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De-ubiquitination and ubiquitin ligase domains of A20 downregulate NF-kappaB signalling

Ingrid E Wertz1, Karen M O'Rourke, Honglin Zhou

  • 1Department of Molecular Oncology, School of Medicine, University of California, Davis, Davis, California 95616, USA.

Nature
|July 20, 2004
PubMed

Insights

A20 protein inhibits chronic inflammation by removing and adding ubiquitin chains to RIP, a key signaling molecule. This dual action targets RIP for degradation, downregulating NF-kappaB signaling and preventing cell death.

Area of Science:

  • Molecular Biology
  • Immunology
  • Biochemistry

Background:

  • NF-kappaB transcription factors are crucial mediators of pro-inflammatory cytokines, including tumor necrosis factor-alpha and interleukin-1beta.
  • Dysregulated NF-kappaB activity leads to chronic inflammation and cell death, as evidenced in A20-deficient mice.
  • A20 is recognized as a potent inhibitor of NF-kappaB signaling, yet its precise mechanism of action remained elusive.

Purpose of the Study:

  • To elucidate the mechanism by which A20 downregulates NF-kappaB signaling.
  • To characterize the distinct roles of A20's ubiquitin-editing domains in regulating inflammatory pathways.
  • To identify novel ubiquitin ligase domains and sequential regulatory mechanisms.

Main Methods:

  • Investigated the enzymatic activities of A20's N-terminal de-ubiquitinating (DUB) and C-terminal ubiquitin ligase domains.
  • Analyzed the ubiquitination status of receptor interacting protein (RIP) in response to TNF receptor 1 (TNFR1) signaling.
  • Utilized proteasomal degradation assays to assess the fate of RIP.

Main Results:

  • A20's N-terminal OTU domain removes K63-linked ubiquitin chains from RIP.
  • A20's C-terminal zinc finger domain polyubiquitinates RIP with K48-linked chains, targeting it for proteasomal degradation.
  • Demonstrated a novel mechanism of NF-kappaB downregulation through sequential ubiquitin editing of RIP.

Conclusions:

  • A20 employs a dual ubiquitin-editing strategy involving de-ubiquitination and subsequent polyubiquitination of RIP.
  • This coordinated action effectively terminates NF-kappaB signaling, preventing chronic inflammation.
  • Highlighted A20 as a key example of a protein with distinct DUB and ubiquitin ligase domains mediating specific regulatory functions.

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