Ezrin-dependent promotion of glioma cell clonogenicity, motility, and invasion mediated by BCL-2 and transforming growth factor-β2

Abstract

Ezrin belongs to the ezrin-radixin-moesin family proteins, which cross-link actin cytoskeleton and plasma membrane. Malignant glioma cells are paradigmatic for their strong migratory and invasive properties. Here, we report that the expression of dominant-negative ezrins inhibits clonogenicity, migration, and invasiveness of human malignant glioma cells. Furthermore, dominant-negative ezrins block hepatocyte growth factor (HGF)-mediated stimulation of clonogenicity and migration, without altering HGF-induced protein kinase B/Akt and focal adhesion kinase phosphorylation. Glioma cells expressing dominant-negative ezrins exhibit a shift of the BCL-2/ BAX rheostat toward apoptosis, reduced αvβ3 integrin expression and reduced matrix metalloproteinase (MMP) expression and activity. These changes are associated with a dramatic loss of transforming growth factor β2 (TGF-β2) release. Exogenous supplementation of TGF-β2 overcomes the inhibitory effects of dominant-negative ezrins on migration and clonogenicity. A neutralizing TGF-β2 antibody mimics the effects of dominant-negative ezrins on clonogenicity and migration. Exogenous HGF markedly induces TGF-β2 protein levels, and a neutralizing TGF-β2 antibody abolishes the HGF-mediated increase in glioma cell motility. Finally, TGF-β2 does not modulate BCL-2 or BAX expression, but BCL-2 gene transfer increases the levels of latent and active TGF-β2. Intracranial xenografts of U87MG glioma cells transfected with the dominant-negative ezrins in athymic mice grow to significantly smaller volumes, and the median survival of these mice is 50 d compared with 28 d in the control group. These data define a novel pathway for HGF-induced glioma cell migration and invasion, which requires ezrin, changes in the BCL-2/BAX rheostat, and the induction of TGF-β2 expression in vitro, and underscore the important role of HGF signaling in vivo.