Cutting Edge: NKG2D-Dependent Cytotoxicity Is Controlled by Ligand Distribution in the Target Cell Membrane

Molecular and Cellular Immunology Section, Laboratory of Immunogenetics, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852, USA.
The Journal of Immunology (Impact Factor: 4.92). 04/2011; 186(10):5538-42. DOI: 10.4049/jimmunol.1002254
Source: PubMed


Although the importance of membrane microdomains in receptor-mediated activation of lymphocytes has been established, much less is known about the role of receptor ligand distribution on APC and target cells. Detergent-resistant membrane domains, into which GPI-linked proteins partition, are enriched in cholesterol and glycosphingolipids. ULBP1 is a GPI-linked ligand for natural cytotoxicity receptor NKG2D. To investigate how ULBP1 distribution on target cells affects NKG2D-dependent NK cell activation, we fused the extracellular domain of ULBP1 to the transmembrane domain of CD45. Introduction of this transmembrane domain eliminated the association of ULBP1 with the detergent-resistant membrane fraction and caused a significant reduction of cytotoxicity and degranulation by NK cells. Clustering and lateral diffusion of ULBP1 was not affected by changes in the membrane anchor. These results show that the partitioning of receptor ligands in discrete membrane domains of target cells is an important determinant of NK cell activation.

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    • "Independent, and more direct examinations of the role of the GPI anchor for the human NKG2D ligands ULBP-1 and ULBP-2 revealed curiously discordant findings. While ULBP-1 may be expressed stably at the cell surface as a transmembrane fusion protein, it is significantly less potent in activating NK cell cytotoxicity, and the authors concluded that NKG2D ligand distribution within the membrane influences the NK cell-target cell interaction [32]. Although ULBP1-3 are normally GPI-anchored proteins, ULBP2 is unique in that a minor fraction exists on the surface as a transmembrane protein. "
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    • "Clustering of the GPI-anchored ULBPs within lipid rafts, that are known to polarize to the site of interaction between the NK cell and the susceptible target cell (Lou et al., 2000), could increase the avidity of interaction of these molecules with the NKG2D receptor. In support of this hypothesis, Martinez et al. (2011) have observed that redistribution of ULBP1 outside of DRM, through the replacement of the GPI linkage in ULBP1 by the TM region of CD45, resulted in diminished NK cell responses to target cells expressing these molecules. In contrast, a naturally occurring TM form of ULBP2 was as capable of enhancing NK cell activation as the GPI-linked form of ULBP2 (Fernandez-Messina et al., 2011). "
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