Journal of Nutrition LabDiet, Your World of Nutritional Answers

Home Help [Feedback] [For Subscribers] [Archive] [Search] [Contents]
QUICK SEARCH:   [advanced]


     

This Article
Right arrow Full Text (PDF)
Right arrow Purchase Article
Right arrow View Shopping Cart
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by St. Clair, D.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by St. Clair, D.
© 2004 The American Society for Nutritional Sciences J. Nutr. 134:3190S-3191S, November 2004

Supplement: Free Radicals: The Pros and Cons of Antioxidants

Manganese Superoxide Dismutase: Genetic Variation and Regulation1

Daret St. Clair2

Graduate Center for Toxicology, University of Kentucky, Lexington, KY 40536

2To whom correspondence should be addressed. E-mail: DSTCL00{at}uky.edu.

KEY WORDS: • superoxide dismutase • reactive oxygen species


   EXPANDED ABSTRACT
TOP
 EXPANDED ABSTRACT
LITERATURE CITED
 
Manganese superoxide dismutase (MnSOD)3 is a nuclear-encoded antioxidant enzyme that localizes to the mitochondria (1). Increased expression of MnSOD suppresses cancer phenotypes in a large number of human and murine tumors (2). MnSOD can also regulate tumor formation in MnSOD-overexpressing and MnSOD-deficient mice by modulating apoptotic and proliferation pathways in situ (3,4). The presence of MnSOD in mitochondria can influence the role of mitochondria as a source of reactive oxygen species (ROS) generation as well as a source of ROS removal. Given the evidence that links mitochondria to cell death and MnSOD to playing a role in the suppression of cancer, it has been proposed that alteration of MnSOD levels might contribute to cancer susceptibility and resistance to cancer therapeutic agents.

To elucidate the mechanisms by which the expression of the human sod2 gene is regulated, we cloned, sequenced, and characterized the human sod2 gene from various normal and human cancer cell lines as well as from human tissues. We found that sod2 is a single-copy gene consisting of 5 exons interrupted by 4 introns (5). Unique characteristics of this gene include a TATA-less promoter and an intronic enhancer element responsible for the induction of the gene (Fig. 1). The constitutive expression of this gene is controlled by a GC-rich promoter containing several specificity protein 1 (SP-1) and activating protein 2 (AP-2) binding sites. Transcription factor SP-1 is essential and sufficient, whereas AP-2 is unnecessary for and antagonistic to the constitutive expression of the gene (6,7). Interestingly, a unique set of 3 mutations was found in the promoter region of sod2 genes isolated from several human cancer cells. These mutations lead to an increase in an AP-2 binding site and a reduction in transcription activity of the basal promoter. The unique mutations were found in 60% of colon cancer cell lines examined (8). Preliminary studies using peripheral blood of human samples suggest that the unique mutations are present in a high percentage of colon cancer patients. These findings may provide an explanation for the reduced MnSOD activity found in some human cancer cells. However, a larger sample size is needed to establish the link between mutation in the transcription regulatory region of the sod2 gene and colon cancer.



View larger version (10K):
[in this window]
[in a new window]
  		FIGURE 1 Organization of the human sod2 gene and sites where polymorphic variants have been identified.

 
Although MnSOD may be present at a low level in some normal tissues, its expression is highly inducible by a wide range of agents, including cytokines and alcohol, suggesting that MnSOD is a stress-responsive gene. The induction of MnSOD by cytokine is mediated by nuclear factor {kappa}B (NF-{kappa}B). However, the presence of NF-{kappa}B is essential but not sufficient for a high-level induction of MnSOD (9). Thus far, there are no published reports of polymorphisms in the enhancer region of this gene in the human population. Therefore, it is highly likely that a deficiency of MnSOD can be alleviated by induction of sod2. A number of recent studies indicate that the level of MnSOD is inducible by nutrient constituents, including those from cruciferous vegetables (10), retinoic acid (11), and vitamin E (12). However, the mechanisms by which these agents mediate MnSOD induction remain unclear. Understanding how endogenous defense enzymes such as MnSOD can be enhanced by dietary intake of antioxidants could provide a novel strategy for designing cancer intervention.

In addition to the transcriptional regulation, accumulating data suggest that genetic polymorphisms in the human sod2 gene may be associated with a risk of developing cancer. Polymorphisms of the human sod2 gene were found in the regions that code for the mature protein and the mitochondria targeting peptide. Two polymorphic variants coding for isoleucine or threonine at amino acid 58 (I58T) in the mature protein were found in human cells. Due to its stability at the tetrameric interface, the mature protein containing isoleucine is more stable and less susceptible to inactivation by S-thiolation reactions than the threonine-containing protein (13). However, identification of genetic polymorphisms of these variants in cancer patients remains to be established. More recently, an additional thiol-sensitive mutant form of the sod2 gene was identified in Jurkat human T-cell leukemia (14). The leucine-to-phenylalanine mutation occurs at position 60 (L60F) in the mature protein. Cells containing the L60F heterozygous mutation have markedly less SOD activity in the presence of thiol agents. This finding explains the observed loss of MnSOD activity in some leukemia cells and suggests paradoxical effects from supplementation by the thiols class of antioxidants.

Two polymorphic variants at codon 16 that lead to incorporation of either alanine or valine in the mitochondrial targeting sequence are frequently detected in humans. The alanine-containing MnSOD is actively targeted into the mitochondrial matrix, whereas the valine-containing MnSOD is partially arrested within the inner mitochondrial membrane (15). The structural dimorphism in this region is associated with risk for development of breast cancer (16,17). Premenopausal women who are homozygous for the A/A allele have an increased risk of breast cancer compared to those with 1 or 2 V alleles. Furthermore, the risk is more pronounced among women whose consumption of fruit and vegetables, ascorbic acid, and {alpha}-tocopherol is low. These findings support the use of sod2 gene polymorphism as a biomarker and the risk-modification benefit of dietary manipulation. In contrast to breast cancer, a study of lung cancer that involved 1101 patients with lung cancer and 1239 control subjects indicated a markedly increased risk of lung cancer in individuals with A/V and V/V genotypes (18). This result may reflect the constant chronic exposure of the lung to ROS. Ongoing studies in lung cancer models using MnSOD-deficient mice should verify this possibility.


   FOOTNOTES
 
1 Presented as part of the conference "Free Radicals: The Pros and Cons of Antioxidants," held June 26–27 in Bethesda, MD. This conference was sponsored by the Division of Cancer Prevention (DCP) and the Division of Cancer Treatment and Diagnosis, National Cancer Institute, NIH, Department of Health and Human Services (DHHS); the National Center for Complementary and Alternative Medicine (NCCAM), NIH, DHHS; the Office of Dietary Supplements (ODS), NIH, DHHS; the American Society for Nutritional Science; and the American Institute for Cancer Research and supported by the DCP, NCCAM, and ODS. Guest editors for the supplement publication were Harold E. Seifried, National Cancer Institute, NIH; Barbara Sorkin, NCCAM, NIH; and Rebecca Costello, ODS, NIH. Back

3 Abbreviations used: AP-2, activating protein 2; I58T, isoleucine–threonine polymorphism at position 58; L60F, leucine–phenylalanine polymorphism at position 60; NF-{kappa}B, nuclear factor {kappa}B; MnSOD, manganese superoxide dismutase; ROS, reactive oxygen species; SP-1, specificity protein 1. Back


   LITERATURE CITED
TOP
 EXPANDED ABSTRACT
 LITERATURE CITED
 

1. Weisiger, R. A. & Fridovich, I. J. (1973) Mitochondrial superoxide dismutase. Site of synthesis and intramitochondrial localization. J. Biol. Chem. 248:4793-4796.[Abstract/Free Full Text]

2. St. Clair, D. K. (1996) Tumor suppression by manganese superoxide dismutase: a novel function of MnSOD?. A commentary. Oncol. Rep. 3:429-432.

3. Zhao, Y., Xue, Y., Oberley, T. D., Kiningham, K. K., Lin, S. M., Yen, H. C., Majima, H., Hines, J. & St. Clair, D. K. (2001) Overexpression of manganese superoxide dismutase suppresses tumor formation by modulation of activator protein-1 signaling in a multistage skin carcinogenesis model. Cancer Res 61:6082-6088.[Abstract/Free Full Text]

4. Zhao, Y., Oberley, T. D., Chaiswing, L., Lin, S. M., Epstein, C. J., Huang, T. T. & St. Clair, D. K. (2002) Manganese superoxide dismutase deficiency enhances cell turnover via tumor promoter-induced alterations in AP-1 and p53-mediated pathways in a skin cancer model. Oncogene 21:3836-3846.[Medline]

5. Wan, X. S., Devalaraja, M. N. & St. Clair, D. K. (1994) Molecular structure and organization of the human manganese superoxide dismutase gene. DNA Cell Biol 13:1127-1136.[Medline]

6. Zhu, C. H., Huang, Y., Oberley, L. W. & Domann, F. D. (2001) A family of AP-2 proteins down-regulate manganese superoxide dismutase expression. J. Biol. Chem. 276:14407-14413.[Abstract/Free Full Text]

7. Xu, Y., Porntadavity, S. & St. Clair, D. K. (2002) Transcriptional regulation of the human manganese superoxide dismutase gene: the role of specificity protein 1 (Sp1) and activating protein-2 (AP-2). Biochem. J. 362:401-412.[Medline]

8. Xu, Y., Krishnan, A., Wan, X. S., Majima, H., Yeh, C. C., Ludewig, G., Kasarskis, E. J. & St. Clair, D. K. (1999) Mutations in the promoter reveal a cause for the reduced expression of the human manganese superoxide dismutase gene in cancer cells. Oncogene 18:93-102.[Medline]

9. Xu, Y., Kiningham, K. K., Devalaraja, M. N., Yeh, C. C., Majima, H., Kasarskis, E. J. & St. Clair, D. K. (1999) An intronic NF-{kappa}B element is essential for induction of the human manganese superoxide dismutase gene by tumor necrosis factor-{alpha} and interleukin-1ß. DNA Cell Biol 18:709-722.[Medline]

10. Otieno, M. A., Kensler, T. W. & Guyto, K. Z. (2000) Chemoprotective 3H-1,2-dithiole-3-thione induces antioxidant genes in vivo. Free Radic. Biol. Med. 28:944-952.[Medline]

11. Mantymaa, P., Guttoem, T., Siitonen, T., Saily, M., Savolainen, E. R., Levenon, A. L., Kinnula, V. & Koistinen, P. (2000) Cellular redox state and its relationship to the inhibition of clonal cell growth and the induction of apoptosis during all-trans retinoic acid exposure in acute myeloblastic leukemia cells. Haematogica 85:238-245.

12. Koch, O., Farre, S., De Leo, M. E., Palozza, P., Palazzotti, B., Borrelo, S., Palombibi, G., Cravero, A. & Galeotti, T. (2000) Regulation of manganese superoxide dismutase (MnSOD) in chronic experimental alcoloholism: effects of vitamin E–supplemented and –deficient diets. Alcohol Alcohol 35:159-163.[Abstract/Free Full Text]

13. Borgstahl, G. E., Parge, H. E., Hickey, M. J., Johnson, M. J., Boissinot, M., Hallewell, R. A., Lepock, J. R., Cabelli, D. E. & Tainner, J. A. (1996) Human mitochondrial manganese superoxide dismutase polymorphic variant Ile58Thr reduces activity by destabilizing the tetrameric interface. Biochemistry 35:4287-4297.[Medline]

14. Hernandez-Saavedra, D. & McCord, J. M. (2003) Paradoxical effects of thiol reagents on Jurkat cells and a new thiol-sensitive mutant form of human mitochondrial superoxide dismutase. Cancer Res 63:159-163.[Abstract/Free Full Text]

15. Sutton, A., Khoury, H., Prip-Buus, C., Cepanec, C., Pessayre, D. & Degoul, F. (2003) The Ala16Val genetic dimorphism modulates the import of human manganese superoxide dismutase into rat liver mitochondria. Pharmacogenetics 13:145-157.[Medline]

16. Ambrosone, C. B., Freudenheim, J. L., Thompson, P. A., Bowman, E., Vena, J. E., Marshall, J. R., Graham, S., Laughlin, R., Nemoto, T. & Shields, P. G. (1999) Manganese superoxide dismutase (MnSOD) genetic polymorphisms, dietary antioxidants, and risk of breast cancer. Cancer Res 59:602-606.[Abstract/Free Full Text]

17. Mitrunen, K., Sillanpaa, P., Kataja, V., Eskelinen, M., Kosma, V. M., Benhamou, S., Unsitupa, M. & Hirvonen, A. (2001) Association between manganese superoxide dismutase (MnSOD) gene polymorphism and breast cancer risk. Carcinogenesis 22:827-829.[Abstract/Free Full Text]

18. Wang, L. I., Miller, D. P., Sai, Y., Liu, G., Su, L., Wain, J. C., Lynch, T. J. & Christiani, D. C. (2001) Manganese superoxide dismutase alanine-to-valine polymorphism at codon 16 and lung cancer risk. J. Natl. Cancer Inst. 93:1818-1821.[Free Full Text]




This article has been cited by other articles:


Home page
 J. Nutr.Home page
H. E. Seifried, D. E. Anderson, B. C. Sorkin, and R. B. Costello
Executive Summary Report
J. Nutr., November 1, 2004; 134(11): 3143S - 3163S.
[Full Text] [PDF]

This Article
Right arrow Full Text (PDF)
Right arrow Purchase Article
Right arrow View Shopping Cart
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by St. Clair, D.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by St. Clair, D.

Home Help [Feedback] [For Subscribers] [Archive] [Search] [Contents]
Copyright © 2004 by American Society for Nutrition