Enhanced Orai1 and STIM1 expression as well as store operated Ca2+ entry in therapy resistant ovary carcinoma cells

Abstract

Mechanisms underlying therapy resistance of tumor cells include protein kinase Akt. Putative Akt targets include store-operated Ca2+-entry (SOCE) accomplished by pore forming ion channel unit Orai1 and its regulator STIM1. We explored whether therapy resistant (A2780cis) differ from therapy sensitive (A2780) ovary carcinoma cells in Akt, Orai1, and STIM1 expression, Ca2+-signaling and cell survival following cisplatin (100μM) treatment. Transcript levels were quantified with RT-PCR, protein abundance with Western blotting, cytosolic Ca2+-activity ([Ca2+]i) with Fura-2-fluorescence, SOCE from increase of [Ca2+]i following Ca2+-readdition after Ca2+-store depletion, and apoptosis utilizing flow cytometry. Transcript levels of Orai1 and STIM1, protein expression of Orai1, STIM1, and phosphorylated Akt, as well as SOCE were significantly higher in A2780cis than A2780 cells. SOCE was decreased by Akt inhibitor III (SH-6, 10μM) in A2780cis but not A2780 cells and decreased in both cell lines by Orai1 inhibitor 2-aminoethoxydiphenyl borate (2-ABP, 50μM). Phosphatidylserine exposure and late apoptosis following cisplatin treatment were significantly lower in A2780cis than A2780 cells, a difference virtually abolished by SH-6 or 2-ABP. In conclusion, Orai1/STIM1 expression and function are increased in therapy resistant ovary carcinoma cells, a property at least in part due to enhanced Akt activity and contributing to therapy resistance in those cells.

Localized Store-Operated Calcium Influx Represses CD95-Dependent Apoptotic Effects of Rituximab in Non-Hodgkin B Lymphomas

“…The involvement of the Orai1-driven Ca 2+ entry in apoptosis has been demonstrated in various cell types (23)(24)(25). However, its proor antiapoptotic role seems highly dependent on the stimulus and cell type studied.…”

Inhibition of store-operated Ca2+ entry counteracts the apoptosis of nasopharyngeal carcinoma cells induced by sodium butyrate

“…A sustained increase in cytosolic Ca 2+ activity triggers apoptosis (34). The roles of SOCE, a major calcium-entry pathway for non-excitable cells, and those of the CRAC channel, a key channel in mediating SOCE, in apoptotic regulation appear to be paradoxical (7,16,17,34,35). Indeed, SOCE can serve as a pro-apoptotic or an anti-apoptotic factor in cancerous cells under different conditions (7,16,17,34,35).…”

“…The roles of SOCE, a major calcium-entry pathway for non-excitable cells, and those of the CRAC channel, a key channel in mediating SOCE, in apoptotic regulation appear to be paradoxical (7,16,17,34,35). Indeed, SOCE can serve as a pro-apoptotic or an anti-apoptotic factor in cancerous cells under different conditions (7,16,17,34,35). For example, enhanced SOCE resulted from upregulated Orai1 and Stim1 expression, which was observed in drug-resistant cancer cells, and impairing SOCE by using specific inhibitors or by knocking down Orai1 and Stim1 can sensitize the drug-resistant cells to chemotherapy (34,35).…”

“…Indeed, SOCE can serve as a pro-apoptotic or an anti-apoptotic factor in cancerous cells under different conditions (7,16,17,34,35). For example, enhanced SOCE resulted from upregulated Orai1 and Stim1 expression, which was observed in drug-resistant cancer cells, and impairing SOCE by using specific inhibitors or by knocking down Orai1 and Stim1 can sensitize the drug-resistant cells to chemotherapy (34,35). In addition, enhanced SOCE commonly occurs during the cell apoptosis induced by anti-tumor or chemotherapeutic agents (17).…”

“…Differences of SOCE in apoptosis may contribute to the dual roles of Ca 2+ in signaling transduction: On one hand, a physiological Ca 2+ concentration is necessary to activate signaling pathways that promote cell growth, survival and metastasis, which are the hallmarks of cancers; on the other hand, overloaded Ca 2+ concentrations would also induce apoptosis through the activation of apoptotic pathways (12,13,31,33). Therefore, the anti-apoptotic role of enhanced SOCE in untreated cancer cells is to maintain their own characteristics, which must be regulated and controlled by upstream proteins (13,34). However, the enhanced SOCE observed in the pro-apoptosis of cancer cells treated with anti-tumor agents may be due to the impaired upstream control signaling disrupted by anti-tumor agents, which leads to a sustained increase in intracellular Ca 2+ levels and triggers apoptosis.…”