STEM-14CELLULAR RESTING TRANSMEMBRANE POTENTIAL INSTRUCTS DIFFERENTIATION STATE OF GBM STEM-LIKE CELLS

INTRODUCTION: Glioblastoma (GBM) is the most common malignant brain tumor in adults with a poor prognosis despite maximal treatment. Resting membrane potential (RMP) has been shown to be an important regulator of the differentiation state of embryonic and somatic stem cells. We evaluated the relevance of RMP in GBM stem-like cells (GSC). METHODS: Whole cell patch clamp technique was used to determine the RMP. RESULTS: Undifferentiated GSC had a RMP of -5mV +/-4 (n = 33) compared to their differentiated counterparts, which had a mean RMP of -24mV +/-20 (n = 31, P < 0.001). To determine whether the cellular RMP played an instructive role in the differentiation state of GSC we used pharmacologic and genetic approaches to alter the potential. We added additional potassium chloride (KCl) to differentiated GCS in order to induce depolarization, and compared to osmotic controls using sodium chloride (NaCl). We found that GSC exposed to high KCl retained stem markers and sphere forming capacity compared to controls. We then examined whether hyperpolarization was sufficient to induce differentiation. We treated GSC with vacuolar ATPase inhibitors and salinomycin (potassium ionophore), which induced relative hyperpolarization of GSC and induction of differentiation. Transduction of GSC with inducible potassium ion channel led to hyperpolarization and differentiation. To identify potential mechanisms coupling electrical alterations to biochemical signal transduction pathways we performed extensive phospho-protein array studies comparing the undifferentiated GSC and cells hyperpolarized with omeprazole or salinomycin. Attenuation of key developmental and pro-growth signaling pathways was observed. CONCLUSIONS: Alteration of RMP may represent a new therapeutic strategy.