title: Characterization of the murine macrophage mannose receptor: demonstration that the downregulation of receptor expression mediated by interferon-gamma occurs at the level of transcription.
abstract: The macrophage mannose receptor (MMR) is a 175-Kd cell-surface transmembrane glycoprotein that is expressed on tissue macrophages where it functions both to mediate the uptake of mannose-rich glycoproteins and as a phagocytic receptor for bacteria, yeasts, and other pathogenic microorganisms. In this report we describe the cloning of the full-length cDNA of the mouse macrophage mannose receptor and we investigate the level at which interferon gamma (IFN-gamma) downregulates mannose receptor expression. The latter is a marker of the functional state of the cell as high levels are expressed on resident and inflammatory macrophages, whereas cells activated by treatment with IFN-gamma have decreased-to-absent cell-surface mannose receptor expression. The murine MMR cDNA contains an open reading frame that predicts a protein of 1,456 amino acids. Transient expression of the protein in heterologous cells shows that this cDNA encodes a functional mannose receptor. The deduced amino acid sequence of this protein has an overall 82% homology with the human mannose receptor and as such, the ectodomain contains an N-terminus that is cysteine-rich followed by a fibronectin type II domain and eight carbohydrate recognition domains (CRDs). The ectodomain is linked to a hydrophobic transmembrane region and a 46-amino acid cytoplasmic tail. All of the eight CRDs are particularly well conserved, especially CRD4, which shows 92% homology with the equivalent region of the human protein. Steady-state levels of murine MMR mRNA were measured in the macrophage cell line J774E, which is known to express the protein at the cell surface. These levels were decreased by a 4- to 8-hour incubation with IFN-gamma, but were almost abolished by overnight treatment with this cytokine. Nuclear run-on experiments showed that IFN-gamma inhibits MMR gene transcription. Therefore, the regulation of mannose receptor expression by IFN-gamma provides a novel system in which to study the mechanisms by which this cytokine represses gene expression.
authors.affiliation: Division of Hematology/Oncology, Children's Hospital, Boston, MA 02115.
authors.forename: N
authors.initials: N
authors.lastname: Harris
authors.forename: M
authors.initials: M
authors.lastname: Super
authors.forename: M
authors.initials: M
authors.lastname: Rits
authors.forename: G
authors.initials: G
authors.lastname: Chang
authors.forename: R A
authors.initials: RA
authors.lastname: Ezekowitz
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002460:Cell Line; D002478:Cells, Cultured; D015536:Down-Regulation / Q000187:drug effects*; D015870:Gene Expression; D015723:Gene Library; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology*; D037181:Lectins, C-Type; D008264:Macrophages / Q000187:drug effects / Q000502:physiology*; D008358:Mannose / Q000378:metabolism; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins; D008562:Membrane Glycoproteins; D051379:Mice; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides; D016133:Polymerase Chain Reaction; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic / Q000096:biosynthesis / Q000187:drug effects / Q000235:genetics*; D011994:Recombinant Proteins; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection
chemical_list: D037181:Lectins, C-Type; C581013:MRC1 protein, mouse; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins; D008562:Membrane Glycoproteins; D009838:Oligodeoxyribonucleotides; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic; D011994:Recombinant Proteins; D007371:Interferon-gamma; D008358:Mannose