Methylation-dependent Tissue Factor Suppression Contributes to the Reduced Malignancy of IDH1-mutant Gliomas.

Abstract

Gliomas with <i>isocitrate dehydrogenase 1</i> mutations (IDH1^mut) are less aggressive than IDH1 wild-type (IDH1^wt) gliomas and have global genomic hypermethylation. Yet it is unclear how specific hypermethylation events contribute to the IDH1^mut phenotype. Previously, we showed that the gene encoding the procoagulant tissue factor (TF), <i>F3</i>, is among the most hypermethylated and downregulated genes in IDH1^mut gliomas, correlating with greatly reduced thrombosis in patients with IDH1^mut glioma. Because TF also increases the aggressiveness of many cancers, the current study explored the contribution of TF suppression to the reduced malignancy of IDH1^mut gliomas.<b>Experimental Design:</b> TF expression was manipulated in patient-derived IDH1^mut and IDH1^wt glioma cells, followed by evaluation of <i>in vitro</i> and <i>in vivo</i> behavior and analyses of cell signaling pathways. A demethylating agent, decitabine, increased <i>F3</i> transcription and TF-dependent coagulative activity in IDH1^mut cells, but not in IDH1^wt cells. TF induction enhanced the proliferation, invasion, and colony formation of IDH1^mut cells, and increased the intracranial engraftment of IDH1^mut GBM164 from 0% to 100% (<i>P</i> = 0.0001). Conversely, TF knockdown doubled the median survival of mice engrafted with IDH1^wt/EGFRvIII^amp GBM6, and caused complete regression of IDH1^wt/EGFR^amp GBM12 (<i>P</i> = 0.001). <i>In vitro</i> and <i>in vivo</i> effects were linked to activation of receptor tyrosine kinases (RTK) by TF through a Src-dependent intracellular pathway, even when extracellular RTK stimulation was blocked. TF stimulated invasion predominately through upregulation of β-catenin. These data show that TF suppression is a component of IDH1^mut glioma behavior, and that it may therefore be an attractive target against IDH1^wt gliomas.