Complex Topology of Ubiquitin Chains Mediates Lysosomal Degradation of MrgC Proteins.

Background: Activation of Mas-related G protein-coupled receptor C (MrgC) receptors relieves pain, but also leads to ubiquitination of MrgC receptors. Ubiquitination mediates MrgC receptor endocytosis and degradation. However, MrgC degradation pathways and ubiquitin-linked chain types are not known.

Methods: N2a cells were treated with cycloheximide (CHX, protein synthesis inhibitor), Mg132 (proteasome inhibitor), 3-Methyladenine (3MA, autophagy lysosome inhibitor) and Chloroquine (CQ, autophagy lysosome inhibitor) to observe the half-life and degradation pathway of MrgC. The location of internalized MrgC receptors and lysosomes (Lyso-Tracker) was observed by immunofluorescence staining. N2a cells were transfected with Myc-MrgC and a series of HA-tagged ubiquitin mutants to study the ubiquitin-linked chain type of MrgC.

Results: The amount of MrgC protein decreased with time after CHX treatment of N2a cells. Autophagy lysosome inhibitors can inhibit the degradation of MrgC. The amount of MrgC protein decreased with time after CHX treatment of N2a cells. 3-MA and CQ inhibited the degradation of MrgC protein, whereas Mg-132 did not inhibit it. Partially internalized MrgC receptors were co-labeled with lysosomes. MrgC proteins have multiple topologies of ubiquitin-modified chains.

Conclusion: As a member of the G protein-coupled receptor family, MrgC receptors can be degraded over time. The complex topology of the ubiquitin-linked chain mediates the lysosomal degradation of MrgC proteins.