No abstract

Cellular resistance to multiple proapoptotic stimuli and invasion of surrounding brain tissue by migrating tumor cells are main obstacles to an e ective therapy for human malignant glioma. Here, we report that the Wnt family of embryonic di erentiation genes modulate growth of malignant glioma cells in vitro and in vivo and inhibit cellular migration in vitro. sFRPs (soluble Frizzled-related proteins) are soluble proteins that bind to Wnt and interfere with Wnt signaling. We ®nd that sFRP-1 and sFRP-2 are produced by the majority of longterm and ex vivo malignant glioma cell lines. Glioma cells that ectopically express sFRPs exhibit increased clonogenicity and enhanced resistance to serum starvation. In contrast, sFRPs do not modulate glioma cell susceptibility to apoptosis induced by the cytotoxic cytokines, CD95 (Fas/APO-1) ligand (CD95L) or Apo2 ligand/tumor necrosis factor-related apoptosisinducing ligand (Apo2L/TRAIL), or various cytotoxic drugs. sFRP-2 strongly promotes the growth of intracranial glioma xenografts in nude mice. In contrast, enhanced expression of sFRPs inhibits the motility of glioma cells in vitro. sFRP-mediated e ects on glioma cells are accompanied by decreased expression and activity of matrix metalloproteinase-2 (MMP-2) and decreased tyrosine phosphorylation of b-catenin. Thus, sFRPs promote survival under non-supportive conditions and inhibit the migration of glioma cells. We suggest that the regulation of these cellular processes involves expression of MMP-2 and tyrosine phosphorylation of bcatenin. These data support a function for Wnt signaling and its modulation by sFRPs in the biology of human gliomas. Oncogene (2000) 19, 4210 ± 4220.

No abstract

Activities of MMP-2 and MMP-9 are the best predictors of glioma cell invasion. The alpha(v)beta3 integrin mediates migration and invasion in a subset of glioma cell lines, but these processes do not depend on alpha(v)beta3 integrin expression. Antiapoptotic BCL-2 family protein expression is a predictor of efficient migration and invasion.

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 ␣ V ␤ 3 integrin expression and reduced matrix metalloproteinase (MMP) expression and activity. These changes are associated with a dramatic loss of transforming growth factor ␤ 2 (TGF-␤ 2 ) release. Exogenous supplementation of TGF-␤ 2 overcomes the inhibitory effects of dominant-negative ezrins on migration and clonogenicity. A neutralizing TGF-␤ 2 antibody mimics the effects of dominantnegative ezrins on clonogenicity and migration. Exogenous HGF markedly induces TGF-␤ 2 protein levels, and a neutralizing TGF-␤ 2 antibody abolishes the HGF-mediated increase in glioma cell motility. Finally, TGF-␤ 2 does not modulate BCL-2 or BAX expression, but BCL-2 gene transfer increases the levels of latent and active TGF-␤ 2 . 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 HGFinduced glioma cell migration and invasion, which requires ezrin, changes in the BCL-2/BAX rheostat, and the induction of TGF-␤ 2 expression in vitro, and underscore the important role of HGF signaling in vivo.