Inactivation of necroptosis-promoting protein MLKL creates a therapeutic vulnerability in colorectal cancer cells.

Mortality from colorectal cancer (CRC) is significant, and novel CRC therapies are needed. A pseudokinase MLKL typically executes necroptotic cell death, and MLKL inactivation protects cells from such death. However, we found unexpectedly that MLKL gene knockout enhanced CRC cell death caused by a protein synthesis inhibitor homoharringtonine used for chronic myeloid leukemia treatment. In an effort to explain this finding, we observed that MLKL gene knockout reduced CRC cell autophagy and rendered such autophagy critically dependent on the presence of VPS37A, a component of the ESCRT-I complex. Moreover, homoharringtonine-induced activation of p38 MAP kinase (p38MAPK) prevented VPS37A from supporting autophagy in MLKL-deficient cells and triggered their parthanatos, a cell death type driven by poly(ADP-ribose) polymerase hyperactivation. Finally, a pharmacological MLKL inhibitor necrosulfonamide strongly cooperated with homoharringtonine in suppressing CRC cell tumorigenicity in mice. Thus, while MLKL mediates necroptosis, MLKL protects CRC cells from death caused by drugs blocking basal autophagy, e.g., homoharringtonine, and MLKL inhibition creates a therapeutic vulnerability that could be utilized for CRC treatment.