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Assays for the Degradation of Misfolded Proteins in Cells
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The Cdc48 Complex Alleviates the Cytotoxicity of Misfolded Proteins by Regulating Ubiquitin Homeostasis

Ryan Higgins1, Marie-Helene Kabbaj1, Delaney Sherwin1

  • 1Department of Biomedical Sciences, College of Medicine, Florida State University, 1115 West Call Street, Tallahassee, FL 32306, USA.

Cell Reports
|July 16, 2020
PubMed

Insights

The Cdc48/p97 machinery clears misfolded proteins, but its deficiency causes toxicity due to ubiquitin depletion. Restoring ubiquitin levels rescues this toxicity, revealing Cdc48

Area of Science:

  • Cell Biology
  • Neuroscience
  • Biochemistry

Background:

  • Misfolded protein accumulation is linked to neurodegeneration.
  • Mechanisms of protein misfolding-induced cytotoxicity are not fully understood.

Purpose of the Study:

  • Investigate the role of the Cdc48/p97 segregase machinery in clearing misfolded proteins.
  • Elucidate the cause of cytotoxicity in Cdc48-deficient cells.

Main Methods:

  • Utilized a model misfolded protein, Huntingtin (Htt103QP).
  • Examined the function of nuclear ubiquitin ligase San1 and cytosolic Ubr1.
  • Assessed protein ubiquitination levels and free ubiquitin concentrations.
  • Tested rescue strategies by enhancing free ubiquitin levels.

Main Results:

  • Cdc48/p97 machinery clears ubiquitinated Htt103QP and limits its aggregation.
  • San1 ubiquitinates Htt103QP upstream of Cdc48.
  • Deletion of SAN1 or UBR1 rescues toxicity in Cdc48-deficient cells.
  • Cdc48 deficiency leads to ubiquitin depletion, not just compromised proteolysis.
  • Increased free ubiquitin rescues toxicity in various Cdc48 pathway mutants.

Conclusions:

  • Cdc48/p97 plays a critical role in clearing misfolded proteins.
  • Ubiquitin depletion, dependent on San1/Ubr1, causes toxicity in Cdc48-deficient cells.
  • Cdc48 ensures monoubiquitin regeneration, essential for cellular function.
Keywords:
Cdc48San1/Ubr1 E3 ligasesmutated Huntingtinproteotoxicityubiquitin homeostasis

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