Phosphorylation State of RB Modulates Ferroptotic Sensitivity.

Tumor suppressor RB is a central regulator of cell cycle progression. By binding to E2F transcription factors, RB can inhibit transcription of E2F target genes to cause cell cycle arrest. Cyclin dependent kinases (CDK) regulate the interaction of RB/E2F by phosphorylating RB at multiple sites. Previously, we observed that CDK2, RB and E2F inhibit ferroptosis. Ferroptosis is a non-apoptotic, iron-dependent form of cell death characterized by toxic lipid peroxidation. Here, we investigate whether RB is a downstream target of CDK activity in the regulation of ferroptosis. We approach this question by overexpressing wild-type (WT) RB or a mutant RB that cannot be phosphorylated by CDKs (RBΔCDK) followed by analysis of ferroptosis. Overexpressing WT-RB reduced sensitivity to ferroptosis while the RBΔCDK mutant increased sensitivity. As we previously found, increasing CDK2 expression reduced ferroptotic sensitivity. This reduction persisted in cells expressing RBΔCDK. However, WT-RB blocked the ability of CDK2 to inhibit ferroptosis. These observations suggest that at least part of the mechanism by which CDK2 inhibits ferroptosis is by phosphorylating RB.