One of the first quality control checkpoints is in the ER, where misfolded proteins are recognized and eliminated by ERAD. facilitated the turnover of T17M rhodopsin and prevented apoptosis and ER stress induced by T17M rhodopsin. == Conclusions == Chemical chaperone could attenuate UPR signaling and ER stress induced by T17M rhodopsin and NVP-ACC789 has potential therapeutic significance for retinitis pigmentosa. Keywords:Retinitis pigmentosa, Rhodopsin, UPR, Misfolded, ERAD == Background == Retinitis pigmentosa (RP) is considered the most commonly inherited retinal dystrophy with an estimated prevalence of approximately 1:4000 [1]. RP is caused by the progressive loss of rod and cone photoreceptors with clinical hallmarks including the sensitivity to dim light, abnormal visual function and characteristic bone spicule deposits of pigment in the retina [2]. Mutations in rhodopsin, a photon receptor that initiates phototransduction, have been linked to autosomal dominant retinitis pigmentosa (ADRP), accounting for about 10% of all reported cases of RP [3,4]. Since the identification of the P23H mutation, more than 130 different mutations of rhodopsin have been shown to cause RP [5]. A mouse model of ADRP was created with a threonine-to-methionine mutation at the 17th residue of rhodopsin, which abolishes the glycosylation site at Asn15 and results in a class I RP phenotype [6,7]. Transgenic mice carrying human T17M rhodopsin gene showed significant photoreceptor apoptosis as early as 24 h after illumination, while mice expressing a rhodopsin transgene with P23H mutation were only minimally affected [8]. Further study showed that endoplasmic reticulum NVP-ACC789 (ER) stress response is involved in retinal degeneration in T17M rhodopsin retinasin vivo, accompanied by the up-regulation of autophagy markers and the activation of mitochondrial apoptosis via the up-regulation of pro-apoptotic Bcl2 [9]. Our previous study showed that T17M rhodopsin accumulated in ER, increased the cytotoxicity and predisposed the cells to ER stress induced cell death [10]. Misfolded proteins that do not pass ER quality control (ERQC) are selectively recognized and cleared during a process called ER-associated degradation (ERAD) that involves the export of misfolded proteins from ER followed by proteasomal degradation [11]. Up to now, the role of ERAD in the clearance of T17M rhodopsin is unclear. We proposed that T17M rhodopsin may be misfolded and eliminated via ERAD, and chemical chaperone 4-phenylbutyrate may prevent ER stress induced by rhodopsin T17M. In this study, we used a spontaneously arising retinal pigment epithelia (RPE) ARPE-19 cell line as the experimental model to investigate the role of ERAD in the clearance of T17M rhodopsin and the effects of 4-phenylbutyrate (4-PBA) on ER stress induced by rhodopsin T17M. == Methods == == Cell culture and plasmid constructs == WT and T17M rhodopsin-myc constructs were described previously [10]. p97/VCP QQ-HA construct was described previously [12]. ARPE-19 cells were obtained from ATCC and cultured with DMEM supplemented with 10% FBS and penicillin-streptomycin (50 g/ml) at 37C Rabbit polyclonal to HEPH in 5% CO2. 4-PBA (Sigma, St. Louis, MO, USA) was dissolved in filtered sterile water at 1 M stock concentration. == Immunoblotting == Cells were lysed with RIPA sample buffer, the supernatant was NVP-ACC789 collected and protein concentration was determined using a Pierce protein assay kit (Thermo Scientific). 30 g proteins were separated on SDS-PAGE gel and transferred to PVDF membrane (Millipore). The membrane was incubated for 1 h in a blocking solution (5% dry milk in 0.1% triton X-100/PBS buffer) followed by incubation with appropriate primary antibodies in a blocking solution. After being washed in 0.1% triton X-100/PBS buffer, the membrane was incubated in appropriate secondary antibodies for 1 h and visualized via an enhanced chemiluminescence kit (GE Health) according to the manufacturers instruction. Antibodies were as follows: actin, HA antibodies (Abcam), Myc, Erasin, GRP78, GRP94, CHOP, peIF-2, eIF-2, and active ATF-6 antibodies (Cell Signaling), GFP antibody (Invitrogen). == Analysis of protein turnover == ARPE-19 cells were transfected with erasin SMARTpool siRNAs (Dharmacon) using Dharmafect 1 reagent (Thermo Fisher Scientific) according to the manufacturers instructions. 48 h later, cells were transfected with Myc-tagged rhpdopsin using lipofection 2000 (Invitrogen). After 24 h, cells were treated with 50 g/ml cycloheximide (Sigma) and collected at the indicated time points. For turnover experiments with p97/VCP QQ-HA, DNA construct was co-transfected with Myc-tagged rhpdopsin plasmid DNA followed by the inhibition of protein synthesis with cycloheximide. Equal amounts of protein in.