title: Iron depletion suppresses mTORC1-directed signalling in intestinal Caco-2 cells via induction of REDD1.
abstract: Iron is an indispensable micronutrient that regulates many aspects of cell function, including growth and proliferation. These processes are critically dependent upon signalling via the mammalian or mechanistic target of rapamycin complex 1 (mTORC1). Herein, we test whether iron depletion induced by cell incubation with the iron chelator, deferoxamine (DFO), mediates its effects on cell growth through mTORC1-directed signalling and protein synthesis. We have used Caco-2 cells, a well-established in vitro model of human intestinal epithelia. Iron depletion increased expression of iron-regulated proteins (TfR, transferrin receptor and DMT1, divalent metal transporter, as predicted, but it also promoted a marked reduction in growth and proliferation of Caco-2 cells. This was strongly associated with suppressed mTORC1 signalling, as judged by reduced phosphorylation of mTOR substrates, S6K1 and 4E-BP1, and diminished protein synthesis. The reduction in mTORC1 signalling was tightly coupled with increased expression and accumulation of REDD1 (regulated in DNA damage and development 1) and reduced phosphorylation of Akt and TSC2. The increase in REDD1 abundance was rapidly reversed upon iron repletion of cells but was also attenuated by inhibitors of gene transcription, protein phosphatase 2A (PP2A) and by REDD1 siRNA--strategies that also antagonised the loss in mTORC1 signalling associated with iron depletion. Our findings implicate REDD1 and PP2A as crucial regulators of mTORC1 activity in iron-depleted cells and indicate that their modulation may help mitigate atrophy of the intestinal mucosa that may occur in response to iron deficiency.
authors.affiliation: Division of Cell Signalling & Immunology, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK.
authors.forename: Ailsa
authors.initials: A
authors.lastname: Watson
authors.affiliation: Division of Cell Signalling & Immunology, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK.
authors.forename: Christopher
authors.initials: C
authors.lastname: Lipina
authors.affiliation: The Rowett Institute of Nutrition and Health, University of Aberdeen, Bucksburn, Aberdeen AB21 9SB, UK.
authors.forename: Harry J
authors.initials: HJ
authors.lastname: McArdle
authors.affiliation: Division of Cell Signalling & Immunology, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Taylor
authors.affiliation: Division of Cell Signalling & Immunology, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK. Electronic address: h.s.hundal@dundee.ac.uk.
authors.forename: Harinder S
authors.initials: HS
authors.lastname: Hundal
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D018938:Caco-2 Cells; D049109:Cell Proliferation / Q000187:drug effects; D003676:Deferoxamine / Q000494:pharmacology; D015536:Down-Regulation; D006801:Humans; D007413:Intestinal Mucosa / Q000201:enzymology / Q000378:metabolism*; D007502:Iron Chelating Agents / Q000494:pharmacology; D000090463:Iron Deficiencies; D000076222:Mechanistic Target of Rapamycin Complex 1; D046912:Multiprotein Complexes / Q000378:metabolism*; D014176:Protein Biosynthesis; D054648:Protein Phosphatase 2 / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*; D014157:Transcription Factors / Q000096:biosynthesis / Q000378:metabolism*
chemical_list: D000596:Amino Acids; C469991:DDIT4 protein, human; D007502:Iron Chelating Agents; D046912:Multiprotein Complexes; D014157:Transcription Factors; D000076222:Mechanistic Target of Rapamycin Complex 1; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; D054648:Protein Phosphatase 2; D003676:Deferoxamine
keywords: 4E-BP1; Akt; Deferoxamine; PP2A; Rheb; S6K1; TSC2
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