Morita Takao, Tanimura Akihiko, Baba Yoshihiro, Kurosaki Tomohiro, Tojyo Yosuke
Department of Pharmacology, School of Dentistry, Health Sciences University of Hokkaido, Ishikari-Tobetsu, Hokkaido 061-0293, Japan.
J Cell Sci. 2009 Apr 15;122(Pt 8):1220-8. doi: 10.1242/jcs.041640.
The depletion of intracellular Ca(2+) stores activates capacitative Ca(2+) entry (CCE), which is a Ca(2+)-selective and La(3+)-sensitive entry pathway. Here, we report a novel mechanism of La(3+)-resistant Ca(2+) entry that is synergistically regulated by B-cell-receptor (BCR) stimulation and Ca(2+) store depletion. In DT40 cells, stimulation of BCRs with anti-IgM antibodies induced Ca(2+) release and subsequent Ca(2+) entry in the presence of 0.3 microM La(3+), a condition in which CCE is completely blocked. This phenomenon was not observed in inositol 1,4,5-trisphosphate receptor-deficient DT40 (IP3R-KO) cells. However, in response to thapsigargin pretreatment, BCR stimulation induced La(3+)-resistant Ca(2+) entry into both wild-type and IP3R-KO cells. These results indicate that BCR stimulation alone does not activate Ca(2+) entry, whereas BCR stimulation and depleted Ca(2+) stores (either due to IP3R-mediated Ca(2+) release or Ca(2+) uptake inhibition) work in concert to activate La(3+)-resistant Ca(2+) entry. This Ca(2+) entry was inhibited by genistein. In addition, BCR-mediated Ca(2+) entry was completely abolished in Stim1-deficient DT40 cells and was restored by overexpression of YFP-Stim1, but was unaffected by double knockdown of Orai1 and Orai2. These results demonstrate a unique non-CCE pathway, in which Ca(2+) entry depends on Stim1- and BCR-mediated activation of tyrosine kinases.
细胞内钙离子库的耗竭会激活容量性钙离子内流（CCE），这是一种对钙离子具有选择性且对镧离子（La(3+)）敏感的内流途径。在此，我们报告一种新型的抗镧离子钙离子内流机制，该机制受B细胞受体（BCR）刺激和钙离子库耗竭协同调控。在DT40细胞中，用抗IgM抗体刺激BCR会在存在0.3微摩尔镧离子的情况下诱导钙离子释放及随后的钙离子内流，而在这种条件下CCE会被完全阻断。这种现象在缺乏肌醇1,4,5 -三磷酸受体的DT40（IP3R - KO）细胞中未观察到。然而，响应于毒胡萝卜素预处理，BCR刺激会诱导抗镧离子钙离子内流进入野生型和IP3R - KO细胞。这些结果表明，单独的BCR刺激不会激活钙离子内流，而BCR刺激和耗竭的钙离子库（无论是由于IP3R介导的钙离子释放还是钙离子摄取抑制）协同作用以激活抗镧离子钙离子内流。这种钙离子内流被染料木黄酮抑制。此外，在缺乏Stim1的DT40细胞中，BCR介导的钙离子内流完全被消除，通过过表达黄色荧光蛋白标记的Stim1得以恢复，但不受Orai1和Orai2双重敲低的影响。这些结果证明了一种独特的非CCE途径，其中钙离子内流依赖于Stim1和BCR介导的酪氨酸激酶激活。
