Despite therapeutical progress, lung cancer is the leading cause of cancer-associated deaths worldwide, and non-small cell lung cancer (NSCLC) accounts for almost 80% of lung cancer deaths. Therefore, it is desirable to develop therapeutic agents that prevent cancer proliferation. A number of studies have shown that Ca2+ influx, capacitative calcium entry (CCE) or store-operated Ca2+ entry (SOCE), mediated by store-operated channels (SOCs) triggers several physiological processes including proliferation and apoptosis. Recently, Orai3 channels have been reported to constitute SOCs and to mediate CCE in breast cancer (1). Moreover, they are overexpressed in breast cancer and regulate cell proliferation and survival (2). However, their expression and role in lung cancer are still unknown. In the present study, we analyzed Orai3 expression in normal and cancerous lung tissue samples, and investigated their role in adenocarcinoma cell lines. We found that Orai3 and STIM1 are expressed in both A549 and NCI-H23 cell lines where they mediated a SOC entry. Down-regulation of Orai3 inhibited 60% of protein expression and reduced both NCI-H23 and A549 cell proliferation by 50% 72h post-transfection. In contrast, no significant effect was observed on cell mortality in both cell lines using trypan blue exclusion test. To elucidate the mechanism by which the inhibition of Orai3 reduced lung cancer cell proliferation, we performed flow cytometry to study the effect of Orai3 down-regulation on cell-cycle progression. The silencing of Orai3 led to NCI-H23 and A549 cell-cycle arrest with a significant accumulation of cells in the G0/G1 phase (13% for NCI-H23, and 20% for A549, p<0.001), and to a concomitant decrease in the cell percentage in both S (13% for NCI-H23 and 16% for A549, p<0.001) and G2/M (4% for NCI-H23, p<0.001, and 3.5% for A549, p<0.05) phases. This phenomenon is associated with a reduction in the expression of Cyclin D1, cdk4 and cdk2 (cyclin-dependent kinases) in siOrai-3 transfected NCI-H23 cells but not in A549 cells. Interestingly, in A549 cells, Orai3 silencing induced an increase of apoptosis (8%, p<0.05) and a decrease of 50% of c-myc expression. Indeed, c-myc has been reported to be involved in lung survival (3). Finally, the expression of Orai3 was evaluated in 30 human lung adenocarcinoma specimens using Tissue Macro Array. We found that Orai3 was over-expressed in 70% of cases. Our results provide evidence for a significant effect of Orai3 on lung cell proliferation and survival in vitro and show that this effect is associated with the induction of cell cycle and apoptosis resistance. Our study highlights the role of Orai-3 channel as an essential actor of pulmonary tumorogenesis, and supports its role as a potential prognostic or diagnostic marker in NSCLC.