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. (C) 2003 Elsevier Ltd. All rights reserved.
Subject classification (UKÄ)
- Immunology in the medical area