Malignant glioma, the most common and lethal type of primary brain cancer, affects about 5 in 100,000 people. Despite decades of research and aggressive treatments consisting of surgery, radiotherapy, and chemotherapy, the median survival for this cancer is only about 1 year. To make headway in the clinical management of this devastating neurological disease, research to understand the unique pathophysiology of gliomas may reveal new targets for therapy. Recent research has implicated ion channels in the ability of glioma cells to aggressively migrate and proliferate. More specifically, expression of certain K+ and Cl- channels endows glioma cells with an enhanced ability to concomitantly extrude K+ and Cl-, leading to obligated water release and dynamic cell volume change that are essential for cell invasion and proliferation. One of the ion channels expressed by glioma cells critical to this process is ClC-3, a voltage-gated chloride channel. ClC-3 plays a major role in glioma cell migration and proliferation, but the mechanism by which ClC-3 is activated in glioma cells is not known. Several lines of evidence suggest that ClC-3 may be regulated by Ca2+/calmodulin-dependent protein kinase II, a Ca2+-sensitive kinase. Regulation of ClC-3 by CaMKII is particularly interesting, given that ligands and channels regulating glioma Ca2+ levels also play critical roles in glioma migration and proliferation. Therefore the goal of the current study is to understand if Ca2+ activation of CaMKII leading to ClC-3 phosphorylation will lead to enhanced glioma cell migration and proliferation. This will be accomplished by first determining in Specific Aim 1 if ClC-3 currents in glioma cells are enhanced by CaMKII phosphorylation by using whole-cell patch clamp electrophysiology, immunocytochemistry, and other biochemical assays. Next, in Specific Aim 2, imaging, genetic knockdown, and electrophysiological experiments will be performed to determine if increases in intracellular Ca2+ activate ClC-3 conductance via CaMKII phosphorylation in glioma cells. Finally, Specific Aim 3 is designed to determine if CaMKII-mediated activation of ClC-3 actually plays a role in the migration and proliferation of glioma cells. CaMKII may be a molecular translator, converting intracellular Ca2+ signals into changes in chloride conductance via ClC-3 phosphorylation. Therefore novel therapeutics interfering with ClC-3 activity or CaMKII activation of ClC-3 may lead to better clinical outcomes. Indeed, Chlorotoxin, an inhibitor of chloride currents, is currently entering Phase III trials for the treatment of malignant gliomas.
Despite aggressive treatment, the prognosis for patients suffering from glioblastoma multiforme, a Grade IV primary brain cancer, is very poor. Therefore understanding the unique features of glioblastoma biology will lead to the identification of novel targets for the development of therapeutic agents leading to better clinical outcomes.
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|Cuddapah, Vishnu Anand; Turner, Kathryn L; Sontheimer, Harald (2013) Calcium entry via TRPC1 channels activates chloride currents in human glioma cells. Cell Calcium 53:187-94|
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