Oligomerization-driven MLKL ubiquitylation antagonizes necroptosis.

Area of Science:

• Cellular biology
• Molecular mechanisms of cell death
• Programmed cell death pathways

Background:

• Mixed lineage kinase domain-like (MLKL) is the effector protein in necroptosis, a programmed cell death pathway.
• Receptor-interacting serine/threonine protein kinase 3 (RIPK3) activates MLKL, leading to membrane disruption.
• The role and mechanism of MLKL ubiquitylation during necroptosis remain unclear.

Purpose of the Study:

• To elucidate the mechanism and significance of MLKL ubiquitylation in necroptosis.
• To investigate the regulation of MLKL activity by ubiquitylation.
• To understand how ubiquitylation controls basal MLKL levels and prevents unwanted cell death.

Main Methods:

• Analysis of MLKL ubiquitylation in response to necroptotic stimuli.
• Cellular fractionation to localize ubiquitylated MLKL.
• Expression of deubiquitylating enzymes to assess ubiquitylation's impact.
• Site-directed mutagenesis to identify ubiquitylation sites on MLKL.
• MLKL-deubiquitylating enzyme (DUB) fusion strategy to study constitutive deubiquitylation.

Main Results:

• Necroptosis-specific multi-mono-ubiquitylation of MLKL occurs post-activation and oligomerization.
• Ubiquitylated MLKL localizes to membranes and protein aggregates.
• MLKL ubiquitylation occurs on at least four lysine residues and targets MLKL for proteasomal and lysosomal degradation.
• Constitutive deubiquitylation of MLKL leads to its auto-activation, independent of necroptosis signaling.

Conclusions:

• Ubiquitylation of MLKL is a crucial regulatory event in necroptosis.
• Ubiquitylation controls the turnover of activated MLKL and prevents spontaneous necroptosis.
• This study reveals a dual role for ubiquitylation in regulating necroptosis kinetics and basal cell death prevention.