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

ras Oncogenes play an important role in causing cellular transformation and proliferation. They have been implicated in the formation of many human tumors but only rarely been identified in pituitary adenomas. We studied the effect of ras activation on growth hormone (GH) production. Transcriptional regulation of human GH was investigated by transient transfections in a pituitary cell line GH4 using different promoter fragments cloned 5' of the luciferase reporter gene (-344 to -83). Co-transfection of the constitutively active valine 12 mutant ras oncogene (V-12 ras) resulted in a selective and dose-dependent stimulation of -344-GH/Luc activity. This effect is pituitary-cell specific as activation of the human GH promoter by ras was absent in a human chorion carcinoma cell line JEG3. Co-transfection of protein kinase inhibitor did not influence ras mediated stimulation of the human GH promoter. Investigations of several deletion constructs of the human GH promoter revealed that elements between - 145 and - 83 are sufficient to transduce ras signaling. This region contains two Pit-1 bindings sites as well as a Zn-15 binding site. These studies demonstrate transduction of ras signaling to the human GH promoter through a protein kinase A (PKA) independent signaling pathway. This separate transduction mechanism may convey regulation by yet unknown factors.
Mol Cell Endocrinol 1997 Apr 25
PMID:Transcriptional activation of the human growth hormone gene by ras oncogene. 917 28

The gene encoding the rat gonadotropin-releasing hormone (GnRH) receptor was isolated, and its structural organization and promoter region were characterized. The gene was found to consist of three exons that encode the receptor protein, and spanned about 20 kb. Of two genomic clones analyzed, one contained the 5'-untranslated region and the first exon, and the other contained the second and third exons. The sizes of the first, second, and third exons are 625, 217, and 1476 nt, respectively. The first intron is at least 12 kb in length and is located between nucleotides 522 and 523 of the cDNA reading frame, in the middle of the fourth transmembrane domain. The second intron is about 2.5 kb and is also located in the reading frame between nucleotides 739 and 740, separating the fifth and sixth transmembrane domains. Genomic blots in combination with cloning and sequencing suggested that a single GnRH receptor gene is present in the rat genome. Primer extension indicated that the transcription start site is located 103 nt upstream of the translational start codon. A putative TATA box is positioned 23 nt in front of the transcription initiation site. The 1.8 kb 5' flanking sequence contains an SF-1 site, an AP-1 site, CCAAT sequences, a Pit-1 binding site, and a potential CRE-like sequence. To evaluate promoter activity, the 1.8 kb and two 5' deleted fragments of 1.2 and 0.6 kb were fused to the luciferase reporter gene and transiently expressed in immortalized pituitary gonadotrophs (alphaT3-1 cells) and hypothalamic neurons (GT1-7 cells), and in nonpituitary (COS-7) cells. Luciferase gene expression was significantly increased by all three fragments in pituitary and hypothalamic cells, but not in COS-7 cells. The promoter activity of the 1.2 kb fragment was higher than that of the other fragments. Forskolin and cAMP analogs increased luciferase gene expression in both alphaT3-1 and GT1-7 cells, but activation of protein kinase C by phorbol myristate acetate had no effect. These studies indicate that positive and negative regulatory elements are present within the 1.8 kb 5' flanking sequence of the GnRH receptor. Knowledge of the genomic organization and analysis of the promoter region of the rat GnRH receptor gene will facilitate the elucidation of its transcriptional control in pituitary gonadotrophs and hypothalamic neurons.
Mol Cell Endocrinol 1997 Jun 20
PMID:Structural organization and characterization of the promoter region of the rat gonadotropin-releasing hormone receptor gene. 922 16

The heterotrimeric G protein Gs couples several surface ligand receptors to cAMP production, as well as to both growth hormone (GH) and prolactin (PRL) gene expression in pituitary and GH cells. It has been shown that constitutively active alpha s stimulates transient expression of both PRL- and GH- chloramphenicol acetyl transferase (CAT) constructions, which indicates that both the PRL and GH promoter regions are under the influence of signal pathways mediated by alpha s. We have previously shown that the cholesterol lowering drug lovastatin decreases both the amount of G alpha s subunit in the membrane and the adenylyl cyclase activity in GH4C1 cells. Thus, we tried to verify whether that decrease in alpha s levels could affect PRL and GH secretion, as well as the expression of PRL- and GH-CAT constructions. Since the regulation of these two genes is dependent on the pituitary specific transcription factor Pit-1, the effect of lovastatin on the expression of Pit-1-CAT constructions was also studied. Our results show that lovastatin decreased the basal expression of these three cAMP-responsive genes in GH4C1 cells, being partially reversed by the addition of mevalonate to the culture medium. This effect of lovastatin on the promoter activities of the transfected constructions was also observed in PRL and GH secretion to the medium, suggesting that this drug produces similar changes in the endogenous promoters of both hormones. Moreover, the presence of lovastatin did not prevent the response to the cAMP activator forskolin, indicating that the main effect of this drug could be exerted through upstream adenylyl cyclase. In conclusion, our data indicate that lovastatin decreases the basal expression of Pit-1 and consequently of both GH and PRL genes through a mechanism probably mediated by the decrease of G alpha s levels in the cell membrane. Taken together, these results suggest that the activity of membrane heterotrimeric G proteins regulates the basal transcription of specific cellular genes in GH4C1 cells. Moreover the effects of lovastatin may be taken into account in the study of constitutively endocrine disorders associated with an increased secretion of either PRL or GH.
Mol Cell Endocrinol 1997 Jun 20
PMID:Lovastatin decreases prolactin and growth hormone gene expression in GH4C1 cells through a cAMP dependent mechanism. 922 25

Pituitary-specific transcription of the evolutionarily related rat (r) GH and PRL genes involves synergistic interactions between Pit-1 and other promoter-binding factors including nuclear receptors. We show that Pit-1/thyroid hormone receptor (TR) and Pit-1/estrogen receptor (ER) synergistic activation of the rGH and rPRL promoters are globally similar. Both synergies depend upon the same activation functions in Pit-1 and also require activation function-2 conserved in TR and ER. The activation function-2 binding protein, RIP140, previously thought to be a nuclear receptor coactivator, strongly inhibits both Pit-1/TR and Pit-1/ER synergy. RIP140 inhibition is profoundly influenced, in a promoter-specific fashion, by a synergism-selective function in Pit-1: deletion of Pit-1 amino acids 72-100 switches RIP140 to an activator of Pit-1/ER and Pit-1/TR synergy at the rPRL promoter but not at the rGH promoter. Pit-1 amino acids 101-125 are required for RIP140 inhibition or activation again only at the rPRL promoter. Therefore, functions within one factor can determine the activity of a coactivator binding to its synergistic partner. This promoter context-specific synergistic interplay between transcription factors and coactivators is likely an essential determinant of cell-specific transcriptional regulation.
Mol Endocrinol 1997 Aug
PMID:Activities in Pit-1 determine whether receptor interacting protein 140 activates or inhibits Pit-1/nuclear receptor transcriptional synergy. 925 23

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.
Mol Cell Endocrinol 1997 Sep 19
PMID:Characterization of DNA regions mediating the ability of Ca2+/calmodulin dependent protein kinase II to stimulate prolactin promoter activity. 932 52

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.
Mol Cell Endocrinol 1994 May
PMID:A constitutively active form of CREB can activate expression of the rat prolactin promoter in non-pituitary cells. 939 71

Treatment of reaggregate pituitary cell cultures of 14-day-old female rats with nerve growth factor (NGF) augmented the number of [3H]thymidine ([3H]T)-incorporating lactotrophs in a dose-dependent manner (0.03-3 nM). At least during short-term treatment NGF increased the total number of cells expressing prolactin (PRL) mRNA and enlarged the cytoplasmic area occupied by PRL mRNA but did not affect the number of cells and the cytoplasmic area containing PRL, suggesting that NGF recruits lactotrophs expressing PRL mRNA but not yet PRL. NGF also stimulated [3H]T incorporation in ACTH cells but not in somatotrophs, thyrotrophs and gonadotrophs. In addition, NGF augmented the total number of [3H]T-incorporating cells to a much higher extent than was expected from its effect on lactotrophs and ACTH cells, suggesting NGF also stimulates [3H]T-incorporation in non-hormone producing cells (progenitors or stem cells?). Around 40% of these [3H]T-incorporating cells in both control and NGF treated cultures showed immunoreactivity for the transcription factor Pit-1 in the nuclei, which is twice the percentage expected (18%) if these [3H]T-incorporating cells were the only known Pit-1 expressing cells in the pituitary i.e. lactotrophs, somatotrophs and thyrotrophs. The present data suggest that NGF has a mitogenic effect on several cell lineages in the pituitary: lactotrophs, corticotrophs and non-hormone-containing cells. The high proportion of mitotic non-hormone containing cells that express Pit-1 is consistent with the proposed role of Pit-1 in cell proliferation in the developing lactosomatotroph lineage.
Mol Cell Endocrinol 1997 Nov 15
PMID:Mitogenic effects of nerve growth factor on different cell types in reaggregate cell cultures of immature rat pituitary. 942 55

Glucocorticoids have been shown to inhibit the activity of the human prolactin (hPRL) promoter. Using transient expression experiments in rat pituitary cells, we located the sequence conferring glucocorticoid inhibition to a region which contains Pit-1 binding sites, responsible for pituitary-specific expression, but does not seem to contain a glucocorticoid receptor (GR) binding site. Co-transfection experiments in non-pituitary cell lines, using expression vectors for Pit-1 and different mutants of the human GR show that inhibition of the hPRL gene is seen only in the presence of Pit-1 and GR, and that the DNA binding function of the receptor is not required. Immunoprecipitation studies show that either anti-GR or anti-Pit-1 antibodies are able to co-precipitate GR and Pit-1, suggesting an interaction between these factors. We conclude that the activated GR functionally interferes with the pituitary specific factor Pit-1, thereby leading to the observed transcriptional repression.
Mol Cell Endocrinol 1997 Nov 15
PMID:The glucocorticoid receptor inhibits the human prolactin gene expression by interference with Pit-1 activity. 942 56

Dopamine is present in the human placenta. The major function of dopamine is the inhibition of human placental lactogen (hPL) release from human trophoblastic cells. This effect is mediated by cAMP through dopamine D2 receptors. However, studies on the effects of cAMP in the control of hPL release have yielded conflicting results. The purpose of this study is to explore the distribution of dopamine receptors in the rat placenta. Dopamine D1 and D2 receptor mRNAs were colocalized in the rat placenta by in situ hybridization histochemistry using radiolabeled cRNA probes. Dopamine D1 and D2 receptor mRNAs were detected in large cells of the endometrium of the uterus on day 10 of gestation. On days 12-16 of gestation, hybridization signals were localized mainly in the spongiotrophoblast and giant cells of the junctional zone of the placenta. With the development of the placenta, signals were moving from the junctional zone to the labyrinth zone. Pit-1 mRNA was detected in the placental lactotrophs and was also colocalized in neighboring placental sections. Our results clearly showed that dopamine D1 and D2 receptor mRNAs were coexpressed in the placental lactotrophs that express Pit-1 mRNA.
Mol Cells 1997 Dec 31
PMID:Colocalization of dopamine D1 and D2 receptor mRNAs in rat placenta. 950 9

Pituitary-specific transcription factor Pit-1 regulates growth hormone and prolactin gene expression in the pituitary. Recently, Pit-1 was shown to be locally synthesized in the rat placenta and is involved in the regulation of rat placental lactogen (PL) gene expression. Pit-1 has three different splicing variants. They are well known as being biologically active. In the present study, we found that Pit-1 beta is also synthesized in the rat placenta and we tried to examine the effects of dopamine and estrogen on the regulation of Pit-1 alpha, beta and PL-II genes expression using the reverse transcription-polymerase chain reaction (RT-PCR) and Northern blot hybridization. A dopamine receptor agonist, bromocriptine, significantly decreased placental Pit-1 alpha, beta, and PL-II mRNA levels. To examine the effect of estrogen on the gene expression of Pit-1 beta, pregnant female rats were ovariectomized (OVX) and injected daily with 17 beta-estradiol. OVX markedly lowered the amount of Pit-1 beta mRNA. Estrogen injection recovered the OVX-induced inhibition of Pit-1 beta mRNA level. Finally, we investigated the site-specific transcription of Pit-1 alpha and beta mRNA in the labyrinth zone and junctional zone of the placental in 15 and 20 days of gestation. The main site of Pit-1 alpha and beta synthesis was shifted from the junctional zone to the labyrinth zone from 15 to 20 days of gestation. Together, these data presume that Pit-1 beta may play a more important role in the placenta than in the pituitary and that Pit-1 may be involved in the regulation of the PL and prolactin-like peptide by estrogen and dopamine in the rat placenta.
Mol Cells 1998 Apr 30
PMID:Effects of dopamine and estrogen on the regulation of Pit-1 alpha, Pit-1 beta, and PL-II gene expression in the rat placenta. 963 53


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