The SH2 domain containing inositol 5-phosphatase SHIP2 associates to the immunoreceptor tyrosine-based inhibition motif of Fc gamma RIIB in B cells under negative signaling

Fc gamma RIIB are single-chain low-affinity receptors for IgG that bear an immunoreceptor tyrosine-based inhibition motif (ITIM) in their intracytopla smic domain and that negatively regulate immunoreceptor tyrosine-based acti vation motif (ITAM)-dependent cell activation. In B cells, coaggregation of the B cell receptor (BCR) and Fc gamma RIIB leads to an inhibition of B ce ll activation. Inhibitory properties of Fc gamma RIIB have been related to the recruitment of SHIP, an SH2 domain-containing inositol 5-phosphatase (r eferred to as SHIP1), via ITIM phosphorylated Fc gamma RIIB. Here, we demon strate that the second SH2 domain-containing inositol 5-phosphatase SHIP2 c ould also bind to the Fc gamma RIIB ITIM. As a model, a Fc gamma RIIB defic ient B cell line (IIA1.6), transfected with a cDNA encoding either w.t. Fc gamma RIIB1' or Fc gamma RIIB1' whose ITIM tyrosine was mutated has been us ed. SHIP2 tyrosine phosphorylation and association to the adaptator protein Shc were only found in transfectants expressing w.t. Fc gamma RIIB1'. SHIP 2 was also found to bind to a phosphopeptide corresponding to the ITIM sequ ence of Fc gamma RIIB. There was no binding to the nonphosphorylated peptid e. Finally, both SHIP2 and SHIP1 were coprecipitated with Fc gamma RIIB1' u pon coaggregation with BCR in IIA1.6 transfectants. (C) 2000 Elsevier Scien ce B.V. All rights reserved.