Invasion of human glioma cells is regulated by multiple chloride channels including ClC-3

Abstract

Background: Glioblastoma is a type of highly malignant primary brain tumour. By means of ion excretion and the associated obligatory water loss, glioma cells can change shapes and undergo extensive migration and invasion. This study investigated the effects of inhibition of ion excretion in glioma cells. Materials and Methods: The expression of chloride channels (ClCs) and metalloproteinase-2 (MMP-2) was studied in two human glioma cell lines (STTG1 and U251-MG). The effects of ClC inhibition with chlorotoxin (a ClC-3 inhibitor), 5-nitro-2-3-phenylpropylamino benzoic acid (NPPB) (a non-specific ClC inhibitor), and ClC-3 siRNA knockdown were studied. Results: Both STTG1 and U251-MG cells expressed ClC family members ClC-2, -3, -4, -5, -6 and -7, as well as MMP-2. Glioma cell invasion was markedly but not completely inhibited by ClC-3 and MMP-2 siRNA knockdown, and by chlorotoxin treatment. Addition of chlorotoxin to siRNA-treated glioma cells only slightly increased the suppression of invasion. In contrast, invasion was completely blocked by the non-specific ClC blocker NPPB. Conclusion: ClCs are crucial in glioma cell migration and invasion. Blockade of a single ClC, however, is not sufficient to achieve complete inhibition of glioma cell invasion, suggesting that any future therapy should be targeted at pharmacological blockade of multiple ClCs.