GPX4-dependent ferroptosis sensitivity is a fitness trade-off for cell enlargement.

Despite wide variation, each cell type has an optimal size. Maintaining optimal size is essential for cellular fitness and function but the biological basis for this remains elusive. Here, we performed fitness analysis involving genome-wide CRISPR-Cas9 knockout data from tens of human cell lines and identified that cell size influences the essentiality of genes related to mitochondria and membrane repair. These genes also included glutathione peroxidase 4 (GPX4), which safeguards membranes from oxidative damage and prevents ferroptosis-iron-dependent death. Growth beyond normal size, with or without cell-cycle arrest, increased lipid peroxidation, resulting in a ferroptosis-sensitive state. Proteomic analysis revealed cell-cycle-independent superscaling of endoplasmic reticulum, accumulation of iron, and lipidome remodeling. Even slight increases from normal cell size sensitized proliferating cells to ferroptosis as evidenced by deep-learning-based single-cell analysis. Thus, lipid peroxidation may be a fitness trade-off that constrains cell enlargement and contributes to the establishment of an optimal cell size.