Endoplasmic reticulum stress and BCL-2 family members

Role of Ca2+, Calnexin and Calreticulin in Platelet from Adult Patients with Chronic Immune Thrombocytopenic Purpura

BACKGROUND

Adult chronic immune thrombocytopenia (chronic ITP) is a common autoimmune hemorrhagic disease characterized by decreased platelet production and increased platelet destruction, leading to thrombocytopenia. In this study, Ca²⁺, calnexin (CNX) and calreticulin (CRT) within platelets from adult patients with chronic ITP were investigated.

METHODS

Platelets were isolated from blood specimen collected from 20 adult patients with chronic ITP and 20 healthy volunteers. Ca²⁺, CNX and CRT were determined by flow cytometry, and the results were analyzed with EXPO32 ADC software.

RESULTS

Flow cytometry showed the expressions of Ca²⁺ (74.19±19.40% vs 22.79±10.47%) was elevated (P<0.05). However, CNX (15.10±7.32% vs 41.79±14.45%) and CRT (25.11±12.66% vs 38.58±12.02%) were decreased markedly in platelets from adult patients with chronic ITP (P<0.05 compared with healthy volunteers).

CONCLUSION

Based on enhanced expression of Ca²⁺ and attenuated expression of CNX and CRT in patients with chronic ITP, Ca²⁺ concentration and its associated down-regulated proteins may be important regulatory signals in the pathogenesis of chronic ITP.

Anti‑Nogo‑A antibody promotes brain function recovery after cardiopulmonary resuscitation in rats by reducing apoptosis

Brain injury after cardiac arrest (CA) and cardiopulmonary resuscitation (CPR) is the main cause of neurological dysfunction and death in cardiac arrest. To assess the effect of Nogo-A antibody on brain function in rats following CPR and to explore the underlying mechanisms, CA/CPR (ventricular fibrillation) rats were divided into the CPR+Nogo-A, CPR+saline and sham groups. Hippocampal caspase-3 levels were detected by RT-PCR and immunoblotting. Next, Nogo-A, glucose regulated protein 78 (GRP78), C/EBP homologous protein (CHOP), cysteinyl aspartate specific proteinase-12 (casapse-12), Bcl-2 and Bax protein levels in the hippocampus were detected by immunoblotting. Coronal brain sections were analyzed by TUNEL assay to detect apoptosis at 72 h, while Nissl staining and electron microscopy were performed to detect Nissl bodies and microstructure at 24 h, respectively. Finally, rats were assessed for neurologic deficits at various times. Nissl staining revealed morphological improvement after Nogo-A antibody treatment. Sub-organelle structure was preserved as assessed by electron microscopy in model animals post-antibody treatment; neurological function was improved as well (P<0.05), while the apoptosis index was decreased (26.2±9.85 vs. 46.6±12.95%; P<0.05). Hippocampal caspase-3 mRNA and protein, Nogo-A protein levels were significantly decreased after antibody treatment (P<0.05). Hippocampal Nogo-A expression was positively correlated with caspase-3 (Pearson's correlation; r=0.790, P=0.000). Hippocampal GRP78 and Bcl-2 protein levels were higher after antibody treatment than these levels noted in the model animals (P<0.05), while CHOP, caspase-12 and Bax levels were reduced (P<0.05). Nogo-A antibody ameliorates neurological function after restoration of spontaneous circulation (ROSC), possibly by suppressing apoptosis induced by endoplasmic reticulum stress.

SERCA control of cell death and survival

Intracellular calcium (Ca²⁺⁾ is a critical coordinator of various aspects of cellular physiology. It is increasingly apparent that changes in cellular Ca²⁺ dynamics contribute to the regulation of normal and pathological signal transduction that controls cell growth and survival. Aberrant perturbations in Ca²⁺ homeostasis have been implicated in a range of pathological conditions, such as cardiovascular diseases, diabetes, tumorigenesis and steatosis hepatitis. Intracellular Ca²⁺ concentrations are therefore tightly regulated by a number of Ca²⁺ handling enzymes, proteins, channels and transporters located in the plasma membrane and in Ca²⁺ storage organelles, which work in concert to fine tune a temporally and spatially precise Ca²⁺ signal. Chief amongst them is the sarco/endoplasmic reticulum (SR/ER) Ca²⁺ ATPase pump (SERCA) which actively re-accumulates released Ca²⁺ back into the SR/ER, therefore maintaining Ca²⁺ homeostasis. There are at least 14 different SERCA isoforms encoded by three ATP2A1-3 genes whose expressions are species- and tissue-specific. Altered SERCA expression and activity results in cellular malignancy and induction of ER stress and ER stress-associated apoptosis. The role of SERCA misregulation in the control of apoptosis in various cell types and disease setting with prospective therapeutic implications is the focus of this review. Ca²⁺ is a double edge sword for both life as well as death, and current experimental evidence supports a model in which Ca²⁺ homeostasis and SERCA activity represent a nodal point that controls cell survival. Pharmacological or genetic targeting of this axis constitutes an incredible therapeutic potential to treat different diseases sharing similar biological disorders.

DR5 and caspase-8 are dispensable in ER stress-induced apoptosis

The endoplasmic reticulum (ER) stress response constitutes cellular reactions triggered by a wide variety of stimuli that disturb folding of proteins, often leading to apoptosis. ER stress-induced apoptotic cell death is thought to be an important contributor to many human pathological conditions. The molecular mechanism of this apoptosis process has been highly controversial with both the receptor and the mitochondrial pathways being implicated. Using knockout mouse models and RNAi-mediated gene silencing in cell lines, our group and others had demonstrated the importance of the mitochondrial apoptotic pathway in ER stress-induced cell death, particularly the role of the pro-apoptotic BH3-only BCL-2 family members, BIM and PUMA. However, a recent report suggested a central role for the death receptor, DR5, activated in a ligand-independent manner, and the initiator caspase, caspase-8, in ER stress-induced cell death. This prompted us to re-visit our previous observations and attempt to reproduce the newly published findings. Here we report that the mitochondrial apoptotic pathway, activated by BH3-only proteins, is essential for ER stress-induced cell death and that, in contrast to the previous report, DR5 as well as caspase-8 are not required for this process.

Shiga Toxins as Multi-Functional Proteins: Induction of Host Cellular Stress Responses, Role in Pathogenesis and Therapeutic Applications

Shiga toxins (Stxs) produced by Shiga toxin-producing bacteria Shigella dysenteriae serotype 1 and select serotypes of Escherichia coli are primary virulence factors in the pathogenesis of hemorrhagic colitis progressing to potentially fatal systemic complications, such as hemolytic uremic syndrome and central nervous system abnormalities. Current therapeutic options to treat patients infected with toxin-producing bacteria are limited. The structures of Stxs, toxin-receptor binding, intracellular transport and the mode of action of the toxins have been well defined. However, in the last decade, numerous studies have demonstrated that in addition to being potent protein synthesis inhibitors, Stxs are also multifunctional proteins capable of activating multiple cell stress signaling pathways, which may result in apoptosis, autophagy or activation of the innate immune response. Here, we briefly present the current understanding of Stx-activated signaling pathways and provide a concise review of therapeutic applications to target tumors by engineering the toxins.

Cryptotanshinone deregulates unfolded protein response and eukaryotic initiation factor signaling in acute lymphoblastic leukemia cells

BACKGROUND

Unfolded protein responses (UPR) determine cell fate and are recognized as anticancer targets. In a previous research, we reported that cryptotanshinone (CPT) exerted cytotoxic effects toward acute lymphoblastic leukemia cells through mitochondria-mediated apoptosis.

PURPOSE

In the present study, we further investigated the role of UPR in CPT-induced cytotoxicity on acute lymphoblastic leukemia cells by applying tools of pharmacogenomics and bioinformatics.

METHODS

Gene expression profiling was performed by mRNA microarray hybridization. Potential transcription factor binding motifs were identified in the promoter regions of the deregulated genes by Cistrome software. Molecular docking on eIF-4A and PI3K was performed to investigate the inhibitory activity of CPT on translation initiation.

RESULTS

CPT regulated genes related to UPR and eIF2 signaling pathways. The DNA-Damage-Inducible Transcript 3 (DDIT3) gene, which is activated as consequence of UPR malfunction during apoptosis, was induced and validated by in vitro experiments. Transcription factor binding motif analysis of the microarrary-retrieved deregulated genes in the promoter region emphasized the relevance of transcription factors, such as ATF2, ATF4 and XBP1, regulating UPR and cell apoptosis. Molecular docking suggested inhibitory effects of CPT by binding to eIF-4A and PI3K providing evidence for a role of CPT's in the disruption of protein synthesis.

CONCLUSION

CPT triggered UPR and inhibited protein synthesis via eIF-mediated translation initiation, potentially supporting CPT-induced cytotoxic effects toward acute leukemia cells.

Neuroprotective effects of atorvastatin against cerebral ischemia/reperfusion injury through the inhibition of endoplasmic reticulum stress

Cerebral ischemia triggers secondary ischemia/reperfusion injury and endoplasmic reticulum stress initiates cell apoptosis. However, the regulatory mechanism of the signaling pathway remains unclear. We hypothesize that the regulatory mechanisms are mediated by the protein kinase-like endoplasmic reticulum kinase/eukaryotic initiation factor 2α in the endoplasmic reticulum stress signaling pathway. To verify this hypothesis, we occluded the middle cerebral artery in rats to establish focal cerebral ischemia/reperfusion model. Results showed that the expression levels of protein kinase-like endoplasmic reticulum kinase and caspase-3, as well as the phosphorylation of eukaryotic initiation factor 2α, were increased after ischemia/reperfusion. Administration of atorvastatin decreased the expression of protein kinase-like endoplasmic reticulum kinase, caspase-3 and phosphorylated eukaryotic initiation factor 2α, reduced the infarct volume and improved ultrastructure in the rat brain. After salubrinal, the specific inhibitor of phosphorylated eukaryotic initiation factor 2α was given into the rats intragastrically, the expression levels of caspase-3 and phosphorylated eukaryotic initiation factor 2α in the were decreased, a reduction of the infarct volume and less ultrastructural damage were observed than the untreated, ischemic brain. However, salubrinal had no impact on the expression of protein kinase-like endoplasmic reticulum kinase. Experimental findings indicate that atorvastatin inhibits endoplasmic reticulum stress and exerts neuroprotective effects. The underlying mechanisms of attenuating ischemia/reperfusion injury are associated with the protein kinase-like endoplasmic reticulum kinase/eukaryotic initiation factor 2α/caspase-3 pathway.

Combination treatment of tamoxifen with risperidone in breast cancer

Tamoxifen has long been used and still is the most commonly used endocrine therapy for treatment of both early and advanced estrogen receptor-positive breast cancer in pre- and post-menopause women. Tamoxifen exerts its cytotoxic effect primarily through cytostasis which is associated with the accumulation of cells in the G0/G1 phase of the cell cycle. Apoptotic activity can also be exerted by tamoxifen which involves cleavage of caspase 9, caspase 7, caspase 3, and poly-ADP-ribose polymerase (PARP). Down-regulation of anti-apoptotic proteins Bcl-2 and Bcl-xL and up-regulation of pro-apoptotic proteins Bax and Bak have also been observed. In addition, stress response protein of GRP 94 and GRP 78 have also been induced by tamoxifen in our study. However, side effects occur during tamoxifen treatment in breast cancer patients. Researching into combination regimen of tamoxifen and drug(s) that relieves tamoxifen-induced hot flushes is important, because drug interactions may decrease tamoxifen efficacy. Risperidone has been shown to be effective in reducing or eliminating hot flushes on women with hormonal variations. In this present study, we demonstrated that combination of tamoxifen with risperidone did not interfered tamoxifen-induced cytotoxic effects in both in vitro and in vivo models, while fluoxetine abrogated the effects of tamoxifen. This is the first paper suggesting the possibility of combination treatment of tamoxifen with risperidone in breast cancer patients, providing a conceivable resolution of tamoxifen-induced side effects without interfering the efficacy of tamoxifen against breast cancer.

New Insights into the Pathogenesis of Alcohol-Induced ER Stress and Liver Diseases

Alcohol-induced liver disease increasingly contributes to human mortality worldwide. Alcohol-induced endoplasmic reticulum (ER) stress and disruption of cellular protein homeostasis have recently been established as a significant mechanism contributing to liver diseases. The alcohol-induced ER stress occurs not only in cultured hepatocytes but also  in vivo  in the livers of several species including mouse, rat, minipigs, zebrafish, and humans. Identified causes for the ER stress include acetaldehyde, oxidative stress, impaired one carbon metabolism, toxic lipid species, insulin resistance, disrupted calcium homeostasis, and aberrant epigenetic modifications. Importance of each of the causes in alcohol-induced liver injury depends on doses, duration and patterns of alcohol exposure, genetic disposition, environmental factors, cross-talks with other pathogenic pathways, and stages of liver disease. The ER stress may occur more or less all the time during alcohol consumption, which interferes with hepatic protein homeostasis, proliferation, and cell cycle progression promoting development of advanced liver diseases. Emerging evidence indicates that long-term alcohol consumption and ER stress may directly be involved in hepatocellular carcinogenesis (HCC). Dissecting ER stress signaling pathways leading to tumorigenesis will uncover potential therapeutic targets for intervention and treatment of human alcoholics with liver cancer.

Disruption of microRNA biogenesis confers resistance to ER stress-induced cell death upstream of the mitochondrion

Global downregulation of microRNAs (miRNAs) is a common feature of human tumors and has been shown to enhance cancer progression. Several components of the miRNA biogenesis machinery (XPO5, DICER and TRBP) have been shown to act as haploinsufficient tumor suppressors. How the deregulation of miRNA biogenesis promotes tumor development is not clearly understood. Here we show that loss of miRNA biogenesis increased resistance to endoplasmic reticulum (ER) stress-induced cell death. We observed that HCT116 cells with a DICER hypomorphic mutation (Exn5/Exn5) or where DICER or DROSHA were knocked down were resistant to ER stress-induced cell death. Extensive analysis revealed little difference in the unfolded protein response (UPR) of WT compared to Exn5/Exn5 HCT116 cells upon ER stress treatment. However, analysis of the intrinsic apoptotic pathway showed that resistance occurred upstream of the mitochondria. In particular, BAX activation and dissipation of mitochondrial membrane potential was attenuated, and there was altered expression of BCL-2 family proteins. These observations demonstrate a key role for miRNAs as critical modulators of the ER stress response. In our model, downregulation of miRNA biogenesis delays ER stress-induced apoptosis. This suggests that disrupted miRNA biogenesis may contribute to cancer progression by inhibiting ER stress-induced cell death.

Frog virus 3 open reading frame 97R localizes to the endoplasmic reticulum and induces nuclear invaginations

Frog virus 3 (FV3) is the type species of the genus Ranavirus, family Iridoviridae. The genome of FV3 is 105,903 bases in length and encodes 97 open reading frames (ORFs). The FV3 ORF 97R contains a B-cell lymphoma 2 (Bcl-2) homology 1 (BH1) domain and has sequence similarity to the myeloid cell leukemia-1 (Mcl-1) protein, suggesting a potential role in apoptosis. To begin to understand the role of 97R, we characterized 97R through immunofluorescence and mutagenesis. Here we demonstrated that 97R localized to the endoplasmic reticulum (ER) at 24 h posttransfection. However, at 35 h posttransfection, 97R localized to the ER but also began to form concentrated pockets continuous with the nuclear membrane. After 48 h posttransfection, 97R was still localized to the ER, but we began to observe the ER and the outer nuclear membrane invaginating into the nucleus. To further explore 97R targeting to the ER, we created a series of C-terminal transmembrane domain deletion mutants. We found that deletion of 29 amino acids from the C terminus of 97R abolished localization to the ER. In contrast, deletion of 12 amino acids from the C terminus of 97R did not affect 97R localization to the ER. In addition, a hybrid protein containing the 97R C-terminal 33 amino acids was similarly targeted to the ER. These data indicate that the C-terminal 33 amino acids of 97R are necessary and sufficient for ER targeting.

Interconnections between apoptotic, autophagic and necrotic pathways: implications for cancer therapy development

The rapid accumulation of knowledge on apoptosis regulation in the 1990s was followed by the development of several experimental anticancer- and anti-ischaemia (stroke or myocardial infarction) drugs. Activation of apoptotic pathways or the removal of cellular apoptotic inhibitors has been suggested to aid cancer therapy and the inhibition of apoptosis was thought to limit ischaemia-induced damage. However, initial clinical studies on apoptosis-modulating drugs led to unexpected results in different clinical conditions and this may have been due to co-effects on non-apoptotic interconnected cell death mechanisms and the ‘yin-yang’ role of autophagy in survival versus cell death. In this review, we extend the analysis of cell death beyond apoptosis. Upon introduction of molecular pathways governing autophagy and necrosis (also called necroptosis or programmed necrosis), we focus on the interconnected character of cell death signals and on the shared cell death processes involving mitochondria (e.g. mitophagy and mitoptosis) and molecular signals playing prominent roles in multiple pathways (e.g. Bcl2-family members and p53). We also briefly highlight stress-induced cell senescence that plays a role not only in organismal ageing but also offers the development of novel anticancer strategies. Finally, we briefly illustrate the interconnected character of cell death forms in clinical settings while discussing irradiation-induced mitotic catastrophe. The signalling pathways are discussed in their relation to cancer biology and treatment approaches.

Cigarette smoking affects oxidative protein folding in endoplasmic reticulum by modifying protein disulfide isomerase

The endoplasmic reticulum (ER) stress response (ERSR) and associated protein aggregation, is under investigation for its role in human diseases, including chronic obstructive pulmonary disease (COPD) where cigarette smoking (CS) is a risk factor for disease development. Our hypothesis states that CS-associated oxidative stress interferes with oxidative protein folding in the ER and elicits ERSR. We investigated ERSR induction following acute CS exposure and delineated mechanisms of CS-induced ERSR. Lung lysates from mice exposed or not to one cigarette were tested for activation of the ERSR. Up to 4-fold increase in phosphorylation of eIF2α and nuclear form of ATF6 was detected in CS-exposed animals. CS affected the formation of disulfide bonds through excessive posttranslational oxidation of protein disulfide isomerase (PDI). Increased amounts of complexes between PDI and its client proteins persisted in CS-exposed samples. BiP was not a constituent of these complexes, demonstrating the specificity of the early effects of CS exposure on ER. Disturbances in protein folding were accompanied by changes in the organization of ER network and ER exit sites. Our results provide evidence that ERSR is induced early in response to CS exposure and identifies the first known ER-resident target of CS PDI, demonstrating that CS affects oxidative protein folding.

Endoplasmic reticulum protein BI-1 regulates Ca²⁺-mediated bioenergetics to promote autophagy

Autophagy is a lysosomal degradation pathway that converts macromolecules into substrates for energy production during nutrient-scarce conditions such as those encountered in tumor microenvironments. Constitutive mitochondrial uptake of endoplasmic reticulum (ER) Ca²⁺ mediated by inositol triphosphate receptors (IP₃Rs) maintains cellular bioenergetics, thus suppressing autophagy. We show that the ER membrane protein Bax inhibitor-1 (BI-1) promotes autophagy in an IP₃R-dependent manner. By reducing steady-state levels of ER Ca²⁺ via IP₃Rs, BI-1 influences mitochondrial bioenergetics, reducing oxygen consumption, impacting cellular ATP levels, and stimulating autophagy. Furthermore, BI-1-deficient mice show reduced basal autophagy, and experimentally reducing BI-1 expression impairs tumor xenograft growth in vivo. BI-1's ability to promote autophagy could be dissociated from its known function as a modulator of IRE1 signaling in the context of ER stress. The results reveal BI-1 as a novel autophagy regulator that bridges Ca²⁺ signaling between ER and mitochondria, reducing cellular oxygen consumption and contributing to cellular resilience in the face of metabolic stress.

Endoplasmic reticulum stress-related factors protect against diabetic retinopathy

The endoplasmic reticulum (ER) is a principal mediator of signal transduction in the cell, and disruption of its normal function (a mechanism known as ER stress) has been associated with the pathogenesis of several diseases. ER stress has been demonstrated to contribute to onset and progression of diabetic retinopathy (DR) by induction of multiple inflammatory signaling pathways. Recent studies have begun to describe the gene expression profile of ER stress-related genes in DR; moreover, genes that play a protective role against DR have been identified. P58^IPK was determined to be able to reduce retinal vascular leakage under high glucose conditions, thus protecting retinal cells. It has also been found by our lab that ER-associated protein degradation factors exhibit significantly different expression patterns in rat retinas under sustained high glucose conditions. Future research based upon these collective genomic findings will contribute to our overall understanding of DR pathogenesis as well as identify potential therapeutic targets.

Metformin differentially activates ER stress signaling pathways without inducing apoptosis

Endoplasmic reticulum stress signaling (ERSS) plays an important role in the pathogenesis of diabetes and heart disease. The latter is a common comorbidity of diabetes and worsens patient outcome. Results from clinical studies suggest beneficial effects of metformin – a widely used oral drug for the treatment of type 2 diabetes – on the heart of diabetic patients with heart failure. We therefore analyzed the effect of metformin on ERSS in primary rat cardiomyocytes. We found that metformin activates the PERK-ATF4 but not the ATF6 or IRE1-XBP1 branch in ERSS and leads to a strong upregulation of CHOP mRNA and protein. Surprisingly, long-term induction of CHOP by metformin is not accompanied by apoptosis even though CHOP is regarded to be a mediator of ER-stress-induced apoptosis. In conclusion, metformin induces distinct ER stress pathways in cardiomyocytes and our results indicate that CHOP is not necessarily a mediator of apoptosis. Metformin might exert its cardioprotective effect through selective activation of ERSS pathways in the cardiomyocyte.

Ion channnels and transporters in cancer. 5. Ion channels in control of cancer and cell apoptosis

Ion channels contribute to virtually all basic cellular processes, including such crucial ones for maintaining tissue homeostasis as proliferation, differentiation, and apoptosis. The involvement of ion channels in regulation of programmed cell death, or apoptosis, has been known for at least three decades based on observation that classical blockers of ion channels can influence cell death rates, prolonging or shortening cell survival. Identification of the central role of these channels in regulation of cell cycle and apoptosis as well as the recent discovery that the expression of ion channels is not limited solely to the plasma membrane, but may also include membranes of internal compartments, has led researchers to appreciate the pivotal role of ion channels plays in development of cancer. This review focuses on the aspects of programmed cell death influenced by various ion channels and how dysfunctions and misregulations of these channels may affect the development and progression of different cancers.