EZH2 suppresses IR-induced ferroptosis by forming a co-repressor complex with HIF-1α to inhibit ACSL4: Targeting EZH2 enhances radiosensitivity in KDM6A-deficient esophageal squamous carcinoma

The mutation status of the lysine demethylase 6 A (KDM6A), a gene antagonist to Enhancer of zeste homolog 2 (EZH2), is closely related to the therapeutic efficacy of EZH2 inhibitors in several malignancies. However, the mutational landscape of KDM6A and the therapeutic targetability of EZH2 inhibitors in esophageal squamous carcinoma (ESCC) remain unreported. Here, we found that approximately 9.18% (9/98) of our study ESCC tissues had KDM6A mutations of which 7 cases resulted in a complete loss of expression and consequent loss of demethylase function. We found that KDM6A-deficient ESCC cells exhibited increased sensitivity to EZH2 inhibitor, and the radiosensitizing activity of EZH2 inhibitor was evident in KDM6A-dficient ESCC cells. Further transcriptome analysis revealed that ferroptosis is implicated in the radiosensitizing effect exerted by EZH2 inhibition on KDM6A-deficient ESCC cells. The following Chromatin Immunoprecipitation (ChIP), co-immunoprecipitation, and luciferase reporter assays demonstrated that in KDM6A-deficient ESCC cells, (1) Acyl-CoA Synthetase Long Chain Family Member 4 (ACSL4) is the target gene for EZH2 to regulate ferroptosis; (2) The IR-induced hypoxia inducible factor 1 subunit alpha (HIF-1α) is a predominant mediator of EZH2 to repress ACSL4; (3) the HRE7-8 regions of the ACSL4 promoter are required for the repressive function of EZH2 on ACSL4; (4) EZH2 regulates ACSL4 by forming a co-repressive complex with HIF-1α. Our study provides preclinical evidence supporting that EZH2 inhibitors may confer therapeutic benefit in KDM6A-deficient ESCC patients.