Chronic exposure to 12-O-tetradecanoylphorbol-13-acetate represses sod2 induction in vivo: the negative role of p50

Lycopene prevents carcinogen-induced cutaneous tumor by enhancing activation of the Nrf2 pathway through p62-triggered autophagic Keap1 degradation

Biologically active natural products have been used for the chemoprevention of cutaneous tumors. Lycopene is the main active phytochemical in tomatoes. We herein aimed to assess the cancer preventive effects of lycopene and to find potential molecular targets. In chemically-induced cutaneous tumor mice and cell models, lycopene attenuated cutaneous tumor incidence and multiplicity as well as the tumorigenesis of normal cutaneous cells in phase-selectivity (only in the promotion phase) manners. By utilizing a comprehensive approach combining bioinformatics with network pharmacology, we predicted that intracellular autophagy and redox status were associated with lycopene’s preventive effect on cutaneous tumors. Lycopene stimulated the activation of antioxidant enzymes and the translocation of the transcription factor Nrf2 (nuclear factor erythroid 2-related factor 2) that predominantly maintained intracellular redox equilibrium. The cancer chemopreventive effects were mediated by Nrf2. Further, lycopene enhanced the expression of autophagy protein p62. Therefore this led to the degradation of Keap1(Kelch ECH associating protein 1), the main protein locking Nrf2 in cytoplasm. In conclusion, our study provides preclinical evidence of the chemopreventive effects of lycopene on cutaneous tumors and reveals the mechanistic link between lycopene’s stimulation of Nrf2 signaling pathway and p62-mediated degradation of Keap1 via the autophagy-lysosomal pathway.

Dietary AGEs involvement in colonic inflammation and cancer: insights from an in vitro enterocyte model

The number of colon cancer cases is increasing worldwide, and type II diabetes patients have an increased risk of developing colon cancer. Diet-borne advanced glycation end-products (AGEs) may promote neoplastic transformation; however, the mechanisms involved remain elusive. The present study helped to define the relationship between dietary AGEs and cancer progression. C2BBe1 adenocarcinoma enterocytes were exposed to 200 µg/mL glycated casein (AGEs-Csn) for up to 24 h. AGEs-Csn exposure resulted in increased cell proliferation, maladaptative changes in SOD and CAT activity and moderate levels of hydrogen peroxide (H₂O₂) intracellular accumulation. AGEs-Csn activated pro-survival and proliferation signalling, such as the phosphorylation of mTOR (Ser2448) and Akt (Ser473). GSK-3β phosphorylation also increased, potentially inducing extracellular matrix remodelling and thus enabling metastasis. Moreover, AGEs-Csn induced MMP-1, -3, -7, -9 and -10 expression and activated MMP-2 and MMP-9, which are regulators of the extracellular matrix and cytokine functions. AGEs-Csn induced inflammatory responses that included extracellular IL-1β at 6 h; time-dependent increases in IL-8; RAGE and NF-κB p65 upregulation; and IκB inhibition. Co-treatment with anti-RAGE or anti-TNF-α blocking antibodies and AGEs-Csn partially counteracted these changes; however, IL-8, MMP-1 and -10 expression and MMP-9 activation were difficult to prevent. AGEs-Csn perpetuated signalling that led to cell proliferation and matrix remodelling, strengthening the link between AGEs and colorectal cancer aggressiveness.

Diet phytochemicals and cutaneous carcinoma chemoprevention: A review

Cutaneous carcinoma, which has occupied a peculiar place among worldwide populations, is commonly responsible for the considerably increasing morbidity and mortality rates. Currently available medical procedures fail to completely avoid cutaneous carcinoma development or to prevent mortality. Cancer chemoprevention, as an alternative strategy, is being considered to reduce the incidence and burden of cancers through chemical agents. Derived from dietary foods, phytochemicals have become safe and reliable compounds for the chemoprevention of cutaneous carcinoma by relieving multiple pathological processes, including oxidative damage, epigenetic alteration, chronic inflammation, angiogenesis, etc. In this review, we presented comprehensive knowledges, main molecular mechanisms for the initiation and development of cutaneous carcinoma as well as effects of various diet phytochemicals on chemoprevention.

Redox Regulation of the Superoxide Dismutases SOD3 and SOD2 in the Pulmonary Circulation

When evaluating the role of redox-regulating signaling in pulmonary vascular diseases, it is intriguing to consider the modulation of key antioxidant enzymes like superoxide dismutase (SOD) because SOD isoforms are regulated by redox reactions, and, in turn, modulate downstream redox sensitive processes. The emerging field of redox biology is built upon understanding the regulation and consequences of tightly controlled and specific reduction-oxidation reactions that are critical for diverse cellular processes including cell signaling. Of relevance, both the site of production of specific reactive oxygen and nitrogen species and the site of the antioxidant defenses are highly compartmentalized within the cell. For example, superoxide is generated during oxidative phosphorylation in the mitochondria as well as by a number of enzymatic sources within the cytosol and at the cell membrane. In the pulmonary circulation, these sources include the mitochondrial electron transport chain, NADPH oxidases (NOX1-4, Duox1,2), nitric oxide synthases, and xanthine oxidase; this important topic has been thoroughly reviewed recently [1]. In parallel with these different cellular sites of superoxide production, the three SOD isoforms are also specifically localized to the cytosol (SOD1), mitochondria (SOD2) or extracellular compartment (SOD3). This chapter focuses on the role of redox mechanisms regulating SOD2 and SOD3, with an emphasis on these processes in the setting of pulmonary hypertension.

FUsed in sarcoma is a novel regulator of manganese superoxide dismutase gene transcription

AIMS

FUsed in sarcoma (FUS) is a multifunctional DNA/RNA-binding protein that possesses diverse roles, such as RNA splicing, RNA transport, DNA repair, translation, and transcription. The network of enzymes and processes regulated by FUS is far from being fully described. In this study, we have focused on the mechanisms of FUS-regulated manganese superoxide dismutase (MnSOD) gene transcription.

RESULTS

Here we demonstrate that FUS is a component of the transcription complex that regulates the expression of MnSOD. Overexpression of FUS increased MnSOD expression in a dose-dependent manner and knockdown of FUS by siRNA led to the inhibition of MnSOD gene transcription. Reporter analyses, chromatin immunoprecipitation assay, electrophoretic mobility shift assay, affinity chromatography, and surface plasmon resonance analyses revealed the far upstream region of MnSOD promoter as an important target of FUS-mediated MnSOD transcription and confirmed that FUS binds to the MnSOD promoter and interacts with specificity protein 1 (Sp1). Importantly, overexpression of familial amyotropic lateral sclerosis (fALS)-linked R521G mutant FUS resulted in a significantly reduced level of MnSOD expression and activity, which is consistent with the decline in MnSOD activity observed in fibroblasts from fALS patients with the R521G mutation. R521G-mutant FUS abrogates MnSOD promoter-binding activity and interaction with Sp1.

INNOVATION AND CONCLUSION

This study identifies FUS as playing a critical role in MnSOD gene transcription and reveals a previously unrecognized relationship between MnSOD and mutant FUS in fALS.

NFκB1 (p50) suppresses SOD2 expression by inhibiting FoxO3a transactivation in a miR190/PHLPP1/Akt-dependent axis

This study reports a novel function of p50 in its regulation of SOD2 transcription via an NFκB-independent pathway. p50-regulated FoxO3a phosphorylation and transactivation contributes to SOD2 transcription, and p50–down-regulated PHLPP1 translation via miR190 is responsible for activation of Akt and FoxO3a.

The biological functions of nuclear factor κB1 (NFκB1; p50) have not been studied as often as those of other members of the NFκB family due to its lack of a transcriptional domain. Our recent studies showed that p50 functions as an apoptotic mediator via its inhibition of GADD45α protein degradation and increase in p53 protein translation. Here we report a novel function of p50 in its regulation of superoxide dismutase 2 (SOD2) transcription via an NFκB-independent pathway. We find that deletion of p50 in mouse embryonic fibroblasts (MEFs; p50^−/−) up-regulates SOD2 expression at both protein and mRNA levels. SOD2 promoter–driven luciferase is also up-regulated in p50^−/− cells compared with wild-type (WT) MEF (p50^+/+) cells, suggesting p50 regulation of SOD2 at the transcriptional level. Our results also show that p50 deficiency specifically results in down-regulation of phosphorylation and increased transactivation of FoxO3a compared with WT cells. Further studies indicate that p50–down-regulated FoxO3a phosphorylation is mediated by activated Akt via up-regulation of microRNA 190 (miR190), in turn inhibiting PH domain and leucine-rich repeat protein phosphatase 1 (PHLPP1) translation. Together our studies identify a novel p50 function in the regulation of SOD2 transcription by modulating the miR190/PHLPP1/Akt-FoxO3a pathway, which provides significant insight into the physiological function of p50.

Epigenetic modification of Sod2 in the development of diabetic retinopathy and in the metabolic memory: role of histone methylation

PURPOSE

Mitochondrial superoxide levels are elevated in the retina in diabetes, and their scavenging enzyme, MnSOD, becomes subnormal. The objective of this study is to investigate the role of histone methylation of Sod2, the gene that encodes MnSOD, in the development of diabetic retinopathy and in the metabolic memory phenomenon associated with its continued progression after termination of hyperglycemia.

METHODS

Effect of high glucose on monomethyl H3K4 (H3K4me1), dimethyl H3K4 (H3K4me2), and lysine-specific demethylase-1 (LSD1) was quantified at Sod2 by chromatin immunoprecipitation in isolated retinal endothelial cells. The role of histone methylation in the metabolic memory phenomenon was investigated in the retina of rats maintained in poor glycemic control (PC, approximately 12% glycated hemoglobin [GHb]) for 3 months followed by in good glycemic control (GC, approximately 6% GHb) for 3 months.

RESULTS

Hyperglycemia reduced H3K4me1 and -me2, and increased the binding of LSD1 and Sp1 at Sod2. Regulation of LSD1 by LSD1-siRNA ameliorated glucose-induced decrease in H3K4 methylation at Sod2, and prevented decrease in Sod2 gene expression. In rats, re-institution of GC failed to reverse decrease in H3K4me1 and -me2 at Sod2, and LSD1 remained active with increased binding of LSD1 and Sp1 at Sod2. Retina from human donors with diabetic retinopathy also had decreased H3K4me2 and increased LSD1 at Sod2.

CONCLUSIONS

Histone methylation of retinal Sod2 has an important role in the development of diabetic retinopathy and in the metabolic memory phenomenon associated with its continued progression. Targeting enzymes important for histone methylation may serve as a potential therapy to halt the development of diabetic retinopathy.

Manganese superoxide dismutase regulation and cancer

Mitochondria are the power plants of the eukaryotic cell and the integrators of many metabolic activities and signaling pathways important for the life and death of a cell. Normal aerobic cells use oxidative phosphorylation to generate ATP, which supplies energy for metabolism. To drive ATP production, electrons are passed along the electron transport chain, with some leaking as superoxide during the process. It is estimated that, during normal respiration, intramitochondrial superoxide concentrations can reach 10⁻¹² M. This extremely high level of endogenous superoxide production dictates that mitochondria are equipped with antioxidant systems that prevent consequential oxidative injury to mitochondria and maintain normal mitochondrial functions. The major antioxidant enzyme that scavenges superoxide anion radical in mitochondria is manganese superoxide dismutase (MnSOD). Extensive studies on MnSOD have demonstrated that MnSOD plays a critical role in the development and progression of cancer. Many human cancer cells harbor low levels of MnSOD proteins and enzymatic activity, whereas some cancer cells possess high levels of MnSOD expression and activity. This apparent variation in MnSOD level among cancer cells suggests that differential regulation of MnSOD exists in cancer cells and that this regulation may be linked to the type and stage of cancer development. This review summarizes current knowledge of the relationship between MnSOD levels and cancer with a focus on the mechanisms regulating MnSOD expression.

Manganese superoxide dismutase is a p53-regulated gene that switches cancers between early and advanced stages

Manganese superoxide dismutase (MnSOD) plays a critical role in the survival of aerobic life, and its aberrant expression has been implicated in carcinogenesis and tumor resistance to therapy. However, despite extensive studies in MnSOD regulation and its role in cancer, when and how the alteration of MnSOD expression occurs during the process of tumor development in vivo are unknown. Here, we generated transgenic mice expressing a luciferase reporter gene under the control of human MnSOD promoter-enhancer elements and investigated the changes of MnSOD transcription using the 7,12-dimethylbenz(α)anthracene (DMBA)/12-O-tetradecanoylphorbol-l3-acetate (TPA) multistage skin carcinogenesis model. The results show that MnSOD expression was suppressed at a very early stage but increased at late stages of skin carcinogenesis. The suppression and subsequent restoration of MnSOD expression were mediated by two transcription-factors, Sp1 and p53. Exposure to DMBA and TPA activated p53 and decreased MnSOD expression via p53-mediated suppression of Sp1 binding to the MnSOD promoter in normal-appearing skin and benign papillomas. In squamous cell carcinomas, Sp1 binding increased because of the loss of functional p53. We used chromatin immunoprecipitation, electrophoretic mobility shift assay, and both knockdown and overexpression of Sp1 and p53 to verify their roles in the expression of MnSOD at each stage of cancer development. The results identify MnSOD as a p53-regulated gene that switches between early and advanced stages of cancer. These findings also provide strong support for the development of means to reactivate p53 for the prevention of tumor progression.

Epigenetic changes in mitochondrial superoxide dismutase in the retina and the development of diabetic retinopathy

OBJECTIVE

To investigate the role of epigenetic regulation of the manganese superoxide dismutase gene (sod2) in the development of diabetic retinopathy and the metabolic memory phenomenon associated with its continued progression after hyperglycemia is terminated.

RESEARCH DESIGN AND METHODS

Streptozotocin-induced diabetic rats were maintained in poor glycemic control (PC, GHb ∼12%) or in good glycemic control (GC, GHb ~7.0%) for 4 months, or were allowed to maintain PC for 2 months, followed by GC for 2 additional months (PC-Rev). For experimental galactosemia, a group of normal rats were fed a 30% galactose diet for 4 months or for 2 months, followed by a normal diet for 2 additional months. Trimethyl histone H4 lysine 20 (H4K20me3), acetyl histone H3 lysine 9 (H3K9), and nuclear transcriptional factor NF-κB p65 and p50 at the retinal sod2 promoter and enhancer were examined by chromatin immunoprecipitation.

RESULTS

Hyperglycemia (diabetes or galactosemia) increased H4K20me3, acetyl H3K9, and NF-κB p65 at the promoter and enhancer of retinal sod2, upregulated protein and gene expression of SUV420h2, and increased the interactions of acetyl H3K9 and NF-κB p65 to H4K20me3. Reversal of hyperglycemia failed to prevent increases in H4K20me3, acetyl H3K9, and NF-κB p65 at sod2, and sod2 and SUV420h2 continued to be abnormal. Silencing SUV420h2 by its small interfering RNA in retinal endothelial cells prevented a glucose-induced increase in H4K20me3 at the sod2 enhancer and a decrease in sod2 transcripts.

CONCLUSIONS

Increased H4K20me3 at sod2 contributes to its downregulation and is important in the development of diabetic retinopathy and in the metabolic memory phenomenon. Targeting epigenetic changes may serve as potential therapeutic targets to retard the development and progression of diabetic retinopathy.

Nuclear factor kappaB- and specificity protein 1-dependent p53-mediated bi-directional regulation of the human manganese superoxide dismutase gene

Tumor suppressor p53 is known to activate certain sets of genes while suppressing others. However, whether p53 can both activate and suppress the same gene is unclear. To address this question, concentration-dependent p53 effect on the manganese superoxide dismutase (MnSOD) gene was investigated. By transfecting p53 in PC-3 cells, we demonstrate that low concentrations of p53 increase while high concentrations suppress MnSOD expression. The physiological relevance of this effect was determined in vitro and in vivo using combined UVB-mediated activation and small interference RNA-mediated suppression of p53. Results were consistent with the bi-directional effect of p53 on MnSOD expression. MnSOD-promoter/enhancer analysis demonstrates that p53 is suppressive to the promoter activity regardless of the presence or absence of putative p53 binding sites. However, a low level of p53 increases MnSOD gene transcription in the presence of the intronic-enhancer element, and this effect is dependent on nuclear-factor kappaB (NF-kappaB) binding sites. Expression of p53 enhances nuclear levels of p65 with corresponding increase in the DNA-binding activity of NF-kappaB as detected by electrophoretic mobility shift and chromatin immunoprecipitation assays. Transfection of p65 small interference RNA reduces the positive effect of p53 on MnSOD gene transcription. These data suggest that p65 can overcome the negative effect of p53 on MnSOD expression. However, when the level of p53 was further increased, the suppressive effect of p53 outweighed the positive effect of p65 and led to the suppression of MnSOD gene transcription. These results demonstrated that p53 can both suppress and induce MnSOD expression depending on the balance of promoter and enhancer binding transcription factors.

Clair DK. Regulation of superoxide dismutase genes: implications in disease

Numerous short-lived and highly reactive oxygen species (ROS) such as superoxide (O2(.-)), hydroxyl radical, and hydrogen peroxide are continuously generated in vivo. Depending upon concentration, location, and intracellular conditions, ROS can cause toxicity or act as signaling molecules. The cellular levels of ROS are controlled by antioxidant enzymes and small-molecule antioxidants. As major antioxidant enzymes, superoxide dismutases (SODs), including copper-zinc superoxide dismutase (Cu/ZnSOD), manganese superoxide dismutase, and extracellular superoxide dismutase, play a crucial role in scavenging O2(.-). This review focuses on the regulation of the sod genes coding for these enzymes, with an emphasis on the human genes. Current knowledge about sod structure and regulation is summarized and depicted as diagrams. Studies to date on genes coding for Cu/ZnSOD (sod1) are mostly focused on alterations in the coding region and their associations with amyotrophic lateral sclerosis. Evaluation of nucleotide sequences reveals that regulatory elements of the sod2 gene reside in both the noncoding and the coding region. Changes associated with sod2 lead to alterations in expression levels as well as protein function. We also discuss the structural basis for the changes in SOD expression associated with pathological conditions and where more work is needed to establish the relationship between SODs and diseases.

[Advances in the expression and regulation of MnSOD gene]

MnSOD, which is an important oxygen free radical scavenger in organisms, has an effect to resist oxidative stress and tumor. The expression and regulation of MnSOD gene is a complicated process, which includes many kinds of transcription factors, cell signal molecules and cell signal pathways. It refers to three aspects including transcription regulation, post-transcription regulation and translation regulation. Transcription regulation is the primary step for MnSOD gene expression and plays a key role during the expression of MnSOD gene. The activity of transcription factors, which controls MnSOD gene expression, such as SP-1, AP-2, AP-1, NF-kB and so on, can be changed in the course of transcription regulation. Drugs and metalions can also affect those transcription factors' activity. Furthermore some genes mutation and depletion also have an influence on the activity of those transcription factors. Post-transcription regulation is in a way of changing the stability of mRNA and its translation. Translation regulation is a process to regulate edition, modification, binding to metalion and site-specific of MnSOD polypeptide. Recently a kind of manganese trafficking factor for mitochondrial MnSOD called MTMl which is very important for activation of MnSOD has been discovered. Here, we review the advances in this field with an emphasis on transcription regulation and translation regulation of MnSOD gene. And at last, we discussed the prospect of MnSOD gene expression and regulation.