MLKL Requires the Inositol Phosphate Code to Execute Necroptosis

Necroptosis is an important form of lytic cell death triggered by injury and infection, but whether mixed lineage kinase domain-like (MLKL) is sufficient to execute this pathway is unknown. In a genetic selection for human cell mutants defective for MLKL-dependent necroptosis, we identified mutations in IPMK and ITPK1, which encode inositol phosphate (IP) kinases that regulate the IP code of soluble molecules. We show that IP kinases are essential for necroptosis triggered by death receptor activation, herpesvirus infection, or a pro-necrotic MLKL mutant. In IP kinase mutant cells, MLKL failed to oligomerize and localize to membranes despite proper receptor-interacting protein kinase-3 (RIPK3)-dependent phosphorylation. We demonstrate that necroptosis requires IP-specific kinase activity and that a highly phosphorylated product, but not a lowly phosphorylated precursor, potently displaces the MLKL auto-inhibitory brace region. These observations reveal control of MLKL-mediated necroptosis by a metabolite and identify a key molecular mechanism underlying regulated cell death. [Display omitted] •IP kinases are critical for necroptosis induced by TNF and viral infection•MLKL fails to oligomerize in IP kinase mutants despite phosphorylation by RIPK3•Necroptosis requires IP kinase activity to produce the IP code•IP6—but not IP3—displaces the MLKL auto-inhibitory brace region Dovey et al. report an unexpected layer of regulation governing a form of cell death termed necroptosis. They find that the inositol phosphate code controls the executioner protein MLKL to induce cell lysis. This study deepens our understanding of cell death mechanisms important for infection, inflammation, and cancer.