Non-Selective Cation Channel-Mediated Ca²⁺-Entry and Activation of Ca²⁺/Calmodulin-Dependent Kinase II Contribute to G₂/M Cell Cycle Arrest and Survival of Irradiated Leukemia Cells

Abstract

Genotoxic stress induces cell cycle arrest and DNA repair which may enable tumor cells to survive radiation therapy. Here, we defined the role of Ca²⁺ signaling in the cell cycle control and survival of chronic myeloid leukemia (CML) cells subjected to ionizing radiation (IR). To this end, K562 erythroid leukemia cells were irradiated (0-10 Gy). Tumor survival was analyzed by clonogenic survival assay and cell cycle progression via flow cytometry. Plasma membrane cation conductance was assessed by patch-clamp whole-cell recording and the cytosolic free Ca²⁺ concentration ([Ca²⁺]_i) was measured by fura-2 Ca²⁺ imaging. Nuclear activity of Ca²⁺/calmodulin-dependent kinase II (CaMKII) was defined by Western blotting. In addition, the effect of IR (5 Gy) on the cation conductance of primary CML cells was determined. The results indicated that IR (10 Gy) induced a G₂/M cell cycle arrest of K562 cells within 24 h post-irradiation (p.i.) and decreased the clonogenic survival to 0.5 % of that of the control cells. In K562 cells, G₂/M cell cycle arrest was preceded by activation of TRPV5/6-like nonselective cation channels in the plasma membrane 1-5 h p.i., resulting in an elevated Ca²⁺ entry as evident from fura-2 Ca²⁺ imaging. Similarly, IR stimulated a Ca²⁺-permeable nonselective cation conductance in primary CML cells within 2-4 h p.i.. Ca²⁺ entry, into K562 cells was paralleled by an IR-induced activation of nuclear CaMKII. The IR-stimulated accumulation in G₂ phase was delayed upon buffering [Ca²⁺]_i with the Ca²⁺ chelator BAPTA-AM or inhibiting CaMKII with KN93 (1 nM). In addition, KN93 decreased the clonogenic survival of irradiated cells but not of control cells. In conclusion, the data suggest that IR-stimulated cation channel activation, Ca²⁺ entry and CaMKII activity participate in control of cell cycle progression and survival of irradiated CML cells.

Ca2+-Activated IK K+ Channel Blockade Radiosensitizes Glioblastoma Cells

“…The present study demonstrates IR-induced Ca 2þ signaling and activation of Ca IR-induced modifications of Ca 2þ signaling and/or K þ channel activity have been reported by our group in different tumor entities such as lung adenocarcinoma (28), leukemia cells (27,29), or glioblastoma (21). In lung adenocarcinoma, K þ channels contribute to an elevated glucose uptake by the irradiated cells.…”

Cellular Effects of the Antiepileptic Drug Valproic Acid in Glioblastoma

“…CaMKII, in turn, has been reported to regulate the cell cycle via inactivation of cdc25 isoforms and subsequent inactivation of cdc2 (CDK1) [39-42]. To define putative Ca 2+ -mediated VPA effects on cell cycle, VPA (0 or 750 µM for 48 h)-treated U251 cells were probed against cdc25A, -B, -C and cdc2 as well as against the phosphorylated forms of these proteins by immunoblotting.…”

Expression and Prognostic Roles of TRPV5 and TRPV6 in Non-Small Cell Lung Cancer after Curative Resection

“…In addition to their role in maintaining the calcium homeostasis (de Groot et al, 2011), some reports have also suggested TRPV5 and TRPV6 as important biomarkers in tumor development and progression (Heise et al, 2010). This has been proved in prostate, breast, thyroid, colon, pancreatic and ovary cancers.…”