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Characterization of MLKL-mediated Plasma Membrane Rupture in Necroptosis
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Characterization of MLKL-mediated Plasma Membrane Rupture in Necroptosis

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Cathepsins limit macrophage necroptosis through cleavage of Rip1 kinase

Scott McComb1, Bojan Shutinoski1, Susan Thurston1

  • 1Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Ontario, K1H 8M5, Canada.

Journal of Immunology (Baltimore, Md. : 1950)
|May 7, 2014
PubMed

Insights

Programmed necrosis (necroptosis) in macrophages involves receptor-interacting protein kinase-1 (Rip1) cleavage. Cysteine cathepsins B and S, not just caspases, cleave Rip1, regulating necroptosis in inflammatory diseases.

Area of Science:

  • Immunology
  • Cellular Biology
  • Molecular Medicine

Background:

  • Programmed necrosis, or necroptosis, is increasingly recognized for its role in inflammation.
  • Understanding necroptosis regulation in immune cells is crucial for inflammatory disease pathology.

Purpose of the Study:

  • To investigate the regulation of necroptosis in macrophages.
  • To identify novel mechanisms controlling receptor-interacting protein kinase-1 (Rip1) cleavage and necroptosis induction.

Main Methods:

  • Macrophages were treated with pan-caspase inhibitors and TLR agonists.
  • Receptor-interacting protein kinase-1 (Rip1) phosphorylation and cleavage were analyzed.
  • Small interfering RNA (siRNA) knockdown, cathepsin inhibitors, and cell-free assays were used to assess cathepsin activity.
  • Combined inhibition of cathepsins and caspase-8 was evaluated for necroptosis induction.

Main Results:

  • Pan-caspase inhibition (zVAD-FMK) induced Rip1 phosphorylation and necroptosis dependent on TNF signaling.
  • TLR agonists with zVAD-FMK induced Rip1 phosphorylation via a TNFR-independent pathway.
  • Cysteine cathepsins B and S were identified as novel enzymes that directly cleave Rip1 in macrophages.
  • Combined inhibition of cathepsins and caspase-8 was required for potent macrophage necroptosis.

Conclusions:

  • Cysteine cathepsins B and S represent a novel regulatory mechanism for Rip1 cleavage and necroptosis in macrophages.
  • This finding offers new therapeutic targets for inflammatory diseases involving necroptosis.

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