Switch between apoptosis and autophagy: radiation-induced endoplasmic reticulum stress?

A novel approach of using Maca root as a radioprotector in a rat testicular damage model focusing on GRP78/CHOP/Caspase-3 pathway

PURPOSE

Despite the effectiveness of ionizing radiation in treating cancer, it can damage healthy tissues in the vicinity. Due to the high radio-sensitivity of testicular tissues, radiation therapy may affect spermatogenesis, which may result in infertility. Hence, in this study testicular damage model is constructed to investigate the mitigation effect of Maca root powder and its potential radioprotective activity through both oxidative and endoplasmic reticulum (ER) stresses, besides the apoptotic pathway.

METHODS

Male albino rats were exposed to 6Gy of whole-body gamma radiation single dose. Maca root powder (1 g/kg b.wt./day, by oral gavage) was administered for a week before irradiation, then d-galactose (300 mg/kg, by oral gavage) and Maca daily for another week.

RESULTS

Gamma radiation and d-galactose revealed a significant decrease in serum testosterone, sperm count, and motility and higher percentage of the sperm head abnormality, while Maca root treatment maintained all sperm morphology parameters. Maca root treatment demonstrated a notable defense against radiation-induced oxidative stress and ameliorated malonaldehyde (MDA), reactive oxygen species (ROS), nitric oxide (NO), glutathione-S-transferase (GST) levels, reduced glutathione (GSH), oxidized glutathione (GSSG) and the ratio of GSH/GSSG in testis tissues. Exposure to gamma rays and d-galactose displayed a significant elevation in GRP78, CHOP, total caspase-3 as well as active (cleaved) caspase-3 levels, whereas treatment with Maca significantly reduced the ER and apoptotic markers levels. Also, Maca improved the histological changes of the disorganized seminiferous tubules induced by irradiation.

CONCLUSION

Our findings show for the first time that Maca has a protective effect on male reproductive damage induced by radiotherapy. Maca root reveals anti-apoptotic effect and protection against testicular damage via GRP78/CHOP/caspase-3 pathway.

Targeted Inhibition of Hsp90 in Combination with Metformin Modulates Programmed Cell Death Pathways in A549 Lung Cancer Cells

The pathophysiology of lung cancer is dependent on the dysregulation in the apoptotic and autophagic pathways. The intricate link between apoptosis and autophagy through shared signaling pathways complicates our understanding of how lung cancer pathophysiology is regulated. As drug resistance is the primary reason behind treatment failure, it is crucial to understand how cancer cells may respond to different therapies and integrate crosstalk between apoptosis and autophagy in response to them, leading to cell death or survival. Thus, in this study, we have tried to evaluate the crosstalk between autophagy and apoptosis in A549 lung cancer cell line that could be modulated by employing a combination therapy of metformin (6 mM), an anti-diabetic drug, with gedunin (12 µM), an Hsp90 inhibitor, to provide insights into the development of new cancer therapeutics. Our results demonstrated that metformin and gedunin were cytotoxic to A549 lung cancer cells. Combination of metformin and gedunin generated ROS and promoted MMP loss and DNA damage. The combination further increased the expression of AMPKα1 and promoted the nuclear localization of AMPKα1/α2. The expression of Hsp90 was downregulated, further decreasing the expression of its clients, EGFR, PIK3CA, AKT1, and AKT3. Inhibition of the EGFR/PI3K/AKT pathway upregulated TP53 and inhibited autophagy. The combination was promoting nuclear localization of p53; however, some cytoplasmic signals were also detected. Further increase in the expression of caspase 9 and caspase 3 was observed. Thus, we concluded that the combination of metformin and gedunin upregulates apoptosis by inhibiting the EGFR/PI3K/AKT pathway and autophagy in A549 lung cancer cells.

Mitochondrial Signaling Pathways Associated with DNA Damage Responses

Under physiological and stress conditions, mitochondria act as a signaling platform to initiate biological events, establishing communication from the mitochondria to the rest of the cell. Mitochondrial adenosine triphosphate (ATP), reactive oxygen species, cytochrome C, and damage-associated molecular patterns act as messengers in metabolism, oxidative stress response, bystander response, apoptosis, cellular senescence, and inflammation response. In this review paper, the mitochondrial signaling in response to DNA damage was summarized. Mitochondrial clearance via fusion, fission, and mitophagy regulates mitochondrial quality control under oxidative stress conditions. On the other hand, damaged mitochondria release their contents into the cytoplasm and then mediate various signaling pathways. The role of mitochondrial dysfunction in radiation carcinogenesis was discussed, and the recent findings on radiation-induced mitochondrial signaling and radioprotective agents that targeted mitochondria were presented. The analysis of the mitochondrial radiation effect, as hypothesized, is critical in assessing radiation risks to human health.

Inhibition of autophagy reduces the rate of fluoride-induced LS8 apoptosis via regulating ATG5 and ATG7

Excessive fluoride affects ameloblast differentiation and tooth development. The fate of fluorinated ameloblasts is determined by multiple signaling pathways in response to a range of stimuli. Both autophagy and apoptosis are involved in the regulation of dental fluorosis as well as in protein synthesis and enamel mineralization. Emerging evidence suggests that autophagy and apoptosis are interconnected and that their interaction greatly influences cell death. However, the effect of autophagy on apoptosis in fluoride-treated ameloblasts is unclear. Here, we employed an in vitro cellular model of fluorosis in mouse ameloblast-like LS8 cells and induced autophagy using sodium fluoride (NaF). Our findings suggest that NaF treatment induces autophagy in LS8 cells, and ATG5 and ATG7 are important molecules involved in this process. We also showed that NaF treatment reduced cell viability in Atg5/7 siRNA and autophagy inhibitor-treated LS8 cells. More importantly, NaF-induced apoptosis can be reversed by inhibiting early stage of autophagy. In conclusion, our study shows that autophagy is closely related to dental fluorosis, and inhibition of autophagy, especially ATG5/7, reduces fluoride-induced cell death and apoptosis.

Comparison of the Medical Uses and Cellular Effects of High and Low Linear Energy Transfer Radiation

Exposure to ionizing radiation can occur during medical treatments, from naturally occurring sources in the environment, or as the result of a nuclear accident or thermonuclear war. The severity of cellular damage from ionizing radiation exposure is dependent upon a number of factors including the absorbed radiation dose of the exposure (energy absorbed per unit mass of the exposure), dose rate, area and volume of tissue exposed, type of radiation (e.g., X-rays, high-energy gamma rays, protons, or neutrons) and linear energy transfer. While the dose, the dose rate, and dose distribution in tissue are aspects of a radiation exposure that can be varied experimentally or in medical treatments, the LET and eV are inherent characteristics of the type of radiation. High-LET radiation deposits a higher concentration of energy in a shorter distance when traversing tissue compared with low-LET radiation. The different biological effects of high and low LET with similar energies have been documented in vivo in animal models and in cultured cells. High-LET results in intense macromolecular damage and more cell death. Findings indicate that while both low- and high-LET radiation activate non-homologous end-joining DNA repair activity, efficient repair of high-LET radiation requires the homologous recombination repair pathway. Low- and high-LET radiation activate p53 transcription factor activity in most cells, but high LET activates NF-kB transcription factor at lower radiation doses than low-LET radiation. Here we review the development, uses, and current understanding of the cellular effects of low- and high-LET radiation exposure.

The role of autophagy in calcium oxalate kidney stone: A systematic review of the literature

Background: Calcium oxalate kidney stone is one of the common diseases in the urinary system and has a high recurrence rate. Currently, the pathogenesis of kidney stone and the methods to prevent recurrence are still being investigated. Autophagy, as an event of cellular self-repair, has received attention in the field of kidney stone in recent years. In some current studies, autophagy has shown destructiveness and protectiveness in the pathogenesis of kidney stone. The inhibition or promotion of autophagy may be a key target for future kidney stone therapy. This systematic literature review discusses the function of autophagy in kidney stone pathogenesis in the context of current research and synthesizes the evidence analysis to provide a basis for new future therapies.

Method: We systematically reviewed the literature during September 2021 according to the Preferred Reporting Items for Systematic Evaluation and Meta-Analysis (PRISMA) guidelines. Articles on studying the role of autophagy in the pathogenesis of calcium oxalate kidney stone were extracted from PubMed, MEDLINE, Embase and Scopus, including in vivo versus in vitro experiments. The study topic, language and publication date were not restricted. Two authors (Li and Zhou) searched and screened the literature.

Results: We screened 18 articles from the 33 collected articles, of which 6 conducted in vitro cellular studies, four conducted animal studies, eight conducted cellular studies with animal studies, and five studied human specimens. In early studies, the literature generally concluded that autophagy is deleterious in the development of kidney stone. In 2020, the idea of the protectiveness of autophagy associated with kidney stone was first proposed and focused on targeting transcription factor EB. In addition, the interaction of autophagy with other cellular events and the regulation of signaling molecules are focused on in this paper.

Conclusion: This systematic review provides advances in research on the role of autophagy in renal calculi. The current studies suggest that both upregulation and downregulation of autophagy may ameliorate injury in kidney stone models. The authors prefer the upregulation of autophagy as a future research direction for kidney stone treatment.

Modulating the Antioxidant Response for Better Oxidative Stress-Inducing Therapies: How to Take Advantage of Two Sides of the Same Medal?

Oxidative stress-inducing therapies are characterized as a specific treatment that involves the production of reactive oxygen and nitrogen species (RONS) by external or internal sources. To protect cells against oxidative stress, cells have evolved a strong antioxidant defense system to either prevent RONS formation or scavenge them. The maintenance of the redox balance ensures signal transduction, development, cell proliferation, regulation of the mechanisms of cell death, among others. Oxidative stress can beneficially be used to treat several diseases such as neurodegenerative disorders, heart disease, cancer, and other diseases by regulating the antioxidant system. Understanding the mechanisms of various endogenous antioxidant systems can increase the therapeutic efficacy of oxidative stress-based therapies, leading to clinical success in medical treatment. This review deals with the recent novel findings of various cellular endogenous antioxidant responses behind oxidative stress, highlighting their implication in various human diseases, such as ulcers, skin pathologies, oncology, and viral infections such as SARS-CoV-2.

Targeting ERK induced cell death and p53/ROS-dependent protective autophagy in colorectal cancer

In recent years, many studies have shown that autophagy plays a vital role in the resistance of tumor chemotherapy. However, the interaction between autophagy and cell death has not yet been clarified. In this study, a new specific ERK inhibitor CC90003 was found to suppress colorectal cancer growth by inducing cell death both in vitro and in vivo. Studies have confirmed that higher concentrations of ROS leads to autophagy or cell death. In this research, the role of CC90003-induced ROS was verified. But after inhibiting ROS by two kinds of ROS inhibitors NAC and SFN, the autophagy induced by CC90003 decreased, while cell death strengthened. In parallel, protective autophagy was also induced, while in a p53-dependent manner. After silencing p53 or using the p53 inhibitor PFTα, the autophagy induced by CC90003 was weakened and the rate of cell death increases. Therefore, we confirmed that CC90003 could induce autophagy by activating ROS/p53. Furthermore, in the xenograft mouse model, the effect was obtained remarkably in the combinational treatment group of CC90003 plus CQ, comparing with that of the single treatment groups. In a word, our results demonstrated that targeting ERK leads to cell death and p53/ROS-dependent protective autophagy simultaneously in colorectal cancer, which offers new potential targets for clinical therapy.

The Kidney-Related Effects of Polystyrene Microplastics on Human Kidney Proximal Tubular Epithelial Cells HK-2 and Male C57BL/6 Mice

BACKGROUND

Understanding the epidemic of chronic kidney disease of uncertain etiology may be critical for health policies and public health responses. Recent studies have shown that microplastics (MPs) contaminate our food chain and accumulate in the gut, liver, kidney, muscle, and so on. Humans manufacture many plastics-related products. Previous studies have indicated that particles of these products have several effects on the gut and liver. Polystyrene (PS)-MPs (PS-MPs) induce several responses, such as oxidative stress, and affect living organisms.

OBJECTIVES

The aim of this study was to investigate the effects of PS-MPs in kidney cells in vitro and in vivo.

METHODS

PS-MPs were evaluated in human kidney proximal tubular epithelial cells (HK-2 cells) and male C57BL/6 mice. Mitochondrial reactive oxygen species (ROS), endoplasmic reticulum (ER) stress, inflammation, and autophagy were analyzed in kidney cells. In vivo, we evaluated biomarkers of kidney function, kidney ultrastructure, muscle mass, and grip strength, and urine protein levels, as well as the accumulation of PS-MPs in the kidney tissue.

RESULTS

Uptake of PS-MPs at different concentrations by HK-2 cells resulted in higher levels of mitochondrial ROS and the mitochondrial protein Bad. Cells exposed to PS-MPs had higher ER stress and markers of inflammation. MitoTEMPO, which is a mitochondrial ROS antioxidant, mitigated the higher levels of mitochondrial ROS, Bad, ER stress, and specific autophagy-related proteins seen with PS-MP exposure. Furthermore, cells exposed to PS-MPs had higher protein levels of LC3 and Beclin 1. PS-MPs also had changes in phosphorylation of mitogen-activated protein kinase (MAPK) and protein kinase B (AKT)/mitogen-activated protein kinase (mTOR) signaling pathways. In an in vivo study, PS-MPs accumulated and the treated mice had more histopathological lesions in the kidneys and higher levels of ER stress, inflammatory markers, and autophagy-related proteins in the kidneys after PS-MPs treatment by oral gavage.

CONCLUSIONS

The results suggest that PS-MPs caused mitochondrial dysfunction, ER stress, inflammation, and autophagy in kidney cells and accumulated in HK-2 cells and in the kidneys of mice. These results suggest that long-term PS-MPs exposure may be a risk factor for kidney health. https://doi.org/10.1289/EHP7612.

The effect of baicalein on endoplasmic reticulum stress and autophagy on liver damage

Carbon tetrachloride (CCl₄) is a toxic chemical that causes liver injury. CCl₄ triggers endoplasmic reticulum (ER) stress and unfolded protein response (UPR). UPR triggers autophagy to deal with the damage. The aim of this study was to investigate the effect of baicalein, derived from Scutellaria baicalensis, on CCl₄-induced liver damage concerning ER stress and autophagy. Two groups of Wistar albino rats (n = 7/groups) were treated with 0.2 ml/kg CCl₄ for 10 days with and without baicalein. Histological and transmission electron microscopy (TEM) analysis, autophagy, and ER stress markers measurements were carried out to evaluate the effect of baicalein. Histological examinations showed that baicalein reduced liver damage. TEM analysis indicated that baicalein inhibited ER stress and triggered autophagy. CCl4-induced elevation of C/EBP homologous protein (CHOP), glucose-regulating protein 78 (GRP78), activating transcription factor 4 (ATF4), activating transcription factor 6 (ATF6), inositol requiring enzyme 1 (IRE1), pancreatic ER kinase (PERK), and active/spliced form of X-box-binding protein 1 (XBP1s) ER stress markers were decreased by baicalein. Baicalein also increased the autophagy-related 5 (ATG5), Beclin1, and Microtubule-associated protein 1A/1B-light chain 3-phosphatidylethanolamine-conjugated form (LC3-II) autophagy marker levels. In conclusion, baicalein reduced the CCl₄-induced liver damage by inhibiting ER stress and the trigger of autophagy.

Biological Evaluation of Oxindole Derivative as a Novel Anticancer Agent against Human Kidney Carcinoma Cells

Renal cell carcinoma has emerged as one of the leading causes of cancer-related deaths in the USA. Here, we examined the anticancer profile of oxindole derivatives (SH-859) in human renal cancer cells. Targeting 786-O cells by SH-859 inhibited cell growth and affected the protein kinase B/mechanistic target of rapamycin 1 pathway, which in turn downregulated the expression of glycolytic enzymes, including lactate dehydrogenase A and glucose transporter-1, as well as other signaling proteins. Treatment with SH-859 altered glycolysis, mitochondrial function, and levels of adenosine triphosphate and cellular metabolites. Flow cytometry revealed the induction of apoptosis and G0/G1 cell cycle arrest in renal cancer cells following SH-859 treatment. Induction of autophagy was also confirmed after SH-859 treatment by acridine orange and monodansylcadaverine staining, immunocytochemistry, and Western blot analyses. Finally, SH-859 also inhibited the tumor development in a xenograft model. Thus, SH-859 can serve as a potential molecule for the treatment of human renal carcinoma.

Inhibition of autophagy by chloroquine enhances the antitumor activity of gemcitabine for gallbladder cancer

Gemcitabine (GEM), as an anti-metabolic nucleoside analog, has been shown to have anticancer effects in various tumors, but its chemotherapy resistance is still an important factor leading to poor prognosis of cancer patient. A large number of studies in recent years have shown that autophagy plays an important role in the chemotherapy sensitivity of many tumors, including pancreatic, non-small cell lung, and bladder cancer. However, whether GEM causes autophagy in gallbladder cancer (GBC) and whether it is related to chemotherapy resistance is unknown. In the present study, we demonstrated that GEM induced apoptosis and protective autophagy in GBC cells, which may be related to the AKT/mTOR signaling pathway, and GEM in combination with autophagy inhibitor chloroquine can strengthen the cytotoxic effect of GEM on GBC in vitro and in vivo. These findings showed that both autophagy and AKT/mTOR signals were engaged in GBC cell death evoked by GEM, GBC patients might benefit from this new treatment strategy, and molecular targeted treatment in combination with autophagy inhibitors shows promise as a treatment improvement.

Chlorpyrifos induces apoptosis and autophagy in common carp lymphocytes by influencing the TCR γ-dependent PI3K/AKT/JNK pathway

Chlorpyrifos is an insecticide that is widely used in agricultural production. However, little is known about how chlorpyrifos disrupts lymphocyte homeostasis in common carp. Herein, we identified TCRγ through the results of transcriptome analysis. Subsequently, we established TCR γ knockdown and overexpression models in carp head kidney lymphocyte respectively using RNA interference and the pcDNA3.1 plasmid, respectively. Real-time PCR, fluorescent staining, ultrastructure observation and flow cytometry were used to detect the levels of the PI3K/AKT pathway, autophagy and apoptosis. Our results demonstrated that chlorpyrifos significantly decreased the expression of TCR γ, TCR γ suppression thereby induced increased mRNA expression of TNF-α, Bax, caspase-3, caspase-8, caspase-9 and significantly inhibited the expression of Bcl-2, which indicated that apoptosis was triggered. This conclusion was supported by our flow cytometry and ultrastructure observation results. In addition, the control and TCR γ overexpression groups had normal cell morphology. Moreover, TCR γ suppression activated the expression of Becline-1, ATG5, ATG10, ATG12, ATG16 and reduced the expression of mTOR, with the opposite results observed in the TCR γ overexpression group. Together, these results suggested that TCR γ imbalance triggers apoptosis and autophagy in lymphocyte. Moreover, we found that TCR γ knockdown significantly increased the mRNA expression of JNK and decreased the expression of PI3K and AKT, which indicated that the PI3K/AKT/JNK pathway was activated. Our results reported here indicated that chlorpyrifos induces apoptosis and autophagy in head kidney lymphocyte through the inhibition of TCR γ.

Significant contribution of autophagy in mitigating cytotoxicity of gadolinium ions

Gadolinium-based contrast agents (GBCAs) are widely used in clinical magnetic resonance imaging (MRI). Free gadolinium ions (Gd³⁺) released from GBCAs potentially increase the risk of GBCA-related toxicity. However, the cellular responses to Gd³⁺ and the underlying mechanisms responsible for protection against Gd³⁺ remain poorly understood. Recently, autophagy has been considered a cell survival mechanism against various toxic metals. Here, we investigated the relationship between Gd³⁺ and autophagy, as well as the effect of autophagy inhibition on the survival of cells exposed to Gd³⁺. We found that the increased expression of microtubule-associated protein 1 light chain 3 (LC3)-II, a marker protein of autophagy, in Gd³⁺-exposed human embryonic kidney 293 (HEK293) cells. Moreover, we found a greater accumulation of LC3-II after exposure to an autophagy inhibitor, chloroquine (CQ), combined with Gd³⁺ than that after exposure to CQ alone, suggesting that Gd³⁺ activated autophagy in HEK293 cells. Furthermore, we found that Gd³⁺ reduced cell viability, which was more pronounced after CQ treatment. Our findings indicated that autophagy exerted a cytoprotective effect against Gd³⁺ toxicity, suggesting a potential link between autophagy and GBCA-associated adverse events.

Naringenin Ameliorate Carbon Tetrachloride-Induced Hepatic Damage Through Inhibition of Endoplasmic Reticulum Stress and Autophagy in Rats

Hepatic fibrosis emerges upon exposure of liver to various chemicals and if not treated, it develops various diseases such as cirrhosis and cancer. Carbon tetrachloride (CCl₄) is a widely used toxin in animal models to develop hepatic fibrosis. Accumulation of unfolded proteins in cells causes stress in the endoplasmic reticulum (ER) and various mechanisms are involved in the cell to reduce the damage caused by these unfolding proteins. The most well known of these is the unfolded protein response. Further, autophagy works to remove these proteins if the damage cannot be repaired and is permanent. In our study, we investigated the effects of naringenin (NRG), a flavanon abundant in citrus fruits, on ER stress and autophagy in CCl₄-injured rat liver. The animals were given 0.2 mL/kg of CCl₄ for 10 days and treatment group was administered 100 mg/kg of NRG for 14 days. Histopathological examination was performed to show liver damage and to determine the therapeutic properties of the active substance. Transmission electron microscopy (TEM) analysis was carried out to establish cell level damage and effect of treatment. In addition, levels of ER stress and autophagy markers of liver were measured. According to our findings, TEM demonstrated positive effect of NRG and histological examinations reported ameliorative effects. In addition, NRG reduced levels of ER stress markers and inhibited autophagy significantly compared to CCl₄-treated group. As a result, NRG significantly reduced damage in hepatocytes and provided a significant amelioration.

Inhibition of endoplasmic reticulum stress-induced autophagy promotes the killing effect of X-rays on sarcoma in mice

Endoplasmic reticulum (ER) stress is a conserved cellular process for cells to clear unfolded or misfolded proteins and maintain cell homeostasis under stress conditions. Autophagy may act as a pro-survival strategy to cope with multiple stress conditions in tumor progression and distant metastasis. Although many studies have demonstrated that there is a close correlation between radiation-induced ER stress and autophagy, the molecular mechanisms currently remain unclear. In the present study, we performed an in vivo study concerning the effect of autophagy induced by ER stress on the radiosensitivity of mouse sarcoma using X-rays. Our results documented that X-rays could induce ER stress in sarcoma and then autophagy was activated by unfolded protein response (UPR) through the IRE1-JNK-pBcl2-Beclin1 signaling axis. The induction of autophagy caused a decline in cell apoptosis while inhibiting the autophagy resulted in increased apoptosis and inhibition of tumor progression. Combined treatment of X-ray exposure and chloroquine increased ER stress-related apoptosis and enhanced the radiosensitivity of mouse sarcoma that was not sensitive to X-ray irradiation alone. Thus, our study indicates that inhibition of ER stress-induced autophagy might be a novel strategy to improve the efficacy of radiotherapy against radioresistant sarcoma.

Targeting valosin-containing protein enhances the efficacy of radiation therapy in esophageal squamous cell carcinoma

Overcoming resistance to radiation is a great challenge in cancer therapy. Here, we highlight that targeting valosin‐containing protein (VCP) improves radiation sensitivity in esophageal squamous cell carcinoma (ESCC) cell lines and show the potential of using VCP as a prognosis marker in locally advanced ESCC treated with radiation therapy. Esophageal squamous cell carcinoma cell lines with high VCP expression were treated with VCP inhibitor combined with radiotherapy. Cell proliferation, colony formation, cell death, and endoplasmic reticulum (ER) stress signaling were evaluated. Moreover, patients with newly diagnosed locally advanced ESCC who were treated with radiotherapy were analyzed. Immunohistochemistry was used to detect the expression of VCP. The correlation between overall survival and VCP was investigated. Esophageal squamous cell carcinoma cells treated with VCP inhibitor and radiotherapy showed attenuated cell proliferation and colony formation and enhanced apoptosis. Further investigation showed this combined strategy activated the ER stress signaling involved in unfolded protein response, and inhibited the ER‐associated degradation (ERAD) pathway. Clinical analysis revealed a significant survival benefit in the low VCP expression group. Targeting VCP resulted in antitumor activity and enhanced the efficacy of radiation therapy in ESCC cells in vitro. Valosin‐containing protein is a promising and novel target. In patients with locally advanced ESCC who received radiotherapy, VCP can be considered as a useful prognostic indicator of overall survival. Valosin‐containing protein inhibitors could be developed for use as effective cancer therapies, in combination with radiation therapy.

Radiation induces EIF2AK3/PERK and ERN1/IRE1 mediated pro-survival autophagy

Cellular effects of ionizing radiation include oxidative damage to macromolecules, unfolded protein response (UPR) and metabolic imbalances. Oxidative stress and UPR have been shown to induce macroautophagy/autophagy in a context-dependent manner and are crucial factors in determining the fate of irradiated cells. However, an in-depth analysis of the relationship between radiation-induced damage and autophagy has not been explored. In the present study, we investigated the relationship between radiation-induced oxidative stress, UPR and autophagy in murine macrophage cells. A close association was observed between radiation-induced oxidative burst, UPR and induction of autophagy, with the possible involvement of EIF2AK3/PERK (eukaryotic translation initiation factor 2 alpha kinase 3) and ERN1/IRE1 (endoplasmic reticulum [ER] to nucleus signaling 1). Inhibitors of either UPR or autophagy reduced the cell survival indicating the importance of these processes after radiation exposure. Moreover, modulation of autophagy affected lethality in the whole body irradiated C57BL/6 mouse. These findings indicate that radiation-induced autophagy is a pro-survival response initiated by oxidative stress and mediated by EIF2AK3 and ERN1. Abbreviations: ACTB: actin, beta; ATF6: activating transcription factor 6; ATG: autophagy-related; BafA1: bafilomycin A1; CQ: chloroquine; DBSA: 3,5-dibromosalicylaldehyde; EIF2AK3: eukaryotic translation initiation factor 2 alpha kinase 3; ERN1: endoplasmic reticulum (ER) to nucleus signaling 1; IR: ionizing radiation; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; 3-MA: 3-methyladenine; MTOR: mechanistic target of rapamycin kinase; NAC: N-acetyl-L-cysteine; PARP1: poly (ADP-ribose) polymerase family, member 1; 4-PBA: 4-phenylbutyrate; Rap: rapamycin; ROS: reactive oxygen species; UPR: unfolded protein response; XBP1: x-box binding protein 1.

PRKCSH contributes to tumorigenesis by selective boosting of IRE1 signaling pathway

Unfolded protein response (UPR) is an adaptive mechanism that aims at restoring ER homeostasis under severe environmental stress. Malignant cells are resistant to environmental stress, which is largely due to an activated UPR. However, the molecular mechanisms by which different UPR branches are selectively controlled in tumor cells are not clearly understood. Here, we provide evidence that PRKCSH, previously known as glucosidase II beta subunit, functions as a regulator for selective activation of the IRE1α branch of UPR. PRKCSH boosts ER stress–mediated autophosphorylation and oligomerization of IRE1α through mutual interaction. PRKCSH contributes to the induction of tumor-promoting factors and to tumor resistance to ER stress. Increased levels of PRKCSH in various tumor tissues are positively correlated with the expression of XBP1-target genes. Taken together, our data provide a molecular rationale for selective activation of the IRE1α branch in tumors and adaptation of tumor cells to severe environmental stress.

Cancer cells utilise the unfolded protein response (UPR) to adapt to environmental and ER stress. Here, the authors show that the glycosidase II beta subunit, PRKSCH, protects cancer cells from ER stress, by interacting with IRE1α and activating the IRE1α-XBP1 branch of the UPR.

Ginsenoside Rb1 Ameliorates Autophagy of Hypoxia Cardiomyocytes from Neonatal Rats via AMP-Activated Protein Kinase Pathway

OBJECTIVE

To investigate whether ginsenoside-Rb1 (Gs-Rb1) improves the CoCl-induced autophagy of cardiomyocytes via upregulation of adenosine 5'-monophosphate-activated protein kinase (AMPK) pathway.

METHODS

Ventricles from 1- to 3-day-old Wistar rats were sequentially digested, separated and incubated in Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum for 3 days followed by synchronization. Neonatal rat cardiomyocytes were randomly divided into 7 groups: control group (normal level oxygen), hypoxia group (500 μmol/L CoCl₂), Gs-Rb1 group (200 μmol/L Gs-Rb1 + 500 μmol/L CoCl₂), Ara A group (500 μmol/L Ara A + 500 μmol/L CoCl₂), Ara A+ Gs-Rb1 group (500 μmol/L Ara A + 200 μmol/L Gs-Rb1 + 500 μmol/L CoCl₂), AICAR group [1 mmol/L 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) + 500 μmol/L CoCl₂], and AICAR+Gs-Rb1 group (1 mmol/L AICAR + 200 μmol/L Gs-Rb1 + 500 μmol/L CoCl₂). Cells were treated for 12 h and cell viability was determined by methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay and cardiac troponin I (cTnI) levels were detected by enzyme-linked immunosorbent assay (ELISA). AMPK activity was assessed by 2',7'-dichlorofluorescein diacetate (DCFH-DA) ELISA assay. The protein expressions of Atg4B, Atg5, Atg6, Atg7, microtubule-associated protein 1A/1B-light chain 3 (LC3), P62, and active-cathepsin B were measured by Western blot.

RESULTS

Gs-Rb1 significantly improved the cell viability of hypoxia cardiomyocytes (P<0.01). However, the viability of hypoxia-treated cardiomyocytes was significantly inhibited by Ara A (P<0.01). Gs-Rb1 increased the AMPK activity of hypoxia-treated cardiomyocytes. The AMPK activity of hypoxia-treated cadiomyocytes was inhibited by Ara A (P<0.01) and was not affected by AICAR =0.983). Gs-Rb1 up-regulated Atg4B, Atg5, Beclin-1, Atg7, LC3B II, the LC3B II/I ratio and cathepsin B activity of hypoxia cardiomyocytes (P<0.05), each of these protein levels was significantly enhanced by Ara A (all P<0.01), but was not affected by AICAR (all P>0.05). Gs-Rb1 significantly down-regulated P62 levels of hypoxic cardiomyocytes (P<0.05). The P62 levels of hypoxic cardiomyocytes were inhibited by Ara A (P<0.05) and were not affected by AICAR (P=0.871).

CONCLUSION

Gs-Rb1 may improve the viability of hypoxia cardiomyocytes by ameliorating cell autophagy via the upregulation of AMPK pathway.

Role of reciprocal interaction between autophagy and endoplasmic reticulum stress in apoptosis of human bronchial epithelial cells induced by cigarette smoke extract

Endoplasmic reticulum stress (ERS)-induced apoptosis of airway epithelial cells plays an important role in the pathogenesis of chronic obstructive pulmonary disease (COPD). Furthermore, autophagy is closely related to ERS under apoptosis. Here, this study aimed to investigate the role of the reciprocal interaction between autophagy and ERS in the cigarette smoke extract (CSE)-induced apoptosis of human bronchial epithelial (HBE) cells. Cell apoptosis was detected by flow cytometry analysis. Protein expression was examined by Western blot. The mRNA expression was detected using real-time quantitative reverse transcription PCR (qRT-PCR). The results showed that CSE treatment induced apoptosis, autophagy, and expression of ERS-related proteins in HBE cells. Furthermore, autophagy inhibition by 3-MA significantly decreased protein expression of GRP78, p-PERK, and p-eIF2α and increased CHOP, ATF4, and caspase-4, whereas ERS inhibition by 4-PBA led to autophagy suppression. Moreover, the CSE-induced autophagy was diminished by knockdown of GRP78, PERK, or eIF2α but enhanced by knockdown of ATF4 or CHOP; however, the CSE-induced HBE apoptosis was enhanced by knockdown of GRP78, PERK, or eIF2α but was attenuated by knockdown of ATF4 or CHOP. Additionally, both sodium hydrosulfide (NaHS) and melatonin attenuated the CSE-induced apoptosis, enhanced the CSE-induced autophagy, increased GRP78, p-PERK, and p-eIF2α, and decreased CHOP, ATF4, and caspase-4, via SIRT1/ORP150 pathway. Collectively, this study provided evidence about the role of the reciprocal interaction between autophagy and ERS in CSE-induced apoptosis of HBE cells. © 2018 IUBMB Life, 71(1):66-80, 2019.

Proteomic Profiling of Human Hepatic Stellate Cell Line LX2 Responses to Irradiation and TGF-β1

Hepatic stellate cells (HSCs) are the main target of radiation damage and primarily contribute to the development of radiation-induced liver fibrosis. However, the molecular events underlying the radiation-induced activation of HSCs are not fully elucidated. In the present study, human HSC line LX2 was treated with X-ray irradiation and/or TGF-β1, and profibrogenic molecules were evaluated. The iTRAQ LC-MS/MS technology was performed to identify global protein expression profiles in LX2 following exposure to different stimuli. Irradiation or TGF-β1 alone increased expression of α-SMA, collagen 1, CTGF, PAI-1, and fibronectin. Irradiation and TGF-β1 cooperatively induced expression of these profibrotic markers. In total, 102, 137, 155 dysregulated proteins were identified in LX2 cell samples affected by irradiation, TGF-β1, or cotreatment, respectively. Bioinformatic analyses showed that the three differentially expressed protein sets were commonly associated with cell cycle and protein processing in endoplasmic reticulum. The expression of a set of proteins was properly validated: CDC20, PRC1, KIF20A, CCNB1, SHCBP, TACC3 were upregulated upon irradiation or irradiation and TGF-β1 costimulation, whereas SPARC and THBS1 were elevated by TGF-β1 or TGF-β1 plus irradiation treatment. Furthermore, CDC20 inhibition suppressed expression of profibrotic markers in irradiated and TGF-β1-stimulated LX2 cells. Detailed data on potential molecular mechanisms causing the radiation-induced HSC activation presented here would be instrumental in developing radiotherapy strategies that minimize radiation-induced liver fibrosis.

A Flow Cytometric Study of ER Stress and Autophagy

The mechanistic link between ER stress, autophagy, and resultant cell death was investigated by the use of drugs Thapsigargin (Tg) and Chloroquine (CQ) with prior induction and or blockade of autophagy and apoptosis which modulated the ER stress response and resultant form of cell death. All these biological processes can be measured flow cytometrically allowing the determination of the type of cell death, G₁ cell cycle arrest, cell cycle dependent measurement of ER stress transducer PERK, misfolded proteins, reticulophagy, and autophagy marker LC3B. Jurkat cells after Tg or CQ treatment became necrotic and apoptotic, showed G₁ cell cycle arrest, autophagy, and ER stress. Prior induction of autophagy before ER stress increased levels of necrotic and apoptotic cell death. Autophagy was further up-regulated, while PERK was reduced or abrogated. CQ showed reduced levels of misfolded proteins and reticulophagy, while Tg showed no change in misfolded protein levels but increased reticulophagy and thus displayed more ER stress. Prior blockade of apoptosis before induction of ER stress resulted in cell survival except with high Tg levels which induced necrosis. Autophagy was up-regulated with modulation of PERK and reticulophagy levels with an abrogation of the misfolded protein response. Blockade of apoptosis with induction of autophagy before ER stress showed death by necrosis with high dose drugs and cell survival with low doses of drugs. CQ induced reduced levels G₁ cell cycle arrest while it was maintained with Tg. Autophagy was also maintained with reduced levels of ER stress. These data demonstrates a profound link between the processes of ER stress, autophagy, and the resultant form of cell death all of which can be modulated depending upon the sequence and concentration of drugs employed. © 2018 International Society for Advancement of Cytometry.

Apatinib-induced protective autophagy and apoptosis through the AKT-mTOR pathway in anaplastic thyroid cancer

Apatinib, an inhibitor of vascular endothelial growth factor receptor-2, has been shown to promote anti-cancer action across a wide range of malignancies, including gastric, lung, and breast cancers. Our previous study showed that apatinib increases apoptosis in anaplastic thyroid carcinoma (ATC), but the direct functional mechanism of tumor lethality mediated by apatinib is still unknown. In this study, we demonstrated that apatinib induced both autophagy and apoptosis in human ATC cells through downregulation of p-AKT and p-mTOR signals via the AKT/mTOR pathway. Moreover, inhibition of apatinib-induced autophagy increased apatinib-induced apoptosis in ATC cells, and additional tumor suppression was critically produced by the combination of apatinib and the autophagy inhibitor chloroquine in vivo and in vitro. These findings showed that both autophagy and AKT/mTOR signals were engaged in ATC cell death evoked by apatinib. ATC patients might benefit from the new anti-cancer drug, and molecular targeted treatment in combination with autophagy inhibitors shows promise as a treatment improvement.

Radiation, inflammation and the immune response in cancer

Radiation is an important component of cancer treatment with more than half of all patients receive radiotherapy during their cancer experience. While the impact of radiation on tumour morphology is routinely examined in the pre-clinical and clinical setting, the impact of radiation on the tumour microenvironment and more specifically the inflammatory/immune response is less well characterised. Inflammation is a key contributor to short- and long-term cancer eradication, with significant tumour and normal tissue consequences. Therefore, the role of radiation in modulating the inflammatory response is highly topical given the current wave of targeted and immuno-therapeutic treatments for cancer. This review provides a general overview of how radiation modulates the inflammatory and immune response—(i) how radiation induces the inflammatory/immune system, (ii) the cellular changes that take place, (iii) how radiation dose delivery affects the immune response, and (iv) a discussion on research directions to improve patient survival, reduce side effects, improve quality of life, and reduce financial costs in the immediate future. Harnessing the benefits of radiation on the immune response will enhance its maximal therapeutic benefit and reduce radiation-induced toxicity.

ER stress and genomic instability induced by gamma radiation in mice primary cultured glial cells

Ionizing radiation induces various pathophysiological conditions by altering central nervous system (CNS) homeostasis, leading to neurodegenerative diseases. However, the potential effect of ionizing radiation response on cellular physiology in glial cells is unclear. In the present study, micronucleus test, comet assay, and RT-PCR were performed to investigate the potential effect of gamma radiation in cultured oligodendrocytes and astrocytes with respect to genomic instability, Endoplasmic Reticulum (ER) stress, and inflammation. Further, we studied the effect of alteration in ER stress specific gene expression in cortex post whole body radiation in mice. Results showed that exposure of gamma radiation of 2Gy in-vitro cultured astrocytes and oligodendrocytes and 7Gy in-vivo induced ER stress and Inflammation along with profuse DNA damage and Chromosomal abnormality. Additionally, we observed downregulation of myelin basic protein levels in cultured oligodendrocytes exposed to radiation. The present data suggests that ER stress and pro inflammatory cytokines serve as the major players in inducing glial cell dysfunction post gamma irradiation along with induction of genomic instability. Taken together, these results indicate that ER stress, DNA damage, and inflammatory pathways may be critical events leading to glial cell dysfunction and subsequent cell death following exposure to ionizing radiation.

Calcifying nanoparticles induce cytotoxicity mediated by ROS-JNK signaling pathways

Calcifying nanoparticles (CNPs) play an important role in kidney stone formation, but the mechanism(s) are unclear. CNPs were isolated and cultured from midstream urine of patients with kidney stones. CNP morphology and characteristics were examined by electron microscopy and electrophoresis analysis. Chemical composition was analyzed using energy-dispersive X-ray microanalysis and Western blotting. Human renal proximal convoluted tubule cell (HK-2) cultures were exposed to CNPs for 0, 12 and 72 h, and production of reactive oxygen species (ROS), mitochondrial membrane potential and apoptosis levels were evaluated. CNPs isolated from patients showed classical morphology, the size range of CNPs were 15-500 nm and negative charge; they were found to contain fetuin-A. Exposure of HK-2 cells to CNPs induced ROS production, decreased mitochondrial membrane potential and decreased cell viability. Transmission electron microscopy showed that CNPs can enter the cell by phagocytosis, and micrographs revealed signs of apoptosis and autophagy. CNPs increased the proportion of apoptotic cells, down-regulated Bcl-2 expression and up-regulated Bax expression. CNPs also up-regulated expression of LC3-B, Beclin-1and p-JNK.CNPs are phagocytosed by HK-2 cells, leading to autophagy, apoptosis and ROS production, in part through activation of JNK signaling pathways. ROS and JNK pathways may contribute to CNP-induced cell injury and kidney stone formation.

IRE1α deficiency promotes tumor cell death and eIF2α degradation through PERK dipendent autophagy

Sensors of endoplasmic reticulum (ER) stress function in a co-ordinated manner. In the present study we investigated the relationship between IRE1α and PERK pathways and survival of ER stressed U937 cells and BC3 cells. To this end, we investigated the effects of a subcytotoxic concentration of Tunicamycin in IRE1α-proficient and in IRE1α-deficient cells, by pharmacological inhibition with 4μ8 C or down-regulation by specific siRNA. We show that either type of IRE1α deficiency affects eIF2α expression and causes cell death increase. GSK2606414, a PERK inhibitor, and PERK specific siRNA prevent eIF2α down-regulation and restore cell survival. Degradation of this protein is due to autophagy, as it is prevented by bafilomycin and not by proteasome inhibition. Furthermore, activation of the autophagy flux is PERK dependent. Also the Cathepsin B inhibitor CA074 prevents eIF2α from degradation and reduces cell death. Altogether, these results show that IRE1α deficiency in ER stressed cells leads to an unexpected decrease of eIF2α, an important molecule for protein translation, through PERK dependent autophagy. Thus, IRE1/XBP1 inhibitors may represent a feasible strategy for tumor therapy, while PERK inhibitors may vanish the goal.

The TRPV1 ion channel regulates thymocyte differentiation by modulating autophagy and proteasome activity

Autophagy and the ubiquitin-proteasome system (UPS) control thymus cell homeostasis under resting and endoplasmic reticulum (ER) stress conditions. Several evidence support a cross-talk between UPS and autophagy; abrogation of UPS responses stimulates autophagy, and vice versa the inhibition of autophagy alters the UPS functions.

Herein, we found that TRPV1 activation induces ER stress, proteasome dysfunction and autophagy in thymocytes by modulating the expression of UPR-related genes. The TRPV1-mediated autophagy prevents the UPR activation by inhibiting BiP, Grp94 and ERp57 chaperone protein expression.

Thymocytes from TRPV1 KO mice display both autophagy and proteasome dysfunctions, resulting in increased apoptotic cells and reduced total DP thymocyte number.

In addition, positive selection of thymocytes triggered by anti-TCRβ/CD2 Ab-mediated costimulation induces apoptosis in thymocytes from TRPV1 KO as compared with WT mice. Stimulation of TRPV1 KO thymocytes with anti-TCRβ/CD2 mAbs modulates the expression of CD4 antigen on purified DP thymocytes, with reduced number of mature, single positive (SP) CD4 and increased number of immature SP CD4^low and DP CD4^lowCD8⁺ thymocytes, further supporting the intrinsic role of TRPV1 in T cell maturation. Finally, a reduction in CD8⁺ and CD4⁺ T cells is evidenced in the peripheral blood and spleen of TRPV1 KO, as compared with WT mice. Therapeutic strategy by restraining or stimulating the TRPV1 expression and functions in thymocytes might represent a new pharmacological tool in the regulation of different inflammatory T cell responses.

Stressed Out - Therapeutic Implications of ER Stress Related Cancer Research

The unfolded protein response (UPR) is an established and well-studied cellular response to the stress and serves to relieve the stress and reinstate cellular homeostasis. It occurs in the endoplasmic reticulum (ER), responsible of properly folding and processing of secretory and transmembrane proteins. It is extremely sensitive to alteration in homeostasis caused by various internal or external stressors which leads to accumulation of misfolded or unfolded proteins in the ER lumen. The UPR works by restoring protein homeostasis in the ER, either through the boosting of protein-folding and degradation capability or by assuaging the demands for such effects, and can cause the activation of cell death if unable to do so. Cancer cells have adapted to gain advantage from the UPR and keeping the cell away from apoptosis and promoting survival, including survival of the cancer stem cells and evading the immune system. Several components of the UPR are overexpressed in a malignant cell and are responsible for resistance from various chemotherapy options and radiotherapy, which are also responsible for causing ER stress and activating the UPR. In this review, we discuss the various ways in which UPR can aid different cancers to survive and evade therapy and highlight recent research, which exploits the UPR to confer sensitivity to these cancer cells against various drugs and radiation.

Pterostilbene exerts anticancer activity on non-small-cell lung cancer via activating endoplasmic reticulum stress

Pterostilbene (PT), the natural dimethylated analog of resveratrol (RSV), is a potent anticarcinogen for non-small-cell lung cancer (NSCLC), but its anti-NSCLC mechanisms remain unclear. In this study, we show that PT treatment time- and dose-dependently enhanced the endoplasmic reticulum stress (ERS) signaling (i.e., p-PERK, IRE1, ATF4, CHOP), thus decreasing the cell viability and inducing apoptosis in human PC9 and A549 NSCLC cell lines. Moreover, the decreased migratory and adhesive abilities, downregulation of intracellular glutathione (GSH) level, enhanced reactive oxygen species (ROS) generation, Caspase 3 activity and mitochondrial membrane depolarization were observed in NSCLC cells treated with PT. These effects were reversed by CHOP siRNA which inhibited the ERS signaling pathway, but were promoted by thapsigargin (a classical ERS inducer) in vitro. Besides, in vivo studies also verify that PT exerted anticancer activity by mobilizing ERS signaling and apoptosis-related proteins, and these effects were enhanced by thapsigargin. Therefore, ERS activation may represent a new mechanism of anti-NSCLC action by PT, and a novel therapeutic intervention for lung cancer.

The novel autophagy inhibitor elaiophylin exerts antitumor activity against multiple myeloma with mutant TP53 in part through endoplasmic reticulum stress-induced apoptosis

Elaiophylin is a natural compound and a novel and potent inhibitor of late stage autophagy with outstanding antitumor activity in human ovarian cancer cells. However, the possible biologic effects and functional linkage between elaiophylin and multiple myeloma (MM) have not been explored. This study aimed to assess the effect of elaiophylin on MM cells with mutant TP53 and the possible molecular mechanism. The results suggested that elaiophylin exerted anti-myeloma activity by inducing apoptosis and proliferation arrest. As expected, elaiophylin blocked autophagy flux in MM cells. Subsequently, persistent activation of endoplasmic reticulum (ER) stress was induced. Moreover, the apoptotic effect was to some extent attenuated by the ER stress inhibitor tauroursodeoxycholic acid (TUDCA). Further studies indicated that elaiophylin effectively suppressed MM cell growth without obvious side effects in zebrafish embryo and mouse xenograft models. Taken together, our data are the first to demonstrate that exposure of human MM cells with mutant TP53 to elaiophylin blocked autophagy flux and thus induced cell death, which partially involved ER stress-associated apoptosis. Targeted disruption of the cellular protein handling system by elaiophylin is therefore a promising therapeutic strategy for overcoming incurable MM, even when TP53 mutations are present.

PERM Hypothesis: The Fundamental Machinery Able to Elucidate the Role of Xenobiotics and Hormesis in Cell Survival and Homeostasis

In this article the Proteasome, Endoplasmic Reticulum and Mitochondria (PERM) hypothesis is discussed. The complex machinery made by three homeostatic mechanisms involving the proteasome (P), endoplasmic reticulum (ER) and mitochondria (M) is addressed in order to elucidate the beneficial role of many xenobiotics, either trace metals or phytochemicals, which are spread in the human environment and in dietary habits, exerting their actions on the mechanisms underlying cell survival (apoptosis, cell cycle regulation, DNA repair and turnover, autophagy) and stress response. The "PERM hypothesis" suggests that xenobiotics can modulate this central signaling and the regulatory engine made fundamentally by the ER, mitochondria and proteasome, together with other ancillary components such as peroxisomes, by acting on the energetic balance, redox system and macromolecule turnover. In this context, reactive species and stressors are fundamentally signalling molecules that could act as negative-modulating signals if PERM-mediated control is offline, impaired or dysregulated, as occurs in metabolic syndrome, degenerative disorders, chronic inflammation and cancer. Calcium is an important oscillatory input of this regulation and, in this hypothesis, it might play a role in maintaining the correct rhythm of this PERM modulation, probably chaotic in its nature, and guiding cells to a more drastic decision, such as apoptosis. The commonest effort sustained by cells is to maintain their survival balance and the proterome has the fundamental task of supporting this mechanism. Mild stress is probably the main stimulus in this sense. Hormesis is therefore re-interpreted in the light of this hypothetical model and that experimental evidence arising from flavonoid and hormesis reasearch.

Inhibiting autophagy with chloroquine enhances the anti-tumor effect of high-LET carbon ions via ER stress-related apoptosis

Energetic carbon ions (CI) offer great advantages over conventional radiations such as X- or γ-rays in cancer radiotherapy. High linear energy transfer (LET) CI can induce both endoplasmic reticulum (ER) stress and autophagy in tumor cells under certain circumstances. The molecular connection between ER stress and autophagy in tumor exposed to high-LET radiation and how these two pathways influence the therapeutic effect against tumor remain poorly understood. In this work, we studied the impact of autophagy and apoptosis induced by ER stress following high-LET CI radiation on the radiosensitivity of S180 cells both in vitro and in vivo. In the in vitro experiment, X-rays were also used as a reference radiation. Our results documented that the combination of CI radiation with chloroquine (CQ), a special autophagy inhibitor, produced more pronounced proliferation suppression in S180 cells and xenograft tumors. Co-treatment with CI radiation and CQ could block autophagy through the IRE1/JNK/Beclin-1 axis and enhance apoptotic cell death via the activation of C/EBP homologous protein (CHOP) by the IRE1 pathway rather than PERK in vitro and in vivo. Thus, our study indicates that inhibiting autophagy might be a promising therapeutic strategy in CI radiotherapy via aggravating the ER stress-related apoptosis.

Neuroprotective effects of Activin A on endoplasmic reticulum stress-mediated apoptotic and autophagic PC12 cell death

Activin A, a member of the transforming growth factor-beta superfamily, plays a neuroprotective role in multiple neurological diseases. Endoplasmic reticulum (ER) stress-mediated apoptotic and autophagic cell death is implicated in a wide range of diseases, including cerebral ischemia and neurodegenerative diseases. Thapsigargin was used to induce PC12 cell death, and Activin A was used for intervention. Our results showed that Activin A significantly inhibited morphological changes in thapsigargin-induced apoptotic cells, and the expression of apoptosis-associated proteins [cleaved-caspase-12, C/EBP homologous protein (CHOP) and cleaved-caspase-3] and biomarkers of autophagy (Beclin-1 and light chain 3), and downregulated the expression of thapsigargin-induced ER stress-associated proteins [inositol requiring enzyme-1 (IRE1), tumor necrosis factor receptor-associated factor 2 (TRAF2), apoptosis signal-regulating kinase 1 (ASK1), c-Jun N-terminal kinase (JNK) and p38]. The inhibition of thapsigargin-induced cell death was concentration-dependent. These findings suggest that administration of Activin A protects PC12 cells against ER stress-mediated apoptotic and autophagic cell death by inhibiting the activation of the IRE1-TRAF2-ASK1-JNK/p38 cascade.

The ATF6 pathway of the ER stress response contributes to enhanced viability in glioblastoma

Therapeutic resistance is a major barrier to improvement of outcomes for patients with glioblastoma. The endoplasmic reticulum stress response (ERSR) has been identified as a contributor to chemoresistance in glioblastoma; however the contributions of the ERSR to radioresistance have not been characterized. In this study we found that radiation can induce ER stress and downstream signaling associated with the ERSR. Induction of ER stress appears to be linked to changes in ROS balance secondary to irradiation. Furthermore, we observed global induction of genes downstream of the ERSR in irradiated glioblastoma. Knockdown of ATF6, a regulator of the ERSR, was sufficient to enhance radiation induced cell death. Also, we found that activation of ATF6 contributes to the radiation-induced upregulation of glucose regulated protein 78 (GRP78) and NOTCH1. Our results reveal ATF6 as a potential therapeutic target to enhance the efficacy of radiation therapy.

Different Roles of CHOP and JNK in Mediating Radiation-Induced Autophagy and Apoptosis in Breast Cancer Cells

Unfolded protein response (UPR) is comprised of complex and conserved stress pathways that function as a short-term adaptive mechanism to reduce levels of unfolded or misfolded proteins and maintain homeostasis in the endoplasmic reticulum (ER). UPR can be triggered by prolonged or persistent ER stress under many physiological or pathological conditions, including radiation exposure. Radiation-induced ER stress elicits autophagy and apoptosis in cancer cells, where C/EBP homologous protein (CHOP) and c-Jun NH2-terminal kinase (JNK) may play crucial roles. However, the specific mechanisms that regulate autophagy and apoptosis through CHOP and JNK after radiation exposure and how the balance of these activities determines the cellular radiosensitivity remain largely unclear. In this study, we found that exposure to X-ray radiation induced ER stress, UPR and high expression of CHOP and JNK. Furthermore, autophagy and apoptosis occurred in sequential order when breast cancer MDA-MB-231 and MCF-7 cells were exposed to X-ray radiation. CHOP gene knockdown with RNA interference inhibited autophagy and enhanced radiosensitivity in MDA-MB-231 cells, while impacting apoptosis and subsequently increasing radioresistance in MCF-7 cells. However, treatment with JNK inhibitor decreased autophagy while promoting apoptosis, thereby leading to radiosensitivity in both cell lines. Our results indicate that CHOP mediates radiation-induced autophagy and apoptosis in a cellular environment. Importantly, the functional consistency of regulating apoptosis and autophagy in these two irradiated breast cancer cell lines suggests that JNK may be more useful as a potential target for maximizing the efficacy of radiation therapy for breast cancers.

Radiation-induced autophagy promotes esophageal squamous cell carcinoma cell survival via the LKB1 pathway

Radiotherapy is an important treatment modality for esophageal cancer; however, the clinical efficacy of radiotherapy is limited by tumor radioresistance. In the present study, we explored the hypothesis that radiation induces tumor cell autophagy as a cytoprotective adaptive response, which depends on liver kinase B1 (LKB1) also known as serine/threonine kinase 11 (STK11). Radiation-induced Eca-109 cell autophagy was found to be dependent on signaling through the LKB1 pathway, and autophagy inhibitors that disrupted radiation-induced Eca-109 cell autophagy increased cell cycle arrest and cell death in vitro. Inhibition of autophagy also reduced the clonogenic survival of the Eca-109 cells. When treated with radiation alone, human esophageal carcinoma xenografts showed increased LC3B and p-LKB1 expression, which was decreased by the autophagy inhibitor chloroquine. In vivo inhibition of autophagy disrupted tumor growth and increased tumor apoptosis when combined with 6 Gy of ionizing radiation. In summary, our findings elucidate a novel mechanism of resistance to radiotherapy in which radiation-induced autophagy, via the LKB1 pathway, promotes tumor cell survival. This indicates that inhibition of autophagy can serve as an adjuvant treatment to improve the curative effect of radiotherapy.

Mitochondrial reactive oxygen species-mediated genomic instability in low-dose irradiated human cells through nuclear retention of cyclin D1

Mitochondria are associated with various radiation responses, including adaptive responses, mitophagy, the bystander effect, genomic instability, and apoptosis. We recently identified a unique radiation response in the mitochondria of human cells exposed to low-dose long-term fractionated radiation (FR). Such repeated radiation exposure inflicts chronic oxidative stresses on irradiated cells via the continuous release of mitochondrial reactive oxygen species (ROS) and decrease in cellular levels of the antioxidant glutathione. ROS-induced oxidative mitochondrial DNA (mtDNA) damage generates mutations upon DNA replication. Therefore, mtDNA mutation and dysfunction can be used as markers to assess the effects of low-dose radiation. In this study, we present an overview of the link between mitochondrial ROS and cell cycle perturbation associated with the genomic instability of low-dose irradiated cells. Excess mitochondrial ROS perturb AKT/cyclin D1 cell cycle signaling via oxidative inactivation of protein phosphatase 2A after low-dose long-term FR. The resulting abnormal nuclear accumulation of cyclin D1 induces genomic instability in low-dose irradiated cells.

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.

Anticipatory activation of the unfolded protein response by epidermal growth factor is required for immediate early gene expression and cell proliferation

The onco-protein epidermal growth factor (EGF) initiates a cascade that includes activation of the ERK and AKT signaling pathways and alters gene expression. We describe a new action of EGF-EGF receptor (EGFR), rapid anticipatory activation of the endoplasmic reticulum stress sensor, the unfolded protein response (UPR). Within 2 min, EGF elicits EGFR dependent activation of phospholipase C γ (PLCγ), producing inositol triphosphate (IP3), which binds to IP3 receptor (IP3R), opening the endoplasmic reticulum IP3R Ca(2+) channels, resulting in increased intracellular Ca(2+). This calcium release leads to transient and moderate activation of the IRE1α and ATF6α arms of the UPR, resulting in induction of BiP chaperone. Knockdown or inhibition of EGFR, PLCγ or IP3R blocks the increase in intracellular Ca(2+). While blocking the increase in intracellular Ca(2+) by locking the IP3R calcium channel with 2-APB had no effect on EGF activation of the ERK or AKT signaling pathways, it abolished the rapid EGF-mediated induction and repression of gene expression. Knockdown of ATF6α or XBP1, which regulate UPR-induced chaperone production, inhibited EGF stimulated cell proliferation. Supporting biological relevance, increased levels of EGF receptor during tumor progression were correlated with increased expression of the UPR gene signature. Anticipatory activation of the UPR is a new role for EGF. Since UPR activation occurs in <2 min, it is an initial cell response when EGF binds EGFR.

Effect of combined radiation injury on cell death and inflammation in skin

In the event of a nuclear disaster, the individuals proximal to the source of radiation will be exposed to combined radiation injury. As irradiation delays cutaneous repair, the purpose of this study was to elucidate the effect of combined radiation and burn injury (CRBI) on apoptosis and inflammation at the site of skin injury. Male C57Bl/6 mice were exposed to no injury, thermal injury only, radiation only (1 and 6 Gy) and CRBI (1 and 6 Gy) and euthanized at various times after for skin collection. TUNEL staining revealed that the CRBI 6 Gy group had a delayed and increased apoptotic response. This correlated with decreased recovery of live cells as compared to the other injuries. Similar response was observed when cleaved-caspase-3 immunohistochemical staining was compared between CRBI 6 Gy and thermal injury. TNFR1, caspase 8, Bax and IL-6 mRNA expression revealed that the higher CRBI group had delayed increase in mRNA expression as compared to thermal injury alone. RIPK1 mRNA expression and necrotic cell counts were delayed in the CRBI 6 Gy group to day 5. TNF-α and NFκB expression peaked in the CRBI 6 Gy group at day 1 and was much higher than the other injuries. Also, inflammatory cell counts in the CRBI 6 Gy group were lower at early time points as compared to thermal injury by itself. These data suggest that CRBI delays and exacerbates apoptosis and inflammation in skin as well as increases necrosis thus resulting in delayed wound healing.

Herp depletion inhibits zearalenone-induced cell death in RAW 264.7 macrophages

Herp is an endoplasmic reticulum (ER) membrane protein and strongly induced by the ER stress that not only participates in the unfolded protein response (UPR) under the ER stress, but also in cell autophagy under glucose starvation (GS). However, we do not know whether Herp plays any roles in other responses, such as zearalenone (ZEA). In this study, we constructed recombinant lentiviral vectors for Herp shRNA expression and generated stable Herp knockdown RAW 264.7 macrophages. Flow cytometry analysis showed Herp depletion could inhibit cell death induced by ZEA. Western blot analysis revealed that Herp depletion could up-regulate autophagy-related protein LC3-I conversion into LC3-II and the expression of ER stress-related protein CHOP. These results suggest that Herp depletion inhibits cell death by up-regulating autophagy.

ER stress: Autophagy induction, inhibition and selection

An accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER) leads to stress conditions. To mitigate such circumstances, stressed cells activate a homeostatic intracellular signaling network cumulatively called the unfolded protein response (UPR), which orchestrates the recuperation of ER function. Macroautophagy (hereafter autophagy), an intracellular lysosome-mediated bulk degradation pathway for recycling and eliminating wornout proteins, protein aggregates, and damaged organelles, has also emerged as an essential protective mechanism during ER stress. These 2 systems are dynamically interconnected, and recent investigations have revealed that ER stress can either stimulate or inhibit autophagy. However, the stress-associated molecular cues that control the changeover switch between induction and inhibition of autophagy are largely obscure. This review summarizes the crosstalk between ER stress and autophagy and their signaling networks mainly in mammalian-based systems. Additionally, we highlight current knowledge on selective autophagy and its connection to ER stress.