Sequential quality-control checkpoints triage misfolded cystic fibrosis transmembrane conductance regulator

Area of Science:

• Cellular Biology
• Protein Quality Control
• Molecular Mechanisms of Disease

Background:

• Cystic fibrosis is caused by misfolded CFTR Delta F508, a chloride ion channel.
• The cellular machinery responsible for CFTR Delta F508 degradation and misfolding mechanisms remain unclear.

Purpose of the Study:

• To identify the protein quality control machinery involved in CFTR Delta F508 degradation.
• To elucidate the sequential action of ubiquitin ligases in monitoring CFTR folding.

Main Methods:

• Investigated ER membrane-associated ubiquitin ligase complexes.
• Utilized co-immunoprecipitation and protein interaction studies.
• Analyzed the roles of RMA1, Ubc6e, Derlin-1, Hsc70, and CHIP in CFTR processing.

Main Results:

• Identified an ER complex (RMA1, Ubc6e, Derlin-1) and a cytosolic complex (Hsc70/CHIP) that triage CFTR and CFTR Delta F508.
• Derlin-1 retains CFTR in the ER membrane, facilitating degradation via RMA1 and Ubc6e.
• RMA1 recognizes co-translational folding defects, while CHIP acts post-translationally.

Conclusions:

• RMA1 and CHIP E3 ubiquitin ligases act sequentially in the ER membrane and cytosol.
• These ligases monitor the folding status of CFTR and CFTR Delta F508, targeting misfolded proteins for degradation.
• Understanding this pathway offers insights into cystic fibrosis pathogenesis.