Mutational analysis of immunoreceptor tyrosine-based inhibition motifs of the Ig-like transcript 2 (CD85j) leukocyte receptor

The inhibitory receptor Ig-like transcript (ILT)2 (leukocyte Ig-like receptor or CD85j) is a type I transmembrane protein expressed by different leukocyte lineages. The extracellular region of ILT2 binds HLA class I molecules, and its cytoplasmic domain displays four immunoreceptor tyrosine-based inhibition motifs. Upon tyrosine phosphorylation ILT2 recruits the Src homology 2 domain-containing protein tyrosine phosphatase 1 (SHP-1) that is involved in negative signaling. To address the structural basis of ILT2-mediated inhibitory signaling, deletion and single tyrosine mutants were generated and transfected in the COS-7 and rat basophilic leukemia cell lines; their abilities to bind SHP-1 and to inhibit FcepsilonR-induced serotonin release in rat basophilic leukemia cells were studied. Both biochemical and functional analyses revealed tyrosines 644 (SIYATL) and 614 (VTYAQL) as the SHP-1 docking sites required for ILT2 inhibitory function. Substitution of tyrosine 562 (VTYAEV) did not alter receptor function. By contrast, mutation of tyrosine 533 (NLYAAV) interfered with ILT2 tyrosine phosphorylation and the subsequent SHP-1 recruitment, thus supporting a regulatory role for this motif.