DIFFERENTIAL ASSOCIATION OF PHOSPHATASES WITH HEMATOPOIETIC CO-RECEPTORS BEARING IMMUNORECEPTOR TYROSINE-BASED INHIBITION MOTIFS

A novel family of inhibitory co-receptors has been recently defined ac cording to the presence in their intracytoplasmic domain of immunorece ptor tyrosine-based inhibition motifs (ITIM). In particular, this fami ly includes a low-affinity receptor for IgG, Fc gamma RIIB, which is w idely expressed on hematopoietic cells, as well as killer cell inhibit ory receptors (KIR) for major histocompatibility complex (MHC) class I proteins, expressed on both T and natural killer (NK) lymphocytes. Fc gamma RIIB and KIR inhibitory function depends upon the tyrosine phos phorylation of their respective ITIM. Phosphorylated Fc gamma RIIB and KIR ITIM bind the tandem SH2 tyrosine phosphatases, SHP-1 and SHP-2. Recently, Fc gamma RIIB has been shown to associate with a polyphospha te inositol 5-phosphatase, SHIP which appears to be involved in its in hibitory function. Using cell lysate adsorption to phosphorylated ITIM peptides and surface plasmon resonance, we demonstrate here that, in contrast to Fc gamma RIIB, KIR (CD158b: p58.2) do not bind to SHIP, an d only recruit SHP-1 and SHP-2. In addition, we show that point mutati on of the amino acid residue in position tyrosine-2 of Fc gamma RIIB a nd KIR ITIM abolihes their binding to SHP-1 and SHP-2, but leaves inta ct the association of SHIP with Fc gamma RIIB ITIM. These data contrib ute to the structural definition of ITIM and document a differential r ecruitment of phosphatases by distinct ITIM. These findings also revea l that diverse strategies of inhibition are used by distinct members o f the ITIM-bearing coreceptor family.