Rapid turnover of CTLA4 is associated with a complex architecture of reversible ubiquitylation

Area of Science:

• Immunology
• Cell Biology
• Protein Degradation

Background:

• Cytotoxic T-lymphocyte-associated protein 4 (CTLA4) is a crucial immune checkpoint regulator.
• CTLA4 is known for its unusually short lifespan as a membrane protein, suggesting rapid turnover mechanisms.
• Understanding CTLA4's degradation pathway is vital for modulating T-cell responses in cancer and autoimmunity.

Approach:

• Investigated the ubiquitylation sites and degradation pathway of CTLA4 using cycloheximide treatment and v-ATPase inhibition.
• Utilized co-immunoprecipitation and UbiCRest analysis to identify interacting proteins and ubiquitin chain linkages.
• Examined the role of the deubiquitylase USP8 and its adapter protein HD-PTP in CTLA4 trafficking and degradation.

Key Points:

• CTLA4 degradation is dependent on ubiquitylation at Lysine 203 and 213.
• USP8 deubiquitylase and its adapter HD-PTP promote CTLA4 turnover.
• CTLA4 is also secreted via exosomes, a process influenced by USP8 and HD-PTP.
• Specific ubiquitin chain linkages (Lys63, Lys27, Lys29) on CTLA4 contribute to its rapid degradation.

Conclusions:

• The study elucidates a novel ubiquitylation-dependent lysosomal degradation pathway for CTLA4 involving USP8.
• Identified distinct roles for USP8 and HD-PTP in CTLA4 degradation and exosome secretion.
• The findings provide new insights into the regulation of CTLA4 stability and function, with implications for immunotherapy.