 Glutathion peroxidase 4, GPX4, inhibits feroptosis, but protein synthesis is inefficient and costly. Here, the authors reveal that cystin uptake promotes GPX4 synthesis by activating MTORC1 and show that cancer cells are sensitized to feroptosis by MTORC1 inhibition. This article was authored by Ile Jong, Robert the 5th swander, Litong Nye, and others.