DPB162-AE, an inhibitor of store-operated Ca entry, can deplete the endoplasmic reticulum Ca store.

Store-operated Ca entry (SOCE), an important Ca signaling pathway in non-excitable cells, regulates a variety of cellular functions. To study its physiological role, pharmacological tools, like 2-aminoethyl diphenylborinate (2-APB), are used to impact SOCE. 2-APB is one of the best characterized SOCE inhibitors. However, 2-APB also activates SOCE at lower concentrations, while it inhibits inositol 1,4,5-trisphosphate receptors (IPRs), sarco/endoplasmic reticulum Ca-ATPases (SERCAs) and other ion channels, like TRP channels. Because of this, 2-APB analogues that inhibit SOCE more potently and more selectively compared to 2-APB have been developed. The recently developed DPB162-AE is such a structural diphenylborinate isomer of 2-APB that selectively inhibits SOCE currents by blocking the functional coupling between STIM1 and Orai1. However, we observed an adverse effect of DPB162-AE on the ER Ca-store content at concentrations required for complete SOCE inhibition. DPB162-AE increased the cytosolic Ca levels by reducing the ER Ca store in cell lines as well as in primary cells. DPB162-AE did not affect SERCA activity, but provoked a Ca leak from the ER, even after application of the SERCA inhibitor thapsigargin. IPRs partly contributed to the DPB162-AE-induced Ca leak, since pharmacologically and genetically inhibiting IPR function reduced, but not completely blocked, the effects of DPB162-AE on the ER store content. Our results indicate that, in some conditions, the SOCE inhibitor DPB162-AE can reduce the ER Ca-store content by inducing a Ca-leak pathway at concentrations needed for adequate SOCE inhibition.