Store-Operated Calcium Channels Control Proliferation and Self-Renewal of Cancer Stem Cells from Glioblastoma

SIMPLE SUMMARY: Glioblastoma is a high-grade primary brain tumor that contains a subpopulation of cells called glioblastoma stem cells, which are responsible for tumor initiation, growth and recurrence after treatment. Recent transcriptomic studies have highlighted that calcium pathways predominate in glioblastoma stem cells. Calcium channels have the ability to transduce signals from the microenvironment and are therefore ideally placed to control cellular behavior. Using multiple approaches, we demonstrate in five different primary cultures, previously derived from surgical specimens, that glioblastoma stem cells express store-operated channels (SOC) that support calcium entry into these cells. Pharmacological inhibition of SOC dramatically reduces cell proliferation and stem cell self-renewal in these cultures. By identifying SOC as a critical mechanism involved in the maintenance of the stem cell population in glioblastoma, our study will contribute to the framework for the identification of new therapies against this deadly tumor. ABSTRACT: Glioblastoma is the most frequent and deadly form of primary brain tumors. Despite multimodal treatment, more than 90% of patients experience tumor recurrence. Glioblastoma contains a small population of cells, called glioblastoma stem cells (GSC) that are highly resistant to treatment and endowed with the ability to regenerate the tumor, which accounts for tumor recurrence. Transcriptomic studies disclosed an enrichment of calcium (Ca(2+)) signaling transcripts in GSC. In non-excitable cells, store-operated channels (SOC) represent a major route of Ca(2+) influx. As SOC regulate the self-renewal of adult neural stem cells that are possible cells of origin of GSC, we analyzed the roles of SOC in cultures of GSC previously derived from five different glioblastoma surgical specimens. Immunoblotting and immunocytochemistry experiments showed that GSC express Orai1 and TRPC1, two core SOC proteins, along with their activator STIM1. Ca(2+) imaging demonstrated that SOC support Ca(2+) entries in GSC. Pharmacological inhibition of SOC-dependent Ca(2+) entries decreased proliferation, impaired self-renewal, and reduced expression of the stem cell marker SOX2 in GSC. Our data showing the ability of SOC inhibitors to impede GSC self-renewal paves the way for a strategy to target the cells considered responsible for conveying resistance to treatment and tumor relapse.