Abstract
Many tumor cells express highly elevated activities of voltage-gated K+ channels in the plasma membrane which are indispensable for tumor growth. To test for K+ channel function during DNA damage response, we subjected human chronic myeloid leukemia (CML) cells to sub-lethal doses of ionizing radiation (0–8 Gy, 6 MV photons) and determined K+ channel activity, K+ channel-dependent Ca2+ signaling, cell cycle progression, DNA repair, and clonogenic survival by whole-cell patch clamp recording, fura-2 Ca2+ imaging, Western blotting, flow cytometry, immunofluorescence microscopy, and pre-plating colony formation assay, respectively. As a result, the human erythroid CML cell line K562 and primary human CML cells functionally expressed hERG1. Irradiation stimulated in both cell types an increase in the activity of hERG1 K+ channels which became apparent 1–2 h post-irradiation. This increase in K+ channel activity was paralleled by an accumulation in S phase of cell cycle followed by a G2/M cell cycle arrest as analyzed between 8 and 72 h post-irradiation. Attenuating the K+ channel function by applying the hERG1 channel inhibitor E4031 modulated Ca2+ signaling, impaired inhibition of the mitosis promoting subunit cdc2, overrode cell cycle arrest, and decreased clonogenic survival of the irradiated cells but did not affect repair of DNA double strand breaks suggesting a critical role of the hERG1 K+ channels for the Ca2+ signaling and the cell cycle control during DNA damage response.
Highlights
Tumor cells express ion channel toolkits that differ from that of their healthy parental counterparts
Primary chronic myeloid leukemia (CML) cells were isolated by density gradient centrifugation after obtaining informed consent in accordance with the Helsinki protocol, and the study was performed according to the guidelines of the local ethics committee
Primary CML cells and K562 human erythroid CML cells were cultivated in Roswell Park Memorial Institute (RPMI) 1640 medium containing L-glutamine (Gibco, Karlsruhe, Germany) supplemented with 10% fetal calf serum (FCS) and penicillin (100 U/ml)/streptomycin (100 μg/ml)
Summary
Tumor cells express ion channel toolkits that differ from that of their healthy parental counterparts This altered ion channel expression serves pivotal functions in neoplastic transformation, survival, proliferation, migration, invasion and metastasis, or therapy resistance of tumor cells suggesting ion channels as potential targets in antitumor therapy. Certain individual types of ion channels are overexpressed in several different tumor entities classifying them as channel with high oncogenic function [for review see (Huber, 2013)]. Among those are ether-à-go-go-related (hERG1, Kv11.1, KCNH2) voltage-gated, fast inactivating human K+ channels (Vandenberg et al, 2012) that have been reported in several tumor entities including chronic hERG1 in Leukemia myeloid leukemia (CML) cells (Arcangeli, 2005). HERG1 reportedly may promote tumor vascularization (Crociani et al, 2013) and confer resistance against chemotherapeutics (Pillozzi et al, 2011)
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