Abstract
Ubiquitination is essential for the endocytic sorting of various G protein-coupled receptors to lysosomes. Here we identify a distinct function of this covalent modification in controlling the later proteolytic processing of receptors. Mutation of all cytoplasmic lysine residues in the murine delta-opioid receptor blocked receptor ubiquitination without preventing ligand-induced endocytosis of receptors or their subsequent delivery to lysosomes, as verified by proteolysis of extramembrane epitope tags and down-regulation of radioligand binding to the transmembrane helices. Surprisingly, a functional screen revealed that the E3 ubiquitin ligase AIP4 specifically controls down-regulation of wild type receptors measured by radioligand binding without detectably affecting receptor delivery to lysosomes defined both immunochemically and biochemically. This specific AIP4-dependent regulation required direct ubiquitination of receptors and was also regulated by two deubiquitinating enzymes, AMSH and UBPY, which localized to late endosome/lysosome membranes containing internalized delta-opioid receptor. These results identify a distinct function of AIP4-dependent ubiquitination in controlling the later proteolytic processing of G protein-coupled receptors, without detectably affecting their endocytic sorting to lysosomes. We propose that ubiquitination or ubiquitination/deubiquitination cycling specifically regulates later proteolytic processing events required for destruction of the receptor's hydrophobic core.
Original language | English |
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Pages (from-to) | 19361-19370 |
Number of pages | 10 |
Journal | The Journal of Biological Chemistry |
Volume | 284 |
Issue number | 29 |
Early online date | 11 May 2009 |
DOIs | |
Publication status | Published - 17 Jul 2009 |
Keywords
- endoplasmic-reticulum
- mediates ubiquitination
- multivesicular body pathway
- CXCR4
- BETA(2)-adrenergic receptor
- induced down-regulation
- proteasome
- molecular-mechanisms
- endocytic membrane trafficking
- delta-opioid receptor