Sodium regulates PLC and IP3R‐mediated calcium signaling in invasive breast cancer cells

Abstract

AbstractIntracellular Ca2+ signaling and Na+ homeostasis are inextricably linked via ion channels and co‐transporters, with alterations in the concentration of one ion having profound effects on the other. Evidence indicates that intracellular Na+ concentration ([Na+]i) is elevated in breast tumors, and that aberrant Ca2+ signaling regulates numerous key cancer hallmark processes. The present study therefore aimed to determine the effects of Na+ depletion on intracellular Ca2+ handling in metastatic breast cancer cell lines. The relationship between Na+ and Ca2+ was probed using fura‐2 and SBFI fluorescence imaging and replacement of extracellular Na+ with equimolar N‐methyl‐D‐glucamine (0Na+/NMDG) or choline chloride (0Na+/ChoCl). In triple‐negative MDA‐MB‐231 and MDA‐MB‐468 cells and Her2+ SKBR3 cells, but not ER+ MCF‐7 cells, 0Na+/NMDG and 0Na+/ChoCl resulted in a slow, sustained depletion in [Na+]i that was accompanied by a rapid and sustained increase in intracellular Ca2+ concentration ([Ca2+]i). Application of La3+ in nominal Ca2+‐free conditions had no effect on this response, ruling out reverse‐mode NCX activity and Ca2+ entry channels. Moreover, the Na+‐linked [Ca2+]i increase was independent of membrane potential hyperpolarization (NS‐1619), but was inhibited by pharmacological blockade of IP3 receptors (2‐APB), phospholipase C (PLC, U73122) or following depletion of endoplasmic reticulum Ca2+ stores (cyclopiazonic acid). Thus, Na+ is linked to PLC/IP3‐mediated activation of endoplasmic reticulum Ca2+ release in metastatic breast cancer cells and this may have an important role in breast tumors where [Na+]i is perturbed.