Highlights d Hypoxic microenvironment is essential for propagation and growth of PFA ependymoma d Hypoxia controls metabolic intermediates that maintain an H3K27 hypomethylated genome d Inhibition or potentiation of histone lysine methylation diminishes PFA survival d Gliogenic lineage of developing fetal hindbrain mirrors PFA metabolic alterations

Although immunotherapy has revolutionized cancer care, patients with pancreatic ductal adenocarcinoma (PDA) rarely respond to these treatments, a failure that is attributed to poor infiltration and activation of T cells in the tumor microenvironment (TME). We performed an in vivo CRISPR screen and identified lysine demethylase 3A (KDM3A) as a potent epigenetic regulator of immunotherapy response in PDA. Mechanistically, KDM3A acts through Krueppel-like factor 5 (KLF5) and SMAD family member 4 (SMAD4) to regulate the expression of the epidermal growth factor receptor (EGFR). Ablation of KDM3A, KLF5, SMAD4, or EGFR in tumor cells altered the immune TME and sensitized tumors to combination immunotherapy, whereas treatment of established tumors with an EGFR inhibitor, erlotinib, prompted a dose-dependent increase in intratumoral T cells. This study defines an epigenetic-transcriptional mechanism by which tumor cells modulate their immune microenvironment and highlights the potential of EGFR inhibitors as immunotherapy sensitizers in PDA.SIGnIFICanCE: PDA remains refractory to immunotherapies. Here, we performed an in vivo CRISPR screen and identified an epigenetic-transcriptional network that regulates antitumor immunity by converging on EGFR. Pharmacologic inhibition of EGFR is sufficient to rewire the immune microenvironment. These results offer a readily accessible immunotherapy-sensitizing strategy for PDA.

Epithelial plasticity -reversible modulation of a cell's epithelial and mesenchymal features -is associated with tumor metastasis and chemoresistance, leading causes of cancer mortality. While different master transcription factors and epigenetic modifiers have been implicated in this process in various contexts, the extent to which a unifying, generalized mechanism of transcriptional regulation underlies epithelial plasticity remains largely unknown. Here, through targeted CRISPR-Cas9 screening, we discovered two histone-modifying enzymes involved in the writing and erasing of H3K36me2 that act reciprocally to regulate epithelial-mesenchymal identity, tumor differentiation, and metastasis. Using a K-to-M histone mutant to directly inhibit H3K36me2, we found that global modulation of the mark is a conserved mechanism underlying the mesenchymal state in various contexts. Mechanistically, regulation of H3K36me2 reprograms enhancers associated with master regulators of epithelialmesenchymal state. Our results thus outline a unifying epigenome-scale mechanism by which a specific histone modification regulates cellular plasticity and metastasis in cancer. STATEMENT OF SIGNIFICANCEAlthough epithelial plasticity contributes to cancer metastasis and chemoresistance, no strategies exist for pharmacologically inhibiting the process. Here, we show that global regulation of a specific histone mark, H3K36me2, is a universal epigenome-wide mechanism that underlies EMT and MET in carcinoma cells. These results offer a new strategy for targeting epithelial plasticity in cancer. Research.on August 5, 2020.