ER stress induced by ionising radiation in IEC-6 cells

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.

Expression of 3q Oncogene SEC62 Predicts Survival in Head and Neck Squamous Cell Carcinoma Patients Treated with Primary Chemoradiation

Primary chemoradiotherapy (CRT) is an established treatment option for locally advanced head and neck squamous cell carcinomas (HNSCC) usually combining intensity modified radiotherapy with concurrent platinum-based chemotherapy. Though the majority of patients can be cured with this regimen, treatment response is highly heterogeneous and can hardly be predicted. SEC62 represents a metastasis stimulating oncogene that is frequently overexpressed in various cancer entities and is associated with poor outcome. Its role in HNSCC patients undergoing CRT has not been investigated so far. A total of 127 HNSCC patients treated with primary CRT were included in this study. The median follow-up was 5.4 years. Pretherapeutic tissue samples of the primary tumors were used for immunohistochemistry targeting SEC62. SEC62 expression, clinical and histopathological parameters, as well as patient outcome, were correlated in univariate and multivariate survival analyses. High SEC62 expression correlated with a significantly shorter overall survival (p = 0.015) and advanced lymph node metastases (p = 0.024). Further significant predictors of poor overall and progression-free survival included response to therapy (RECIST1.1), nodal status, distant metastases, tobacco consumption, recurrence of disease, and UICC stage. In a multivariate Cox hazard proportional regression analysis, only SEC62 expression (p = 0.046) and response to therapy (p < 0.0001) maintained statistical significance as independent predictors of the patients' overall survival. This study identified SEC62 as an independent prognostic biomarker in HNSCC patients treated with primary CRT. The role of SEC62 as a potential therapeutic target and its interaction with radiation-induced molecular alterations in head and neck cancer cells should further be investigated.

Endoplasmic Reticulum Stress and Cancer: Could Unfolded Protein Response Be a Druggable Target for Cancer Therapy?

Unfolded protein response (UPR) is an adaptive response which is used for re-establishing protein homeostasis, and it is triggered by endoplasmic reticulum (ER) stress. Specific ER proteins mediate UPR activation, after dissociation from chaperone Glucose-Regulated Protein 78 (GRP78). UPR can decrease ER stress, producing an ER adaptive response, block UPR if ER homeostasis is restored, or regulate apoptosis. Some tumour types are linked to ER protein folding machinery disturbance, highlighting how UPR plays a pivotal role in cancer cells to keep malignancy and drug resistance. In this review, we focus on some molecules that have been revealed to target ER stress demonstrating as UPR could be a new target in cancer treatment.

Circulating T Cell Activation and Exhaustion Markers Are Associated With Radiation Pneumonitis and Poor Survival in Non-Small-Cell Lung Cancer

Introduction

Persistent inflammation and immune activation in the lungs are associated with adverse outcomes such as radiation pneumonitis (RP) and poor survival in non-small-cell lung cancer (NSCLC) patients. However, it is unknown how this is reflected by leukocyte activation markers in serum.

Objective

The aim was to evaluate the serum levels of activation of different leukocyte subsets and to examine those in relation to the pathogenesis of RP and survival in NSCLC.

Methods

We analyzed the serum levels of MPO, sCD25, sTIM-3, sPD-L1, sCD14, sCD163, CCL19 and CCL21 in 66 inoperable NSCLC patients with stage IA-IIIA disease. The patients were treated with stereotactic body radiation therapy (SBRT) or concurrent chemoradiation therapy (CCRT), followed by regular blood sampling for 12 months after treatment and for 5 years for survival.

Results

Nineteen (29%) patients developed RP, which occurred more frequently and earlier in patients receiving CCRT than in those receiving SBRT. Increases in sCD25, sTIM-3 and CCL21 levels were observed at the last 6 months of follow-up in patients who had RP after SBRT. Patients who had RP after CCRT had higher sTIM-3 levels during the first 3 months of follow-up. Baseline sCD25 was independently associated with both 2- and 5-year mortality outcomes, while baseline sTIM-3 was independently associated with 2-year mortality.

Conclusion

We showed that T cell activation and exhaustion markers such as sCD25 and sTIM-3 are enhanced in patients developing RP and are associated with poor survival in NSCLC.

Brain Damage and Patterns of Neurovascular Disorder after Ionizing Irradiation. Complications in Radiotherapy and Radiation Combined Injury

Exposure to ionizing radiation, mechanical trauma, toxic chemicals or infections, or combinations thereof (i.e., combined injury) can induce organic injury to brain tissues, the structural disarrangement of interactive networks of neurovascular and glial cells, as well as on arrays of the paracrine and systemic destruction. This leads to subsequent decline in cognitive capacity and decompensation of mental health. There is an ongoing need for improvement in mitigating and treating radiation- or combined injury-induced brain injury. Cranial irradiation per se can cause a multifactorial encephalopathy that occurs in a radiation dose- and time-dependent manner due to differences in radiosensitivity among the various constituents of brain parenchyma and vasculature. Of particular concern are the radiosensitivity and inflammation susceptibility of: 1. the neurogenic and oligodendrogenic niches in the subependymal and hippocampal domains; and 2. the microvascular endothelium. Thus, cranial or total-body irradiation can cause a plethora of biochemical and cellular disorders in brain tissues, including: 1. decline in neurogenesis and oligodendrogenesis; 2. impairment of the blood-brain barrier; and 3. ablation of vascular capillary. These changes, along with cerebrovascular inflammation, underlie different stages of encephalopathy, from the early protracted stage to the late delayed stage. It is evident that ionizing radiation combined with other traumatic insults such as penetrating wound, burn, blast, systemic infection and chemotherapy, among others, can exacerbate the radiation sequelae (and vice versa) with increasing severity of neurogenic and microvascular patterns of radiation brain damage.

Genome-wide translation patterns in gliomas: An integrative view

Gliomas are the most frequent tumors of the central nervous system (CNS) and include the highly malignant glioblastoma (GBM). Characteristically, gliomas have translational control deregulation related to overactivation of signaling pathways such as PI3K/AKT/mTORC1 and Ras/ERK1/2. Thus, mRNA translation appears to play a dominant role in glioma gene expression patterns. The, analysis of genome-wide translated transcripts, together known as the translatome, may reveal important information for understanding gene expression patterns in gliomas. This review provides a brief overview of translational control mechanisms altered in gliomas with a focus on the current knowledge related to the translatomes of glioma cells and murine glioma models. We present an integrative meta-analysis of selected glioma translatome data with the aim of identifying recurrent patterns of gene expression preferentially regulated at the level of translation and obtaining clues regarding the pathological significance of these alterations. Re-analysis of several translatome datasets was performed to compare the translatomes of glioma models with those of their non-tumor counterparts and to document glioma cell responses to radiotherapy and MNK modulation. The role of recurrently altered genes in the context of translational control and tumorigenesis are discussed.

Inhibition of Endoplasmic Reticulum Stress-Mediated Autophagy Enhances the Anticancer Effect of Iodine-125 Seed Radiation on Esophageal Squamous Cell Carcinoma

Autophagy has been reported to play a radioresistance role in high-dose-rate irradiation. However, its mechanisms and roles in continuous low-dose-rate (CLDR) irradiation have not been clearly understood. Iodine-125 (I-125) seed brachytherapy is a modality of CLDR irradiation and has been used in the treatment of various cancers. In this study, we investigated the mechanisms and roles of autophagy induced by I-125 seed radiation in human esophageal squamous cell carcinoma (ESCC) cell lines (Eca-109 and EC-109) and a xenograft mouse model. The results of this work showed that I-125 seed radiation induced a dose-dependent increase in autophagy in both cell lines. In Eca-109 cells, I-125 seed radiation-induced endoplasmic reticulum (ER) stress, manifesting as the increased levels of intracellular Ca2+ and Grp78/BiP, and activated PERK-eIF2α, IRE1, and ATF6 pathways of the unfolded protein response. Knockdown of PERK led to the decreased expression of autophagy marker, LC3B-II. Inhibition of autophagy by chloroquine or knockdown of ATG5 enhanced I-125 seed radiation-induced cell proliferation inhibition and apoptosis. Interestingly, chloroquine did not aggravate ER stress but promoted apoptosis via the mitochondrial pathway. The animal experiment showed that inhibition of autophagy by chloroquine improved the efficacy of I-125 seed radiation. In summary, our data demonstrate that I-125 seed CLDR radiation induces ER stress-mediated autophagy in ESCC. Autophagy plays a pro-survival role in I-125 seed CLDR irradiation, and chloroquine is a potential candidate for use in combination therapy with I-125 seed radiation treatment to improve efficacy against ESCC.

Radiation-induced lung toxicity - cellular and molecular mechanisms of pathogenesis, management, and literature review

Lung, breast, and esophageal cancer represent three common malignancies with high incidence and mortality worldwide. The management of these tumors critically relies on radiotherapy as a major part of multi-modality care, and treatment-related toxicities, such as radiation-induced pneumonitis and/or lung fibrosis, are important dose limiting factors with direct impact on patient outcomes and quality of life. In this review, we summarize the current understanding of radiation-induced pneumonitis and pulmonary fibrosis, present predictive factors as well as recent diagnostic and therapeutic advances. Novel candidates for molecularly targeted approaches to prevent and/or treat radiation-induced pneumonitis and pulmonary fibrosis are discussed.

Lipids in the tumor microenvironment: From cancer progression to treatment

Over the past decade, the study of metabolic abnormalities in cancer cells has risen dramatically. Cancer cells can thrive in challenging environments, be it the hypoxic and nutrient-deplete tumor microenvironment or a distant tissue following metastasis. The ways in which cancer cells utilize lipids are often influenced by the complex interactions within the tumor microenvironment and adjacent stroma. Adipocytes can be activated by cancer cells to lipolyze their triglyceride stores, delivering secreted fatty acids to cancer cells for uptake through numerous fatty acid transporters. Cancer-associated fibroblasts are also implicated in lipid secretion for cancer cell catabolism and lipid signaling leading to activation of mitogenic and migratory pathways. As these cancer-stromal interactions are exacerbated during tumor progression, fatty acids secreted into the microenvironment can impact infiltrating immune cell function and phenotype. Lipid metabolic abnormalities such as increased fatty acid oxidation and de novo lipid synthesis can provide survival advantages for the tumor to resist chemotherapeutic and radiation treatments and alleviate cellular stresses involved in the metastatic cascade. In this review, we highlight recent literature that demonstrates how lipids can shape each part of the cancer lifecycle and show that there is significant potential for therapeutic intervention surrounding lipid metabolic and signaling pathways.

Measuring Cancer Hallmark Mediation of the TET1 Glioma Survival Effect with Linked Neural-Network Based Mediation Experiments

This paper examines the effect of TET1 expression on survival in glioma patients using open-access data from the Genomic Data Commons. A neural network-based survival model was built on expression data from a selection of genes most affected by TET1 knockdown with a median cross-validated survival concordance of 82.5%. A synthetic experiment was then conducted that linked two separately trained neural networks: a multitask model estimating cancer hallmark gene expression from TET1 expression, and a survival neural network. This experiment quantified the mediation of the TET1 survival effect through eight cancer hallmarks: apoptosis, cell cycle, cell death, cell motility, DNA repair, immune response, two phosphorylation pathways, and a randomized gene sets. Immune response, DNA repair, and apoptosis displayed greater mediation than the randomized gene set. Cell motility was inversely associated with only 12.5% mediated concordance. We propose the neural network linkage mediation experiment as an approach to collecting evidence of hazard mediation relationships with prognostic capacity useful for designing interventions.

The Unfolded Protein Response: Neutron-Induced Therapy Autophagy as a Promising Treatment Option for Osteosarcoma

Radiotherapy using high linear energy transfer (LET) radiation results in effectively killing tumor cells while minimizing dose (biological effective) to normal tissues to block toxicity. It is well known that high LET radiation leads to lower cell survival per absorbed dose than low LET radiation. High-linear energy transfer (LET) neutron treatment induces autophagy in tumor cells, but its precise mechanisms in osteosarcoma are unknown. Here, we investigated this mechanism and the underlying signaling pathways. Autophagy induction was examined in gamma-ray-treated KHOS/NP and MG63 osteosarcoma cells along with exposure to high-LET neutrons. The relationship between radiosensitivity and autophagy was assessed by plotting the cell surviving fractions against autophagy levels. Neutron treatment increased autophagy rates in irradiated KHOS/NP and MG63 cells; neutrons with high-LETs showed more effective inhibition than those with lower LET gamma-rays. To determine whether the unfolded protein response and Akt-mTOR pathways triggered autophagy, phosphorylated eIF2α and JNK levels, and phospho-Akt, phosphor-mTOR, and phospho-p70S6 levels were, respectively, investigated. High-LET neutron exposure inhibited Akt phosphorylation and increased Beclin 1 expression during the unfolded protein response, thereby enhancing autophagy. The therapeutic efficacy of high-LET neutron radiation was also assessed in vivo using an orthotopic mouse model. Neutron-irradiated mice showed reduced tumor growth without toxicity relative to gamma-ray-treated mice. The effect of high-LET neutron exposure on the expression of signaling proteins LC3, p-elF2a, and p-JNK was investigated by immunohistochemistry. Tumors in high-LET-neutron radiation-treated mice showed higher apoptosis rates, and neutron exposure significantly elevated LC3 expression, and increased p-elF2a and p-JNK expression levels. Overall, these results demonstrate that autophagy is important in radiosensitivity, cell survival, and cellular resistance against high-LET neutron radiation. This correlation between cellular radiosensitivity and autophagy may be used to predict radiosensitivity in osteosarcoma.

Cellular Stress Responses in Radiotherapy

Radiotherapy is one of the major cancer treatment strategies. Exposure to penetrating radiation causes cellular stress, directly or indirectly, due to the generation of reactive oxygen species, DNA damage, and subcellular organelle damage and autophagy. These radiation-induced damage responses cooperatively contribute to cancer cell death, but paradoxically, radiotherapy also causes the activation of damage-repair and survival signaling to alleviate radiation-induced cytotoxic effects in a small percentage of cancer cells, and these activations are responsible for tumor radio-resistance. The present study describes the molecular mechanisms responsible for radiation-induced cellular stress response and radioresistance, and the therapeutic approaches used to overcome radioresistance.

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-Induced Lung Injury (RILI)

Radiation pneumonitis (RP) and radiation fibrosis (RF) are two dose-limiting toxicities of radiotherapy (RT), especially for lung, and esophageal cancer. It occurs in 5-20% of patients and limits the maximum dose that can be delivered, reducing tumor control probability (TCP) and may lead to dyspnea, lung fibrosis, and impaired quality of life. Both physical and biological factors determine the normal tissue complication probability (NTCP) by Radiotherapy. A better understanding of the pathophysiological sequence of radiation-induced lung injury (RILI) and the intrinsic, environmental and treatment-related factors may aid in the prevention, and better management of radiation-induced lung damage. In this review, we summarize our current understanding of the pathological and molecular consequences of lung exposure to ionizing radiation, and pharmaceutical interventions that may be beneficial in the prevention or curtailment of RILI, and therefore enable a more durable therapeutic tumor response.

TET1 regulates DNA repair in human glial cells

Glioblastomas are the most aggressive of malignant brain cancers with a median patient survival of approximately 18 months. We recently demonstrated that Tet methylcytosine dioxygenase 1(TET1) is involved in cellular responses to ionizing radiation (IR) in glial-, glioblastoma-, and non-tumor-derived cells. This study used a lentiviral-mediated knockdown of TET1 to further dissect the contribution of TET1 to the DNA damage response in glial cell lines by evaluating its role in DNA repair. TET1-deficient glial cell lines displayed attenuated cytotoxicity compared to non-targeted knockdown after treatment with IR but these differences were not observed between control and TET1 deficient in response to inhibitors of Na⁺/K⁺-ATPase. Additionally, the percentage of glial cells displaying γH2A.x foci was greatly reduced in TET1-deficient glial cells compared to non-targeted knockdown conditions in response to IR and topoisomerase inhibitors. We also observed a lower percentage and a delay in 53BP1 foci formation, a marker of non-homologous end-joining, in response to IR and topoisomerase inhibitors in TET1-deficient glial cells. DNA-PK, another marker of non-homologous end-joining, was also lower in TET1-deficient glial cell lines. Interestingly, TET1-deficient glial cells displayed higher numbers of DNA strand breaks compared to control cells and repaired DNA breaks less efficiently in Comet assays. We suggest that attenuated DNA repair in TET1 deficient gliomas leads to genomic instability, which underlies poor patient survival.

β-Arrestin1-mediated decrease in endoplasmic reticulum stress impairs intestinal stem cell proliferation following radiation

Gastrointestinal toxicity limits the clinical application of abdominal and pelvic radiotherapy and currently has no effective treatment. Intestinal leucine-rich-repeat-containing GPCR 5 (Lgr5)-positive stem cell depletion and loss of proliferative ability due to radiation may be the primary factors causing intestinal injury following radiation. Here, we report the critical role of β-arrestin1 (βarr1) in radiation-induced intestinal injury. Intestinal βarr1 was highly expressed in radiation enteritis and in a radiation model. βarr1 knockout (KO) or knockdown mice exhibited increased proliferation in intestinal Lgr5+ stem cell, crypt reproduction, and survival following radiation. Unexpectedly, the beneficial effects of βarr1 deficiency on intestinal stem cells in response to radiation were compromised when the endoplasmic reticulum stress-related protein kinase RNA-like ER kinase (PERK)/eukaryotic initiation factor-2α (eIF2α) pathway was inhibited, and this result was further supported in vitro. Furthermore, we found that βarr1 knockdown with small interfering RNA significantly enhanced intestinal Lgr5⁺ stem cell proliferation after radiation via directly targeting PERK. βarr1 offers a promising target for mitigating radiation-induced intestinal injury.-Liu, Z., Jiang, J., He, Q., Liu, Z., Yang, Z., Xu, J., Huang, Z., Wu, B. β-Arrestin1-mediated decrease in endoplasmic reticulum stress impairs intestinal stem cell proliferation following radiation.

SMER28 is a mTOR-independent small molecule enhancer of autophagy that protects mouse bone marrow and liver against radiotherapy

Effective cytoprotectors that are selective for normal tissues could decrease radiotherapy and chemotherapy sequelae and facilitate the safe administration of higher radiation doses. This could improve the cure rates of radiotherapy for cancer patients. Autophagy is a cytoplasmic cellular process that is necessary for the clearance of damaged or aged proteins and organelles. It is a strong determinant of post-irradiation cell fate. In this study, we investigated the effect of the mTOR-independent small molecule enhancer of autophagy (SMER28) on mouse liver autophagy and post-irradiation recovery of mouse bone marrow and liver. SMER28 enhanced the autophagy flux and improved the survival of normal hepatocytes. This effect was specific for normal cells because SMER28 had no protective effect on hepatoma or other cancer cell line survival in vitro. In vivo subcutaneous administration of SMER28 protected mouse liver and bone marrow against radiation damage and facilitated survival of mice after lethal whole body or abdominal irradiation. These findings open a new field of research on autophagy-targeting radioprotectors with clinical applications in oncology, occupational, and space medicine.

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.

Transient PP2A inhibition alleviates normal tissue stem cell susceptibility to cell death during radiotherapy

Unintended outcomes of cancer therapy include ionizing radiation (IR)-induced stem cell depletion, diminished regenerative capacity, and accelerated aging. Stem cells exhibit attenuated DNA damage response (DDR) and are hypersensitive to IR, as compared to differentiated non-stem cells. We performed genomic discovery research to compare stem cells to differentiated cells, which revealed Phosphoprotein phosphatase 2A (PP2A) as a potential contributor to susceptibility in stem cells. PP2A dephosphorylates pATM, γH2AX, pAkt etc. and is believed to play dual role in regulating DDR and apoptosis. Although studied widely in cancer cells, the role of PP2A in normal stem cell radiosensitivity is unknown. Here we demonstrate that constitutively high expression and radiation induction of PP2A in stem cells plays a role in promoting susceptibility to irradiation. Transient inhibition of PP2A markedly restores DNA repair, inhibits apoptosis, and enhances survival of stem cells, without affecting differentiated non-stem and cancer cells. PP2Ai-mediated stem cell radioprotection was demonstrated in murine embryonic, adult neural, intestinal, and hematopoietic stem cells.

Transgenerational DNA Methylation Changes in Daphnia magna Exposed to Chronic γ Irradiation

Our aim was to investigate epigenetic changes in Daphnia magna after a 25-day chronic external γ irradiation (generation F0 exposed to 6.5 μGy·h^-1 or 41.3 mGy·h^-1) and their potential inheritance by subsequent recovering generations, namely, F2 (exposed as germline cells in F1 embryos) and F3 (the first truly unexposed generation). Effects on survival, growth, and reproduction were observed and DNA was extracted for whole-genome bisulfite sequencing in all generations. Results showed effects on reproduction in F0 but no effect in the subsequent generations F1, F2, and F3. In contrast, we observed significant methylation changes at specific CpG positions in every generation independent of dose rate, with a majority of hypomethylation. Some of these changes were shared between dose rates and between generations. Associated gene functions included gene families and genes that were previously shown to play roles during exposure to ionizing radiation. Common methylation changes detected between generations F2 and F3 clearly showed that epigenetic modifications can be transmitted to unexposed generations, most likely through the germline, with potential implications for environmental risk.

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.

CYP2E1 regulates the development of radiation-induced pulmonary fibrosis via ER stress- and ROS-dependent mechanisms

Radiation-induced pulmonary fibrosis (RIPF) is one of the most common side effects of lung cancer radiotherapy. This study was conducted to identify the molecular mechanism responsible for RIPF. We revealed that the transcriptional level of cytochrome P450 2E1 (CYP2E1) was elevated by examining expression profile analysis of RIPF mouse models. We also confirmed that CYP2E1 regulated levels of endoplasmic reticulum (ER) stress and reactive oxygen species (ROS) in alveolar epithelial type II (AE2) cells and lung fibroblasts. Inhibition of CYP2E1 via its siRNA or inhibitor significantly attenuated epithelial-to-mesenchymal transition and apoptosis of AE2 cells, as well as myofibroblast formation induced by radiation. Finally, the effects of a CYP2E1 inhibitor on development of RIPF were evaluated by in vivo studies. Taken together, the results of the present study suggest that CYP2E1 is an important mediator of RIPF development that functions by increasing cellular ER stress and ROS levels.

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.

Crosstalk between autophagy and intracellular radiation response (Review)

Autophagy induced by radiation is critical to cell fate decision. Evidence now sheds light on the importance of autophagy induced by cancer radiotherapy. Traditional view considers radiation can directly or indirectly damage DNA which can activate DNA damage the repair signaling pathway, a large number of proteins participating in DNA damage repair signaling pathway such as p53, ATM, PARP1, FOXO3a, mTOR and SIRT1 involved in autophagy regulation. However, emerging recent evidence suggests radiation can also cause injury to extranuclear targets such as plasma membrane, mitochondria and endoplasmic reticulum (ER) and induce accumulation of ceramide, ROS, and Ca2+ concentration which activate many signaling pathways to modulate autophagy. Herein we review the role of autophagy in radiation therapy and the potent intracellular autophagic triggers induced by radiation. We aim to provide a more theoretical basis of radiation-induced autophagy, and provide novel targets for developing cytotoxic drugs to increase radiosensitivity.

Endoplasmic reticulum stress, unfolded protein response and development of colon adenocarcinoma

When misfolded proteins accumulate in the endoplasmic reticulum (ER), the cell is said to experience ER stress. This triggers an unfolded protein response (UPR) to restore the balance between misfolded proteins and ER chaperones such as BiP. UPR signalling is required for the growth of many solid cancers. In chronic ER stress, factors including CHOP have been shown to mediate cell death. Colorectal adenocarcinoma arises due to progressive changes within pre-malignant lesions. Our aim was to test the hypothesis that the expression of BiP and CHOP correlates with the progression of those pre-malignant lesions.Eighty-one patients with colon neoplasms treated at Rouen University Hospital between January 1, 2003 and January 1, 2013 were randomly selected. The expression of BiP and CHOP was estimated by immunohistochemical staining of a tissue microarray generated from colon cores: normal tissue, low-grade and high-grade adenoma, invasive colon adenocarcinoma and lymph node metastasis of colon adenocarcinoma. In parallel, nine cases comprising areas from normal epithelium to dyplasia to invasive carcinoma and included in the TMA were analysed on whole sections.As colon epithelium shows increasing evidence of pre-malignant and then malignant changes, BiP expression significantly increases (p for trend < 0.001), whereas CHOP expression is attenuated (p for trend < 0.001).We identified a positive relationship between BiP expression and colon carcinogenesis, and a negative correlation for CHOP expression. These findings are consistent with a model in which ER stress accompanies oncogenesis and in which loss of proteins that mediate the toxicity of ER stress, such as CHOP, may facilitate tumorigenesis. This raises the exciting possibility that restoration of the negative feedback loop of UPR, if achievable, might antagonise the malignant process.

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.

Hypoxia-Inducible Factor-1: A Critical Player in the Survival Strategy of Stressed Cells

HIF-1 activation has been well known as an adaptive strategy to hypoxia. Recently it became clear that hypoxia was often accompanied by insufficient supply of glucose or amino acids as a common result of poor circulation that frequently occurs in solid tumors and ischemic lesions, creating a mixed nutrient insufficiency. In response to nutrient insufficiency, stressed cells elicit survival strategies including activation of AMPK and HIF-1 to cope with the stress. Particularly, in solid tumors, HIF-1 promotes cell survival and migration, stimulates angiogenesis, and induces resistance to radiation and chemotherapy. Interestingly, radiation and some chemotherapeutics are reported to trigger the activation of AMPK. Here we discuss the recent advances that may potentially link the stress responsive mechanisms including AMPK activation, ATF4 activation and the enhancement of Hsp70/Hsp90 function to HIF-1 activation. Potential implication and application of the stress-facilitated HIF-1 activation in solid tumors and ischemic disorders will be discussed. A better understanding of HIF-1 activation in cells exposed to stresses is expected to facilitate the design of therapeutic approaches that specifically modulate cell survival strategy.

Colorectal Carcinogenesis, Radiation Quality, and the Ubiquitin-Proteasome Pathway

Adult colorectal epithelium undergoes continuous renewal and maintains homeostatic balance through regulated cellular proliferation, differentiation, and migration. The canonical Wnt signaling pathway involving the transcriptional co-activator β-catenin is important for colorectal development and normal epithelial maintenance, and deregulated Wnt/β-catenin signaling has been implicated in colorectal carcinogenesis. Colorectal carcinogenesis has been linked to radiation exposure, and radiation has been demonstrated to alter Wnt/β-catenin signaling, as well as the proteasomal pathway involved in the degradation of the signaling components and thus regulation of β-catenin. The current review discusses recent progresses in our understanding of colorectal carcinogenesis in relation to different types of radiation and roles that radiation quality plays in deregulating β-catenin and ubiquitin-proteasome pathway (UPP) for colorectal cancer initiation and progression.

Carbon ions induce autophagy effectively through stimulating the unfolded protein response and subsequent inhibiting Akt phosphorylation in tumor cells

Heavy ion beams have advantages over conventional radiation in radiotherapy due to their superb biological effectiveness and dose conformity. However, little information is currently available concerning the cellular and molecular basis for heavy ion radiation-induced autophagy. In this study, human glioblastoma SHG44 and cervical cancer HeLa cells were irradiated with carbon ions of different linear energy transfers (LETs) and X-rays. Our results revealed increased LC3-II and decreased p62 levels in SHG44 and HeLa cells post-irradiation, indicating marked induction of autophagy. The autophagic level of tumor cells after irradiation increased in a LET-dependent manner and was inversely correlated with the sensitivity to radiations of various qualities. Furthermore, we demonstrated that high-LET carbon ions stimulated the unfolded protein response (UPR) and mediated autophagy via the UPR-eIF2α-CHOP-Akt signaling axis. High-LET carbon ions more severely inhibited Akt-mTOR through UPR to effectively induce autophagy. Thus, the present data could serve as an important radiobiological basis to further understand the molecular mechanisms by which high-LET radiation induces cell death.

Radioprotective effects of genistein on HL-7702 cells via the inhibition of apoptosis and DNA damage

Radiation induced normal tissue damage is the most important limitation for the delivery of a high potentially curative radiation dose. Genistein (GEN), one of the main soy isoflavone components, has drawn wide attention for its bioactivity in alleviating radiation damage. However, the effects and molecular mechanisms underlying the radioprotective effects of GEN remain unclear. In the present study, we showed that low concentration of GEN (1.5 µM) protected L-02 cells against radiation damage via inhibition of apoptosis, alleviation of DNA damage and chromosome aberration, down-regulation of GRP78 and up-regulation of HERP, HUS1 and hHR23A. In contrast, high concentration of GEN (20 µM) demonstrated radiosensitizing characteristics through the promotion of apoptosis and chromosome aberration, impairment of DNA repair, up-regulation of GRP78, and down-regulation of HUS1, SIRT1, RAD17, RAD51 and RNF8. These findings shed light on using low, but not high-concentration GEN, as a potential candidate for adjuvant therapy to alleviate radiation-induced injuries to human recipients of ionizing radiation.

Targeting the endoplasmic reticulum mediates radiation sensitivity in colorectal cancer

BACKGROUND

Radiotherapy is an established treatment modality for early and locally advanced rectal cancer as part of short course radiotherapy and long course chemoradiotherapy. The unfolded protein response (UPR) is a cellular stress response pathway often activated in human solid tumours which has been implicated in resistance to both chemotherapy and radiotherapy. This research has investigated whether the UPR pathway is upregulated in ex-vivo samples of human colorectal cancer and characterised the interaction between radiotherapy and UPR activation in two human colorectal cancer cell lines in vitro.

METHODS

In vitro UPR expression was determined in response to clinical doses of radiotherapy in both the human colorectal adenocarcinoma (HT-29) cell line and a radio-resistant clone (HT-29R) using western blotting and quantitative polymerase chain reaction. The UPR was induced using a glucose deprivation culture technique before irradiation and radiosensitivity assessed using a clonogenic assay. Ex-vivo human colorectal cancer tissue was immuno-histochemically analysed for expression of the UPR marker glucose regulated protein 78 (GRP-78).

RESULTS

The UPR was strongly up regulated in ex-vivo human colorectal tumours with 36 of 50 (72.0%) specimens demonstrating moderate to strong staining for the classic UPR marker GRP-78. In vitro, therapeutic doses of radiotherapy did not induce UPR activation in either radiosensitive or radioresistant cell lines. UPR induction caused significant radiosensitisation of the radioresistant cell line (HT-29R SF2Gy=0.90 S.E.M. +/-0.08; HT-29RLG SF2Gy=0.69 S.E.M. +/-0.050).

CONCLUSION

This suggests that UPR induction agents may be potentially useful response modifying agents in patients undergoing therapy for colorectal cancer.

Protracted Oxidative Alterations in the Mechanism of Hematopoietic Acute Radiation Syndrome

The biological effects of high-dose total body ionizing irradiation [(thereafter, irradiation (IR)] are attributed to primary oxidative breakage of biomolecule targets, mitotic, apoptotic and necrotic cell death in the dose-limiting tissues, clastogenic and epigenetic effects, and cascades of functional and reactive responses leading to radiation sickness defined as the acute radiation syndrome (ARS). The range of remaining and protracted injuries at any given radiation dose as well as the dynamics of post-IR alterations is tissue-specific. Therefore, functional integrity of the homeostatic tissue barriers may decline gradually within weeks in the post-IR period culminating with sepsis and failure of organs and systems. Multiple organ failure (MOF) leading to moribundity is a common sequela of the hemotapoietic form of ARS (hARS). Onset of MOF in hARS can be presented as “two-hit phenomenon” where the “first hit” is the underlying consequences of the IR-induced radiolysis in cells and biofluids, non-septic inflammation, metabolic up-regulation of pro-oxidative metabolic reactions, suppression of the radiosensitive hematopoietic and lymphoid tissues and the damage to gut mucosa and vascular endothelium. While the “second hit” derives from bacterial translocation and spread of the bacterial pathogens and inflammagens through the vascular system leading to septic inflammatory, metabolic responses and a cascade of redox pro-oxidative and adaptive reactions. This sequence of events can create a ground for development of prolonged metabolic, inflammatory, oxidative, nitrative, and carbonyl, electrophilic stress in crucial tissues and thus exacerbate the hARS outcomes. With this perspective, the redox mechanisms, which can mediate the IR-induced protracted oxidative post-translational modification of proteins, oxidation of lipids and carbohydrates and their countermeasures in hARS are subjects of the current review. Potential role of ubiquitous, radioresistant mesenchymal stromal cells in the protracted responses to IR and IR-related septicemia is also discussed.

X-ray-induced changes in the expression of inflammation-related genes in human peripheral blood

Using quantitative real-time polymerase chain reaction (PCR) array, we explored and compared the expression changes of inflammation-related genes in human peripheral blood irradiated with 0.5, 3, and 10 Gy doses of X-rays 24 h after exposure. Results indicated that the expression of 62 out of 84 genes was significantly altered after X-ray radiation. Among these 62 genes, 35 (such as TNFSF4) are known to be associated with radiation response, but others are novel. At a low radiation dose (0.5 Gy), 9 genes were up-regulated and 19 were down-regulated. With further increased dose to 3 Gy, 8 unique genes were up-regulated and 19 genes were down-regulated. We also identified 48 different genes that were differentially expressed significantly after 10 Gy of irradiation, and among these transcripts, up-regulated genes accounted for only one-third (16 genes) of the total. Of the 62 genes, 31 were significantly altered only at a specific dose, and a total of 10 genes were significantly expressed at all 3 doses. The dose- and time-dependent expression of CCL2 was confirmed by quantitative real-time reverse-transcription PCR. A number of candidate genes reported herein may be useful molecular biomarkers of radiation exposure in human peripheral blood.

The unfolded protein response as a target for cancer therapy

Various physiological and pathological conditions generate an accumulation of misfolded proteins in the endoplasmic reticulum (ER). This results in ER stress followed by a cellular response to cope with this stress and restore homeostasis: the unfolded protein response (UPR). Overall, the UPR leads to general translational arrest and the induction of specific factors to ensure cell survival or to mediate cell death if the stress is too severe. In multiple cancers, components of the UPR are overexpressed, indicating increased dependence on the UPR. In addition, the UPR can confer resistance to anti-cancer treatment. Therefore, modification of the UPR should be explored for its anti-cancer properties. This review discusses factors associated with the UPR that represent potential therapeutic targets.

Chemical chaperones reduce ionizing radiation-induced endoplasmic reticulum stress and cell death in IEC-6 cells

Radiotherapy, which is one of the most effective approaches to the treatment of various cancers, plays an important role in malignant cell eradication in the pelvic area and abdomen. However, it also generates some degree of intestinal injury. Apoptosis in the intestinal epithelium is the primary pathological factor that initiates radiation-induced intestinal injury, but the mechanism by which ionizing radiation (IR) induces apoptosis in the intestinal epithelium is not clearly understood. Recently, IR has been shown to induce endoplasmic reticulum (ER) stress, thereby activating the unfolded protein response (UPR) signaling pathway in intestinal epithelial cells. However, the consequences of the IR-induced activation of the UPR signaling pathway on radiosensitivity in intestinal epithelial cells remain to be determined. In this study, we investigated the role of ER stress responses in IR-induced intestinal epithelial cell death. We show that chemical ER stress inducers, such as tunicamycin or thapsigargin, enhanced IR-induced caspase 3 activation and DNA fragmentation in intestinal epithelial cells. Knockdown of Xbp1 or Atf6 with small interfering RNA inhibited IR-induced caspase 3 activation. Treatment with chemical chaperones prevented ER stress and subsequent apoptosis in IR-exposed intestinal epithelial cells. Our results suggest a pro-apoptotic role of ER stress in IR-exposed intestinal epithelial cells. Furthermore, inhibiting ER stress may be an effective strategy to prevent IR-induced intestinal injury.

Assessment of ER Stress and autophagy induced by ionizing radiation in both radiotherapy patients and ex vivo irradiated samples

Acute radiation leads to several toxic clinical states and triggers some molecular pathways. To shed light on molecular mechanisms triggered by ionizing radiation (IR), we examined the expression profiles of endoplasmic reticulum (ER) stress and autophagy-related genes in individuals who were exposed to IR. Blood samples were collected from 50 cancer patients before radiotherapy and on the 5th, 15th, and 25th days of the treatment. Peripheral blood samples from 10 healthy volunteers were also obtained for ex vivo irradiation, divided into five and irradiated at a rate of 373 kGy/h to 0, 0.1, 0.5, 1, and 3Gy γ-rays using a constant gamma source. GRP78, ATG5, LC3, ATF4, XBP1, and GADD153 genes were analyzed by quantitative real-time polymerase chain reaction (QRT-PCR) using beta 2 microglobulin (B2M) and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) as references. In both groups, expressions of the selected genes have increased. It can be concluded that IR induces ER stress and related authophagy pathway in the peripheral lymphocyte cells proportionally by dose.

Ionizing radiation activates PERK/eIF2α/ATF4 signaling via ER stress-independent pathway in human vascular endothelial cells

PURPOSE

Perturbations in protein folding induce endoplasmic reticulum (ER) stress, which elicits coordinated response, namely the unfolded protein response (UPR), to cope with the accumulation of misfolded proteins in ER. In this study, we characterized mechanisms underlying ionizing radiation (IR)-induced UPR signaling pathways.

MATERIALS AND METHODS

We analyzed alterations in UPR signaling pathways in human umbilical vein endothelial cells (HUVEC) and human coronary artery endothelial cells (HCAEC) irradiated with 15 Gy IR.

RESULTS

IR selectively activated the eIF2α/ATF4 branch of the UPR signaling pathway, with no alterations in the IRE1 and ATF6 branches in HUVEC and HCAEC. Phosphorylation of PERK was enhanced in response to IR, and the IR-induced activation of the eIF2α/ATF4 signaling pathway was completely inhibited by PERK knockdown with siRNA. Surprisingly, chemical chaperones, which inhibit the formation of misfolded proteins and sequential protein aggregates to reduce ER stress, failed to prevent the IR-induced phosphorylation of PERK and the subsequent activation of the eIF2α/ATF4 signaling pathway.

CONCLUSIONS

PERK mediates the IR-induced selective activation of the eIF2α/ATF4 signaling pathway, and the IR-induced activation of PERK/eIF2α/ATF4 signaling in human vascular endothelial cells is independent of alterations in protein-folding homeostasis in the ER.

Dissecting the molecular mechanism of ionizing radiation-induced tissue damage in the feather follicle

Ionizing radiation (IR) is a common therapeutic agent in cancer therapy. It damages normal tissue and causes side effects including dermatitis and mucositis. Here we use the feather follicle as a model to investigate the mechanism of IR-induced tissue damage, because any perturbation of feather growth will be clearly recorded in its regular yet complex morphology. We find that IR induces defects in feather formation in a dose-dependent manner. No abnormality was observed at 5 Gy. A transient, reversible perturbation of feather growth was induced at 10 Gy, leading to defects in the feather structure. This perturbation became irreversible at 20 Gy. Molecular and cellular analysis revealed P53 activation, DNA damage and repair, cell cycle arrest and apoptosis in the pathobiology. IR also induces patterning defects in feather formation, with disrupted branching morphogenesis. This perturbation is mediated by cytokine production and Stat1 activation, as manipulation of cytokine levels or ectopic Stat1 over-expression also led to irregular feather branching. Furthermore, AG-490, a chemical inhibitor of Stat1 signaling, can partially rescue IR-induced tissue damage. Our results suggest that the feather follicle could serve as a useful model to address the in vivo impact of the many mechanisms of IR-induced tissue damage.

Characterization of H460R, a Radioresistant Human Lung Cancer Cell Line, and Involvement of Syntrophin Beta 2 (SNTB2) in Radioresistance

A radioresistant cell line was established by fractionated ionizing radiation (IR) and assessed by a clonogenic assay, flow cytometry, and Western blot analysis, as well as zymography and a wound healing assay. Microarray was performed to profile global expression and to search for differentially expressed genes (DEGs) in response to IR. H460R cells demonstrated increased cell scattering and acidic vesicular organelles compared with parental cells. Concomitantly, H460R cells showed characteristics of increased migration and matrix metalloproteinase activity. In addition, H460R cells were resistant to IR, exhibiting reduced expression levels of ionizing responsive proteins (p-p53 and γ-H2AX); apoptosis-related molecules, such as cleaved poly(ADP ribose) polymerase; and endoplasmic reticulum stress-related molecules, such as glucose-regulated protein (GRP78) and C/EBP-homologous protein compared with parental cells, whereas the expression of anti-apoptotic X-linked inhibitor of apoptosis protein was increased. Among DEGs, syntrophin beta 2 (SNTB2) significantly increased in H460R cells in response to IR. Knockdown of SNTB2 by siRNA was more sensitive than the control after IR exposure in H460, H460R, and H1299 cells. Our study suggests that H460R cells have differential properties, including cell morphology, potential for metastasis, and resistance to IR, compared with parental cells. In addition, SNTB2 may play an important role in radioresistance. H460R cells could be helpful in in vitro systems for elucidating the molecular mechanisms of and discovering drugs to overcome radioresistance in lung cancer therapy.

The PERK/ATF4/LAMP3-arm of the unfolded protein response affects radioresistance by interfering with the DNA damage response

BACKGROUND AND PURPOSE

Lysosome-associated membrane protein 3 (LAMP3) is induced by the PKR-like ER kinase (PERK)/activating transcription factor 4 (ATF4)-arm of the unfolded protein response (UPR) during hypoxia. LAMP3 has prognostic value in breast cancer patients treated with radiotherapy. Here, we specifically investigated the role of the PERK/ATF4/LAMP3-arm in the radiation response of breast cancer cells.

MATERIAL AND METHODS

Radiosensitivity of breast cancer cells was examined after siRNA-mediated knockdown of PERK, ATF4 and LAMP3. Activation of DNA damage repair proteins was evaluated by Western blotting and immunocytochemistry.

RESULTS

Knockdown of the PERK/ATF4/LAMP3-arm and chemical inhibition of PERK could radiosensitise MDA-MB-231 cells significantly. Western blot analysis of several DNA damage repair proteins showed that LAMP3 knockdowns had an attenuated DNA damage response after radiation compared to controls. γ-H2AX foci analysis revealed that LAMP3 knockdowns had a reduced number of positive cells after irradiation, indicating that their DNA damage repair signalling response is decreased. In addition, the effect of autophagy inhibition was examined and revealed a radiosensitising effect and the presence of residual γ-H2AX foci.

CONCLUSIONS

The PERK/ATF4/LAMP3-arm causes radioresistance of breast cancer cells by increasing DNA damage repair signalling. Inhibition of PERK and/or autophagy may sensitise tumours to radiotherapy.

α-Synuclein is involved in manganese-induced ER stress via PERK signal pathway in organotypic brain slice cultures

Overexposure to manganese (Mn) has been known to induce neuronal damage involving endoplasmic reticulum (ER) stress. However, the exact mechanism of Mn-induced ER stress is unclear. Increasing evidence suggested that the overexpression of alpha-synuclein played a critical role in Mn-induced neurotoxicity. To explore whether the occurrence of ER stress was associated with alpha-synuclein overexpression, we made the rat brain slices model of silencing alpha-synuclein using short-interference RNA. After non-silencing alpha-synuclein slices were treated with Mn (0-400 μM) for 24 h, there was a dose-dependent increase in apoptotic rates of cells and levels of lactate dehydrogenase in the culture medium. Moreover, there was a dose-dependent increase in the protein expression of 78, 94-kDa glucose-regulated protein (GRP78/94), C/EBP homologous protein (CHOP), and caspase-12. Moreover, PKR-like ER kinase (PERK) phosphorylation, PERK-mediated phosphorylation of eIF2a, and ATF4 expression also increased. Inositol-requiring enzyme 1 (IRE1) activation and X-box-binding protein-1 (Xbp1) mRNA splicing increased. Activating transcription factor 6 p90 levels did not change. However, after silencing alpha-synuclein slices were treated with 400 μM Mn for 24 h, there was a significant decrease in the expression of GRP78/94, CHOP, and caspase-12 compared with 400 μM Mn-treated non-silencing alpha-synuclein slices. Furthermore, PERK phosphorylation, PERK-mediated phosphorylation of eIF2a, and ATF4 mRNA expression also decreased. However, IRE1 phosphorylation and Xbp1 mRNA splicing did not change. The findings revealed that Mn induced ER stress via activation of PERK and IRE1 signaling pathways and subsequent apoptosis in cultured slices. Moreover, alpha-synuclein protein was associated with Mn-induced activation of PERK signaling pathway.

Mechanisms of radiation toxicity in transformed and non-transformed cells

Radiation damage to biological systems is determined by the type of radiation, the total dosage of exposure, the dose rate, and the region of the body exposed. Three modes of cell death—necrosis, apoptosis, and autophagy—as well as accelerated senescence have been demonstrated to occur in vitro and in vivo in response to radiation in cancer cells as well as in normal cells. The basis for cellular selection for each mode depends on various factors including the specific cell type involved, the dose of radiation absorbed by the cell, and whether it is proliferating and/or transformed. Here we review the signaling mechanisms activated by radiation for the induction of toxicity in transformed and normal cells. Understanding the molecular mechanisms of radiation toxicity is critical for the development of radiation countermeasures as well as for the improvement of clinical radiation in cancer treatment.

Celecoxib enhances radiosensitivity of hypoxic glioblastoma cells through endoplasmic reticulum stress

BACKGROUND

Refractoriness of glioblastoma multiforme (GBM) largely depends on its radioresistance. We investigated the radiosensitizing effects of celecoxib on GBM cell lines under both normoxic and hypoxic conditions.

METHODS

Two human GBM cell lines, U87MG and U251MG, and a mouse GBM cell line, GL261, were treated with celecoxib or γ-irradiation either alone or in combination under normoxic and hypoxic conditions. Radiosensitizing effects were analyzed by clonogenic survival assays and cell growth assays and by assessing apoptosis and autophagy. Expression of apoptosis-, autophagy-, and endoplasmic reticulum (ER) stress-related genes was analyzed by immunoblotting.

RESULTS

Celecoxib significantly enhanced the radiosensitivity of GBM cells under both normoxic and hypoxic conditions. In addition, combined treatment with celecoxib and γ-irradiation induced marked autophagy, particularly in hypoxic cells. The mechanism underlying the radiosensitizing effect of celecoxib was determined to be ER stress loading on GBM cells.

CONCLUSION

Celecoxib enhances the radiosensitivity of GBM cells by a mechanism that is different from cyclooxygenase-2 inhibition. Our results indicate that celecoxib may be a promising radiosensitizing drug for clinical use in patients with GBM.