The SH2 domain-containing inositol 5-phosphatase SHIP1 is recruited to the intracytoplasmic domain of human FcγRIIB and is mandatory for negative regulation of B cell activation

Abstract

Murine FcgammaRIIB were demonstrated to recruit SH2 domain-containing inositol 5-phosphatases (SHIP1/2), when their ITIM is tyrosyl-phosphorylated upon co-aggregation with BCR, and SHIP1 to account for FcgammaRIIB-dependent negative regulation of murine B cell activation. Although human FcgammaRIIB share the same ITIM as murine FcgammaRIIB and similarly inhibit human B cell activation, which among the four known SH2 domain-containing (tyrosine or inositol) phosphatases is/are recruited by human FcgammaRIIB is unclear. Our recent finding that, besides the ITIM, a second tyrosine-based motif is mandatory for murine FcgammaRIIB to recruit SHIP1 challenged the possibility that human FcgammaRIIB recruit this phosphatase. Human FcgammaRIIB indeed lack this motif. Using an experimental model which enabled us to compare human FcgammaRIIB and murine FcgammaRIIB under strictly controlled conditions, we show that SHIP1 is recruited to the intracytoplasmic domain of human FcgammaRIIB and inhibits the same biological responses and intracellular signals as when recruited by murine FcgammaRIIB. Identical results were observed in murine and in human B cells. We demonstrate that SHIP is necessary for human FcgammaRIIB to inhibit BCR signaling, and cannot be replaced by SHP-1 or SHP-2. Although it contains no tyrosine, the C-terminal segment of human FcgammaRIIB was as mandatory as the tyrosine-containing C-terminal segment of murine FcgammaRIIB for SHIP1 to be recruited to the ITIM. This segment, however, did not recruit the adapters Grb2/Grap which were demonstrated to stabilize the recruitment of SHIP1 to the ITIM in murine FcgammaRIIB.

FcγRIIB-Independent Mechanisms Controlling Membrane Localization of the Inhibitory Phosphatase SHIP in Human B Cells

“…SHIP controls the accumulation of PI3K products at the plasma membrane by converting PI(3,4,5)P 3 to phosphatidylinositol 3,4-bisphosphate (9,10). SHIP was found to mediate most of the inhibitory functions of FcgRIIB in B cells (11). Taken together, these findings established the paradigm that SHIP recruitment to the ITIM of FcgRIIB is a dominant mechanism controlling SHIP activity and thus B cell activation via the PI3K pathway.…”

“…Previous studies report that SHIP-mediated inhibition of PI(3,4,5)P 3 and Ca 2+ flux is most active when FcgRIIB is coligated with the BCR (11,21). SHIP is also more highly phosphorylated in its C terminus with FcgRIIB coligation (22).…”

G6b-B Inhibits Constitutive and Agonist-induced Signaling by Glycoprotein VI and CLEC-2

“…However, unexpectedly, this inhibitory effect is retained in DT40 cells in the combined absence of the SH2 domain-containing tyrosine phosphatases, SHP1 and SHP2, which have been shown to bind to G6b-B (9, 10). The inhibitory effect of G6b-B is also retained in the absence of the SH2 domain-containing inositol phosphatase, SHIP, which has been shown to inhibit B cell receptor signaling through association with the Fc␥RIIb ITIM (43,44). An alternative pathway of inhibition could be through recruitment of the SH2 domain-containing inhibitor of Src kinases, Csk, to the two ITIMs in G6b-B.…”

Deletion of microRNA-155 reduces autoantibody responses and alleviates lupus-like disease in theFaslprmouse

“…It has been suggested that loss of tolerance in lpr mice results from the down-regulation of the low-affinity IgG inhibitory receptor FcγRIIB (Fc γ receptor IIB), thereby rendering their B cells incapable of terminating stimulatory signals delivered by autoantigen-containing immune complexes (6-8). However, the mechanisms whereby lack of FcγRIIB engagement would lead to autoimmunity, and whether additional factors contribute to autoimmunity, are still unclear.The SH2 domain-containing inositol 5′-phosphatase 1 (SHIP-1) phosphatase acts downstream of inhibitory cell-surface receptors (9-12), including the FcγRIIB, which is essential in opposing B-cell activation signals in mice and humans (13,14). FcγRIIB inactivation has been implicated in the development of autoreactive GC B cells and plasma cells (15), as well as in the regulation of the persistence and longevity of bone marrow plasma cells (16).…”

“…The SH2 domain-containing inositol 5′-phosphatase 1 (SHIP-1) phosphatase acts downstream of inhibitory cell-surface receptors (9)(10)(11)(12), including the FcγRIIB, which is essential in opposing B-cell activation signals in mice and humans (13,14). FcγRIIB inactivation has been implicated in the development of autoreactive GC B cells and plasma cells (15), as well as in the regulation of the persistence and longevity of bone marrow plasma cells (16).…”