FcγRIIb-mediated negative regulation of BCR signalling is associated with the recruitment of the MAPkinase-phosphatase, Pac-1, and the 3′-inositol phosphatase, PTEN

Differential signalling during B-cell maturation

“…The key signalling element recruited to this ITIM is SHIP (SH2 domain-containing inositol 5 -phosphatase), a phosphatase that removes the 5 -phosphate residue from PI lipids. SHIP thus depletes the cells of PI-3,4,5-P 3 (PIP 3 ) [96,107,108], impairing the ability of the BCR to recruit PH domain-containing proteins resulting in suppression of PLC␥, Akt and Btk activation [107][108][109][110]. Moreover, since SHIP and Grb-2 directly compete for binding sites on Shc, Fc␥RIIB signalling disrupts the formation of Grb-2/SOS complexes and further impairs Erk-MAPK signalling [107].…”

The development of mature B lymphocytes requires the combined function of CD19 and the p110δ subunit of PI3K

“…Cells were analyzed using LSR II flow cytometer (Becton Dickinson) and FlowJo software (Treestar, Ashland, OR). The following antibodies were used: anti-c-kit (CD117, ACK45), anti-CD25 (7D4), anti-B220 (RA3-6B2), anti-CD21 (7G6), anti-CD23 (B3B4), anti-kappa (187.1), anti-lambda1 (R11-153) (all from BD/Pharmingen); anti-IgD (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26) Cell viability assay. Purified lymph node B cells were cultured at 5 x 10 5 cells/ml in IMDM supplemented with 10% FCS, 50 µM β-mercaptoethanol, 2 mM glutamine, 100 U/ml penicillin and 100 µg/ml streptomycin (culture medium) in the presence or absence of 200 ng/ml BAFF (Peprotech).…”

“…11,12 Furthermore, FcγRIIb, a crucial negative regulator of BCR signaling regulates PIP3 levels through recruitment of PTEN and SHIP. 13 Recently we reported that immature B cells from mice lacking p110δ failed to properly suppress the expression of the RAG genes. As a consequence these B cells inappropriately initiated LC recombination resulting in elevated levels of antibody bearing λ LC, or, in the context of a BCR transgene loss of antigen specificity.…”

Immune complex-mediated co-ligation of the BCR with FcγRIIB results in homeostatic apoptosis of B cells involving Fas signalling that is defective in the MRL/Lpr model of systemic lupus erythematosus

“…The precise mechanisms underlying apoptosis resulting from co-ligation of the BCR with FcγRIIB have yet to be delineated but we and others have previously reported recruitment of negative elements (eg SHIP, SHP, DOK, PTEN and PAC-1) that antagonise BCR signalling [10][11][12][13] as well as disruption of the mitochondrial membrane potential (MMP) [14], the loss of which is considered to be the so called 'point of no return', after which cells irreversibly engage the 'intrinsic' or mitochondrial apoptosis programme [15]. We now show that such FcγRIIB-driven apoptosis is mediated by both mitochondrial-and lysosomal-effector mechanisms and by upregulation of Fas and consequent coupling to caspase 8-dependent death receptor signalling.…”