AMPK-Mediated BECN1 Phosphorylation Promotes Ferroptosis by Directly Blocking System X_c^- Activity

Ferroptosis is a form of regulated cell death triggered by lipid peroxidation after inhibition of the cystine/glutamate antiporter system X_c^-. However, key regulators of system X_c^- activity in ferroptosis remain undefined. Here, we show that BECN1 plays a hitherto unsuspected role in promoting ferroptosis through directly blocking system Xc^- activity via binding to its core component, SLC7A11 (solute carrier family 7 member 11). Knockdown of BECN1 by shRNA inhibits ferroptosis induced by system X_c^- inhibitors (e.g., erastin, sulfasalazine, and sorafenib), but not other ferroptosis inducers including RSL3, FIN56, and buthionine sulfoximine. Mechanistically, AMP-activated protein kinase (AMPK)-mediated phosphorylation of BECN1 at Ser90/93/96 is required for BECN1-SLC7A11 complex formation and lipid peroxidation. Inhibition of PRKAA/AMPKα by siRNA or compound C diminishes erastin-induced BECN1 phosphorylation at S93/96, BECN1-SLC7A11 complex formation, and subsequent ferroptosis. Accordingly, a BECN1 phosphorylation-defective mutant (S90,93,96A) reverses BECN1-induced lipid peroxidation and ferroptosis. Importantly, genetic and pharmacological activation of the BECN1 pathway by overexpression of the protein in tumor cells or by administration of the BECN1 activator peptide Tat-beclin 1, respectively, increases ferroptotic cancer cell death (but not apoptosis and necroptosis) in vitro and in vivo in subcutaneous and orthotopic tumor mouse models. Collectively, our work reveals that BECN1 plays a novel role in lipid peroxidation that could be exploited to improve anticancer therapy by the induction of ferroptosis.