Zinc Inhibits Orai1-Mediated Calcium Signals in Esophageal Cancer Cells

Intracellular Ca2+ signals, such as oscillations, regulate proliferation, migration and other cellular events in cancer cells. Zinc (Zn), a major dietary micronutrient, plays important roles in chemoprevention. However, the molecular mechanisms underlying Zn-preventive function as well as the cross-talk with Ca2+ signaling are still unclear. We previously demonstrated that Orai1, a store-operated Ca2+ entry (SOCE) channel, is highly expressed in esophageal squamous cell carcinoma (ESCC) compared to adjacent normal tissues from patients, and the elevated expression of Orai1 is strongly associated with poor prognosis. The present study shows that Zn can greatly inhibit cell proliferation and Orai1-mediated SOCE in ESCC cells. We also found that the inhibitory function of Zn on SOCE is redox sensitive; reducing agent DTT could recover the full activity of Orai1-mediated SOCE. Based on the topology information of Orai1, we hypothesized that a histidine residue in the linker region between two transmembranes of Orai1 (H113) as well as three cysteine residues may play critical roles in the Zn-inhibitory effects. The data showed that, in the cells containing H113A-mutated Orai1, the Zn-inhibitory effect is vanished whereas Zn treatment reduces SOCE in the cell expressing wildtype Orai1. Similarly, the ESCC cells expressing any of three mutations in cysteine residues (C126A, C143A and C195A) of Orai1 displayed partial loss of the Zn-inhibitory function. These results suggest that the H113 and three cysteine residues likely bind Zn, which modulate Zn-inhibitory functions on the Orai1-mediated SOCE in ESCC cells.This study reveals how dietary Zn inhibits SOCE and thus Zn and Ca2+ signals may cross-talk, which in turn regulates cancer cell proliferation and migration in esophageal epithelia. Further investigations are required to search for novel and effective prevention strategies as well as therapeutic options targeting on Zn and Ca2+ signaling in ESCC.