The 3' untranslated region of manganese superoxide dismutase RNA contains a translational enhancer element

Exploiting Systematic Engineering of the Expression Cassette as a Powerful Tool to Enhance Heterologous Gene Expression in Trichoderma reesei

Many endeavors in expressing a heterologous gene in microbial hosts rely on simply placing the gene of interest between a selected pair of promoters and terminator. However, although the expression efficiency could be improved by engineering the host cell, how modifying the expression cassette itself systematically would affect heterologous gene expression remains largely unknown. As the promoter and terminator bear plentiful cis-elements, herein using the Aspergillus niger mannanase with high application value in animal feeds and the eukaryotic filamentous fungus workhorse Trichoderma reesei as a model gene/host, systematic engineering of an expression cassette was investigated to decipher the effect of its mutagenesis on heterologous gene expression. Modifying the promoter, signal peptide, the eukaryotic-specific Kozak sequence, and the 3'-UTR could stepwise improve extracellular mannanase production from 17 U/mL to an ultimate 471 U/mL, representing a 27.7-fold increase in expression. The strategies can be generally applied in improving the production of heterologous proteins in eukaryotic microbial hosts.

HuR-dependent SOD2 protein synthesis is an early adaptation to anchorage-independence

During metastasis cancer cells must adapt to survive loss of anchorage and evade anoikis. An important pro-survival adaptation is the ability of metastatic tumor cells to increase their antioxidant capacity and restore cellular redox balance. Although much is known about the transcriptional regulation of antioxidant enzymes in response to stress, how cells acutely adapt to alter antioxidant enzyme levels is less well understood. Using ovarian cancer cells as a model, we demonstrate that an increase in mitochondrial superoxide dismutase SOD2 protein expression is a very early event initiated in response to detachment, an important step during metastasis that has been associated with increased oxidative stress. SOD2 protein synthesis is rapidly induced within 0.5-2 h of matrix detachment, and polyribosome profiling demonstrates an increase in the number of ribosomes bound to SOD2 mRNA, indicating an increase in SOD2 mRNA translation in response to anchorage-independence. Mechanistically, we find that anchorage-independence induces cytosolic accumulation of the RNA binding protein HuR/ELAVL1 and promotes HuR binding to SOD2 mRNA. Using HuR siRNA-mediated knockdown, we show that the presence of HuR is necessary for the increase in SOD2 mRNA association with the heavy polyribosome fraction and consequent nascent SOD2 protein synthesis in anchorage-independence. Cellular detachment also activates the stress-response mitogen-activated kinase p38, which is necessary for HuR-SOD2 mRNA interactions and induction of SOD2 protein output. These findings illustrate a novel translational regulatory mechanism of SOD2 by which ovarian cancer cells rapidly increase their mitochondrial antioxidant capacity as an acute stress response to anchorage-independence.

SOD2, a Potential Transcriptional Target Underpinning CD44-Promoted Breast Cancer Progression

CD44, a cell-adhesion molecule has a dual role in tumor growth and progression; it acts as a tumor suppressor as well as a tumor promoter. In our previous work, we developed a tetracycline-off regulated expression of CD44's gene in the breast cancer (BC) cell line MCF-7 (B5 clone). Using cDNA oligo gene expression microarray, we identified SOD2 (superoxide dismutase 2) as a potential CD44-downstream transcriptional target involved in BC metastasis. SOD2 gene belongs to the family of iron/manganese superoxide dismutase family and encodes a mitochondrial protein. SOD2 plays a role in cell proliferation and cell invasion via activation of different signaling pathways regulating angiogenic abilities of breast tumor cells. This review will focus on the findings supporting the underlying mechanisms associated with the oncogenic potential of SOD2 in the onset and progression of cancer, especially in BC and the potential clinical relevance of its various inhibitors.

Regulation of MnSOD enzymatic activity by Sirt3 connects the mitochondrial acetylome signaling networks to aging and carcinogenesis

SIGNIFICANCE

It is a well-established scientific observation that mammalian cells contain fidelity or watchdog proteins that maintain the correct function of cellular organelles.

RECENT ADVANCES

Over the past several years, the Sirtuin deacetylase family protein Sirt3 has emerged as a mitochondrial fidelity protein that directs energy generation and regulates reactive oxygen species (ROS) scavenging proteins. Loss of function or genetic mutation of these fidelity proteins has been shown to create a cellular environment that is permissive for the development of cellular damage associated with processes such as aging and carcinogenesis.

CRITICAL ISSUES

Mitochondria are the primary organelles that direct oxidative metabolism for the production of ATP; however, this is also a significant source of ROS. Thus, it is reasonable to propose that mitochondria should contain proteins that would signal downstream target molecules and/or ROS scavenger enzymes to maintain mitochondrial and cellular homeostatic poise. It is also reasonable to hypothesize that the mitochondria contain fidelity proteins similar to those found in the nucleus and cytoplasm. We discuss a new role of Sirt3 in the direction of the primary superoxide scavenger protein, manganese superoxide dismutase (MnSOD), and how the acetylation or deacetylation of several specific lysines appears to direct MnSOD enzymatic dismutase activity.

FUTURE DIRECTIONS

Aberrant downstream regulation of MnSOD by Sirt3 may be a potential source of cellular damage that accumulates with aging to create a tumor-permissive phenotype. Future studies can explore the role of MnSOD in age-related illness using this new mechanism of enzymatic regulation.

Modulation of MnSOD in Cancer:Epidemiological and Experimental Evidence

Since it was first observed in late 1970s that human cancers often had decreased manganese superoxide dismutase (MnSOD) protein expression and activity, extensive studies have been conducted to verify the association between MnSOD and cancer. Significance of MnSOD as a primary mitochondrial antioxidant enzyme is unquestionable; results from in vitro, in vivo and epidemiological studies are in harmony. On the contrary, studies regarding roles of MnSOD in cancer often report conflicting results. Although putative mechanisms have been proposed to explain how MnSOD regulates cellular proliferation, these mechanisms are not capitulated in epidemiological studies. This review discusses most recent epidemiological and experimental studies that examined the association between MnSOD and cancer, and describes emerging hypotheses of MnSOD as a mitochondrial redox regulatory enzyme and of how altered mitochondrial redox may affect physiology of normal as well as cancer cells.

Curcumin and vitamin E modulate hepatic antioxidant gene expression in PTU-induced hypothyroid rats

In the present study, regulatory role of vitamin E and curcumin on antioxidant gene (AOG) expression in hypothyroid rat liver is reported. Adult male rats were rendered hypothyroid by administration of 0.05 % 6-propyl-thiouracil in their drinking water, while vitamin E (200 mg/kg body weight) and curcumin (30 mg/kg body weight) were supplemented orally for 30 days. Expression of antioxidant genes (Cu/Zn-superoxide dismutase; SOD1, Mn superoxide dismutase; SOD2, catalase; CAT, glutathione peroxidase; GPx1 and glutathione reductase; GR) was evaluated using RT-PCR and Western blot analyses. The activities of antioxidant enzymes were measured in mitochondrial fraction (MF) and post-mitochondrial fraction (PMF) of rat liver. In addition measurement of glutathione redox status was also carried out in both the fractions. The enhanced transcripts of CAT, GPx1 and GR in hypothyroid rat liver were alleviated by administration of vitamin E and curcumin. Elevated levels of translated product of all AOGs in hypothyroid group were remained unchanged after antioxidant administration. However, enhanced SOD1, GPx1 and decreased GR activities in PMF were normalized by vitamin E and curcumin. Similarly the increased SOD2, GPx1 and decreased CAT activities in MF were also normalized by vitamin E and curcumin supplementation. Administration of vitamin E and curcumin enhanced mitochondrial GSH level; whereas the enhanced GSH level in PMF of hypothyroid rats was alleviated by vitamin E. Thus it can be concluded that besides the antioxidant role of vitamin E and curcumin, they also regulate hepatic antioxidant gene expression in hypothyroid rats.

Water restriction increases renal inner medullary manganese superoxide dismutase (MnSOD)

Oxidative stress damages cells. NaCl and urea are high in renal medullary interstitial fluid, which is necessary to concentrate urine, but which causes oxidative stress by elevating reactive oxygen species (ROS). Here, we measured the antioxidant enzyme superoxide dismutases (SODs, MnSOD, and Cu/ZnSOD) and catalase in mouse kidney that might mitigate the oxidative stress. MnSOD protein increases progressively from the cortex to the inner medulla, following the gradient of increasing NaCl and urea. MnSOD activity increases proportionately, but MnSOD mRNA does not. Water restriction, which elevates renal medullary NaCl and urea, increases MnSOD protein, accompanied by a proportionate increase in MnSOD enzymatic activity in the inner medulla, but not in the cortex or the outer medulla. In contrast, Cu/ZnSOD and TNF-α (an important regulator of MnSOD) do not vary between the regions of the kidney, and expression of catalase protein actually decreases from the cortex to the inner medulla. Water restriction increases activity of mitochondrial enzymes that catalyze production of ROS in the inner medulla, but reduces NADPH oxidase activity there. We also examined the effect of high NaCl and urea on MnSOD in Madin-Darby canine kidney (MDCK) cells. High NaCl and high urea both increase MnSOD in MDCK cells. This increase in MnSOD protein apparently depends on the elevation of ROS since it is eliminated by the antioxidant N-acetylcysteine, and it occurs without raising osmolality when ROS are elevated by antimycin A or xanthine oxidase plus xanthine. We conclude that ROS, induced by high NaCl and urea, increase MnSOD activity in the renal inner medulla, which moderates oxidative stress.

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.

Expression of antioxidant genes in renal cortex of PTU-induced hypothyroid rats: effect of vitamin E and curcumin

The present study was undertaken to investigate the effect of vitamin E and curcumin on the expression of antioxidant genes in 6-propyl-2-thiouracil (PTU)-induced hypothyroid rat renal cortex. The levels of lipid peroxidation and protein carbonylation were increased in hypothyroid rat kidney. Co-administration of vitamin E and curcumin to hypothyroid rats resulted in amelioration of lipid peroxidation level, whereas curcumin alone alleviated the protein carbonylation level. The mRNA levels of SOD1 and SOD2 were decreased in hypothyroid rats. Decreased level of SOD1 transcripts was observed in hypothyroid rats supplemented with curcumin alone or co-administrated with vitamin E. Translated products of SOD1 and SOD2 in hypothyroid rats was elevated in response to supplementation of both the antioxidants. Decreased SOD1 and SOD2 activities in hypothyroid rats compared to control were either unaltered or further decreased in response to the antioxidants. Expressions of CAT at transcript and translate level along with its activity were down regulated in hypothyroid rats. Administration of vitamin E to hypothyroid rats resulted in elevated CAT mRNA level. In contrast, expression of CAT protein was elevated in response to both the antioxidants. However, CAT activity was unaltered in response to vitamin E and curcumin. GPx1 and GR mRNA level and the activity of glutathione peroxidase (GPx) were not affected in response to induced hypothyroidism. The activity of GPx was increased in response to vitamin E treatment, whereas decreased GR activity in hypothyroid rats was further declined by the administration of antioxidants. The over all results suggest that vitamin E and curcumin differentially modulate the altered antioxidant defence mechanism of rat kidney cortex under experimental hypothyroidism.

Dietary manganese modulates expression of the manganese-containing superoxide dismutase gene in chickens

To investigate the possible mechanism(s) by which dietary manganese (Mn) levels and sources modulate the expression of the manganese-containing superoxide dismutase (MnSOD) gene at both the transcriptional and translational levels, we used 432 8-d-old male broiler chicks in a 1 plus 4 × 2 design. Chickens were given either a diet without Mn supplementation [control (C)] or diets supplemented with 100 (optimal) or 200 (high) mg Mn/kg diet from inorganic Mn sulfate (I) or 3 organic complexes of Mn and amino acids with weak (W), moderate (M), or strong (S) chelation strength up to 21 d of age. Compared with C chicks, chicks fed Mn-supplemented diets had higher (P < 0.01) Mn concentrations, specificity protein 1 (Sp1) DNA-binding activities, MnSOD mRNA levels, MnSOD mRNA-binding protein (MnSOD-BP) RNA-binding activities, MnSOD protein concentrations, and MnSOD activities within heart tissue, but lower (P < 0.01) heart activating protein-2 (AP-2) DNA-binding activities. Chicks fed M diets had higher (P < 0.05) heart Mn concentrations, MnSOD mRNA levels, and MnSOD-BP RNA-binding activities compared with those fed the I and W diets and lower (P < 0.01) AP-2 DNA-binding activities than those fed other treatment diets. These results suggest that dietary Mn could modulate the expression of the MnSOD gene in broilers by altering Sp1 and AP-2 DNA-binding activities at the transcriptional level and enhancing MnSOD-BP RNA-binding activity at the translational level. Additionally, an organic Mn source with moderate chelation strength could be more effective than other Mn sources in activating MnSOD gene expression at both the transcriptional and translational levels.

Redox control in mammalian embryo development

The development of an embryo constitutes a complex choreography of regulatory events that underlies precise temporal and spatial control. Throughout this process the embryo encounters ever changing environments, which challenge its metabolism. Oxygen is required for embryogenesis but it also poses a potential hazard via formation of reactive oxygen and reactive nitrogen species (ROS/RNS). These metabolites are capable of modifying macromolecules (lipids, proteins, nucleic acids) and altering their biological functions. On one hand, such modifications may have deleterious consequences and must be counteracted by antioxidant defense systems. On the other hand, ROS/RNS function as essential signal transducers regulating the cellular phenotype. In this context the combined maternal/embryonic redox homeostasis is of major importance and dysregulations in the equilibrium of pro- and antioxidative processes retard embryo development, leading to organ malformation and embryo lethality. Silencing the in vivo expression of pro- and antioxidative enzymes provided deeper insights into the role of the embryonic redox equilibrium. Moreover, novel mechanisms linking the cellular redox homeostasis to gene expression regulation have recently been discovered (oxygen sensing DNA demethylases and protein phosphatases, redox-sensitive microRNAs and transcription factors, moonlighting enzymes of the cellular redox homeostasis) and their contribution to embryo development is critically reviewed.

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.

Anti-oxidant enzyme activities and expression and oxidative damage in patients with non-immediate reactions to drugs

Adverse drug reactions with an immunological basis (ADRIB) may involve activation of other concomitant, non-specific mechanisms, amplifying the specific response and contributing to the severity and duration. One concomitant mechanism could be the generation of reactive oxygen species (ROS) and/or their detoxification by anti-oxidants, including anti-oxidant enzymes. We analysed the activity of the anti-oxidant enzymes Cu/Zn-superoxide dismutase (SOD), catalase (CAT) and cellular glutathione peroxidase (GPX), as well as certain markers of oxidative damage (thiobarbituric acid reactive substances (TBARS) and carbonyl content) in peripheral blood mononuclear cells from patients with non-immediate ADRIB using spectrophotometric methods and the anti-oxidant enzymes expression by quantitative real-time reverse transcription-polymerase chain reaction. SOD activity and expression were increased in all types of non-immediate reactions (urticaria, maculopapular exanthema and toxic epidermal necrolysis). Regarding oxidative damage, TBARS were increased in urticaria and maculopapular exanthema, and carbonyl groups in all types of reactions. Our observations indicate that oxidative damage occurs in non-immediate reactions. Carbonyl stress and the inadequacy of the anti-oxidant defences are probable causes.

Extracellular superoxide dismutase tissue distribution and the patterns of superoxide dismutase mRNA expression following ultraviolet irradiation on mouse skin

Superoxide dismutases (SODs) are believed to play a crucial role in protecting cells against oxygen toxicity. There are three forms of SOD: cytosolic Cu-Zn SOD, mitochondrial Mn SOD, and extracellular SOD (EC SOD). Extracellular SOD is primarily a tissue enzyme, but the role of EC SOD in skin is unclear. Therefore, this study investigated the distribution of EC SOD in the skin using immunohistochemistry and examining the patterns of EC SOD gene expression following ultraviolet (UV) irradiation in comparison with those of Cu-Zn SOD and Mn SOD in mouse dorsal skin using Northern blot analysis. Immunohistochemical analysis showed that EC SOD was abundantly located in the epidermis as well as in the dermis, but the gene expression of EC SOD mRNA was more abundant in the dermis than in the epidermis. The gene expression levels of all three types of SODs after UV irradiation were induced differently according to the type and UV irradiation dose. The EC SOD mRNA expression level was increased relatively later than that of Cu-Zn SOD and Mn SOD. The EC SOD mRNA level was significantly higher at 6 h and 48 h after UVA irradiation and psoralen plus ultraviolet-A treatment, respectively. Ultraviolet-B irradiation increased the EC SOD mRNA expression level, with maximum at 48 h. These suggest that EC SOD participates in the majority of antioxidant systems in the skin, and it may have different defensive roles from Cu-Zn SOD and Mn SOD against UV-induced injury of the skin.

Superoxide dismutases in the lung and human lung diseases

The lungs are directly exposed to higher oxygen concentrations than most other tissues. Increased oxidative stress is a significant part of the pathogenesis of obstructive lung diseases such as asthma and chronic obstructive pulmonary disease, parenchymal lung diseases (e.g., idiopathic pulmonary fibrosis and lung granulomatous diseases), and lung malignancies. Lung tissue is protected against these oxidants by a variety of antioxidant mechanisms among which the superoxide dismutases (SODs) are the only ones converting superoxide radicals to hydrogen peroxide. There are three SODs: cytosolic copper-zinc, mitochondrial manganese, and extracellular SODs. These enzymes have specific distributions and functions. Their importance in protecting lung tissue has been confirmed in transgenic and knockout animal studies. Relatively few studies have been conducted on these enzymes in the normal human lung or in human lung diseases. Most human studies suggest that there is induction of manganese SOD and, possibly, extracellular SOD during inflammatory, but not fibrotic, phases of parenchymal lung diseases and that both copper-zinc SOD and manganese SOD may be downregulated in asthmatic airways. Many previous antioxidant therapies have been disappointing, but newly characterized SOD mimetics are being shown to protect against oxidant-related lung disorders in animal models.

Poly(A)-binding protein positively affects YB-1 mRNA translation through specific interaction with YB-1 mRNA

The major protein of cytoplasmic mRNPs from rabbit reticulocytes, YB-1, is a member of an ancient family of proteins containing a common structural feature, cold-shock domain. In eukaryotes, this family is represented by multifunctional mRNA/Y-box DNA-binding proteins that control gene expression at different stages. To address possible post-transcriptional regulation of YB-1 gene expression, we examined effects of exogenous 5'- and 3'-untranslatable region-containing fragments of YB-1 mRNA on its translation and stability in a cell-free system. The addition of the 3' mRNA fragment as well as its subfragment I shut off protein synthesis at the initiation stage without affecting mRNA stability. UV cross-linking revealed four proteins (69, 50, 46, and 44 kDa) that specifically interacted with the 3' mRNA fragment; the inhibitory subfragment I bound two of them, 69- and 50-kDa proteins. We have identified these proteins as PABP (poly(A)-binding protein) (69 kDa) and YB-1 (50 kDa) and demonstrated that titrating out of PABP by poly(A) strongly and specifically inhibits YB-1 mRNA cap(+)poly(A)(-) translation in a cell-free system. Thus, PABP is capable of positively affecting YB-1 mRNA translation in a poly(A) tail-independent manner.

PKA-dependent binding of mRNA to the mitochondrial AKAP121 protein

Protein kinase A (PKA) anchoring proteins (AKAPs) tether PKA to various subcellular locations. AKAP121, which tethers PKAII to the outer mitochondrial membrane, includes a K homology (KH) RNA-binding motif. Purified AKAP121 KH domain binds the 3' untranslated regions (3'UTRs) of transcripts encoding the Fo-f subunit of mitochondrial ATP synthase and manganese superoxide dismutase (MnSOD). Binding requires a structural motif in the 3'UTR and is stimulated by PKA phosphorylation of the domain or a mutation that mimics this phosphorylation. AKAP121 expressed in HeLa cells promotes the translocation of MnSOD mRNA from cytosol to mitochondria and an increase in mitochondrial MnSOD. Both reactions are stimulated by cAMP. Thus, by focusing translation at the mitochondrial membrane, AKAP121 may facilitate import of mitochondrial proteins in response to cAMP stimulation.

Exercise, antioxidants, and HSP72: protection against myocardial ischemia/reperfusion

Endurance exercise is associated with protection against myocardial ischemia/reperfusion (I/R) injury and has been shown to increase heat shock protein 72 (HSP72). Dietary antioxidants have also been reported to decrease I/R-induced injury. Because exercise and antioxidants may provide cardioprotection via different mechanisms, combining these countermeasures could provide additive protection. Alternatively, because exercise-induced oxidant production may promote expression of HSP72, antioxidants could attenuate exercise-induced HSP72 expression and decrease exercise-related cardioprotection. These experiments examined the individual and combined effects of exercise and antioxidants on myocardial I/R injury (in vivo). Rats receiving a mixed antioxidant diet or control diet were assigned to exercise or sedentary groups and randomized to receive: (i) short I/R (myocardial stunning), (ii) long I/R (myocardial infarction), or (iii) sham surgery. Antioxidants significantly increased total antioxidant capacity and attenuated exercise-related HSP72 accumulation. Nonetheless, during short I/R, exercise-trained animals demonstrated improved left ventricular developed pressure (LVDP), independent of diet. Further, antioxidants alone resulted in improved LVDP. Finally, compared to control diet/sedentary animals, both exercise groups (control and antioxidant diets) and the antioxidant diet/sedentary group sustained smaller infarctions. We conclude that exercise and antioxidants can independently provide protection against myocardial contractile dysfunction and infarction, and the combination of these two strategies does not enhance or inhibit the protection observed with each individual countermeasure.

Up-regulation of early growth response gene-1 via the CXCR3 receptor induces reactive oxygen species and inhibits Na+/K+-ATPase activity in an immortalized human proximal tubule cell line

The CXCR3 chemokine receptor, a member of the CXCR family, has been linked to a pathological role in autoimmune disease, inflammatory disease, allograft rejection, and ischemia. In the kidney, expression of the CXCR3 receptor and its ligands is up-regulated in states of glomerulonephritis and in allograft rejection, but little is known about the expression and functional role the CXCR3 receptor might play. Here, we study the function of the CXCR3 chemokine receptor in an immortalized human proximal tubular cell line (IHKE-1). Stimulation of the CXCR3 receptor by its selective agonist monokine induced by IFN-gamma leads via a Ca(2+)-dependent mechanism to an up-regulation of early growth response gene (EGR)-1. Overexpression of EGR-1 induces down-regulation of copper-zinc superoxide dismutase and manganese superoxide dismutase and stimulates the generation of reactive oxygen species (ROS) via the NADH/NADPH-oxidase system. EGR-1 overexpression or treatment with monokine induced by IFN-gamma resulted in a ROS-dependent inhibition of basolateral Na(+)/K(+)-ATPase activity, compromising sodium transport in these cells. Thus, activation of the CXCR3 receptor in proximal tubular cells might disturb natriuresis during inflammatory and ischemic kidney disease via EGR-1-mediated imbalance of ROS.

Superoxide dismutase multigene family: a comparison of the CuZn-SOD (SOD1), Mn-SOD (SOD2), and EC-SOD (SOD3) gene structures, evolution, and expression

Superoxide dismutases are an ubiquitous family of enzymes that function to efficiently catalyze the dismutation of superoxide anions. Three unique and highly compartmentalized mammalian superoxide dismutases have been biochemically and molecularly characterized to date. SOD1, or CuZn-SOD (EC 1.15.1.1), was the first enzyme to be characterized and is a copper and zinc-containing homodimer that is found almost exclusively in intracellular cytoplasmic spaces. SOD2, or Mn-SOD (EC 1.15.1.1), exists as a tetramer and is initially synthesized containing a leader peptide, which targets this manganese-containing enzyme exclusively to the mitochondrial spaces. SOD3, or EC-SOD (EC 1.15.1.1), is the most recently characterized SOD, exists as a copper and zinc-containing tetramer, and is synthesized containing a signal peptide that directs this enzyme exclusively to extracellular spaces. What role(s) these SODs play in both normal and disease states is only slowly beginning to be understood. A molecular understanding of each of these genes has proven useful toward the deciphering of their biological roles. For example, a variety of single amino acid mutations in SOD1 have been linked to familial amyotrophic lateral sclerosis. Knocking out the SOD2 gene in mice results in a lethal cardiomyopathy. A single amino acid mutation in human SOD3 is associated with 10 to 30-fold increases in serum SOD3 levels. As more information is obtained, further insights will be gained.

A coding region determinant of instability regulates levels of manganese superoxide dismutase mRNA

The mitochondria-localized manganese superoxide dismutase (MnSOD), serves a key cytoprotective role against reactive oxygen species arising from a variety of cellular processes and immunological stresses. Previous data from our laboratory suggest that the regulation of the rat MnSOD gene may occur not only at the transcriptional but quite possibly at the post-transcriptional level. To verify this hypothesis, we have attempted to identify regions within the rat MnSOD cDNA that may be functionally involved in regulating the stability of the mRNA. Using a c-fos-based promoter activation system, we have identified an approximately 280-nucleotide fragment within the MnSOD mRNA coding region that, when fused to a rabbit beta-globin gene, destabilizes the normally stable beta-globin mRNA. This cis-directed destabilization phenomenon confers its effects independent of position and stimulus. Most importantly, the MnSOD coding region determinant functions when placed in the 3'-untranslated region of the beta-globin transcript, demonstrating its activity in the absence of ribosome transit. We feel that these data provide a mechanistic basis for both the basal and stimulus-dependent post-transcriptional regulation of MnSOD.

Different regulatory mechanisms modulate the expression of a dinoflagellate iron-superoxide dismutase

Regulation of antioxidant enzymes is critical to control the levels of reactive oxygen species in cell compartments highly susceptible to oxidative stress. In this work, we studied the regulation of a chloroplastic iron superoxide dismutase (Fe-SOD) from Lingulodinium polyedrum (formerly Gonyaulax polyedra) under different physiological conditions. A cDNA-encoding Fe-SOD was isolated from this dinoflagellate, showing high sequence similarity to cyanobacterial, algal, and plant Fe-SODs. Under standard growth conditions, on a 12:12-h light-dark cycle, Lingulodinium polyedrum Fe-SOD exhibited a daily rhythm of activity and cellular abundance with the maximum occurring during the middle of the light phase. Northern analyses showed that this rhythmicity is not related to changes in Fe-SOD mRNA levels, indicative of translational regulation. By contrast, conditions of metal-induced oxidative stress resulted in higher levels of Fe-SOD transcripts, suggesting that transcriptional control is responsible for increased protein and activity levels. Daily (circadian) and metal-induced up-regulation of Fe-SOD expression in L. polyedrum are thus mediated by different regulatory pathways, allowing biochemically distinct changes appropriate to oxidative challenges.

The 3' UTR of human MnSOD mRNA hybridizes to a small cytoplasmic RNA and inhibits gene expression

Human MnSOD localizes to the mitochondria and plays a key protective role by detoxifying oxygen free radicals. The MnSOD mRNA 3' UTR contains a 280-bp region (Alu-like element or Alu-E) that shows high homology to human Alu and 7SL sequences. MnSOD 3' UTR probes hybridize to a specific cytoplasmic RNA species of approximately 300 nucleotides. This antisense RNA is most likely 7SL RNA based on its size, ubiquitousness, high levels, and lack of inducibility. Hybridization of this small RNA to the MnSOD 3' UTR may modulate posttranscriptional MnSOD gene expression. This regulation could occur by several means including inhibition of translation and mRNA destabilization. Regulation at the level of translational initiation does not seem to occur as MnSOD mRNA containing the Alu-E is efficiently bound by ribosomes. To test the role of the MnSOD 3' UTR, and in particular the Alu-E in gene expression, luciferase reporter gene constructs were made containing various regions of the MnSOD 3' UTR including the Alu-E. These constructs were transfected into human A549 lung carcinoma cells and luciferase activity was measured. Reporter constructs containing the MnSOD 3' UTR and the Alu-E repress luciferase activity. Taken together, these results suggest that naturally occurring antisense RNA may bind MnSOD mRNA and repress its expression. These results also suggest that other mRNAs containing Alu elements may be similarly repressed.

Post-transcriptional regulation of lung antioxidant enzyme gene expression

It is an honor, and indeed fitting, to have a chapter on pulmonary oxygen toxicity included in a Festschrift for Dan Gilbert, whose contributions to the free radical theory of oxygen toxicity have been a catalyst to the last half-century of investigation in this field. There is cellular damage that results in pulmonary edema and even death if the increase in reactive oxygen species produced in the lung during exposure to hyperoxia is not counterbalanced by an increase in the cell's antioxidant defense systems. In this chapter experimental evidence will substantiate the importance of post-transcriptional regulation of antioxidant enzyme gene expression in animal models of pulmonary oxygen toxicity and tolerance to hyperoxia with special emphasis given to the role of manganese superoxide dismutase (MnSOD) synthesis, specific activity, and RNA half-life and to a proposed function of a MnSOD RNA-binding protein as a positive regulator in the control of translational efficiency.

A region in the 3' UTR of MnSOD RNA enhances translation of a heterologous RNA

The studies reported in this paper were designed to test the hypothesis that a cis element located in the 3' UTR of manganese superoxide dismutase (MnSOD) RNA, designated MnSOD-response element (MnSOD-RE), is a translational enhancer in vivo. NIH/3T3 cells were transfected with a posttranscriptional reporter construct in which MnSOD-RE was placed 3' of the coding region of chloramphenicol acetyltransferase (CAT); this construct is designated CAT-RMS. Transient transfection of CAT-RMS did not change the concentration of CAT mRNA but increased CAT activity by approximately 400% compared to a control construct, CAT-V, which contains approximately the same size of non-MnSOD 3' UTR sequence. Transfection of CAT-RMS had no effect on endogenous MnSOD protein, mRNA, or MnSOD RNA-binding protein activity. Because of its ability to increase translation of a heterologous RNA, MnSOD-RE may be useful in designing expression vectors for in vitro expression systems and in vivo gene therapy.