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Biological events and molecular signaling following MLKL activation during necroptosis.

ABSTRACT: Necroptosis is a form of programmed necrotic cell death mediated by the kinase RIPK3 and its substrate MLKL. MLKL, which displays plasma membrane (PM) pore-forming activity upon phosphorylation, functions as the executioner during necroptosis. Thus, it was previously assumed that MLKL phosphorylation is the endpoint of the necroptotic signaling pathway. Here, we summarize several events that characterize the dying necroptotic cells after MLKL phosphorylation, including Ca2+ influx, phosphatidylserine (PS) externalization, PM repair by ESCRT-III activation, and the final compromise of PM integrity. These processes add several unexpected regulatory events downstream of MLKL signaling. We have also observed that CoCl2, which may mimic hypoxia, can induce necroptosis, which suggests that in vivo triggers of necroptosis might include a transient lack of O2.

SUBMITTER: Gong YN

PROVIDER: S-EPMC5628637 | biostudies-literature | 2017 Oct

REPOSITORIES: biostudies-literature

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Biological events and molecular signaling following MLKL activation during necroptosis.

Gong Yi-Nan YN Guy Cliff C Crawford Jeremy Chase JC Green Douglas R DR

Cell cycle (Georgetown, Tex.) 20170830 19

Necroptosis is a form of programmed necrotic cell death mediated by the kinase RIPK3 and its substrate MLKL. MLKL, which displays plasma membrane (PM) pore-forming activity upon phosphorylation, functions as the executioner during necroptosis. Thus, it was previously assumed that MLKL phosphorylation is the endpoint of the necroptotic signaling pathway. Here, we summarize several events that characterize the dying necroptotic cells after MLKL phosphorylation, including Ca<sup>2+</sup> influx, ph ...[more]

PMID: 28854080

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Oligomerization-driven MLKL ubiquitylation antagonizes necroptosis.

Project description:Mixed lineage kinase domain-like (MLKL) is the executioner in the caspase-independent form of programmed cell death called necroptosis. Receptor-interacting serine/threonine protein kinase 3 (RIPK3) phosphorylates MLKL, triggering MLKL oligomerization, membrane translocation and membrane disruption. MLKL also undergoes ubiquitylation during necroptosis, yet neither the mechanism nor the significance of this event has been demonstrated. Here, we show that necroptosis-specific multi-mono-ubiquitylation of MLKL occurs following its activation and oligomerization. Ubiquitylated MLKL accumulates in a digitonin-insoluble cell fraction comprising organellar and plasma membranes and protein aggregates. Appearance of this ubiquitylated MLKL form can be reduced by expression of a plasma membrane-located deubiquitylating enzyme. Oligomerization-induced MLKL ubiquitylation occurs on at least four separate lysine residues and correlates with its proteasome- and lysosome-dependent turnover. Using a MLKL-DUB fusion strategy, we show that constitutive removal of ubiquitin from MLKL licences MLKL auto-activation independent of necroptosis signalling in mouse and human cells. Therefore, in addition to the role of ubiquitylation in the kinetic regulation of MLKL-induced death following an exogenous necroptotic stimulus, it also contributes to restraining basal levels of activated MLKL to avoid unwanted cell death.

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