TY - JOUR T1 - The Ubiquitin-Specific Protease Usp4 Regulates the Cell Surface Level of the A<sub>2a</sub> Receptor JF - Molecular Pharmacology JO - Mol Pharmacol SP - 1083 LP - 1094 DO - 10.1124/mol.105.015818 VL - 69 IS - 4 AU - Tetyana Milojević AU - Veronika Reiterer AU - Eduard Stefan AU - Vladimir M. Korkhov AU - Mario M. Dorostkar AU - Eszter Ducza AU - Egon Ogris AU - Stefan Boehm AU - Michael Freissmuth AU - Christian Nanoff Y1 - 2006/04/01 UR - http://molpharm.aspetjournals.org/content/69/4/1083.abstract N2 - Many membrane proteins incur a folding problem during biosynthesis; only a fraction thereof is exported from the endoplasmic reticulum (ER), because quality control is stringent. This is also true for G protein-coupled receptors. Here, we identify the deubiquitinating enzyme Usp4 as an interaction partner of the A2a adenosine receptor, a Gs-coupled receptor. Usp4 binds to the carboxyl terminus of the A2A receptor and allows for its accumulation as deubiquinated protein. This relaxes ER quality control and enhances cell surface expression of functionally active receptor. The effect of Usp4 on the A2A receptor was specific because 1) it was not seen in C-terminally truncated versions of the receptor; 2) it was not mimicked by Usp14, another member of the ubiquitin-specific protease family; and 3) it was not seen with the metabotropic glutamate receptor-5, another G protein-coupled receptor with a high propensity for intracellular retention. These observations show that deubiquinating enzymes can regulate quality control in the ER. ER -