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Baldwin GS, Sims I. Tyrosine modification increases the affinity of gastrin for ferric ions. SPRINGERPLUS 2015; 4:815. [PMID: 26722635 PMCID: PMC4690827 DOI: 10.1186/s40064-015-1622-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/09/2015] [Accepted: 12/15/2015] [Indexed: 01/25/2023]
Abstract
The peptide hormone gastrin17, which occurs naturally in both tyrosine sulphated and unsulphated forms, binds two ferric ions with pM affinities. The aim of this study was to investigate the hypothesis that sulphation or phosphorylation of gastrin17 altered ferric ion binding, and/or affinity for the CCK1 or CCK2 receptor. To investigate the effect of tyrosine modification on ferric ion binding, the changes in absorbance of gastrin17, gastrin17SO4 and gastrin17PO4 on addition of Fe3+ ions were monitored. Binding of gastrin17, gastrin17SO4 and gastrin17PO4 to the human CCK1 and CCK2 receptors was assessed by competition with [125I]-Bolton and Hunter-labelled cholecystokinin8 in transiently transfected COS cells. Tyrosine sulphation or phosphorylation increased the affinity of gastrin17 for the first ferric ion bound from 267 to 83 pM and 14 pM, respectively, but had no effect on the stoichiometry of ferric ion binding. In contrast the affinity of gastrin17 for the second ferric ion bound was reduced from 94 pM to 7.32 µM and 671 nM, respectively. While sulphation of gastrin17 increased its affinity for the CCK2 receptor approximately 50 fold, phosphorylation had no effect on receptor binding. These results demonstrate that tyrosine modification may have profound effects on the interaction of gastrins with ferric ions and with the CCK2 receptor.
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Affiliation(s)
- Graham S Baldwin
- Department of Surgery, Austin Health, The University of Melbourne, Heidelberg, VIC 3084 Australia
| | - Ioulia Sims
- Department of Surgery, Austin Health, The University of Melbourne, Heidelberg, VIC 3084 Australia
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Marshall KM, Laval M, Sims I, Shulkes A, Baldwin GS. Retro-inverso forms of gastrin5-12 are as biologically active as glycine-extended gastrin in vitro but not in vivo. Peptides 2015; 74:16-22. [PMID: 26471904 DOI: 10.1016/j.peptides.2015.09.012] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/17/2015] [Revised: 09/24/2015] [Accepted: 09/29/2015] [Indexed: 01/04/2023]
Abstract
Non-amidated gastrin peptides such as glycine-extended gastrin (Ggly) are biologically active in vitro and in vivo and have been implicated in the development of gastric and colonic cancers. Previous studies have shown that the truncated form of Ggly, the octapeptide LE5AY, was still biologically active in vitro, and that activity was dependent on ferric ion binding but independent of binding to the cholecystokinin 2 (CCK2) receptor. The present work was aimed at creating more stable gastrin-derived 'super agonists' using retro-inverso technology. The truncated LE5AY peptide was synthesized using end protecting groups in three forms with l-amino acids (GL), d-amino acids (GD) or retro-inverso (reverse order with d-amino acids; GRI). All of these peptides bound ferric ions with a 2:1 (Fe: peptide) ratio. As predicted, Ggly, GL and GRI were biologically active in vitro and increased cell proliferation in mouse gastric epithelial (IMGE-5) and human colorectal cancer (DLD-1) cell lines, and increased cell migration in DLD-1 cells. These activities were likely via the same mechanism as Ggly since no CCK1 or CCK2 binding was identified, and GD remained inactive in all assays. Surprisingly, unlike Ggly, GL and GRI were not active in vivo. While Ggly stimulated colonic crypt height and proliferation rates in gastrin knockout mice, GL and GRI did not. The apparent lack of activity may be due to rapid clearance of these smaller peptides. Nevertheless further work designing and testing retro-inverso gastrins is warranted, as it may lead to the generation of super agonists that could potentially be used to treat patients with gastrointestinal disorders with reduced mucosal function.
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Affiliation(s)
- Kathryn M Marshall
- Department of Surgery, University of Melbourne, Austin Health, Lance Townsend Building, Level 8, Studley Road, Heidelberg, Victoria 3084 Australia.
| | - Marie Laval
- Department of Surgery, University of Melbourne, Austin Health, Lance Townsend Building, Level 8, Studley Road, Heidelberg, Victoria 3084 Australia.
| | - Ioulia Sims
- Department of Surgery, University of Melbourne, Austin Health, Lance Townsend Building, Level 8, Studley Road, Heidelberg, Victoria 3084 Australia.
| | - Arthur Shulkes
- Department of Surgery, University of Melbourne, Austin Health, Lance Townsend Building, Level 8, Studley Road, Heidelberg, Victoria 3084 Australia.
| | - Graham S Baldwin
- Department of Surgery, University of Melbourne, Austin Health, Lance Townsend Building, Level 8, Studley Road, Heidelberg, Victoria 3084 Australia.
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You LL, Cao DH, Jiang J, Hou Z, Suo YE, Wang SD, Cao XY. Transgenic mouse models of gastric cancer: Pathological characteristic and applications. Shijie Huaren Xiaohua Zazhi 2015; 23:2754-2760. [DOI: 10.11569/wcjd.v23.i17.2754] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Transgenic animal models of gastric cancer have high specificity and similar tumor characteristics to human gastric cancer. Current research and application of transgenic animal models of gastric cancer are wide, and several models have been developed. In transgenic animal models of gastric cancer, primary gastric carcinoma can develop spontaneously. These transgenic animal models have been widely used to study the mechanism of gastric cancer development, and have great significance for clinical diagnosis and treatment of gastric cancer. This paper systematically summarizes several different kinds of transgenic animal models and describes the molecular pathogenic mechanisms and pathological characteristics of gastric mucosal lesions in these models as well as their applications.
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Laval M, Baldwin GS, Shulkes A, Marshall KM. Increased gastrin gene expression provides a physiological advantage to mice under hypoxic conditions. Am J Physiol Gastrointest Liver Physiol 2015; 308:G76-84. [PMID: 25394662 DOI: 10.1152/ajpgi.00344.2014] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Hypoxia, or a low concentration of O2, is encountered in humans undertaking activities such as mountain climbing and scuba diving and is important pathophysiologically as a limiting factor in tumor growth. Although data on the interplay between hypoxia and gastrins are limited, gastrin expression is upregulated by hypoxia in gastrointestinal cancer cell lines, and gastrins counterbalance hypoxia by stimulating angiogenesis in vitro and in vivo. The aim of this study was to determine if higher concentrations of the gastrin precursor progastrin are protective against hypoxia in vivo. hGAS mice, which overexpress progastrin in the liver, and mice of the corresponding wild-type FVB/N strain were exposed to normoxia or hypoxia. Iron status was assessed by measurement of serum iron parameters, real-time PCR for mRNAs encoding critical iron regulatory proteins, and Perls' stain and atomic absorption spectrometry for tissue iron concentrations. FVB/N mice lost weight at a faster rate and had higher sickness scores than hGAS mice exposed to hypoxia. Serum iron levels were lower in hGAS than FVB/N mice and decreased further when the animals were exposed to hypoxia. The concentration of iron in the liver was strikingly lower in hGAS than FVB/N mice. We conclude that increased circulating concentrations of progastrin provide a physiological advantage against systemic hypoxia in mice, possibly by increasing the availability of iron stores. This is the first report of an association between progastrin overexpression, hypoxia, and iron homeostasis.
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Affiliation(s)
- Marie Laval
- Department of Surgery, University of Melbourne, Austin Health, Melbourne, Victoria, Australia
| | - Graham S Baldwin
- Department of Surgery, University of Melbourne, Austin Health, Melbourne, Victoria, Australia
| | - Arthur Shulkes
- Department of Surgery, University of Melbourne, Austin Health, Melbourne, Victoria, Australia
| | - Kathryn M Marshall
- Department of Surgery, University of Melbourne, Austin Health, Melbourne, Victoria, Australia
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Abstract
The existence of the hormone gastrin in the distal stomach (antrum) has been known for almost 110 years, and the physiological function of this amidated peptide in regulating gastric acid secretion via the CCK2 receptor is now well established. In this brief review we consider important additional roles of gastrin, including regulation of genes encoding proteins such as plasminogen activator inhibitors and matrix metalloproteinases that have important actions on extracellular matrix remodelling. These actions are, at least in part, effected by paracrine signalling pathways and make important contributions to maintaining functional integrity of the gastric epithelium. Recent studies also provide support for the idea that gastrin, in concert with other hormones, could potentially contribute a post-prandial incretin effect. We also review recent developments in the biology of other gastrin gene products, including the precursor progastrin, which causes proliferation of the colonic epithelium and in certain circumstances may induce cancer formation. Glycine-extended biosynthetic processing intermediates also have proliferative effects in colonic mucosa and in some oesophageal cancer cell lines. Whether these additional gene products exert their effects through the CCK2 receptor or a separate entity is currently a matter of debate.
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Affiliation(s)
- Rod Dimaline
- Department of Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Crown Street, Liverpool L69 3BX, UK
| | - Andrea Varro
- Department of Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Crown Street, Liverpool L69 3BX, UK
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DUCKWORTH CARRIEA, CLYDE DANIEL, WORTHLEY DANIELL, WANG TIMOTHYC, VARRO ANDREA, PRITCHARD DMARK. Progastrin-induced secretion of insulin-like growth factor 2 from colonic myofibroblasts stimulates colonic epithelial proliferation in mice. Gastroenterology 2013; 145:197-208.e3. [PMID: 23523669 PMCID: PMC4087195 DOI: 10.1053/j.gastro.2013.03.012] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/29/2012] [Revised: 02/15/2013] [Accepted: 03/10/2013] [Indexed: 01/10/2023]
Abstract
BACKGROUND & AIMS Many colon cancers produce the hormone progastrin, which signals via autocrine and paracrine pathways to promote tumor growth. Transgenic mice that produce high circulating levels of progastrin (hGAS) have increased proliferation of colonic epithelial cells and are more susceptible to colon carcinogenesis than control mice. We investigated whether progastrin affects signaling between colonic epithelial and myofibroblast compartments to regulate tissue homeostasis and cancer susceptibility. METHODS Colonic myofibroblast numbers were assessed in hGAS and C57BL/6 mice by immunohistochemistry. Human CCD18Co myofibroblasts were incubated with recombinant human progastrin (rhPG)(1-80) for 18 hours, and proliferation was assessed in the presence of pharmacologic inhibitors. The proliferation of human HT29 colonic epithelial cells was assessed after addition of conditioned media from CCD18Co cells incubated with progastrin. The effects of the insulin-like growth factor (IGF)-I receptor antagonist AG1024 were investigated in cultured HT29 cells and on the colonic epithelium of hGAS mice compared with mice that did not express transgenic progastrin (controls). RESULTS The colonic mucosa of hGAS mice contained greater numbers of myofibroblasts that expressed α-smooth muscle actin and vimentin than controls. Incubation of CCD18Co myofibroblasts with 0.1 nmol/L rhPG(1-80) increased their proliferation, which required activation of protein kinase C and phosphatidylinositol-3 kinase. CCD18Co cells secreted IGF-II in response to rhPG(1-80), and conditioned media from CCD18Co cells that had been incubated with rhPG(1-80) increased the proliferation of HT29 cells. The colonic epithelial phenotype of hGAS mice (crypt hyperplasia, increased proliferation, and altered proportions of goblet and enteroendocrine cells) was inhibited by AG1024. CONCLUSIONS Progastrin stimulates colonic myofibroblasts to release IGF-II, which increases proliferation of colonic epithelial cells. Progastrin might therefore alter colonic epithelial cells via indirect mechanisms to promote neoplasia.
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Affiliation(s)
- CARRIE A. DUCKWORTH
- Department of Gastroenterology, Institute of Translational Medicine, University of Liverpool, Liverpool, England
| | - DANIEL CLYDE
- Department of Gastroenterology, Institute of Translational Medicine, University of Liverpool, Liverpool, England
| | - DANIEL L. WORTHLEY
- Division of Digestive and Liver Diseases, Columbia University Medical Center, New York, New York
| | - TIMOTHY C. WANG
- Division of Digestive and Liver Diseases, Columbia University Medical Center, New York, New York
| | - ANDREA VARRO
- Department of Physiology, Institute of Translational Medicine, University of Liverpool, Liverpool, England
| | - D. MARK PRITCHARD
- Department of Gastroenterology, Institute of Translational Medicine, University of Liverpool, Liverpool, England
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Abstract
C-terminally amidated gastrins act at cholecystokinin-2 receptors (CCK2R), which are normally expressed by gastric parietal and enterochromaffin-like (ECL) cells and smooth muscle; there is also extensive expression in the CNS where the main endogenous ligand is cholecystokinin. A variety of neoplasms express CCK2R, or splice variants, including neuroendocrine, pancreatic, medullary thyroid and lung cancers. Other products of the gastrin gene (progastrin, the Gly-gastrins) may stimulate cell proliferation but are not CCK2R ligands. Depending on the cell type, stimulation of CCK2R evokes secretion, increases proliferation and cell migration, inhibits apoptosis, and controls the expression of various genes. These effects are mediated by increased intracellular calcium and activation of protein kinase C, MAPkinase and other protein kinase cascades. There has been recent progress in developing CCK2R ligands that can be used for imaging tumours expressing the receptor. New antagonists have also been developed, and there is scope for using these for suppression of gastric acid and for treatment of neuroendocrine and other CCK2R-expressing tumours.
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Kowalski-Chauvel A, Najib S, Tikhonova IG, Huc L, Lopez F, Martinez LO, Cohen-Jonathan-Moyal E, Ferrand A, Seva C. Identification of the F1-ATPase at the cell surface of colonic epithelial cells: role in mediating cell proliferation. J Biol Chem 2012; 287:41458-68. [PMID: 23055519 DOI: 10.1074/jbc.m112.382465] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
F1 domain of F(1)F(o)-ATPase was initially believed to be strictly expressed in the mitochondrial membrane. Interestingly, recent reports have shown that the F1 complex can serve as a cell surface receptor for apparently unrelated ligands. Here we show for the first time the presence of the F(1)-ATPase at the cell surface of normal or cancerous colonic epithelial cells. Using surface plasmon resonance technology and mass spectrometry, we identified a peptide hormone product of the gastrin gene (glycine-extended gastrin (G-gly)) as a new ligand for the F(1)-ATPase. By molecular modeling, we identified the motif in the peptide sequence (E(E/D)XY), that directly interacts with the F(1)-ATPase and the amino acids in the F(1)-ATPase that bind this motif. Replacement of the Glu-9 residue by an alanine in the E(E/D)XY motif resulted in a strong decrease of G-gly binding to the F(1)-ATPase and the loss of its biological activity. In addition we demonstrated that F(1)-ATPase mediates the growth effects of the peptide. Indeed, blocking F(1)-ATPase activity decreases G-gly-induced cell growth. The mechanism likely involves ADP production by the membrane F(1)-ATPase, which is induced by G-gly. These results suggest an important contribution of cell surface F(1)-ATPase in the pro-proliferative action of this gastrointestinal peptide.
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Affiliation(s)
- Aline Kowalski-Chauvel
- INSERM UMR 1037, Cancer Research Centre of Toulouse, Université Paul Sabatier Toulouse III, 31052 Toulouse, France
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Kovac S, Loh SW, Lachal S, Shulkes A, Baldwin GS. Bismuth ions inhibit the biological activity of non-amidated gastrins in vivo. Biochem Pharmacol 2011; 83:524-30. [PMID: 22172990 DOI: 10.1016/j.bcp.2011.11.030] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2011] [Revised: 11/28/2011] [Accepted: 11/30/2011] [Indexed: 12/15/2022]
Abstract
The peptide hormone gastrin binds two ferric ions with high affinity, and iron binding is essential for the biological activity of non-amidated gastrins in vitro and in vivo. Bi3+ ions also bind to glycine-extended gastrin17 (Ggly), but inhibit Ggly-induced cell proliferation and migration in gastrointestinal cell lines in vitro. The aims of the present study were firstly, to establish the mechanism by which Bi3+ ions inhibit the binding of Fe3+ ions to Ggly, and secondly, to test the effect of Bi3+ ions on the activity of non-amidated gastrins in vivo. The interaction between Bi3+ ions, Fe3+ ions and Ggly was investigated by ultraviolet spectroscopy. The effect of Bi3+ ions on colorectal mucosal proliferation was measured in three animal models. In vitro in the presence of Bi3+ ions the affinity of Fe3+ ions for Ggly was substantially reduced; the data was better fitted by a mixed, rather than a competitive, inhibition model. In rats treated with Ggly alone proliferation in the rectal mucosa was increased by 318%, but was reduced to control values (p < 0.001) in animals receiving oral bismuth plus Ggly. Proliferation in the colonic mucosa of mice overexpressing Ggly or progastrin was significantly greater than in wild-type mice, but was no greater than control (p < 0.01) in animals receiving oral bismuth. Thus a reduction in the binding of Fe3+ ions to Ggly and progastrin in the presence of Bi3+ ions is a likely explanation for the ability of oral bismuth to block the biological activity of non-amidated gastrins in vivo.
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Affiliation(s)
- Suzana Kovac
- The University of Melbourne Department of Surgery, Austin Health, Heidelberg, Victoria, Australia
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Impact of JNK1, JNK2, and ligase Itch on reactive oxygen species formation and survival of prostate cancer cells treated with diallyl trisulfide. Eur J Nutr 2011; 51:573-81. [PMID: 21863240 DOI: 10.1007/s00394-011-0241-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2010] [Accepted: 08/08/2011] [Indexed: 02/01/2023]
Abstract
PURPOSE In our previous study, we demonstrated that diallyl trisulfide (DATS) induced iron-dependent G2-M arrest of prostate cancer cell cycle. Moreover, ferritin degradation and an increase of labile iron pool has been linked to the activation of the JNK signaling axis. In the present work, we extended this study to determine which of the c-jun kinases is responsible for ferritin degradation and the role of iron in DATS-induced cell death. We hypothesized that JNK1 activates Itch ligase which will lead to ferritin ubiquitination, an increase in iron-dependent ROS formation and cell death. METHODS PC-3 prostate cancer cells were used in this study. Cell viability, concentration of ROS, labile iron pool, and changes in ferritin and P-Itch and DNA damage were determined. RESULTS We observed that DATS induced ferritin degradation through JNK, Itch signaling axis. DATS did not induce neither ROS formation nor increase the LIP in JNK1-DN transfected cells. We also observed that DATS increased JNK-dependent activating phosphorylation of E3ligase Itch. The cells transfected with inactive form of Itch were more resistant against cytotoxicity of DATS and showed lower DATS-induced ferritin degradation. Desferrioxamine a specific iron chelator had no effect neither on cell viability nor DNA damage evaluated by comet assay. CONCLUSIONS These results suggest that JNK1-dependent increase in LIP is mediated by Itch ubiquitin ligase.
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Kovac S, Anderson GJ, Alexander WS, Shulkes A, Baldwin GS. Gastrin-deficient mice have disturbed hematopoiesis in response to iron deficiency. Endocrinology 2011; 152:3062-73. [PMID: 21652729 PMCID: PMC3138233 DOI: 10.1210/en.2010-1474] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Gastrins are peptide hormones important for gastric acid secretion and growth of the gastrointestinal mucosa. We have previously demonstrated that ferric ions bind to gastrins, that the gastrin-ferric ion complex interacts with the iron transport protein transferrin in vitro, and that circulating gastrin concentrations positively correlate with transferrin saturation in vivo. Here we report the effect of long-term dietary iron modification on gastrin-deficient (Gas(-/-)) and hypergastrinemic cholecystokinin receptor 2-deficient (Cck2r(-/-)) mice, both of which have reduced basal gastric acid secretion. Iron homeostasis in both strains appeared normal unless the animals were challenged by iron deficiency. When fed an iron-deficient diet, Gas(-/-) mice, but not Cck2r(-/-) mice, developed severe anemia. In iron-deficient Gas(-/-) mice, massive splenomegaly was also apparent with an increased number of splenic megakaryocytes accompanied by thrombocytosis. The expression of the mRNA encoding the iron-regulatory peptide hepcidin, Hamp, was down-regulated in both Cck2r(-/-) and Gas(-/-) mice on a low-iron diet, but, interestingly, the reduction was greater in Cck2r(-/-) mice and smaller in Gas(-/-) mice than in the corresponding wild-type strains. These data suggest that gastrins play an important direct role, unrelated to their ability to stimulate acid secretion, in hematopoiesis under conditions of iron deficiency.
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Affiliation(s)
- Suzana Kovac
- University of Melbourne Department of Surgery, Austin Health, Heidelberg, Victoria 3084, Australia.
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Kovac S, Anderson GJ, Baldwin GS. Gastrins, iron homeostasis and colorectal cancer. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2011; 1813:889-95. [PMID: 21320535 DOI: 10.1016/j.bbamcr.2011.02.007] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2010] [Revised: 02/04/2011] [Accepted: 02/07/2011] [Indexed: 02/08/2023]
Abstract
The peptide hormone gastrin has been identified as a major regulator of acid secretion and a potent mitogen for normal and malignant gastrointestinal cells. The importance of gastric acid in the absorption of dietary iron first became evident 50 years ago when iron deficiency anemia was recognized as a long-term consequence of partial gastrectomy. This review summarizes the connections between circulating gastrins, iron status and colorectal cancer. Gastrins bind two ferric ions with micromolar affinity and, in the case of non-amidated forms of the hormone, iron binding is essential for biological activity in vitro and in vivo. The demonstration of an interaction between gastrin and transferrin by biochemical techniques led to the proposal that gastrins catalyze the loading of transferrin with iron. Several lines of evidence, including the facts that the concentrations of circulating gastrins are increased in mice and humans with the iron overload disease hemochromatosis and that transferrin saturation positively correlates with circulating gastrin concentration, suggest the potential involvement of gastrins in iron homeostasis. Conversely, recognition that ferric ions play an unexpected role in the biological activity of gastrins may assist in the development of useful therapies for colorectal carcinoma and other disorders of mucosal proliferation in the gastrointestinal tract. This article is part of a Special Issue entitled: 11th European Symposium on Calcium.
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Affiliation(s)
- Suzana Kovac
- The University of Melbourne Department of Surgery, Austin Health, Heidelberg, Victoria, Australia
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Bramante G, Patel O, Shulkes A, Baldwin GS. Ferric ions inhibit proteolytic processing of progastrin. Biochem Biophys Res Commun 2010; 404:1083-7. [PMID: 21195058 DOI: 10.1016/j.bbrc.2010.12.117] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2010] [Accepted: 12/22/2010] [Indexed: 11/15/2022]
Abstract
The gastrointestinal hormone gastrin is generated from an 80 amino acid precursor (progastrin) by cleavage after dibasic residues by prohormone convertase 1. Phosphorylation of Ser(75) has previously been suggested, on the basis of indirect evidence, to inhibit cleavage of progastrin after Arg(73)Arg(74). Gastrins bind two ferric ions with high affinity, and iron binding is essential for the biological activity of non-amidated gastrins in vitro and in vivo. This study directly investigated the effect of iron binding and of serine phosphorylation on the cleavage of synthetic progastrin-derived peptides. The affinity of synthetic progastrin(55-80) for ferric ions, and the rate of cleavage by prohormone convertase 1, were not affected by phosphorylation of Ser(75). In contrast, in the presence of ferric ions the rate of cleavage of both progastrin(55-80) and phosphoSer(75)progastrin(55-80) by prohormone convertase 1 was significantly reduced. Hence iron binding to progastrin may regulate processing and secretion in vivo, and regulation may be particularly important in diseases with altered iron homeostasis.
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Affiliation(s)
- Gianni Bramante
- The University of Melbourne, Department of Surgery, Austin Health, Heidelberg, 3084 Victoria, Australia
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