Expression and Modulation of the Intermediate- Conductance Ca²⁺-Activated K⁺ Channel in Glioblastoma GL-15 Cells

Abstract

We report here the expression and properties of the intermediate-conductance Ca²⁺-activated K⁺ (IK_Ca) channel in the GL-15 human glioblastoma cell line. Macroscopic IK_Ca currents on GL-15 cells displayed a mean amplitude of 7.2±0.8 pA/pF at 0 mV, at day 1 after plating. The current was inhibited by clotrimazole (CTL, IC₅₀=257 nM), TRAM-34 (IC₅₀=55 nM), and charybdotoxin (CTX, IC₅₀=10.3 nM). RT-PCR analysis demonstrated the expression of mRNA encoding the IK_Ca channel in GL-15 cells. Unitary currents recorded using the inside-out configuration had a conductance of 25 pS, a K_D for Ca²⁺ of 188 nM at -100 mV, and no voltage dependence. We tested whether the IKCa channel expression in GL-15 cells could be the result of an increased ERK activity. Inhibition of the ERK pathway with the MEK antagonist PD98059 (25 µM, for 5 days) virtually suppressed the IK_Ca current in GL-15 cells. PD98059 treatment also increased the length of cellular processes and up-regulated the astrocytic differentiative marker GFAP. A significant reduction of the IKCa current amplitude was also observed with time in culture, with mean currents of 7.17±0.75 pA/pF at 1-2 days, and 3.11±1.35 pA/pF at 5-6 days after plating. This time-dependent downregulation of the IK_Ca current was not accompanied by changes in the ERK activity, as assessed by immunoblot analysis. Semiquantitative RT-PCR analysis demonstrated a ~35% reduction of the IK_Ca channel mRNA resulting from ERK inhibition and a ~50% reduction with time in culture.

PRL-3 promotes the proliferation of LoVo cells via the upregulation of KCNN4 channels

“…Previous studies have attributed the upregulation of KCNN4 channels to the activation of extracellular signal-regulated kinases (ERK1/2) in vascular smooth muscle cells (23,24) and that the NF-κB transcription factor critically regulates the expression of small conductance Ca 2+ channels (25). In agreement with these findings, we have shown that expression of TNF-α was increased with transfection of the PAcGFP-PRL-3 vector.…”

Renal fibrosis is attenuated by targeted disruption of K Ca 3.1 potassium channels

“…We found that mitogenic stimulation with bFGF induced a robust and rather selective up-regulation of the intermediate-conductance K Ca subtype K Ca 3.1 in renal fibroblasts. The principle signal transduction pathway involved in this mitogen-induced K Ca 3.1 up-regulation appeared to rely on the Ras/Raf/MEK/ERK-signaling cascade, which is in line with observations in other cell types (15,21,23,34). In contrast, expression levels of the related K Ca channels K Ca 1.1 and K Ca 2.3 were unchanged in response to bFGF, underscoring a certain specificity of K Ca 3.1 up-regulation and suggesting a pivotal role for K Ca 3.1 in the promotion of renal fibroblast proliferation.…”

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

“…Glioblastoma cells functionally express high numbers of Ca 2þ -activated IK K þ channels (other names are hIKCa1, hKCa4, hSK4, KCa3.1) in their plasma membrane (3)(4)(5)(6). Notably, IK channels are low expressed or even absent in human astrocytes (7) but upregulated during neoplastic transformation and malignant progression of the glioma (8).…”