Manganese Superoxide Dismutase Transcription Research Articles

Selenium supplementation increases liver MnSOD expression: Molecular mechanism for hepato-protection

Selenium is recognized as essential in animal and human nutrition. Several hypotheses have been advanced for its biological activity. The aim of this study was to investigate the in vivo effect of selenium on rat liver manganese superoxide dismutase (MnSOD), a key antioxidant enzyme, under naïve and inflammatory conditions. Rats received sodium selenite supplementation and LPS injection. Whole-liver samples, isolated hepatocytes, Kupffer cells and blood samples were subjected to protein, RNA and biochemical analysis. Liver enrichment with selenium increased whole-liver MnSOD levels due to an increase in MnSOD transcription in hepatocytes. This was due to an increase in the ratio of specificity protein 1 to activating enhancer binding protein 2 DNA-binding activity. The inflammatory stimulus further elevated MnSOD levels in the whole-liver that was abrogated in sodium selenite supplementation due to reduced transcription of MnSOD in Kupffer cells. Moreover, selenium enrichment decreased Kupffer cells IL-6 transcription in LPS-injected animals. Anti-inflammatory activity of selenium was demonstrated by normalized blood levels of ALT and IL-6 in LPS-injected animals. In conclusion, selenium up-regulates hepatocytes MnSOD expression, probably improving their anti-oxidant defense, while decreasing MnSOD and IL-6 transcription in Kupffer cells in the presence of inflammatory stimuli, attenuating their inflammatory response. This selective mechanism may explain the anti-inflammatory and hepato-protective effect of selenium.

Down-regulation of Manganese-Superoxide Dismutase through Phosphorylation of FOXO3a by Akt in Explanted Vascular Smooth Muscle Cells from Old Rats

Manganese-superoxide dismutase (MnSOD) is one of the major cellular antioxidant defense systems. To study the effect of age on the regulation of MnSOD in the vasculature, we compared MnSOD expression and its transcriptional regulation in explanted vascular smooth muscle cells (VSMC) isolated from old (24 months old) versus young (6 months old) rats and grown in a normal (5 mM) or high (12.5 and 25 mM) glucose or tumor necrosis factor alpha (5 ng/ml) environment to induce oxidative stress. Both MnSOD protein and activity were reduced in VSMC from old compared with young animals. FOXO3a, a member of the family of Forkhead transcription factors, interacted with the promoter of the rat MnSOD gene at a specific binding site. Inhibition of FOXO3a transcription with small interfering RNA led to a reduction in MnSOD gene expression. VSMC from old rats had increased phosphorylated FOXO3a at Ser(253), which paralleled the reduction of MnSOD protein. Treatment of VSMC with 5 nm insulin-like growth factor-1 induced phosphorylation of Akt and FOXO3a over time, repressing FOXO3a DNA binding and consequently MnSOD gene expression. Furthermore, Akt activity was selectively increased in VSMC from the old, supporting the hypothesis that increased age-related Akt activity might be responsible for the phosphorylation and inactivation of FOXO3a, which in turn down-regulates MnSOD transcription.

Stochasticity of Manganese Superoxide Dismutase mRNA Expression in Breast Carcinoma Cells by Molecular Beacon Imaging

Visual and quantitative monitoring of cell-to-cell variation in the expression of manganese superoxide dismutase (MnSOD) mRNA by using novel ratiometric imaging with molecular beacons (MB) reveals a distinct change in patterns following induction of human breast-carcinoma cells with lipopolysaccharide. Interestingly, the pattern of cell-to-cell variation in a cell line stably transfected with a plasmid bearing a cDNA clone of MnSOD and overproducing the enzyme is significantly different from the pattern associated with MnSOD induction. The levels and the patterns of cell-population heterogeneity for beta-actin mRNA expression do not show distinct changes either following induction or in stably transfected cells. These results are significant in light of the reported relationship between this enzyme and malignant phenotype of breast-carcinoma cells. Use of MBs in ratiometric image analyses for cytoplasmic mRNAs represents a novel means of directly examining the stochasticity of transcription of MnSOD and other genes implicated in cellular phenotype regulation.

Progesterone Antagonizes the Vasoprotective Effect of Estrogen on Antioxidant Enzyme Expression and Function

Oxidative stress plays an important role in the pathogenesis of atherosclerosis and can be effectively influenced by radical scavenging enzymes. Estrogens exert antioxidative effects in the vasculature; however, cotreatment with progesterone may abrogate the vasoprotective effects of estrogen. Therefore, the effects of progesterone on the production of reactive oxygen species (ROS) and expression and function of antioxidant and oxidant enzymes were investigated in cultured vascular smooth muscle cells (VSMCs) and vascular tissue of mice. Progesterone time- and concentration-dependently downregulated extracellular superoxide dismutase (ecSOD) and manganese superoxide dismutase (MnSOD) expression and enzyme activity and reversed 17beta-estradiol-induced overexpression of ecSOD and MnSOD in VSMCs. Nuclear run-on assays revealed that progesterone decreases MnSOD and ecSOD transcription rates. Consequently, progesterone increased ROS release in VSMCs that was prevented by concomitant treatment with 17beta-estradiol. Estrogen deficiency in ovariectomized mice was associated with an increase in vascular superoxide release and NADPH oxidase activity. Estrogen replacement prevented this increase, whereas progesterone substitution enhanced ROS production and NADPH oxidase activity. The modulation of superoxide release coincided with decreased expression of ecSOD and MnSOD and upregulation of the p22phox and p67phox subunits of the NADPH oxidase complex in progesterone-treated animals. Furthermore, administration of progesterone to ovariectomized mice treated with 17beta-estradiol abrogated the antioxidative effects of estrogen. Progesterone antagonizes the vasoprotective effects of estrogen on ecSOD and MnSOD expression and increases NADPH oxidase activity. These findings may in part explain why hormone replacement therapy with estrogen plus progesterone displayed no beneficial effect on cardiovascular event rates in the prospective clinical trials.

Different Roles of Sp Family Members in HIV-1 Tat-Mediated Manganese Superoxide Dismutase Suppression in Hepatocellular Carcinoma Cells

The expression of manganese superoxide dismutase (MnSOD) is regulated by agents associated with cancer development. It has been shown that infection with the human immunodeficiency virus type 1 (HIV-1) is associated with the development of liver cancer and that the transactivating transcriptional factor (Tat) of human HIV-1 reduces the expression of MnSOD in several cell types. However, the role of Tat in the expression of MnSOD in hepatocellular carcinoma is unknown. Furthermore, the precise mechanisms whereby Tat suppresses MnSOD expression in hepatocellular carcinoma cells remain unclear. In this report, we build on our original observations that Tat changes the distribution of Sp family members on the MnSOD promoter, which accounts for Tat-dependent changes in basal expression. In hepatic cells, Tat expression upregulates Sp1/Sp3, which play different roles in regulating MnSOD transcription. While overexpression of Sp1 stimulates, overexpression of Sp3 represses transcriptional activity. The transcription repression effect of Sp3 is not due to Sp3 competing for the binding site with Sp1 because only the full-length Sp3 but not the truncated Sp3 suppresses MnSOD promoter activity. These findings suggest a novel mechanism by which Tat modulates the repression of the MnSOD gene and establish a link between HIV infection and liver cancer.

No apparent association between genetic polymorphisms (−102 C>T) and (−9 T>C) in the human manganese superoxide dismutase gene and gastric cancer 1

Manganese superoxide dismutase (MnSOD) plays a critical role in the detoxification of mitochondrial reactive oxygen species, constituting a major cellular defense mechanism against agents that induce oxidative stress. A genetic polymorphism in the mitochondrial targeting sequence of this gene has been associated with increased cancer risk. This one base pair transition (-9 T>C) leads to a Val to Ala amino acid change in the mitochondrial targeting sequence. In addition, the MnSOD promoter contains an activator protein-2 (AP-2) binding site that modifies transcription of MnSOD. Mutations have been identified in the proximal region of the promoter in human tumor cell lines. One of these mutations (-102 C>T) has been shown to change the binding pattern of AP-2, leading to a reduction in transcriptional activity. The aim of our study was to investigate possible associations of the (-9 T>C) and (-102 C>T) polymorphisms with gastric cancer in a population-based case-control study conducted in Warsaw, Poland. DNA was obtained from a population based case-control study of stomach cancer conducted in Warsaw, Poland, between 1994 and 1996. The MnSOD -9 T>C genotype was determined by PCR-RFLP assay. The MnSOD -102 C>T genotype was determined using a TaqMan allele discrimination assay. The frequency of the -102 C>T polymorphism was 41% (38/91) in gastric cancer cases and 38% (50/130) in the controls (odds ratio [OR] 1.1, 95% confidence interval [CI] 0.6-2.1). The frequency of the -9 T>C polymorphism was 44% (202/464) in cases and 56% (262/464) in controls (OR 1.1; 95% CI 0.9-1.37). The lack of association was observed in both non-smokers (OR 1.5; 95% CI 0.7-2.34) and smokers (OR 1.1; 95% CI 0.7-1.7). Furthermore, the association was not significant when smokers were segregated by extent of smoking history. The association of the manganese superoxide dismutase polymorphisms at -102 C>T and the -9 T>C were not found to be associated with gastric cancer in a Polish case-control study.

Method for determination of (-102C>T) single nucleotide polymorphism in the human manganese superoxide dismutase promoter

BackgroundManganese superoxide dismutase (MnSOD) plays a critical role in the detoxification of mitochondrial reactive oxygen species constituting a major cellular defense mechanism against agents that induce oxidative stress. The MnSOD promoter contains an activator protein-2 (AP-2) binding site that modifies transcription of MnSOD. Mutations have been identified in the proximal region of the promoter in human tumor cell lines. One of these mutations (-102C>T) has been shown to change the binding pattern of AP-2 leading to a reduction in transcriptional activity. The aim of our study was to develop a method to identify and determine the frequency of this (-102C>T) polymorphism in human tissues.ResultsA new TaqMan allelic discrimination genotype method was successfully applied to genomic DNA samples derived from blood, buccal swabs, snap frozen tissue and paraffin blocks. The polymorphism was shown to be in Hardy-Weinberg Equilibrium in an evaluation of 130 Caucasians from Warsaw, Poland: 44 (33.8%) were heterozygous and 6 (4.6%) were homozygous for -102T.ConclusionThis report represents the first description of the MnSOD -102C>T polymorphism in human subjects by a novel Taqman allelic discrimination assay. This method should enable molecular epidemiological studies to evaluate possible associations of this polymorphism with malignancies and other diseases related to reactive oxygen species.

Genomic regions responsible for manganese superoxide dismutase regulation in Drosophila melanogaster.

The transcription of manganese superoxide dismutase (MnSOD), expression of which is essential for detoxification of superoxide radicals from mitochondria, has been shown to be regulated in vitro by many factors and conditions including oxidative stress, cytokines, lipopolysaccharide, cytoplasmic myc (c-myc), p53 and tumour necrosis factors. Here we describe genomic regions in Drosophila melanogaster with regulatory effects on transcription of the MnSOD gene at an organism-wide level. To understand the integrated regulation of MnSOD expression we screened chromosomes of D. melanogaster to locate deficiencies that altered the expression of MnSOD. Suppressors of MnSOD were screened by assessing the relative message abundance of MnSOD in 149 deletions covering approximately 81% of the Drosophila genome. The chromosomal deficiency Df(2R)017 significantly up-regulated MnSOD mRNA by 1.7-fold. Deficiency in four other genomic intervals, Df(1)ct-J4, Df(2L)BSC4, Df(3L)66C-G28 and Df(3R)Scr, down-regulated MnSOD expression. Changes in MnSOD expression were positively associated with paraquat sensitivity of the deletion genotypes. Thus, at least one candidate enhancer and four candidate suppressors exist in the Drosophila genome to regulate the transcriptional activity of the MnSOD gene in vivo.

Mitochondrial and peroxisomal manganese superoxide dismutase: differential expression during leaf senescence.

In pea (Pisum sativum L.) leaves, manganese superoxide dismutase (Mn-SOD) is mainly localized in mitochondria as well as in peroxisomes. In this work, the effect of leaf senescence on the peroxisomal and mitochondrial Mn-SOD was studied in detached leaves from pea plants which were incubated in the dark at 25 degrees C for 3-11 d. Northern blots hybridized with a cDNA encoding mitochondrial Mn-SOD from pea leaves and a mitochondrial Mn-SOD transit peptide-specific probe showed increased Mn-SOD transcript levels during leaf senescence, due in part to in creased mitochondrial Mn-SOD mRNA. Recombinantly-expressed mitochondrial Mn-SOD was used to raise polyclonal antibodies which cross-reacted with Mn-SOD in peroxisomes purified from pea leaves. Western blot assays of crude extracts with the antibodies to pea mitochondrial Mn-SOD showed that the levels of total Mn-SOD protein gradually increased with leaf senescence. By native PAGE, the total Mn-SOD activity of pea leaves increased with senescence. EM immunocytochemistry was used to distinguish mitochondrial and peroxisomal Mn-SOD in senescent leaves. Increased Mn-SOD labelling in mitochondria was intensified, whereas the immunogold labelling of peroxisomes did not change with senescence. Overall, these results show that mitochondrial and peroxisomal Mn-SOD expression is regulated differently. The expression of mitochondrial Mn-SOD is induced during the senescence of pea leaves, whereas peroxisomal Mn-SOD could be post-translationally activated. Previously described results showing decreased mitochondrial Mn-SOD activity and increased peroxisomal Mn-SOD activity may be reflective of post-translational events regulating enzymatic activity during leaf senescence.

Tumor Necrosis Factor-α Selectively InducesMnSOD Expression via Mitochondria-to-Nucleus Signaling, whereas Interleukin-1β Utilizes an Alternative Pathway

Mitochondrial levels of the anti-oxidant enzyme, manganese superoxide dismutase (MnSOD), are dramatically elevated in response to stimulation with tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), and lipopolysaccharide (LPS). However, the precise intracellular signaling pathways responsible for this inducible expression are poorly understood. MnSOD expression in pulmonary epithelial and endothelial cells, treated with inflammatory mediators and various inhibitors, was studied by Northern analysis. The mitochondrial electron transport chain inhibitors, antimycin A and myxothiazol, selectively blocked TNF-alpha-inducible expression of MnSOD but not that of IL-1beta or LPS, indicating different signaling pathways. N-Acetylcysteine could reliably decrease inducible MnSOD expression by TNF-alpha, but not IL-1, linking reactive oxygen species (ROS) to the TNF-alpha signaling pathway. Elevated levels of arachidonic acid have been demonstrated previously to generate mitochondrial ROS. A specific cytoplasmic phospholipase A(2) inhibitor reduced stimulated MnSOD expression by TNF-alpha, but not by IL-1beta, further supporting the role of ROS. Other investigators have shown that MnSOD expression may be regulated by NF-kappaB. Our results with a specific inhibitory kappa-kinase inhibitor indicate that NF-kappaB modulates IL-1beta signaling but not the TNF-alpha pathway. Thus, we have demonstrated that although inducible MnSOD transcription may appear similar at the messenger RNA level, the intracellular signaling pathways are differentially regulated.

Inducible expression of manganese superoxide dismutase by phorbol 12-myristate 13-acetate is mediated by Sp1 in endothelial cells.

The expression of manganese superoxide dismutase (Mn-SOD), an important component of the cellular defense system against oxidative stress, is induced in response to a variety of stimuli, including cytokines and phorbol esters, in endothelial cells. To define the molecular mechanisms regulating the expression of Mn-SOD, we have characterized the promoter of the human Mn-SOD gene. In calf pulmonary artery endothelial cells, phorbol 12-myristate 13-acetate (PMA) gradually increased Mn-SOD mRNA levels, with a peak at 6 to 12 hours after stimulation. The increase in Mn-SOD mRNA was significantly inhibited by a protein kinase C (PKC) inhibitor (calphostin C) but not by a mitogen-activated protein kinase kinase-1 inhibitor (PD98059) or a p38 mitogen-activated protein kinase inhibitor (SB203580). By reporter gene transfection experiments of a series of promoter deletions and site-directed mutation constructs, we found 2 consensus Sp1 binding sequences located at -97 and at -77 to play an important role in PMA-induced Mn-SOD transcription. Electrophoretic gel mobility shift assays have indicated that this sequence serves as an Sp1 binding site. Northern and Western blot analysis has revealed that PMA-induced promoter activity of Mn-SOD correlates with an increased expression of Sp1. Nuclear proteins from PMA-treated calf pulmonary artery endothelial cells displayed an increased DNA binding to the Sp1 site. Furthermore, the Mn-SOD promoter was activated either by overexpression of Sp1 or the constitutively activated form of PKCbeta in an Sp1 site-dependent manner. These results suggest that PMA stimulates transcription of the Mn-SOD gene through an increase in Sp1 expression and thus implicate Sp1 as an effector mediating the PKC-signaling pathway elicited by extracellular signals.

HIV type 1 infection of human macrophages induces an upregulation of manganese superoxide dismutase gene that may protect cells from death.

It has been previously demonstrated that HIV-1 infection induces a downregulation of MnSOD transcription in CD4+ lymphocytes. Using clinical isolates of macrophage-tropic HIV-1 strains we report here that conversely, purified normal human monocyte-derived macrophages (MDMs) overexpress the manganese superoxide dismutase (MnSOD) gene in response to infection and viral replication. This upregulation of MnSOD gene expression is concomitant with tumor necrosis factor alpha (TNF-alpha) and interleukin 6 (IL-6) production and treatment of HIV-1-infected MDMs with a specific transcriptional inhibitor of TNF-alpha synthesis counteracts the HIV-1-induced MnSOD gene activation. Moreover, TNF-alpha but not IL-6 addition mimicks the effects of HIV-1 infection on MnSOD gene regulation in normal MDM cultures. These observations strongly suggest that the MnSOD gene induction detected in HIV-1-infected MDMs is triggered by TNF-alpha produced in culture supernatants in parallel to HIV-1 particle release. In contrast to MnSOD, HIV-1 infection or replication in human MDMs has no effect on copper-zinc superoxide dismutase (Cu/ZnSOD) gene expression.

The manganese superoxide dismutase gene of Drosophila: structure, expression, and evidence for regulation by MAP kinase.

The gene encoding manganese superoxide dismutase (MnSOD) from Drosophila melanogaster has been isolated and its expression has been studied. In contrast to several mammalian MnSOD genes, the Drosophila gene contains a single intron and is transcribed into a single 0.8-kb transcript. Whole-mount in situ hybridization reveals extensive transcript accumulation in ovarian nurse cells and a heavy maternal contribution to the early embryo. Larval imaginal discs are enriched with MnSOD transcripts relative to other larval tissues, further suggesting a possible relationship between high MnSOD expression and mitotic activity. The 5'-upstream region contains several well-known regulatory elements including metal response, antioxidant response, and xenobiotic response elements (MRE, ARE, and XRE, respectively), sites for activator protein-1 (AP-1), nuclear factor-kappaB (NF-kappaB), adenosine 3',5'-cyclic monophosphate regulator binding element factor (CREB), as well as classic TATA and CAAT boxes. That MnSOD expression in Drosophila is regulated in part by the transcription factor AP-1 via the MAP kinase signal transduction pathway is suggested by experiments which show that a hypomorphic mutation of the MAP kinase-encoding rolled gene substantially reduces levels of MnSOD transcripts and correlates with reduced resistance to oxidative stress in rolled mutants.

Increased mRNA expression of manganese superoxide dismutase in psoriasis skin lesions and in cultured human keratinocytes exposed to IL-1β and TNF-α

Because reactive oxygen species have been implicated in the pathogenesis of various hyperproliferative and inflammatory diseases, the mRNA expression of the antioxidant enzyme superoxide dismutase was studied in psoriatic skin tissue. By using reverse transcription-PCR we found similar expression of copper, zinc superoxide dismutase (CuZnSOD) in the involved vs. uninvolved psoriatic skin. In contrast, the level of the manganese superoxide dismutase (MnSOD) mRNA message was consistently higher in lesional psoriatic skin as compared to adjacent uninvolved skin and healthy control skin. Parallel investigation of those cytokines that are thought to be direct or indirect inducers of the MnSOD activity revealed an increased mRNA expression of IL-1β, TNF-α, and GM-CSF in lesional psoriatic skin. To study if these cytokines exert a direct effect on dismutase expression in epidermal cells, human keratinocytes in culture were challenged with IL-1β, TNF-α, and GM-CSF. It was found that IL-1β and TNF-α, but not GM-CSF, induced the mRNA expression of MnSOD, and an additive effect was demonstrated for the two former cytokines. Further, the expression of both CuZnSOD and MnSOD transcripts was similar in cultured keratinocytes maintained at low differentiation (low Ca 2+ medium) and cells forced to terminal differentiation (by high Ca 2+ medium). Our results indicate that the abnormal expression of MnSOD mRNA in lesional psoriatic skin is not directly linked to the pathologic state of keratinocyte differentiation in the skin. It seems more likely that the cutaneous overexpression of MnSOD in psoriatic epidermis represents a protective cellular response evoked by cytokines released from inflammatory cells invading the diseased skin.

Expression of manganese superoxide dismutase in ovine kidney cortex during development.

Manganese superoxide dismutase (MnSOD) is one of the main antioxidant enzymes in mammalian tissue. Previous studies have shown that the activity of MnSOD increases in the rat kidney during development. To define further the developmental change in MnSOD activity and better understand some of the steps involved in the control of MnSOD expression during kidney development, we measured MnSOD messenger RNA and enzyme activity in the ovine kidney cortex during fetal life, in the newborn period, and in adults. MnSOD mRNA and enzyme activity were detected at 0.65 gestation. Hybridization of the Northern blot with a human MnSOD cDNA probe showed evidence of two transcripts of 4.0 and 1.5 kb, respectively. There was a significant increase with age of MnSOD activity and MnSOD mRNA (p < 0.0001). The abundance of each MnSOD transcript significantly increased with age (p < 0.001). In the fetuses, both transcripts increase in parallel; in newborns and adults the 1.5-kb increase was significantly greater than the 4.0-kb increase. Enzyme activity and mRNA were strongly correlated (r = 0.89, p < 0.0001). These data indicate that the expression of MnSOD is developmentally regulated in the ovine kidney cortex. This increase seems to be dependent largely on pretranslational events.

Distribution of Manganese Superoxide Dismutase mRNA in Normal and Hyperoxic Rat Lung

Aerobic metabolism requires a continuous oxygen supply, which in turn can form partially reduced species (free radicals) that damage cellular components. To prevent this, organisms have elaborate free radical-scavenging defenses that include the superoxide dismutases. The lungs are unique in their role as an oxygen-gathering system, making these defenses critical to lung integrity. Manganese superoxide dismutase (Mn-SOD) levels increase in rats exposed to sublethal doses of hyperoxia and correlate with the development of tolerance to higher levels of hyperoxia. Although pulmonary Mn-SOD protein and mRNA levels both change with hyperoxia, the timing and levels differ dramatically. Lung heterogeneity makes extrapolation of data from whole tissue homogenates or cultures difficult. In this study, in situ hybridization of Mn-SOD in the lungs of adult rats exposed to air or to 85% O2 for 3 days was performed. In animals exposed to either air or 85% O2, Mn-SOD transcripts were present in arterioles, the septal tips of alveolar ducts, alveolar type II cells, and mesothelial cells. Hyperoxic lung had an intense, continuous labeling of the pleura that was distinctly greater than the intermittent labeling of the pleura found in control animals. The high level of expression of Mn-SOD mRNA in alveolar duct septal tips in both control and O2-exposed animals may be secondary to increased aerobic activity in these regions, which contain collagen and elastin and are important stress-bearing elements in the lung. Alveolar type II cells are metabolically active secretory cells and thus may experience increased endogenously generated oxidative stress. Pleural effusions are common after hyperoxic exposures, suggesting damage to the mesothelium.(ABSTRACT TRUNCATED AT 250 WORDS)

Multiple mRNA species generated by alternate polyadenylation from the rat manganese superoxide dismutase gene.

The mitochondrial enzyme, manganese superoxide dismutase (MnSOD) is an integral component of the cell's defense against superoxide-mediated cellular damage. We have isolated and characterized four cDNA clones and the structural gene for rat MnSOD. Northern analyses using MnSOD cDNA probes detected at least five mRNAs in all tissues and cell types examined. Southern and Northern analysis using a 3' non-coding sequence probe, common to all the cDNAs, showed hybridization only to genomic restriction fragments that correspond to our genomic clone and the five MnSOD mRNAs. These data demonstrate that all of the rat MnSOD transcripts are derived from a single functional gene. Primer extension data indicate that transcription initiation is clustered within a few bases. Northern analysis using intron probes demonstrates that all five transcripts are fully processed. Northern analysis using cDNA and genomic probes from sequences progressively 3' to the end of the coding sequence indicates that size heterogeneity in the MnSOD transcripts results from variations in the length of the 3' non-coding sequence. From this data and the location of potential polyadenylation signals near the expected sites of transcript termination, we conclude that the existence of multiple MnSOD mRNA species originate as the result of alternate polyadenylation.

Manganese Superoxide Dismutase Expression in Human Cancer Cells: A Possible Role of mRNA Processing

The level of manganese superoxide dismutase (MnSOD) as determined by an immunoreactive assay was reduced in human cancer cells. The reduced amount of immunoreactive MnSOD in these cells was observed regardless of the growth state of the cells. The decrease in the enzyme protein was associated with a decrease in the mature form of MnSOD transcript as determined by Northern Analysis. The decreased amount of the mature form of MnSOD transcript was accompanied by an increase in the amount of the partially processed form of MnSOD transcript. These results suggest that RNA processing or translation of MnSOD mRNA may be responsible for the decreased amount of MnSOD activity in human tumor cells.