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:2.7.7.6 (RNA polymerase)
34,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Pancreatic beta-cell-type-specific expression of the insulin gene requires both ubiquitous and cell-enriched activators, which are organized within the enhancer region into a network of protein-protein and protein-DNA interactions to promote transcriptional synergy. Protein-protein-mediated communication between DNA-bound activators and the RNA polymerase II transcriptional machinery is inhibited by the adenovirus E1A protein as a result of E1A's binding to the p300 coactivator. E1A disrupts signaling between the non-DNA-binding p300 protein and the basic helix-loop-helix DNA-binding factors of insulin's E-element activator (i.e., the islet-enriched BETA2 and generally distributed E47 proteins), as well as a distinct but unidentified enhancer factor. In the present report, we show that E1A binding to p300 prevents activation by insulin's beta-cell-enriched PDX-1 activator. p300 interacts directly with the N-terminal region of the PDX-1 homeodomain protein, which contains conserved amino acid sequences essential for activation. The unique combination of PDX-1, BETA2, E47, and p300 was shown to promote synergistic activation from a transfected insulin enhancer-driven reporter construct in non-beta cells, a process inhibited by E1A. In addition, E1A inhibited the level of PDX-1 and BETA2 complex formation in beta cells. These results indicate that E1A inhibits insulin gene transcription by preventing communication between the p300 coactivator and key DNA-bound activators, like PDX-1 and BETA2:E47.
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PMID:Insulin gene transcription is mediated by interactions between the p300 coactivator and PDX-1, BETA2, and E47. 1175 38

The adipocyte hormone, leptin, acts via the central nervous system to modulate glucose metabolism by skeletal muscle, but the direct effects of leptin on glucose metabolism by skeletal muscle are unclear. In this study, we have examined effects of leptin on glucose uptake by cultured L6 muscle cells assessed with the non-metabolised glucose analogue 2-deoxy-D-glucose. Reverse-transcriptase polymerase chain reaction (RT-PCR) analysis of RNA showed that L6 muscle cells express a short isoform of the leptin receptor (ObRa), but not the long isoform (ObRb). In the absence of added insulin, incubation of L6 muscle cells with murine leptin (10( -11)-10( -8) M) for 10 min and 1 h increased glucose uptake by 15 % - 23 %. This effect of leptin was lost by 4 h. Leptin (10( -10) - 10( -9) M) initially (after 10 min) suppressed insulin-stimulated glucose uptake by 14 - 16 %, but had no effect in the longer term. Leptin-stimulated glucose uptake was inhibited by the phosphatidylinositol 3-kinase (PI3K) inhibitor wortmannin, but not by the janus kinase-2 (JAK-2) inhibitor tyrphostin AG490. The results suggest that leptin can act directly on L6 muscle cellsvia a short leptin receptor isoform to acutely stimulate basal (but not insulin-stimulated) glucose uptake via a PI3K-dependent pathway.
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PMID:Acute stimulation of glucose uptake by leptin in l6 muscle cells. 1197 98

Cell therapy may have the potential for the treatment of Type I diabetes. To date, cells suitable for this purpose have not been developed. This study investigates the feasibility of modifying Vero, a cell line that may be considered safe to implant into humans, for this purpose. Stable Vero transfectants containing full-length human preproinsulin complementary deoxyribonucleic acid (cDNA) were generated using a liposomal transfection reagent. Reverse transcriptase-polymerase chain reaction, immunocytochemistry, Western blotting, and enzyme-linked immunosorbent assays were used to assess the resulting cells. Proinsulin was expressed but was not processed to insulin by these cells. Proinsulin cDNA was genetically modified, resulting in a form that is furin sensitive. The resulting stably transfected Vero clones constitutively release approximately 34%/h (32.68 +/- 2.21 to 35.62 +/- 3.14%) of the product formed, approximately 62% (59.99 +/- 6.45 to 64.64 +/- 4.57%) of which is mature insulin. These Vero transfectants did not exhibit glucose-stimulated insulin secretion. As GLUT2 and glucokinase (GCK) are not constitutively expressed by these cells, human GLUT2 cDNA and GCK cDNA were cotransfected with furin-sensitive preproinsulin cDNA into Vero cells. Insulin and GCK proteins were detected in the cytoplasmic region of the resulting cells, whereas GLUT2 was predominantly expressed in the nucleus. Coexpression of GLUT2 and GCK did not result in glucose-stimulated insulin secretion. The results from this study demonstrate the feasibility of engineering a relatively "safe" nonbeta cell line to produce human insulin. Coexpression of GLUT2 and GCK, at the levels achieved here, is not adequate enough to induce glucose-stimulated insulin secretion in such cells; the subcellular location of transfected components may be relevant.
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PMID:Engineering Vero cells to secrete human insulin. 1202 63

Hormones regulate glucose homeostasis, in part, by controlling the expression of gluconeogenic enzymes, such as phosphoenolpyruvate carboxykinase (PEPCK). Insulin and glucocorticoids reciprocally regulate PEPCK expression primarily at the level of gene transcription. We demonstrate here that glucocorticoids promote, whereas insulin disrupts, the association of CREB-binding protein (CBP) and RNA polymerase II with the hepatic PEPCK gene promoter in vivo. We also show that accessory factors, such as CCAAT/enhancer-binding protein beta (C/EBP beta), can recruit CBP to drive transcription. Insulin increases protein levels of liver-enriched transcriptional inhibitory protein (LIP), an inhibitory form of C/EBP beta, in a phosphatidylinositol 3-kinase-dependent manner. LIP concomitantly replaces liver-enriched transcriptional activator protein on the PEPCK gene promoter, which can abrogate the recruitment of CBP and polymerase II, culminating in the repression of PEPCK expression and the attenuation of hepatocellular glucose production.
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PMID:Insulin inhibits hepatocellular glucose production by utilizing liver-enriched transcriptional inhibitory protein to disrupt the association of CREB-binding protein and RNA polymerase II with the phosphoenolpyruvate carboxykinase gene promoter. 1207 Jan 72

The insulin receptor substrate-1 (IRS-1) is one of the major substrates of both the insulin and IGF-I receptors and is generally localized in the cytosol/membrane fraction of the cell. We show here that a substantial fraction of IRS-1 is translocated to the nucleus in mouse embryo fibroblasts (MEF) expressing the simian virus 40 T antigen. Nuclear translocation of IRS-1 occurs also in MEF stimulated with IGF-I or in MEF expressing the oncogene v-src. Nuclear translocation of IRS-1 can be demonstrated by confocal microscopy, immunohistochemistry, or subcellular fractionation. An antibody to IRS-1 immunoprecipitates from nuclear fractions (but not from cytosolic fractions) the upstream binding factor, which is a key regulator of RNA polymerase I activity and ribosomal RNA (rRNA) synthesis. In agreement with this finding, in 32D murine hemopoietic cells, nuclear translocation of IRS-1 correlates with a markedly increased rRNA synthesis. Our experiments suggest that nuclear IRS-1 may play a specialized role in rRNA synthesis and/or processing.
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PMID:Nuclear translocation of insulin receptor substrate-1 by oncogenes and Igf-I. Effect on ribosomal RNA synthesis. 1220 93

We investigated the effect of a chronic exposure to high levels of free fatty acid (FFA; 2 mmol/L oleate/palmitate 2:1) or glucose (16.7 mmol/L) on islet cell apoptosis. Apoptosis was detected using 4 different methods: (1) cell staining with annexin-V fluorescien isothiocyanate (FITC) conjugate and propidium iodide (PI); (2) quantification of cytoplasmatic DNA fragments by an enzyme-linked immunosorbent assay (ELISA); (3) assay of caspase 3 activity; and (4) TdT-mediated dUTP nick-end labeling (TUNEL). Islet cells were also costained with an anti-insulin antibody to identify apoptotic beta cells. We also evaluated by reverse-transcriptase polymerase chain reaction (RT-PCR) the expression of bax, bcl-2, and caspas 3, genes involved in apoptosis. In islets cultured for 7 days in the presence of high FFA or for 3 days in the presence of high glucose levels, we observed: (1) a 2- to 3-fold increase of apoptotic cells conjugated with annexin-V FITC and PI; (2) a 4- to 6-fold increase of cytoplasmatic DNA fragments; (3) a 3- to 4-fold increase of caspase 3 activity; and (4) a significant increase of insulin positive apoptotic cells as detected with the TUNEL method. RT-PCR analysis indicated in islets exposed to high FFA or glucose levels an increase of bax (proapoptotic gene), a reduction of bcl-2 (antiapoptotic gene), and a slight (although not significant) increase in caspase 3 expression. Western blot analysis also showed an increase of Bax protein levels in islets exposed to high FFA or glucose. The simultaneous presence of both metabolic abnormalities did not further increase the amount of apoptotic cells, although the time-course of the cellular damage induced by FFA was accelerated by the contemporary presence of high glucose. To elucidate the mechanism by which FFA and glucose may induce pancreatic beta-cell damage, we examined whether nicotinamide prevents apoptosis in pancreatic islets cultured for 7 days with high FFA or for 3 days with high glucose. Nicotinamide was able to prevent beta-cell damage by significantly reducing apoptosis in both experimental conditions. Also, the increase of Bax protein level was prevented by nicotinamide. These data indicate that chronic exposure to elevated FFA or glucose levels increases apoptosis in rat pancreatic islets and these cytotoxic effects could be mediated by oxidative stress. This may contribute to the beta-cell failure that occurs in most in type 2 diabetic patients few years after clinical diabetes onset.
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PMID:Chronic exposure to free fatty acids or high glucose induces apoptosis in rat pancreatic islets: possible role of oxidative stress. 1237 Aug 56

One approach to target the long-term metabolic toxicity and disfiguring body-shape changes associated with antiretroviral therapy is to switch one component of a regimen to an alternative drug, usually from a different class of antiretrovirals. Most commonly, substitutions have involved protease inhibitors, but the thymidine analogue nucleosides, especially stavudine, have been investigated more recently. Certain trends from these studies have emerged. First, if the patient has had sustained viral suppression, switching therapy is generally virologically safe. Second, metabolic disturbances, such as insulin resistance and dyslipidemia, appear to be at least partially reversible. Substitution of other agents for protease inhibitors has not been associated with reversal or improvement in fat redistribution. Studies in which thymidine analogue reverse-transcriptase inhibitors have been switched have reported modest improvements in peripheral lipoatrophy. Larger, controlled, long-term studies and a more standardized approach to definition of metabolic and morphological abnormalities are needed.
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PMID:Switching effective antiretroviral therapy: a review. 1268 30

Thirty-two normal LEW/Sea rats were transplanted a piece of syngeneic pancreas between the peritoneum and abdominal muscle. Among them, 17 (68%) of the 25 rats that received pancreatic transplantation at 41-50 days of age had a surviving beta-cell mass at 5.5-7.1 months after transplantation. Among the 25 rats, 12 rats injected with interleukin-1 receptor (IL-1R) and IL-2Rbeta peptides at post-transplantation showed better surviving grafts at 5.5 months' observation. Only 2 (25%) of the other 7 young rats that received a pancreatic graft at 20 days of age had a small mass at 21 days post-transplantation. Flow cytometer (FCM) analyses showed that thymus OX40(+) (CD134(+)) T-cells were increased up to 37+/-4% at the graft rejection in the 13 old rats without the IL-R peptide injections. The 7 young rats had 99% of thymus OX40(+) T-cells. However, the 12 old rats injected with the IL-R peptides showed suppressed numbers of thymus OX40(+) T-cells (8-13+/-3%). The long-term surviving, but apoptotic, grafted beta-cells were stained positively both with anti-insulin monoclonal antibody (mAb) and with anti-c-erbB-2/human epidermal growth factor receptor (HER)-2/neu mAb. Expression of a c-erb family oncogene was shown on the pancreatic graft surviving for 7.1 months. Electron microscopic analysis of the grafted beta-cells showed abnormally large beta granules and loss of functioning mitochondria in the cytoplasm. In 18 (56%) of the 32 rats, the 220-bp and 380-bp specific products of insulin-degrading enzyme (IDE) gene were amplified using the polymerase chain reaction (PCR) of the liver DNA. Among the 18 rats, 6 rats expressed 2 extra hands of 280-bp and 700-bp in a correlation with the high levels of the transforming growth factor-alpha (TGF-alpha) cDNA of 120-bp which was amplified in the quantitative reverse-transcriptase (RT)-PCR of the liver cDNA. Among the selected 11 rats, 5 rats showed large amounts of the 120-bp TGF-alpha cDNA. Host pancreatic RT-PCR showed 235-bp or 250-bp bcl-2 and 181-bp bcl-xS gene products. The bcl-2 cDNA of the host pancreas was amplified actively when the pancreatic graft was being rejected. Exceptionally, the one female injected with the IL-R peptides showed a low level of the liver TGF-alpha cDNA together with the pancreatic expressions of Bax (140-bp), bcl-2 and like interleukin converting enzyme (LICE) (318-bp) cDNA. Insulin secretion from the grafted beta-cells and IL-1beta-induced Fas-mediated apoptosis of the beta-cells were suspected to be present at the same time in the female with the best graft survival.
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PMID:Oncogene expression on the syngeneic beta-cells of long-term surviving pancreatic grafts and better effects of interleukin-1 receptor (IL-1R) and IL-2Rbeta on the grafted beta-cells in LEW/Sea strain rats. 1272 75

Conjugated linoleic acid (CLA) has chemoprotective properties in a variety of experimental cancer models. We have previously observed that dietary CLA inhibits colon tumorigenesis induced by 1,2-dimethylhydrazine in rats. In addition, our in vitro studies have shown that CLA inhibits DNA synthesis and induces apoptosis in HT-29 cells, the human colon adenocarcinoma cell line. The insulin-like growth factor (IGF) system regulates the growth of HT-29 cells by an autocrine mechanism. The present study examined whether the growth inhibitory effect of CLA is related to changes in the IGF system in HT-29 cells. To determine whether CLA inhibits IGF-II production, HT-29 cells were incubated in serum-free medium in the presence of various concentrations of CLA. CLA decreased protein levels of both mature and pro IGF-II and IGF-II transcripts. Whereas exogenous IGF-I and IGF-II produced an increase in cell number, neither IGF-I nor IGF-II counteracted the negative growth regulatory effect of CLA. Reverse transcriptase-polymerase chain reaction and Western blot analysis of total cell lysates revealed that CLA decreased IGF-I receptor (IGF-IR) transcript and protein levels in a dose-dependent manner. Immunoprecipitation/Western blot studies revealed that CLA inhibited IGF-I-induced phosphorylation of IGF-IR and insulin-receptor substrate (IRS)-1, recruitment of the p85 regulatory subunit of phosphatidylinositol 3-kinase (PI3K) to IGF-IR, IGF-IR-associated PI3K activity, and phosphorylated Akt and extracellular signal-regulated kinase (ERK)-1/2 levels. In conclusion, the inhibition of cell proliferation and induction of apoptosis by CLA in HT-29 cells may be mediated in part by its ability to decrease IGF-II synthesis and to downregulate IGF-IR signaling and the PI3K/Akt and ERK-1/2 pathways.
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PMID:Conjugated linoleic acid downregulates insulin-like growth factor-I receptor levels in HT-29 human colon cancer cells. 1288 57

In vivo effects of milrinone, a selective phosphodiesterase 3 (PDE-3) inhibitor, on plasma free fatty acids (FFA), glucose, and insulin levels were examined in alert rats. In dose response studies, intravenous injection of 1, 5 or 25 micromol/kg of milrinone provoked an immediate increase in plasma concentrations of FFA and insulin, while glucose levels rose only in response to the 5- and 25-micromol/kg doses. During euglycemic-hyperinsulinemic (approximately 450 pmol/L) clamps, intravenous injection of milrinone (25 micromol/kg) completely inhibited insulin suppression of lipolysis and of endogenous glucose production, while having no effect on insulin-stimulated glucose uptake (ISGU). To explore the reason why ISGU was not affected, we performed reverse-transcriptase polymerase chain reaction (RT-PCR) with RNA from skeletal muscle, fat, and liver. The results showed that PDE-3B mRNA was expressed in adipose tissue and liver, but it was not detected in skeletal muscle. We conclude that PDE-3 plays a major role in the inhibitory action of insulin on lipolysis in fat and on glucose production in liver and, in addition, seems to be involved in insulin secretion in pancreatic beta cells.
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PMID:Milrinone, a selective phosphodiesterase 3 inhibitor, stimulates lipolysis, endogenous glucose production, and insulin secretion. 1462 13


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