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The TRC8 ubiquitin ligase is sterol regulated and interacts with lipid and protein biosynthetic pathways

Jason P Lee1, Anne Brauweiler, Michael Rudolph

  • 1Department of Medicine and Hollings Cancer Center, Medical University of South Carolina, Charleston, South Carolina, USA.

Molecular Cancer Research : MCR
|January 14, 2010
PubMed

Insights

TRC8, an E3 ubiquitin ligase, regulates sterol metabolism by destabilizing SREBP precursors. This endoplasmic reticulum protein links lipid and protein synthesis pathways.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Cell Biology

Background:

  • TRC8 (RNF139) is an endoplasmic reticulum-resident E3 ubiquitin ligase.
  • TRC8 possesses a sterol-sensing domain and regulates cell growth.
  • The precise mechanisms of TRC8's function in cellular pathways remain to be fully elucidated.

Purpose of the Study:

  • To investigate the role of TRC8 in sterol metabolism and protein homeostasis.
  • To determine the interaction partners and ubiquitylation targets of TRC8.
  • To explore the functional consequences of TRC8 activity on transcription factors and protein synthesis.

Main Methods:

  • Sterol response assays for TRC8 protein levels.
  • Co-immunoprecipitation to identify binding partners.
  • Ubiquitylation assays and proteasome activity assessment.
  • Analysis of SREBP precursor and mature forms.
  • Drosophila genetics and mammalian cell culture experiments.
  • Polysome profiling and immunoprecipitation studies.

Main Results:

  • TRC8 protein levels are sterol-responsive and it ubiquitylates INSIG.
  • TRC8 induction destabilizes SREBP-1 and SREBP-2 precursors in a proteasome-dependent manner.
  • TRC8 interacts with eIF3 subunits (eIF3f, eIF3h) in both Drosophila and mammalian cells.
  • TRC8 overexpression inhibits protein synthesis, indicated by altered polysome profiles and ubiquitylated proteins associated with eIF3.

Conclusions:

  • TRC8 acts as a sterol-responsive E3 ligase impacting lipid biosynthesis via SREBP regulation.
  • TRC8's interaction with eIF3 suggests a role in coordinating protein synthesis with lipid metabolism.
  • TRC8 may serve as a crucial regulatory link between lipid and protein biosynthetic pathways.

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