Hashimoto A, Hirose K, Okada H, Kurosaki T, Iino M
Department of Pharmacology, Faculty of Medicine, University of Tokyo, and CREST, Japan Science and Technology Corporation, Tokyo 113, Japan.
J Biol Chem. 1999 Apr 16;274(16):11203-8. doi: 10.1074/jbc.274.16.11203.
Src homology 2 domain-containing inositol 5'-phosphatase (SHIP) mediates inhibitory signals that attenuate intracellular Ca2+ mobilization in B cells upon B cell receptor (BCR) stimulation. To clarify the mechanisms affected by SHIP, we analyzed Ca2+ mobilization in the DT40 B cell line in which the SHIP gene was disrupted. In SHIP-deficient cells, Ca2+ transient elicited by BCR stimulation was more prolonged than that in control cells both in the presence and absence of extracellular Ca2+. Inositol 1,4, 5-trisphosphate production following BCR stimulation was enhanced in SHIP-deficient cells. In SHIP-deficient cells in comparison with the control cells, BCR stimulation in the absence of extracellular Ca2+ induced a greater degree of Ca2+ store depletion and the Ca2+ influx upon re-addition of extracellular Ca2+ was also greater. However, store-operated Ca2+ influx (SOC) elicited by thapsigargin-induced store depletion was not affected by SHIP. These results indicate that the primary target pathway of SHIP is the Ca2+ release from the stores, and that Ca2+ influx by the SOC mechanism is secondarily controlled by the level of Ca2+ in the stores without direct inhibition of SOC. In this way, SHIP may play an important role in ensuring the robust tuning of Ca2+ signaling in B cells.
含Src同源2结构域的肌醇5'-磷酸酶（SHIP）介导抑制性信号，该信号在B细胞受体（BCR）刺激后减弱B细胞内的Ca2+动员。为了阐明受SHIP影响的机制，我们分析了SHIP基因被破坏的DT40 B细胞系中的Ca2+动员情况。在SHIP缺陷细胞中，无论有无细胞外Ca2+，BCR刺激引发的Ca2+瞬变都比对照细胞中的持续时间更长。SHIP缺陷细胞中BCR刺激后肌醇1,4,5-三磷酸的产生增加。与对照细胞相比，在无细胞外Ca2+的情况下，SHIP缺陷细胞中的BCR刺激导致更大程度的Ca2+储存耗竭，重新添加细胞外Ca2+后的Ca2+内流也更大。然而，毒胡萝卜素诱导的储存耗竭引发的储存操纵性Ca2+内流（SOC）不受SHIP影响。这些结果表明，SHIP的主要靶标途径是Ca2+从储存中释放，并且SOC机制介导的Ca2+内流其次受储存中Ca2+水平的控制，而不是直接抑制SOC。通过这种方式，SHIP可能在确保B细胞中Ca2+信号的稳健调节方面发挥重要作用。
