The ATM protein is required for sustained activation of NF-kappaB following DNA damage

The Molecular Mechanisms in Senescent Cells Induced by Natural Aging and Ionizing Radiation

This review discusses the relationship between cellular senescence and radiation exposure. Given the wide range of ionizing radiation sources encountered by people in professional and medical spheres, as well as the influence of natural background radiation, the question of the effect of radiation on biological processes, particularly on aging processes, remains highly relevant. The parallel relationship between natural and radiation-induced cellular senescence reveals the common aspects underlying these processes. Based on recent scientific data, the key points of the effects of ionizing radiation on cellular processes associated with aging, such as genome instability, mitochondrial dysfunction, altered expression of miRNAs, epigenetic profile, and manifestation of the senescence-associated secretory phenotype (SASP), are discussed. Unraveling the molecular mechanisms of cellular senescence can make a valuable contribution to the understanding of the molecular genetic basis of age-associated diseases in the context of environmental exposure.

Reactive oxygen species and its role in pathogenesis and resistance to therapy in acute myeloid leukemia

Relapse following a short clinical response to therapy is the major challenge for the management of acute myeloid leukemia (AML) patients. Leukemic stem cells (LSC), as the source of relapse, have been investigated for their metabolic preferences and their alterations at the time of relapse. As LSC rely on oxidative phosphorylation (OXPHOS) for energy requirement, reactive oxygen species (ROS), as by-products of OXPHOS, have been investigated for their role in the effectiveness of the standard AML therapy. Increased levels of non-mitochondrial ROS, generated by nicotinamide adenine dinucleotide phosphate oxidase, in a subgroup of AML patients add to the complexity of studying ROS. Although there are various studies presenting the contribution of ROS to AML pathogenesis, resistance, and its inhibition or activation as a target, a model that can clearly explain its role in AML has not been conceptualized. This is due to the heterogeneity of AML, the dynamics of ROS production, which is influenced by factors such as the type of treatment, cell differentiation state, mitochondrial activity, and also the heterogeneous generation of non-mitochondrial ROS and limited available data on their interaction with the microenvironment. This review summarizes these challenges and the recent progress in this field.

CLK2 and CLK4 are regulators of DNA damage-induced NF-κB targeted by novel small molecule inhibitors

Transcription factor NF-κB potently activates anti-apoptotic genes, and its inactivation significantly reduces tumor cell survival following genotoxic stresses. We identified two structurally distinct lead compounds that selectively inhibit NF-κB activation by DNA double-strand breaks, but not by other stimuli, such as TNFα. Our compounds do not directly inhibit previously identified regulators of this pathway, most critically including IκB kinase (IKK), but inhibit signal transmission in-between ATM, PARP1, and IKKγ. Deconvolution strategies, including derivatization and in vitro testing in multi-kinase panels, yielded shared targets, cdc-like kinase (CLK) 2 and 4, as essential regulators of DNA damage-induced IKK and NF-κB activity. Both leads sensitize to DNA damaging agents by increasing p53-induced apoptosis, thereby reducing cancer cell viability. We propose that our lead compounds and derivatives can be used in context of genotoxic therapy-induced or ongoing DNA damage to increase tumor cell apoptosis, which may be beneficial in cancer treatment.

Crosstalk between cGAS-STING pathway and autophagy in cancer immunity

The cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway is critical in cancer immunity. Autophagy is a highly conserved process that is responsible for the degradation of cytoplasmic material and is involved in both innate and adaptive immunity. Recently, cGAS-STING and autophagy have been shown to be interconnected, which may influence the progression of cancer. Although cGAS-STING and autophagy have been shown to be interrelated in innate immunity, little has been reported about cancer immunity. As cancer immunity is key to treating tumors, it is essential to summarize the relationship and interactions between the two. Based on this, we systematically sorted out the recent findings of cGAS-STING and autophagy in cancer immunity and explored the interactions between cGAS-STING and autophagy, although these interactions have not been extensively studied. Lastly, we provide an outlook on how cGAS-STING and autophagy can be combined, with the hope that our research can help people better understand their potential roles in cancer immunity and bring light to the treatment of cancer.

Genome integrity and inflammation in the nervous system

Preservation of genomic integrity is crucial for nervous system development and function. DNA repair deficiency results in several human diseases that are characterized by both neurodegeneration and neuroinflammation. Recent research has highlighted a role for compromised genomic integrity as a key factor driving neuropathology and triggering innate immune signaling to cause inflammation. Here we review the mechanisms by which DNA damage engages innate immune signaling and how this may promote neurological disease. We also consider the contributions of different neural cell types towards DNA damage-driven neuroinflammation. A deeper knowledge of genome maintenance mechanisms that prevent aberrant immune activation in neural cells will guide future therapies to ameliorate neurological disease.

TSG101 associates with PARP1 and is essential for PARylation and DNA damage-induced NF-κB activation

In a genome-wide screening for components of the dsDNA-break-induced IKK-NF-κB pathway, we identified scores of regulators, including tumor susceptibility gene TSG101. TSG101 is essential for DNA damage-induced formation of cellular poly(ADP-ribose) (PAR). TSG101 binds to PARP1 and is required for PARP1 activation. This function of TSG101 is independent of its role in the ESCRT-I endosomal sorting complex. In the absence of TSG101, the PAR-dependent formation of a nuclear PARP1-IKKγ signalosome, which triggers IKK activation, is impaired. According to its requirement for PARP1 and NF-κB activation, TSG101-deficient cells are defective in DNA repair and apoptosis protection. Loss of TSG101 results in PARP1 trapping at damage sites and mimics the effect of pharmacological PARP inhibition. We also show that the loss of TSG101 in connection with inactivated tumor suppressors BRCA1/2 in breast cancer cells is lethal. Our results imply TSG101 as a therapeutic target to achieve synthetic lethality in cancer treatment.

Mechanisms of DNA damage-mediated neurotoxicity in neurodegenerative disease

Neurons are highly susceptible to DNA damage accumulation due to their large energy requirements, elevated transcriptional activity, and long lifespan. While newer research has shown that DNA breaks and mutations may facilitate neuron diversity during development and neuronal function throughout life, a wealth of evidence indicates deficient DNA damage repair underlies many neurological disorders, especially age-associated neurodegenerative diseases. Recently, efforts to clarify the molecular link between DNA damage and neurodegeneration have improved our understanding of how the genomic location of DNA damage and defunct repair proteins impact neuron health. Additionally, work establishing a role for senescence in the aging and diseased brain reveals DNA damage may play a central role in neuroinflammation associated with neurodegenerative disease.

Disruption of NBS1/MRN Complex Formation by E4orf3 Supports NF-κB That Licenses E1B55K-Deleted Adenovirus-Infected Cells to Accumulate DNA>4n

Cells increase their DNA content greater than the G2/M (DNA > 4n) phases along the path to cancer. The signals that support this increase in DNA content remain poorly understood. Cells infected with adenovirus (Ad) similarly develop DNA > 4n and share a need to bypass the DNA damage response (DDR) signals that trigger cell cycle arrest, and/or cell death. Ads with deletion in early region 1B55K (ΔE1B Ad) are oncolytic agents that are currently being explored for use in vaccine delivery. Interestingly, they promote higher levels of DNA > 4n than Ads that contain E1B55K. Existing in these and almost all Ads that are being explored for clinical use, is early region 4 (E4). The Ad E4 open reading frame 3 (E4orf3) is a viral oncogene that interferes with the ability of cells to respond to DNA damage by disrupting MRN complex formation. Our study reveals that E4orf3 is required for the enhanced fraction of ΔE1B Ad-infected cells with DNA > 4n. For that reason, we explored signaling events mediated by E4orf3. We found that in ΔE1B Ad-infected cells, E4orf3, as reported by others, isolates NBS1 in nuclear dots and tracks. This allows for elevated levels of phosphorylated ATM that is linked to transcriptionally active NF-κB. Pharmacological inhibition of NF-κB reduced the fraction of ΔE1B Ad-infected cells with DNA > 4n while pharmacological inhibition of ATM reduced the levels of nuclear NF-κB and the fraction of ΔE1B Ad-infected cells with DNA > 4n and increased the fraction of dead or dying cells with fragmented DNA. This ability of E4orf3 to disrupt MRN complex formation that allows cells to bypass the cell cycle, evade death, and accumulate DNA > 4n, may be linked to its oncogenic potential. IMPORTANCE Genome instability, a hallmark of cancer, exists as part of a cycle that leads to DNA damage and DNA > 4n that further enhances genome instability. Ad E4orf3 is a viral oncogene. Here, we describe E4orf3 mediated signaling events that support DNA > 4n in ΔE1B Ad-infected cells. These signaling events may be linked to the oncogenic potential of E4orf3 and may provide a basis for how some cells survive with DNA > 4n.

Cinnamophilin enhances temozolomide-induced cytotoxicity against malignant glioma: the roles of ROS and cell cycle arrest

Background

Temozolomide (TMZ) has been widely used to treat glioblastoma multiforme (GBM). However, many mechanisms are known to quickly adapt GBM cells to chemotherapy with TMZ, leading to drug resistance and expansion of tumor cell populations.

Methods

We subjected human glioblastoma cell lines and an animal model of glioblastoma xenografts with TMZ-based adjuvant treatments to evaluate the synergistic effect of cinnamophilin (CINN), a free radical scavenger.

Results

Our results showed that the combined treatment of CINN and TMZ potentiated the anticancer effect and apoptotic cell death in glioma cell lines and enhanced antitumor action in glioma xenografts. TMZ induced reactive oxygen species (ROS) burst and elevated G2 arrest in glioma cells. The CINN-suppressed ROS burst in TMZ-treated glioma cells might be associated with increased apoptosis, as indicated by the upregulation of TUNEL-positive glioma cells. CINN-pretreated glioma cells exhibited increased cyclin B expression and reduced phosphorylation of Cdk1, suggesting reduced G2 arrest in the combined treatment group. Moreover, CINN lowered the protein level of LC3, a hallmark of autophagy, in TMZ-treated cells.

Conclusions

These findings suggest that CINN may restore TMZ toxicity in glioma cancer by suppressing the ROS/G2 arrest pathway.

DNA damage independent inhibition of NF-κB transcription by anthracyclines

Anthracyclines are among the most used and effective anticancer drugs. Their activity has been attributed to DNA double-strand breaks resulting from topoisomerase II poisoning and to eviction of histones from select sites in the genome. Here, we show that the extensively used anthracyclines Doxorubicin, Daunorubicin, and Epirubicin decrease the transcription of nuclear factor kappa B (NF-κB)-dependent gene targets, but not interferon-responsive genes in primary mouse (Mus musculus) macrophages. Using an NMR-based structural approach, we demonstrate that anthracyclines disturb the complexes formed between the NF-κB subunit RelA and its DNA-binding sites. The anthracycline variants Aclarubicin, Doxorubicinone, and the newly developed Dimethyl-doxorubicin, which share anticancer properties with the other anthracyclines but do not induce DNA damage, also suppressed inflammation, thus uncoupling DNA damage from the effects on inflammation. These findings have implications for anticancer therapy and for the development of novel anti-inflammatory drugs with limited side effects for life-threatening conditions such as sepsis.

Radiosensitizing Effect of Bromelain Using Tumor Mice Model via Ki-67 and PARP-1 Inhibition

Recent reports have shown that bromelain (BL), a pineapple extract, acts as an adjuvant therapy in cancer treatment and prevention of carcinogenesis. The present study was designed to investigate the possible mechanisms by which BL could radiosensitize tumor cells in vitro and in a mouse tumor model. BL has shown a significant reduction in the viability of the radioresistant human breast carcinoma (MCF-7) cell line using cell proliferation assay. The in vivo study was designed using the Ehrlich model in female albino mice, treated with BL (6 mg/kg b. wt., intraperitoneal, once daily for 10 days) 1 hour before exposure to a fractionated dose of gamma radiation (5 Gy, 1 Gy for 5 subsequent days). The radiosensitizing effect of BL was evident in terms of a significant reduction in tumor volume, poly ADP ribose polymerase-1 (PARP-1), the proliferation marker Ki-67 and nuclear factor kappa activated B cells (NF-κB) with a significant elevation in the reactive oxygen species (ROS) content and lipid peroxidation (LPO) in tumor cells. The present findings offer a novel insight into the radiosensitizing effect of BL and its potential application in the radiotherapy course.

Hepatic stellate cell senescence in liver fibrosis: Characteristics, mechanisms and perspectives

Myofibroblasts play an important role in fibrogenesis. Hepatic stellate cells are the main precursors of myofibroblasts. Cellular senescence is the terminal cell fate in which proliferating cells undergo irreversible cell cycle arrest. Senescent hepatic stellate cells were identified in liver fibrosis. Senescent hepatic stellate cells display decreased collagen production and proliferation. Therefore, induction of senescence could be a protective mechanism against progression of liver fibrosis and the concept of therapy-induced senescence has been proposed to treat liver fibrosis. In this review, characteristics of senescent hepatic stellate cells and the essential signaling pathways involved in senescence are reviewed. Furthermore, the potential impact of senescent hepatic stellate cells on other liver cell types are discussed. Senescent cells are cleared by the immune system. The persistence of senescent cells can remodel the microenvironment and interact with inflammatory cells to induce aging-related dysfunction. Therefore, senolytics, a class of compounds that selectively induce death of senescent cells, were introduced as treatment to remove senescent cells and consequently decrease the disadvantageous effects of persisting senescent cells. The effects of senescent hepatic stellate cells in liver fibrosis need further investigation.

Harnessing Genomic Stress for Antitumor Immunity

Significance: Genomic instability, a hallmark of cancer, renders cancer cells susceptible to genomic stress from both endogenous and exogenous origins, resulting in the increased tendency to accrue DNA damage, chromosomal instability, or aberrant DNA localization. Apart from the cell autonomous tumor-promoting effects, genomic stress in cancer cells could have a profound impact on the tumor microenvironment. Recent Advances: Recently, it is increasingly appreciated that harnessing genomic stress could provide a promising strategy to revive antitumor immunity, and thereby offer new therapeutic opportunities in cancer treatment. Critical Issues: Genomic stress is closely intertwined with antitumor immunity via mechanisms involving the direct crosstalk with DNA damage response components, upregulation of immune-stimulatory/inhibitory ligands, release of damage-associated molecular patterns, increase of neoantigen repertoire, and activation of DNA sensing pathways. A better understanding of these mechanisms will provide molecular basis for exploiting the genomic stress to boost antitumor immunity. Future Directions: Future research should pay attention to the heterogeneity between individual cancers in the genomic instability and the associated immune response, and how to balance the toxicity and benefit by specifying the types, potency, and treatment sequence of genomic stress inducer in therapeutic practice. Antioxid. Redox Signal. 34, 1128-1150.

The guardian's choice: how p53 enables context-specific decision-making in individual cells

p53 plays a central role in defending the genomic integrity of our cells. In response to genotoxic stress, this tumour suppressor orchestrates the expression of hundreds of target genes, which induce a variety of cellular outcomes ranging from damage repair to induction of apoptosis. In this review, we examine how the p53 response is regulated on several levels in individual cells to allow precise and context-specific fate decisions. We discuss that the p53 response is not only controlled by its canonical regulators but also controlled by interconnected signalling pathways that influence the dynamics of p53 accumulation upon damage and modulate its transcriptional activity at target gene promoters. Additionally, we consider how the p53 response is diversified through a variety of mechanisms at the promoter level and beyond to induce context-specific outcomes in individual cells. These layers of regulation allow p53 to react in a stimulus-specific manner and fine-tune its signalling according to the individual needs of a given cell, enabling it to take the right decision on survival or death.

The Function of SUMOylation and Its Role in the Development of Cancer Cells under Stress Conditions: A Systematic Review

Malignant tumors still pose serious threats to human health due to their high morbidity and mortality. Recurrence and metastasis are the most important factors affecting patient prognosis. Chemotherapeutic drugs and radiation used to treat these tumors mainly interfere with tumor metabolism, destroy DNA integrity, and inhibit protein synthesis. The upregulation of small ubiquitin-like modifier (SUMO) is a prevalent posttranslational modification (PTM) in various cancers and plays a critical role in tumor development. The dysregulation of SUMOylation can protect cancer cells from stresses exerted by external or internal stimuli. SUMOylation is a dynamic process finely regulated by SUMOylation enzymes and proteases to maintain a balance between SUMOylation and deSUMOylation. An increasing number of studies have reported that SUMOylation imbalance may contribute to cancer development, including metastasis, angiogenesis, invasion, and proliferation. High level of SUMOylation is required for cancer cells to survive internal or external stresses. Downregulation of SUMOylation may inhibit the development of cancer, making it an important potential clinical therapeutic target. Some studies have already begun to treat tumors by inhibiting the expression of SUMOylation family members, including SUMO E1 or E2. The tumor cells become more aggressive under internal and external stresses. The prevention of tumor development, metastasis, recurrence, and radiochemotherapy resistance by attenuating SUMOylation requires further exploration. This review focused on SUMOylation in tumor cells to discuss its effects on tumor suppressor proteins and oncoproteins as well as classical tumor pathways to identify new insights for cancer clinical therapy.

Parp3 promotes astrocytic differentiation through a tight regulation of Nox4-induced ROS and mTorc2 activation

Parp3 is a member of the Poly(ADP-ribose) polymerase (Parp) family that has been characterized for its functions in strand break repair, chromosomal rearrangements, mitotic segregation and tumor aggressiveness. Yet its physiological implications remain unknown. Here we report a central function of Parp3 in the regulation of redox homeostasis in continuous neurogenesis in mice. We show that the absence of Parp3 provokes Nox4-induced oxidative stress and defective mTorc2 activation leading to inefficient differentiation of post-natal neural stem/progenitor cells to astrocytes. The accumulation of ROS contributes to the decreased activity of mTorc2 as a result of an oxidation-induced and Fbxw7-mediated ubiquitination and degradation of Rictor. In vivo, mTorc2 signaling is compromised in the striatum of naïve post-natal Parp3-deficient mice and 6 h after acute hypoxia-ischemia. These findings reveal a physiological function of Parp3 in the tight regulation of striatal oxidative stress and mTorc2 during astrocytic differentiation and in the acute phase of hypoxia-ischemia.

Melatonin increases the chemosensitivity of diffuse large B-cell lymphoma cells to epirubicin by inhibiting P-glycoprotein expression via the NF-κB pathway

Background

Epirubicin is a first-line chemotherapeutic drug for the clinical treatment of diffuse large B cell lymphoma (DLBCL), but the overexpression of multidrug resistance (MDR) transporter proteins, especially P-glycoprotein (P-gp), renders epirubicin ineffective. Some studies reveal the potential role of melatonin in chemotherapeutic synergy and MDR.

Methods

The cell viability and apoptosis were determined by CCK-8 assay and acridine orange/ethidium bromide (AO/EB) fluorescence staining assay. Immunofluorescence and immunohistochemical staining were used to detect the expression of P-gp in DLBCL cells and tissues. Rhodamine-123 accumulation assay was used to evaluate the pump function of P-gp. The possible mechanisms of melatonin sensitize DLBCL cells to epirubicin were explored by western blotting, cytochrome C release, and pulldown assay.

Results

Melatonin significantly enhanced the epirubicin-induced cell proliferation suppression, epirubicin-induced apoptosis, and reduced the IC50 value of epirubicin. Further, melatonin synergized with epirubicin to promote the activation of the mitochondria-mediated apoptosis pathway and increased the accumulation of epirubicin in DLBCL cells by inhibiting the expression and function of P-gp. Immunohistochemical staining studies revealed that P-gp expression was positively correlated with P65 expression. Epirubicin was subsequently discovered to upregulate the expression of P-gp by activating the NF-κB pathway in the DLBCL cells. Melatonin reduced the amount of P65 protein in the nucleus and abrogated the ability of P65 to bind to the ABCB1 promoter, decisively suppressing P-gp expression.

Conclusions

Our results demonstrated that melatonin inactivates the NF-κB pathway and downregulates the expression of P-gp, ultimately sensitizing DLBCL cells to the epirubicin that suppresses their growth.

DNA double-strand breaks: a potential therapeutic target for neurodegenerative diseases

The complexity of neurodegeneration restricts the ability to understand and treat the neurological disorders affecting millions of people worldwide. Therefore, there is an unmet need to develop new and more effective therapeutic strategies to combat these devastating conditions and that will only be achieved with a better understanding of the biological mechanism associated with disease conditions. Recent studies highlight the role of DNA damage, particularly, DNA double-strand breaks (DSBs), in the progression of neuronal loss in a broad spectrum of human neurodegenerative diseases. This is not unexpected because neurons are prone to DNA damage due to their non-proliferative nature and high metabolic activity. However, it is not clear if DSBs is a primary driver of neuronal loss in disease conditions or simply occurs concomitant with disease progression. Here, we provide evidence that supports a critical role of DSBs in the pathogenesis of the neurodegenerative diseases. Among different kinds of DNA damages, DSBs are the most harmful and perilous type of DNA damage and can lead to cell death if left unrepaired or repaired with error. In this review, we explore the current state of knowledge regarding the role of DSBs repair mechanisms in preserving neuronal function and survival and describe how DSBs could drive the molecular mechanisms resulting in neuronal death in neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. We also discuss the potential implications of DSBs as a novel therapeutic target and prognostic marker in patients with neurodegenerative conditions.

Non-canonical Activation of the DNA Sensing Adaptor STING by ATM and IFI16 Mediates NF-κB Signaling after Nuclear DNA Damage

DNA damage can be sensed as a danger-associated molecular pattern by the innate immune system. Here we find that keratinocytes and other human cells mount an innate immune response within hours of etoposide-induced DNA damage, which involves the DNA sensing adaptor STING but is independent of the cytosolic DNA receptor cGAS. This non-canonical activation of STING is mediated by the DNA binding protein IFI16, together with the DNA damage response factors ATM and PARP-1, resulting in the assembly of an alternative STING signaling complex that includes the tumor suppressor p53 and the E3 ubiquitin ligase TRAF6. TRAF6 catalyzes the formation of K63-linked ubiquitin chains on STING, leading to the activation of the transcription factor NF-κB and the induction of an alternative STING-dependent gene expression program. We propose that STING acts as a signaling hub that coordinates a transcriptional response depending on its mode of activation.

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Etoposide-induced nuclear DNA damage causes an innate immune response

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ATM and IFI16 can activate STING in a cGAS-independent manner

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Non-canonical STING signaling predominantly activates NF-κB, rather than IRF3

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This involves the TRAF6-mediated assembly of K63-linked ubiquitin chains on STING

Cellular Stresses and Stress Responses in the Pathogenesis of Insulin Resistance

Insulin resistance (IR), a key component of the metabolic syndrome, precedes the development of diabetes, cardiovascular disease, and Alzheimer's disease. Its etiological pathways are not well defined, although many contributory mechanisms have been established. This article summarizes such mechanisms into the hypothesis that factors like nutrient overload, physical inactivity, hypoxia, psychological stress, and environmental pollutants induce a network of cellular stresses, stress responses, and stress response dysregulations that jointly inhibit insulin signaling in insulin target cells including endothelial cells, hepatocytes, myocytes, hypothalamic neurons, and adipocytes. The insulin resistance-inducing cellular stresses include oxidative, nitrosative, carbonyl/electrophilic, genotoxic, and endoplasmic reticulum stresses; the stress responses include the ubiquitin-proteasome pathway, the DNA damage response, the unfolded protein response, apoptosis, inflammasome activation, and pyroptosis, while the dysregulated responses include the heat shock response, autophagy, and nuclear factor erythroid-2-related factor 2 signaling. Insulin target cells also produce metabolites that exacerbate cellular stress generation both locally and systemically, partly through recruitment and activation of myeloid cells which sustain a state of chronic inflammation. Thus, insulin resistance may be prevented or attenuated by multiple approaches targeting the different cellular stresses and stress responses.

Ionizing Radiation-Induced Cellular Senescence in Normal, Non-transformed Cells and the Involved DNA Damage Response: A Mini Review

Cellular senescence is identified by a living cell in irreversible and persistent cell cycle arrest in response to various cellular stresses. Senescent cells secrete senescence-associated secretory phenotype factors that can amplify cellular senescence and alter the microenvironments. Radiotherapy, via ionizing radiation, serves as an effective treatment for local tumor control with side effects on normal cells, which can induce inflammation and fibrosis in irradiated and nearby regions. Research has revealed that senescent phenotype is observable in irradiated organs. This process starts with DNA damage mediated by radiation, after which a G2 arrest occurs in virtually all eukaryotic cells and a mitotic bypass is possibly necessary to ultimately establish cellular senescence. Within this complex DNA damage response signaling network, ataxia telangiectasia-mutated protein, p53, and p21 stand out as the crucial mediators. Senolytic agents, a class of small molecules that can selectively kill senescent cells, hold great potential to substantially reduce the side effects caused by radiotherapy while reasonably steer clear of carcinogenesis.

Millepachine, a potential topoisomerase II inhibitor induces apoptosis via activation of NF-κB pathway in ovarian cancer

Millepachine (MIL) was a novel chalcone that was separated from Millettia pachycarpa Benth (Leguminosae). We found MIL induced apoptosis through activating NF-κB pathway both in SK-OV-3 and A2780S cells. Western blot showed that MIL increased the levels of IKKα, p-IKKα/β, p-IκBα and NF-κB (p65) proteins, and decreased the expression of IκBα protein. Immunohistochemistry analysis indicated that translocation of NF-κB into the nucleus increased in both ovarian cancer cells. EMSA assay proved MIL enhanced NF-κB DNA-binding activity in the nuclear. That specific NF-κB inhibitors alleviated MIL-induced apoptosis suggested NF-κB activation showed a pro-apoptotic function in SK-OV-3 and A2780S cells. Since NF-κB could be activated by double strand breaks and showed a pro-apoptotic function in the DNA damage response, SCGE assay and western blot revealed that MIL caused DNA strand breaks and significantly increased the level of p-ATM protein and further increased the levels of p-IKKα/β and NF-κB (p65) protein in SK-OV-3 and A2780S cells, while a specific ATM inhibitor could alleviated these effects. Moreover, Topoisomerase II drug screening kit and computer modeling assay were used to prove that MIL induced the production of linear DNA and inhibited the activity of topoisomerase II through binding with Topoisomerase II-Cleaved DNA complex to stabilize the complex. Taken together, our results identified that MIL exhibited anti-tumor activity through inhibiting topoisomerase II activity to induce tumor cells DNA damage, and MIL-activated NF-κB pathway showed a pro-apoptotic function in response to DNA damage.

Afatinib, an Irreversible EGFR Family Inhibitor, Shows Activity Toward Pancreatic Cancer Cells, Alone and in Combination with Radiotherapy, Independent of KRAS Status

BACKGROUND

Pancreatic adenocarcinoma is characterized by a high frequency of KRAS mutations and frequent deregulation of the epidermal growth factor receptor (EGFR) and other EGFR family members such as HER2/ErbB2. The EGFR inhibitor erlotinib is approved for treatment of pancreatic cancer, but has shown modest activity in most patients.

OBJECTIVE

Here we investigated the activity of afatinib, a second-generation irreversible pan-EGFR family kinase inhibitor, alone or in combination with ionizing radiation, toward pancreatic cancer cells.

METHODS

The influence of afatinib on cell proliferation, cell cycle distribution, clonogenic survival, nuclear fragmentation, ploidy, and centrosome amplification following irradiation was determined. Expression and phosphorylation of HER receptors, Akt, DNA-PKcs, and ERK1/2 was characterized by Western blot analysis.

RESULTS

Afatinib was growth-inhibitory for all three cell lines but cytotoxic only toward BxPC3 (KRAS (wt)) and Capan-2 (KRAS (mut)) cells, both of which express high levels of EGFR, HER2, and HER3 receptors. Afatinib increased the radiosensitivity of BxPC3 and Capan-2 cells, prevented the radio-induced phosphorylation of Akt, and induced mitotic catastrophe following irradiation. In comparison, Panc-1 cells (KRAS (mut)) expressing low levels of EGFR family receptors were resistant to afatinib-induced radiosensitization.

LIMITATIONS

These results must be confirmed in vivo.

CONCLUSIONS

Afatinib showed cytotoxic and radiosensitizing effects toward a subset of pancreatic cancer cells which was closely correlated with expression of EGFR, HER2, and HER3 receptors, but not with KRAS status.

DNA damage-induced nuclear factor-kappa B activation and its roles in cancer progression

DNA damage is a vital challenge to cell homeostasis. Cellular responses to DNA damage (DDR) play essential roles in maintaining genomic stability and survival, whose failure could lead to detrimental consequences such as cancer development and aging. Nuclear factor-kappa B (NF-κB) is a family of transcription factors that plays critical roles in cellular stress response. Along with p53, NF-κB modulates transactivation of a large number of genes which participate in various cellular processes involved in DDR. Here the authors summarize the recent progress in understanding DNA damage response and NF-κB signaling pathways. This study particularly focuses on DNA damage-induced NF-κB signaling cascade and its physiological and pathological significance in B cell development and cancer therapeutic resistance. The authors also discuss promising strategies for selectively targeting this genotoxic NF-κB signaling aiming to antagonize acquired resistance and resensitize refractory cancer cells to cytotoxic treatments.

Pan-cancer analysis distinguishes transcriptional changes of aneuploidy from proliferation

Patterns of gene expression in tumors can arise as a consequence of or result in genomic instability, characterized by the accumulation of somatic copy number alterations (SCNAs) and point mutations (PMs). Expression signatures have been widely used as markers for genomic instability, and both SCNAs and PMs could be thought to associate with distinct signatures given their different formation mechanisms. Here we test this notion by systematically investigating SCNA, PM, and transcriptome data from 2660 cancer patients representing 11 tumor types. Notably, our data indicate that similar expression signatures can be derived from correlating gene expression with either SCNA or PM load. Gene sets related to cell growth and proliferation generally associated positively, and immunoregulatory gene sets negatively, with variant burden. In-depth analyses revealed several genes whose de-regulation correlates with SCNA but not with PM burden, yielding downstream effectors of TP53 and MYC signaling unique to high-SCNA tumors. We compared our findings to expression changes observed in two different cancer mouse models with persistent mitotic chromosomal instability, observing a decrease in proliferative expression signatures. Our results suggest that overexpression of cell-cycle-related genes are a characteristic of proliferation, and likely tumor evolution, rather than ongoing genomic instability.

Effects of an Encapsulated Fruit and Vegetable Juice Concentrate on Obesity-Induced Systemic Inflammation: A Randomised Controlled Trial

Phytochemicals from fruit and vegetables reduce systemic inflammation. This study examined the effects of an encapsulated fruit and vegetable (F&V) juice concentrate on systemic inflammation and other risk factors for chronic disease in overweight and obese adults. A double-blinded, parallel, randomized placebo-controlled trial was conducted in 56 adults aged ≥40 years with a body mass index (BMI) ≥28 kg/m². Before and after eight weeks daily treatment with six capsules of F&V juice concentrate or placebo, peripheral blood gene expression (microarray, quantitative polymerase chain reaction (qPCR)), plasma tumour necrosis factor (TNF)α (enzyme-linked immunosorbent assay (ELISA)), body composition (Dual-energy X-ray absorptiometry (DEXA)) and lipid profiles were assessed. Following consumption of juice concentrate, total cholesterol, low-density lipoprotein (LDL) cholesterol and plasma TNFα decreased and total lean mass increased, while there was no change in the placebo group. In subjects with high systemic inflammation at baseline (serum C-reactive protein (CRP) ≥3.0 mg/mL) who were supplemented with the F&V juice concentrate (n = 16), these effects were greater, with decreased total cholesterol, LDL cholesterol and plasma TNFα and increased total lean mass; plasma CRP was unchanged by the F&V juice concentrate following both analyses. The expression of several genes involved in lipogenesis, the nuclear factor-κB (NF-κB) and 5' adenosine monophosphate-activated protein kinase (AMPK) signalling pathways was altered, including phosphomevalonate kinase (PMVK), zinc finger AN1-type containing 5 (ZFAND5) and calcium binding protein 39 (CAB39), respectively. Therefore, F&V juice concentrate improves the metabolic profile, by reducing systemic inflammation and blood lipid profiles and, thus, may be useful in reducing the risk of obesity-induced chronic disease.

Sam68/KHDRBS1-dependent NF-κB activation confers radioprotection to the colon epithelium in γ-irradiated mice

Previously we reported that Src-associated-substrate-during-mitosis-of-68kDa (Sam68/KHDRBS1) is pivotal for DNA damage-stimulated NF-κB transactivation of anti-apoptotic genes (Fu et al., 2016). Here we show that Sam68 is critical for genotoxic stress-induced NF-κB activation in the γ-irradiated colon and animal and that Sam68-dependent NF-κB activation provides radioprotection to colon epithelium in vivo. Sam68 deletion diminishes γ-irradiation-triggered PAR synthesis and NF-κB activation in colon epithelial cells (CECs), thus hampering the expression of anti-apoptotic molecules in situ and facilitating CECs to undergo apoptosis in mice post whole-body γ-irradiation (WBIR). Sam68 knockout mice suffer more severe damage in the colon and succumb more rapidly from acute radiotoxicity than the control mice following WBIR. Our results underscore the critical role of Sam68 in orchestrating genotoxic stress-initiated NF-κB activation signaling in the colon tissue and whole animal and reveal the pathophysiological relevance of Sam68-dependent NF-κB activation in colonic cell survival and recovery from extrinsic DNA damage.

DOI:http://dx.doi.org/10.7554/eLife.21957.001

Modulation of inflammation and disease tolerance by DNA damage response pathways

The accurate replication and repair of DNA is central to organismal survival. This process is challenged by the many factors that can change genetic information such as replication errors and direct damage to the DNA molecule by chemical and physical agents. DNA damage can also result from microorganism invasion as an integral step of their life cycle or as collateral damage from host defense mechanisms against pathogens. Here we review the complex crosstalk of DNA damage response and immune response pathways that might be evolutionarily connected and argue that DNA damage response pathways can be explored therapeutically to induce disease tolerance through the activation of tissue damage control processes. Such approach may constitute the missing pillar in the treatment of critical illnesses caused by multiple organ failure, such as sepsis and septic shock.

The intersection of radiotherapy and immunotherapy: mechanisms and clinical implications

By inducing DNA damage, radiotherapy both reduces tumor burden and enhances anti-tumor immunity. Here, we will review the mechanisms by which radiation induces anti-tumor immune responses that can be augmented using immunotherapies to facilitate tumor regression. Radiotherapy increases inflammation in tumors by activating the NF-κB and the Type I interferon response pathways to induce expression of pro-inflammatory cytokines. This inflammation coupled with antigen release from irradiated cells facilitates dendritic cell maturation and cross-presentation of tumor antigens to prime tumor-specific T cell responses. Radiation also sensitizes tumors to these T cell responses by enhancing T cell infiltration into tumors and the recognition of both malignant cancer cells and non-malignant stroma that present cognate antigen. Yet, these anti-tumor immune responses may be blunted by several mechanisms including regulatory T cells and checkpoint molecules that promote T cell tolerance and exhaustion. Consequently, the combination of immunotherapy using vaccines and/or checkpoint inhibitors with radiation is demonstrating early clinical potential. Overall, this review will provide a global view for how radiation and the immune system converge to target cancers and the early attempts to exploit this synergy in clinical practice.

The DNA damage-induced cell death response: a roadmap to kill cancer cells

Upon massive DNA damage cells fail to undergo productive DNA repair and trigger the cell death response. Resistance to cell death is linked to cellular transformation and carcinogenesis as well as radio- and chemoresistance, making the underlying signaling pathways a promising target for therapeutic intervention. Diverse DNA damage-induced cell death pathways are operative in mammalian cells and finally culminate in the induction of programmed cell death via activation of apoptosis or necroptosis. These signaling routes affect nuclear, mitochondria- and plasma membrane-associated key molecules to activate the apoptotic or necroptotic response. In this review, we highlight the main signaling pathways, molecular players and mechanisms guiding the DNA damage-induced cell death response.

Sam68/KHDRBS1 is critical for colon tumorigenesis by regulating genotoxic stress-induced NF-κB activation

Nuclear factor kappa B (NF-κB)-mediated transcription is an important mediator for cellular responses to DNA damage. Genotoxic agents trigger a 'nuclear-to-cytoplasmic' NF-κB activation signaling pathway; however, the early nuclear signaling cascade linking DNA damage and NF-κB activation is poorly understood. Here we report that Src-associated-substrate-during-mitosis-of-68kDa/KH domain containing, RNA binding, signal transduction associated 1 (Sam68/KHDRBS1) is a key NF-κB regulator in genotoxic stress-initiated signaling pathway. Sam68 deficiency abolishes DNA damage-stimulated polymers of ADP-ribose (PAR) production and the PAR-dependent NF-κB transactivation of anti-apoptotic genes. Sam68 deleted cells are hypersensitive to genotoxicity caused by DNA damaging agents. Upregulated Sam68 coincides with elevated PAR production and NF-κB-mediated anti-apoptotic transcription in human and mouse colon cancer. Knockdown of Sam68 sensitizes human colon cancer cells to genotoxic stress-induced apoptosis and genetic deletion of Sam68 dampens colon tumor burden in mice. Together our data reveal a novel function of Sam68 in the genotoxic stress-initiated nuclear signaling, which is crucial for colon tumorigenesis.

DOI:http://dx.doi.org/10.7554/eLife.15018.001

Cells use signaling pathways to detect and respond to harmful conditions by switching on genes that keep the cell healthy. One important pathway is the nuclear factor kappa B (NF-κB) signaling pathway, which is activated by many stimuli. These stimuli may come from infections from outside the cell or may originate inside the cell, as seen for DNA damage caused by irradiation, chemicals or rapid DNA replication in cancer cells.

Most of a cell’s DNA is located in the cell nucleus. However, NF-κB proteins are normally located outside the nucleus, in the cell’s cytoplasm. Damage to DNA triggers a signal from the nucleus to the cytoplasm. This signal activates the NF-κB proteins, which move into the nucleus and turn on genes that help the cell to recover from the damage. These genes include those that prevent the cell from self-destructing. In one step of the NF-κB activation process, chain-like molecules called polymers are made from a compound called poly(ADP-ribose), or PAR for short. However, few other details are known about how the damaged DNA in the nucleus signals to the cytoplasm.

A protein called Sam68, which is found in the cell nucleus, has been linked to DNA damage signaling. Fu, Sun et al. now present evidence that suggests that if mouse cells lack Sam68, they do not produce PAR polymers in response to DNA damage. In addition, these cells could not trigger the PAR-dependent signaling cascade that is essential for activating NF-κB and for turning on the protective genes. Consequently, cells that lacked Sam68 were extremely sensitive to agents that cause DNA damage, such as chemicals and irradiation.

The NF-κB pathway is regulated incorrectly in some cancers, but is also activated by DNA damage caused by cancer treatments. Therefore, Fu, Sun et al. also explored the role of Sam68 in cancer. Reducing the levels of Sam68 made human colon cancer cells more likely to self-destruct when they were exposed to DNA-damaging agents. Furthermore, removing Sam68 from mice that spontaneously grow colon cancer caused their tumors to develop more slowly than mice that retained Sam68 in their cells.

Overall, the findings presented by Fu, Sun et al. suggest that Sam68 regulates the signal from the nucleus to the cytoplasm that activates NF-κB proteins in response to DNA damage. Sam68 also appears to be important for helping colon cancer cells grow and survive. Future challenges will be to understand how Sam68 regulates the production of the PAR polymer in this response and to explore whether Sam68 can be targeted for treating cancer.

DOI:http://dx.doi.org/10.7554/eLife.15018.002

MLL1 is essential for the senescence-associated secretory phenotype

Capell et al. show that MLL1 inhibition represses expression of critical proproliferative cell cycle regulators required for DNA replication and DNA damage response activation, thus disabling senescence-associated secretory phenotype (SASP) expression. These inhibitory effects of MLL1 on SASP gene expression do not impair oncogene-induced senescence and abolish the ability of the SASP to enhance cancer cell proliferation.

Oncogene-induced senescence (OIS) and therapy-induced senescence (TIS), while tumor-suppressive, also promote procarcinogenic effects by activating the DNA damage response (DDR), which in turn induces inflammation. This inflammatory response prominently includes an array of cytokines known as the senescence-associated secretory phenotype (SASP). Previous observations link the transcription-associated methyltransferase and oncoprotein MLL1 to the DDR, leading us to investigate the role of MLL1 in SASP expression. Our findings reveal direct MLL1 epigenetic control over proproliferative cell cycle genes: MLL1 inhibition represses expression of proproliferative cell cycle regulators required for DNA replication and DDR activation, thus disabling SASP expression. Strikingly, however, these effects of MLL1 inhibition on SASP gene expression do not impair OIS and, furthermore, abolish the ability of the SASP to enhance cancer cell proliferation. More broadly, MLL1 inhibition also reduces “SASP-like” inflammatory gene expression from cancer cells in vitro and in vivo independently of senescence. Taken together, these data demonstrate that MLL1 inhibition may be a powerful and effective strategy for inducing cancerous growth arrest through the direct epigenetic regulation of proliferation-promoting genes and the avoidance of deleterious OIS- or TIS-related tumor secretomes, which can promote both drug resistance and tumor progression.

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.

Physalin A induces G2/M phase cell cycle arrest in human non-small cell lung cancer cells: involvement of the p38 MAPK/ROS pathway

Physalin A (PA) is an active withanolide isolated from Physalis alkekengi var. franchetii, a traditional Chinese herbal medicine named Jindenglong, which has long been used for the treatment of sore throat, hepatitis, and tumors in China. In the present study, we firstly investigated the effects of PA on proliferation and cell cycle distribution of the human non-small cell lung cancer (NSCLC) A549 cell line, and the potential mechanisms involved. Here, PA inhibited cell growth in dose- and time-dependent manners. Treatment of A549 cells with 28.4 μM PA for 24 h resulted in approximately 50 % cell death. PA increased the amount of intracellular ROS and the proportion of cells in G2/M. G2/M arrest was attenuated by the addition of ROS scavenger NAC. ERK and P38 were triggered by PA through phosphorylation in a time-dependent manner. The phosphorylation of ERK and P38 were not attenuated by the addition of NAC, but the use of the p38 inhibitor could reduce, at least in part, PA-induced ROS and the proportion of cells in G2/M. PA induces G2/M cell cycle arrest in A549 cells involving in the p38 MAPK/ROS pathway. This study suggests that PA might be a promising therapeutic agent against NSCLC.

PPM1G Binds 7SK RNA and Hexim1 To Block P-TEFb Assembly into the 7SK snRNP and Sustain Transcription Elongation

Transcription elongation programs are vital for the precise regulation of several biological processes. One key regulator of such programs is the P-TEFb kinase, which phosphorylates RNA polymerase II (Pol II) once released from the inhibitory 7SK small nuclear ribonucleoprotein (snRNP) complex. Although mechanisms of P-TEFb release from the snRNP are becoming clearer, how P-TEFb remains in the 7SK-unbound state to sustain transcription elongation programs remains unknown. Here we report that the PPM1G phosphatase (inducibly recruited by nuclear factor κB [NF-κB] to target promoters) directly binds 7SK RNA and the kinase inhibitor Hexim1 once P-TEFb has been released from the 7SK snRNP. This dual binding activity of PPM1G blocks P-TEFb reassembly onto the snRNP to sustain NF-κB-mediated Pol II transcription in response to DNA damage. Notably, the PPM1G-7SK RNA interaction is direct, kinetically follows the recruitment of PPM1G to promoters to activate NF-κB transcription, and is reversible, since the complex disassembles before resolution of the program. Strikingly, we found that the ataxia telangiectasia mutated (ATM) kinase regulates the interaction between PPM1G and the 7SK snRNP through site-specific PPM1G phosphorylation. The precise and temporally regulated interaction of a cellular enzyme and a noncoding RNA provides a new paradigm for simultaneously controlling the activation and maintenance of inducible transcription elongation programs.

Ablation of XP-V gene causes adipose tissue senescence and metabolic abnormalities

Obesity and the metabolic syndrome have evolved to be major health issues throughout the world. Whether loss of genome integrity contributes to this epidemic is an open question. DNA polymerase η (pol η), encoded by the xeroderma pigmentosum (XP-V) gene, plays an essential role in preventing cutaneous cancer caused by UV radiation-induced DNA damage. Herein, we demonstrate that pol η deficiency in mice (pol η(-/-)) causes obesity with visceral fat accumulation, hepatic steatosis, hyperleptinemia, hyperinsulinemia, and glucose intolerance. In comparison to WT mice, adipose tissue from pol η(-/-) mice exhibits increased DNA damage and a greater DNA damage response, indicated by up-regulation and/or phosphorylation of ataxia telangiectasia mutated (ATM), phosphorylated H2AX (γH2AX), and poly[ADP-ribose] polymerase 1 (PARP-1). Concomitantly, increased cellular senescence in the adipose tissue from pol η(-/-) mice was observed and measured by up-regulation of senescence markers, including p53, p16(Ink4a), p21, senescence-associated (SA) β-gal activity, and SA secretion of proinflammatory cytokines interleukin 6 (IL-6) and tumor necrosis factor α (TNF-α) as early as 4 wk of age. Treatment of pol η(-/-) mice with a p53 inhibitor, pifithrin-α, reduced adipocyte senescence and attenuated the metabolic abnormalities. Furthermore, elevation of adipocyte DNA damage with a high-fat diet or sodium arsenite exacerbated adipocyte senescence and metabolic abnormalities in pol η(-/-) mice. In contrast, reduction of adipose DNA damage with N-acetylcysteine or metformin ameliorated cellular senescence and metabolic abnormalities. These studies indicate that elevated DNA damage is a root cause of adipocyte senescence, which plays a determining role in the development of obesity and insulin resistance.

Dissecting NF-κB signaling induced by genotoxic agents via genetic complementation of NEMO-deficient 1.3E2 cells

The transcription factor NF-κB regulates expression of a diverse set of genes to modulate multiple biological and pathological processes. Among these, NF-κB activation in response to genotoxic agents has received considerable attention due to its role in regulating cancer cell resistance to chemo- and radiation therapy. Furthermore, induction of this pathway by endogenous damage is further implicated in normal developmental processes, such as B cell development, and premature aging, among others. This pathway also serves as a signaling model in which nuclear initiated signals (DNA damage) are communicated to a cytoplasmic target (IκB kinase and NF-κB). Several of the critical molecular events of this nuclear to cytoplasmic NF-κB signaling cascade were discovered, in part, by genetic complementation analyses of the NEMO-deficient 1.3E2 mouse pre-B cell line. This chapter describes methods used to generate and analyze such reconstitution cell systems and certain caveats that are critical for proper interpretation of NEMO mutant defects.

Bystander communication and cell cycle decisions after DNA damage

The DNA damage response (DDR) has two main goals, to repair the damaged DNA and to communicate the presence of damaged DNA. This communication allows the adaptation of cellular behavior to minimize the risk associated with DNA damage. In particular, cell cycle progression must be adapted after a DNA-damaging insult, and cells either pause or terminally exit the cell cycle during a DDR. As cells can accumulate mutations after a DDR due to error-prone DNA repair, terminal cell cycle exit may prevent malignant transformation. The tumor suppressor p53 plays a key role in promoting terminal cell cycle exit. Interestingly, p53 has been implicated in communication of a stress response to surrounding cells, known as the bystander response. Recently, surrounding cells have also been shown to affect the damaged cell, suggesting the presence of intercellular feedback loops. How such feedback may affect terminal cell cycle exit remains unclear, but its presence calls for caution in evaluating cellular outcome without controlling the cellular surrounding. In addition, such feedback may contribute to how the cellular environment affects malignant transformation after DNA damage.

The many interactions between the innate immune system and the response to radiation

The role of the immune system in the protection of the organism against biological aggressions is long established and well-studied. A new role emerged more recently in the protection from - and the response to - physical trauma such as exposure to ionizing radiation. A pre-existing inflammation, induced by administration of an inflammatory cytokine or of a Toll-like receptor agonist, is indeed able to mitigate the toxic effects of acute radiation exposure. Conversely, it appears that the innate immune system can be activated during the course of the cellular response to radiation. Activation of different sensors and pattern recognition receptors by intra-cellular molecules such as HMGB1 or DNA released in the extra-cellular milieu or in the cytosol by irradiated cells induces the production of inflammatory and anti-viral cytokines. In addition, in human monocytes and macrophages, the expression of inflammatory cytokine genes can be directly induced by p53- and ATM-dependent mechanisms. This last finding establishes a direct link between radiation-induced DNA damage response and radiation-induced inflammation.

Carbon ions and X‑rays induce pro‑inflammatory effects in 3D oral mucosa models with and without PBMCs

Oral mucositis is a severe complication of radiotherapy. Hence, it may constitute a serious medical safety risk for astronauts during extended space flights, such as missions to Mars, during which they are exposed to heavy-ion irradiation. For risk assessment of developing radiation-induced mucositis, a three-dimensional (3D) organotypic oral mucosa model was irradiated with 12C heavy ions or X‑rays. The present study focused mainly on early radiation‑induced effects, such as the activation of nuclear factor κB (NFκB) and the expression or release of pro-inflammatory marker molecules. The 3D oral mucosa models with or without peripheral blood mononuclear cells (PBMCs) were irradiated with X‑rays or 12C heavy ions followed by snap freezing. Subsequently, cryosections were derived from the specimens, which were immunostained for analysis of compactness, DNA double strand breaks (DSB) and activation of NFκB. Radiation‑induced release of interleukin 6 (IL6) and interleukin 8 (IL8) was quantified by ELISA. Quantification of the DNA damage in irradiated mucosa models revealed distinctly more DSB after heavy-ion irradiation compared to X‑rays at definite time points, suggesting a higher gene toxicity of heavy ions. NFκB activation was observed after treatment with X‑rays or 12C particles. ELISA analyses showed significantly higher IL6 and IL8 levels after irradiation with X‑rays and 12C particles compared to non-irradiated controls, whereas co‑cultures including PBMCs released 2 to 3-fold higher interleukin concentrations compared to mucosa models without PBMCs. In this study, we demonstrated that several pro-inflammatory markers are induced by X‑rays and heavy-ion irradiation within an oral mucosa model. This suggests that oral mucositis indeed poses a risk for astronauts on extended space flights.

Linking JNK Activity to the DNA Damage Response

The activity of c-Jun N-terminal kinase (JNK) was initially described as ultraviolet- and oncogene-induced kinase activity on c-Jun. Shortly after this initial discovery, JNK activation was reported for a wider variety of DNA-damaging agents, including γ-irradiation and chemotherapeutic compounds. As the DNA damage response mechanisms were progressively uncovered, the mechanisms governing the activation of JNK upon genotoxic stresses became better understood. In particular, a recent set of papers links the physical breakage in DNA, the activation of the transcription factor NF-κB, the secretion of TNF-α, and an autocrine activation of the JNK pathway. In this review, we will focus on the pathway that is initiated by a physical break in the DNA helix, leading to JNK activation and the resultant cellular consequences. The implications of these findings will be discussed in the context of cancer therapy with DNA-damaging agents.

Bystander effects as manifestation of intercellular communication of DNA damage and of the cellular oxidative status

It is becoming increasingly clear that cells exposed to ionizing radiation (IR) and other genotoxic agents (targeted cells) can communicate their DNA damage response (DDR) status to cells that have not been directly irradiated (bystander cells). The term radiation-induced bystander effects (RIBE) describes facets of this phenomenon, but its molecular underpinnings are incompletely characterized. Consequences of DDR in bystander cells have been extensively studied and include transformation and mutation induction; micronuclei, chromosome aberration and sister chromatid exchange formation; as well as modulations in gene expression, proliferation and differentiation patterns. A fundamental question arising from such observations is why targeted cells induce DNA damage in non-targeted, bystander cells threatening thus their genomic stability and risking the induction of cancer. Here, we review and synthesize available literature to gather support for a model according to which targeted cells modulate as part of DDR their redox status and use it as a source to generate signals for neighboring cells. Such signals can be either small molecules transported to adjacent non-targeted cells via gap-junction intercellular communication (GJIC), or secreted factors that can reach remote, non-targeted cells by diffusion or through the circulation. We review evidence that such signals can induce in the recipient cell modulations of redox status similar to those seen in the originating targeted cell - occasionally though self-amplifying feedback loops. The resulting increase of oxidative stress in bystander cells induces, often in conjunction with DNA replication, the observed DDR-like responses that are at times strong enough to cause apoptosis. We reason that RIBE reflect the function of intercellular communication mechanisms designed to spread within tissues, or the entire organism, information about DNA damage inflicted to individual, constituent cells. Such responses are thought to protect the organism by enhancing repair in a community of cells and by eliminating severely damaged cells.

ATM-NFκB axis-driven TIGAR regulates sensitivity of glioma cells to radiomimetics in the presence of TNFα

Gliomas are resistant to radiation therapy, as well as to TNFα induced killing. Radiation-induced TNFα triggers Nuclear factor κB (NFκB)-mediated radioresistance. As inhibition of NFκB activation sensitizes glioma cells to TNFα-induced apoptosis, we investigated whether TNFα modulates the responsiveness of glioma cells to ionizing radiation-mimetic Neocarzinostatin (NCS). TNFα enhanced the ability of NCS to induce glioma cell apoptosis. NCS-mediated death involved caspase-9 activation, reduction of mitochondrial copy number and lactate production. Death was concurrent with NFκB, Akt and Erk activation. Abrogation of Akt and NFκB activation further potentiated the death inducing ability of NCS in TNFα cotreated cells. NCS-induced p53 expression was accompanied by increase in TP53-induced glycolysis and apoptosis regulator (TIGAR) levels and ATM phosphorylation. siRNA-mediated knockdown of TIGAR abrogated NCS-induced apoptosis. While DN-IκB abrogated NCS-induced TIGAR both in the presence and absence of TNFα, TIGAR had no effect on NFκB activation. Transfection with TIGAR mutant (i) decreased apoptosis and γH2AX foci formation (ii) decreased p53 (iii) elevated ROS and (iv) increased Akt/Erk activation in cells cotreated with NCS and TNFα. Heightened TIGAR expression was observed in GBM tumors. While NCS induced ATM phosphorylation in a NFκB independent manner, ATM inhibition abrogated TIGAR and NFκB activation. Metabolic gene profiling indicated that TNFα affects NCS-mediated regulation of several genes associated with glycolysis. The existence of ATM-NFκB axis that regulate metabolic modeler TIGAR to overcome prosurvival response in NCS and TNFα cotreated cells, suggests mechanisms through which inflammation could affect resistance and adaptation to radiomimetics despite concurrent induction of death.

Type-3 metabotropic glutamate receptors regulate chemoresistance in glioma stem cells, and their levels are inversely related to survival in patients with malignant gliomas

Drug treatment of malignant gliomas is limited by the intrinsic resistance of glioma stem cells (GSCs) to chemotherapy. GSCs isolated from human glioblastoma multiforme (GBM) expressed metabotropic glutamate receptors (mGlu3 receptors). The DNA-alkylating agent, temozolomide, killed GSCs only if mGlu3 receptors were knocked down or pharmacologically inhibited. In contrast, mGlu3 receptor blockade did not affect the action of paclitaxel, etoposide, cis-platinum, and irinotecan. mGlu3 receptor blockade enabled temozolomide toxicity by inhibiting a phosphatidylinositol-3-kinase/nuclear factor-κB pathway that supports the expression of O(6)-methylguanine-DNA methyltransferase (MGMT), an enzyme that confers resistance against DNA-alkylating agents. In mice implanted with GSCs into the brain, temozolomide combined with mGlu3 receptor blockade substantially reduced tumor growth. Finally, 87 patients with GBM undergoing surgery followed by adjuvant chemotherapy with temozolomide survived for longer time if tumor cells expressed low levels of mGlu3 receptors. In addition, the methylation state of the MGMT gene promoter in tumor extracts influenced survival only in those patients with low expression of mGlu3 receptors in the tumor. These data encourage the use of mGlu3 receptor antagonists as add-on drugs in the treatment of GBM, and suggest that the transcript of mGlu3 receptors should be measured in tumor specimens for a correct prediction of patients' survival in response to temozolomide treatment.