Rifampicin has been proposed as a therapeutic candidate for Parkinson’s disease (PD). activating transcription factor 6 (ATF 6), and how they regulated rifampicin-stimulated GRP78 expression. Our results showed that PERK, eukaryotic initiation factor 2 (eIF2), and activating transcription factor 4 (ATF4) were activated in rifampicin-treated PC12 cells. Silencing the ATF4 gene using RNAi inhibited GRP78 stimulation. Interestingly, we did not detect significant IRE activation, X-box binding protein 1 mRNA splicing, or ATF6 cleavage up to 24 h after rifampicin treatment. Taken together, our data suggested that rifampicin induced GRP78 via the PERK-eIF2-ATF4 pathway to protect neurons against rotenone-induced cell damage. Targeting molecules in this pathway could be a novel therapeutic approach for PD treatment. Introduction Parkinson’s disease (PD) is the second most common neurodegenerative disorder after Alzheimer’s disease. Neuropathologically, it is characterized by the progressive loss of dopaminergic neurons within the substantia nigra pars compacta of the midbrain . Current PD treatments are focused on symptomatic relief, which have risks of causing severe side effects and fail to prevent or delay the progression of the disease . Therefore, searching for novel therapies to reduce the loss of dopaminergic neurons will shed Celgosivir manufacture new light on PD treatments. Rifampicin is an antibiotic that is widely used for tuberculosis and leprosy. It has been proposed to treat Parkinson’s disease . Reports using PD models have demonstrated that it is neuroprotective in vivo  and in vitro Celgosivir manufacture . In line with this, our previous study showed that rifampicin protected PC12 cells against 1-methyl-4-phenylpyridinium (MPP+)-induced apoptosis . Pre-treatment with rifampicin decreased rotenone-induced neurotoxicity in rats . However, the molecular mechanisms underlying the neuroprotection of rifampicin remain unknown. In the present study, we performed a comprehensive proteomic analysis to explore the mechanisms by which rifampicin elicited protective cellular responses. The expression of the glucose-regulated protein 78 (GRP78) was significantly increased in rifampicin-treated PC12 cells. This result was confirmed by Western blot analysis. Gene silencing using RNA interference verified the mediation of GRP78 in rifampicin-induced neuroprotection. GRP78, also known as Bip, is a chaperone protein localized in the endoplasmic reticulum (ER) and plays an important role in cytoprotection and cell survival , . GRP78 is the hallmark of unfolded protein response (UPR) . UPR is a cellular defense system in response to the accumulation of misfolded proteins under ER stress . UPR induces the expression of GRP78 by activating ER-resident transmembrane proteins, including the activated pancreatic ER kinase-like ER kinase (PERK), inositol requiring kinase (IRE) and activating transcription factor 6 (ATF 6) . Increasing evidence has suggested that GRP78 activation prevents neurons from apoptosis , , . Therefore, we hypothesized that rifampicin protected PC12 cells against rotenone-induced cytotoxicity by regulating the GRP78 gene expression. We also investigated the signaling pathways through which rifampicin stimulated GRP78. Our study was aimed Celgosivir manufacture to explore potential novel therapeutic targets for PD treatment. Methods Materials Rifampicin, Rotenone, dimethyl sulfoxide (DMSO), 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), 4,6-diamidino-2-phenylindole (DAPI) and thapsigargin (Tg) were purchased from Sigma (St. Louis, MO, USA). Rifampicin was dissolved in less than 0.1% of DMSO solution. RPMI medium 1640, fetal horse serum (FCS), fetal bovine serum (FBS), penicillin, streptomycin, and other tissue culture reagents were purchased from Gibco (Grand Island, NY, USA). Antibodies against PERK(sc-13073), p-PERK(sc-32577), ATF6, and beta-actin were from Santa Cruz Biotechnology (Santa Cruz, CA, USA). Antibodies against GRP78, p-eIF2, eIF2 and ATF4 were from Cell Signaling (Beverly, MA, USA). Antibodies against p-IRE were from Abcam (Hong Kong, China). Cell Culture PC12 cells were purchased from the Cell Center of the Institute of Basic Medical Science Research (Chinese Academy of Medical Sciences, China). Cells were cultivated in RPMI medium 1640 supplemented with 10% heat-inactivated fetal horse serum, 5% heat-inactivated fetal bovine serum, 100 U/mL penicillin, and 100 g/mL streptomycin. Cells were kept at 37 C in a humidified atmosphere with 5% CO2. Growth medium was changed three times a week. Unless indicated otherwise, prior to the experimental investigation, PC12 cells were differentiated by adding nerve growth factor (NGF) at 50 Rabbit polyclonal to PFKFB3 ng/mL every Celgosivir manufacture other day for 6 days, followed by rifampicin treatment at 150 M for 24 h. In GRP78 gene silencing study,.