Ca2+-independent phospholipase A2 is a novel determinant of store-operated Ca2+ entry

Store-operated cation (SOC) channels and capacitative Ca2+ entry (CCE) play very important role in cellular function, but the mechanism of their activation remains one of the most intriguing and long lasting mysteries in the field of Ca2+ signaling. Here, we present the first evidence that Ca2+-independent phospholipase A(2) (iPLA(2)) is a crucial molecular determinant in activation of SOC channels and store-operated Ca2+ entry pathway. Using molecular, imaging, and electrophysiological techniques, we show that directed molecular or pharmacological impairment of the functional activity of iPLA(2) leads to irreversible inhibition of CCE mediated by nonselective SOC channels and by Ca2+-release-activated Ca2+ (CRAC) channels. Transfection of vascular smooth muscle cells (SMC) with antisense, but not sense, oligonucleotides for iPLA(2) impaired thapsigargin (TG)-induced activation of iPLA(2) and TG-induced Ca2+ and Mn2+ influx. Identical inhibition of TG-induced Ca2+ and Mn2+ influx (but not Ca2+ release) was observed in SMC, human platelets, and Jurkat T-lymphocytes when functional activity of iPLA(2) was inhibited by its mechanism-based suicidal substrate, bromoenol lactone (BEL). Moreover, irreversible inhibition of iPLA(2) impaired TG-induced activation of single nonselective SOC channels in SMC and BAPTA (1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid)-induced activation of whole-cell CRAC current in rat basophilic leukemia cells. Thus, functional iPLA(2) is required for activation of store-operated channels and capacitative Ca2+ influx in wide variety of cell types.