Human NKG2F is expressed and can associate with DAP12

The NKG2 family of C-lectin type molecules is important for regulating the function of natural killer and subpopulations of T cells. NKG2A/B contains an immunoreceptor tyrosine-based inhibitory motif (ITIM) and accordingly functions as an inhibitory receptor, whereas NKG2C and -E/H associate with DAP12 via a positively charged residue in their transmembrane domains and function as activation receptors. Each of these molecules is paired with CD94 for expression and recognizes HLA-E as a ligand. NKG2F is an orphan gene within the NKG2 family whose translated product would contain both a positively charged residue in its transmembrane region, an intracellular ITIM-like sequence and an extracellular domain (62 residues) that is truncated relative to other NKG2 molecules. We show that NKG2F is expressed as a protein in NK cells. Expression appears to be confined to intracellular compartments probably due to its inability to associate with CD94. It can however associate with DAP12 thereby providing activation signaling potential. We were unable to demonstrate phosphorylation of the Tyr residue in the ITIM-like motif suggesting that it is a mock ITIM. NKG2F could be a receptor component with an as yet unidentified partner(s), could function to regulate cell activation through competition for DAP12 with other receptors, such as NKG2C and -E/H, or it could simply be a vestigial gene product.