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)

E1a adenoviral oncoproteins have been known to modulate genes important for the growth and differentiation of cells. Our laboratory is interested in understanding how insulin promotes the growth and proliferation of cells. In this report, we have examined the ability of E1a to modulate the insulin receptor gene expression. In HepG2 cells, expression of the 243-amino acid E1a protein stimulated expression of the chloramphenicol acetyltransferase reporter under the control of the insulin receptor promoter. 5'-Deletion analysis of the insulin receptor promoter indicated that the region between -630 and -607 is important for regulation by E1a. This region contains two GA and four overlapping GC boxes that are putative Sp1-binding sites. A DNA fragment containing these sites was used as a probe in gel retardation assays. Three specific protein-DNA complexes were detected with HepG2 nuclear extract. These complexes could be competed partially by the DNA fragments with mutations in either the GA or GC boxes, but not by the DNA fragment with a mutation in both the GA and GC boxes. In addition, mutation of each of these sites lowered the basal activity of the promoter and partially reduced transactivation by E1a. Simultaneous mutation in both GA and GC boxes further reduced the basal activity and abrogated transactivation by E1a. Taken together, these results indicate that the loss of binding ability of Sp1 (or Sp1-like factors) is concomitant with reduction of the basal activity and the loss of E1a inducibility of the gene.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:E1a activation of insulin receptor gene expression is mediated by Sp1-binding sites. 777 68

Glucocorticoids have been shown to increase the levels of cell surface insulin receptors and their mRNA in many different cell types. Previously, we have reported that glucocorticoids induce the transcription of the human insulin receptor (hIR) gene in rat 208F cells and we also identified a putative glucocorticoid response element (GRE) to which the glucocorticoid receptor binds in a specific manner. In this study we have mapped four additional regions of the hIR promoter to which glucocorticoid receptor binds specifically; one residues at -1340 and the others are distributed within a 100 base pair region from -750 to -650. Within each DNase I footprinting region resides at least one putative GRE sequence. They function as GREs to confer glucocorticoid inducibility when fused to a heterologous promoter-chloramphenicol acetyltransferase reporter construct. The functional significance of these putative GREs was further substantiated by mutational analysis. Taken together, our results indicate that these GREs are capable of conferring glucocorticoid-dependent transcriptional induction similar to those observed in vivo. Therefore, the increase of hIR mRNA and insulin binding to surface receptor in response to glucocorticoids is likely mediated by enhancement of transcription. The functional redundancy of the GREs may reflect the biological mechanism which ensures the glucocorticoid regulation of the hIR gene at the transcriptional level.
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PMID:Multiple hormone response elements can confer glucocorticoid regulation on the human insulin receptor gene. 805 70

Expression of the very low density apolipoprotein II (apoVLDLII) gene in the chicken is absolutely dependent on estrogen. ApoVLDLII mRNA is expressed in the Leghorn male hepatoma (LMH) cell line in response to estrogen in completely defined medium. Addition of serum to these cultures results in a decrease in apoVLDLII mRNA. Data in this report demonstrate that 1 nM insulin has the same inhibitory effect as 10% serum. Insulin inhibits apoVLDLII mRNA in a dose-dependent manner; 100 fM insulin inhibits the estrogen-dependent response by 76%. After transfection of LMH cells with apoVLDLII sequences from an 8.9-kilobase (kb) genomic clone (pApo107) that contains the entire 2.9-kb coding sequence along with approximately 3 kb each of 5'- and 3'-flanking DNA, the estrogen-dependent expression of apoVLDLII mRNA from both the endogenous gene and transfected DNA is reduced by insulin. Furthermore, insulin reduces by more than 90% the estrogen-dependent expression from a chimeric construct, pApoCAT, which contains apoVLDLII sequences -900/+1455 cloned 5' of the bacterial chloramphenicol acetyltransferase (CAT) reporter gene. To determine the specificity of the response, expression of the pApoCAT construct was tested with insulin-like growth factor-I and insulin. Three hundred picomolar insulin inhibits the estrogen-mediated CAT activity by 50%. Insulin-like growth factor-I at this concentration has no effect or slightly increases the estrogen-dependent expression of pApoCAT, suggesting that the observed inhibitory action is mediated by the insulin receptor. Consequently, the LMH cells provide an excellent model system in which to study the molecular mechanism of insulin and estrogen interaction in the regulation of gene expression.
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PMID:Insulin inhibits the estrogen-dependent expression of the chicken very low density apolipoprotein II gene in Leghorn male hepatoma cells. 850 36

The hexokinases, by converting glucose to glucose 6-phosphate, help maintain the glucose concentration gradient that results in the movement of glucose into cells through the facilitative glucose transporters. Hexokinase II (HKII) is the major hexokinase isoform in skeletal muscle, heart, and adipose tissue. Insulin induces HKII gene transcription in L6 myotubes, and this, in turn, increases HKII mRNA and the rates of HKII protein synthesis and glucose phosphorylation in these cells. Inhibitors of distinct insulin signaling pathways were used to dissect the molecular mechanism by which HKII gene expression is induced by insulin in L6 myotubes. Treatment with wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PI 3-kinase), or with rapamycin, an inhibitor of the pathway from the insulin receptor to p70/p85 ribosomal S6 protein kinase (p70(s6k)), prevented the induction of HKII mRNA by insulin. In contrast, treatment with PD98059, an inhibitor of mitogen-activated protein kinase activation, had no effect on insulin-induced HKII mRNA. In addition, rapamycin blocked the insulin-induced expression of an HKII promoter-chloramphenicol acetyltransferase fusion gene transiently transfected into L6 myotubes, whereas PD98059 had no such effect. These results suggest that a phosphatidylinositol 3-kinase/p70(s6k)-dependent pathway is required for regulation of HKII gene transcription by insulin and that the Ras-mitogen-activated protein kinase-dependent pathway is probably not involved.
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PMID:Analysis of the signaling pathway involved in the regulation of hexokinase II gene transcription by insulin. 866 15

Insulin receptor substrate 1 (IRS-1) is one of the major substrates of insulin receptor tyrosine kinase and mediates multiple insulin signals downstream. We have previously shown that the levels of IRS-1 mRNA varied in different tissues. To elucidate the molecular mechanisms of the tissue specific regulation of IRS-1, we have studied the cis-acting elements and transacting factors in CHO and HepG2 cells. Using the chloramphenicol acetyltransferase (CAT) assay with the various deletion mutants of the IRS-1 promoter-CAT fusion plasmids, several regions responsible for positive or negative regulation in each cell line were identified. A region from -1645 to -1585 bp, which regulated expression negatively in CHO cells and positively in HepG2 cells, was further analyzed. Within this region a fragment from -1645 to -1605 bp upregulated the IRS-1 promoter only in HepG2 cells, whereas a fragment from -1605 to -1585 bp downregulated only in CHO cells. In the gel mobility shift assay, several nuclear proteins that bind to these fragments were detected, and among them, two nuclear proteins that bind to a potential E box (nucleotide [nt] -1635 to -1630) and two nuclear proteins that bind to a potential C/EBP binding site (nt -1599 to -1591) were identified in HepG2 and CHO cells, respectively. CAT assays using promoters mutated at the E box or at the C/EBP binding site revealed that these sequences were responsible for cell-specific regulation of the IRS-1 gene. We therefore concluded that the two nuclear proteins that bind to the E box regulate IRS-1 gene expression positively in HepG2 cells and the two nuclear proteins that bind to the C/EBP binding site regulate it negatively in CHO cells.
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PMID:Cell-specific regulation of IRS-1 gene expression: role of E box and C/EBP binding site in HepG2 cells and CHO cells. 903 89

A physiologically relevant response to insulin, stimulation of prolactin promoter activity in GH4 pituitary cells, was used as an assay to study the specificity of protein-tyrosine phosphatase function. Receptor-like protein-tyrosine phosphatase alpha (RPTPalpha) blocks the effect of insulin to increase prolactin gene expression but potentiates the effects of epidermal growth factor and cAMP on prolactin promoter activity. RPTPalpha was the only protein-tyrosine phosphatase tested that did this. Thus, the effect of RPTPalpha on prolactin-chloramphenicol acetyltransferase (CAT) promoter activity is specific by two criteria. A number of potential RPTPalpha targets were ruled out by finding (a) that they are not affected or (b) that they are not on the pathway to insulin-increased prolactin-CAT activity. The negative effect of RPTPalpha on insulin activation of the prolactin promoter is not due to reduced phosphorylation or kinase activity of the insulin receptor or to reduced phosphorylation of insulin receptor substrate-1 or Shc. Inhibitor studies suggest that insulin-increased prolactin gene expression is mediated by a Ras-like GTPase but is not mitogen-activated protein kinase dependent. Experiments with inhibitors of phosphatidylinositol 3-kinase suggest that insulin-increased prolactin-CAT expression is phosphatidylinositol 3-kinase-independent. These results suggest that RPTPalpha may be a physiological regulator of insulin action.
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PMID:Receptor-like protein-tyrosine phosphatase alpha specifically inhibits insulin-increased prolactin gene expression. 946 45

Transcriptional regulation of ATP citrate-lyase (ACL, one of the lipogenic enzymes) gene by glucose/insulin, polyunsaturated fatty acid (PUFA), and leptin has been investigated in hepatocytes and adipocytes of obese Wistar fatty rats and their lean littermates. The sequence spanning nucleotides -64 to -41 of the ACL gene, which is responsive to glucose/insulin stimulation [Eur. J. Biochem. 247, 497-502, 1997], was linked to a reporter gene and transfected into rat hepatocytes or adipocytes. The chloramphenicol acetyltransferase (CAT) activities in the presence of glucose alone were similar in primary cultured cells from both obese and lean rats. In the presence of glucose/insulin, however, the CAT activities were markedly increased in the hepatocytes of lean rats, but were not significantly increased in those of obese rats. The stimulation by glucose/insulin was reduced in PUFA-treated cells of lean rats. The stimulation was also reduced in leptin-treated cells or ob gene expression vector-containing cells. However, PUFA- or leptin-treated cells from obese rats did not show a significant reduction in insulin stimulation. The same effects were observed at the endogenous mRNA and enzyme levels. Similar results were seen in adipocytes, although the stimulation and suppression levels were much smaller than in hepatocytes. The expression of endogenous insulin receptor in hepatocytes and adipocytes was reduced in the presence of leptin or PUFA. We previously found that insulin-binding capacities are also reduced in the presence of leptin or PUFA and are very low in obese rats in comparison with lean. Moreover, gel mobility shift assays using end-labeled ACL(-64/-41) revealed that nuclear factor(s) including Sp1 bind specifically to the sequence, and DNA-protein complex formation is reduced in the obese rats. Thus, the reductions in the insulin-stimulated ACL transcription may be ascribed in part to reductions in insulin binding to receptors and DNA-protein complex formation.
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PMID:Regulation of ATP citrate-lyase gene expression in hepatocytes and adipocytes in normal and genetically obese rats. 1042 41

In the present study, we have examined the insulin-signaling pathways involved in myogenesis in mouse C2C12 skeletal muscle cell line, a cellular system that expresses high number of high affinity insulin receptors. Insulin (50 nM) rapidly (5 min) stimulated beta-chain insulin receptor, activated the phosphatidylinositol (PI) 3-kinase/Akt/p70S6-kinase signaling pathway, as well as phosphorylated both p44/p42- and p38-mitogen-activated protein kinases (MAPKs). Preconfluent cells were differentiated in a serum-free medium in response to 50 nM insulin for 72 h, as revealed by the formation of multinucleated myotubes and the induction of the creatine kinase activity. This differentiation process was also monitored by the inhibition of the PCNA content and induction of the cell cycle inhibitor p21. Furthermore, insulin induced nuclear factor-kappaB (NF-kappaB) DNA binding activity and down-regulated activating protein-1 (AP-1) DNA binding activity throughout the differentiation process. The use of specific inhibitors of the insulin-signaling pathways indicated that myogenesis was precluded by treatment for 72 h with LY294002 (an inhibitor of PI 3-kinase), rapamycin (a p70S6-kinase blocker), and SB203580 or PD169316 (p38-MAPK inhibitors). These inhibitors abolished insulin induction of NF-kappaB DNA binding activity and kappaB-chloramphenicol acetyltransferase (CAT) promoter activity, maintaining expressed cytosolic IkappaB-alpha protein, and increased AP-1 DNA binding activity and TRE-CAT promoter activity. These data suggest that insulin induces myogenesis in C2C12 through PI 3-kinase/ p70S6-kinase and p38-MAPK pathways, the signaling through p44/p42-MAPK being inhibited.
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PMID:Insulin produces myogenesis in C2C12 myoblasts by induction of NF-kappaB and downregulation of AP-1 activities. 1114 17

Two Chinese hamster ovary (CHO) cell lines stably transfected with human insulin receptor cDNA, CHO-wt and CHO-mut, which express an equivalent number of normal and kinase-defective human insulin receptors, respectively, were used to assess the roles of insulin receptor tyrosine kinase activity in insulin-regulated gene expression. The effect of insulin on gene-33-promoter-driven chloramphenicol acetyltransferase (CAT), RSVLTR-driven beta-galactosidase (pRSVLTR-betagal) and SV40 late-promoter-driven hepatitis B surface antigen (pMLSV(2)HBsAg) were examined in CHO-wt and CHO-mut cells. Insulin-stimulated gene 33 promoter is 10- to 50-fold more effective in CHO-wt cells than that in parental CHO cells. However, no enhancement of insulin sensitivity of gene 33 promoter in CHO-mut cells relative to parental CHO cells was found. Similar phenomena were also observed, in that insulin regulated pRSVLTR-betagal and pMLSV(2)HBsAg in these three CHO lines. Our data indicated that the protein kinase activity of the insulin receptor is essential for the stimulatory activity of insulin toward the activities of different promoters. Copyright 1994 S. Karger AG, Basel
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PMID:Protein Kinase Activity of the Insulin Receptor Is Essential for Insulin-Regulated Gene Expression. 1172


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