MLKL Compromises Plasma Membrane Integrity by Binding to Phosphatidylinositol Phosphates

TLDR

MLKL is a key necroptosis effector, yet the mechanism by which it transduces the death signal remains poorly understood. MLKL’s N‑terminal four‑helical bundle domain oligomerizes and, via a positively charged surface patch that binds phosphatidylinositol phosphates, targets the plasma membrane, directly permeabilizing it and driving necroptosis, while blocking PI(5)P/PI(4,5)P2 synthesis selectively suppresses TNF‑mediated necroptosis without affecting apoptosis.

Abstract

Although mixed lineage kinase domain-like (MLKL) protein has emerged as a specific and crucial protein for necroptosis induction, how MLKL transduces the death signal remains poorly understood. Here, we demonstrate that the full four-helical bundle domain (4HBD) in the N-terminal region of MLKL is required and sufficient to induce its oligomerization and trigger cell death. Moreover, we found that a patch of positively charged amino acids on the surface of the 4HBD binds to phosphatidylinositol phosphates (PIPs) and allows recruitment of MLKL to the plasma membrane. Importantly, we found that recombinant MLKL, but not a mutant lacking these positive charges, induces leakage of PIP-containing liposomes as potently as BAX, supporting a model in which MLKL induces necroptosis by directly permeabilizing the plasma membrane. Accordingly, we found that inhibiting the formation of PI(5)P and PI(4,5)P2 specifically inhibits tumor necrosis factor (TNF)-mediated necroptosis but not apoptosis.