title: Cystatin F is secreted, but artificial modification of its C-terminus can induce its endocytic targeting.
abstract: Cystatins constitute a superfamily of cysteine protease inhibitors. A member of the type II secreted cystatin family, cystatin F, has been identified through different gene array experiments to be specifically expressed in hematopoietic cells as well as to be associated with several malignant tumors, suggesting a role in immunity or cancer progression. Cystatin F specificity as a protease inhibitor is still elusive, and understanding the cellular traffic of this molecule is therefore a major step in its characterization. Although the mannosylation-6 phosphate of cystatin F has been suggested, no conclusive evidences of its endosomal targeting have been reported. Here we show using U937 cells that cystatin F is secreted as a disulfide bridge-linked dimer and is not associated with endosomes intracellularly. Interestingly, although cystatin F targeting to endosomes or lysosomes is not observed in U937, modification of its C-terminal end by the addition of several amino acids promotes its accumulation in the lysosomes of transfected HeLa cells. This observation suggests that cystatin F can be targeted to the endocytic pathway under specific conditions and its C-terminal domain might contribute to this event.
authors.affiliation: Centre d'Immunologie de Marseille-Luminy, CNRS-INSERM-Université de la Méditerranée, 13288 Marseille, Cedex 09, France.
authors.forename: Fanny
authors.initials: F
authors.lastname: Cappello
authors.forename: Evelina
authors.initials: E
authors.lastname: Gatti
authors.forename: Voahirana
authors.initials: V
authors.lastname: Camossetto
authors.forename: Alexandre
authors.initials: A
authors.lastname: David
authors.forename: Hugues
authors.initials: H
authors.lastname: Lelouard
authors.forename: Philippe
authors.initials: P
authors.lastname: Pierre
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry*; D000818:Animals; D014408:Biomarkers, Tumor; D015891:Cystatins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D019281:Dimerization; D004220:Disulfides / Q000737:chemistry; D004705:Endocytosis; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006031:Glycosylation; D049452:Green Fluorescent Proteins; D006367:HeLa Cells; D006801:Humans; D007801:Langerhans Cells / Q000166:cytology / Q000378:metabolism; D008164:Luminescent Proteins; D051379:Mice; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D020298:U937 Cells
chemical_list: D000596:Amino Acids; D014408:Biomarkers, Tumor; C116891:CST7 protein, human; D015891:Cystatins; D004220:Disulfides; D008164:Luminescent Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins