MARCH6 and TRC8 facilitate the quality control of cytosolic and tail-anchored proteins

Area of Science:

• Cell Biology
• Molecular Biology
• Protein Degradation

Background:

• Misfolded or damaged proteins are degraded by the proteasome, but the involved mammalian ubiquitin machinery is not fully understood.
• Endoplasmic reticulum (ER)-resident E3 ligases play crucial roles in protein quality control.

Purpose of the Study:

• To identify the E3 ligases involved in the proteasome-mediated degradation of misfolded proteins.
• To investigate the role of ER-resident E3 ligases in the turnover of specific protein types.

Main Methods:

• Forward genetic screens in human cells using a soluble misfolded reporter (mCherry-CL1).
• Quantitative mass spectrometry to analyze protein turnover.
• Analysis of E3 ligase association with signal peptide peptidase (SPP).

Main Results:

• The degradation of mCherry-CL1 requires the ER-resident E3 ligases MARCH6 and TRC8.
• Depletion of MARCH6 and TRC8 stabilizes mCherry-CL1, indicating their essential role.
• MARCH6 and TRC8 also regulate the turnover of the tail-anchored protein heme oxygenase-1 (HO-1).
• These E3 ligases function independently to degrade distinct protein substrates.

Conclusions:

• MARCH6 and TRC8 are key E3 ligases in the ER-mediated degradation pathway for misfolded soluble and tail-anchored proteins.
• The study reveals independent yet complementary roles for ER-resident E3 ligases in protein quality control.
• This work sheds light on the complex mechanisms governing protein homeostasis in mammalian cells.