DPB162-AE, an inhibitor of store-operated Ca2+ entry, can deplete the endoplasmic reticulum Ca2+ store

Abstract

Store-operated Ca²⁺ entry (SOCE), an important Ca²⁺ 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 (IP₃Rs), sarco/endoplasmic reticulum Ca²⁺-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 Ca²⁺-store content at concentrations required for complete SOCE inhibition. DPB162-AE increased the cytosolic Ca²⁺ levels by reducing the ER Ca²⁺ store in cell lines as well as in primary cells. DPB162-AE did not affect SERCA activity, but provoked a Ca²⁺ leak from the ER, even after application of the SERCA inhibitor thapsigargin. IP₃Rs partly contributed to the DPB162-AE-induced Ca²⁺ leak, since pharmacologically and genetically inhibiting IP₃R 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 Ca²⁺-store content by inducing a Ca²⁺-leak pathway at concentrations needed for adequate SOCE inhibition.

Keywords: 2-APB analogue; Ca(2+)-leak pathway; Calcium; DPB162-AE; Endoplasmic reticulum; Store-operated Ca(2+) entry.