Ribosome stalling during selenoprotein translation exposes a ferroptosis vulnerability in cancer

ABSTRACT Ferroptosis is a regulated, iron-dependent form of necrosis that is triggered by the accumulation of oxidatively damaged phospholipids 1–3 . Glutathione peroxidase 4 (GPX4) prevents ferroptosis by converting phospholipid hydroperoxides into non-toxic lipid alcohols 4, 5 . Ferroptosis has been implicated in the pathology of several degenerative conditions and inhibiting GPX4 activity has emerged as a therapeutic strategy to induce cancer cell death 1, 2 . However, many cancer cell lines are resistant to GPX4 inhibition 6 , and the mechanisms that regulate GPX4 activity and ferroptosis resistance remain incompletely understood. Here, employing a synthetic lethal CRISPR-Cas9 screen in a triple negative breast cancer (TNBC) cell line, we identify LRP8 (also known as ApoER2) as a ferroptosis resistance factor. LRP8 is upregulated in cancer, and we find that it promotes ferroptosis resistance in cancer cells in both 2-dimensional (2-D) cell culture and 3-dimensional (3-D) spheroid models. Mechanistically, loss of LRP8 decreases cellular selenium levels, resulting in the reduced expression of a subset of selenoproteins, including GPX4. Remarkably, the reduction in GPX4 is not due to the classic hierarchical selenoprotein regulatory program 7, 8 . Instead, our findings demonstrate that the translation of GPX4 is severely impaired in the selenium-deficient LRP8 knockout (KO) cells due to extensive ribosome stalling at the inefficiently decoded GPX4 selenocysteine (SEC) UGA codon, which results in ribosome collisions and early translation termination. Thus, our findings reveal ribosome stalling and collisions during GPX4 translation as targetable ferroptosis vulnerabilities in cancer cells.