Irradiation Increases Manganese Superoxide Dismutase mRNA Levels in Human Fibroblasts.

Irradiation induces the production of superoxide radicals (O), which play an important causative role in radiation damage. Manganese superoxide dismutase (MnSOD) is a mitochondrial enzyme involved in scavenging O. This study examined MnSOD gene regulation by irradiation in WI38 human fibroblasts. Unstimulated fibroblasts constitutively expressed MnSOD activity and mRNA; irradiation markedly increased MnSOD activity and mRNA levels. The increase in MnSOD transcripts by irradiation was both time- and dose-dependent. WI38 fibroblasts constitutively produce low levels of interleukin-1 (IL-1). The induction of MnSOD mRNA by irradiation was partially blocked by anti-IL-1 antibodies, and treatment of cells with IL-1 also increased MnSOD mRNA levels. Inhibition of the cyclo-oxygenase pathway with indomethacin augmented the induction MnSOD mRNA by irradiation and prostaglandin E2 inhibited the accumulation of MnSOD mRNA by irradiation. Transcriptional run-on analysis showed that irradiation increased the rate of MnSOD transcription 2-fold. Stability studies of MnSOD mRNA in these cells showed that the half-life increased from 4 h in irradiated cells. These results suggest that induction of the MnSOD gene after irradiation is regulated, at least in part, by IL-1 production and that increased levels of MnSOD transcripts also occur through a pathway of endogenous prostaglandin E2 production. Our data indicate that the increase in MnSOD mRNA observed after irradiation occurs through both transcriptional and post-transcriptional mechanisms. Irradiation induces the production of superoxide radicals (O), which play an important causative role in radiation damage. Manganese superoxide dismutase (MnSOD) is a mitochondrial enzyme involved in scavenging O. This study examined MnSOD gene regulation by irradiation in WI38 human fibroblasts. Unstimulated fibroblasts constitutively expressed MnSOD activity and mRNA; irradiation markedly increased MnSOD activity and mRNA levels. The increase in MnSOD transcripts by irradiation was both time- and dose-dependent. WI38 fibroblasts constitutively produce low levels of interleukin-1 (IL-1). The induction of MnSOD mRNA by irradiation was partially blocked by anti-IL-1 antibodies, and treatment of cells with IL-1 also increased MnSOD mRNA levels. Inhibition of the cyclo-oxygenase pathway with indomethacin augmented the induction MnSOD mRNA by irradiation and prostaglandin E2 inhibited the accumulation of MnSOD mRNA by irradiation. Transcriptional run-on analysis showed that irradiation increased the rate of MnSOD transcription 2-fold. Stability studies of MnSOD mRNA in these cells showed that the half-life increased from 4 h in irradiated cells. These results suggest that induction of the MnSOD gene after irradiation is regulated, at least in part, by IL-1 production and that increased levels of MnSOD transcripts also occur through a pathway of endogenous prostaglandin E2 production. Our data indicate that the increase in MnSOD mRNA observed after irradiation occurs through both transcriptional and post-transcriptional mechanisms. INTRODUCTIONIrradiation produces physical and chemical damage to tissues that may lead to cell death or neoplastic transformation. In the presence of oxygen, irradiation or some chemicals increase the formation of superoxide radicals (O)(1Hall E.J. Radiobiology for the Radiologist. Lippincott, Philadelphia, PA1988: 10-11Google Scholar, 2Fridovich I. Science. 1978; 201: 875-880Crossref PubMed Scopus (2746) Google Scholar), which are important mediators of tissue damages(3Scott M.D. Meshnick S.R. Eaton J.W. J. Biol. Chem. 1989; 264: 2498-2501Abstract Full Text PDF PubMed Google Scholar, 4Hirose K. Longo D.L. Oppenheim J.J. Matsushima K. FASEB J. 1993; 7: 361-368Crossref PubMed Scopus (335) Google Scholar). Superoxide radicals also have been implicated as important pathologic mediators in various disorders including cancer, inflammation, or ischemia(5Cross C.E. Halliwell B. Borish E.T. Pryor W.A. Ames B.N. Saul R.L. McCord J.M. Harman D. Ann. Intern. Med. 1987; 107: 526-545Crossref PubMed Scopus (1553) Google Scholar, 6Clark I.A. Cowden W.B. Hunt N.H. Med. Res. Rev. 1985; 5: 297-332Crossref PubMed Scopus (128) Google Scholar). The reaction of these radicals with DNA results in DNA strand breaks, which play an important role in radiation-induced carcinogenesis(6Clark I.A. Cowden W.B. Hunt N.H. Med. Res. Rev. 1985; 5: 297-332Crossref PubMed Scopus (128) Google Scholar). In response to these stresses, cells induce the synthesis or activation of proteins with protective capacities. Previous studies have shown that cytokines such as granulocyte-macrophage colony-stimulating factor, tumor necrosis factor (TNF),1( 1The abbreviations used are: TNFtumor necrosis factorSODsuperoxide dismutaseMnSODmanganese superoxide dismutaseILinterleukinPGprostaglandinGyGrayNBTnitroblue tetrazoliumCHXcycloheximide. )and interleukin-1 (IL-1) are produced after irradiation in various cells(7Akashi M. Hachiya M. Koeffler H.P. Suzuki G. Biochem. Biophys. Res. Commun. 1992; 189: 986-993Crossref PubMed Scopus (27) Google Scholar, 8Hachiya M. Suzuki G. Koeffler H.P. Akashi M. Exp. Cell Res. 1994; 214: 343-350Crossref PubMed Scopus (14) Google Scholar, 9Woloschak G.E. Chang-Liu C.M. Jones P.S. Jones C.A. Cancer Res. 1990; 50: 339-344PubMed Google Scholar, 10Hallahan D.E. Spriggs D.R. Beckett M.A. Weichselbaum R.R. Proc. Natl. Acad. Sci. U. S. A. 1989; 86: 10104-10107Crossref PubMed Scopus (397) Google Scholar, 11Sherman M.L. Datta R.D. Hallahan D.E. Weichselbaum R.R. Kufe D.W. Weichselbaum R.R. J. Clin. Invest. 1991; 87: 1794-1797Crossref PubMed Scopus (124) Google Scholar, 12Hallahan D.E. Virudachalam S. Sherman M.L. Huberman E. Kufe D.W. Weichselbaum R.R. Cancer Res. 1991; 51: 4565-4569PubMed Google Scholar, 13Witte L. Fuks Z. Haimovitiz-Friedman A. Vlodavsky I. Goodman D.S. Eldor A. Cancer Res. 1989; 49: 5066-5072PubMed Google Scholar).Superoxide dismutases (SODs, EC 1.15.1.1) are metalloenzymes that catalyze the dismutation of O to H2O2 (hydrogen peroxide) and O2 (oxygen)(14Fridovich I. J. Biol. Chem. 1989; 264: 7761-7764Abstract Full Text PDF PubMed Google Scholar, 15Taniguchi N. Adv. Clin. Chem. 1992; 29: 1-59Crossref PubMed Scopus (102) Google Scholar). Thus, SODs are important initial components in the cellular defense against O (14Fridovich I. J. Biol. Chem. 1989; 264: 7761-7764Abstract Full Text PDF PubMed Google Scholar) and radiation-induced tissue damage. Three forms of SODs with distinctive cellular distributions and metal requirements are found; MnSOD is found in prokaryotes and in mitochondria of eukaryotes, copper-zinc SOD occurs in eukaryotes, and iron SOD is located in the cytosol of prokaryotes. Whereas production of copper-zinc SOD and iron SOD is constitutive, MnSOD is inducible by various stimuli, such as IL-1, TNF, lipopolysaccharide, interferon-γ, or hypoxia(16Fujii J. Taniguchi N. J. Biol. Chem. 1991; 266: 23142-23146Abstract Full Text PDF PubMed Google Scholar, 17Masuda A. Longo D.L. Kobayashi Y. Appella E. Oppenheim J.J. Matsushima K. FASEB J. 1988; 2: 3087-3091Crossref PubMed Scopus (196) Google Scholar, 18Wong G.H.W. Kamd A. Elwell J.H. Oberley L.W. Goeddel D.V. Beutler B. Tumor Necrosis Factor: The Molecules and Their Emerging Role in Medicine. Raven Press, Ltd., New York1992: 473-484Google Scholar, 19Wong G.H.W. Goeddel D.V. Science. 1988; 242: 941-944Crossref PubMed Scopus (833) Google Scholar, 20Visner G.A. Dougall W.C. Wilson J.M. Burr I.A. Nick H.S. J. Biol. Chem. 1990; 265: 2856-2864Abstract Full Text PDF PubMed Google Scholar, 21Harris C.A. Derbin K.S. Hunte-McDonough B. Krauss M.R. Chen K.T. Smith D.M. Epstein L.B. J. Immunol. 1990; 147: 149-154Google Scholar).Fibroblasts constitute a major element of bone marrow stroma and submucosal and subcutaneous tissues, where they are important for repair of tissue injury. In this study, we examined the effects of irradiation on expression of the MnSOD gene and found an intracellular accumulation of MnSOD induced by irradiation in human fibroblasts. We also explored the mechanisms for regulation of the MnSOD gene by irradiation.MATERIALS AND METHODSCells and CultureNormal human embryonic lung fibroblasts (WI38, obtained from American Type Culture Collection) were cultured in α-medium (Cosmo Bio Co. Ltd., Tokyo, Japan) supplemented with 7% fetal calf serum (Mitsubishi Kasei Co., Tokyo, Japan) in a humidified atmosphere containing 5% CO2. Flasks containing confluent cells were used for from confluent of or irradiated fibroblasts were by the at for and at were irradiated with by a at a rate of as by was from The against and were and and were by Co. Ltd., These of IL-1 at a of in the The against was and of this of in the cell and were from for MnSOD MnSOD activity was by the as a of O as L.W. D.R. PubMed Scopus Google Scholar, L.W. D.R. of for Press, Scholar). or irradiated cells were and in with on the were the were for MnSOD and a was O to at a rate The rate of was by at of SOD was as the of enzyme activity that inhibited the rate by The activity of MnSOD was in the presence of to copper-zinc activity of was levels in cell were by the R.L. J. Biol. Chem. Full Text PDF PubMed Google and were to or indomethacin in in for were with of or of for h at with in 5% in at for a with and at for was by a were with of unirradiated for of by WI38 fibroblasts in was by as This is the of with for The of this and or and was and the of by was or irradiated cells were cultured for h in fetal calf serum were of of and of or were at for were at with of a and at at for The were and the in the was on a The of was with a and the of in the was of activity in from WI38 cells was by by that been to Oppenheim J.J. J. Immunol. Google Scholar). of was by with human MnSOD was a from Cancer and were from and Y. M. M. J. M. M. S. Res. 1985; PubMed Scopus Google Scholar, A. C.A. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). DNA was from L. Biol. PubMed Google Scholar). These were by a B. Biochem. PubMed Scopus Google Scholar). The activity was and of of WI38 cells were in and with was by a as and Press, D. Scholar, M. M. Koeffler H.P. 1989; PubMed Google Scholar). at was in a and to a Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). were with for h at in and were to a of for at and to Co. Ltd., were with MnSOD and The of MnSOD mRNA in were with a of the or the of the to that of fibroblasts were to irradiation and were by in an for and in a containing were by in a and in were for at in a reaction containing and of The reaction was by at The reaction was with of in and by The was at with in the presence of The was by and in in and in was through a to DNA containing the was by and were to a and by was to the containing were with of in and of DNA for at were in at and in and at of MnSOD and in or irradiated cells were by of MnSOD was by a of of MnSOD by Irradiation in WI38 fibroblasts were cultured for h after to irradiation at a unirradiated cells were cultured for were and for MnSOD activity by the fibroblasts MnSOD activity increase of MnSOD activity was observed at of irradiation the increase of MnSOD activity in a MnSOD activity was that from unirradiated cells of Irradiation on of MnSOD mRNA in were cultured for h after of irradiation. the of irradiation on MnSOD gene analysis was with MnSOD fibroblasts a low of MnSOD which was increased by irradiation with a of The induction of MnSOD was increased in a of and the induction of the MnSOD gene was after to of irradiation on levels of MnSOD mRNA in fibroblasts. were cultured for h after irradiation. was and by and to a as and was with MnSOD of of irradiation on levels of MnSOD mRNA in fibroblasts. Cell were cultured for various after irradiation at analysis of mRNA was by of MnSOD mRNA induction by fibroblasts were irradiated at and at analysis showed that a increase in MnSOD mRNA was observed after h and that to increase h after irradiation of Irradiation on of MnSOD mRNA in the of cultured with or synthesis by or as with that of cells. with the accumulation of MnSOD by irradiation irradiation or treatment with increased the of MnSOD transcripts produced results of of on expression of MnSOD mRNA after irradiation. were with irradiation for or or with for h and irradiated for h was by and of IL-1 on of MnSOD mRNA after fibroblasts constitutively produce IL-1 at low K. Z. Koeffler H.P. J. 1989; PubMed Scopus Google Scholar). We IL-1 a of WI38 cells cultured for of IL-1 analysis showed that WI38 cells low levels of and and that was increase of levels of IL-1 after irradiation in these cells the of produced IL-1 in the expression of MnSOD mRNA by cells were with against human or which of IL-1 for cells were irradiated with in the presence of or cells were and levels of MnSOD mRNA were with levels in cells that were cultured in In to the levels of MnSOD mRNA in cells and the levels in cells with anti-IL-1 and also to the the with MnSOD was to of the endogenous IL-1 with anti-IL-1 in a in levels of expression of MnSOD mRNA in levels by and expression by with and also blocked the increase in MnSOD transcripts by and treatment with which of as the of MnSOD mRNA or the induction of MnSOD by irradiation in these cells WI38 fibroblasts were cultured with of IL-1 for h of cells with IL-1 induced MnSOD mRNA in these cells in a of IL-1 production on expression of MnSOD mRNA in fibroblasts to irradiation. were for h with or at a that or or with that These cells were irradiated at in the presence of the unirradiated and irradiated cells were and levels of MnSOD mRNA were The was to for cells were cultured with or for and was of MnSOD mRNA were by of of MnSOD mRNA after studies have shown that cyclo-oxygenase is a of production and that are by M. M.A. J. D. J. Biol. Chem. 1988; Full Text PDF PubMed Google Scholar, J. Spriggs D. K. Kufe D. Biol. 1989; PubMed Scopus Google Scholar, S. M. S. M. N. J. 1989; PubMed Scopus Google Scholar, C.A. M.A. L. J. Clin. Invest. PubMed Scopus Google Scholar). In to are involved in the regulation of the MnSOD gene by induction of MnSOD mRNA by irradiation was examined in the presence of a cyclo-oxygenase indomethacin WI38 cells were cultured with of indomethacin for h and to of irradiation. h of cells were and MnSOD mRNA levels were of cells with indomethacin the induction of MnSOD mRNA by irradiation. We also levels of in by Irradiation with inhibited synthesis a of production was observed with of irradiation of blocked the induction of MnSOD mRNA by irradiation in a of synthesis on the induction of MnSOD transcripts to irradiation in fibroblasts. were with of indomethacin or were irradiated in the presence of indomethacin and cultured for was and was were irradiated in the presence of and cultured for h and of MnSOD in of in the cell is on the of both transcription and the mechanisms for accumulation of MnSOD transcripts by irradiation in these transcriptional run-on were MnSOD was constitutively at a low in WI38 cells of the cells to irradiation increased the transcriptional rate of MnSOD 2-fold. post-transcriptional regulation of MnSOD mRNA in irradiated unirradiated or fibroblasts were cultured for and was to the were cultured for an h and were and examined for MnSOD mRNA levels The half-life of MnSOD mRNA in unirradiated fibroblasts was 4 run-on analysis of MnSOD in irradiated fibroblasts. WI38 cells were or irradiated at and h were as and transcripts were to the containing of or the of MnSOD mRNA in fibroblasts to irradiation. cells or cells irradiated at were cultured with for in cells and in irradiated was and by as and The of was by of of the cells were to have of the effects of irradiation are by E.J. Radiobiology for the Radiologist. Lippincott, Philadelphia, PA1988: 10-11Google Scholar, 4Hirose K. Longo D.L. Oppenheim J.J. Matsushima K. FASEB J. 1993; 7: 361-368Crossref PubMed Scopus (335) Google Scholar, G. J. Res. PubMed Scopus Google Scholar). Irradiation the rate of O and O DNA and J.H. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). The data that the of MnSOD mRNA and activity by irradiation in human fibroblasts. We also found that accumulation of MnSOD mRNA after to irradiation occurs at least in part, the activation of IL-1 and the of prostaglandin production. are to a major intracellular for damage such as irradiation and chemical J.H. J. Biol. Chem. 1985; Full Text PDF Google Scholar, J.H. PubMed Scopus Google Scholar, G. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar, Ames B.N. Proc. Natl. Acad. Sci. U. S. A. 1988; PubMed Scopus Google Scholar). study shown that damage is to mitochondrial DNA to DNA after Ames B.N. Proc. Natl. Acad. Sci. U. S. A. 1988; PubMed Scopus Google Scholar). have also shown that MnSOD is involved in to irradiation and that of MnSOD the of cells to K. Longo D.L. Oppenheim J.J. Matsushima K. FASEB J. 1993; 7: 361-368Crossref PubMed Scopus (335) Google Scholar). Our results suggest that the increase in cellular accumulation of MnSOD may an important response to irradiation and may to the effects of the study, both irradiation and a synthesis increased levels of MnSOD irradiation the of MnSOD transcripts after treatment with studies the induction of MnSOD mRNA expression by irradiation WI38 fibroblasts constitutively produced IL-1 at a low treatment of cells with or the expression of MnSOD IL-1 expression of MnSOD mRNA in fibroblasts. These results suggest that IL-1 these cells to produce MnSOD in an this expression of IL-1 augmented after have that irradiation induced IL-1 G.E. Chang-Liu C.M. Jones P.S. Jones C.A. Cancer Res. 1990; 50: 339-344PubMed Google Scholar, 13Witte L. Fuks Z. Haimovitiz-Friedman A. Vlodavsky I. Goodman D.S. Eldor A. Cancer Res. 1989; 49: 5066-5072PubMed Google Scholar, K. M. Res. 1993; PubMed Scopus Google Scholar) and that irradiation also induced the of IL-1 in human J. U. J. Clin. Invest. 1987; PubMed Scopus Google Scholar). In this study, in the levels of IL-1 anti-IL-1 blocked induction of MnSOD gene by irradiation as with the of MnSOD mRNA in cells or data Irradiation been to some proteins at levels J.W. Biol. 1992; PubMed Scopus Google Scholar). Our results indicate that irradiation may induce the expression of MnSOD mRNA through the pathway the activation of the irradiation increased levels of MnSOD transcripts in the presence of IL-1 with treatment with This induction may through the in the an on the of the cells. studies are of of increase levels of MnSOD including mediators such as IL-1 or J. Taniguchi N. J. Biol. Chem. 1991; 266: 23142-23146Abstract Full Text PDF PubMed Google Scholar, 17Masuda A. Longo D.L. Kobayashi Y. Appella E. Oppenheim J.J. Matsushima K. FASEB J. 1988; 2: 3087-3091Crossref PubMed Scopus (196) Google Scholar, 20Visner G.A. Dougall W.C. Wilson J.M. Burr I.A. Nick H.S. J. Biol. Chem. 1990; 265: 2856-2864Abstract Full Text PDF PubMed Google Scholar). play an important role in the of the inflammation, and augmented synthesis of prostaglandin by fibroblasts in response to various is a of is by cyclo-oxygenase of and the have shown that is a of J. Spriggs D. K. Kufe D. Biol. 1989; PubMed Scopus Google Scholar, S. M. S. M. N. J. 1989; PubMed Scopus Google Scholar, C.A. M.A. L. J. Clin. Invest. PubMed Scopus Google Scholar). irradiation in human M. J. Clin. Invest. 1990; 86: PubMed Scopus Google Scholar). In the study, of cyclo-oxygenase the induction of MnSOD mRNA by irradiation. blocked the induction of MnSOD mRNA by and irradiation production Our data suggest that induction of MnSOD mRNA by irradiation is to through the cyclo-oxygenase with of indomethacin inhibited the accumulation of MnSOD mRNA by irradiation. of indomethacin also synthesis by as with In of the half-life of MnSOD we that the accumulation of MnSOD in the presence of indomethacin is a of mRNA in the cell is on the of both transcription and Transcriptional regulation is of the important mechanisms for mRNA Our results showed that irradiation increased the rate of MnSOD transcription in human fibroblasts. study that or irradiation increased the gene containing the of D. Proc. Acad. Sci. U. S. A. 1990; 87: PubMed Scopus Google Scholar). The human expression of also been shown to by irradiation in the of the A. M. M. S. G. J. Clin. Invest. 1990; 86: PubMed Scopus Google Scholar, K. A. M. 1987; Scopus Google Scholar). The of human MnSOD gene both the and the 1988; Google Scholar). the this the and of the for transcriptional factor 1988; Google Scholar). These studies indicate the that may play a role in activation of transcription by MnSOD mRNA levels were also increased to the of the The of MnSOD in fibroblasts was irradiation markedly MnSOD mRNA >4 of mRNA is an important for the levels of the for cytokines and these are D. Beutler B. K. S. A. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar, G. Full Text PDF PubMed Scopus Google Scholar, M. G. Hachiya M. E. Suzuki G. Koeffler H.P. 1994; PubMed Google Scholar). Irradiation been shown to various M. Hachiya M. Koeffler H.P. Suzuki G. Biochem. Biophys. Res. Commun. 1992; 189: 986-993Crossref PubMed Scopus (27) Google Scholar, 8Hachiya M. Suzuki G. Koeffler H.P. Akashi M. Exp. Cell Res. 1994; 214: 343-350Crossref PubMed Scopus (14) Google Scholar, 10Hallahan D.E. Spriggs D.R. Beckett M.A. Weichselbaum R.R. Proc. Natl. Acad. Sci. U. S. A. 1989; 86: 10104-10107Crossref PubMed Scopus (397) Google Scholar, 11Sherman M.L. Datta R.D. Hallahan D.E. Weichselbaum R.R. Kufe D.W. Weichselbaum R.R. J. Clin. Invest. 1991; 87: 1794-1797Crossref PubMed Scopus (124) Google Scholar). we found that irradiation granulocyte-macrophage colony-stimulating factor mRNA through containing M. Hachiya M. Koeffler H.P. Suzuki G. Biochem. Biophys. Res. Commun. 1992; 189: 986-993Crossref PubMed Scopus (27) Google Scholar, 8Hachiya M. Suzuki G. Koeffler H.P. Akashi M. Exp. Cell Res. 1994; 214: 343-350Crossref PubMed Scopus (14) Google Scholar). MnSOD containing in the Y. B. A. M. Res. 1987; PubMed Scopus Google Scholar). irradiation MnSOD transcripts is and including produce a of in response to various M. M. Koeffler H.P. J. Clin. Invest. 1990; PubMed Scopus Google Scholar, M. Koeffler H.P. E. E. and Scholar). constitute a major element of bone marrow stroma as as submucosal and subcutaneous We have shown that WI38 fibroblasts constitutively the MnSOD gene and produce the increased of MnSOD in response to irradiation. Irradiation is the production of O DNA and induces Thus, that irradiation induces MnSOD in fibroblasts. MnSOD cells to including fibroblasts may the cells for irradiation in the repair of tissue injury. INTRODUCTIONIrradiation produces physical and chemical damage to tissues that may lead to cell death or neoplastic transformation. In the presence of oxygen, irradiation or some chemicals increase the formation of superoxide radicals (O)(1Hall E.J. Radiobiology for the Radiologist. Lippincott, Philadelphia, PA1988: 10-11Google Scholar, 2Fridovich I. Science. 1978; 201: 875-880Crossref PubMed Scopus (2746) Google Scholar), which are important mediators of tissue damages(3Scott M.D. Meshnick S.R. Eaton J.W. J. Biol. Chem. 1989; 264: 2498-2501Abstract Full Text PDF PubMed Google Scholar, 4Hirose K. Longo D.L. Oppenheim J.J. Matsushima K. FASEB J. 1993; 7: 361-368Crossref PubMed Scopus (335) Google Scholar). Superoxide radicals also have been implicated as important pathologic mediators in various disorders including cancer, inflammation, or ischemia(5Cross C.E. Halliwell B. Borish E.T. Pryor W.A. Ames B.N. Saul R.L. McCord J.M. Harman D. Ann. Intern. Med. 1987; 107: 526-545Crossref PubMed Scopus (1553) Google Scholar, 6Clark I.A. Cowden W.B. Hunt N.H. Med. Res. Rev. 1985; 5: 297-332Crossref PubMed Scopus (128) Google Scholar). The reaction of these radicals with DNA results in DNA strand breaks, which play an important role in radiation-induced carcinogenesis(6Clark I.A. Cowden W.B. Hunt N.H. Med. Res. Rev. 1985; 5: 297-332Crossref PubMed Scopus (128) Google Scholar). In response to these stresses, cells induce the synthesis or activation of proteins with protective capacities. Previous studies have shown that cytokines such as granulocyte-macrophage colony-stimulating factor, tumor necrosis factor (TNF),1( 1The abbreviations used are: TNFtumor necrosis factorSODsuperoxide dismutaseMnSODmanganese superoxide dismutaseILinterleukinPGprostaglandinGyGrayNBTnitroblue tetrazoliumCHXcycloheximide. )and interleukin-1 (IL-1) are produced after irradiation in various cells(7Akashi M. Hachiya M. Koeffler H.P. Suzuki G. Biochem. Biophys. Res. Commun. 1992; 189: 986-993Crossref PubMed Scopus (27) Google Scholar, 8Hachiya M. Suzuki G. Koeffler H.P. Akashi M. Exp. Cell Res. 1994; 214: 343-350Crossref PubMed Scopus (14) Google Scholar, 9Woloschak G.E. Chang-Liu C.M. Jones P.S. Jones C.A. Cancer Res. 1990; 50: 339-344PubMed Google Scholar, 10Hallahan D.E. Spriggs D.R. Beckett M.A. Weichselbaum R.R. Proc. Natl. Acad. Sci. U. S. A. 1989; 86: 10104-10107Crossref PubMed Scopus (397) Google Scholar, 11Sherman M.L. Datta R.D. Hallahan D.E. Weichselbaum R.R. Kufe D.W. Weichselbaum R.R. J. Clin. Invest. 1991; 87: 1794-1797Crossref PubMed Scopus (124) Google Scholar, 12Hallahan D.E. Virudachalam S. Sherman M.L. Huberman E. Kufe D.W. Weichselbaum R.R. Cancer Res. 1991; 51: 4565-4569PubMed Google Scholar, 13Witte L. Fuks Z. Haimovitiz-Friedman A. Vlodavsky I. Goodman D.S. Eldor A. Cancer Res. 1989; 49: 5066-5072PubMed Google Scholar).Superoxide dismutases (SODs, EC 1.15.1.1) are metalloenzymes that catalyze the dismutation of O to H2O2 (hydrogen peroxide) and O2 (oxygen)(14Fridovich I. J. Biol. Chem. 1989; 264: 7761-7764Abstract Full Text PDF PubMed Google Scholar, 15Taniguchi N. Adv. Clin. Chem. 1992; 29: 1-59Crossref PubMed Scopus (102) Google Scholar). Thus, SODs are important initial components in the cellular defense against O (14Fridovich I. J. Biol. Chem. 1989; 264: 7761-7764Abstract Full Text PDF PubMed Google Scholar) and radiation-induced tissue damage. Three forms of SODs with distinctive cellular distributions and metal requirements are found; MnSOD is found in prokaryotes and in mitochondria of eukaryotes, copper-zinc SOD occurs in eukaryotes, and iron SOD is located in the cytosol of prokaryotes. Whereas production of copper-zinc SOD and iron SOD is constitutive, MnSOD is inducible by various stimuli, such as IL-1, TNF, lipopolysaccharide, interferon-γ, or hypoxia(16Fujii J. Taniguchi N. J. Biol. Chem. 1991; 266: 23142-23146Abstract Full Text PDF PubMed Google Scholar, 17Masuda A. Longo D.L. Kobayashi Y. Appella E. Oppenheim J.J. Matsushima K. FASEB J. 1988; 2: 3087-3091Crossref PubMed Scopus (196) Google Scholar, 18Wong G.H.W. Kamd A. Elwell J.H. Oberley L.W. Goeddel D.V. Beutler B. Tumor Necrosis Factor: The Molecules and Their Emerging Role in Medicine. Raven Press, Ltd., New York1992: 473-484Google Scholar, 19Wong G.H.W. Goeddel D.V. Science. 1988; 242: 941-944Crossref PubMed Scopus (833) Google Scholar, 20Visner G.A. Dougall W.C. Wilson J.M. Burr I.A. Nick H.S. J. Biol. Chem. 1990; 265: 2856-2864Abstract Full Text PDF PubMed Google Scholar, 21Harris C.A. Derbin K.S. Hunte-McDonough B. Krauss M.R. Chen K.T. Smith D.M. Epstein L.B. J. Immunol. 1990; 147: 149-154Google Scholar).Fibroblasts constitute a major element of bone marrow stroma and submucosal and subcutaneous tissues, where they are important for repair of tissue injury. In this study, we examined the effects of irradiation on expression of the MnSOD gene and found an intracellular accumulation of MnSOD induced by irradiation in human fibroblasts. We also explored the mechanisms for regulation of the MnSOD gene by irradiation.