STEM-28. TISSUE FACTOR PROMOTES THE GLIOMA STEM CELL PHENOTYPE, AND IS SUPPRESSED BY MUTANT IDH1. (5th November 2018) - Unruh, Dusten
Abstract: Isocitrate dehydrogenase 1 mutant (IDH1 mut ) gliomas have global genomic hypermethylation, are less aggressive than IDH1 wild-type (IDH1 wt ) gliomas, and generally grow poorly in vitro and in vivo . Yet little data exist that connect specific hypermethylation targets to this unique phenotype. We previously reported that the gene encoding Tissue Factor (TF), F3, which promotes both thrombosis and malignant behavior, is among the most hypermethylated and downregulated genes in IDH1 mut gliomas. In multiple IDH1 wt and IDH1 mut patient-derived glioma cell lines, F3 was hypermethylated in IDH1 mut cells compared to IDH1 wt cells, with reduced TF protein expression. A demethylating agent, decitabine, increased F3 transcription in IDH1 mut glioma cells, but not in IDH1 wt cells. TF knockdown greatly reduced proliferation, colony formation, glioma stem cell (GSC) marker expression, and xenograft growth of IDH1 wt /EGFRvIII amp GBM6 cells and IDH1 wt /EGFR amp GBM12 cells, but not of NF1 -mutant GBM43 cells. Conversely, TF induction enhanced the proliferation and colony formation of IDH1 mut GBM164 and TB09 cells, especially GBM164. TF also increased the in vivo "take rate" of intracranial GBM164 xenografts from 0% to 100%, but did not enable TB09 xenograft growth. TF activated receptor tyrosine kinases (RTKs) in GBM6, GBM12, and GBM164, but RTK expression was very low in GBM43 and TB09. Transcriptomic profiling showed that only two genes were downregulated after TF knockdown in GBM6 and GBM12, and also upregulated after TF induction in GBM164: PROM1, encoding CD133, and CTNND2, encoding δ-catenin. Neither gene was affected by TF manipulation in GBM43 or TB09. High F3 mRNA correlated with enrichment of GSC markers, and worse outcome, in TCGA gliomas. These data suggest that: (i) TF promotes a GSC phenotype through RTKs; (ii) CD133 and δ-catenin may be critical effectors of TF-induced GSC behavior; (iii) TF methylation reduces IDH1 mut glioma malignancy; (iv) TF is an attractive, novel therapeutic target in IDH1 wt gliomas.