Involvement of ERK-Nrf-2 signaling in ionizing radiation induced cell death in normal and tumor cells

Txnrd1 as a prognosticator for recurrence, metastasis and response to neoadjuvant chemotherapy and radiotherapy in breast cancer patients

Thioredoxin reductase 1 (Txnrd1) is known to have prognostic significance in a subset of breast cancer patients. Despite the pivotal role of Txnrd1 in regulating several cellular and physiological processes in cancer progression and metastasis, its clinical significance is largely unrecognized. Here, we undertook a retrospective comprehensive meta-analysis of 13,322 breast cancer patients from 43 independent cohorts to assess prognostic and predictive roles of Txnrd1. We observed that Txnrd1 has a positive correlation with tumor grade and size and it is over-expressed in higher-grade and larger tumors. Further, hormone receptor-negative and HER2-positive tumors exhibit elevated Txnrd1 gene expression. Patients with elevated Txnrd1 expression exhibit significant hazards for shorter disease-specific and overall survival. While Txnrd1 has a positive correlation with tumor recurrence and metastasis, it has a negative correlation with time to recurrence and metastasis. Txnrd1High patients exhibit 2.5 years early recurrence and 1.3 years early metastasis as compared to Txnrd1Low cohort. Interestingly, patients with high Txnrd1 gene expression exhibit a pathologic complete response (pCR) to neoadjuvant chemotherapy, but they experience early recurrence after radiotherapy. Txnrd1High MDA-MB-231 cells exhibit significant ROS generation and reduced viability after doxorubicin treatment compared to Txnrd1Low MCF7 cells. Corroborating with findings from meta-analysis, Txnrd1 depletion leads to decreased survival, enhanced sensitivity to radiation induced killing, poor scratch-wound healing, and reduced invasion potential in MDA-MB-231 cells. Thus, Txnrd1 appears to be a potential predictor of recurrence, metastasis and therapy response in breast cancer patients.

Pterocarpus santalinus L. extract mitigates gamma radiation-inflicted derangements in BALB/c mice by Nrf2 upregulation

Plant-based natural extracts contain several nutrients and bioactive compounds, such as phenolics and flavonoids, that possess various health-promoting activities. This study investigated the effects of polyphenols from Pterocarpus santalinus hydroalcoholic extract (PSHE) against gamma radiation-induced derangements via the upregulation of Nrf2. Ultra High Performance Liquid Chromatography Coupled to High Resolution Mass Spectrometry (UHPLC-HRMS/MS) analysis was performed to identify the possible radioprotectors. In vivo and in vitro studies, namely Real-Time-PCR (RT-PCR) analysis, Reactive Oxygen Species (ROS) scavenging activity, lipid peroxidation and GSH levels, DNA damage and cell death studies, anti-inflammatory (Sandwich ELISA), immunomodulatory studies (antibody staining), and model free radical scavenging assays, were performed. Vanillic acid, protocatechuic acid, para-hydroxybenzoic acid, chlorogenic acid, TNF-α inhibitor (Eudesmin), isoflavone (Daidzein 7-o-glucoside), astragalin (Kaempferol 3-o-glycoside), and other polyphenols were identified in PSHE using UHPLC-HRMS/MS analysis. Prophylactic administration of PSHE (-1 h) rendered more than 33% survival in mice exposed to 8 Gy whole-body-irradiation with increased mice survival and recovery of bone marrow and spleen cellularity. Real-time RT-PCR analysis showed that PSHE treatment (50 µg/mL) upregulated Nrf2, HO-1, and GPX-1 in mice splenocytes. At 50 µg/mL, PSHE reduced ROSscavenging activity, mitochondrial and spleen membrane lipid peroxidation levels, DNA damage, and cell death, and increased GSH levels. At 10 µg/mL, PSHE treatment diminished the content of IL-6 and TNF-α. At 50 µg/mL, PSHE suppressed lymphocyte proliferation. These findings indicate that polyphenols of PSHE possess marked antioxidant, anti-inflammatory, and immunomodulatory capacities, which play important roles in the prevention of radiation damage.

Oxidative stress associated metabolic adaptations regulate radioresistance in human lung cancer cells

Differential inherent and acquired radioresistance of human lung cancer cells contribute to poor therapeutic outcome and tumor recurrence after radiotherapy. Inherent radioresistance of lung cancer cells is known to be associated with ROS^Low cancer stem cells (CSCs). However, mechanism of acquired radioresistance in lung cancer cells is poorly understood. Here, we exposed human lung cancer cells (A549) to a cumulative dose of 40Gy and allowed the radioresistant (RR) survivors to divide and form macroscopic colonies after each fraction of 5Gy dose. The RR subline exhibited enrichment of cytosolic ROS^High cells without specific increase in mitochondrial ROS levels. We found a concomitant increase in the expression of redox regulatory transcription factor Nrf2 and its dependent antioxidant genes in RR cells and cell cycle delay as compared to parental cells. The treatment of RR cells with Nrf2 inhibitor resulted in decreased clonogenic survival indicating their addiction to Nrf2 for metabolic adaptations under high levels of cytosolic ROS. A causal role of inherent ROS levels in conferring radioresistance was established by sorting ROS^High and ROS^Low populations from parental and RR cells. It was observed that ROS^High population from both parental and RR cells exhibited radioresistance as observed by clonogenic assay. Interestingly, ROS^High population of cells exhibited higher levels of cellular thiols in both parental and RR cells. Thus, our observations highlight presence of a novel subpopulation in lung cancer cells, which exhibits radioresistance by maintaining 'oxidative stress' and Nrf2 dependent metabolic adaptations. We also posit Nrf2 pathway as a druggable target for radiosensitization of RR A549 cells.

Ascorbyl stearate stimulates cell death by oxidative stress-mediated apoptosis and autophagy in HeLa cervical cancer cell line in vitro

In this study, Asc-s was evaluated for anti-cancer effect using cervical cancer cells (HeLa). Results determine that Asc-s treatment-induced dose-dependent inhibition of proliferation of HeLa cells and induced apoptosis. Flow-cytometry analysis shows Asc-s treatment-induced accumulation of cells at sub-G0/G1 stage of cell cycle and induced apoptosis as confirmed by DAPI, propodium iodide, and acridine staining in HeLa cells. Asc-s entered the cells and metabolized to ascorbate and stearate moieties, increased membrane permeability, and decreased membrane fluidity in HeLa cells. Asc-s treatment-induced dose-dependent increase in autophagy protein LC3-II, mRNA levels and decreased Nrf-2 levels in HeLa cells. It is hypothesized that both ascorbyl radical and stearoyl moieties of Asc-s induced cytotoxicity by generating reactive oxygen species (ROS) and modulating membrane fluidity/permeability leading to apoptosis/autophagy of HeLa cells. Thus, our findings demonstrate that Asc-s as anti-proliferative and apoptosis inducing compound in cervical cancer cells.

Pathological effects of ionizing radiation: endothelial activation and dysfunction

The endothelium, a tissue that forms a single layer of cells lining various organs and cavities of the body, especially the heart and blood as well as lymphatic vessels, plays a complex role in vascular biology. It contributes to key aspects of vascular homeostasis and is also involved in pathophysiological processes, such as thrombosis, inflammation, and hypertension. Epidemiological data show that high doses of ionizing radiation lead to cardiovascular disease over time. The aim of this review is to summarize the current knowledge on endothelial cell activation and dysfunction after ionizing radiation exposure as a central feature preceding the development of cardiovascular diseases.

Defenses against Pro-oxidant Forces - Maintenance of Cellular and Genomic Integrity and Longevity

There has been enormous recent progress in understanding how human cells respond to oxidative stress, such as that caused by exposure to ionizing radiation. We have witnessed a significant deciphering of the events that underlie how antioxidant responses counter pro-oxidant damage to key biological targets in all cellular compartments, including the genome and mitochondria. These cytoprotective responses include: 1. The basal cellular repertoire of antioxidant capabilities and its supporting cast of facilitator enzymes; and 2. The inducible phase of the antioxidant response, notably that mediated by the Nrf2 transcription factor. There has also been frenetic progress in defining how reactive electrophilic species swamp existing protective mechanisms to augment DNA damage, events that are embodied in the cellular "DNA-damage response", including cell cycle checkpoint activation and DNA repair, which occur on a time scale of hours to days, as well as the implementation of cellular responses such as apoptosis, autophagy, senescence and reprograming that extend the time period of damage sensing and response into weeks, months and years. It has become apparent that, in addition to the initial oxidative insult, cells typically undergo further waves of secondary reactive oxygen/nitrogen species generation, DNA damage and signaling and that these may reemerge long after the initial events have subsided, probably being driven, at least in part, by persisting DNA damage. These reactive oxygen/nitrogen species are an integral part of the pathological consequences of radiation exposure and may persist across multiple cell divisions. Because of the pervasive nature of oxidative stress, a cell will manifest different responses in different subcellular compartments and to different levels of stress injury. Aspects of these compartmentalized responses can involve the same proteins (such as ATM, p53 and p21) but in different functional guises, e.g., in cytoplasmic versus nuclear responses or in early- versus late-phase events. Many of these responses involve gene activation and new protein synthesis as well as a plethora of post-translational modifications of both basal and induced response proteins. It is these responses that we focus on in this review.

Early antioxidant responses via the concerted activation of NF-κB and Nrf2 characterize the gamma-radiation-induced adaptive response in quiescent human peripheral blood mononuclear cells

The radiation-induced adaptive response (RI-AR) is a non-targeted effect which is outside the scope of the classical Linear-No-Threshold (LNT) dose-response paradigm. However, the mechanisms of the RI-AR are not well understood. We have studied the RI-AR in quiescent human peripheral blood mononuclear cells (PBMCs). PBMCs in G₀ phase were 'primed' with a low dose (100 mGy gamma radiation) and then, after an 'adaptive window' of 4 h, 'challenged' with a high dose (2 Gy). A small (5.7%) increase in viability and a decrease in DNA strand breaks were seen in primed cells, compared to non-primed cells. This was consistent with lower levels of reactive oxygen species, higher mitochondrial membrane potential, and increased activity of antioxidant enzymes such as catalase, superoxide dismutase, thioredoxin reductase, and glutathione peroxidase, in the primed cells. Reduced oxidative stress in primed PBMCs correlated with greater nuclear translocation of the redox-sensitive transcription factors Nuclear factor kappa B (NF-κB) and Nuclear factor E2-related factor 2 (Nrf2). Distinct differences in responses were seen in PBMCs irradiated with low dose (100 mGy) and high dose (2 Gy). These findings provide insight into the mechanisms of radioadaptation in human cells.

Exposure to far-infrared rays attenuates methamphetamine-induced recognition memory impairment via modulation of the muscarinic M1 receptor, Nrf2, and PKC

We demonstrated that activation of protein kinase Cδ (PKCδ) and inactivation of the glutathione peroxidase-1 (GPx-1)-dependent systems are critical for methamphetamine (MA)-induced recognition memory impairment. We also demonstrated that exposure to far-infrared rays (FIR) causes induction of the glutathione (GSH)-dependent system, including induction of the GPx-1 gene. Here, we investigated whether exposure to FIR rays affects MA-induced recognition memory impairment and whether it modulates PKC, cholinergic receptors, and the GSH-dependent system. Because the PKC activator bryostatin-1 mainly induces PKCα, PKCε, and PKCδ, we assessed expression of these proteins after MA treatment. MA treatment selectively increased PKCδ expression and its phosphorylation. Exposure to FIR rays significantly attenuated MA-induced increases in PKCδ phosphorylation. Importantly, bryostatin-1 potentiated MA-induced phosphorylation of PKCδ. MA treatment significantly decreased M1, M3, and M4 muscarinic acetylcholine receptors (mAChRs) and β2 nicotinic acetylcholine receptor expression. Of these, the decrease was most pronounced in M1 mAChR. Exposure to FIR significantly attenuated MA-induced decreases in the M1 mAChR and phospho-ERK_1/2, while it facilitated Nrf2-dependent GSH induction. Dicyclomine, an M1 mAChR antagonist, and l-buthionine-(S, R)-sulfoximine (BSO), an inhibitor of GSH synthesis, counteracted against the protective potentials mediated by FIR. More importantly, the memory-enhancing potential of FIR rays was significantly counteracted by bryostatin-1, dicyclomine, and BSO. Our results suggest that exposure to FIR rays attenuates MA-induced impairment in recognition memory via up-regulation of M1 mAChR, Nrf2-dependent GSH induction, and ERK_1/2 phosphorylation by inhibiting PKCδ phosphorylation by bryostatin-1.

Mitochondrial targeted curcumin exhibits anticancer effects through disruption of mitochondrial redox and modulation of TrxR2 activity

Mitocurcumin is a derivative of curcumin, which has been shown to selectively enter mitochondria. Here we describe the anti-tumor efficacy of mitocurcumin in lung cancer cells and its mechanism of action. Mitocurcumin, showed 25-50 fold higher efficacy in killing lung cancer cells as compared to curcumin as demonstrated by clonogenic assay, flow cytometry and high throughput screening assay. Treatment of lung cancer cells with mitocurcumin significantly decreased the frequency of cancer stem cells. Mitocurcumin increased the mitochondrial reactive oxygen species (ROS), decreased the mitochondrial glutathione levels and induced strand breaks in the mitochondrial DNA. As a result, we observed increased BAX to BCL-2 ratio, cytochrome C release into the cytosol, loss of mitochondrial membrane potential and increased caspase-3 activity suggesting that mitocurcumin activates the intrinsic apoptotic pathway. Docking studies using mitocurcumin revealed that it binds to the active site of the mitochondrial thioredoxin reductase (TrxR2) with high affinity. In corroboration with the above finding, mitocurcumin decreased TrxR activity in cell free as well as the cellular system. The anti-cancer activity of mitocurcumin measured in terms of apoptotic cell death and the decrease in cancer stem cell frequency was accentuated by TrxR2 overexpression. This was due to modulation of TrxR2 activity to NADPH oxidase like activity by mitocurcumin, resulting in higher ROS accumulation and cell death. Thus, our findings reveal mitocurcumin as a potent anticancer agent with better efficacy than curcumin. This study also demonstrates the role of TrxR2 and mitochondrial DNA damage in mitocurcumin mediated killing of cancer cells.

α-Actinin-4 confers radioresistance coupled invasiveness in breast cancer cells through AKT pathway

Acquired radioresistance accompanied with increased metastatic potential is a major hurdle in effective radiotherapy of breast cancers. However, the nature of their inter-dependence and the underlying mechanism remains largely intangible. By employing radioresistant (RR) cell lines, we herein demonstrate that MCF-7 RR cells display phenotypic and molecular alterations evocative of epithelial to mesenchymal transition (EMT) with increased traction forces and membrane ruffling culminating in boosted invasiveness. We then show that these changes can be attributed to overexpression of alpha-actinin-4 (ACTN4), with ACTN4 knockdown near-completely abrogating both radioresistance and EMT-associated changes. We further found that in MCF-7 RR cells, ACTN4 mediates the observed effects by activating AKT, and downstream AKT/GSK3β signalling. Though ACTN4 plays a similar role in mediating radioresistance and invasiveness in MDA-MB-231 RR cells, co-immunoprecipitation studies reveal that these changes are effected through increased association with AKT and not by overexpression of AKT. Taken together, our study identifies ACTN4/AKT/GSK3β as a novel pathway regulating radioresistance coupled invasion which can be further explored to improve the radiotherapeutic gain.

Spatio-temporal changes in glutathione and thioredoxin redox couples during ionizing radiation-induced oxidative stress regulate tumor radio-resistance

Ionizing radiation (IR)-induced oxidative stress in tumor cells is effectively managed by constitutive and inducible antioxidant defense systems. This study was initiated to understand the relative contribution of different redox regulatory systems in determining the tumor radio-resistance. In this study, human T-cell lymphoma (Jurkat) cells were exposed to IR (4 Gy) and monitored for the spatio-temporal changes in cellular redox regulatory parameters. We monitored the changes in the levels of reactive oxygen species (ROS) (total, mitochondrial, primary, and secondary), thiols (total, surface, and intracellular), GSH/GSSG ratio, antioxidant enzyme activity viz. thioredoxin (Trx), Trx reductase (TrxR), glutathione peroxidase, and glutathione reductase with respect to time. We have also measured protein glutathionylation. We observed that tumor cells mount a biphasic response after IR exposure which can be divided into early (0-6 h) and late (16-48 h) responses in terms of changes in cellular redox parameters. During early response, constitutively active GSH and Trx systems respond to restore cellular redox balance to pre-exposure levels and help in activation of redox-sensitive transcription factor Nrf-2. During late response, increase in the levels of antioxidants GSH and Trx rescue cells against IR-mediated damage. We observed that disruption of either glutathione or thioredoxin metabolism led to partial impairment of ability of cells to survive against IR-induced damage. But simultaneous disruption of both the pathways significantly increased radio sensitivity of Jurkat cells. This highlighted the importance of these two antioxidant pathways in regulating redox homeostasis under conditions of IR-induced oxidative stress.

Transcription Factors in the Cellular Response to Charged Particle Exposure

Charged particles, such as carbon ions, bear the promise of a more effective cancer therapy. In human spaceflight, exposure to charged particles represents an important risk factor for chronic and late effects such as cancer. Biological effects elicited by charged particle exposure depend on their characteristics, e.g., on linear energy transfer (LET). For diverse outcomes (cell death, mutation, transformation, and cell-cycle arrest), an LET dependency of the effect size was observed. These outcomes result from activation of a complex network of signaling pathways in the DNA damage response, which result in cell-protective (DNA repair and cell-cycle arrest) or cell-destructive (cell death) reactions. Triggering of these pathways converges among others in the activation of transcription factors, such as p53, nuclear factor κB (NF-κB), activated protein 1 (AP-1), nuclear erythroid-derived 2-related factor 2 (Nrf2), and cAMP responsive element binding protein (CREB). Depending on dose, radiation quality, and tissue, p53 induces apoptosis or cell-cycle arrest. In low LET radiation therapy, p53 mutations are often associated with therapy resistance, while the outcome of carbon ion therapy seems to be independent of the tumor's p53 status. NF-κB is a central transcription factor in the immune system and exhibits pro-survival effects. Both p53 and NF-κB are activated after ionizing radiation exposure in an ataxia telangiectasia mutated (ATM)-dependent manner. The NF-κB activation was shown to strongly depend on charged particles' LET, with a maximal activation in the LET range of 90-300 keV/μm. AP-1 controls proliferation, senescence, differentiation, and apoptosis. Nrf2 can induce cellular antioxidant defense systems, CREB might also be involved in survival responses. The extent of activation of these transcription factors by charged particles and their interaction in the cellular radiation response greatly influences the destiny of the irradiated and also neighboring cells in the bystander effect.

Investigation of radiation-induced multilayered signalling response of the inflammatory pathway

Ionising radiation exposure of cells might induce the perturbation of cell functions and, in particular, the activation or inhibition of several important pathways. This perturbation can cause the deregulation of both intra- and extra-cellular signalling cascades (such as the inflammatory pathway) and alter not only the behaviour of directly exposed cells but also the neighbouring non-irradiated ones, through the so-called bystander effect. The aim of the present work was to investigate the complex nonlinear interactions between the inflammatory pathway and other strictly interlaced signalling pathways, such as Erk1/2 and Akt/PKB, focusing on the radiation-induced perturbation of such pathways in the dose range of 0-2 Gy. The results show how radiation affects these interconnected pathways and how confounding factors, such as the change of culture medium, can hide radiation-induced perturbations.

Analysis of immune cell populations and cytokine profiles in murine splenocytes exposed to whole-body low-dose irradiation

PURPOSE

In contrast to high-dose therapeutic irradiation, definitive research detailing the physiological effects of low-dose irradiation is limited. Notably, the immunological response elicited after low-dose irradiation remains controversial.

MATERIALS AND METHODS

Female C57BL/6 mice were whole- body-irradiated with a single or three daily fractions up to a total dose of 0.1, 1, or 10 cGy. Blood and spleen were harvested 2, 7 and 14 days after irradiation.

RESULTS

The splenic CD4(+) T cell subpopulations were temporarily increased at 2 days after single or fractionated irradiation, whereas the percentage of dendritic cells (DC) and macrophages was decreased. Whereas CD8(+) T cell populations were decreased in single-dose irradiated mice at day 7, early and sustained reduction of CD8(+) T cell numbers was observed in fractionated- dose-irradiated mice from day 2 until day 14. In addition, single-dose irradiation resulted in a Th1 cytokine expression profile, whereas fractionated-dose irradiation drove a Th2 shift. Additionally, increased expression of immune-related factors was observed at early time-points with single-dose irradiation, in contrast to the dose-independent induction following fractionated-dose irradiation.

CONCLUSIONS

Our results demonstrate that low-dose irradiation modulates the immune response in mice, where the sensitivity and kinetics of the induced response vary according to the dosing method.

Effects of ionizing radiation on biological molecules--mechanisms of damage and emerging methods of detection

SIGNIFICANCE

The detrimental effects of ionizing radiation (IR) involve a highly orchestrated series of events that are amplified by endogenous signaling and culminating in oxidative damage to DNA, lipids, proteins, and many metabolites. Despite the global impact of IR, the molecular mechanisms underlying tissue damage reveal that many biomolecules are chemoselectively modified by IR.

RECENT ADVANCES

The development of high-throughput "omics" technologies for mapping DNA and protein modifications have revolutionized the study of IR effects on biological systems. Studies in cells, tissues, and biological fluids are used to identify molecular features or biomarkers of IR exposure and response and the molecular mechanisms that regulate their expression or synthesis.

CRITICAL ISSUES

In this review, chemical mechanisms are described for IR-induced modifications of biomolecules along with methods for their detection. Included with the detection methods are crucial experimental considerations and caveats for their use. Additional factors critical to the cellular response to radiation, including alterations in protein expression, metabolomics, and epigenetic factors, are also discussed.

FUTURE DIRECTIONS

Throughout the review, the synergy of combined "omics" technologies such as genomics and epigenomics, proteomics, and metabolomics is highlighted. These are anticipated to lead to new hypotheses to understand IR effects on biological systems and improve IR-based therapies.

Deficient expression of aldehyde dehydrogenase 1A1 is consistent with increased sensitivity of Gorlin syndrome patients to radiation carcinogenesis

Human phenotypes that are highly susceptible to radiation carcinogenesis have been identified. Sensitive phenotypes often display robust regulation of molecular features that modify biological response, which can facilitate identification of the pathways/networks that contribute to pathophysiological outcomes. Here we interrogate primary dermal fibroblasts isolated from Gorlin syndrome patients (GDFs), who display a pronounced inducible tumorigenic response to radiation, in comparison to normal human dermal fibroblasts (NHDFs). Our approach exploits newly developed thiol reactive probes to define changes in protein thiol profiles in live cell studies, which minimizes artifacts associated with cell lysis. Redox probes revealed deficient expression of an apparent 55 kDa protein thiol in GDFs from independent Gorlin syndrome patients, compared with NHDFs. Proteomics tentatively identified this protein as aldehyde dehydrogenase 1A1 (ALDH1A1), a key enzyme regulating retinoic acid synthesis, and ALDH1A1 protein deficiency in GDFs was confirmed by Western blot. A number of additional protein thiol differences in GDFs were identified, including radiation responsive annexin family members and lamin A/C. Collectively, candidates identified in our study have plausible implications for radiation health effects and cancer susceptibility.

ERK plays the baddie (again)

It has been known for many years that elevated signaling by the ERK1/2 pathway is frequently associated with the growth and survival of many tumor cell types under a variety of normal and stressful conditions, including the response of cells to other cancer interventional therapeutic strategies e.g., references 1–4. There is, however, a modest significant literature showing that enhanced ERK1/2 signaling can also cause tumor cell death e.g., references 5–8. The role of ERK1/2 signaling is clearly complex, for example as shown by the Koumenis group where inhibition of radiation-induced ERK1/2 signaling caused radiosensitization, whereas inhibition of curcumin-hyper-stimulated ERK1/2 signaling reduced radiosensitivity. 7 Presumably this Janus-faced behavior of the ERK1/2 pathway in terms of cell survival regulation will depend upon the tumor cell type, the intensity of ERK1/2 stimulation, and the molecular intervention/drug being used.