Identification of Key Signaling Molecules Involved in the Activation of the Swelling-Activated Chloride Current in Human Glioblastoma Cells

The swelling-activated chloride current (I (Cl,Vol)) is abundantly expressed in glioblastoma (GBM) cells, where it controls cell volume and invasive migration. The transduction pathway mediating I (Cl,Vol) activation in GBM cells is, however, poorly understood. By means of pharmacological and electrophysiological approaches, on GL-15 human GBM cells we found that I (Cl,Vol) activation by hypotonic swelling required the activity of a U73122-sensitive phospholipase C (PLC). I (Cl,Vol) activation could also be induced by the membrane-permeable diacylglycerol (DAG) analog OAG. In contrast, neither calcium (Ca2+) chelation by BAPTA-AM nor changes in PKC activity were able to affect I (Cl,Vol) activation by hypotonic swelling. We further found that R59022, an inhibitor of diacylglycerol kinase (DGK), reverted I (Cl,Vol) activation, suggesting the involvement of phosphatidic acid. In addition, I (Cl,Vol) activation required the activity of a EHT1864-sensitive Rac1 small GTPase and the resulting actin polymerization, as I (Cl,Vol) activation was prevented by cytochalasin B. We finally show that I (Cl,Vol) can be activated by the promigratory fetal calf serum in a PLC- and DGK-dependent manner. This observation is potentially relevant because blood serum can likely come in contact with glioblastoma cells in vivo as a result of the tumor-related partial breakdown of the blood-brain barrier. Given the relevance of I (Cl,Vol) in GBM cell volume regulation and invasiveness, the several key signaling molecules found in this study to be involved in the activation of the I (Cl,Vol) may represent potential therapeutic targets against this lethal cancer.