Inhibition of histone H3K27 demethylases inactivates brachyury (TBXT) and promotes chordoma cell death [RNA-Seq II]

The expression of transcription factor brachyury (TBXT) is normally restricted to embryonic development and its silencing after mesoderm development is epigenetically regulated. In chordoma, a rare tumour of notochordal differentiation, TBXT acts as a putative oncogene, and we hypothesised that its expression could be contolled through epigenetic inhibition. Screening of five chordoma cell lines revealed that inhibitors of the histone 3 lysine 27 demethylases KDM6A (UTX) and KDM6B (Jmjd3) reduce TBXT expression and lead to cell death, findings validated in primary patient-derived culture systems. Pharmacological inhibition was phenocopied by genetic inactivation of KDM4/B using CRISPR/Cas9. Transcriptional profiles in response to a novel KDM6A/B inhibitor, KDOBA67, revealed downregulation of critical genes and transcription factor networks for chordoma survival pathways, characterised by paired and homeobox genes, whereas upregulated pathways are dominated by stress, cell cycle and pro-apoptotic response pathways. This study supports previous data showing that the function of TBXT is essential for maintaining notochord cell fate and function and provides further evidence that TBXT is an oncogenic driver in chordoma. The data suggest that TBXT can potentially be targeted therapeutically by modulating epigenetic control mechanisms such as H3K27 demethylases. Examination of gene expression differences in 3 chordoma cell lines in the presence of DMSO or KDOBA67