Ubiquitin chains earmark GPCRs for BBSome-mediated removal from cilia

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• G protein-coupled receptors (GPCRs) regulate ciliary signaling pathways.
• The BBSome complex and β-arrestin are essential for ciliary GPCR exit, but their interaction is unclear.

Purpose of the Study:

• To elucidate the functional relationship between β-arrestin and the BBSome in ciliary GPCR trafficking.
• To investigate the role of ubiquitination in the regulated exit of GPCRs from cilia.

Main Methods:

• Investigated GPCR ubiquitination using β-arrestin-dependent tagging with K63-linked ubiquitin chains (UbK63).
• Utilized receptor mutants lacking ubiquitin acceptor sites (SSTR3, GPR161) to assess ubiquitination's role in ciliary exit.
• Examined the impact of a UbK63-specific deubiquitinase on ciliary protein exit (GPR161, SSTR3, SMO).
• Observed ciliary protein accumulation in cells with compromised BBSome function.

Main Results:

• Activated ciliary GPCRs are ubiquitinated with UbK63 chains in a β-arrestin-dependent manner prior to BBSome-mediated exit.
• Ubiquitination of GPCRs is essential for their regulated removal from cilia.
• Inhibition of deubiquitination in cilia blocks the exit of multiple ciliary proteins, including GPCRs and SMO.
• Impaired BBSome function leads to the accumulation of ubiquitinated proteins within cilia.

Conclusions:

• Ubiquitin chains serve as a signal for the ciliary exit machinery, marking GPCRs and other proteins for removal.
• This UbK63-dependent mechanism integrates β-arrestin and BBSome functions for precise control of ciliary protein homeostasis and signaling.