* Graduate Center for Nutritional Sciences,
Graduate Center for Toxicology,
Department of Microbiology, Immunology, and Molecular Genetics,
Department of Nutrition and Food Science, and
¶ Department of Pathology and Laboratory Medicine, University of Kentucky, Lexington, Kentucky 40536
Received April 17, 2003; accepted July 14, 2003
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ABSTRACT |
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Key Words: liver; NF-B; proliferation; apoptosis; peroxisome proliferator; ciprofibrate; gene knock-out mice.
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INTRODUCTION |
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In addition to these biochemical changes, peroxisome proliferators increase cell proliferation in the liver soon after they are administered (Reddy and Lalwani, 1983). Cell proliferation eventually returns to basal levels for many peroxisome proliferators, but remains elevated for others (Chen et al., 1994
; Eacho et al., 1991
; Marsman et al., 1988
; Yeldandi et al., 1989
). In addition to stimulating DNA synthesis, peroxisome proliferators have been shown to inhibit apoptosis in normal and preneoplastic hepatocytes (Bayly et al., 1993
, 1994
; Roberts et al., 1995
; Schulte-Hermann et al., 1995
). The withdrawal of peroxisome proliferators leads to rapid reduction in liver weight, presumably in part by apoptosis (Schulte-Hermann et al., 1995
).
In spite of numerous studies, the link between peroxisome proliferators and hepatocarcinogenesis on a molecular and cellular level is not fully understood. In addition, the link between active oxygen production by peroxisome proliferator-induced enzymes and carcinogenesis has not been demonstrated. Recently, we have shown that the peroxisome proliferator ciprofibrate increases the DNA binding activity of the transcription factor nuclear factor-B (NF-
B) in rats and mice (Li et al., 1996
; Nilakantan et al., 1998
; Tharappel et al., 2001
). NF-
B is normally found in the cytoplasm as an inactive complex consisting of two subunits (p50 and p65), which are bound to an inhibitory subunit, I
B; upon activation, NF-
B is released from I
B and translocates to the nucleus, where it increases the transcription of specific genes (Verma et al., 1995
). NF-
B is important in the activation of genes that regulate cell proliferation and apoptosis in various cell types (Barkett and Gilmore, 1999
; Beg et al., 1995
; Demartin et al., 1999
; Sha et al., 1995
). Reactive oxygen species, including H2O2, are potent activators of NF-
B, while the addition of antioxidants such as vitamin E can block activation of NF-
B (Gabbita et al., 2000
; Meyer et al., 1994
). This has led us to hypothesize that peroxisome proliferators activate NF-
B through the induction of H2O2-generating enzymes such as FAO or through the down-regulation of antioxidants and antioxidant enzymes, such as vitamin E and glutathione peroxidase. We subsequently found that NF-
B can be activated by the overexpression of FAO in Cos cells, and that ciprofibrate-induced NF-
B activation can be inhibited by vitamin E or N-acetyl cysteine in rat hepatoma cells, by dietary vitamin E in rats, and by catalase overexpression in mice (Calfee et al., 1998
; Li et al., 2000a
,b
; Nilakantan et al., 1998
). Catalase overexpression also inhibited ciprofibrate-induced cell proliferation in hepatocytes (Nilakantan et al., 1998
), thus raising the question of whether NF-
B activation is important in changes in cell proliferation induced by peroxisome proliferators.
In this study, we examined the hypothesis that the activation of NF-B is necessary for peroxisome proliferator-induced changes in hepatocyte cell proliferation and apoptosis. We used a mouse model that is deficient in the p50 subunit of NF-
B (Sha et al., 1995
). Wild-type and p50-/- mice were administered the peroxisome proliferator ciprofibrate for 10 days; cell proliferation, apoptosis, and the expression of genes related to cell proliferation and apoptosis were then quantified.
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MATERIALS AND METHODS |
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Experimental design.
Eight 78-week-old male B6.129 mice homozygous for NF-B (p50) mutation (p50-/-) and eight B6129SF2/J age-matched wild-type controls were obtained from the Jackson Laboratory (Bar Harbor, ME). Four mice from each group were fed either a diet containing 0.01% ciprofibrate or a control diet for 10 days; after eight days Alzet 1003D osmotic pumps containing 20 mg/ml BrdU solution were implanted sc. After 10 days, mice were euthanized and livers removed. A portion of the liver was fixed in formalin for histology, and the remainder was frozen in liquid nitrogen and then stored at -80°C.
Electrophoretic mobility shift assay.
Nuclear extracts were prepared from the frozen tissue by the method of Derykere and Gannon (1994), as modified by Tharappel et al. (2001)
. Five µg of nuclear extract was incubated with 0.5 µg poly (dI-dC) in a binding buffer (50 mM KCl, 10 mM Hepes-KOH, pH 7.9, 6.5 mM dithiothreitol, and 10% glycerol) for 5 min, followed by 20 min incubation at room temperature after adding 20,000 cpm of the
32P end-labeled NF-
B oligonucleotide probe. After incubation, samples were resolved on 7% nondenaturing polyacrylamide gels, which were then dried under vacuum and exposed overnight at -80°C to Kodak XOMAT-AR film.
BrdU immunostaining.
Tissue sections were fixed in formalin and embedded in paraffin blocks. Sections (5 µm thick) were prepared and stained with an anti-BrdU antibody using the Vecta Stain ABC kit according to the manufacturers protocol. Cells containing newly synthesized DNA were visualized by dark brown labeled nuclei. Roughly 3000 total nuclei were randomly counted from each slide and labeling indices were calculated.
Apoptosis assay.
The terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick end labeling (TUNEL) apoptosis assay kit was purchased from Intergen (Purchase, NY). The assay was performed on paraffin sections following the manufacturers protocol. At least 3000 nuclei were randomly counted per slide and the apoptotic index was expressed as the percentage of number of labeled apoptotic bodies of the total number of nuclei counted.
Western blotting.
Lysis buffer (1% Nonidet P-40, 0.1% SDS, 0.1 mg/ml PMSF, 2 µg/ml aprotinin, 2 µg/ml leupeptin, 2 µg/ml pepstatin A, and 1x PBS) was added to frozen liver tissue (1 part liver tissue to 4 parts lysis buffer) and homogenized using an Ultra-Turrax homogenizer (Tekmar Co. Cincinnati, OH). Homogenates were centrifuged at 10,000 x g for 20 min, and the supernatants were again centrifuged at 100,000 x g for one h. Supernatants were collected, aliquoted, and stored at -80°C. One aliquot was used for a protein assay using the BCA protocol (Pierce, Rockford, IL). The samples were denatured by boiling for 5 min with 2x gel loading buffer (17.3% glycerol, 1.25 M ß-mercaptoethanol, 5.2% SDS, 0.22 M Tris, pH 6.8, 12 mg bromophenol blue). Twenty-five µg of protein from each sample was electrophoresed (4% stacking gel and 8.5% separating gel at 175 volts for one h) and then electroblotted onto nitrocellulose membranes (Life Technologies, Carlsbad, California) at 100 volts for one h. Membranes were then incubated for one h in a blocking buffer (5% fat-free dry instant powdered milk, 1mM Tris-base, 15 mM NaCl, and 0.05% Tween-20) at room temperature with shaking. The primary and secondary antibodies were diluted in blocking buffer. They were then incubated with the membrane while shaking for one h, starting with the primary antibody and followed by the secondary antibody at room temperature. The membranes were then washed with 3 changes of wash buffer (1mM Tris-base, 15 mM NaCl, and 0.05% Tween-20) after the primary and secondary antibody incubations. A Super Signal chemiluminescent substrate kit from Pierce was used to detect antibodies bound to the membrane.
Ribonuclease protection assays.
Total RNA was prepared from frozen liver sections using the LiCl method. The RiboQuantTM RNase Protection Assay Kits were obtained from Becton Dickinson Pharmingen (San Diego, CA). RNase protection assays (RPAs) were performed with 30 µg of total RNA following the manufacturers protocol. The Fos/Jun (cat# 556194) and apoptosis (cat# 556192) multiprobe templates were used.
FAO assay.
FAO activity in liver tissue homogenates was determined using lauroyl CoA as the substrate as described by Poosch and Yamazaki (1986).
Statistical analysis.
Results were first analyzed by two-way analysis of variance (ANOVA). If a significant interaction was observed, results were further analyzed using Bonferronis test. The results are reported as means ± SEM.
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RESULTS |
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DISCUSSION |
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These findings provide direct evidence that NF-B is involved in peroxisome proliferator-induced changes in hepatic cell proliferation. Earlier studies have provided indirect evidence that NF-
B is important in the induction of cell proliferation by peroxisome proliferators. Nilakantan et al. (1998)
found that catalase overexpression decreased both the activation of NF-
B and the induction of cell proliferation by ciprofibrate in mice. In studies comparing species that are responsive (rats) or nonresponsive (hamsters) to peroxisome proliferator-induced carcinogenesis, NF-
B was found to be activated by peroxisome proliferators in rats but not in hamsters, which correlated with the induction of cell proliferation in these two species (Durnford et al., 1998
; Tharappel et al., 2001
). While these previous studies only show correlations between peroxisome proliferator exposure, NF-
B activation, and the induction of cell proliferation, the present study clearly demonstrates that NF-
B activity is necessary for the maximum induction of cell proliferation by the peroxisome proliferator ciprofibrate.
In this study, we observed that c-Jun mRNA levels were increased and that JunB mRNA levels were decreased after ciprofibrate administration, whereas the protein levels of c-Jun and JunB were increased. This suggests that post-transcriptional mechanisms must account for differences in the levels of the Jun proteins after ciprofibrate treatment. In previous studies, peroxisome proliferators have been shown to increase the expression of c-Fos, c-Jun, JunB, FosB, and/or JunD in the BNL-CL.2 or ML-457 mouse liver cell lines and in primary rat hepatocytes (Ledwith et al., 1993, 1996
; Pauley et al., 2002
). The administration of peroxisome proliferators to rats, however, was found to have no effect on Fos expression (Bardot et al., 1995
; Goldsworthy et al., 1994
), or to slightly increase the expression of c-Fos and c-Jun (Hasmall et al., 1997
). In a study that examined hepatic expression of the Fos/Jun family in p50-/- mice, DeAngelis et al.(2001)
observed that c-Fos expression was the same in p50-/- and wild-type mice, both in untreated mice and in mice subjected to partial hepatectomy. The reasons for the lack of agreement among these studies and the present study are not clear.
Peroxisome proliferators have previously been shown to inhibit apoptosis in hepatocytes (Schulte-Hermann et al., 1995). NF-
B has been found to have anti-apoptotic activity in several cell types, including hepatic cell lines, by several agents, including TNF-
and TGF-ß (Barkett and Gilmore, 1999
). In the present study, apoptosis was increased in untreated p50-/- mice compared to untreated wild-type mice, consistent with an anti-apoptotic role for NF-
B in the liver. Apoptosis was inhibited by ciprofibrate administration. One explanation for this inhibition is that ciprofibrate increases the DNA binding activity of other NF-
B family members, e.g., p65 homodimers or p65/p52 heterodimers, which have anti-apoptotic activity. Alternatively, ciprofibrate could be altering apoptosis through other signal transduction pathways. In this study, ciprofibrate administration to wild-type mice did not affect apoptosis; however, the apoptotic index was so low in wild-type mice that it would have been difficult to observe a further decrease induced by ciprofibrate.
The mRNA levels of several apoptosis-related genes were higher in untreated p50-/- mice compared to untreated wild-type mice, which correlates with the TUNEL data. However, levels of these mRNAs increased in both groups of mice after ciprofibrate treatment, despite the fact that apoptosis decreased or remained unchanged in p50-/- and wild-type mice, respectively. This suggests that additional anti-apoptotic mechanisms must also be occurring in the ciprofibrate-treated mice. Using specific inhibitors, Mounho and Thrall (1999) demonstrated that the extracellular signal-regulated kinase (ERK) pathway is important in the suppression of apoptosis by peroxisome proliferators in primary mouse hepatocytes. The peroxisome proliferator nafenopin reduced the expression of the negative growth regulator TGF-ß in primary rat hepatocytes (Strange and Roberts, 1996
). Using proteomic analysis, Chevalier et al. (2000)
observed the accumulation of three actin fragments, which are substrates of a pro-apoptotic enzyme, in primary rat hepatocytes after nafenopin treatment. No changes in apoptotic enzymes were observed, however, in proteomic analysis of diethylhexylphthalate-treated mice (Macdonald et al., 2001
). Mice treated with Wy-14,643 showed increased expression of cell-death-inducing DNA-fragmentation factor-alpha in a microarray analysis (Cherkaoui-Malki et al., 2001
). Clearly, more research is needed to understand the mechanisms by which peroxisome proliferators inhibit hepatocyte apoptosis, and the role of NF-
B in this process.
Several studies have used genetically modified mice to examine the role of NF-B subunits on cell proliferation and apoptosis in the liver and other tissues. A clear role for NF-
B in inhibiting apoptosis by TNF-
or other apoptosis inducers in several cell types, including hepatocytes, has been demonstrated in studies in which NF-
B activity has been inhibited by the deletion of one of its subunits, the inhibition of its translocation, or the expression of a dominant negative form of I
B (Beg and Baltimore, 1996
; Schoemaker et al., 2002
; Vanantwerp et al., 1996
; Wang et al., 1996
; Xu et al., 1998b
). In contrast to the dramatic affect that p50 has in the response to ciprofibrate, DNA synthesis and liver regeneration following partial hepatectomy or carbon tetrachloride treatment were not affected by the absence of the p50 subunit. In this latter study, increased levels of the p65 subunit may have compensated for the lack of p50 (DeAngelis et al., 2001
). Similarly, the hepatic-specific expression of a truncated I
B
super-repressor did not affect DNA synthesis, apoptosis, or liver regeneration following partial hepatectomy, but led to increased apoptosis after treatment with TNF-
(Chaisson et al., 2002
). Also, the hepatic inflammatory response after ischemia/reperfusion was not altered in p50-/- mice (Kato et al., 2002
). In the RALA 25510G rat hepatocyte cell line, expression of an I
B super-repressor inhibited cell proliferation but not apoptosis by TNF-
(Xu et al., 1998a
). In addition, B cells lacking p50, RelB, or c-Rel (but not p52 or p65) have decreased proliferation in response to LPS (Horwitz et al., 1999
; Kontgen et al., 1995
; Sha et al., 1995
; Snapper et al., 1996a
,b
). Overall, whether specific NF-
B subunits are essential for cell proliferation depends on the tissue and the stimulus for DNA synthesis.
Interestingly, the liver-to-body-weight ratios were higher in the p50-/- mice as well as in the ciprofibrate-treated mice. Higher liver weights have been observed many times previously in peroxisome proliferator-treated rats and mice, and the higher liver weights seen here correlate well with the induction of cell proliferation and inhibition of apoptosis by ciprofibrate. In the p50-/- mice, the increases in the liver to body weight ratio were much lower than those seen in mice administered ciprofibrate. The increases also did not correlate with changes in cell proliferation or apoptosis: in the untreated mice, both cell proliferation and apoptosis were increased by the deletion of p50, and in the ciprofibrate-treated mice, apoptosis was increased and cell proliferation was decreased. It is possible that the ratio was more affected by changes in body weight or that liver weights were even higher in p50-/- at the beginning of the study, a time at which this ratio could not be measured.
This study clearly shows that NF-B is important in the proliferative and apoptotic changes induced by ciprofibrate. The molecular mechanisms of these changes, however, are not clear at this time. We found that ciprofibrate altered the expression of genes involved in cell proliferation and apoptosis, but the changes observed did not necessarily correlate with the effects on cell proliferation and apoptosis. Future studies will be needed to determine which NF-
B-regulated genes are responsible for alterations in cell proliferation and apoptosis induced by peroxisome proliferators.
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ACKNOWLEDGMENTS |
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NOTES |
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REFERENCES |
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Bardot, O., Clemencet, M. C., Malki, M. C., and Latruffe, N. (1995). Delayed effects of ciprofibrate on rat liver peroxisomal properties and proto-oncogene expression. Biochem. Pharmacol. 50, 10011006.[CrossRef][ISI][Medline]
Barkett, M., and Gilmore, T. D. (1999). Control of apoptosis by Rel/NF-kappaB transcription factors. Oncogene 18, 69106924.[CrossRef][ISI][Medline]
Bayly, A. C., French, N. J., Dive, C., and Roberts, R. A. (1993). Non-genotoxic hepatocarcinogenesis invitrothe fao hepatoma line responds to peroxisome proliferators and retains the ability to undergo apoptosis. J. Cell. Sci. 104, 307315.
Bayly, A. C., Roberts, R. A., and Dive, C. (1994). Suppression of liver cell apoptosis invitro by the non-genotoxic hepatocarcinogen and peroxisome proliferator nafenopin. J. Cell Biol. 125, 197203.[Abstract]
Beg, A. A., and Baltimore, D. (1996). An essential role for NF-kappa B in preventing TNF-alpha-induced cell death. Science 274, 782784.
Beg, A. A., Sha, W. C., Bronson, R. T., Ghosh, S., and Baltimore, D. (1995). Embryonic lethality and liver degeneration in mice lacking the RelA component of NF-kappa B. Nature 376, 167170.[CrossRef][ISI][Medline]
Calfee, K. G., Spear, B. T., and Glauert, H. P. (1998). Increased dietary vitamin E leads to decreased activation of hepatic NF-kB by the peroxisome proliferator ciprofibrate. FASEB J. 12, A563.
Cattley, R. C., DeLuca, J., Elcombe, C., Fenner-Crisp, P., Lake, B. G., Marsman, D. S., Pastoor, T. A., Popp, J. A., Robinson, D. E., Schwetz, B., et al. (1998). Do peroxisome proliferating compounds pose a hepatocarcinogenic hazard to humans? Regul. Toxicol. Pharmacol. 27, 4760.[CrossRef][ISI]
Cattley, R. C., and Glover, S. E. (1993). Elevated 8-hydroxydeoxyguanosine in hepatic DNA of rats following exposure to peroxisome proliferators: Relationship to carcinogenesis and nuclear localization. Carcinogenesis 14, 24952499.[Abstract]
Chaisson, M. L., Brooling, J. T., Ladiges, W., Tsai, S., and Fausto, N. (2002). Hepatocyte-specific inhibition of NF-kappa B leads to apoptosis after TNF treatment, but not after partial hepatectomy. J. Clin. Invest. 110, 193202.
Chen, H., Huang, C. Y., Wilson, M. W., Lay, L. T., Robertson, L. W., Chow, C. K., and Glauert, H. P. (1994). Effect of the peroxisome proliferators ciprofibrate and perfluorodecanoic acid on hepatic cell proliferation and toxicity in Sprague-Dawley rats. Carcinogenesis 15, 28472850.[Abstract]
Cherkaoui-Malki, M., Meyer, K., Cao, W. Q., Latruffe, N., Yeldandi, A. V., Rao, M. S., Bradfield, C. A., and Reddy, J. K. (2001). Identification of novel peroxisome proliferator-activated receptor alpha (PPARalpha) target genes in mouse liver using cDNA microarray analysis. Gene Expr. 9, 291304.[ISI][Medline]
Chevalier, S., Macdonald, N., Tonge, R., Rayner, S., Rowlinson, R., Shaw, J., Young, J., Davison, M., and Roberts, R. A. (2000). Proteomic analysis of differential protein expression in primary hepatocytes induced by EGF, tumour necrosis factor alpha or the peroxisome proliferator nafenopin. Eur. J. Biochem. 267, 46244634.
Conway, J. G., Tomaszewski, K. E., Olson, M. J., Cattley, R. C., Marsman, D. S., and Popp, J. A. (1989). Relationship of oxidative damage to the hepatocarcinogenicity of the peroxisome proliferators di(2-ethylhexyl)phthalate and Wy-14,643. Carcinogenesis 10, 513519.[Abstract]
DeAngelis, R. A., Kovalovich, K., Cressman, D. E., and Taub, R. (2001). Normal liver regeneration in p50/nuclear factor kappa B1 knockout mice. Hepatology 33, 915924.[CrossRef][ISI][Medline]
Demartin, R., Schmid, J. A., and Hoferwarbinek, R. (1999). The NF-kappa B/Rel family of transcription factors in oncogenic transformation and apoptosis. Mutat. Res. 437, 231243.[CrossRef][ISI][Medline]
Deryckere, F., and Gannon, F. (1994). A one-hour minipreparation technique for extraction of DNA-binding proteins from animal tissues. Biotechniques 16, 405.[ISI][Medline]
Durnford, J. M., Hejtmancik, M. R., Kurtz, P. J., Renne, R. A., Gideon, K. M., Marsman, D. S., Vallant, M., Chhabra, R., and Cunningham, M. L. (1998). Peroxisomal enzyme activity and cell proliferation in rats, mice and hamsters exposed for 13-weeks to Wy-14,643 and gemfibrozil. Toxicol. Sci. 42, 11.[CrossRef]
Eacho, P. I., and Feller, D. R. (1991). Hepatic peroxisome proliferation induced by hypolipidemic drugs and other chemicals. In Antilipidemic Drugs, Medicinal, Chemical and Biochemical Aspects (D. T. Witiak, H. A. I. Newman, and D. R. Feller, Eds.), pp. 375426. Elsevier Science, Amsterdam.
Eacho, P. I., Lanier, T. L., and Brodhecker, C. A. (1991). Hepatocellular DNA synthesis in rats given peroxisome proliferating agents: Comparison of WY-14,643 to clofibric acid, nafenopin and LY171883. Carcinogenesis 12, 15571561.[Abstract]
Elliott, B. M., and Elcombe, C. R. (1987). Lack of DNA damage or lipid peroxidation measured in vivo in the rat liver following treatment with peroxisomal proliferators. Carcinogenesis 8, 12131218.[Abstract]
Gabbita, S. P., Robinson, K. A., Stewart, C. A., Floyd, R. A., and Hensley, K. (2000). Redox regulatory mechanisms of cellular signal transduction. Arch. Biochem. Biophys. 376, 113.[CrossRef][ISI][Medline]
Glauert, H. P., Srinivasan, S., Tatum, V. L., Chen, L. C., Saxon, D. M., Lay, L. T., Borges, T., Baker, M., Chen, L. H., Robertson, L. W., et al. (1992). Effects of the peroxisome proliferators ciprofibrate and perfluorodecanoic acid on hepatic cellular antioxidants and lipid peroxidation in rats. Biochem. Pharmacol. 43, 13531359.[CrossRef][ISI][Medline]
Goel, S. K., Lalwani, N. D., and Reddy, J. K. (1986). Peroxisome proliferation and lipid peroxidation in rat liver. Cancer Res. 46, 13241330.[Abstract]
Goldsworthy, T. L., Goldsworthy, S. M., Sprankle, C. S., and Butterworth, B. E. (1994). Expression of myc, fos and Ha-ras associated with chemically induced cell proliferation in the rat liver. Cell Prolif. 27, 269278.[ISI][Medline]
Hasmall, S. C., Pyrah, I. T. G., Soames, A. R., and Roberts, R. A. (1997). Expression of the immediate-early genes, c-fos, c-jun, and c-myc: A comparison in rats of nongenotoxic hepatocarcinogens with noncarcinogenic liver mitogens. Fundam. Appl. Toxicol. 40, 129137.[CrossRef][ISI][Medline]
Hegi, M. E., Ulrich, D., Sagelsdorff, P., Richter, C., and Lutz, W. K. (1990). No measurable increase in thymidine glycol or 8-hydroxydeoxyguanosine in liver DNA of rats treated with nafenopin or choline-devoid low-methionine diet. Mutat. Res. 238, 325329.[ISI][Medline]
Horwitz, B. H., Zelazowski, P., Shen, Y., Wolcott, K. M., Scott, M. L., Baltimore, D., and Snapper, C. M. (1999). The p65 subunit of NF-kappa B is redundant with p50 during B cell proliferative responses, and is required for germline C-H transcription and class switching to IgG3. J. Immunol. 162, 19411946.
Huang, C. Y., Wilson, M. W., Lay, L. T., Chow, C. K., Robertson, L. W., and Glauert, H. P. (1994). Increased 8-hydroxydeoxyguanosine in hepatic DNA of rats treated with the peroxisome proliferators ciprofibrate and perfluorodecanoic acid. Cancer Lett. 87, 223228.[ISI][Medline]
Huber, W., Kraupp-Grasl, B., Esterbauer, H., and Schulte-Hermann, R. (1991). Role of oxidative stress in age dependent hepatocarcinogenesis by the peroxisome proliferator nafenopin in the rat. Cancer Res. 51, 17891792.[Abstract]
Kasai, H., Okada, Y., Nishimura, S., Rao, M. S., and Reddy, J. K. (1989). Formation of 8-hydroxydeoxyguanosine in liver DNA of rats following long-term exposure to a peroxisome proliferator. Cancer Res. 49, 26032605.[Abstract]
Kato, A., Edwards, M. J., and Lentsch, A. B. (2002). Gene deletion of NF-kappa B p50 does not alter the hepatic inflammatory response to ischemia/reperfusion. J. Hepatol. 37, 4855.[CrossRef][ISI][Medline]
Kontgen, F., Grumont, R. J., Strasser, A., Metcalf, D., Li, R., Tarlinton, D., and Gerondakis, S. (1995). Mice lacking the c-rel proto-oncogene exhibit defects in lymphocyte proliferation, humoral immunity, and interleukin-2 expression. Genes Dev. 9, 19651977.[Abstract]
Lake, B. G., Gray, T. J., Korosi, S. A., and Walters, D. G. (1989). Nafenopin, a peroxisome proliferator, depletes hepatic vitamin E content and elevates plasma oxidised glutathione levels in rats. Toxicol. Lett. 45, 221229.[CrossRef][ISI][Medline]
Lake, B. G., Kozlen, S. L., Evans, J. G., Gray, T. J. B., Young, P. J., and Gangolli, S. D. (1987). Effect of prolonged administration of clofibric acid and di-(2-ethylhexyl)phthalate on hepatic enzyme activities and lipid peroxidation in the rat. Toxicology 44, 213228.[CrossRef][ISI][Medline]
Ledwith, B. J., Johnson, T. E., Wagner, L. K., Pauley, C. J., Manam, S., Galloway, S. M., and Nichols, W. W. (1996). Growth regulation by peroxisome proliferators: Opposing activities in early and late G1. Cancer Res. 56, 32573264.[Abstract]
Ledwith, B. J., Manam, S., Troilo, P., Joslyn, D. J., Galloway, S. M., and Nichols, W. W. (1993). Activation of immediate-early gene expression by peroxisome proliferators in vitro. Mol. Carcinog. 8, 2027.[ISI][Medline]
Li, Y., Leung, L. K., Glauert, H. P., and Spear, B. T. (1996). Treatment of rats with the peroxisome proliferator ciprofibrate results in increased liver NF-kappa B activity. Carcinogenesis 17, 23052309.[Abstract]
Li, Y. X., Glauert, H. P., and Spear, B. T. (2000a). Activation of nuclear factor-kappa B by the peroxisome proliferator ciprofibrate in H4IIEC3 rat hepatoma cells and its inhibition by the antioxidants N-acetylcysteine and vitamin E. Biochem. Pharmacol. 59, 427434.[CrossRef][ISI][Medline]
Li, Y. X., Tharappel, J. C., Cooper, S., Glenn, M., Glauert, H. P., and Spear, B. T. (2000b). Expression of the hydrogen peroxide-generating enzyme fatty acyl CoA oxidase activates NF-kappa B. DNA Cell Biol. 19, 113120.[CrossRef][ISI][Medline]
Macdonald, N., Chevalier, S., Tonge, R., Davison, N., Rowlinson, R., Young, J., Rayner, S., and Roberts, R. (2001). Quantitative proteomic analysis of mouse liver response to the peroxisome proliferator diethylhexylphthalate (DEHP). Arch. Toxicol. 75, 415424.[CrossRef][ISI][Medline]
Marsman, D. S., Cattley, R. C., Conway, J. G., and Popp, J. A. (1988). Relationship of hepatic peroxisome proliferation and replicative DNA synthesis to the hepatocarcinogenicity of the peroxisome proliferators di(2-ethylhexyl)phthalate and [4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio]acetic acid (Wy-14,643) in rats. Cancer Res. 48, 67396744.[Abstract]
Meyer, M., Pahl, H. L., and Baeuerle, P. A. (1994). Regulation of the transcription factors NF-kappa B and AP-1 by redox changes. Chem. Biol. Interact. 91, 91100.[CrossRef][ISI][Medline]
Mounho, B. J., and Thrall, B. D. (1999). The extracellular signal-regulated kinase pathway contributes to mitogenic and antiapoptotic effects of peroxisome proliferators in vitro. Toxicol. Appl. Pharmacol. 159, 125133.[CrossRef][ISI][Medline]
Nilakantan, V., Spear, B. T., and Glauert, H. P. (1998). Liver-specific catalase expression in transgenic mice inhibits NF-kappaB activation and DNA synthesis induced by the peroxisome proliferator ciprofibrate. Carcinogenesis 19, 631637.[Abstract]
Pauley, C. J., Ledwith, B. J., and Kaplanski, C. (2002). Peroxisome proliferators activate growth regulatory pathways largely via peroxisome proliferator-activated receptor alpha-independent mechanisms. Cell. Signal. 14, 351358.[CrossRef][ISI][Medline]
Poosch, M. S., and Yamazaki, R. K. (1986). Determination of peroxisomal fatty acyl-CoA oxidase activity using a lauroyl-CoA-based fluorometric assay. Biochim. Biophys. Acta 884, 585593.[ISI][Medline]
Rao, M. S., and Reddy, J. K. (1987). Peroxisome proliferation and hepatocarcinogenesis. Carcinogenesis 8, 631636.[ISI][Medline]
Reddy, J. K., and Lalwani, N. D. (1983). Carcinogenesis by hepatic peroxisome proliferators: Evaluation of the risk of hypolipidemic drugs and industrial plasticizers to humans. CRC Crit. Rev. Toxicol. 12, 158.[ISI]
Reddy, J. K., Lalwani, N. D., Reddy, M. K., and Qureshi, S. A. (1982). Excessive accumulation of autofluorescent lipofuscin in the liver during hepatocarcinogenesis by methyl clofenapate and other hypolipidemic peroxisome proliferators. Cancer Res. 42, 259266.[ISI][Medline]
Roberts, R. A., Soames, A. R., Gill, J. H., James, N. H., and Wheeldon, E. B. (1995). Non-genotoxic hepatocarcinogens stimulate DNA synthesis and their withdrawal induces apoptosis, but in different hepatocyte populations. Carcinogenesis 16, 16931698.[Abstract]
Schoemaker, M. H., Ros, J. E., Homan, M., Trautwein, C., Liston, P., Poelstra, K., vanGoor, H., Jansen, P. L. M., and Moshage, H. (2002). Cytokine regulation of pro- and anti-apoptotic genes in rat hepatocytes: NF-kappa B-regulated inhibitor of apoptosis protein 2 (CIAP2) prevents apoptosis. J. Hepatol. 36, 742750.[CrossRef][ISI][Medline]
Schoonjans, K., Staels, B., and Auwerx, J. (1996). Role of the peroxisome proliferator-activated receptor (PPAR) in mediating the effects of fibrates and fatty acids on gene expression. J. Lipid Res. 37, 907925.[Abstract]
Schulte-Hermann, R., Bursch, W., and Grasl-Kraupp, B. (1995). Active cell death (apoptosis) in liver biology and disease. In Progress in Liver Disease (J. L. Boyer and R. K. Ockner, Eds.), pp. 135. Saunders, Philadelphia.
Sha, W. C., Liou, H. C., Tuomanen, E. I., and Baltimore, D. (1995). Targeted disruption of the p50 subunit of NF-kB leads to multifocal defects in immune responses. Cell 80, 321330.[ISI][Medline]
Snapper, C. M., Rosas, F. R., Zelazowski, P., Moorman, M. A., Kehry, M. R., Bravo, R., and Weih, F. (1996a). B cells lacking RelB are defective in proliferative responses, but undergo normal B cell maturation to Ig secretion and Ig class switching. J. Exp. Med. 184, 15371541.[Abstract]
Snapper, C. M., Zelazowski, P., Rosas, F. R., Kehry, M. R., Tian, M., Baltimore, D., and Sha, W. C. (1996b). B cells from p50/NF-kappa B knockout mice have selective defects in proliferation, differentiation, germ-line CH transcription, and Ig class switching. J. Immunol. 156, 183191.[Abstract]
Srinivasan, S. R., Chow, C. K., and Glauert, H. P. (1990). Effect of the peroxisome proliferator ciprofibrate on hepatic DNA synthesis and hepatic composition following partial hepatectomy in rats. Toxicology 62, 321332.[CrossRef][ISI][Medline]
Strange, J., and Roberts, R. A. (1996). Reduced expression of mature TGF beta 1 correlates with the suppression of rat hepatocyte apoptosis by the peroxisome proliferator, nafenopin. Mutat. Res. 372, 107113.[ISI][Medline]
Takagi, A., Sai, K., Umemura, T., Hasegawa, R., and Kurokawa, Y. (1990a). Relationship between hepatic peroxisome proliferation and 8-hydroxydeoxyguanosine formation in liver DNA of rats following long-term exposure to three peroxisome proliferators: Di(2-ethylhexyl)phthalate, aluminium clofibrate and simfibrate. Cancer Lett. 53, 3338.[ISI][Medline]
Takagi, A., Sai, K., Umemura, T., Hasegawa, R., and Kurokawa, Y. (1990b). Signifigant increase of 8-hydroxydeoxyguanosine in liver DNA of rats following short-term exposure to the peroxisome proliferators di(2-ethylhexyl)phthalate and di(2-ethylhexyl)adipate. Jpn. J. Cancer Res. 81, 213215.[ISI][Medline]
Tharappel, J. C., Cunningham, M. L., Spear, B. T., and Glauert, H. P. (2001). Differential activation of hepatic NF-kappa B in rats and hamsters by the peroxisome proliferators Wy-14,643, gemfibrozil, and dibutyl phthalate. Toxicol. Sci. 62, 2027.
Vanantwerp, D. J., Martin, S. J., Kafri, T., Green, D. R., and Verma, I. M. (1996). Suppression of TNF-alpha-induced apoptosis by NF-kappa B. Science 274, 787789.
Verma, I. M., Stevenson, J. K., Schwarz, E. M., Van Antwerp, D., and Miyamoto, S. (1995). Rel/NF-kB/IkB family: Intimate tales of association and dissociation. Genes Dev. 9, 27232735.[CrossRef][ISI][Medline]
Wang, C. Y., Mayo, M. W., and Baldwin, A. S. (1996). TNF-and cancer therapy-induced apoptosis: Potentiation by inhibition of NF-kappa B. Science 274, 784787.
Xu, Y., Bialik, S., Jones, B. E., Iimuro, Y., Kitsis, R. N., Srinivasan, A., Brenner, D. A., and Czaja, M. J. (1998a). NF-kappa B inactivation converts a hepatocyte cell line TNF-alpha response from proliferation to apoptosis. Amer. J. Physiol. Cell Physiol. 44, C1058C1066.
Xu, Y., Bialik, S., Jones, B. E., Iimuro, Y., Kitsis, R. N., Srinivasan, A., Brenner, D. A., and Czaja, M. J. (1998b). NF-kappaB inactivation converts a hepatocyte cell line TNF-alpha response from proliferation to apoptosis. Am. J. Physiol. 275, C1058C1066.[ISI][Medline]
Yeldandi, A. V., Milano, M., Subbarao, V., Reddy, J. K., and Rao, M. S. (1989). Evaluation of liver cell proliferation during ciprofibrate-induced hepatocarcinogenesis. Cancer Lett. 47, 2127.[ISI][Medline]