Upregulation of Orai1 and STIM1 expression as well as store-operated Ca2+ entry in ovary carcinoma cells by placental growth factor

Placental growth factor (PLGF) is produced by tumor cells and stimulates tumor growth and metastasis in part by upregulation of hypoxia inducible factor HIF1α. Orchestration of tumor cell proliferation and migration involves oscillations of cytosolic Ca²⁺ activity ([Ca²⁺]_i). The [Ca²⁺]_i oscillations could be accomplished by triggering of intracellular Ca²⁺ release followed by store-operated Ca²⁺-entry (SOCE). Mechanisms accomplishing SOCE include the pore-forming ion channel unit Orai1 and its regulator STIM1. The present study explored whether PLGF influences the expression of Orai1 and STIM1, as well as SOCE and whether this effect impacts on HIF1α expression. To this end, ovary carcinoma cells were cultured for 24 h without and with PLGF (10 ng/ml). Orai1, STIM1 and HIF1α transcript levels were quantified utilizing RT-PCR and Orai1, STIM1 and HIF1α protein levels by Western blotting. [Ca²⁺]_i was estimated from Fura-2-fluorescence and SOCE from increase of [Ca²⁺]_i following Ca²⁺ re-addition after Ca²⁺-store depletion with extracellular Ca²⁺ removal and sarcoendoplasmatic Ca²⁺-ATPase (SERCA) inhibitor thapsigargin (1 μM). As a result, exposure of ovary carcinoma cells to PLGF was followed by a significant increase of Orai1 as well as STIM1 transcript and protein levels. PLGF significantly increased store-operated Ca²⁺-entry following re-addition of extracellular Ca²⁺, an effect virtually abrogated by Orai1 inhibitor MRS1845 (10 μM). PLGF further increased HIF1α transcript and protein levels, an effect again significantly blunted by MRS1845 (10 μM). In conclusion, PLGF upregulates expression of both, Orai1 and STIM1 thus enhancing store-operated Ca²⁺-entry with subsequent upregulation of HIF1α.