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Negative Control of Store-Operated Ca²⁺ Influx by B Cell Receptor Cross-Linking

Akiko Hashimoto^*, Kenzo Hirose^*, Tomohiro Kurosaki and Masamitsu Iino^1,*

^* Department of Pharmacology, Graduate School of Medicine, University of Tokyo, and Core Research for Engineering, Science, and Technology, Japan Science and Technology Corporation, Tokyo, Japan; and Department of Molecular Genetics, Institute for Liver Research, Kansai Medical University, Moriguchi, Japan

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 inhibition of SOC was still observed. Thus, the BCR-mediated inhibition of SOC involves both depolarization-dependent and depolarization-independent mechanisms of SOC inhibition. The depolarization-independent inhibition of the SOC was abolished in Lyn-deficient, but not in Bruton’s tyrosine kinase-, Syk- or SHIP (Src homology 2 domain containing phosphatidylinositol 5'-phosphatase)-deficient cells, indicating that Lyn is involved in the inhibition. These results show novel pathways of BCR-mediated SOC regulations.

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