SIGNALING THROUGH HUMAN KILLER-CELL ACTIVATING RECEPTORS TRIGGERS TYROSINE PHOSPHORYLATION OF AN ASSOCIATED PROTEIN COMPLEX

Our understanding of the biology of human natural killer (NK) cells ha s significantly advanced in recent years upon identification of a fami ly of NK cell-expressed genes that encode killer cell inhibitory recep tors (KIR). Individual KIR can selectively bind various HLA class I al lotypes and consequently transduce inhibitory signals that block NK ce ll lysis of ligand-bearing target cells. A distinct subset of related and linked genes express truncated versions of KIR that are otherwise highly homologous in amino acid sequence. Interestingly, these recepto rs appear to transmit stimulatory signals into NK cells and have been termed killer cell activating receptors (KAR). In this report, we demo nstrate that recognition of HLA-Cw3 by the p50 KAR, NKAT8, can potenti ate the cytotoxic response of appropriate NK cell clones. Specific cro ss-linking of this KAR with a monoclonal antibody resulted in intracel lular calcium mobilization, protein tyrosine phosphorylation, and phos phorylation of the MAP kinases, ERK1 and ERK2. In addition, we identif ied a KAR-associated disulfide-linked dimer of a 13-kDa protein that w as absent in the Jurkat T cell line and is predicted to participate in these activation signaling events. Upon treatment of NK cells with pe rvanadate, the disulfide-linked p13 and additional proteins of 25, 30, 37 and 50-95 kDa were identified as KAR-associated tyrosine phosphopr oteins. Importantly, p13 was inducibly tyrosine phosphorylated upon cr oss-linking of NKAT8, which strongly suggests that the associated p13 provides KAR with appropriate cytoplasmic structure to couple with tyr osine kinase-mediated signaling effectors.