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The carboxyl-terminal tail of Noxa protein regulates the stability of Noxa and Mcl-1

Xiaming Pang1, Jingjing Zhang2, Hernando Lopez1

  • 1From the Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, Nebraska 68198-7696.

The Journal of Biological Chemistry
|May 10, 2014
PubMed

Insights

The BH3-only protein Noxa, a key apoptosis regulator, is degraded independently of ubiquitylation. Its C-terminal tail controls Noxa stability and Mcl-1 protein levels.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Biochemistry

Background:

  • Noxa is a BH3-only protein crucial for apoptosis induction.
  • Noxa primarily inactivates the antiapoptotic protein Mcl-1.
  • Noxa is known to be a labile protein degraded by the proteasome.

Purpose of the Study:

  • To investigate the mechanism of Noxa degradation.
  • To determine how Noxa regulates Mcl-1 stability.
  • To identify the specific regions responsible for Noxa degradation.

Main Methods:

  • Proteasome activity assays.
  • Ubiquitylation assays.
  • Site-directed mutagenesis to identify degron sequences.
  • Analysis of protein stability and interactions.

Main Results:

  • Noxa degradation is ubiquitylation-independent and does not require Mcl-1 binding.
  • A specific C-terminal sequence acts as a degron for proteasomal degradation.
  • Mutating this degron stabilizes Noxa and endogenous Mcl-1 via direct BH3 interaction.
  • Ectopic expression of the degron confers instability to other proteins.

Conclusions:

  • The C-terminal tail of Noxa is a critical determinant of its proteasomal degradation.
  • Noxa's C-terminal tail regulates the stability of both Noxa and Mcl-1.
  • This mechanism highlights a novel regulatory role for Noxa's C-terminus in apoptosis control.
Keywords:
BH3-only ProteinsBcl-2 Family ProteinsMcl-1Mitochondrial ApoptosisNoxaProtein ComplexProtein StabilityUbiquitylation (Ubiquitination)

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