Disruption of the endoplasmic reticulum by cytotoxins in LLC-PK1 cells

Prior induction of an endoplasmic reticulum stress response results in protection against reactive cytotoxins in the LLC-PK1 cell line. The purpose of this investigation was to determine therefore if the endoplasmic reticulum was disrupted by iodoacetamide, tert-butylhydroperoxide or sulfamethoxazole hydroxylamine. Toxic concentrations of the three toxins caused a dramatic loss of GRP94 protein within 3-8h of exposure, while induction of GRP78 and calreticulin occurred at 8 and 24h following exposure. There was no evidence of cytosolic elevation of calcium and neither dantrolene nor xestospongin were able to block the cytotoxicity of IDAM and TBHP. Exposure to the toxins led to DNA degradation and cleavage of procaspase-12. There was only evidence of procaspase-3 cleavage after TBHP exposure. These results demonstrate that the ER is disrupted by the reactive cytotoxins examined in LLC-PK1cells and suggest that the cytoprotection against low to moderate concentrations of cytotoxins observed following endoplasmic reticulum stress protein induction is likely due to a mechanism other than maintenance of calcium homeostasis.     

Effect of endoplasmic reticulum stress preconditioning on cytotoxicity of clinically relevant nephrotoxins in renal cell lines.

The cytoprotection of LLC-PK1 cells afforded by endoplasmic reticulum (ER) stress preconditioning suggests that the ER plays an important role during drug-induced renal toxicity. However, in vitro studies have been largely limited to LLC-PK1 cells and model toxins. Therefore, we tested the hypothesis that cytoprotection following ER stress preconditioning is a common property of renal cell lines (LLC-PK1 (pig), NRK-52E (rat), HEK293 (human), MDCK (dog)) and extends to clinically relevant nephrotoxins. ER stress inducers (tunicamycin, thapsigargin and oxidized dithiothreitol (DTTox)) resulted in a dose-dependent increase in GRP78 and GRP94 stress protein expression, but the magnitude of induction was cell line- and inducer-dependent. Toxicity of the model toxins iodoacetamide and tert-butylhydroperoxide was modified by preconditioning. DTTox was effective in decreasing the toxicity in all cell lines, but protection was variable with tunicamycin and thapsigargin. Toxicity of clinically relevant drugs (cisplatin, gentamicin, glyoxylate, cyclosporine A, p-aminophenol) was significantly decreased in cells preconditioned by tunicamycin or DTTox. These results demonstrate that ER stress preconditioning offers cytoprotection against clinically relevant nephrotoxins in renal cell lines from multiple species, although there were qualitative and quantitative differences between the cell lines. These results support the hypothesis that ER is involved in drug-induced renal toxicity.     

Calpain-Induced Endoplasmic Reticulum Stress and Cell Death following Cytotoxic Damage to Renal Cells

Calpains and endoplasmic reticulum (ER) stress have both beenimplicated in renal cell death following exposure to reactivechemical toxicants (RCTs). Therefore, we explored the link betweenER stress, calpain, and cell death in renal cell injury dueto model RCTs (iodoacetamide, menadione, tert-butyl hydroperoxide)and ER stress inducers (tunicamycin [TUN], thapsigargin [THAPS]).The calpain inhibitor, PD150606, significantly reduced the RCTand TUN-induced cell death in the renal cell line LLC-PK1, butnot death induced by THAPS. ER stress was confirmed by the significantinduction of GRP78 following exposure to RCTs and ER stressinducers. While GRP94 induction was observed following RCTsand TUN, it was not statistically significant because of variability.THAPS at 5µM significantly induced GRP94, while 20µMcaused a calpain-dependent cleavage of GRP94. Caspase-12 andm-calpain were variably induced and/or cleaved following exposureto all toxicants, supporting activation of these signaling pathways.Inhibition of calpain blocked the induction of GRP78 followingexposure to RCTs suggesting that calpain was contributing tothe observed ER stress following RCTs. In contrast, calpaininhibition did not block ER stress protein induction followingexposure to nontoxic concentrations of TUN or THAPS, indicatingthat calpain inhibition did not block the ER stress proteininduction pathways directly. These studies demonstrate a previouslyunappreciated link between calpain activation and ER stress–associatedcell death in renal cells. While further studies are requiredto clarify the molecular events involved, these results confirmthat calpain activation and the ER are important related playersin chemically induced renal cell damage.     

Tunicamycin induces resistance to camptothecin and etoposide in human hepatocellular carcinoma cells: role of cell-cycle arrest and GRP78

Hepatocellular carcinoma is chemoresistant to many anticancer drugs. Tunicamycin, an N-glycosylation inhibitor, causes unfolded protein response and is widely used as pharmacological inducer of endoplasmic reticulum stress. In this study, several designs were used to investigate the resistance mechanism to camptothecin and etoposide in hepatocellular carcinoma Hep3B cells. Tunicamycin significantly inhibited apoptosis induced by camptothecin or etoposide. Tunicamycin neither modified the topoisomerase levels nor inhibited the ATM activation caused by camptothecin and etoposide. The data suggest that tunicamycin-induced resistance may result from the downstream events of drug-trapped topoisomerase-DNA complexes and DNA double-strand breaks. Camptothecin and etoposide caused an increase of protein expression of several cell-cycle regulators and induced the cleavage of Bcl-2 family of proteins. These intracellular molecular events were abolished by tunicamycin. A design of postaddition of tunicamycin demonstrated that G1 checkpoint arrest contributed to the resistance mechanism. Curcumin, another G1 arrest-inducing agent in this study, was able to induce a similar resistant effect. Furthermore, the cells transfected with GRP78 siRNA were partly resistant to tunicamycin-induced apoptosis but not the inhibitory effect on cell-cycle regulators indicating that GRP78 and G1 arrest are two independent factors to tunicamycin-induced resistance mechanism. In conclusion, the data suggest that tunicamycin induces the resistance to topoisomerase inhibitors through GRP78 up-regulation and G1 arrest of the cell cycle. The findings also prompt the deliberation that the resistance can be caused during combined administration of chemotherapeutic drugs and Chinese herbal medicines, which induce endoplasmic reticulum stress and/or cell-cycle arrest in cancer cells.     

砷及MPST过表达对SH-SY5Y细胞GRP78/CHOP通路的影响

目的探讨内质网应激是否参与亚砷酸钠(NaAsO2)神经毒性损伤,明确3-巯基丙酮酸硫转移酶(3-mercaptopyruvate sulfurtransferase,MPST)过表达是否调节砷诱导的内质网应激。方法通过构建MPST基因慢病毒表达载体来获得稳定表达外源MPST基因的SH-SY5Y细胞株作为SH-MPST过表达组,另设空载体转染细胞为SH-PEB组,染砷组(NaAsO2组),内质网应激阻断剂TUDCA组,TUDCA预处理染砷组。Western blot法分别检测过表达MPST、染砷及TUDCA预处理后细胞内GRP78和CHOP蛋白表达的变化。结果单纯MPST过表达不影响SH-SY5Y细胞内GRP78、CHOP蛋白的表达水平;经NaAsO2处理后,SH-PEB细胞内GRP78、CHOP蛋白明显上调(P<0.01),而被内质网应激阻断剂TUDCA所拮抗;MPST过表达则抑制砷对GRP78、CHOP蛋白的上调(P<0.01);然而,TUDCA预处理则明显逆转MPST过表达对GRP78、CHOP蛋白的影响(P<0.01)。结论GRP78/CHOP内质网应激通路参与了砷诱导的神经毒性损伤;MPST过表达可降低砷诱导的内质网应激水平。     

β受体阻滞剂对乳鼠心肌细胞内质网应激致凋亡途径的影响

目的通过体外培养乳鼠心肌细胞,探讨β受体阻滞剂对乳鼠心肌细胞凋亡率及内质网应激作用的影响。方法培养乳鼠心肌细胞,确定β受体阻滞剂的饱和浓度,原代培养乳鼠心肌细胞72h后给予β受体阻滞剂溶液和衣霉素溶液干预,实验分4组:空白对照组、50μg/ml美托洛尔组、10μg/ml衣霉素组、10μg/ml衣霉素+50μg/ml美托洛尔组。确定美托洛尔的饱和浓度;反转录-聚合酶链反应(RT-PCR)检测各组内质网应激指标GRP78、内质网应激致凋亡指标Caspase12,流式细胞术检测实验各组乳鼠心肌细胞凋亡率,确定美托洛尔对内质网应激致凋亡途径的影响作用。结果①美托洛尔的浓度为50μg/ml时,对内质网应激的影响已达最大。②与空白对照组比较,50μg/ml美托洛尔组心肌细胞内质网应激致凋亡指标Caspase12表达及心肌细胞凋亡率差异无统计学意义(P>0.05)。10μg/ml衣霉素组、50μg/ml美托洛尔+10μg/ml衣霉素组心肌细胞内质网应激致凋亡指标Caspase12及心肌细胞凋亡率较空白对照组均明显增加(均P<0.05),且在衣霉素组时心肌细胞中内质网应激致凋亡指标Caspase12及心肌细胞凋亡率均最高,而50μg/ml美托洛尔+10μg/ml衣霉素组与10μg/ml衣霉素组比较,心肌细胞内质网应激致凋亡指标Casepase12及心肌细胞凋亡率降低,差异有统计学意义(均P<0.05)。结论美托洛尔浓度在50μg/ml时为内质网应激保护的饱和浓度,β受体阻滞剂可以减轻内质网应激所致的凋亡途径。     

Anacardic acid induces cell apoptosis associated with induction of ATF4-dependent endoplasmic reticulum stress

Anacardic acid (6-pentadecylsalicylic acid, AA), a natural compound isolated from the traditional medicine Amphipterygium adstringens, has been reported to possess antitumor activities. However, its molecular targets have not been thoroughly studied. Here, we report that AA is a potent inducer of endoplasmic reticulum (ER) stress, leading to apoptosis in hepatoma HepG2 and myeloma U266 cells. Induction of ER stress by AA was supported by a dose- and time-dependent increase in expression of the ER signaling downstream molecules, such as GRP78/BiP, phosphorylated eIF2α, ATF4 and CHOP in both HepG2 and U266 cell lines. Blockage of ATF4 expression by siRNA partially inhibited, while knockdown of CHOP expression by siRNA slightly increased AA-induced cell death in these cells. In addition, AA suppressed HepG2 xenograft tumor growth, associated with increased ER stress in vivo. These results suggest that AA induces tumor cell apoptosis associated with ATF4-dependent ER stress.     

A norbergenin derivative inhibits neuronal cell damage induced by tunicamycin

Several chemically synthesized compounds were examined for protective effects against the cell damage in tunicamycin-treated human neuroblastoma IMR-32 cells. Among the compounds tested, an antioxidant, Norbergenin-11-caproate (10 microM), exhibited complete protection against the cell growth inhibitory effect of tunicamycin but did not inhibit the induction of Bip/GRP78 mRNA by tunicamycin. Both norbergenin-11-caproate and alpha-tocopherol completely inhibited the production of reactive oxygen species induced by tunicamycin, however, alpha-tocopherol inhibited tunicamycin-induced cell damage only partially, even at 100 microM. These findings suggest the potential of Norbergenin-11-caproate for therapeutic application in endoplasmic reticulum (ER) stress-dependent diseases implicating a specific mechanism other than anti-oxidative one.     

辣椒素经内质网应激反应途径诱导K562/ADM耐药细胞凋亡

目的：研究辣椒素（capsaicin）是否经内质网途径诱导耐药性白血病K562/ADM细胞凋亡。方法：以耐药性白血病K562/ADM细胞为靶细胞,采用MTT比色法测定细胞增殖活性;细胞形态学和AnnexinV/PI双染色法检测细胞凋亡,电镜观察凋亡细胞内质网形态结构变化;实时定量RT-PCR检测GRP78mRNA的表达;Western blot法检测GRP78蛋白的表达。结果：不同浓度的辣椒素显著抑制K562/ADM细胞的增殖活性,20、50μmol/L辣椒素诱导后K562/ADM细胞出现典型的凋亡形态学改变,细胞凋亡率明显增高,分别为39.67%和41.78%。辣椒素诱导凋亡过程中,K562/ADM细胞出现内质网明显扩张和脱颗粒现象,GRP78mRNA的表达增高,GRP78蛋白的表达量分别增高1.5和2.2倍,随时间延长有所降低。结论：辣椒素可能通过内质网应激反应性途径诱导K562/ADM细胞发生凋亡。     

11-Deoxy,16,16-dimethyl prostaglandin E2 induces specific proteins in association with its ability to protect against oxidative stress

Prostaglandins (PGs) act locally to maintain cellular homeostasis and stimulate stress response signaling pathways. These cellular effects are diverse and are tissue-dependent. PGE(2), and the synthetic analogue, 11-deoxy,16,16-dimethyl PGE(2) (DDM-PGE(2)), protect renal proximal tubular epithelial (LLC-PK1) cells against cellular injury induced by the potent nephrotoxic and nephrocarcinogenic metabolite of hydroquinone, 2,3,5-tris-(glutathion-S-yl)hydroquinone. Although this cytoprotective response (in LLC-PK1 cells) is mediated through a thromboxane or thromboxane-like receptor coupled to AP-1 signaling pathways, the mechanism of cytoprotection is unknown. In this study, we utilized HPLC-electrospray ionization tandem mass spectrometric (ESI MS/MS) and matrix-assisted laser desorption ionization time-of-flight mass spectrometric (MALDI TOF) analysis of proteins isolated from DDM-PGE(2)-stimulated LLC-PK1 cells to identify candidate cytoprotective proteins. DDM-PGE(2) selectively stimulated the synthesis of several proteins in LLC-PK1 cells. Peptide sequencing by ESI-MS/MS of in-gel tryptic protein digests revealed the identity of eight proteins: endothelial actin binding protein, myosin, elongation factor 2 (EF-2), elongation factor 1alpha-1 (EF-1alpha), heat shock protein 90beta (HSP90beta), glucose-regulated protein 78 (GRP 78), membrane-organizing extension spike protein, and actin. Both ESI-MS/MS and MALDI-MS analysis resulted in the same protein identification. Western analysis confirmed the temporal induction of the majority of these proteins, including EF-2, EF-1alpha, HSP90beta, GRP78, and actin. The collective expression of these proteins suggests that DDM-PGE(2)-mediated cytoprotection may involve alterations in cytoskeletal organization and/or stimulation of an endoplasmic reticulum (ER) stress response. The present studies provide insights into potential downstream targets of PG signaling.     

辛伐他汀通过内质网应激途径诱导K562细胞凋亡

探讨内质网应激在辛伐他汀诱导K562细胞凋亡中的作用。采用荧光显微镜观察凋亡细胞的形态变化，AnnexinV-FITC/PI双染法检测细胞凋亡率，激光扫描共聚焦显微镜检测细胞内Ｃa²⁺浓度，RT-PCR检测葡萄糖调节蛋白78(glucose regulated protein 78，GRP78)、钙蛋白酶(calpain)基因mRNA表达水平，Western blotting检测GRP78、 calpain、 caspase-3， -6， -7， -9， -12蛋白水平。结果显示，10、 20、 30 μmol·L^-1辛伐他汀(simvastatin，Sim)作用K562细胞72 h后，细胞出现典型的凋亡形态，凋亡率分别为12.41%、 19.08%和23.41%；细胞内Ca²⁺浓度增加，荧光强度分别为43、54和64；GRP78、calpain基因mRNA表达上调；calpain、 caspase-3， -6， -7， -9， -12蛋白剪切活化、GRP78蛋白表达增强。以上结果表明，内质网作为细胞凋亡的重要途径参与了辛伐他汀诱导K562细胞的凋亡。辛伐他汀将可能被用于临床治疗白血病。     

内质网应激对小鼠卵巢卵泡发育的影响

摘要：目的 探索小鼠卵巢内质网应激对卵泡发育的影响。方法 对照组小鼠4只,实验组小鼠6只,应用经典 内质网应激诱导物衣霉素经腹腔注射诱导小鼠卵巢内质网应激激活,实时荧光定量逆转录聚合酶链反应（RT qPCR）检测未折叠蛋白质应答（UPR）标志分子HSPA5、CHOP、ATF4 mRNA表达情况,明确小鼠卵巢内质网应激激活 状态,苏木精伊红染色（HE染色）检测小鼠卵巢卵泡发育状态,明确内质网应激对小鼠卵巢卵泡发育的影响。结果 衣霉素的处理明显上调了小鼠卵巢内质网应激标志分子的表达,与对照组相比,衣霉素处理组小鼠卵巢卵泡发育明 显受限。结论 内质网应激的激活明显抑制了小鼠卵巢卵泡的发育     

Endoplasmic reticulum stress mediates withaferin A-induced apoptosis in human renal carcinoma cells

The accumulation of misfolded proteins in the lumen of the endoplasmic reticulum (ER) results in cellular stress that initiates a specialized response designated as the unfolded protein response. ER stress has been implicated in a variety of common diseases, such as diabetes, ischemia and neurodegenerative disorders. Withaferin A, a major chemical constituent of Withania somnifera, has been reported to inhibit tumor cell growth. We show that withaferin A induced a dose-dependent apoptotic cell death in several types of human cancer cells, as measured by FACS analysis and PARP cleavage. Treatment of Caki cells with withaferin A induced a number of signature ER stress markers, including phosphorylation of eukaryotic initiation factor-2α (eIF-2 α), ER stress-specific XBP1 splicing, and up-regulation of glucose-regulated protein (GRP)-78. In addition, withaferin A caused up-regulation of CAAT/enhancer-binding protein-homologous protein (CHOP), suggesting the induction of ER stress. Pretreatment with N-acetyl cysteine (NAC) significantly inhibited withaferin A-mediated ER stress proteins and cell death, suggesting that reactive oxygen species (ROS) mediate withaferin A-induced ER stress. Furthermore, CHOP siRNA or inhibition of caspase-4 activity attenuated withaferin A-induced apoptosis. Taken together, the present study provides strong evidence supporting an important role of the ER stress response in mediating withaferin A-induced apoptosis.     

Modulating the endoplasmic reticulum stress response with trans-4,5-dihydroxy-1,2-dithiane prevents chemically induced renal injury in vivo.

Agents that disrupt functions of the endoplasmic reticulum (ER) induce expression of ER stress-response genes including ER chaperones. Increased expression of the major ER chaperone, Grp78, protects cells, including renal epithelial cells, from chemically induced injury and death in vitro. In this study, we determined if pharmacological manipulation of the ER stress-response gene is an effective strategy to protect the kidney from chemical stress in vivo. Treatment with trans-4,5-dihydroxy-1,2-dithiane (DTTox), a novel inducer of ER stress proteins, stimulated a time-and dose-dependent increase in Grp78 expression in the kidney, but it did not cause detectable injury. Furthermore, prior treatment with DTTox protected the proximal tubular epithelium against a subsequent challenge with the nephrotoxicant S-(1,1,2,2,-tetrafluoroethyl)-L-cysteine (TFEC). In contrast, activating a heat shock response did not have a protective effect. Prior treatment with DTTox did not reduce covalent binding of radiolabeled reactive metabolites of (35)S-TFEC to renal proteins, indicating that protection was not due to an effect on the metabolic activation of TFEC to the reactive metabolite(s) responsible for renal injury. Antisense grp78 expression in the renal epithelial cell line LLC-PK1 blocked the DTTox-induced Grp78 increase and ablated the protective effect against TFEC damage, indicating that the induction of grp78 expression and the ER stress response were critical for the protective effect of DTTox. These findings suggest that increased expression of Grp78 plays a major role in the protection of renal epithelial cells from reactive intermediate-induced chemical injury in vivo and that pharmacological manipulation is an effective strategy to prevent damage by some classes of nephrotoxicants.