Selective Calcium Sensitivity in Immature Glioma Cancer Stem Cells

Abstract

Tumor-initiating cells are a subpopulation in aggressive cancers that exhibit traits shared with stem cells, including the ability to self-renew and differentiate, commonly referred to as stemness. In addition, such cells are resistant to chemo- and radiation therapy posing a therapeutic challenge. To uncover stemness-associated functions in glioma-initiating cells (GICs), transcriptome profiles were compared to neural stem cells (NSCs) and gene ontology analysis identified an enrichment of Ca2+ signaling genes in NSCs and the more stem-like (NSC-proximal) GICs. Functional analysis in a set of different GIC lines regarding sensitivity to disturbed homeostasis using A23187 and Thapsigargin, revealed that NSC-proximal GICs were more sensitive, corroborating the transcriptome data. Furthermore, Ca2+ drug sensitivity was reduced in GICs after differentiation, with most potent effect in the NSC-proximal GIC, supporting a stemness-associated Ca2+ sensitivity. NSCs and the NSC-proximal GIC line expressed a larger number of ion channels permeable to potassium, sodium and Ca2+. Conversely, a higher number of and higher expression levels of Ca2+ binding genes that may buffer Ca2+, were expressed in NSC-distal GICs. In particular, expression of the AMPA glutamate receptor subunit GRIA1, was found to associate with Ca2+ sensitive NSC-proximal GICs, and decreased as GICs differentiated along with reduced Ca2+ drug sensitivity. The correlation between high expression of Ca2+ channels (such as GRIA1) and sensitivity to Ca2+ drugs was confirmed in an additional nine novel GIC lines. Calcium drug sensitivity also correlated with expression of the NSC markers nestin (NES) and FABP7 (BLBP, brain lipid-binding protein) in this extended analysis. In summary, NSC-associated NES+/FABP7+/GRIA1+ GICs were selectively sensitive to disturbances in Ca2+ homeostasis, providing a potential target mechanism for eradication of an immature population of malignant cells.

Membrane-Depolarizing Channel Blockers Induce Selective Glioma Cell Death by Impairing Nutrient Transport and Unfolded Protein/Amino Acid Responses

“…Hence, there is an urgent need for therapies that would specifically target this tumor cell population, sparing normal cells. In line with other researchers (8,9), we recently showed that tumor-initiating cells are sensitive to disturbed Ca 2þ homeostasis (10), making ion channels appealing targets in GICs. Noteworthy, ion channels are also known to be dysregulated during cancer formation and progression (11).…”

“…All GIC lines are GBM patient-derived primary cell lines grown as monolayer cultures on laminin in neural stem cell culture media, as described previously (2,10,15,16). Cells were used for experiments between passages 15 and 30, at least one passage after thawing.…”

“…GICs were treated as indicated for 7 hours and subsequent sample preparation, sequencing and analysis was done as described previously (10). Briefly, the Illumina Low-Throughput TruSeq RNA Sample Preparation Kit protocol was used for barcoded cDNA library preparation.…”

Epilepsy and brain tumors

“…Disturbances in chloride balance may play a role as well, secondary to changes in chloride co-transporters, suggesting accompanying changes in GABA metabolism and chloride transport (Huberfeld et al, 2007; Pallud et al, 2013). Besides, glutamergic stimulation of NMDA and AMPA receptors may activate intracellular mTOR, AKT, and MAPK signaling pathways, contributing both to cell growth and to epileptogenesis (Wee et al, 2014). …”

Calcium Channels and Associated Receptors in Malignant Brain Tumor Therapy

“…Cancer stem cells are very aggressive as they are highly invasive, mobile, resistant to radiation and chemotherapy, and have the capacity to self-renew (Oh et al, 2012). Recent studies have shown that calcium (Ca 21 ) channel signaling controls a variety of stem cells and cancer cell lines functions, such as proliferation and migration (Wee et al, 2014). Moreover, Ca 21 channel interference was able to drive liver tumor-initiating cells into apoptosis (Zhao et al, 2013) and glioma stem-like cells were more sensitive to Ca 21 disturbances compared with more mature differentiated glioma cells (Wee et al, 2014).…”