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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have examined the effects of the antiestrogen tamoxifen (TAM) and the estrogen 17 beta-estradiol (E2) on several estrogen-regulated responses in GH4C1 pituitary tumor cells. After 5 days of treatment with either TAM (1.0 microM) or E2 (1.0 nM), the level of PRL mRNA was markedly increased when measured by the cytosolic dot blot procedure. In contrast, only E2 was able to increase the levels of beta-actin mRNA and cytosolic protein, suggesting that this estrogen may stimulate cell proliferation over the course of treatment. This apparent difference in the abilities of TAM and E2 to stimulate GH4C1 cell proliferation was examined directly. TAM had no effect on cell proliferation as evidenced by its inability to increase cellular DNA or deoxythymidine triphosphate incorporation by nuclei isolated from treated cells. In contrast, E2 stimulated cell proliferation as evidenced by increases in cellular DNA and deoxythymidine triphosphate incorporation by isolated nuclei. The abilities of TAM and E2 to induce progesterone receptor (PR) and PR mRNA were also examined. TAM was unable to increase the levels of PR or PR mRNA, whereas E2 was effective in both of these regards. When added in combination with E2, TAM acted as a classical antiestrogen, partially blocking the induction of PR by E2. To determine whether the inabilities of TAM to stimulate cell proliferation and induce PR were a function of TAM concentration, dose-response experiments were performed. TAM at concentrations ranging from 10(-8)-10(-6) M was effective in inducing PRL mRNA, but at none of the tested concentrations was TAM effective in stimulating cell proliferation or inducing PR.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Endocrinol 1992 Apr
PMID:The estrogenic and antiestrogenic properties of tamoxifen in GH4C1 pituitary tumor cells are gene specific. 158 21

A prolactin-secreting cell line, SUP1, has been established from rat pituitary tumor 7315a. In radioligand binding experiments, the D2 receptor antagonist (S)-(-)-3-[125I]iodo-2-hydroxy-6-methoxy-N-[(1-ethyl-2- pyrrolidinyl)methyl]benzamide ([125I]IBZM) labeled a single class of sites in homogenates of SUP1 cells (Kd = 0.6 nM; Bmax = 45 fmol/mg of protein). The sites displayed a pharmacological profile consistent with that of D2 receptors. Inhibition of the binding of [125I]IBZM by dopamine was sensitive to GTP, suggesting that D2 receptors in SUP1 cells are coupled to guanine nucleotide-binding protein(s). In the presence of isobutylmethylxanthine, dopamine decreased the level of cAMP accumulation in SUP1 cells. Dopamine also inhibited prolactin secretion from SUP1 cells. Both the inhibition of cAMP accumulation and the inhibition of prolactin secretion were blocked by D2 receptor antagonists, suggesting that these effects of dopamine were mediated by an interaction with D2 receptors. The regulation of D2 receptors in SUP1 cells by D2 receptor agonists was investigated. Exposure of SUP1 cells to dopamine or to the D2 receptor agonist N-propylnorapomorphine led to increased expression of D2 receptors, with no change in the affinity of the receptors for [125I]IBZM. An increase in the density of D2 receptors in SUP1 cells was evident within 7 hr of exposure to dopamine. Spiroperidol, a D2 receptor antagonist, blocked the effect of dopamine on receptor density. These results suggest that exposure of D2 receptors in SUP1 cells to agonists leads to an up-regulation of D2 receptors. Dopamine retained the ability to inhibit cAMP accumulation in SUP1 cells exposed to dopamine for 24 hr, suggesting that D2 receptors in SUP1 cells are not desensitized by prolonged exposure to agonist. SUP1 cells should be a useful model system for future studies of the regulation of the expression and function of D2 receptors in cultured cells.
Mol Pharmacol 1991 Apr
PMID:Regulation of dopamine D2 receptors in a novel cell line (SUP1). 170 89

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.
Mol Cell Endocrinol 1991 Nov
PMID:Transcription of sequences upstream of the rat prolactin gene suggests the existence of a second promoter. 172 77

In a previous report we showed that TRH-induced down-regulation of the density of its receptors (TRH-Rs) on rat pituitary tumor (GH3) cells was preceded by a decrease in the activity of the mRNA for the TRH-R, as assayed in Xenopus oocytes. Here we report the effects of TRH, elevation of cytoplasmic free Ca2+ concentration, phorbol myristate acetate (PMA), and H-7 [1-(5-isoquinolinesulfonyl)2-methylpiperazine dihydrochloride], an inhibitor of protein kinases, on the levels of TRH-R mRNA, which were measured by Northern analysis and in nuclease protection assays using probes made from mouse pituitary TRH-R cDNA, in GH3 cells. These agents were studied to gain insight into the mechanism of the TRH effect, because signal transduction by TRH involves generation of inositol 1,4,5-trisphosphate and elevation of cytoplasmic free Ca2+ concentration, which leads to activation of Ca2+/calmodulin-dependent protein kinase, and of 1,2-diacylglycerol, which leads to activation of protein kinase-C. TRH (1 microM TRH, a maximally effective dose) caused a marked transient decrease in TRH-R mRNA that attained a nadir of 20-45% of control by 3-6 h, increased after 9 h, but was still below control levels after 24 h. Elevation of the cytoplasmic free Ca2+ concentration had no effect on TRH-R mRNA. A maximally effective dose of PMA (1 microM) caused decreases in TRH-R mRNA that were similar in magnitude and time course to those induced by 1 microM TRH. H-7 (20 microM) blocked the effects of TRH and PMA to lower TRH-R mRNA to similar extents.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Endocrinol 1991 Oct
PMID:Thyrotropin-releasing hormone (TRH) and phorbol myristate acetate decrease TRH receptor messenger RNA in rat pituitary GH3 cells: evidence that protein kinase-C mediates the TRH effect. 172 45

In the rat anterior pituitary gland, estrogen increases both prolactin (PRL) mRNA levels and stimulates the proliferation of PRL-producing cells. The temporal sequence of these events suggests that PRL gene expression may be coordinated with cell proliferation. We investigated the relationship between cell cycle progression and the accumulation of the PRL mRNA, as well as several other mRNAs, in the rat pituitary tumor GH3 cell line. Serum-deprived cells progressed from G0 to S phase in 20-24 h following serum stimulation. During this time, beta-actin mRNA levels increased 7-fold in 5 h, then returned to basal levels prior to the beginning of S phase. Histone H1 mRNA levels increased approximately 3-fold as cells entered S phase. These data are consistent with the cell cycle-dependent regulation of beta-actin and histone H1 gene expression reported for other cell types. Glucocorticoid receptor mRNA levels were barely detectable in serum-deprived cells but rapidly increased 3- to 5-fold following serum stimulation. This increase resulted in glucocorticoid receptor mRNA levels that were equivalent to those seen in cells maintained in serum-containing medium, suggesting that serum factors regulate glucocorticoid receptor gene expression. In contrast to these changes in gene expression, the levels of PRL and growth hormone (GH) mRNAs gradually increased 2-fold while the cells progressed through G1 phase. Similarly, in cells synchronized to progress through S and G2 phases following aphidicolin treatment, histone H1 gene expression showed a specific increase in S phase cells, whereas PRL and GH mRNA levels changed little with cell cycle progression. These results indicate that the levels of PRL and GH mRNAs are not regulated in a cell cycle-dependent manner. When changes in estrogen responsiveness were determined during the cell cycle, we found that estradiol treatment was capable of increasing PRL mRNA accumulation independent of cell cycle progression and cell cycle distribution in synchronized GH3 cells. These results support the hypothesis that the hormonal regulation of PRL gene expression is not significantly affected by cell growth.
Mol Cell Endocrinol 1991 Nov
PMID:Growth and cell cycle regulation of mRNA levels in GH3 cells. 176 Nov 63

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.
Mol Cell Endocrinol 1991 Nov
PMID:Potentiation of thyrotropin-releasing hormone-stimulated prolactin mRNA levels in GH3 cells by acetylcholine. 176 Nov 64

Transforming growth factor-beta (TGF beta) is a member of a large family of growth factors, several of which regulate pituitary function. TGF beta has recently been reported to reduce PRL production by GH4 cells. We have examined the effect of TGF beta on PRL gene expression in rat pituitary tumor GH3 cells. TGF beta 1 or TGF beta 2 reduced both basal and Ca(2+)-stimulated PRL mRNA levels. This inhibition was specific, as the mRNA levels for GH, glucose-regulated protein 78, and histone-3 were unaffected by TGF beta. Inhibition of PRL gene expression by TGF beta was dose dependent in the range of 0.5-10 ng/ml. TGF beta inhibited run-on PRL gene transcription in nuclei from treated cells to the same extent that it reduced PRL mRNA levels, indicating a transcriptional mechanism of action. However, TGF beta did not affect Pit-1 mRNA levels or run-on transcription of the Pit-1 gene. Thus, TGF beta does not appear to act through modification of Pit-1 gene expression. The PRL promotor contains two regions of homology, with a consensus sequence found in the promoters of other TGF beta-inhibited genes. These findings are consistent with other studies that have demonstrated transcriptional repression by TGF beta. The potency and specificity of the effects of TGF beta on PRL gene expression suggest that it may be a physiological regulator of lactotroph function.
Mol Endocrinol 1991 Nov
PMID:Inhibition of prolactin gene transcription by transforming growth factor-beta in GH3 cells. 177 73

Tamoxifen, nafoxidine, and clomiphene (1 x 10(-5) M) cause 5- to 15-fold increases in transient expression of plasmids transfected into rat somatomammotrophic pituitary tumor cell lines. To be effective, the antiestrogen must be present during the calcium phosphate transfection though it does not enhance the nuclear uptake or stability of transfected plasmid. The effect occurs with mammalian (rat growth hormone, mouse metallothionein I) or viral (thymidine kinase, Rous sarcoma virus) promoters and is inhibited by prior exposure of cells to high concentrations of estradiol but not glucocorticoid, progesterone or testosterone. Cis-tamoxifen, a conformation with much lower affinity for the estrogen receptor, has only one-fifth the effect of tamoxifen. Neither estradiol nor diethylstilbestrol have similar effects. Tamoxifen also increases endogenous rat growth hormone mRNA in these pituitary tumor cell lines. Transient expression in a number of other cell lines (JEG-3, COS-7, PC-12) is unaffected by tamoxifen suggesting the effect may be cell-type specific though MCF-7 cells are slightly responsive. The mechanism for the potent stimulation of gene transcription by these agents is not apparent but may be relevant to the mechanism of action of these agents as estrogen antagonists in vivo.
Mol Cell Endocrinol 1991 May
PMID:Antiestrogens stimulate expression of transiently transfected and endogenous genes in rat pituitary tumor cell lines. 181 97

Ultrastructural evidence is presented for the presence of membrane-bound glucocorticoid recognition and binding sites. Corticosterone was derivatized at 3 different positions and coupled covalently to bovine serum albumin (BSA). All three derivatives competed for binding of [3H]corticosterone by isolated rat hepatocytes. The most effective competitor, corticosterone-succinate-BSA (CSB), was adsorbed onto colloidal gold particles (CSB-gold, 17 +/- 3 nm dia). When isolated rat hepatocytes or mouse pituitary tumor cells (AtT 20) are incubated with CSB-gold, specific binding in the microvilli-rich region of these cells is seen. This binding of CSB-gold is reduced by about 50% in the presence of unlabelled CSB or corticosterone.
J Steroid Biochem Mol Biol 1991 Sep
PMID:Electron microscopic demonstration of glucocorticoid recognition sites on isolated rat hepatocytes. 191 20

Placental chorionic somatomammotropin (hCS-A or B) and growth hormone variant (hGH-V) are members of the human growth hormone family, and are related by structure and function to pituitary growth hormone (hGH-N). However, while the hGH-N gene is expressed specifically in the anterior pituitary, hGH-V and hCS are produced in the placenta. Hybrid hGH-N, hGH-V and hCS-A genes containing 5'-flanking sequences, including the endogenous promoter, are preferentially expressed in rat pituitary tumor (GC) cells, after gene transfer. Since interaction with a pituitary-specific protein (Pit 1) is required for efficient hGH-N as well as rat growth hormone (rGH) gene expression in GC cells, binding of pituitary proteins to the hGH-V and hCS-A promoter sequences was investigated. Rat Pit 1 binds at two locations on the hGH-N gene, a distal (-140/-107) and proximal site (-97/-66), in a similar manner to that observed with the rGH gene. By contrast, efficient Pit 1 binding was seen only to the distal site of the hGH-V gene and the proximal site of the hCS-A gene. Although binding of a protein to the distal hCS-A sequences was observed, the site of interaction was truncated (-140/-116), not pituitary-specific, and was more consistent with the binding of Sp1. These data indicate that rat Pit 1 binds to the placental hGH-V and hCS-A genes and correlates with their promoter activity in GC cells after gene transfer.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Cell Biochem 1991 Aug 14
PMID:Differential binding of rat pituitary-specific nuclear factors to the 5'-flanking region of pituitary and placental members of the human growth hormone gene family. 192 20


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