Role of Na+/Ca2+ Exchangers in Therapy Resistance of Medulloblastoma Cells.

Background/Aims: Alterations of cytosolic Ca 2+ -activity ([Ca 2+ ] i ) are decisive in the regulation of tumor cell proliferation, migration and survival. Transport processes participating in the regulation of [Ca 2+ ] i include Ca 2+ extrusion through K + -independent (NCX) and/or K + -dependent (NCKX) Na + /Ca 2+ -exchangers. The present study thus explored whether medulloblastoma cells express Na + /Ca 2+ -exchangers, whether expression differs between therapy sensitive D283 and therapy resistant UW228-3 medulloblastoma cells, and whether Na + /Ca 2+ -exchangers participate in the regulation of cell survival. Methods: In therapy sensitive D283 and therapy resistant UW228-3 medulloblastoma cells transcript levels were estimated by RT-PCR, protein abundance by Western blotting, cytosolic Ca 2+ -activity ([Ca 2+ ] i ) from Fura-2-fluorescence, Na + / Ca 2+ -exchanger activity from the increase of [Ca 2+ ] i (Δ[Ca 2+ ] i ) and from whole cell current (I ca ) following abrupt replacement of Na + containing (130 mM) and Ca 2+ free by Na + free and Ca 2+ containing (2 mM) extracellular perfusate as well as cell death from PI -staining and annexin-V binding in flow cytometry. Results: The transcript levels of NCX3, NCKX2, and NCKX5, protein abundance of NCX3, slope and peak of Δ[Ca 2+ ] i as well as I ca were significantly lower in therapy sensitive D283 than in therapy resistant UW228-3 medulloblastoma cells. The Na + /Ca 2+ -exchanger inhibitor KB-R7943 (10 µM) significantly blunted Δ[Ca 2+ ] i , and augmented the ionizing radiation-induced apoptosis but did not significantly modify clonogenicity of medulloblastoma cells. Apoptosis was further enhanced by NCX3 silencing. Conclusions: Na + /Ca 2+ -exchanger activity significantly counteracts apoptosis but does not significantly affect clonogenicity after radiation of medulloblastoma cells.