Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.3.1.28 (chloramphenicol acetyltransferase)
5,100 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Insulin-mediated regulation of glucocorticoid-induced expression of the liver-specific gene tyrosine aminotransferase was studied in a clone of the Reuber rat hepatoma cells. Insulin inhibited dexamethasone-induced chloramphenicol acetyltransferase expression from approximately 4 kb of TAT 5' flanking sequence. The degree of this inhibition was comparable to the response of the endogenous gene. A construct of approximately 3 kbp of 5' flanking sequence exhibited no significant basal expression but retained sensitivity to glucocorticoids and to insulin inhibition of the glucocorticoid response. Results of further analysis of the insulin response in deletion constructs and constructs containing glucocorticoid responsive elements ligated to a heterologous promoter suggest that in addition to the glucocorticoid response elements a region close to the start site in the TAT promoter is necessary for insulin to inhibit glucocorticoid-mediated induction of expression.
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PMID:Insulin-mediated inhibition of the induction of tyrosine aminotransferase by dexamethasone. 135 29

Several endocrine hormones which influence liver metabolism are known to increase in activity during the acute phase of injury or inflammation. We determined whether these hormones have the potential to influence acute-phase protein production in human and rat hepatoma cells. Catecholamines, glucagon, growth hormone, triiodothyronine, and cyclic nucleotides individually or in combination did not modulate the basal or the interleukin-1 (IL-1)-, IL-6-, and dexamethasone-stimulated levels of acute-phase plasma proteins. Insulin, however, was found to be a rapid, nonspecific, and dose-dependent inhibitor of the cytokine and glucocorticoid stimulation of acute-phase protein gene expression and to exert its effect at the transcriptional level. The insulin inhibition applied to all cytokines tested but to various degrees, depending upon the particular acute-phase gene. Insulin resulted in an early and prominent increase in the transcription of genes encoding the AP-1 components of JunA, JunB, and c-Fos, as has been observed for other growth factors. However, the effect of insulin on C/EBP beta was unexpected and paradoxical: while insulin completely inhibited the transcriptional activation of the C/EBP beta gene in cytokine- and dexamethasone-treated cells, the level of cytoplasmic C/EBP beta RNA was elevated. Quantitation of C/EBP beta mRNA by Northern (RNA) blot analysis and of C/EBP beta DNA binding activity by Southwestern (DNA-protein) blot analysis showed that insulin, when combined with cytokines and dexamethasone, stimulated both the mRNA and DNA binding activity by a factor of 1.6 compared with that of cells treated with cytokines and dexamethasone alone. Transient transfection of H-35 and HepG2 cells with a chloramphenicol acetyltransferase (CAT) gene expression vector containing the C/EBP beta response element also resulted in a 1.5-fold increase of C/EBP beta-mediated transcription in insulin-treated cells. Transfection of CAT gene constructs containing increasing lengths of heptaglobin gene 5' flanking sequences indicated that insulin inhibition of IL-6 stimulation required the presence of the region from -4100 to -1030. These results suggest that insulin has the potential to control the transcription of acute-phase genes by at least two separate mechanisms.
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PMID:Insulin is a prominent modulator of the cytokine-stimulated expression of acute-phase plasma protein genes. 137 89

An insulin response element (IRE) has been identified in the prolactin gene using chimeric plasmids in which prolactin promoter DNA directs expression of the bacterial chloramphenicol acetyltransferase gene. A series of 5'-deletion constructs starting between positions -173 and -106 and extending through position +75 of the prolactin gene were all stimulated greater than 10-fold by physiological concentrations of insulin in rat pituitary tumor GH4 cells. However, insulin did not stimulate constructs starting at positions -96 and -46, suggesting that the IRE of the prolactin gene may be located in region -106/-96. Insulin stimulation of prolactin-chloramphenicol acetyltransferase constructs requires cotransfection with a human insulin receptor expression vector. Estimation of insulin receptor levels by beta-subunit phosphorylation indicates that receptor levels are increased approximately 50-fold following transfection with the human insulin receptor expression vector. This requirement for cotransfection suggests that the endogenous receptor levels may not be adequate to couple the response of transfected genes to insulin. Gel mobility shift experiments reveal a nuclear factor from GH4 cells that specifically associates with prolactin DNA fragment -106/-87. The amount or binding activity of this factor is increased following insulin treatment of cells. The concordance between functional and binding analyses of the prolactin promoter confirms the presence of an IRE in region -106/-87. The insulin-sensitive DNA-binding factor may mediate effects of insulin on prolactin gene transcription.
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PMID:An element in the prolactin promoter mediates the stimulatory effect of insulin on transcription of the prolactin gene. 164 45

Phosphoenolpyruvate carboxykinase (PEPCK) governs the rate-limiting step in gluconeogenesis. Glucocorticoids and cAMP increase PEPCK gene transcription and gluconeogenesis, whereas insulin and phorbol esters have the opposite effect. Insulin and phorbol esters are dominant, since they prevent cAMP and glucocorticoid-stimulated transcription. Basal promoter elements and hormone response elements for cAMP, glucocorticoids, and insulin have been defined in previous studies. By using stable transfectants containing a variety of different PEPCK-chloramphenicol acetyltransferase fusion gene constructs, a phorbol ester response sequence, located between positions -437 and -402 relative to the transcription start site, was identified. This region coincides with the insulin response sequence that has recently been defined in the PEPCK promoter. Using a vector containing various wild-type and mutated sequences of this region ligated to the heterologous thymidine kinase promoter, we delineated the boundaries of both elements to the 10 base pairs between positions -416 through -407. Thus, although it has been previously shown that insulin and phorbol esters repress PEPCK gene transcription through distinct pathways, the final target of insulin and phorbol ester action is the same DNA element.
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PMID:Signal transduction convergence: phorbol esters and insulin inhibit phosphoenolpyruvate carboxykinase gene transcription through the same 10-base-pair sequence. 165 Apr 76

Insulin induces a rapid activation of p21ras in NIH 3T3 and Chinese hamster ovary cells that overexpress the insulin receptor. Previously, we suggested that p21ras may mediate insulin-induced gene expression. To test such a function of p21ras more directly, we studied the effect of different dominant inhibitory mutants of p21ras on the induction of gene expression in response to insulin. We transfected a collagenase promoter-chloramphenicol acetyltransferase (CAT) gene or a fos promoter-luciferase gene into NIH 3T3 cells that overexpressed the insulin receptor. The activities of both promoters were strongly induced after treatment with insulin. This induction could be suppressed by cotransfection of two inhibitory mutant ras genes, H-ras(Asn-17) or H-ras(Leu-61,Ser-186). In particular, insulin-induced activation of the fos promoter was inhibited completely by H-ras(Asn-17). These results show that p21ras functions as an intermediate in the insulin signal transduction route leading to the induction of gene expression.
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PMID:Two dominant inhibitory mutants of p21ras interfere with insulin-induced gene expression. 165 21

Insulin-like growth factor binding protein-3 (IGFBP-3) can modulate the mitogenic and metabolic effects of the insulin-like growth factors (IGFs). IGFBP-3 protein levels are developmentally regulated and influenced by a number of hormonal stimuli both in vitro and in vivo. As a first step toward understanding how hormonal and developmental factors regulate IGFBP-3 production, we are characterizing the human IGFBP-3 chromosomal gene and promoter. Southern analysis demonstrates a single copy of the IGFBP-3 gene in the human genome. This gene spans 8.9 kilobases; the protein-coding region is divided into four exons while a fifth exon contains the 3'-untranslated region. Primer extension studies locate the IGFBP-3 mRNA cap site 132 base pairs 5' to the ATG translation initiation codon. On the chromosomal gene, this cap site is located 30 base pairs 3' to the start of a TATA box and 97 base pairs 3' to a consensus GC upstream promoter element, an organization common to many eukaryotic promoters. When this potential IGFBP-3 promoter region is placed upstream to the chloramphenicol acetyltransferase reporter gene, it directs high-level production of chloramphenicol acetyltransferase in transfected COS-1 cells. These observations suggest an uncomplicated organization for the IGFBP-3 chromosomal gene and promoter in the human genome.
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PMID:Insulin-like growth factor binding protein-3. Organization of the human chromosomal gene and demonstration of promoter activity. 169 33

Insulin rapidly lowers serum insulin-like growth factor-binding protein-1 (IGFBP-1) levels in vivo. In studies reported here, HEP G2 cells were used as a model system to investigate how insulin achieves this effect. When HEP G2 cells were incubated with 100 nM insulin for 6, 14, or 24 h, IGFBP-1 protein levels in conditioned medium fell to approximately 50% of control values. This apparently was due to a fall in the rate of IGFBP-1 protein synthesis, since HEP G2 cells incorporated 46% less [35S]methionine into IGFBP-1 during a 4-h incubation with 100 nM insulin. IGFBP-1 mRNA levels were similarly affected by 100 nM insulin, falling to 45% of control values after 2 h, and to 9% of control values after 4 h of incubation with this hormone. The fall in IGFBP-1 mRNA level is consistent with data from nuclear transcription assays. HEP G2 nuclei isolated from cells that were incubated with 100 nM insulin for 2 h synthesized only approximately 1/3 the number of IGFBP-1 transcripts as did control nuclei. Further evidence that insulin decreases IGFBP-1 gene transcription comes from transient transfections using chimeric IGFBP-1 promoter-chloramphenicol acetyltransferase reporter gene constructs. IGFBP-1 promoter activity fell to approximately 50% of control values when HEP G2 cells transfected with a construct containing the first 1205 base pairs of the IGFBP-1 promoter were incubated with 100 nM insulin for 6, 14, or 24 h. Insulin lowered both IGFBP-1 protein levels and promoter activity in a dose-dependent manner. A half-maximal effect was found at approximately 1 nM insulin and a maximal effect was found at approximately 10 nM insulin in each instance. Transfections with constructs containing smaller IGFBP-1 promoter fragments showed that the region spanning from 103 to 529 base pairs 5' to the IGFBP-1 mRNA cap site was necessary to demonstrate the inhibitory effect of insulin. These studies indicate that insulin lowers IGFBP-1 protein levels, at least in part, by rapidly decreasing the rate of IGFBP-1 gene transcription, and suggest that this insulin-mediated fall in transcription is conferred through a specific region of the IGFBP-1 promoter.
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PMID:Insulin inhibits transcription of the human gene for insulin-like growth factor-binding protein-1. 171 56

Numerous physiological agents and conditions modulate cellular insulin sensitivity by downregulating or upregulating total cellular insulin receptors. In this study, we examined the effects of replacing complete medium in the absence or presence of insulin on the regulation of insulin-receptor gene expression in cultured human hepatoma cells (HepG2). Failure to replace complete medium resulted in growth arrest of HepG2 cells and a six- to sevenfold increase in insulin-receptor mRNA due to the prolongation of insulin-receptor mRNA half-life. Northern analysis revealed multiple insulin-receptor mRNA species; the largest species (11 kilobases) was disproportionately increased in growth-arrested cells. High concentrations of insulin (500 ng/ml) induced a 33.8% decrease in the abundance of insulin-receptor mRNA (n = 14). At lower concentrations, a trend of inhibition was observed but was not statistically significant. Insulin (500 ng/ml) did not affect insulin-receptor mRNA stability. The effect of conditioned media, insulin, and dexamethasone on insulin-receptor promoter activity was also examined. Various constructs of the 5'-flanking region of the insulin-receptor gene were attached immediately upstream to a chloramphenicol acetyltransferase (CAT) reporter gene and transiently transfected into HepG2 cells via a pBR322-derived plasmid (pCAT). In cells replaced with complete medium, 12 and 118% of the promoter activity was contained within 578 and 877 base pairs, respectively, from the major translational initiation site. Conditioned media from growth-arrested cells in culture for 7 days increased promoter activity approximately twofold in 48 h. However, this increase failed to localize to any specific region on the insulin-receptor promoter.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effects of media conditions, insulin, and dexamethasone on insulin-receptor mRNA and promoter activity in HepG2 cells. 184 49

Insulin-producing cells and fibroblasts were fused to produce hybrid lines. In hybrids derived from both hamster and rat insulinoma cells, no insulin mRNA could be detected in any of seven lines examined by Northern (RNA) analysis despite the presence in each line of the insulin genes of both parental cells. Hybrid cells were transfected with recombinant chloramphenicol acetyltransferase plasmids containing defined segments of the rat insulin I gene 5' flank. We observed no transcriptional activity of the intact insulin enhancer or of IEB2, a critical cis-acting element of the insulin enhancer. IEB2 has previously been shown to interact in vitro with IEF1, a DNA-binding activity observed selectively in insulin-producing cells. Hybrid cells showed no detectable IEF1 activity. Furthermore, the insulin enhancer was unable to reduce transcription directed by the Moloney sarcoma virus enhancer in a double-enhancer construct. Thus, extinction of insulin gene expression in the hybrids apparently does not operate through a direct action of repressors on the insulin enhancer; rather, extinction is accompanied by, and may be caused by, reduced DNA-binding activity of the putative transcriptional activator IEF1.
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PMID:Extinction of insulin gene expression in hybrids between beta cells and fibroblasts is accompanied by loss of the putative beta-cell-specific transcription factor IEF1. 199 8

Insulin regulates cell function by first binding to the insulin receptor (IR) localized on the cell surface. With the cloning of IR cDNA and the IR-gene promoter, the regulation of the IR gene during differentiation and by various hormones can be studied. Muscle is a major target tissue for insulin action. BC3H1 cells, a mouse muscle cell line in culture, are a model cell type for studying insulin action. Differentiation in these cells results in a 5- to 10-fold increase in IR binding and a 5- to 10-fold increase in IR content. Studies of IR mRNA by Northern and slot-blot analyses reveal a 10-fold increase in IR mRNA after differentiation. These studies indicate that there is a selective increase in IR-gene expression during muscle differentiation. A similar increase in IR-gene expression is observed for the IR during pancreatic acinar cell differentiation. Glucocorticoids increase IR content in several target tissues. Studies in cultured IM-9 lymphocytes indicate that glucocorticoids induce a 5-fold increase in IR mRNA levels. Studies of IR mRNA half-life indicate that glucocorticoids do not alter IR mRNA stability. When the transcription of the IR is measured by elongation assays, glucocorticoids directly stimulate IR transcription 5- to 10-fold. The effect is detectable within 30 min of glucocorticoid treatment and is maximal within 2 h. Therefore, these studies demonstrate that the IR gene is under the direct regulation of glucocorticoids. Insulin downregulates the IR in various target tissues. Prior studies indicate that this downregulation was partly because of accelerated IR degradation. Studying AR42J pancreatic acinar cells, we also found that insulin accelerates IR degradation. Moreover, in these cells, insulin decreases IR biosynthesis by approximately 50%. Studies of IR mRNA indicate there is a concomitant decrease in IR mRNA levels after insulin treatment. Thus, insulin decreases IR-gene expression. The genomic structure of the IR promoter has been elucidated. Primer extension and nuclease S1 analysis indicate that IR mRNA has multiple start sites. The promoter fragment was ligated to a promoterless "reporter" plasmid containing the bacterial gene chloramphenicol acetyltransferase (CAT). When this plasmid is transfected into cultured cells, CAT activity is detected, indicating promoter activity. Various portions of a genomic fragment were ligated to a promoter to study glucocorticoid regulation of the IR promoter. These studies indicate that IR-gene expression is regulated by differentiation and hormonal agents.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Regulating insulin-receptor-gene expression by differentiation and hormones. 240 79


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