetyltransferase construct (-187)PRL-CAT, was stimulated by co-expression of Q209L alpha q, but not by wild-type alpha q. Q209L-alpha q stimulated expression of constructs driven by promoters for either rat prolactin or growth hormone, but not of a control construct driven by the thymidine kinase promoter. Thus, transcriptional effects of alpha q are specific both for the activated state of this G-alpha subunit and the promoter examined. Since both the prolactin and growth hormone promoters are activated by the pituitary cell-specific transcription factor Pit-1, we examined whether a Pit-1 binding site could direct a response to Q209L-alpha q. Two copies of prolactin promoter Pit-1 binding site 1P conferred upon a heterologous metallothionein promoter a response to Q209L-alpha q, implying an involvement of this site in the transcriptional action of Q209L-alpha q on the prolactin promoter. The phorbol ester activator of protein kinase C, 12-O-tetradecanoylphorbol-13-acetate, stimulated (-187)PRL-CAT activity, but opposed the action of Q209L-alpha q on activity of this PRL-CAT construct. Q209L-alpha q stimulation of (-187)PRL-CAT activity was inhibited by co-expression of a dominant negative Raf mutant, Raf-C4, but not by a point mutant of Raf-C4 with reduced inhibitory properties. These results imply that activated alpha q subunits can stimulate prolactin promoter activity via a pathway that involves a Pit-1 DNA binding site(s), is opposed by protein kinase C, and is mediated by a pathway in which Raf-1 kinase plays a role.
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Affiliation(s)
- J Tian
- Department of Physiology and Biophysics, Mount Sinai School of Medicine, City University of New York, NY 10029, USA
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Fischberg DJ, Bancroft C. The D2 receptor: blocked transcription in GH3 cells and cellular pathways employed by D2A to regulate prolactin promoter activity. Mol Cell Endocrinol 1995; 111:129-37. [PMID: 7556874 DOI: 10.1016/0303-7207(95)03555-l] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Although the GH3 line of somatolactotropic rat pituitary cells has proven useful for many regulation studies, the absence of functional D2 receptors on these cells long prevented their use in studies of dopaminergic action. However, it is now possible to employ GH3 cells expressing recombinant D2 receptors for such investigations. We have investigated both the level at which expression of functional D2 receptors in GH3 cells is blocked, and the cellular pathways employed by the major pituitary D2 receptor isoform, D2A, to inhibit prolactin (PRL) gene transcription. In run-off transcription assays with nuclei from either parental GH3 cells or a GH3 cell line stably expressing a D2A expression vector, Pit-1 gene transcription was detectable in either cell line, but only the latter cell line yielded detectable D2 receptor transcription, implying that the block in D2 receptor expression by GH3 cells is transcriptional. Further investigations employed GH3 cells transiently co-transfected with a D2A expression vector plus a rat PRL promoter construct (-1957)PRL-CAT. Pertussis toxin blocked repression by quinpirole, a D2 agonist, of PRL-CAT activity, demonstrating that this action is mediated by a pertussis toxin-sensitive G protein. The observations that neither of two agents expected to raise intracellular Ca2+, Bay K8644 or thyrotropin-releasing hormone, prevented quinpirole repression of PRL-CAT activity, and that the repressive effects on this construct of quinpirole and the Ca2+ channel antagonist were independent, suggested that regulation of intracellular Ca2+ levels does not play a major role in D2A-mediated repression of the PRL promoter.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- D J Fischberg
- Department of Physiology and Biophysics, Mount Sinai School of Medicine, City University of New York, NY 10029, USA
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Hippenmeyer PJ, Rankin AM, Reitz BA, McWilliams DR, Brightwell BB, Wolfe RA, Warren TG. Endogenous and exogenous pituitary-specific promoters are differentially controlled. Mol Cell Endocrinol 1995; 107:155-64. [PMID: 7768327 DOI: 10.1016/0303-7207(94)03439-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
We have engineered GH3 cells with reporter genes under control of the growth hormone and prolactin promoters and measured protein production. The results indicate very low level production of reporter proteins from the cells regardless of the promoter used to drive expression. This was surprising in light of the observation that the cells still produced high levels of endogenous growth hormone and prolactin. Chinese hamster ovary (CHO) cells were engineered to express the Pit-1 transactivator. Transfection of reporter genes under control of the prolactin promoter demonstrated a clear enhancement of expression levels compared to the same promoter in parental CHO cells. Pit-1 expression is not sufficient, however, for high level, stable expression from the growth hormone promoter. These results indicate that the growth hormone and prolactin promoters are not sufficient for high level, stable expression even in normally permissive cells and suggest that Pit-1 alone is not sufficient for strong promoter activity from the integrated plasmids.
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Affiliation(s)
- P J Hippenmeyer
- G.D. Searle and Company, Research and Development, St. Louis, MO 63198, USA
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Wynne AG, Romanski SA, Klee GG, Ory SJ, O'Fallon WM, Fitzpatrick LA. Nifedipine, but not verapamil, acutely elevates parathyroid hormone levels in premenopausal women. Clin Endocrinol (Oxf) 1995; 42:9-15. [PMID: 7889637 DOI: 10.1111/j.1365-2265.1995.tb02592.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
BACKGROUND Calcium channel antagonist therapy in humans has been associated with changes in anterior pituitary, thyroid and adrenal hormone secretion. Human studies assessing effects of calcium channel antagonists on calciotropic hormones have been few and typically involved small numbers of subjects studied for short periods of time. Few of these previously published studies have included women. The endocrine effects of calcium channel antagonists in women have become increasingly important as more women are taking these agents for diseases such as hypertension, angina, Raynaud's phenomenon and migraine. OBJECTIVE To assess both acute and chronic effects of calcium channel antagonists on calciotropic hormones in women. DESIGN A four-week prospective, randomized trial. SUBJECTS Twenty-nine premenopausal women, randomly assigned to receive either 240 mg of sustained release verapamil or 30 mg of sustained release nifedipine daily. LABORATORY END-POINTS: Total and ionized serum calcium, phosphate, creatinine, parathyroid hormone (PTH), parathyroid hormone-related protein (PTHrP) and calcitonin, measured at baseline, after 24 hours, and 28 days of treatment. RESULTS Total and ionized calcium, phosphate, creatinine, PTHrP and calcitonin levels were not altered significantly after 24 hours or 28 days in any of the subjects, when compared to baseline. There were no significant differences in PTH levels after 24 hours or 28 days of verapamil treatment. There was a significant increase in serum PTH levels after 24 hours of nifedipine therapy; however, these differences were not evident after 28 days of therapy. CONCLUSIONS The short-term administration of nifedipine results in increased release of parathyroid hormone; however, long-term administration has no significant effect on the concentrations of calciotropic hormones.
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Affiliation(s)
- A G Wynne
- Department of Medicine, Mayo Clinic, Rochester, MN 55905
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Yan G, Chen X, Bancroft C. A constitutively active form of CREB can activate expression of the rat prolactin promoter in non-pituitary cells. Mol Cell Endocrinol 1994; 101:R25-30. [PMID: 9397971 DOI: 10.1016/0303-7207(94)90255-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The pituitary cell-specific transcription factor Pit-1 has been show to trans-activate expression of the prolactin (PRL) promoter in non-pituitary cells. However, the cyclic AMP response element (CRE)-binding protein CREB is known to play a major role in cell-specific expression of hepatocyte-specific genes. Since the PRL promoter contains an asymmetrical form of a cyclic AMP response element (termed the CLE), we investigated whether CREB could also induce PRL promoter activity in non-pituitary cells. Transient expression in rat glial C6 cells of a constitutively active CREB-VP16 fusion protein strongly trans-activated expression of a co-transfected rat PRL promoter construct, (-187)PRL-CAT. Analysis by 5'-deletion showed that this response requires PRL promoter sequences between positions -113/-75. CREB-VP16 did not stimulate expression in C6 cells of any of three control promoter-CAT constructs, implying that the strong response of the PRL promoter to activated CREB is both promoter-specific, and is not due to non-specific transcriptional effects of the potent VP16 moiety of CREB-VP16. Surprisingly, mutations in the CLE only slightly reduced activation by CREB-VP16 of construct (-204)PRL-CAT, implying that the major action of CREB-VP16 on the PRL promoter does not involve a direct interaction with the CLE. CREB-VP16 stimulated PRL-CAT activity in C6 cells as strongly as, and synergistically with, Pit-1. These results imply that CREB can strongly and specifically activate expression of the PRL promoter in non-pituitary cells, via a mechanism different from that employed by Pit-1.
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Affiliation(s)
- G Yan
- Department of Physiology and Biophysics, Mount Sinai School of Medicine, City University of New York, NY 10029, USA
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15
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Gourdji D, Laverrière JN. The rat prolactin gene: a target for tissue-specific and hormone-dependent transcription factors. Mol Cell Endocrinol 1994; 100:133-42. [PMID: 7914498 DOI: 10.1016/0303-7207(94)90292-5] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Affiliation(s)
- D Gourdji
- Groupe de Biologie de la Cellule Neuroendocrine, CNRS URA 1115, Collège de France, Paris
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16
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Lew A, Yao H, Elsholtz H. G(i) alpha 2- and G(o) alpha-mediated signaling in the Pit-1-dependent inhibition of the prolactin gene promoter. Control of transcription by dopamine D2 receptors. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)32674-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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17
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Tian J, Chen J, Bancroft C. Expression of constitutively active Gs alpha-subunits in GH3 pituitary cells stimulates prolactin promoter activity. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)42305-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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18
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Berwaer M, Peers B, Nalda AM, Monget P, Davis JR, Belayew A, Martial JA. Thyrotropin-releasing hormone and epidermal growth factor induce human prolactin expression via identical multiple cis elements. Mol Cell Endocrinol 1993; 92:1-7. [PMID: 8386115 DOI: 10.1016/0303-7207(93)90068-u] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Pituitary GH3 cells were transfected with different deletion mutants of the human prolactin (hPRL) promoter fused to the CAT reporter gene. The proximal region (-250 to -42) was sufficient to confer stimulation by both thyrotropin-releasing hormone (TRH) and epidermal growth factor (EGF). Further deletion analyses demonstrated the importance of the three proximal Pit-1 binding sites in this response. However, Pit-1 binding oligonucleotides confer neither TRH nor EGF induction to a linked neutral promoter, suggesting that other elements might be involved. We have previously shown that sequence A (-115 to -85) is needed together with Pit-1 binding sites for full cyclic AMP response of hPRL-CAT. Mutation of this sequence strongly affects TRH and EGF induction. On the other hand, three copies of sequence A confer both TRH and EGF response to a linked neutral promoter. In conclusion, although TRH and EGF activate mostly different intracellular pathways, they mediate transcriptional induction of the hPRL promoter via identical cis elements.
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Affiliation(s)
- M Berwaer
- Laboratorie de Biologie Moléculaire et de Génie Génétique, Université de Liège, Sart Tilman, Belgium
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19
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Huff C, Yuspa S, Rosenthal D. Identification of control elements 3' to the human keratin 1 gene that regulate cell type and differentiation-specific expression. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)54161-2] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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20
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Swennen D, Poncelet AC, Sekkali B, Rentier-Delrue F, Martial JA, Belayew A. Structure of the tilapia (Oreochromis mossambicus) prolactin I gene. DNA Cell Biol 1992; 11:673-84. [PMID: 1418624 DOI: 10.1089/dna.1992.11.673] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The tilapia (Oreochromis mossambicus) prolactin-I (PRL-I) gene has been cloned and sequenced. Its transcript (3,677 bases long) begins with a guanine and is organized in five exons and four introns like the other known prolactin genes. Analysis of the 1,555-bp 5'-flanking region suggests that pituitary-specific expression of the gene could be regulated through a trans-factor related to the mammalian pituitary-specific factor Pit-1. Two potential binding sites for such a factor were found in the first intron, suggesting a possible regulatory role for this region. Moreover, two potential Z-DNA regions are located at positions -837 to -812 and -246 to -179 from the transcription start site. These two regions could play an important role in the regulation of PRL gene expression.
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Affiliation(s)
- D Swennen
- Laboratoire de Biologie Moléculaire et de Génie Génétique, Université de Liège, Sart Tilman, Belgium
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21
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Elsholtz H, Lew A, Albert P, Sundmark V. Inhibitory control of prolactin and Pit-1 gene promoters by dopamine. Dual signaling pathways required for D2 receptor-regulated expression of the prolactin gene. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)54442-2] [Citation(s) in RCA: 70] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
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22
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Shull JD. Transcription of sequences upstream of the rat prolactin gene suggests the existence of a second promoter. Mol Cell Endocrinol 1991; 82:R17-23. [PMID: 1722177 DOI: 10.1016/0303-7207(91)90020-s] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The transcription of the rat prolactin gene domain has been examined using a modified Southern blot procedure. Cloned genomic DNAs were resolved by electrophoresis in agarose, transferred to nitrocellulose, and probed with radiolabeled RNA that had been synthesized in vitro by nuclei isolated from pituitary tumor cells. Data presented in this paper illustrate that single copy genomic sequences located within 7.3 kb upstream of exon 1 are transcribed. Single copy or low copy number DNA sequences that reside greater than 7.3 kb upstream of exon 1, or downstream of exon 5 were not transcribed at detectable levels. These data suggest that a second promoter may exist upstream of the rat prolactin gene and that this second promoter may be active in pituitary cells.
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Affiliation(s)
- J D Shull
- Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha 68198-6805
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23
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Wang FF, Mo FE, Yen YT, Fong JC. Potentiation of thyrotropin-releasing hormone-stimulated prolactin mRNA levels in GH3 cells by acetylcholine. Mol Cell Endocrinol 1991; 82:117-23. [PMID: 1761164 DOI: 10.1016/0303-7207(91)90015-k] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
We have examined the effect of acetylcholine (ACh) pretreatment on the thyrotropin-releasing hormone (TRH) induced prolactin gene expression in GH3 cells, a rat pituitary tumor cell line. Prolonged exposure (greater than 6 h) to ACh enhanced the TRH-induced prolactin mRNA accumulation in a time- and concentration-dependent manner while ACh by itself did not affect the basal prolactin mRNA levels appreciably. Maximal augmentation of the TRH-induced prolactin mRNA accumulation was obtained when cells were pretreated with 10(-5) M ACh for 24 h. The activation was mimicked by carbachol and oxotremorine and was blocked by the simultaneous presence of atropine. Preincubation of GH3 cells with pertussis toxin abolished the augmenting effect of ACh. These results indicate that prolonged exposure to muscarinic receptor agonists may enhance the TRH-stimulated prolactin mRNA expression and a pertussis toxin sensitive G-protein may be involved.
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Affiliation(s)
- F F Wang
- Institute of Biochemistry, National Yang-Ming Medical College, Taipei, Taiwan, R.O.C
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24
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Berwaer M, Monget P, Peers B, Mathy-Hartert M, Bellefroid E, Davis JR, Belayew A, Martial JA. Multihormonal regulation of the human prolactin gene expression from 5000 bp of its upstream sequence. Mol Cell Endocrinol 1991; 80:53-64. [PMID: 1955081 DOI: 10.1016/0303-7207(91)90142-f] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
We have cloned DNA sequences extending up to 6000 bp upstream from the first exon of the human prolactin (hPRL) gene. 5000 bp of these upstream sequences were fused to a CAT reporter gene and shown to provide tissue-specific transient expression in rat pituitary GH3 cells. Multihormonal response was found in this transient expression assay, leading to significant 2- to 5-fold induction by addition of 8-chlorophenylthio-cyclic AMP, thyrotropin-releasing hormone, epidermal growth factor, basic fibroblast growth factor, phorbol myristate acetate, a calcium channel agonist (Bay K-8644) and triiodothyronine. A 3-fold inhibition was observed in the presence of the glucocorticoid agonist dexamethasone. The sequence of the hPRL promoter was determined up to coordinate -3470. Computer similarity search between the rat and human sequences showed two highly conserved regions corresponding to the proximal and distal tissue specific enhancers described in both PRL promoters.
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Affiliation(s)
- M Berwaer
- Laboratoire de Biologie Moléculaire et de Génie Génétique, Université de Liège, Sart Tilman, Belgium
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25
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The alpha-adrenergic stimulation of atrial natriuretic factor expression in cardiac myocytes requires calcium influx, protein kinase C, and calmodulin-regulated pathways. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)98495-4] [Citation(s) in RCA: 85] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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26
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McChesney R, Sealfon SC, Tsutsumi M, Dong KW, Roberts JL, Bancroft C. Either isoform of the dopamine D2 receptor can mediate dopaminergic repression of the rat prolactin promoter. Mol Cell Endocrinol 1991; 79:R1-7. [PMID: 1834494 DOI: 10.1016/0303-7207(91)90110-e] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Hypophyseal portal dopamine is a major negative regulator of pituitary prolactin (PRL) production. Dopamine has been reported to repress PRL gene transcription in pituitary cells. To facilitate further study of the effect of dopamine on PRL gene activation, we introduced PRL promoter and D2 receptor (D2R) constructs into GH3 cells. Since two D2R isoforms (termed D2S and D2L) have been cloned previously, we first determined which isoform(s) is present in the lactotroph by measuring the level of each mRNA species in rat prolactinoma. mRNA for each D2R isoform was found to be present, with the D2L mRNA in great (c. 6-fold) excess. Because the lactotroph contains both isoforms, the effect of each on the PRL promoter was investigated. The cDNA for each receptor isoform was synthesized by polymerase chain reaction, and cloned into an RSV-based expression vector. GH3 cells were then transiently co-transfected with either of the resulting RSV-D2R constructs plus a PRL-chloramphenicol acetyltransferase (CAT) construct containing the first 1957 base-pairs of PRL gene 5'-flanking DNA. The cells were then incubated 48 h plus or minus the dopamine agonist ergocryptine (ECR). In the presence of either RSV-D2R isoform, ECR yielded a 4-5-fold decrease in CAT activity, an effect not seen in the absence of the RSV-D2R. The promoter specificity of this effect was demonstrated by the inability of ECR to regulate expression of a control RSV-CAT construct. The PRL promoter repression mediated by each receptor isoform had appropriate pharmacology: the specific D2R agonist, quinpirole, yielded results similar to ECR, and the ECR repression was reversed by the dopamine antagonist spiperone.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- R McChesney
- Department of Physiology and Biophysics, Mount Sinai School of Medicine, New York, NY 10029
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27
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Enyeart JJ, Biagi BA, Day RN, Sheu SS, Maurer RA. Blockade of low and high threshold Ca2+ channels by diphenylbutylpiperidine antipsychotics linked to inhibition of prolactin gene expression. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(17)46233-8] [Citation(s) in RCA: 32] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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28
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DiMattia GE, Gellersen B, Duckworth ML, Friesen HG. Human prolactin gene expression. The use of an alternative noncoding exon in decidua and the IM-9-P3 lymphoblast cell line. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(17)46238-7] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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29
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Abstract
Prolactin gene transcription is critically dependent upon intracellular calcium and the calcium-binding protein calmodulin. The effects of calcium and calmodulin on the prolactin gene appear to involve defined regions of the 5'-flanking sequence, and interactions between nuclear proteins and this DNA may be related to mechanisms of transcriptional control by pituitary cell-type-specific trans-acting factors.
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Affiliation(s)
- J R Davis
- Department of Medicine, University of Manchester, Manchester, UK
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30
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Pan WT, Liu QR, Bancroft C. Identification of a growth hormone gene promoter repressor element and its cognate double- and single-stranded DNA-binding proteins. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(19)39253-1] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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31
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Transcriptional and posttranscriptional regulation of the rat prolactin gene by calcium. Mol Cell Biol 1990. [PMID: 2300047 DOI: 10.1128/mcb.10.2.442] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The rat prolactin gene is expressed at a high basal level in the pituitary tumor GH3 cell line. Culturing GH3 cells in a low-Ca2+, serum-free medium (SFM) depresses prolactin mRNA levels, and subsequent addition of Ca2+ to the SFM results in a specific, gradual, and sustained increase in prolactin mRNA levels. We have now examined whether the observed increase in prolactin mRNA levels can be attributed solely to an increase in the transcriptional rate of the prolactin gene. Treatment of GH3 cells in SFM with 0.4 mM CaCl2 for 24 to 48 h increased cytoplasmic prolactin mRNA levels by 5- to 10-fold, whereas the transcriptional rate of the prolactin gene was increased by less than twofold over values for SFM controls. Prolactin mRNA levels increased progressively during the 24-h period after Ca2+ addition, whereas prolactin gene transcription never exceeded a twofold increase over values for SFM controls. The activities of nuclear extracts from control and Ca2(+)-induced cells were examined in an in vitro transcription assay. The two extracts directed transcription from the prolactin promoter and the adenovirus major late promoter equally well. Cycloheximide had no effect on the ability of Ca2+ to increase or maintain prolactin mRNA levels. In dactinomycin mRNA clearance experiments, prolactin mRNA was cleared at the same rate in the absence and presence of Ca2+. These results demonstrate that although Ca2+ has a small effect on the transcriptional rate of the prolactin gene, Ca2+ produces a significant increase in prolactin mRNA levels by acting at a posttranscriptional site(s). Furthermore, Ca(2+) appears to increase prolactin mRNA levels by posttranslational modification of a stable protein, probably at a nuclear site.
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32
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Jackson AE, Bandyopadhyay SK, Bancroft C. Epidermal growth factor and phorbol ester regulate prolactin gene expression via distinct pathways. Mol Cell Endocrinol 1990; 69:R7-11. [PMID: 2323487 DOI: 10.1016/0303-7207(90)90094-o] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Previous studies, involving phosphorylation of cytoplasmic proteins and localization of DNA regulatory elements, have suggested that epidermal growth factor (EGF) and 12-O-tetradecanoylphorbol-13-acetate (TPA) have similar actions on prolactin (PRL) gene expression by pituitary (GH) cells. However, little is presently known about whether the actions of these two factors involve common gene-distal intermediates. In the present study, we have employed two approaches to examine this question. Chronic exposure of GH3 cells to TPA, which strongly down-regulates protein kinase C activity, completely inhibited acute TPA stimulation of transient expression of a transfected PRL promoter construct ((-187)PRL-CAT), but did not inhibit EGF stimulation of either accumulation of endogenous PRL mRNA or of expression of (-187)PRL-CAT. Furthermore, the acute stimulatory effects of EGF and TPA on expression of (-187)PRL-CAT were additive. Each of these observations implies that EGF and TPA have gene-distal actions on PRL gene expression that are at least partially non-overlapping.
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Affiliation(s)
- A E Jackson
- Department of Physiology and Biophysics, Mount Sinai School of Medicine of City University of New York, NY 10029
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33
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Preston GM, Billis WM, White BA. Transcriptional and posttranscriptional regulation of the rat prolactin gene by calcium. Mol Cell Biol 1990; 10:442-8. [PMID: 2300047 PMCID: PMC360809 DOI: 10.1128/mcb.10.2.442-448.1990] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The rat prolactin gene is expressed at a high basal level in the pituitary tumor GH3 cell line. Culturing GH3 cells in a low-Ca2+, serum-free medium (SFM) depresses prolactin mRNA levels, and subsequent addition of Ca2+ to the SFM results in a specific, gradual, and sustained increase in prolactin mRNA levels. We have now examined whether the observed increase in prolactin mRNA levels can be attributed solely to an increase in the transcriptional rate of the prolactin gene. Treatment of GH3 cells in SFM with 0.4 mM CaCl2 for 24 to 48 h increased cytoplasmic prolactin mRNA levels by 5- to 10-fold, whereas the transcriptional rate of the prolactin gene was increased by less than twofold over values for SFM controls. Prolactin mRNA levels increased progressively during the 24-h period after Ca2+ addition, whereas prolactin gene transcription never exceeded a twofold increase over values for SFM controls. The activities of nuclear extracts from control and Ca2(+)-induced cells were examined in an in vitro transcription assay. The two extracts directed transcription from the prolactin promoter and the adenovirus major late promoter equally well. Cycloheximide had no effect on the ability of Ca2+ to increase or maintain prolactin mRNA levels. In dactinomycin mRNA clearance experiments, prolactin mRNA was cleared at the same rate in the absence and presence of Ca2+. These results demonstrate that although Ca2+ has a small effect on the transcriptional rate of the prolactin gene, Ca2+ produces a significant increase in prolactin mRNA levels by acting at a posttranscriptional site(s). Furthermore, Ca(2+) appears to increase prolactin mRNA levels by posttranslational modification of a stable protein, probably at a nuclear site.
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Affiliation(s)
- G M Preston
- Department of Anatomy, University of Connecticut Health Center, Farmington 06032
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34
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Ramsdell JS, Tashjian AH. GH4 pituitary cell variants selected as nonresponsive to thyrotropin-releasing hormone-enhanced substratum adhesion are nonresponsive to epidermal growth factor: evidence for a common signaling defect. J Cell Physiol 1989; 141:565-72. [PMID: 2480354 DOI: 10.1002/jcp.1041410315] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Thyrotropin-releasing hormone (TRH) and epidermal growth factor both enhance prolactin synthesis and substrate adhesion (a morphological change called stretching) of GH4 rat pituitary cells. We have examined TRH- and EGF-induced cell stretching using genetic and pharmacologic approaches. We selected and isolated a series of GH4 cell variants nonresponsive to TRH-induced cell stretching (str-). This selection yielded several variants that were nonresponsive to both TRH- and EGF-induced stretching but were still responsive to stretching induced by several other agents (tetradecanoylphorbol acetate [TPA], butyrate, and Neplanocin A). One of the str- variants (a14) was examined in detail. TRH, EGF, and TPA each enhanced prolactin synthesis in a14 cells, indicating that the a14 variant contained functional receptor binding sites for all 3 ligands as well as the capacity to generate those intracellular signals required for enhanced prolactin synthesis. Because the str- variants were isolated without selective pressure for EGF-induced stretching and because the possibility of more than one selectable mutation in all the variants is unlikely, we suggest that TRH and EGF share a common mechanism to induce cell stretching. We next examined whether the str- variants had a defect in a signaling pathway or in the biochemical endpoint for TRH- and EGF-induced cell stretching. A pharmacologic approach was utilized to investigate the biochemical basis for induced cell stretching. A synthetic Arg-Gly-Asp-Ser tetrapeptide (RGDS), specific for fibronectin and vitronectin adhesion receptors, inhibited TRH-, EGF-, and TPA-induced GH4 cell stretching and attachment to fibronectin- and vitronectin-coated dishes. These results suggest that the interaction between fibronectin and/or vitronectin and their receptor(s) may be a biochemical endpoint by which several agonists induced stretching of GH4 cells. Because the str- variant has RGDS-specific binding sites for fibronectin and vitronectin and responds to some agents that induce cell stretching via an RGDS receptor, we conclude that the a14 str- variant has a defect in an intracellular signaling pathway, shared by TRH and EGF, which induces cell stretching.
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Affiliation(s)
- J S Ramsdell
- Department of Anatomy and Cell Biology, Medical University of South Carolina, Charleston 29425
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35
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Bandyopadhyay SK, Bancroft C. Calcium Induction of the mRNAs for Prolactin and c-fos Is Independent of Protein Kinase C Activity. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(18)71665-7] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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36
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Davis JR, Belayew A, Sheppard MC. Prolactin and growth hormone. BAILLIERE'S CLINICAL ENDOCRINOLOGY AND METABOLISM 1988; 2:797-834. [PMID: 3077246 DOI: 10.1016/s0950-351x(88)80020-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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