title: Targeting proteins to secretory lysosomes of natural killer cells as a principle for immunoregulation.
abstract: Secretory lysosomes of natural killer (NK) cells combine storage, regulated secretion and lysosomal activity. We asked whether one could target exogenous proteins to the secretory lysosomes of NK-cells for final delivery into a tumor site upon degranulation. cDNAs for both soluble and transmembrane (tm) proteins were expressed in the human YT-Indy NK-cell line. Targeting of a soluble TNF receptor (sTNFR1) was achieved by expressing a cDNA construct with a transmembrane sequence to facilitate ER-export and by incorporating a cytosolic sorting signal (Y) from CD63 to overcome constitutive secretion. The resulting sTNFR1-tm-Y was targeted to secretory lysosomes as confirmed by results from biosynthetic radiolabeling in combination with subcellular fractionation, immunoelectron microscopy, and immunofluorescence microscopy. A soluble sTNFR1 form was generated in the secretory lysosome by endogenous proteolytic activity. Expression of exogenous normally secretory non-membrane proteins, such as alpha1-microglobulin (alpha1-m) and alpha1-antitrypsin (alpha1-at) resulted mostly in constitutive secretion although a small amount of alpha1-microglobulin was targeted to secretory lysosomes. Our results suggest a potential for delivery of pharmacologically active agents into tumor sites by use of the NK-cell secretory lysosome as a carrier.
authors.affiliation: Department of Hematology, C14, BMC, SE-22184, Lund, Sweden. markus.hansson@hematologia.lu.se
authors.forename: Markus
authors.initials: M
authors.lastname: Hansson
authors.forename: Sofia
authors.initials: S
authors.lastname: Jönsson
authors.forename: Ann-Maj
authors.initials: AM
authors.lastname: Persson
authors.forename: Jero
authors.initials: J
authors.lastname: Calafat
authors.forename: Hans
authors.initials: H
authors.lastname: Tapper
authors.forename: Inge
authors.initials: I
authors.lastname: Olsson
mesh_terms: D000818:Animals; D006801:Humans; D007694:Killer Cells, Natural / Q000276:immunology / Q000378:metabolism* / Q000648:ultrastructure; D008247:Lysosomes / Q000378:metabolism*; D008854:Microscopy, Electron; D021381:Protein Transport / Q000502:physiology; D011506:Proteins / Q000378:metabolism*
chemical_list: D011506:Proteins