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Pourvali K, Matak P, Latunde-Dada GO, Solomou S, Mastrogiannaki M, Peyssonnaux C, Sharp PA. Basal expression of copper transporter 1 in intestinal epithelial cells is regulated by hypoxia-inducible factor 2α. FEBS Lett 2012; 586:2423-7. [DOI: 10.1016/j.febslet.2012.05.058] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2012] [Accepted: 05/28/2012] [Indexed: 12/24/2022]
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Vlachodimitropoulou E, Sharp PA, Naftalin RJ. Quercetin-iron chelates are transported via glucose transporters. Free Radic Biol Med 2011; 50:934-44. [PMID: 21238582 DOI: 10.1016/j.freeradbiomed.2011.01.005] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/03/2010] [Revised: 12/31/2010] [Accepted: 01/06/2011] [Indexed: 10/18/2022]
Abstract
Flavonoids are well-known antioxidants and free radical scavengers. Their metal-binding activity suggests that they could be effective protective agents in pathological conditions caused by both extracellular and intracellular oxidative stress linked to metal overload. Quercetin is both a permeant ligand via glucose transport proteins (GLUTs) and a high-affinity inhibitor of GLUT-mediated glucose transport. Chelatable "free iron" at micromolar concentrations in body fluids is a catalyst of hydroxyl radical (OH(•)) production from hydrogen peroxide. A number of flavonoids, e.g., quercetin, luteolin, chrysin, and 3,6-dihydroxyflavone, have been demonstrated to chelate intracellular iron and suppress OH(•) radical production in Madin Darby canine kidney cells. The most effective chelation comes from the flavonone B ring catechol found in both quercetin and luteolin. We show here that quercetin concentrations of <1μM can facilitate chelatable iron shuttling via GLUT1 in either direction across the cell membrane. These siderophoric effects are inhibited by raised quercetin concentrations (>1μM) or GLUT inhibitors, e.g., phloretin or cytochalasin B, and iron efflux is enhanced by impermeant extracellular iron chelators, either desferrioxamine or rutin. This iron shuttling property of quercetin might be usefully harnessed in chelotherapy of iron-overload conditions.
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Chaston TB, Matak P, Pourvali K, Srai SK, McKie AT, Sharp PA. Hypoxia inhibits hepcidin expression in HuH7 hepatoma cells via decreased SMAD4 signaling. Am J Physiol Cell Physiol 2011; 300:C888-95. [PMID: 21289291 DOI: 10.1152/ajpcell.00121.2010] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Hepcidin negatively regulates systemic iron homeostasis in response to inflammation and elevated serum iron. Conversely, hepcidin expression is diminished in response to hypoxia, oxidative stress, and increased erythropoietic demand, though the molecular intermediates involved are incompletely understood. To address this, we have investigated hypoxic hepcidin regulation in HuH7 hepatoma cells either cultured alone or cocultured with activated THP-1 macrophages. HuH7 hepcidin mRNA expression was determined using quantitative polymerase chain reaction (Q-PCR). Hepcidin promoter activity was measured using luciferase reporter constructs containing a 0.9 kb fragment of the wild-type human hepcidin promoter, and constructs containing mutations in bone morphogenetic protein (BMP)/SMAD4, signal transducer and activator of transcription 3 (STAT3), CCAAT/enhancer-binding protein (C/EBP), and E-box-responsive elements. Hepatic expression of bone morphogenetic proteins BMP2 and BMP6 and the BMP inhibitor noggin was determined using Q-PCR, and the protein expression of hemojuvelin (HJV), pSMAD 1/5/8, and SMAD4 was determined by western blotting. Following exposure to hypoxia or H(2)O(2), hepcidin mRNA expression and promoter activity increased in HuH7 cells monocultures but were decreased in HuH7 cells cocultured with THP-1 macrophages. This repression was attenuated by mutation of the BMP/SMAD4-response element, suggesting that modulation of SMAD signaling mediated the response to hypoxia. No changes in hepatocyte BMP2, BMP6 or noggin mRNA, or protein expression of HJV or pSMAD 1/5/8 were detected. However, treatment with hypoxia caused a marked decrease in nuclear and cytosolic SMAD4 protein and SMAD4 mRNA expression in cocultured HuH7 cells. Together these data indicate that hypoxia represses hepcidin expression through inhibition of BMP/SMAD signaling.
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Thumser AE, Rashed AA, Sharp PA, Lodge JK. Ascorbate enhances iron uptake into intestinal cells through formation of a FeCl3–ascorbate complex. Food Chem 2010. [DOI: 10.1016/j.foodchem.2010.04.031] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Sharp PA. Intestinal Iron Absorption: Regulation by Dietary & Systemic Factors. INT J VITAM NUTR RES 2010; 80:231-42. [DOI: 10.1024/0300-9831/a000029] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Iron is an essential trace metal in human metabolism. However, imbalances in iron homeostasis are prevalent worldwide and have detrimental effects on human health. Humans do not have the ability to remove excess iron and therefore iron homeostasis is maintained by regulating the amount of iron entering the body from the diet. Iron is present in the human diet in number of different forms, including heme (from meat) and a variety of non-heme iron compounds. While heme is absorbed intact, the bioavailability of non-heme iron varies greatly depending on dietary composition. A number of dietary components are capable of interacting with iron to regulate its solubility and oxidation state. Interestingly, there is an emerging body of evidence suggesting that some nutrients also have direct effects on the expression and function of enterocyte iron transporters. In addition to dietary factors, body iron status is a major determinant of iron absorption. The roles of these important dietary and systemic factors in regulating iron absorption will be discussed in this review.
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Rapisarda C, Puppi J, Hughes RD, Dhawan A, Farnaud S, Evans RW, Sharp PA. Transferrin receptor 2 is crucial for iron sensing in human hepatocytes. Am J Physiol Gastrointest Liver Physiol 2010; 299:G778-83. [PMID: 20576915 PMCID: PMC2950680 DOI: 10.1152/ajpgi.00157.2010] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Hepcidin expression in vivo is regulated in proportion to iron status (i.e., increased by iron loading and decreased in iron deficiency). However, in vitro studies with hepatoma cell lines often show an inverse relationship between iron status and hepcidin expression. Here, we investigated possible molecular mechanisms responsible for the differences in iron sensing between hepatoma cell lines and human primary hepatocytes. RNA was collected from primary human hepatocytes, and HepG2 and HuH7 hepatoma cells were treated with either transferrin-bound and non-transferrin-bound iron. Expression of hepcidin, transferrin receptor 2, HFE, and hemojuvelin were quantified by real-time PCR. Hepcidin expression was increased in primary human hepatocytes following 24-h exposure to holoferric transferrin. In contrast, hepcidin mRNA levels in hepatoma cells were decreased by transferrin. Hepcidin expression was positively correlated with transferrin receptor 2 mRNA levels in primary human hepatocytes. Compared with primary hepatocytes, transferrin receptor 2 expression was significantly lower in hepatoma cell lines; furthermore, there was no correlation between transferrin receptor 2 and hepcidin mRNA levels in either HepG2 or HuH7 cells. Taken together our data suggest that transferrin receptor 2 is a likely candidate to explain the differences in iron sensing between hepatoma cell lines and primary human hepatocytes.
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Thompson BAV, Sharp PA, Elliott R, Fairweather-Tait SJ. Inhibitory effect of calcium on non-heme iron absorption may be related to translocation of DMT-1 at the apical membrane of enterocytes. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2010; 58:8414-7. [PMID: 20597505 DOI: 10.1021/jf101388z] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Many studies show that calcium reduces iron absorption from single meals, but the underlying mechanism is not known. We tested the hypothesis that calcium alters the expression and/or functionality of iron transport proteins. Differentiated Caco-2 cells were treated with ferric ammonium citrate and calcium chloride, and ferritin, DMT-1, and ferroportin were quantified in whole-cell lysate and cell-membrane fractions. Calcium attenuated the iron-induced increase in cell ferritin levels in a dose-dependent manner; a significant decrease was seen at calcium concentrations of 1.25 and 2.5 mM but was only evident after a 16-24 h incubation period. Calcium and iron treatments decreased DMT-1 protein in Caco-2 cell membranes, although total DMT-1 in whole cell lysates was unchanged by either iron or calcium. No change was seen in ferroportin expression. Our data suggest that calcium reduces iron bioavailability by decreasing DMT-1 expression at the apical cell membrane, thereby downregulating iron transport into the cell.
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Vlachodimitropoulou E, Naftalin RJ, Sharp PA. Quercetin is a substrate for the transmembrane oxidoreductase Dcytb. Free Radic Biol Med 2010; 48:1366-9. [PMID: 20184953 DOI: 10.1016/j.freeradbiomed.2010.02.021] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/15/2009] [Revised: 02/10/2010] [Accepted: 02/13/2010] [Indexed: 11/26/2022]
Abstract
Duodenal cytochrome b (Dcytb) is a transmembrane oxidoreductase protein found in apical membranes of duodenal enterocytes, as well as human erythrocytes, with the capacity to transport electrons donated by cytosolic ascorbate to extracellular electron receptors such as Fe(III), dehydroascorbate, or molecular O(2). We have investigated the capacity of the flavonoid quercetin to act as an electron donor for Dcytb in a manner similar to that of ascorbate by observing the reduction of extracellular Fe(III) to Fe(II) in either Madin-Darby canine kidney (MDCK) cells overexpressing Dcytb (Dcytb(+)) or Dcytb-null MDCK cells. In Dcytb(+) cells there is a saturable increase in extracellular Fe(III) reduction in response to increasing intracellular quercetin concentrations (K(m)=6.53+/-1.57 microM), in addition to a small linear response, whereas in Dcytb-null cells there is only a small linear increase in extracellular Fe(III) reduction. No extracellular Fe(III) reduction occurs in Dcytb-null cells when the cells are preloaded with ascorbate. Flavonoids such as quercetin at their physiological concentrations can therefore function as modulators of ferric reductases, enhancing the import of Fe(II) and also providing extracellular reducing potential.
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Srai SK, Sharp PA, Marks J, Unwin RJ, Debnam ES. The regulation of intestinal iron transport in a rat model of chronic renal failure. FASEB J 2010. [DOI: 10.1096/fasebj.24.1_supplement.1011.3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Chung B, Chaston T, Marks J, Srai SK, Sharp PA. Hepcidin decreases iron transporter expression in vivo in mouse duodenum and spleen and in vitro in THP-1 macrophages and intestinal Caco-2 cells. J Nutr 2009; 139:1457-62. [PMID: 19549758 DOI: 10.3945/jn.108.102905] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Hepcidin is thought to control iron metabolism by interacting with the iron efflux transporter ferroportin. In macrophages, there is compelling evidence that hepcidin directly regulates ferroportin protein expression. However, the effects of hepcidin on intestinal ferroportin levels are less conclusive. In this study, we compared the effects of hepcidin on iron transporter expression in the spleen and duodenum of mice treated with hepcidin over a 24- to 72-h period and observed a marked decrease in the expression of ferroportin in both duodenal enterocytes and splenic macrophages following treatment. Changes in transporter protein expression were associated with significant decreases in duodenal iron transport and serum iron. In THP-1 macrophages, ferroportin protein levels were decreased by 300 and 1000 nmol/L hepcidin. In contrast, ferroportin protein expression was unaltered in intestinal Caco-2 cells following exposure to hepcidin. However, iron efflux from Caco-2 cells was significantly inhibited in the presence of hepcidin, suggesting that the peptide could block ferroportin function in these cells. We conclude that hepcidin regulates the release of iron from both enterocytes and macrophages. However, taken together with our previous work, it is apparent that macrophages are more sensitive than enterocytes to a hepcidin challenge.
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Matak P, Chaston TB, Chung B, Srai SK, McKie AT, Sharp PA. Activated macrophages induce hepcidin expression in HuH7 hepatoma cells. Haematologica 2009; 94:773-80. [PMID: 19454498 DOI: 10.3324/haematol.2008.003400] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
BACKGROUND Hepcidin is an iron regulatory peptide produced by the liver in response to inflammation and elevated systemic iron. Recent studies suggest that circulating monocytes and resident liver macrophages--Küpffer cells--may influence both basal and inflammatory expression of hepcidin. DESIGN AND METHODS We used an in vitro co-culture model to investigate hepatocyte hepcidin regulation in the presence of activated THP1 macrophages. HuH7 hepatoma cells were co-cultured with differentiated THP1 macrophages for 24 h prior to the measurement of HuH7 hepcidin (HAMP) mRNA expression using quantitative polymerase chain reaction, and HAMP promoter activity using a luciferase reporter assay. Luciferase assays were performed using the wild type HAMP promoter, and constructs containing mutations in BMP/SMAD4, STAT3, C/EBP and E-BOX response elements. Neutralizing antibodies against interleukin-6, interleukin-1beta , and the bone morphogenetic protein inhibitor noggin were used to identify the macrophage-derived cytokines involved in the regulation of HAMP expression. RESULTS Co-culturing HuH7 cells with differentiated THP1 cells induced HAMP promoter activity and endogenous HAMP mRNA expression maximally after 24 h. This induction was fully neutralized in the presence of an interleukin-1beta antibody, and fully attenuated by mutations of the proximal C/EBP or BMP/SMAD4 response elements. CONCLUSIONS Our data suggest that the interleukin-1beta and bone morphogenetic protein signaling pathways are central to the regulation of HAMP expression by macrophages in this co-culture model.
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Wyman S, Simpson RJ, McKie AT, Sharp PA. Dcytb (Cybrd1) functions as both a ferric and a cupric reductase in vitro. FEBS Lett 2008; 582:1901-6. [DOI: 10.1016/j.febslet.2008.05.010] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2008] [Revised: 04/18/2008] [Accepted: 05/07/2008] [Indexed: 10/22/2022]
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Schild-Poulter C, Shih A, Tantin D, Yarymowich NC, Soubeyrand S, Sharp PA, Haché RJG. DNA-PK phosphorylation sites on Oct-1 promote cell survival following DNA damage. Oncogene 2007; 26:3980-8. [PMID: 17213819 DOI: 10.1038/sj.onc.1210165] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Octamer transcription factor-1 (Oct-1) has recently been shown to function as a stress sensor that promotes cell survival subsequent to DNA damage. Here, we show that the survival signal imparted by Oct-1 following exposure to ionizing radiation (IR) is dependent upon DNA-dependent protein kinase (DNA-PK)-dependent phosphorylation of a cluster of 13 specific ser/thr residues within the N-terminal transcriptional regulatory domain of Oct-1. Although IR treatment did not affect the recruitment of Oct-1 to the histone H2B promoter, the recruitment of RNA polymerase II, TATA-binding protein and histone H4 acetylation were strongly reduced, consistent with a decrease in Oct-1 transcriptional regulatory potential following IR exposure. Ser/Thr-Ala substitution of 13 sites present in Oct-1 transcriptional regulatory domain eliminated Oct-1 phosphorylation subsequent to IR exposure. Further, these substitutions prevented Oct-1 from rescuing the survival of IR-treated Oct-1-/- murine embryonic fibroblasts, providing a direct link between DNA-PK-dependent phosphorylation and the contribution of Oct-1 to cell survival. These results implicate Oct-1 as a primary effector in a DNA-PK-dependent cell survival pathway that is activated by double-stranded DNA breaks.
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Leung AKL, Sharp PA. Function and localization of microRNAs in mammalian cells. COLD SPRING HARBOR SYMPOSIA ON QUANTITATIVE BIOLOGY 2006; 71:29-38. [PMID: 17381277 DOI: 10.1101/sqb.2006.71.049] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
microRNAs (miRNAs) represent a large set of master regulators of gene expression. They constitute 1-4% of human genes and probably regulate 30% of protein-encoding genes. These small regulatory RNAs act at a posttranscriptional level-mediating translational repression and/or mRNA degradation-through their association with Argonaute protein and target mRNAs. In this paper, we discuss various mechanisms by which miRNAs regulate posttranscriptionally, including their subcellular localization. Recent results indicate that the majority of miRNA-targeted and thus translationally repressed mRNA is probably distributed in the diffuse cytoplasm, even though a small fraction is concentrated in subcellular compartments, such as processing bodies or stress granules; notably, the stress granule localization of Argonaute depends on the presence of miRNAs. Here we discuss the structural requirement of these subcellular compartments in light of their potential miRNA functions.
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Abstract
BACKGROUND Only 10% of dietary iron is absorbed in the duodenum which implies that 90% (approximately 9 mg day(-1)) reaches the lower small intestine and colon. Therefore the purpose of this study was to assess the iron transport capacity of the rat proximal colon and to determine whether iron absorption is regulated by changes in dietary iron content. MATERIALS AND METHODS Rats were fed for 14 days on either iron adequate (44 mg Fe kg(-1) diet) or iron-deficient (< 0.5 mg Fe kg(-1) diet) diets. The 59Fe transport across the colonic epithelium and its subsequent appearance in the blood were measured in vivo. In separate studies the colon was excised and used to measure divalent metal transporter expression. RESULTS Divalent metal transporter (DMT1) was expressed at the apical membrane of the surface epithelium in rat proximal colon. In animals fed an iron-deficient diet, DMT1 mRNA and protein expression were increased. This was accompanied by a significant increase in tissue 59Fe uptake. CONCLUSIONS The proximal colon can absorb non-haem iron from the intestinal lumen. The purpose of this mechanism remains to be elucidated.
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Truskett PG, Shi ECP, Rose M, Sharp PA, Ham JM. Authors' reply. Br J Surg 2005. [DOI: 10.1002/bjs.1800741242] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Johnson DM, Yamaji S, Tennant J, Srai SK, Sharp PA. Regulation of divalent metal transporter expression in human intestinal epithelial cells following exposure to non-haem iron. FEBS Lett 2005; 579:1923-9. [PMID: 15792797 DOI: 10.1016/j.febslet.2005.02.035] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2004] [Revised: 02/01/2005] [Accepted: 02/03/2005] [Indexed: 12/14/2022]
Abstract
A number of regulatory factors including dietary iron levels can dramatically alter the expression of the intestinal iron transporter DMT1. Here we show that Caco-2 cells exposed to iron for 4h exhibited a significant decrease in plasma membrane DMT1 protein, though total cellular DMT1 levels were unaltered. Following biotinylation of cell surface proteins, there was a significant increase in intracellular biotin-labelled DMT1 in iron-exposed cells. Furthermore, iron-treatment increased levels of DMT1 co-localised with LAMP1, suggesting that the initial response of intestinal epithelial cells to iron involves internalisation and targeting of DMT1 transporter protein towards a late endosomal/lysosomal compartment.
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Abstract
Members of the Cu transporter (Ctr) family have been reported to be part of the copper uptake machinery in several organisms. Recently it has been suggested that human Ctr1 (hCtr1) may act as a copper transporter in several tissues including the intestine. hCtr1 is a 190 amino acid protein and is predicted to have three transmembrane-spanning domains and exist in the plasma membrane as a homo-trimer. Ctr1-transfected cell lines exhibit saturable, pH-dependent Cu(I) uptake indicating a role in copper transport. Recent studies with Ctr1 knockout mice have highlighted an essential function in mammalian embryonic development since homozygous mutants die in utero. Heterozygotes are indistinguishable from wild-type littermates but have a severely reduced brain copper content, suggesting that Ctr1 is a key component of the copper uptake pathway in the brain. However, its role in other tissues remains elusive.
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Kim JB, Sharp PA. Positive transcription elongation factor B phosphorylates hSPT5 and RNA polymerase II carboxyl-terminal domain independently of cyclin-dependent kinase-activating kinase. J Biol Chem 2001; 276:12317-23. [PMID: 11145967 DOI: 10.1074/jbc.m010908200] [Citation(s) in RCA: 147] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The CDK9-cyclin T kinase complex, positive transcription elongation factor b (P-TEFb), stimulates the process of elongation of RNA polymerase (Pol) II during transcription of human immunodeficiency virus. P-TEFb associates with the human immunodeficiency virus Tat protein and with the transactivation response element to form a specific complex, thereby mediating efficient elongation. Here, we show that P-TEFb preferentially phosphorylates hSPT5 as compared with the carboxyl-terminal domain of RNA Pol II in vitro. Phosphorylation of hSPT5 by P-TEFb occurred on threonine and serine residues in its carboxyl-terminal repeat domains. In addition, we provide several lines of evidence that P-TEFb is a CDK-activating kinase (CAK)-independent kinase. For example, CDK9 was not phosphorylated by CAK, whereas CDK2-cyclin A kinase activity was dramatically enhanced by CAK. Therefore, it is likely that P-TEFb participates in regulation of elongation by RNA Pol II by phosphorylation of its substrates, hSPT5 and the CTD of RNA Pol II, in a CAK-independent manner.
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Arrow KJ, Axelrod J, Benacerraf B, Berg P, Bishop JM, Bloembergen N, Brown HC, Cibelli J, Cohen S, Cooper LN, Corey EJ, Cronin JW, Curl R, Dulbecco R, Fischer EH, Fitch VL, Fogel R, Friedman JI, Furchgott RF, Gell-Mann M, Gilbert W, Gilman A, Glaser D, Glashow SL, Green RM, Greengard P, Guillemin R, Hayflick L, Hauptman HA, Heckman JJ, Heeger A, Herschbach D, Hubel DH, Hulse R, Kandel E, Karle J, Klein LR, Kohn W, Kornberg A, Krebs EG, Lanza RP, Laughlin R, Lederman L, Lee DM, Lewis E, Lipscomb W, Marcus RA, McFadden D, Merrifield RB, Merton R, Modigliani F, Molina MJ, Murad F, Nirenberg MW, North DC, Olah GA, Osheroff D, Palade GE, Perl M, Ramsey NF, Richter B, Roberts RJ, Samuelson PA, Schwartz M, Sharp PA, Smalley RE, Smith HO, Solow RM, Stormer H, Taube H, Taylor R, Thomas ED, Tobin J, Tonegawa S, Townes C, Watson JD, Weinberg S, Weller TH, West MD, Wieschaus EF, Wiesel TN, Wilson RW. Nobel laureates' letter to President Bush. THE WASHINGTON POST 2001:A02. [PMID: 12462241] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/27/2023]
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Chen K, Liu Q, Xie L, Sharp PA, Wang DI. Engineering of a mammalian cell line for reduction of lactate formation and high monoclonal antibody production. Biotechnol Bioeng 2001; 72:55-61. [PMID: 11084594 DOI: 10.1002/1097-0290(20010105)72:1<55::aid-bit8>3.0.co;2-4] [Citation(s) in RCA: 115] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Lactate and ammonia are the two major waste products formed during mammalian cell growth. Accumulation of these side products can have a negative effect on cell growth, and has drawn recent attention because of their inhibitory effects on the specific product synthesis rate. Our aim is to reduce lactate formation in the cell culture by genetically manipulating of the pathway of lactate synthesis with an aim to achieve high monoclonal antibody production. We have partially disrupted the LDH-A gene by homologous recombination in hybridoma cells (ATCC-CRL-1606). The cells that received the newly introduced DNA were selected by G418, and an LDH-deficient cell was identified by a screening method based on medium color changing in 96-well plates. A variant cell, LDH-neo21, was identified through this screening method and was characterized. The specific productivity of lactate by LDH-neo21 cells was 50% lower than that of parental cells. Intracellular LDH enzyme activity was significantly reduced. The cell growth was improved both in terms of cell density and cell viability. Total cell density potentially reached 5 x 10(6) cells/mL while the parental hybridoma cells had a cell density of 3.5 x 10(6) cells/mL, which represented a 30% increase. The antibody production of LDH-neo21 cells was threefold greater than that of parental cells during 5-day batch culture. Polymerase chain reaction (PCR) results showed that at least one copy of the LDH-A gene was disrupted in the LDH-neo21 cells. The variant of the hybridoma cell exhibited a significant advantage of reduced lactate formation in the cell culture with a high concentration of glucose, which led to a higher production of monoclonal antibody. 2001 John Wiley & Sons, Inc.
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Tuschl T, Sharp PA, Bartel DP. A ribozyme selected from variants of U6 snRNA promotes 2',5'-branch formation. RNA (NEW YORK, N.Y.) 2001; 7:29-43. [PMID: 11214178 PMCID: PMC1370066 DOI: 10.1017/s1355838201001510] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
In vitro selection was used to sample SnRNA-related sequences for ribozyme activities, and several 2',5'-branch-forming ribozymes were isolated. One such ribozyme is highly dependent upon an 11-nt motif that contains a conserved U6 snRNA sequence (ACAGAGA-box) known to be important for pre-mRNA splicing. The ribozyme reaction is similar to the first step of splicing in that an internal 2'-hydroxyl of an unpaired adenosine attacks at the 5'-phosphate of a guanosine. It differs in that the leaving group is diphosphate rather than a 5' exon. The finding that lariat formation can be accomplished by a small RNA with sequences related to U6 snRNA indicates that the RNA available in the spliceosome may be involved in RNA-catalyzed branch formation.
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Sharp PA. View of life sciences in the 21st century. J Dermatol Sci 2000; 24 Suppl 1:S1-14. [PMID: 11137390 DOI: 10.1016/s0923-1811(00)00135-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
As we contemplate the nature of life sciences in the 21st century, we should briefly consider the changes that have occurred in the past century. Surely, the sources of progress of this science in the next century are the advances emerging now. Furthermore, the likely pace of discovery and change in life sciences in the next century can best be estimated by a reflection on its history.
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