1A)

1A). a strict survey by the ER quality control system, they are exported from the ER to their destinations. Mutations that cause protein misfolding lead to the ER retention TRPC6-IN-1 or degradation of mutant proteins and thus prevent the membrane proteins from functioning at their target sites. The accumulation of misfolded proteins also causes ER stress, which can lead to cell death. Thus, the accumulation of mutant membrane proteins in the ER is usually associated with various types of protein misfolding diseases in humans1,2. One such disease is usually retinitis pigmentosa (RP), the most common cause of inherited neurodegenerative blindness3,4. Approximately 25% of autosomal dominant RP cases are caused by mutation of rhodopsin, and over 140 rhodopsin mutations have been reported (www.sph.uth.tmc.edu/Retnet). Rhodopsin is usually a pigment in rod photoreceptor cells. It consists of a G-protein coupled receptor (GPCR), opsin, and a chromophore, 11-gene have been reported to cause protein misfolding and ER accumulation4. The most frequent mutation (~10% of human cases), a proline to histidine substitution at position 23 (P23H) in rhodopsin, causes the mutant protein to misfold and accumulate within the ER, leading to various types of cellular stress, including ER stress, and triggering retinal degeneration3. ER-resident chaperones, including BiP, GRP74, HSJ1B, calnexin, and EDEM1, facilitate the refolding of mutant proteins5,6,7,8,9. Although misfolded P23H rhodopsin is usually degraded by the ER-associated degradation (ERAD) system, the accumulation of mutant proteins ultimately causes excessive cellular stress, leading to cell death10,11. Many other mutations in the transmembrane, intradiscal, or cytosolic domains of rhodopsin cause misfolding and ER retention of the mutant proteins4. Although the ER quality control system for such mutant proteins has been extensively studied3, the mechanism by which these proteins are retained in the ER is not understood. Rer1p was first identified as a sorting receptor required for the correct localization of various ER membrane proteins in yeast12,13,14,15. Rer1p, an early-Golgi membrane protein, recognizes polar residues in transmembrane domains (TMD) and interacts directly with cargo membrane TRPC6-IN-1 proteins16,17. Rer1p then returns cargo proteins to the ER via the Rabbit Polyclonal to GALK1 COP I-dependent pathway16. Rer1p is also required for the ER quality control of unassembled iron transporter subunits and the proper TRPC6-IN-1 formation of iron transporter complexes18. In addition, Rer1p is involved in the ER retention of mutant forms of Ste2p, a GPCR that functions as a sex pheromone receptor in yeast19. The Rer1 gene family is usually widely conserved from yeast to humans14,20,21,22. Recent studies in mammalian cells have shown that Rer1p modulates -secretase complex assembly and function21,23,24,25,26. Rer1p interacts with unassembled nicastrin and PEN-2, subunits of the -secretase complex, and retains them in the ER23,25. Loss of Rer1p disrupts the ER retention of these components and affects -secretase activity23,25. In addition, Rer1p regulates the cell surface expression of muscle acetylcholine receptor by retaining unassembled -subunits in the ER27. Thus, Rer1p is thought to function as a sorting chaperone that modulates the fate of various membrane proteins in the early secretory pathway. In this study, we show that Rer1p interacts with wild-type rhodopsin and modulates its trafficking through the secretory pathway. In addition, we demonstrate that depletion of Rer1p results in the release of the misfolded G51R rhodopsin mutant from the ER, allowing it to move to the plasma membrane or lysosomes. These findings suggest that Rer1p controls the intracellular trafficking of rhodopsin and facilitates the ER retention of mutant rhodopsin. Results Rhodopsin mutants are retained in the ER and partly degraded by the ERAD system To assess the subcellular localization of mutant rhodopsin, we chose.