A RIPK3-independent role of MLKL in suppressing parthanatos promotes immune evasion in hepatocellular carcinoma

Abstract

Mixed lineage kinase domain-like (MLKL) is widely accepted as an executioner of necroptosis, in which MLKL mediates necroptotic signaling and triggers cell death in a receptor-interacting protein kinase 3 (RIPK3)-dependent manner. Recently, it is increasingly noted that RIPK3 is intrinsically silenced in hepatocytes, raising a question about the role of MLKL in hepatocellular carcinoma (HCC). This study reports a previously unrecognized role of MLKL in regulating parthanatos, a programmed cell death distinct from necroptosis. In HCC cells with intrinsic RIPK3 deficiency, knockout of MLKL impedes the orthotopic tumor growth, activates the anti-tumor immune response and enhances the therapeutic effect of immune checkpoint blockade in syngeneic HCC tumor models. Mechanistically, MLKL is required for maintaining the endoplasmic reticulum (ER)-mitochondrial Mg2+ dynamics in HCC cells. MLKL deficiency restricts ER Mg2+ release and mitochondrial Mg2+ uptake, leading to ER dysfunction and mitochondrial oxidative stress, which together confer increased susceptibility to metabolic stress-induced parthanatos. Importantly, pharmacological inhibition of poly(ADP-ribose) polymerase to block parthanatos restores the tumor growth and immune evasion in MLKL-knockout HCC tumors. Together, our data demonstrate a new RIPK3-independent role of MLKL in regulating parthanatos and highlight the role of MLKL in facilitating immune evasion in HCC.

scStateDynamics: deciphering the drug-responsive tumor cell state dynamics by modeling single-cell level expression changes

“…For example, MLKL, a necroptosis regulator, plays complex but little-known roles in cancer development and metastasis 46 , and was recently reported that it can promote immune evasion in HCC 47 . High expression of MAOA was reported to be associated with immunosuppressive tumor microenvironment and poor prognosis 48 .…”

Pervasive loss of regulated necrotic cell death genes in elephants, hyraxes, and sea cows (Paenungualta)

“…Similarly, inhibiting necroptosis reduced tumor-cell-induced endothelial necroptosis, tumor cell extravasation, and metastasis (Strilic et al, 2016). Loss of MLKL may also protect against immune evasion in hepatocellular carcinoma by suppressing parthanatos (Jiang et al, 2023), a cell death mode that occurs following the overactivation of the DNA repair enzyme poly(ADP-ribose) polymerase 1 (PARP1) (David et al, 2009; Yu et al, 2006). Unexpectedly, the deletion of RIPK3 in mouse embryonic fibroblasts dramatically suppressed reprogramming into induced pluripotent stem cells (iPSCs), likely by reducing the expression of cell cycle progression genes (Al-Moujahed et al, 2019).…”

Non-Necroptotic Roles of MLKL in Diet-Induced Obesity, Liver Pathology, and Insulin Sensitivity: Insights from a High-Fat, High-Fructose, High-Cholesterol Diet Mouse Model

“…In support of this, a recent study reported epigenetic silencing of Ripk3 in hepatocytes of a MASH-inducing diet mouse model [ 45 ]. Liver cancer cells are also shown to prevent MLKL-mediated necroptosis by epigenetic silencing of Ripk3 [ 46 ]. Surprisingly, in our study, Mlkl −/− mice on the HFHFrHC diet exhibited elevated levels of TNFα, IL6, IL1β, and Ccl2 in the liver, challenging previous data indicating that MLKL deficiency reduces inflammation [ 23 , 44 ].…”