Manganese superoxide dismutase-mediated gene expression in radiation-induced adaptive responses

Differential induction and activation of NF-kappaB transcription complexes in radiation-induced chromosomally unstable cell lines

Radiation-induced genomic instability is a delayed effect of ionizing radiation that may contribute to radiation carcinogenesis. Prior microarray studies investigating gene expression changes in genomically unstable cell lines isolated after radiation exposure uncovered the differential expression of the NF-kappaB p105 mRNA. In this study, the functionality of the NF-kappaB pathway was examined to determine its role in regulating gene expression changes after oxidative stress in chromosomally stable and unstable human-hamster hybrid clones. Basal DNA-binding activity assays showed no significant differences between the clones; however, further experiments established differences in NF-kappaB induction in three chromosomally unstable clones after acute hydrogen peroxide treatment. A second assay was used to confirm this differential activity in the chromosomally unstable clones by studying reporter gene activation after treatment with hydrogen peroxide. Yet an initial upstream analysis of the pathway revealed no significant increase in the level of IkappaBalpha inhibitor protein in the unstable clones. Downstream tests analyzing the induction of the antiapoptotic target protein Bcl-2 found variable induction among the stable and unstable clones. These differences did not translate to a reduction in clonogenic survival after acute exposure to oxidative stress, as the irradiated but chromosomally stable clone displayed the most sensitivity. Due to its role in regulating a diverse set of cellular functions, including responses to oxidative stress, alterations in the NF-kappaB pathway in chromosomally unstable clones may regulate the differential physiology of a subset of chromosomally unstable clones and could contribute to the perpetuation of the phenotype. However, a specific role for defective induction and activation of this pathway remains unidentified.

Co-activation of ERK, NF-kappaB, and GADD45beta in response to ionizing radiation

NF-kappaB has been well documented to play a critical role in signaling cell stress reactions. The extracellular signal-regulated kinase (ERK) regulates cell proliferation and survival. GADD45beta is a primary cell cycle element responsive to NF-kappaB activation in anti-apoptotic responses. The present study provides evidence demonstrating that NK-kappaB, ERK and GADD45beta are co-activated by ionizing radiation (IR) in a pattern of mutually dependence to increase cell survival. Stress conditions generated in human breast cancer MCF-7 cells by the administration of a single exposure of 5 Gy IR resulted in the activation of ERK but not p38 or JNK, along with an enhancement of the NF-kappaB transactivation and GADD45beta expression. Overexpression of dominant negative Erk (DN-Erk) or pre-exposure to ERK inhibitor PD98059 inhibited NF-kappaB. Transfection of dominant negative mutant IkappaB that blocks NF-kappaB nuclear translocation, inhibited ERK activity and GADD45beta expression and increased cell radiosensitivity. Interaction of p65 and ERK was visualized in living MCF-7 cells by bimolecular fluorescence complementation analysis. Antisense inhibition of GADD45beta strikingly blocked IR-induced NF-kappaB and ERK but not p38 and JNK. Overall, these results demonstrate a possibility that NF-kappaB, ERK, and GADD45beta are able to coordinate in a loop-like signaling network to defend cells against the cytotoxicity induced by ionizing radiation.

An examination of radiation hormesis mechanisms using a multistage carcinogenesis model

A multistage cancer model that describes the putative rate-limiting steps in carcinogenesis is developed and used to investigate the potential impact on cumulative lung cancer incidence of the hormesis mechanisms suggested by Feinendegen and Pollycove. In the model, radiation and endogenous processes damage the DNA of target cells in the lung. Some fraction of the misrepaired or unrepaired DNA damage induces genomic instability and, ultimately, leads to the accumulation of malignant cells. The model explicitly accounts for cell birth and death processes, the clonal expansion of initiated cells, malignant conversion, and a lag period for tumor formation. Radioprotective mechanisms are incorporated into the model by postulating dose and dose-rate-dependent radical scavenging. The accuracy of DNA damage repair also depends on dose and dose rate. As currently formulated, the model is most applicable to low-linear-energy-transfer (LET) radiation delivered at low dose rates. Sensitivity studies are conducted to identify critical model inputs and to help define the shapes of the cumulative lung cancer incidence curves that may arise when dose and dose-rate-dependent cellular defense mechanisms are incorporated into a multistage cancer model. For lung cancer, both linear no-threshold (LNT-), and non-LNT-shaped responses can be obtained. If experiments demonstrate that the effects of DNA damage repair and radical scavenging are enhanced at least three-fold under low-dose conditions, our studies would support the existence of U-shaped responses. The overall fidelity of the DNA damage repair process may have a large impact on the cumulative incidence of lung cancer. The reported studies also highlight the need to know whether or not (or to what extent) multiply damaged DNA sites are formed by endogenous processes. Model inputs that give rise to U-shaped responses are consistent with an effective cumulative lung cancer incidence threshold that may be as high as 300 mGy (4 mGy per year for 75 years) for low-LET radiation.

Response of cyclin B1 to ionizing radiation: regulation by NF-kappaB and mitochondrial antioxidant enzyme MnSOD

BACKGROUND

To understand the molecular response of tumor cells to therapeutic ionizing radiation (IR), we previously reported that human breast cancer cells derived following chronic exposure to fractionated ionizing radiation (MCF+FIR) showed a transient radioresistance. MCF+FIR cells also demonstrated increased activity of NF-kappaB, increased expression of the mitochondrial antioxidant enzyme (MnSOD), and increased expression of a cell cycle regulatory protein (Cyclin B1). The present studies were designed to determine the relationship of NF-kappaB, MnSOD and Cyclin B1 expression in cellular adaptive responses to ionizing radiation.

MATERIALS AND METHODS

The first intron of the cyclin B1 gene with a putative NF-kappaB element was cloned into the pGL3 luciferase reporter (pGL3CB1EI1). PGL3CB1EI1 and control NF-kappaB luciferase activities were determined in MCF-7 and MCF+FIR cells treated with a single dose of radiation, over expression of the dominant negative mutant IkB (mIkB) or over expression of the SOD2 gene.

RESULTS

MCF+FIR cells derived from fractionated IR demonstrated increased transactivation of the pGL3CB1EI1 and NF-kappaB controlled reporter activities, relative to the parental cell line. Transfection of dominant negative mutant IkB that inhibits NF-kappaB nuclear translocation, inhibited pGL3CB1EI1 and NF-kappaB activity, indicating the NF-kappaB dependence of pGL3CB1EI1 mediated transcription. In addition, over expression of the human SOD2 gene (MnSOD) inhibited NF-kappaB and pGL3CB1EI1 activity, indicating that superoxide or some species derived from superoxide may have participated in the up-regulation of reporter activity in response to chronic exposure to fractionated ionizing radiation. These results provide evidence suggesting that a signaling pathway involving NF-kappaB and Cyclin B1 may contribute to adaptive radioresistance induced by chronic exposure to fractionated IR and support the conclusion that MnSOD appears to be a negative regulator of this pathway.

Oxidative stress, radiation-adaptive responses, and aging

Organisms living in an aerobic environment were forced to evolve effective cellular strategies to detoxify reactive oxygen species. Besides diverse antioxidant enzymes and compounds, DNA repair enzymes, and disassembly systems, which remove damaged proteins, regulation systems that control transcription, translation, and activation have also been developed. The adaptive responses, especially those to radiation, are defensive regulation mechanisms by which oxidative stress (conditioning irradiation) elicits a response against damage because of subsequent stress (challenging irradiation). Although many researchers have investigated these molecular mechanisms, they remain obscure because of their complex signaling pathways and the involvement of various proteins. This article reviews the factors concerned with radiation-adaptive response, the signaling pathways activated by conditioning irradiation, and the effects of aging on radiation-adaptive response. The proteomics approach is also introduced, which is a useful method for studying stress response in cells.

Oxidative stress and delayed-onset muscle damage after exercise

Reactive oxygen species (ROS) produced during exercise may be involved in delayed-onset muscle damage related to inflammation. To investigate this hypothesis, we studied whether oxidative stress increases nuclear translocation of nuclear factor-kappaB and chemokine expression in skeletal muscle using myotube L6 cells. We also assessed whether prolonged acute exercise could increase these parameters in rats. In L6 cells, H(2)O(2) induced nuclear translocation of p65 and increased the expression of cytokine-induced neutrophil chemoattractant-1 (CINC-1) and monocyte chemoattractant protein-1 (MCP-1), whereas preincubation with alpha-tocopherol limited the increase in these proteins. Sprague Dawley rats were divided into the following groups: rested control, exercised, rested with a high alpha-tocopherol diet, and exercised with a high alpha-tocopherol diet. After 3 weeks of acclimation, both exercise groups ran on a treadmill at 25 m/min for 60 min. Exercise increased nuclear p65, CINC-1, and MCP-1 in gastrocnemius muscle cells, but these changes were ameliorated by the high alpha-tocopherol diet. Increases in myeloperoxidase and thiobarbituric acid-reactive substrates were ameliorated by a high alpha-tocopherol diet, as were the histological changes. Neutrophil activity was not altered by either exercise or a high alpha-tocopherol diet. These results indicate that delayed-onset muscle damage induced by prolonged exercise is partly related to inflammation via phagocyte infiltration caused by ROS and that alpha-tocopherol (an antioxidant) can attenuate such inflammatory changes.

Manganese superoxide dismutase Ala-9Val polymorphism and risk of breast cancer in a population-based case-control study of African Americans and whites

Introduction

A polymorphism in the manganese superoxide dismutase (MnSOD) gene, Ala-9Val, has been examined in association with breast cancer risk in several epidemiologic studies. Results suggest that the Ala allele increases the risk of breast cancer and modifies the effects of environmental exposures that produce oxidative damage to DNA.

Methods

We examined the role of the MnSOD Ala-9Val polymorphism in a population-based case–control study of invasive and in situ breast cancer in North Carolina. Genotypes were evaluated for 2025 cases (760 African Americans and 1265 whites) and for 1812 controls (677 African Americans and 1135 whites).

Results

The odds ratio for MnSOD Ala/Ala versus any MnSOD Val genotypes was not elevated in African Americans (odds ratio = 0.9, 95% confidence interval = 0.7–1.2) or in whites (odds ratio = 1.0, 95% confidence interval = 0.8–1.2). Greater than additive joint effects were observed for the Ala/Ala genotype and smoking, radiation to the chest, and occupational exposure to ionizing radiation. Antagonism was observed between the Ala/Ala genotype and the use of nonsteroidal anti-inflammatory drugs.

Conclusions

The MnSOD genotype may contribute to an increased risk of breast cancer in the presence of specific environmental exposures. These results provide further evidence for the importance of reactive oxygen species and of oxidative DNA damage in the etiology of breast cancer.

p53 activation in chronic radiation-treated breast cancer cells: regulation of MDM2/p14ARF

Mammalian cells chronically exposed to ionizing radiation (IR) induce stress response with a tolerance to the subsequent cytotoxicity of IR. Although p53 is well documented in IR response, the signaling network causing p53 activation in chronic IR remains to be identified. Using breast carcinoma MCF+FIR cells that showed a transient radioresistance after exposure chronically to fractionated IR (FIR), the present study shows that the basal DNA binding and transcriptional activity of p53 was elevated by FIR. p53-controlled luciferase activity was strikingly induced ( approximately 7.9-fold) with little enhancement of p53/DNA binding activity ( approximately 1.3-fold). The phosphorylated p53 (Thr 55) was increased in the cytoplasm and nucleus of MCF+FIR but not in the sham-FIR control cells. On the contrary, the sham-FIR control MCF-7 cells showed a low p53 luciferase transcription ( approximately 3-fold) but a striking enhancement of p53/DNA binding (12-fold) after 5 Gy of IR. To determine the signaling elements regulating p53 activity, DNA microarray of MCF+FIR using sham-FIR MCF-7 cells as a reference demonstrated that the mRNA of p21, MDM2, and p14ARF was up-regulated. Time course Western blot analysis, however, showed no difference in p21 induction. In contrast, MDM2 that was absent in control cells and was predominantly induced by IR was not induced in MCF+FIR cells. In agreement with MDM2 inhibition, MDM2-inhibitory protein p14ARF was increased in MCF+FIR cells. In summary, these results demonstrate that up-regulation of p14ARF paralleled with MDM2 inhibition contributes to p53 accumulation in the nucleus and causes a high responsiveness of p53 in chronic IR-treated breast cancer cells.

Superoxide dismutases in malignant cells and human tumors

Reactive oxygen metabolites have multifactorial effects on the regulation of cell growth and the capacity of malignant cells to invade. Overexpression of the superoxide dismutases (SODs) in vitro increases cell differentiation, decreases cell growth and proliferation, and can reverse a malignant phenotype to a nonmalignant one. The situation in vivo is more complex due to multiple interactions of tumor cells with their environment. Numerous in vivo studies show that the superoxide dismutases can be highly expressed in aggressive human solid tumors. Furthermore, high SOD has occasionally been associated with a poor prognosis and with resistance to cytotoxic drugs and radiation. Most of the apparent conflicts between the above in vitro and in vivo observations can be reconciled by considering the net redox status of tumor cells in different environments. Administering high concentrations of SOD to cells in vitro is usually associated with a non- or less malignant phenotype, whereas secondary induction of SOD in tumors in vivo can be associated with an aggressive malignant transformation probably due to the altered (oxidative) redox state in the malignant cells. This concept suggests that for many types of tumors antioxidants could be used to diminish the invasive capability of malignant cells.

Expression of ErbB2 enhances radiation-induced NF-kappaB activation

Her-2/neu (ErbB2) oncogene, the second member of the epidermal growth factor receptor (EGFR) family, encodes a transmembrane tyrosine kinase receptor in Her-2-positive tumors. Accumulating evidences demonstrate that signaling networks activated by EGFR and transcription factor NF-kappaB are associated with cell response to ionizing radiation (IR). The present study shows that overexpression of ErbB2 enhanced NF-kappaB activation induced by IR in human breast carcinoma MCF-7 cells transfected with ErbB2 genes (MCF-7/ErbB2). Stable transfection of dominant-negative mutant IkappaB (MCF-7/ErbB2/mIkappaB) or treatment with anti-ErbB2 antibody, Herceptin, inhibited NF-kappaB activation and radiosensitized MCF-7/ErbB2 cells. Consistent with NF-kappaB regulation, basal and IR-induced Akt, a kinase downstream of ErbB2, was activated in MCF-7/ErbB2 cells and inhibited by Herceptin. To identify specific genes affected by ErbB2-mediated NF-kappaB activation, a group of IR-responsive elements Cyclin B1, Cyclin D1, Bcl-2, Bcl/XL, BAD and BAX were evaluated. Basal levels of prosurvival elements Cyclin B1, Cyclin D1, Bcl-2 and Bcl/XL but not apoptotic BAD and BAX were upregulated in MCF-7/ErbB2 cells with striking enhancements in Bcl-2 and Bcl/XL. IR further induced Cyclin B1 and Cyclin D1 expression that was reduced by Herceptin. Bcl-2 kept a high steady level after Herceptin+IR treatment and, in contrast to control MCF-7/Vector cells, Bcl/XL was inhibited in MCF-7/ErbB2 cells by Herceptin+IR treatment. However, all four prosurvival proteins were downregulated by inhibition of NF-kappaB in MCF-7/ErbB2/mIkappaB cells. These results thus provide evidence suggesting that overexpression of ErbB2 is able to enhance NF-kappaB response to IR, and that a specific prosurvival network downstream of NF-kappaB is triggered by treatments using anti-ErbB2 antibody combined with radiation.

Resistance of mitochondrial DNA-depleted cells against cell death: role of mitochondrial superoxide dismutase

We have shown that mitochondrial DNA-depleted (rho(0)) SK-Hep1 hepatoma cells are resistant to apoptosis, contrary to previous papers reporting normal apoptotic susceptibility of rho(0) cells. We studied the changes of gene expression in SK-Hep1 rho(0) cells. DNA chip analysis showed that MnSOD expression was profoundly increased in rho(0) cells. O(2)(.) contents increased during rho(0) cell derivation but became normalized after establishment of rho(0) phenotypes, suggesting that MnSOD induction is an adaptive process to increased O(2)(.). rho(0) cells were resistant to menadione, paraquat, or doxorubicin, and O(2)(.) contents after treatment with them were lower in rho(0) cells compared with parental cells because of MnSOD overexpression. Expression levels and activity of glutathione peroxidases were also increased in rho(0) cells, rendering them resistant to exogenous H(2)O(2). rho(0) cells were resistant to p53, and intracellular ROS contents after p53 expression were lower compared with parental cells. Other types of rho(0) cells also showed increased MnSOD expression and resistance against ROS. Heme oxygenase-1 expression was increased in rho(0) cells, and a heme oxygenase-1 inhibitor decreased the induction of MnSOD in rho(0) cells and their resistance against ROS donors. These results indicate that rho(0) cells are resistant to cell death contrary to previous reports and suggest that an adaptive increase in the expression of antioxidant enzymes renders cancer cells or aged cells with frequent mitochondrial DNA mutations to resist against oxidative stress, host anti-cancer surveillance, or chemotherapeutic agents, conferring survival advantage on them.

Nuclear factor-κB as a predictor of treatment response in breast cancer

PURPOSE OF REVIEW

To examine the links of nuclear factor-kappa B (NF-kappa B) to treatment-induced signaling in breast cancer and to propose further studies to elucidate the role of NF-kappa B in breast cancer response to chemotherapy and radiation.

RECENT FINDINGS

The authors' group and others have investigated the clinical relevance of ubiquitously expressed NF-kappa B in breast cancer. Possibly through its effects on apoptosis, NF-kappa B has been implicated in tumor resistance to chemotherapy and radiation in many types of tumors. Furthermore, both in vitro and in vivo studies have shown that targeted inhibition of NF-kappa B can sensitize tumor cells to chemotherapy and radiation.

SUMMARY

The molecular mechanisms involved in chemotherapy-induced and radiation-induced cell death in breast cancer are not fully known, nor are the mechanisms of treatment resistance. NF-kappa B is a transcription factor for a number of genes involved in tumor progression and resistance to systemic therapies and is a major regulator of the apoptotic pathway. Gaining further insights into molecular factors such as NF-kappa B as biomarkers for treatment response may help clinicians predict treatment outcome and lead to the development of targeted therapeutics.

MnSOD up-regulates maspin tumor suppressor gene expression in human breast and prostate cancer cells

Manganese superoxide dismutase (MnSOD) is an antioxidant enzyme with tumor suppressor activity; however, the molecular mechanisms of MnSOD antitumor effects remain unclear. We hypothesized that MnSOD activity in cancer cells might cause downstream changes in the expression of other tumor suppressor genes. To determine whether maspin, a tumor suppressor gene that inhibits breast cancer cell invasion and metastasis, might be a target of MnSOD, we forced MnSOD expression in several human breast and prostate cancer cell lines by adenovirus-mediated gene transfer and measured maspin mRNA expression. Forced expression of MnSOD caused maspin mRNA to accumulate in a dose-dependent manner in both human breast and prostate cancer cells. Normal p53 was not necessary to mediate the effect of MnSOD because MnSOD up-regulated maspin in cells that harbor wild-type p53 and in cells that harbor mutant p53. Moreover, the effects of MnSOD on maspin were not due to demethylation of the maspin promoter. Analyses of maspin promoter activity, transcriptional run-on, and mRNA stability showed that maspin mRNA stability was the major mechanism for maspin up-regulation by MnSOD. Our findings identify a mechanism underlying MnSOD antitumor effects and provide evidence to support MnSOD as a genetic therapy in the treatment of human breast and prostate cancers.

The relation between the pure-tone audiogram and the click auditory brainstem response threshold in cochlear hearing loss

Auditory brainstem response thresholds for 209 ears with cochlear hearing loss were compared with the pure-tone thresholds. It is shown that the pure-tone threshold in the 2- to 4-kHz region has a one-to-one relationship with the auditory brainstem response threshold. Estimating the pure-tone threshold from the auditory brainstem response threshold, the standard error of the estimate is 11 dB. A small part of this estimation error is due to errors in the measurement of the auditory brainstem response threshold and the mean of the pure-tone thresholds at 2 and 4 kHz. The major part is due to unknown factors that are involved in the physiological relationship between the two thresholds.