Curcumin induces pro-apoptotic endoplasmic reticulum stress in human leukemia HL-60 cells

Curcumin has been shown to induce apoptosis in many cancer cells. However, the molecular mechanism(s) responsible for curcumin-induced apoptosis is not well understood and most probably involves several pathways. In HL-60 cells, curcumin induced apoptosis and endoplasmic reticulum (ER) stress as evidenced by the survival molecules such as phosphorylated protein kinase-like ER-resident kinase, phosphorylated eukaryotic initiation factor-2alpha, glucose-regulated protein-78, and the apoptotic molecules such as caspase-4 and CAAT/enhancer binding protein homologous protein (CHOP). Inhibition of caspase-4 activity by z-LEVD-FMK, blockage of CHOP expression by small interfering RNA, and treatment with salubrinal, an ER inhibitor, significantly reduced curcumin-induced apoptosis. Removing two double bonds in curcumin, which was speculated to form Michael adducts with thiols in secretory proteins, resulted in a loss of the ability of curcumin to induce apoptosis as well as ER stress. Thus, the present study shows that curcumin-induced apoptosis is associated with its ability to cause ER stress.     

CRELD2 is a novel endoplasmic reticulum stress-inducible gene

Recently, endoplasmic reticulum (ER) stress responses have been suggested to play important roles in maintaining various cellular functions and to underlie many tissue dysfunctions. In this study, we first identified cysteine-rich with EGF-like domains 2 (CRELD2) as an ER stress-inducible gene by analyzing a microarray analysis of thapsigargin (Tg)-inducible genes in Neuro2a cells. CRELD2 mRNA is also shown to be immediately induced by treatment with the ER stress-inducing reagents tunicamycin and brefeldin A. In the genomic sequence of the mouse CRELD2 promoter, we found a typical ER stress responsible element (ERSE), which is well conserved among various species. Using a luciferase reporter analyses, we demonstrated that the ERSE in mouse CRELD2 is functional and responds to Tg and ATF6-overexpression. Each mutation of ATF6- or NF-Y-binding sites in the ERSE of the mouse CRELD2 promoter dramatically decreased both the basal activity and responsiveness toward the ER stress stimuli. Our study suggests that CRELD2 could be a novel mediator in regulating the onset and progression of various ER stress-associated diseases.     

酵母PMT1基因参与内质网应激的调控机制

【目的】内质网应激(Endoplasmic reticulum stress,ERS)可激活细胞保护性信号级联反应——未折叠蛋白质反应(Unfolded protein response,UPR)。研究表明,酵母细胞中的UPR信号通路由转录因子Hac1p和ERS感应因子Ire1p共同介导。前期研究发现:蛋白质-O-甘露糖转移酶1(Protein-O-mannosyltransferase 1,PMT1)基因缺失能延长酵母细胞的复制性寿命,其机制与上调UPR通路活性相关。本文进一步探讨PMT1基因缺失在酵母ERS反应中的作用。【方法】观察PMT1基因与IRE1或HAC1基因双缺失酵母菌株(pmt1?hac1?和pmt1?ire1?)在ERS反应条件下的克隆形成能力;通过比色法检测各菌株的细胞增殖活性;RT-PCR检测各菌株UPR通路下游部分靶基因的转录水平。【结果】与对照菌株比较,PMT1基因缺失菌株(pmt1?)在ERS反应条件下生长较慢,而HAC1和IRE1单基因缺失菌株(hac1?和ire1?)在ERS反应条件下无法存活;在hac1?或ire1?菌株的基础上进一步缺失PMT1基因,可以改善hac1?菌株在ERS反应条件下的生长状态;但缺失PMT1基因没有上调hac1?菌株UPR通路靶基因的转录水平。【结论】缺失PMT1基因可增强hac1?菌株对ERS诱导剂衣霉素的抗性,机制与已知的UPR通路不相关,提示可能存在其它途径参与ERS反应的调控。     

Heterotrimeric G protein subunits differentially respond to endoplasmic reticulum stress in Arabidopsis

Canonical heterotrimeric G proteins in eukaryotes are major components that localize at plasma membrane and transmit extracellular stimuli into the cell. Genome of a seed plant Arabidopsis thaliana encodes at least one Gα (GPA1), one Gβ (AGB1), and 3 Gγ (AGG1, AGG2 and AGG3) subunits. The loss-of-function mutations of G protein subunit(s) cause multiple defects in development as well as biotic and abiotic stress responses. However, it remains elusive how these subunits differentially express these defects. Here, we report that Arabidopsis heterotrimeric G protein subunits differentially respond to the endoplasmic reticulum (ER) stress. An isolated homozygous mutant of AGB1, agb1-3, was more sensitive to the tunicamycin-induced ER stress compared to the wild type and the other loss-of-function mutants of G protein subunits. Moreover, ER stress responsive genes were highly expressed in the agb1-3 plant. Our results indicate that AGB1 positively contributes to ER stress tolerance in Arabidopsis.     

Heme oxygenase-1 comes back to endoplasmic reticulum

Originally identified as a rate-limiting enzyme for heme catabolism, heme oxygenase-1 (HO-1) has expanded its roles in anti-inflammation, anti-apoptosis and anti-proliferation for the last decade. Regulation of protein activity by location is well appreciated. Even though multiple compartmentalization of HO-1 has been documented, the functional implication of this enzyme at these subcellular organelles is only partially elucidated. In this review we discuss the endoplasmic reticulum (ER)-residing HO-1 and its cytoprotective activity against ER stress.     

Cytoprotective small molecule modulators of endoplasmic reticulum stress

Cellular health depends on the normal function of the endoplasmic reticulum (ER) to fold, assemble, and modify critical proteins to maintain viability. When the ER cannot process proteins effectively, a condition known as ER stress ensues. When this stress is excessive or prolonged, cell death via apoptotic pathways is triggered. Interestingly, most major diseases have been shown to be intimately linked to ER stress, including diabetes, stroke, neurodegeneration, and many cancers. Thus, controlling ER stress presents a significant strategy for drug development for these diseases. The goal of this review is to present various small molecules that alleviate ER stress with the intention that they may serve as useful starting points for therapeutic agent development.     

疱疹病毒与内质网应激

内质网是分泌型蛋白和膜蛋白折叠及翻译后修饰的主要场所.病毒感染所引起的宿主细胞内环境的改变可使细胞或病毒的未折叠和/或错误折叠蛋白在内质网中大量聚集,使内质网处于生理功能紊乱的应激状态.为了缓解这种应激压力,细胞会启动未折叠蛋白反应(UPR),并通过一系列分子的信号转导维持内质网稳态;同时病毒也会通过对UPR的精密调控...     

Cytoprotective roles of ERK and Akt in endoplasmic reticulum stress triggered by subtilase cytotoxin

Subtilase cytotoxin (SubAB) is the prototype of a distinct AB₅ toxin family produced by Shiga toxigenic Escherichia coli. Recent reports disclosed pro-apoptotic pathways triggered by SubAB, whereas its anti-apoptotic signals have not been elucidated. In the present study, we investigated pro-survival signaling elicited by SubAB, especially focusing on extracellular signal-regulated kinase (ERK) and Akt. We found that SubAB activated ERK and Akt, and inhibition of individual kinases enhanced SubAB-triggered apoptosis. SubAB induced endoplasmic reticulum (ER) stress, and other ER stress inducers mimicked the stimulatory effects of SubAB on ERK and Akt. Attenuation of ER stress reduced SubAB-induced phosphorylation of these kinases, suggesting involvement of the unfolded protein response (UPR). SubAB induced activation of protein kinase-like ER kinase (PERK) and phosphorylation of eukaryotic translation initiation factor 2α (eIF2α), and phosphorylation of eIF2α by salubrinal caused activation of ERK and Akt, leading to cell survival. Dominant-negative inhibition of PERK enhanced SubAB-induced apoptosis and reduced phosphorylation of ERK and Akt. Furthermore, the anti-apoptotic effect of eIF2α was significantly reversed by inhibition of ERK and Akt. These results suggest cytoprotective roles of ERK and Akt in SubAB-triggered, ER stress-mediated apoptosis.     

The Batten disease gene CLN3 confers resistance to endoplasmic reticulum stress induced by tunicamycin

Mutations in CLN3 gene cause juvenile neuronal ceroid lipofuscinosis (JNCL or Batten disease), an early-onset neurodegenerative disorder that is characterized by the accumulation of ceroid lipofuscin within lysosomes. The function of the CLN3 protein remains unclear and is presumed to be related to Endoplasmic reticulum (ER) stress. To investigate the function of CLN3 in the ER stress signaling pathway, we measured proliferation and apoptosis in cells transfected with normal and mutant CLN3 after treatment with the ER stress inducer tunicamycin (TM). We found that overexpression of CLN3 was sufficient in conferring increased resistance to ER stress. Wild-type CLN3 protected cells from TM-induced apoptosis and increased cell proliferation. Overexpression of wild-type CLN3 enhanced expression of the ER chaperone protein, glucose-regulated protein 78 (GRP78), and reduced expression of the proapoptotic protein CCAAT/-enhancer-binding protein homologous protein (CHOP). In contrast, overexpression of mutant CLN3 or siRNA knockdown of CLN3 produced the opposite effect. Together, our data suggest that the lack of CLN3 function in cells leads to a failure of management in the response to ER stress and this may be the key deficit in JNCL that causes neuronal degeneration.     

Calcium signaling at the endoplasmic reticulum: fine-tuning stress responses

Endoplasmic reticulum (ER) calcium signaling is implicated in a myriad of coordinated cellular processes. The ER calcium content is tightly regulated as it allows a favorable environment for protein folding, in addition to operate as a major reservoir for fast and specific release of calcium. Altered ER homeostasis impacts protein folding, activating the unfolded protein response (UPR) as a rescue mechanism to restore proteostasis. ER calcium release impacts mitochondrial metabolism and also fine-tunes the threshold to undergo apoptosis under chronic stress. The global coordination between UPR signaling and energetic demands takes place at mitochondrial associated membranes (MAMs), specialized subdomains mediating interorganelle communication. Here we discuss current models explaining the functional relationship between ER homeostasis and various cellular responses to coordinate proteostasis and metabolic maintenance.     

Suppressive effects of 4-phenylbutyrate on the aggregation of Pael receptors and endoplasmic reticulum stress

Endoplasmic reticulum (ER) stress is defined as an accumulation of unfolded proteins in the endoplasmic reticulum. 4-phenylbutyrate (4-PBA) has been demonstrated to promote the normal trafficking of the DeltaF508 cystic fibrosis transmembrane conductance regulator (CFTR) mutant from the ER to the plasma membrane and to restore activity. We have reported that 4-PBA protected against cerebral ischemic injury and ER stress-induced neuronal cell death. In this study, we revealed that 4-PBA possesses chemical chaperone activity in vitro, which prevents the aggregation of denatured alpha-lactalbumin and bovine serum albumin (BSA). Furthermore, we investigated the effects of 4-PBA on the accumulation of Parkin-associated endothelin receptor-like receptor (Pael-R) pathologically relevant to the loss of dopaminergic neurons in autosomal recessive juvenile parkinsonism (AR-JP). Interestingly, 4-PBA restored the normal expression of Pael-R protein and suppressed ER stress induced by the overexpression of Pael-R. In addition, we showed that 4-PBA attenuated the activation of ER stress-induced signal transduction pathways and subsequent neuronal cell death. Moreover, 4-PBA restored the viability of yeasts that fail to induce an ER stress response under ER stress conditions. These results suggest that 4-PBA suppresses ER stress by directly reducing the amount of misfolded protein, including Pael-R accumulated in the ER.