Inhibitory Modulation of B Cell Receptor-mediated Ca2+ Mobilization by Src Homology 2 Domain-containing Inositol 5′-Phosphatase (SHIP) (original) (raw)
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Although the Src homology 2 domain-containing 5 Ј inositol phosphatase (SHIP) is a wellknown mediator of inhibitory signals after B cell antigen receptor (BCR) coaggregation with the low affinity Fc receptor, it is not known whether SHIP functions to inhibit signals after stimulation through the BCR alone. Here, we show using gene-ablated mice that SHIP is a crucial regulator of BCR-mediated signaling, B cell activation, and B cell development. We demonstrate a critical role for SHIP in termination of phosphatidylinositol 3,4,5-triphosphate (PI[3,4,5]P 3 ) signals that follow BCR aggregation. Consistent with enhanced PI(3,4,5)P 3 signaling, we find that splenic B cells from SHIP-deficient mice display enhanced sensitivity to BCR-mediated induction of the activation markers CD86 and CD69. We further demonstrate that SHIP regulates the rate of B cell development in the bone marrow and spleen, as B cell precursors from SHIP-deficient mice progress more rapidly through the immature and transitional developmental stages. Finally, we observe that SHIP-deficient B cells have increased resistance to BCR-mediated cell death. These results demonstrate a central role for SHIP in regulation of BCR signaling and B cell biology, from signal driven development in the bone marrow and spleen, to activation and death in the periphery. 1 Abbreviations used in this paper: 7AAD, 7-amino-actinomycin D; BCR, B cell antigen receptor; Btk, Bruton's tyrosine kinase; [Ca 2 ϩ ], intracellular free calcium; HSA, heat-stable antigen; IP 3 , inositol 1,4,5-triphosphate; MAP, mitogen-activated protein; mIg, membrane-bound Ig; NF, nuclear factor; PI3-K, phosphatidylinositol 3-kinase; PI(3,4)P 2 , phosphatidylinositol 3,4-biphosphate; PI(3,4,5)P 3 , phosphatidylinositol 3,4,5-triphosphate; PLC, phospholipase C; SHIP, Src homology 2 domain-containing 5 Ј inositol phosphatase; sIg, surface Ig.
Negative Control of Store-Operated Ca2+ Influx by B Cell Receptor Cross-Linking
The Journal of Immunology, 2001
An increase in the intracellular Ca2+ concentration by B cell receptor (BCR) cross-linking plays important roles in the regulation of B cell functions. [Ca2+]i is regulated by Ca2+ release from the Ca2+ store as well as store-operated Ca2+ influx (SOC). Protein tyrosine kinases downstream of BCR cross-linking were shown to regulate the mechanism for Ca2+ release. However, it remains elusive whether BCR cross-linking regulates SOC or not. In this study, we examined the effect of BCR cross-linking on thapsigargin-induced SOC in the DT40 B cells. We found that the SOC-mediated increase in intracellular Ca2+ concentration was inhibited by BCR cross-linking. Using a membrane-potential-sensitive dye, we found that BCR cross-linking induced depolarization, which is expected to decrease the driving force of Ca2+ influx and SOC channel conductance. When membrane potential was held constant by the transmembrane K+ concentration gradient in the presence of valinomycin, the BCR-mediated inhibit...
The Journal of Immunology, 2000
Membrane microdomains (lipid rafts) are enriched in selected signaling molecules and may compartmentalize receptor-mediated signals. Here, we report that in primary human B lymphocytes and in Ramos B cells B cell receptor (BCR) stimulation induces rapid and transient redistribution of a subset of engaged BCRs to lipid rafts and phosphorylation of raft-associated tyrosine kinase substrates. Cholesterol sequestration disrupted the lipid rafts, preventing BCR redistribution, but did not inhibit tyrosine kinase activation or phosphorylation of mitogen-activated protein kinase/extracellular regulated kinase. However, raft disruption enhanced the release of calcium from intracellular stores, suggesting that rafts may sequester early signaling events that downregulate calcium flux. Consistent with this, BCR stimulation induced rapid and transient translocation of the Src homology 2 domain-containing inositol phosphatase, SHIP, into lipid rafts.
2010
Ship is an Src homology 2 domain containing inositol polyphosphate 5-phosphatase which has been implicated as an important signaling molecule in hematopoietic cells. In B cells, Ship becomes associated with Fc ␥ receptor IIB (Fc ␥ RIIB), a low affinity receptor for the Fc portion of immunoglobulin (Ig)G, and is rapidly tyrosine phosphorylated upon B cell antigen receptor (BCR)-Fc ␥ RIIB coligation. The function of Ship in lymphocytes was investigated in Ship Ϫ / Ϫ recombination-activating gene (Rag) Ϫ / Ϫ chimeric mice generated from gene-targeted Ship Ϫ / Ϫ embryonic stem cells. Ship Ϫ / Ϫ Rag Ϫ / Ϫ chimeras showed reduced numbers of B cells and an overall increase in basal serum Ig. Ship Ϫ / Ϫ splenic B cells displayed prolonged Ca 2 ϩ influx, increased proliferation in vitro, and enhanced mitogen-activated protein kinase (MAPK) activation in response to BCR-Fc ␥ RIIB coligation. These results demonstrate that Ship plays an essential role in Fc ␥ RIIB-mediated inhibition of BCR signaling, and that Ship is a crucial negative regulator of Ca 2 ϩ flux and MAPK activation.
The Journal of Experimental Medicine, 2000
Although the Src homology 2 domain–containing 5′ inositol phosphatase (SHIP) is a well-known mediator of inhibitory signals after B cell antigen receptor (BCR) coaggregation with the low affinity Fc receptor, it is not known whether SHIP functions to inhibit signals after stimulation through the BCR alone. Here, we show using gene-ablated mice that SHIP is a crucial regulator of BCR-mediated signaling, B cell activation, and B cell development. We demonstrate a critical role for SHIP in termination of phosphatidylinositol 3,4,5-triphosphate (PI[3,4,5]P3) signals that follow BCR aggregation. Consistent with enhanced PI(3,4,5)P3 signaling, we find that splenic B cells from SHIP-deficient mice display enhanced sensitivity to BCR-mediated induction of the activation markers CD86 and CD69. We further demonstrate that SHIP regulates the rate of B cell development in the bone marrow and spleen, as B cell precursors from SHIP-deficient mice progress more rapidly through the immature and tra...