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 Ca ²⁺-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 Ca ²⁺ 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 Ca ²⁺ 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.