A novel Stim1-dependent, non-capacitative Ca2+ entry pathway is activated by B cell receptor stimulation and depletion of Ca2+ stores

In most non-excitable cells, the depletion of intracellular Ca2+ stores activates capacitative Ca2+ entry (CCE), which is a Ca2+-selective and La3+-sensitive entry pathway. Here, we report a novel mechanism of La3+-resistant Ca2+ entry that is synergistically regulated by B cell receptor (BCR) stimulation and Ca2+ store depletion (B-SOC). In the wildtype (WT) DT40 cells, BCR stimulation with anti-IgM antibodies induced Ca2+ release and subsequent Ca2+ entry in the presence of 0.3 μMLa3+ which blocks CCE completely. In the inositol 1,4,5-trisphosphate receptor-deficient (IP3R-KO) cells, BCR stimulation elicited neither Ca2+ release nor Ca2+ entry. However, under pretreatment of thapsigargin (ThG), BCR stimulation induced La3+-resistant Ca2+ entry into both WT and IP3R-KO cells. These results indicate that BCR stimulation and Ca2+ store depletion work in concert to activate the La3+-resistant Ca2+ entry pathway. B-SOC was inhibited by tyrosine kinase inhibitor, genistein. In addition, B-SOC was completely abolished in Stim1-deficient cells and was restored by overexpression of yellow fluorescent protein (YFP)-tagged Stim1, but was unaffected by double knockdown of Orai1/Orai2. These results demonstrate a unique non-CCE pathway, in which Ca2+ entry depends on Stim1 and tyrosine kinase activation. It is likely that similar regulation of Ca2+ entry occurs in other cell types including salivary gland cells.