Differential expression of ligands for NKG2D and DNAM-1 receptors by epithelial ovarian cancer-derived exosomes and its influence on NK cell cytotoxicity
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Cancers constitutively produce and secrete into the blood and other biofluids 30–150 nm-sized endosomal vehicles called exosomes. Cancer-derived exosomes exhibit powerful influence on a variety of biological mechanisms to the benefit of the tumors that produce them. We studied the immunosuppressive ability of epithelial ovarian cancer (EOC) exosomes on two cytotoxic pathways of importance for anticancer immunity—the NKG2D receptor-ligand pathway and the DNAM-1-PVR/nectin-2 pathway. Using exosomes, isolated from EOC tumor explant and EOC cell-line culture supernatants, and ascitic fluid from EOC patients, we studied the expression of NKG2D and DNAM-1 ligands on EOC exosomes and their ability to downregulate the cognate receptors. Our results show that EOC exosomes differentially and constitutively express NKG2D ligands from both MICA/B and ULBP families on their surface, while DNAM-1 ligands are more seldom expressed and not associated with the exosomal membrane surface. Consequently, the NKG2D ligand-bearing EOC exosomes significantly downregulated the NKG2D receptor expression on peripheral blood mononuclear cells (PBMC) while the DNAM-1 receptor was unaffected. The downregulation of NKG2D receptor expression was coupled to inhibition of NKG2D receptor-ligand-mediated degranulation and cytotoxicity measured in vitro with OVCAR-3 and K562 cells as targets. The EOC exosomes acted as a decoy impairing the NKG2D mediated cytotoxicity while the DNAM-1 receptor-ligand system remained unchanged. Taken together, our results support and explain the mechanism behind the recently reported finding that in EOC, NK-cell recognition and killing of tumor cells was mainly dependent on DNAM-1 signaling while the contribution of the NKG2D receptor-ligand pathway was complementary and uncertain.
KeywordsEpithelial ovarian cancer/EOC Tumor Exosomes NKG2D DNAM-1/CD266 Cytotoxicity MICA/B ULBP PVR Nectin-2
Patients and colleagues from the Dept. of Obstetrics and Gynecology at Norrland’s University Hospital are gratefully acknowledged. This work was supported by Swedish National Cancer Research Foundation (Cancerfonden, 2013/439), Swedish National Research Foundation (Vetenskapsrådet, K2013-54X-22341-01-05), Central ALF fund VLL, and Insamlingsstiftelsen, Umeå University.
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Conflicts of interest
- 16.Stenqvist AC, Nagaeva O, Baranov V, Mincheva-Nilsson L. Exosomes secreted by human placenta carry functional Fas ligand and TRAIL molecules and convey apoptosis in activated immune cells, suggesting exosome-mediated immune privilege of the fetus. J Immunol. 2013;191:5515–23.CrossRefPubMedGoogle Scholar
- 17.Mincheva-Nilsson L, Nagaeva O, Chen T, Stendahl U, Antsiferova J, Mogren I, et al. Placenta-derived soluble MHC class I chain-related molecules down-regulate NKG2D receptor on peripheral blood mononuclear cells during human pregnancy: a possible novel immune escape mechanism for fetal survival. J Immunol. 2006;176:3585–92.CrossRefPubMedGoogle Scholar
- 19.Greening DW, Xu R, Ji H, Tauro BJ, Simpson RJ. A protocol for exosome isolation and characterization: evaluation of ultracentrifugation, density-gradient separation and immunoaffinity capture methods. In Proteomic profiling: Methods and Protocols. Anton Posh (ed). Methods in molecular Biology, vol. 1295, DOI 10.1007/978-1-4939-2550-6_15, 2015.