Superoxide dismutase activity and superoxide dismutase-1 gene methylation in normal and tumoral human breast tissues

LCS-1 inhibition of superoxide dismutase 1 induces ROS-dependent death of glioma cells and degradates PARP and BRCA1

Gliomas are characterized by high morbidity and mortality, and have only slightly increased survival with recent considerable improvements for treatment. An innovative therapeutic strategy had been developed via inducing ROS-dependent cell death by targeting antioxidant proteins. In this study, we found that glioma tissues expressed high levels of superoxide dismutase 1 (SOD1). The expression of SOD1 was upregulated in glioma grade III and V tissues compared with that in normal brain tissues or glioma grade I tissues. U251 and U87 glioma cells expressed high levels of SOD1, low levels of SOD2 and very low levels of SOD3. LCS-1, an inhibitor of SOD1, increased the expression SOD1 at both mRNA and protein levels slightly but significantly. As expected, LCS-1 caused ROS production in a dose- and time-dependent manner. SOD1 inhibition also induced the gene expression of HO-1, GCLC, GCLM and NQO1 which are targeting genes of nuclear factor erythroid 2-related factor 2, suggesting the activation of ROS signal pathway. Importantly, LCS-1 induced death of U251 and U87 cells dose- and time-dependently. The cell death was reversed by the pretreatment of cells with ROS scavenges NAC or GSH. Furthermore, LCS-1 decreased the growth of xenograft tumors formed by U87 glioma cells in nude mice. Mechanistically, the inhibition of P53, caspases did not reverse LCS-1-induced cell death, indicating the failure of these molecules involving in cell death. Moreover, we found that LCS-1 treatment induced the degradation of both PARP and BRCA1 simultaneously, suggesting that LCS-1-induced cell death may be associated with the failure of DNA damage repair. Taking together, these results suggest that the degradation of both PARP and BRCA1 may contribute to cell death induced by SOD1 inhibition, and SOD1 may be a target for glioma therapy.

Manganese superoxide dismutase is dispensable for post-natal development and lactation in the murine mammary gland

Mammary gland development is a multistage process requiring tightly regulated spatial and temporal signalling pathways. Many of these pathways have been shown to be sensitive to oxidative stress. Understanding that the loss of manganese superoxide dismutase (Sod2) leads to increased cellular oxidative stress, and that the loss or silencing of this enzyme has been implicated in numerous pathologies including those of the mammary gland, we sought to examine the role of Sod2 in mammary gland development and function in situ in the mouse mammary gland. Using Cre-recombination driven by the mouse mammary tumor virus (MMTV) promoter, we created a mammary-specific post-natal conditional Sod2 knock-out mouse model. Surprisingly, while substantial decreases in Sod2 were noted throughout both virgin and lactating adult mammary glands, no significant changes in developmental structures either pre- or post-pregnancy were observed histologically. Moreover, mothers lacking mammary gland expression of Sod2 were able to sustain equal numbers of litters, equal pups per litter, and equal pup weights as were control animals. Overall, our results demonstrate that loss of Sod2 expression is not universally toxic to all cell types and that excess mitochondrial superoxide can apparently be tolerated during the development and function of post-natal mammary glands.

ERα-associated protein networks

Estrogen receptor α (ERα) is a ligand-activated transcription factor that, upon binding hormone, interacts with specific recognition sequences in DNA. An extensive body of literature has documented the association of individual regulatory proteins with ERα. It has recently become apparent that, instead of simply recruiting individual proteins, ERα recruits interconnected networks of proteins with discrete activities that play crucial roles in maintaining the structure and function of the receptor, stabilizing the receptor-DNA interaction, influencing estrogen-responsive gene expression, and repairing misfolded proteins and damaged DNA. Together these studies suggest that the DNA-bound ERα serves as a nucleating factor for the recruitment of protein complexes involved in key processes including the oxidative stress response, DNA repair, and transcription regulation.

Deregulation of manganese superoxide dismutase (SOD2) expression and lymph node metastasis in tongue squamous cell carcinoma

Background

Lymph node metastasis is a critical event in the progression of tongue squamous cell carcinoma (TSCC). The identification of biomarkers associated with the metastatic process would provide critical prognostic information to facilitate clinical decision making. Previous studies showed that deregulation of manganese superoxide dismutase (SOD2) expression is a frequent event in TSCC and may be associated with enhanced cell invasion. The purpose of this study is to further evaluate whether the expression level of SOD2 is correlated with the metastatic status in TSCC patients.

Methods

We first examined the SOD2 expression at mRNA level on 53 TSCC and 22 normal control samples based on pooled-analysis of existing microarray datasets. To confirm our observations, we examined the expression of SOD2 at protein level on an additional TSCC patient cohort (n = 100), as well as 31 premalignant dysplasias, 15 normal tongue mucosa, and 32 lymph node metastatic diseases by immunohistochemistry (IHC).

Results

The SOD2 mRNA level in primary TSCC tissue is reversely correlated with lymph node metastasis in the first TSCC patient cohort. The SOD2 protein level in primary TSCC tissue is also reversely correlated with lymph node metastasis in the second TSCC patient cohort. Deregulation of SOD2 expression is a common event in TSCC and appears to be associated with disease progression. Statistical analysis revealed that the reduced SOD2 expression in primary tumor tissue is associated with lymph node metastasis in both TSCC patient cohorts examined.

Conclusions

Our study suggested that the deregulation of SOD2 in TSCC has potential predictive values for lymph node metastasis, and may serve as a therapeutic target for patients at risk of metastasis.

Immunohistochemical analysis of oxidative stress and DNA repair proteins in normal mammary and breast cancer tissues

BACKGROUND

During the course of normal cellular metabolism, oxygen is consumed and reactive oxygen species (ROS) are produced. If not effectively dissipated, ROS can accumulate and damage resident proteins, lipids, and DNA. Enzymes involved in redox regulation and DNA repair dissipate ROS and repair the resulting damage in order to preserve a functional cellular environment. Because increased ROS accumulation and/or unrepaired DNA damage can lead to initiation and progression of cancer and we had identified a number of oxidative stress and DNA repair proteins that influence estrogen responsiveness of MCF-7 breast cancer cells, it seemed possible that these proteins might be differentially expressed in normal mammary tissue, benign hyperplasia (BH), ductal carcinoma in situ (DCIS) and invasive breast cancer (IBC).

METHODS

Immunohistochemistry was used to examine the expression of a number of oxidative stress proteins, DNA repair proteins, and damage markers in 60 human mammary tissues which were classified as BH, DCIS or IBC. The relative mean intensity was determined for each tissue section and ANOVA was used to detect statistical differences in the relative expression of BH, DCIS and IBC compared to normal mammary tissue.

RESULTS

We found that a number of these proteins were overexpressed and that the cellular localization was altered in human breast cancer tissue.

CONCLUSIONS

Our studies suggest that oxidative stress and DNA repair proteins not only protect normal cells from the damaging effects of ROS, but may also promote survival of mammary tumor cells.

Effects of Cu/Zn superoxide dismutase on estrogen responsiveness and oxidative stress in human breast cancer cells

The effects of estrogen on gene expression in mammary cells are mediated by interaction of the estrogen receptor (ER) with estrogen response elements in target DNA. Whereas the ER is the primary initiator of transcription, the recruitment of coregulatory proteins to the DNA-bound receptor influences estrogen responsiveness. To better understand how estrogen alters gene expression, we identified proteins associated with the DNA-bound ERalpha. Surprisingly, the antioxidant enzyme Cu/Zn superoxide dismutase (SOD1), which is known primarily as a scavenger of superoxide, was associated with the DNA-bound receptor. We have now demonstrated that SOD1 interacts with ERalpha from MCF-7 cell nuclear extracts and with purified ERalpha and that SOD1 enhances binding of ERalpha to estrogen response element-containing DNA. Although SOD1 decreases transcription of an estrogen-responsive reporter plasmid in transiently transfected U2 osteosarcoma cells, RNA interference assays demonstrate that SOD1 is required for effective estrogen responsiveness of the endogenous pS2, progesterone receptor, cyclin D1, and Cathepsin D genes in MCF-7 breast cancer cells. Furthermore, ERalpha and SOD1 are associated with regions of the pS2 and progesterone receptor genes involved in conferring estrogen-responsive gene expression. Interestingly, when MCF-7 cells are exposed to 17beta-estradiol and superoxide generated by addition of potassium superoxide (KO2) to the cell medium, SOD1 levels are increased and tyrosine nitration, which is an indicator of oxidative stress-induced protein damage, is significantly diminished. Our studies have identified a new role for SOD1 in regulating estrogen-responsive gene expression and suggest that the 17beta-estradiol- and KO2-induced increase in SOD1 may play a role in the survival of breast cancer cells and the progression of mammary tumors.

Transcriptomic dissection of tongue squamous cell carcinoma

Background

The head and neck/oral squamous cell carcinoma (HNOSCC) is a diverse group of cancers, which develop from many different anatomic sites and are associated with different risk factors and genetic characteristics. The oral tongue squamous cell carcinoma (OTSCC) is one of the most common types of HNOSCC. It is significantly more aggressive than other forms of HNOSCC, in terms of local invasion and spread. In this study, we aim to identify specific transcriptomic signatures that associated with OTSCC.

Results

Genome-wide transcriptomic profiles were obtained for 53 primary OTSCCs and 22 matching normal tissues. Genes that exhibit statistically significant differences in expression between OTSCCs and normal were identified. These include up-regulated genes (MMP1, MMP10, MMP3, MMP12, PTHLH, INHBA, LAMC2, IL8, KRT17, COL1A2, IFI6, ISG15, PLAU, GREM1, MMP9, IFI44, CXCL1), and down-regulated genes (KRT4, MAL, CRNN, SCEL, CRISP3, SPINK5, CLCA4, ADH1B, P11, TGM3, RHCG, PPP1R3C, CEACAM7, HPGD, CFD, ABCA8, CLU, CYP3A5). The expressional difference of IL8 and MMP9 were further validated by real-time quantitative RT-PCR and immunohistochemistry. The Gene Ontology analysis suggested a number of altered biological processes in OTSCCs, including enhancements in phosphate transport, collagen catabolism, I-kappaB kinase/NF-kappaB signaling cascade, extracellular matrix organization and biogenesis, chemotaxis, as well as suppressions of superoxide release, hydrogen peroxide metabolism, cellular response to hydrogen peroxide, keratinization, and keratinocyte differentiation in OTSCCs.

Conclusion

In summary, our study provided a transcriptomic signature for OTSCC that may lead to a diagnosis or screen tool and provide the foundation for further functional validation of these specific candidate genes for OTSCC.

Reactive oxygen species and antioxidant mechanisms in human tissues and their relation to malignancies

Reactive oxygen species (ROS) are formed in mammalian cells as a consequence of aerobic respiration. Despite multiple conserved redox modulating systems, a given proportion of ROS continuously escape from the mitochondrial respiratory chain, being sufficiently potent to damage cells in various ways, including numerous carcinogenic DNA mutations. Oxidative stress resulting from an imbalanced ratio between ROS production and detoxification may also disturb physiological signal transduction, lead to chain reactions in lipid layers, and damage DNA repair enzymes. The significance of ROS and antioxidant systems in carcinogenesis is still complicated and in many ways contradictory. Enhanced antioxidant mechanisms in tumor cells in vivo have been implicated in chemoresistance and lead to poor prognosis, whereas most in vitro studies have reported tumor-suppressing properties of antioxidant enzymes. The present review aims to clarify the significance of oxidative stress and the role of cell redox state modulating systems in human malignancies in light of the current literature.

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.

MnSOD expression is less frequent in tumour cells of invasive breast carcinomas than in in situ carcinomas or non-neoplastic breast epithelial cells

Manganese superoxide dismutase (MnSOD) is an antioxidant enzyme capable of neutralizing superoxide anion molecules. In previous studies it has been suggested to suppress both tumour proliferation and apoptosis. This study investigated 65 invasive, 50 in situ and 19 benign hyperplastic breast lesions for its immunohistochemical expression. MnSOD expression was also tested with in situ hybridization. To study cell proliferation, apoptosis and their association with MnSOD expression the neoplastic breast lesions were immunostained with a monoclonal antibody to Ki-67 and the extent of apoptosis in them was determined by the TUNEL method. 32/65 (49%) of the invasive ductal carcinomas, 41/50 (82%) of the in situ and 15/19 (79%) of the benign hyperplasias expressed the MnSOD protein. There were significantly more MnSOD positive cases in in situ carcinoma and in benign hyperplasia than in invasive carcinoma (p=0.00016 and p=0.022, respectively). Positivity was also more frequently found in non-neoplastic ductal and acinar epithelial cells than in invasive carcinoma. On the other hand, neoplastic epithelial cells of invasive and in situ carcinoma showed strong positivity more often than the epithelial cells of benign hyperplasia or non-neoplastic epithelium. In breast lesions, MnSOD positivity did not associate with proliferation or apoptosis. The lower frequency of MnSOD positive cases in invasive breast carcinoma suggests that the lack of its expression might contribute to the development of an invasive breast carcinoma phenotype and that it could in this way operate as a tumour suppressor gene, as previously suggested.

Trace elements and superoxide dismutase in benign and malignant breast diseases

This study was planned to determine the probable changes in trace element levels and superoxide dismutase (SOD) activity in women with neoplastic breast diseases. Measurements were performed in three different groups. The first group consisted of 20 healthy women, control group, the second group contained 16 patients with benign breast disease and the third group contained 39 patients with malignant breast disease. The trace element concentrations were determined by using atomic absorption spectrophotometry and SOD activity by using spectrophotometry. When compared with the control values, the plasma copper levels were slightly increased in the second group and significantly in the third group (p < 0.001). The difference between the benign and malignant groups was also significant (p < 0.001). The red cell copper values showed a marked decrease in both groups (p < 0 001). Although there were increases in the plasma zinc levels of both patient groups, the differences were not significant statistically. But, the red cell zinc values showed an significant increase in benign and malignant patients compared to the control group (p < 0.001) (p < 0.001). The plasma magnesium and red cell magnesium values did not show significant differences. The red cell SOD activity showed an significant increase in the benign and malignant patient groups (p < 0.001). The results of this study suggested that reactive oxygen metabolites may play a pathogenetic role in the both benign and malignant tumor development, which is reflected by the change in SOD activity, and in trace element concentrations.

Superoxide dismutase, catalase and glutathione peroxidase activities in human blood: influence of sex, age and cigarette smoking

OBJECTIVE

To obtain reference ranges for each of the main antioxidant enzymes (AOE) and analyze the influence of sex, age, and cigarette smoking on AOE activity in human blood.

DESIGN AND METHODS

We investigated superoxide dismutase (SOD), catalase (CAT), and seleno-dependent glutathione peroxidase (GSH-Px) activities in the whole blood from 103 healthy subjects, from 18-67 years old (51 males and 52 females).

RESULTS

We found a large and highly significant interindividual variability in the activity of all the AOE studied (p < 0.001). The interindividual coefficients of variation were 13.5% for SOD, 21.0% for CAT, and 36.2% for GSH-Px, indicating that GSH-Px exhibits the highest interindividual variability. Females showed higher SOD (p < 0.001) and CAT (p < 0.001) activities but lower GSH-Px (p < 0.05) activity than males. We found a significant effect of age on SOD activity (p < 0.001), showing that in human blood it decreases with age and that this decrease is not linear, beginning at 28 years of age. We also observed a linear effect of age on GSH-Px activity indicating that the activity of this enzyme increases with age (p < 0.01). No effect of age on CAT activity was observed (p > 0.05). AOE activity in smokers was found not to be significantly different from that observed in non-smokers (p > 0.05) except in the case of CAT activity in females, which was found to be lower in smokers than in non-smokers (p < 0.05). In addition, we determined reference ranges for the activity of each antioxidant enzyme studied.

CONCLUSIONS

Our results confirm that AOE activity in human blood exhibits a wide interindividual variability and suggest that this variability may be ascribed, at least in part, to the sex and age of the individuals. Moreover, our results suggest that cigarette smoking does not influence AOE activity in human blood. Accordingly, it is suggested that for clinical purposes it may be necessary to consider the sex and age of the subjects involved in the study.

DNA methylation status of the MUC1 gene coding for a breast-cancer-associated protein

The MUC1 gene codes for protein products that are highly expressed in human breast-cancer tissue and that serve as tumor markers for disease progression. The factors contributing to the disease-specific over-expression of the MUC1 gene are under intensive investigation and are yet to be determined. A large transcribed region of the human MUC1 gene is a CpG island that consists of 60-bp tandemly repeating units, each of which contains one SmaI restriction site. The methylation status of regulatory regions, upstream to the transcriptional start site, is essential for the regulation of gene expression. We therefore evaluated whether the methylation status of the various regions of the MUC1 gene may affect its expression. Using SmaI, and its isoschizomer XmaI endonucleases, we demonstrated that in peripheral-blood leukocytes (PBL-DNA) that do not express the MUC1 gene, the repeat array is completely methylated, whereas the same sequences are entirely non-methylated in breast-tumor-tissue DNA (BT-DNA). In contrast, sequences upstream and downstream to the repeat array showed no difference in the methylation pattern in PBL-DNA and BT-DNA. Hypomethylation within the repeat array was also observed in other epithelial tissues that express the MUC1 gene at much lower levels to those seen in breast-cancer tissue. These studies demonstrate that hypomethylation of the tandem repeat array is an absolute requirement for MUC1 gene expression in epithelial tissues, although in breast-cancer tissue additional regulatory mechanisms must pertain for its over-expression.

Toxicity, single-strand breaks, and 5-hydroxymethyl-2'-deoxyuridine formation in human breast epithelial cells treated with hydrogen peroxide

DNA damage induced by oxidants includes formation of DNA strand breaks as well as oxidative damage to DNA bases. We quantified both forms of DNA damage concurrently in two model human breast epithelial cell lines treated with hydrogen peroxide to compare the dose-dependent induction of each form of DNA damage with growth inhibition. Antioxidant defenses also were quantified. MCF-7 breast cancer cells had relatively higher levels of non-protein thiols, oxidized glutathione (GSSG) reductase, catalase, and superoxide dismutase than did the MCF-10A line of immortalized, but not transformed, human breast epithelial cells. The levels of antioxidant defenses were not predictive of endogenous oxidative DNA damage levels nor of toxicity and DNA damage induced by hydrogen peroxide. The endogenous levels of 5-hydroxymethyl-2'-deoxyuridine were higher in MCF-7 than MCF-10A cells. The cells were treated with 10-200 microM hydrogen peroxide for 15 min at 37 degrees C in complete media. Low concentrations of hydrogen peroxide were growth stimulatory to both cell lines. At higher concentrations, growth inhibition by hydrogen peroxide was greater in MCF-7 than in MCF-10A cells. Accordingly, induction of both single-strand DNA breaks and 5-hydroxymethyl-2'-deoxyuridine in DNA was greater in MCF-7 than MCF-10A cells. In both cell lines, the dose-dependent induction of single-strand breaks paralleled growth inhibition more closely than did formation of 5-hydroxymethyl-2'-deoxyuridine.