Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P61278 (somatostatin)
 22,083 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In this report, we describe the isolation and initial characterization of a Drosophila protein, dCREB-A, that can bind the somatostatin cyclic AMP (cAMP)-responsive element and is capable of activating transcription in cell culture. Sequence analysis demonstrates that this protein is a member of the leucine zipper family of transcription factors. dCREB-A is unusual in that it contains six hydrophobic residue iterations in the zipper domain rather than the four or five commonly found in this group of proteins. The DNA-binding domain is more closely related to mammalian CREB than to the AP-1 factors in both sequence homology and specificity of cAMP-responsive element binding. In embryos, dCREB-A is expressed in the developing salivary gland. A more complex pattern of expression is detected in the adult; transcripts are found in the brain and optic lobe cell bodies, salivary gland, and midgut epithelial cells of the cardia. In females, dCREB-A is expressed in the ovarian columnar follicle cells, and in males, dCREB-A RNA is seen in the seminal vesicle, ejaculatory duct, and ejaculatory bulb. These results suggest that the dCREB-A transcription factor may be involved in fertility and neurological functions.
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PMID:A cyclic AMP-responsive element-binding transcriptional activator in Drosophila melanogaster, dCREB-A, is a member of the leucine zipper family. 150 8

We have established mutant SaOS-2 cell lines that express a cyclic AMP (cAMP)-resistant phenotype to investigate the regulation and functional importance of orthophosphoric-monoester phosphohydrolase alkaline optimum (ALPase) in the action of parathyroid hormone (PTH). Cells were stably transfected with a plasmid that directs the synthesis of a mutant form of the type I regulatory subunit of protein kinase A (PKA) under the control of the metallothionein promotor. There was no significant difference between parental SaOS-2 cells and the mutant lines in the affinity or number of receptors for 125I-Nle8,18Tyr34bPTH1-34NH2, either in the absence or presence of Zn2+. When cAMP-dependent gene transcription was examined using transient transfection with a somatostatin promoter-chloramphenicol acetyl transferase (CAT) reporter plasmid, CAT activity stimulated by human PTH and dibutyryl cAMP (DBcAMP) was inhibited by greater than 90% in the presence of Zn2+ in the mutant cell lines. In contrast, activation by a phorbol ester of a pentameric collagenase promoter/CAT construct containing five tandem copies of the AP-1 response element (5x-TRE-CAT) was unaffected in Zn(2+)-treated mutant cells. The inhibitory actions of PTH and DBcAMP on ALPase release were blunted by up to 80-90% in the mutant cell lines in the presence of Zn2+; there were no significant differences in the magnitude of inhibitory effects between these agonists. We conclude that the inhibitory action of PTH on ALPase release in SaOS-2 cells is mediated via activation of PKA. These cAMP-resistant cell lines will be especially useful in elucidating signal transduction mechanism(s) for PTH in human osteoblastic cells.
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PMID:Protein kinase A-dependent inhibition of alkaline phosphatase release by SaOS-2 human osteoblastic cells: studies in new mutant cell lines that express a cyclic AMP-resistant phenotype. 166 91

By screening a lambda gt11 library with the multimerized sequence of the cAMP response element (CRE), we isolated human clones encoding the CRE binding protein, CRE-BP1, from a human brain cDNA library. CRE-BP1 expressed in Escherichia coli bound not only to the CRE element of the somatostatin and fibronectin genes, but also to the CRE element of the adenovirus E4 gene, suggesting that the protein was not distinguishable from the adenovirus transcription factor, ATF. The human CRE-BP1 clone encoded a 54.5 kd protein similar at its carboxy terminus to the leucine zipper motifs found in other enhancer binding proteins such as C/EBP and c-jun/AP-1. CRE-BP1 mRNA was expressed in all of the cells examined and was abundant in brain. The structure of CRE-BP1 and its recognition elements suggest that cellular response to extracellular stimuli is controlled by a family of transcription factors that bind to related cis-active elements and that contain several highly conserved domains.
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PMID:Leucine zipper structure of the protein CRE-BP1 binding to the cyclic AMP response element in brain. 252 17

We have reported previously that the widespread inhibitory actions of somatostatin might be mediated by its ability to inhibit the expression of the immediate early genes c-fos and c-jun. The products of these genes form a heterodimeric transcription factor complex [activator protein 1 (AP-1)], which is known to be induced by treatment with phorbol esters. In the present study, we sought to investigate the mechanisms by which somatostatin inhibits immediate early gene expression. For our experiments, we used a rat pituitary adenoma cell line (GH3), which is known to express multiple subclasses of somatostatin receptors. The phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) stimulated both AP-1 binding and transcriptional activity in GH3 cells and the somatostatin analogue octreotide inhibited this response by 40-70%. In the presence of two different phosphatase inhibitors, sodium orthovanadate or okadaic acid, the ability of somatostatin to inhibit AP-1 binding and transcriptional activity was abolished. This effect of octreotide, which appears to be mediated by the SSTR2 and SSTR5 subtypes of somatostatin receptors, was paralleled by its ability to inhibit TPA-stimulated GH3 cell proliferation. Pretreatment of the GH3 cells with pertussis toxin (200 ng/ml) reversed the inhibitory effect of octreotide on both AP-1 function and cellular proliferation. Our observations lead us to conclude that somatostatin not only inhibits immediate early gene expression but also inhibits AP-1 binding and transcriptional activity via the action of several classes of protein phosphatases. This effect, which is pertussis toxin sensitive, might be one mechanism by which somatostatin inhibits cellular proliferation.
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PMID:Somatostatin inhibits AP-1 function via multiple protein phosphatases. 763 95

The X gene product encoded by the hepatitis B virus, termed pX, is a promiscuous transactivator of a variety of viral and cellular genes under the control of diverse cis-acting elements. Although pX does not appear to directly bind DNA, pX-responsive elements include the NF-kappa B, AP-1, and CRE (cAMP response element) sites. Direct protein-protein interactions occur between viral pX and the CRE-binding transcription factors CREB and ATF. Here we examine the mechanism of the protein-protein interactions occurring between CREB and pX by using recombinant proteins and in vitro DNA-binding assays. We demonstrate that pX interacts with the basic region-leucine zipper domain of CREB but not with the DNA-binding domain of the yeast transactivator protein Gal4. The interaction between CREB and pX increases the affinity of CREB for the CRE site by an order of magnitude, although pX does not alter the rate of CREB dimerization. Methylation interference footprinting reveals differences between the CREB DNA and CREB-pX DNA complexes. These experiments demonstrate that pX titers the way CREB interacts with the CRE DNA and suggest that the basic, DNA-binding region of CREB is the target of pX. Transfection assays in PC12 cells with the CREB-dependent somatostatin promoter demonstrate a nearly 15-fold transcriptional induction after forskolin stimulation in the presence of pX. These results support the significance of the CREB-pX protein-protein interactions in vivo.
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PMID:The hepatitis B virus X protein targets the basic region-leucine zipper domain of CREB. 773 90

The mechanisms by which somatostatin exerts its widespread inhibitory actions have been investigated extensively but understood only partially. Recent studies have shown that somatostatin can inhibit gene transcription directly. In view of the critical importance of early response genes in induction of gene expression, we examined whether the action of somatostatin might be mediated by inhibition of early response genes. The products of some of these genes, such as c-fos and c-jun, are known to form a heterodimeric transcription factor complex (AP-1) that binds specifically to the consensus sequence TGAC(G)TCA. Accordingly, we examined the effects of somatostatin on c-fos gene expression and on the binding of the AP-1 complex to its specific DNA element using isolated gastric parietal cells and the GH3 pituitary cell line. In both parietal and GH3 cells, c-fos-specific mRNA was increased by agents known to act via both adenosine-3',5'-cyclic monophosphate and Ca(2+)-dependent signaling mechanisms, and octreotide significantly inhibited this response. Pertussis toxin pretreatment (200 ng/ml) reversed the inhibitory effect of octreotide. AP-1 binding activity, assessed by gel shift assays using a 32P-labeled AP-1 oligonucleotide probe, was stimulated by dibutyryl adenosine 3',5'-cyclic monophosphate and serum and inhibited by octreotide treatment. Our observations support the notion that the universal inhibitory action of somatostatin may be mediated by inhibition of expression of early response genes via a pertussis toxin-sensitive inhibitory pathway. This effect appears to lead to decreased binding of regulatory nuclear proteins to their specific DNA elements resulting, presumably, in diminished gene expression.
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PMID:Molecular basis for somatostatin action: inhibition of c-fos expression and AP-1 binding. 791 96

The gene encoding the mouse somatostatin receptor subtype 5 has been isolated from a genomic library and the mRNA start point mapped to position -95 relative to the translational start codon. The promoter region is devoid of TATA and CAAT boxes but contains putative binding sites for AP-1, AP-2 and SP1 and response elements for glucocorticoids (GRE) and phorbol esters (TRE). The encoded receptor protein with a predicted molecular weight of 42.5 kDa is comprised of 385 amino acids and thus contains 22 and 21 amino acids more than rat and human counterparts. The extra amino acids are caused by another translational initiation codon located further upstream. In the region of overlap the mouse somatostatin receptor subtype 5 displays 96.7% sequence identity to the rat and 81.7% to the human homologue. Application of somatostatin-14 and -28 to human embryonic kidney cells expressing the recombinant receptor resulted in the inhibition of forskolin-stimulated adenylyl cyclase with comparable EC50 values. Consistent with the observed sequence relationship, the mouse somatostatin receptor subtype 5 displays a pharmacological profile that resembles the rat homologue more closely than the human counterpart. mRNA for the mouse somatostatin type 5 receptor has been detected in pituitary, kidney, spleen and ovary and, to a lesser extent, in brain, stomach, intestine and thymus but was not observed in heart, pancreas and liver.
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PMID:Cloning, expression, pharmacology and tissue distribution of the mouse somatostatin receptor subtype 5. 963 Mar 98

Phosphorylation of transcription factors fos/jun dimer activator protein (AP)-1 and nuclear factor-kappaB (NF-kappaB) plays a cardinal role in vascular smooth muscle cell (SMC) response to growth stimuli. Activity of protein tyrosine (PTP) and serine/threonine phosphatases (PP2A, B, and C) regulates in balance with the activity of protein kinases the level of transcription factor phosphorylation. Somatostatin analog octreotide stimulates phosphatase activity and inhibits cell growth. We examined in rats the activity of tissue phosphatases after arterial wall injury and treatment with octreotide and its effect on AP-1 and NF-kappaB phosphorylation and arterial response to injury. The activity of PTP did not change after balloon injury. Treatment of rats with PTP stimulator octreotide increased the PTP activity by 20% +/- 18% in uninjured arteries (p = 0.04 compared with control) and by 49% +/- 44% compared with injured untreated rats (p = 0.017). Treatment of rats with okadaic acid, a specific phosphatase inhibitor, prevented the octreotide-induced increase in PTP activity. PP2A activity of uninjured arteries was not affected significantly with treatment with octreotide (105% +/- 21%, p = 0.57 compared with control). After balloon injury PP2A activity was significantly reduced, 54% +/- 24% of control (p = 0.001). This reduction was prevented with treatment with octreotide, activity 88% +/- 25% of control. When rats were treated with octreotide and okadaic acid, the activity of PP2A in uninjured arteries was decreased to 65% +/- 12% of control (p = 0.03) and the injury-induced reduction was preserved, activity 54% +/- 8% of control (p = 0.001). There was no change in PP2B and C activity after balloon injury. Increased phosphatase activity with octreotide was associated with stabilization of the unphosphorylated form and reduction in nuclear binding of AP-1 and NF-kappaB and was associated with reduced SMC proliferation after balloon injury. Inhibition of increased phosphatase activity with okadaic acid was associated with increased nuclear binding of AP-1 and NF-kappaB. Increased nuclear binding of AP-1 and NF-kappaB after injury was associated with increased expression of fos, jun, and p105 subunit mRNA and restored the proliferative response of SMC after balloon injury. We conclude that the activity of PP2A is decreased after arterial balloon injury which leads to increased AP-1 and NF-kappaB phosphorylation and nuclear binding and is involved in regulation of SMC proliferation. Treatment with octreotide prevented the injury-induced reduction in PP2A activity and decreased transcription factor phosphorylation and SMC proliferation. Modification of phosphatase activity is a potential regulatory mechanism of arterial wall response to injury.
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PMID:Phosphatase activity in the arterial wall after balloon injury: effect of somatostatin analog octreotide. 1046 31

The transcription factor CHOP (C/EBP homologous protein 10) is a bZIP protein induced by a variety of stimuli that evoke cellular stress responses and has been shown to arrest cell growth and to promote programmed cell death. CHOP cannot form homodimers but forms stable heterodimers with the C/EBP family of activating transcription factors. Although initially characterized as a dominant negative inhibitor of C/EBPs in the activation of gene transcription, CHOP-C/EBP can activate certain target genes. Here we show that CHOP interacts with members of the immediate-early response, growth-promoting AP-1 transcription factor family, JunD, c-Jun, and c-Fos, to activate promoter elements in the somatostatin, JunD, and collagenase genes. The leucine zipper dimerization domain is required for interactions with AP-1 proteins and transactivation of transcription. Analyses by electrophoretic mobility shift assays and by an in vivo mammalian two-hybrid system for protein-protein interactions indicate that CHOP interacts with AP-1 proteins inside cells and suggest that it is recruited to the AP-1 complex by a tethering mechanism rather than by direct binding of DNA. Thus, CHOP not only is a negative or a positive regulator of C/EBP target genes but also, when tethered to AP-1 factors, can activate AP-1 target genes. These findings establish the existence of a new mechanism by which CHOP regulates gene expression when cells are exposed to cellular stress.
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PMID:CHOP enhancement of gene transcription by interactions with Jun/Fos AP-1 complex proteins. 1052 47

Recent advances in the molecular biology has served to unveil the underlying genetic and epigenetic alterations in pituitary adenomas. Three nuclear transcriptional factors, AP-1, CREB, and Pit-1, which are targets of protein kinase C and A, appear to play critical roles in both neoplastic growth and hormone secretion in hormone-producing adenomas. The alteration of G proteins such as Gs and Gi2 is a direct cause of the activation of such transcriptional factors. Autocrine growth factor/cytokine loops also contribute to the augmented signal transductions. Bromocriptine and somatostatin analogs have effects to lower cellular cAMP level through inhibitory G proteins, although the mechanism leading to cellular apoptosis is unknown. On the other hand, most non-functioning adenomas may not have PKC- or PKA-mediated oncogenic mechanisms. Although the loss of Rb and p27Kip1 genes has been demonstrated as a cause of murine pituitary adenomas, the role of tumor suppressor genes for human pituitary adenomas remains elusive. However, potential candidates for the suppressor genes are now emerging. The recently cloned multiple endocrine neoplasia type I gene is one example. Alterations of c-myc/bcl-2, and ras, although rare, appear to be an important cause of the process by which adenoma cells acquire aggressive phenotypes. Further studies on the links between abnormal signal transductions and aberrant tumor suppressor genes will be needed to clarify the whole picture of pituitary oncogenesis.
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PMID:Molecular basis of pituitary oncogenesis. 1072 13


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