Glioblastoma and calcium signaling - analysis of calcium toolbox expression NOÉMIE ROBIL 1,2 , FABIEN PETEL 1 , MARIE-CLAUDE KILHOFFER 2 and JACQUES HAIECH 2 1 Programme Cartes d’Identité des Tumeurs (CIT), Ligue Nationale contre le Cancer, Paris, France and 2 Laboratoire d’Innovation Thérapeutique, Laboratoire d’Excellence Médalis, UMR 7200 Université de Strasbourg / CNRS, Illkirch, France ABSTRACT The characteristics of a cellular calcium signal (calcium signature) are determined, at least partly, by the expression of a subset of genes encoding proteins involved in calcium entry, calcium uptake and calcium modulation. Our aim in the present work was to characterize the set of genes involved in calcium signal generation that are differentially expressed in normal brain tissues versus brain tumor and/or glioma stem cells. Public datasets were analyzed according to a four step methodology consisting of: 1. detecting the outliers by using principal component analysis of the whole transcriptome; 2. building a calcium toolbox composed of 260 genes involved in the generation and modulation of the calcium signal; 3. analyzing the calcium toolbox transcriptome of different human brain areas and 4. detecting genes from the calcium toolbox preferentially expressed in tumor tissues or tumor cells compared to normal brain tissues. Our approach was validated on normal brain tissue. Tumor sample analysis allowed us to disclose a set of eighteen genes characteristic of glioblastoma tissues or glioma stem cells. Interpreting the set of genes highlighted in the study led us to propose that i) the mechanism of store operated calcium entry is strongly perturbed in cancer cells and tissues, ii) the process of calcium reuptake into mitochondria is more important in cancer cells and tissues than in their normal counterparts and iii) these two mechanisms may be coupled in at least one subgroup of the glioblastoma stem cells. KEY WORDS: calcium signal, glioblastoma, cancer stem cell, calcium toolbox Introduction Glioblastoma is rare, but one of the most deadly adult tumors. Similarly to other solid tumors, it can be considered as organ-like, being composed of differentiated cancer cells that exhibit low tumor genesis capacity and cancer stem cells that are able to resume the tumor after treatment of the patient tumor by surgery, chemotherapy and radiotherapy (Levy et al., 2014). Normal cells from the host also infltrate the tumor which therefore appears as a heterogeneous cellular mass behaving as a microsociety. In addition, the tumor cells appear to exhibit an exquisite plasticity with differentiated cells able to recover stemness properties, a characteristic that is reported as a hallmark of their tumorigenicity (Chaffer and Weinberg, 2015). Calcium is considered as the main second messenger in eukaryotic cells. Previous and recent papers have established a generally accepted vocabulary to describe the different elements Int. J. Dev. Biol. 59: 407-415 (2015) doi: 10.1387/ijdb.150200jh www.intjdevbiol.com *Address correspondence to: Jacques Haiech. Laboratoire d’innovation thérapeutique, UMR 7200 University of Strasbourg / CNRS, 74, route du Rhin, 67401 Illkirch, France. Tel: +33-3-6885-4270. Fax: +33-3-6885-4310. E-mail: haiech@unistra.fr - web: http://www-medchem.u-strasbg.fr Supplementary Material (3 tables) for this paper is available at: http://dx.doi.org/10.1387/ijdb.150200jh Accepted: 11 June 2015. ISSN: Online 1696-3547, Print 0214-6282 © 2015 UBC Press Printed in Spain Abbreviations used in this paper: ESC, embryonic stem cell line; GBM, glioblastoma; gCSC, glioblastoma cancer stem cell; HA, primary human astrocyte; PCA, prin- cipal component analysis. involved in setting up a specifc calcium signal in a given cell and in a given physiological state (for review see (Haiech et al., 2011)). The human genome contains more than 250 genes coding for such elements. This ensemble of genes constitutes the calcium toolbox. In a given cell, a subset of the calcium toolbox will be expressed (forming the cell calcium signalosome). Given signalosome proteins assemble to form macromolecular complexes, called calcisomes. Such calcisomes are going to be key elements to encode external information into a calcium signal and then to decipher this calcium signal in order to transduce the external information into cellular events (Haiech et al., 2011). In cancer cells, such cellular events may represent any of the hallmarks described by Weinberg (Hanahan and Weinberg, 2011)