title: A cytoplasmic structure resembling large protein aggregates induced by interferons.
abstract: IFP 35 is an interferon (IFN)-regulated leucine zipper protein, expression of which is observed in a variety of cell types including monocytes/macrophages, epithelial cells and fibroblasts. Using immunofluorescence studies, we demonstrate that IFP 35 is found in characteristic punctate cytoplasmic structures after IFN treatment. Co-localization experiments using double immunofluorescence and confocal laser scanning microscopy failed to show association of IFP 35 with known organelles (mitochondria, peroxisomes, endoplasmic reticulum, lysosomes, endosomes, Golgi complex), ribosomes, or actin filaments. Subcellular fractionation to separate membrane-associated from cytoplasmic proteins demonstrated that IFP 35 localizes to the cytoplasm. Separation of postnuclear supernatant from HeLa cells by gel filtration revealed that IFP 35 eluted at a molecular mass of 200-440 kD, suggesting that IFP 35 is part of protein complexes. Electron microscopic studies showed cytoplasmic clusters of a few aggregates of IFP 35 in IFN-treated cells which were neither associated with nor surrounded by a membrane. A combination of immunoprecipitation and immunofluorescence studies of cells transfected with a hemagglutinin epitope-tagged IFP 35 expression construct demonstrated complex formation and co-localization of endogenous and transfected IFP 35. Taken together, our studies demonstrate that IFP 35 associates with unique cytoplasmic structures that are distinct from known organelles and resemble large protein aggregates.
authors.affiliation: Institut für Medizinische Mikrobiologie Medizinische Hochschule Hannover, Hannover, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Meyerdierks
authors.forename: B
authors.initials: B
authors.lastname: Denecke
authors.forename: M
authors.initials: M
authors.lastname: Rohde
authors.forename: E J
authors.initials: EJ
authors.lastname: Taparowsky
authors.forename: E C
authors.initials: EC
authors.lastname: Böttger
mesh_terms: D015153:Blotting, Western; D002460:Cell Line; D003593:Cytoplasm / Q000378:metabolism*; D003599:Cytoskeleton / Q000378:metabolism; D019084:Fluorescent Antibody Technique, Indirect; D006367:HeLa Cells; D006801:Humans; D007150:Immunohistochemistry; D051796:Inhibitor of Differentiation Proteins; D007372:Interferons / Q000494:pharmacology*; D047908:Intracellular Signaling Peptides and Proteins; D016350:Leucine Zippers / Q000187:drug effects / Q000235:genetics; D008854:Microscopy, Electron; D008870:Microtubules / Q000378:metabolism; D009687:Nuclear Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D013347:Subcellular Fractions; D014162:Transfection
chemical_list: C085378:IFI35 protein, human; D051796:Inhibitor of Differentiation Proteins; D047908:Intracellular Signaling Peptides and Proteins; D009687:Nuclear Proteins; D007372:Interferons