Selective inhibitory effects of zinc on cell proliferation in esophageal squamous cell carcinoma through Orai1

Zinc, an essential micronutrient, has a cancer preventive role. Zinc deficiency has been shown to contribute to the progression of esophageal cancer. Orai1, a store-operated Ca²⁺ entry (SOCE) channel, was previously reported to be highly expressed in tumor tissues removed from patients with esophageal squamous cell carcinoma (ESCC) with poor prognosis, and elevation of its expression contributes to both hyperactive intracellular Ca²⁺ oscillations and fast cell proliferation in human ESCC cells. However, the molecular basis of cancer preventive functions of zinc and its association with Orai1-mediated cell proliferation remains unknown. The present study shows that zinc supplementation significantly inhibits proliferation of ESCC cell lines and that the effect of zinc is reversible with N,N,N9,N9-tetrakis (2-pyridylmethyl) ethylenediamine, a specific Zn²⁺ chelator, whereas nontumorigenic esophageal epithelial cells are significantly less sensitive to zinc treatment. Fluorescence live cell imaging revealed that extracellular Zn²⁺ exerted rapid inhibitory effects on Orai1-mediated SOCE and on intracellular Ca²⁺ oscillations in the ESCC cells. Knockdown of Orai1 or expression of Orai1 mutants with compromised zinc binding significantly diminished sensitivity of the cancer cells to zinc treatment in both SOCE and cell proliferation analyses. These data suggest that zinc may inhibit cell proliferation of esophageal cancer cells through Orai1-mediated intracellular Ca²⁺ oscillations and reveal a possible molecular basis for zinc-induced cancer prevention and Orai1-SOCE signaling pathway in cancer cells.