MRP1 inhibition by lipid-derived electrophiles during ferroptosis illustrates a role for protein alkylation in ferroptotic cell death

Abstract

Ferroptosis is a regulated form of cell death characterized by lipid peroxidation and lipid hydroperoxide (LOOH) generation that offers new therapeutic opportunities. However, the molecular mechanism through which LOOH accumulation leads to cell death remains poorly understood. Importantly, LOOH breakdown forms truncated phospholipids (PLs) and highly reactive lipid-derived electrophiles (LDEs) capable of altering protein function through cysteine alkylation. While truncated PLs have been shown to mediate ferroptotic membrane permeabilization, a functional role for LDEs in the ferroptotic cell death mechanism has not been established. Here, using multidrug resistance protein 1 (MRP1) activity as an example, we demonstrate that LDEs mediate altered protein function during ferroptosis. Applying live cell fluorescence imaging, we first identified that inhibition of MRP1-mediated LDE detoxification occurs across a panel of ferroptosis inducers (FINs) with differing mechanisms of ferroptosis induction (Types I-IV FINs erastin, RSL3, FIN56 and FINO2). This MRP1 inhibition was recreated by both initiation of lipid peroxidation and treatment with the LDE 4-hydroxy-2-nonenal (4-HNE). Importantly, treatment with radical-trapping antioxidants prevented impaired MRP1 activity when working with both FINs and lipid peroxidation initiators but not 4-HNE, pinpointing LDEs as the cause of inhibited MRP1 activity during ferroptosis. Our findings, when combined with reports of widespread LDE-alkylation of key proteins during ferroptosis, sets a precedent for LDEs as critical mediators of ferroptotic cell death. LOOH breakdown to truncated phospholipids and LDEs may fully explain membrane permeabilization and modified protein function during late stage ferroptosis, offering a unified explanation of the molecular ferroptotic cell death mechanism.