Targeting proteins to secretory lysosomes of natural killer cells as a principle for immunoregulation.
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.
Hansson
Markus
M
Department of Hematology, C14, BMC, SE-22184, Lund, Sweden. markus.hansson@hematologia.lu.se
Jönsson
Sofia
S
Persson
Ann-Maj
AM
Calafat
Jero
J
Tapper
Hans
H
Olsson
Inge
I
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*
D011506:Proteins