Calcium licenses lipid droplets for ferroptosis: A PKCβ-ACSL4-ALOX15 phosphorylation relay.

Ferroptosis is executed by iron-dependent phospholipid peroxidation, yet the upstream signals that determine when oxidizable lipid pools become lethal remain incompletely resolved. Recent work identifies a calcium-dependent protein kinase C beta (PKCβ) pathway that phosphorylates acyl-CoA synthetase long-chain family member 4 (ACSL4) and arachidonate 15-lipoxygenase (ALOX15), and reports relocation of an ACSL4-PKCβ-ALOX15 complex to lipid droplets during ferroptotic stress. These findings connect calcium dynamics to lipid metabolism through a spatially organized phosphorylation program. We propose that lipid droplets should not be classified as constitutively protective or pro-ferroptotic organelles. Instead, they may undergo a calcium-gated licensing transition: under basal or transient stress, neutral-lipid storage buffers polyunsaturated fatty acids; under sustained, spatially restricted calcium signaling, PKCβ-dependent phosphorylation may convert the lipid-droplet surface into a catalytic staging platform that supplies and oxidizes ferroptosis-sensitive lipids. This model explains why lipid-droplet biogenesis can suppress ferroptosis in one context but support it in another, and it predicts a relay from lipid droplets to endoplasmic-reticulum and endoplasmic-reticulum-mitochondria contact sites where phospholipid peroxidation can propagate. Distinguishing initiating calcium microdomains from late calcium influx through damaged plasma membranes will be essential. Phosphosite-resolved imaging, organelle-targeted calcium sensors, contact-site lipidomics, and tissue-specific perturbation of PKCβ should test this framework and may enable selective ferroptosis induction in cancer while preserving calcium-overloaded tissues such as the exocrine pancreas.