Evidence that reduction of hepatocyte growth factor (HGF) is not required for peroxisome proliferator-induced hepatocyte proliferation
Andras Kiss1,4,
Roberto Ortiz-Aguayo2,
Richard Sharp3,
Glenn Merlino3,
Snorri S. Thorgeirsson1,
Frank J. Gonzalez2 and
Jeffrey M. Peters2,5,6
1 Laboratory of Experimental Carcinogenesis,
2 Laboratory of Metabolism and
3 Laboratory of Molecular Biology, Division of Basic Sciences, National Cancer Institute, Bethesda, MD 20892, USA and
4 Institute of Pathology, Semmelweis Medical University, Ulloi ut 93, Budapest, H-1091, Hungary and
5 Department of Veterinary Science and Center for Molecular Toxicology, The Pennsylvania State University, University Park, PA 16802, USA
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Abstract
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The mechanisms underlying peroxisome proliferator-induced hepatocarcinogenesis are not understood. Because of the uncertainty of human cancer risk associated with peroxisome proliferators, delineating the mechanisms of carcinogenesis by these agents is of great interest. Alterations in liver growth factors were postulated to contribute to the carcinogenic effect of peroxisome proliferators. Administration of these compounds to rodents results in down-regulation of hepatocyte growth factor (HGF) and supplementing culture medium with HGF is reported to suppress cell proliferation of preneoplastic and neoplastic cells from WY-14,643-treated livers. Combined, these observations suggest that reduced levels of hepatic HGF contribute to the mechanisms underlying peroxisome proliferator-induced hepatocarcinogenesis. To determine if HGF can prevent the effects of peroxisome proliferators in liver, the short-term influence of WY-14,643 in two different lines of HGF transgenic mice was examined. Mice were fed either a control diet or one containing 0.1% WY-14-643 for one week. Hepatomegaly was found in both HGF transgenic mouse lines fed WY-14,643 compared with controls. Additionally, hepatic expression of typical mRNA markers of peroxisome proliferation including those encoding peroxisomal fatty acid metabolizing enzymes and cell cycle control proteins were all significantly elevated in HGF transgenic mice fed WY-14,643 compared with controls. Down-regulation of HGF was found to be dependent on PPAR
since lower levels of HGF mRNA and protein were observed in wild-type mice fed WY-14,643 for 1 week and not in similarly treated PPAR
-null mice. These results demonstrate that the early increase in hepatic mRNAs associated with peroxisome and cell proliferation induced by WY-14,643 treatment can not be prevented by overexpression of HGF in vivo.
Abbreviations: AXO, peroxisomal acyl-CoA oxidase; BIEN, bifunctional enzyme; CDK1, mouse cyclin dependent kinase-1; CDK4, mouse cyclin dependent kinase-4; CYP4A1, microsomal cytochrome P450 4A1; HGF, hepatocyte growth factor; hHGF, human HGF; mHGF, mouse HGF; PPAR
, peroxisome proliferator-activated receptor
; THIOL, thiolase.
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Introduction
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Peroxisome proliferators are a diverse group of structurally unrelated compounds that cause hepatic peroxisome proliferation, hepatomegaly and induction of peroxisomal, microsomal and mitochondrial fatty acid metabolizing enzymes. Peroxisome proliferators include the fibrate class of hypolipidemic drugs, commercially used plasticizers (e.g. phthalates), the naturally occurring steroid dehydroepiandrosterone sulfate, industrial solvents (e.g. trichloroethylene) and synthetic fatty acids and fatty acid derivatives (15). The biological effects of peroxisome proliferators are mediated through the peroxisome proliferator-activated receptor
(PPAR
), a member of the nuclear hormone receptor superfamily (2). In response to ligand activation, PPAR
forms a heterodimer with retinoid X receptor
and modulates expression of target genes containing peroxisome proliferator responsive elements (reviewed in ref. 6).
Chronic, long-term administration of peroxisome proliferators results in hepatocarcinogenesis in rodents (79). In contrast, hepatic peroxisome proliferation is not observed in humans treated with hypolipidemic drugs (1013). Further, two limited epidemiological studies showed no evidence of increased cancer risk as a result of fibrate therapy (14,15). However, the relative risk for humans from long-term exposure to peroxisome proliferators is unclear (16), thus determining the precise mechanisms of peroxisome proliferator-induced liver cancer is of great interest. An obligatory role for PPAR
in peroxisome proliferator-induced hepatocarcinogenesis has been demonstrated using PPAR
-null mice that are refractory to hepatocarcinogenesis and exhibit no biochemical or microscopic alterations as a result of feeding of WY-14,643 (1719).
The mechanisms underlying the effects induced by peroxisome proliferators includes transcriptional upregulation of peroxisomal, microsomal and mitochondrial fatty acid metabolizing enzymes as well as the direct or indirect modulation of genes involved in hepatic cell proliferation and cell cycle control (2023). Administration of peroxisome proliferators causes a large induction of liver acyl-CoA oxidase, an enzyme that mediates peroxisomal fatty acid oxidation and produces H2O2 as a by-product of fatty acid metabolism. Since similar increases in catalase do not occur in the liver after treatment with these chemicals, it is thought that the excess in intracellular H2O2 causes oxidative damage to DNA in the form of 8-hydroxydeoxyguanine residues or strand breaks (24,25). Peroxisome proliferators are classical non-genotoxic carcinogens and a good correlation between peroxisome proliferation and liver tumors has not been established (26). Thus, the role of oxidative damage in the mechanism of action of these agents is unclear. While the correlation between peroxisome proliferation and hepatocarcinogenesis is not good, sustained increases in hepatic cell proliferation correlate better with tumor formation (26). In addition, suppression of apoptosis has also been shown to be involved in peroxisome proliferator-induced increase in liver cell replication (27). Combined, these observations suggest that if DNA-damaged cells that would normally undergo programmed cell death are provided with signals for increased cell proliferation, these cells may contribute to the subsequent formation of tumors.
A role for HGF in peroxisome proliferator-induced cell proliferation and carcinogenesis has recently been suggested. Administration of peroxisome proliferators to rats causes down-regulation of hepatic HGF mRNA after short-term feeding WY-14,643 (28,29) and continues to decline to <50% of control levels after 40 weeks of feeding (28). The reduction in liver HGF mRNA levels was found in non-tumor portions of cancerous livers in peroxisome proliferator-treated rats yet a more striking decrease was found in the tumor regions of the same livers (28,30). HGF was also shown to inhibit colony formation in soft agar of neoplastic or preneoplastic liver cells from WY-14,643-fed rats (28,30). Despite the fact that HGF can function to stimulate hepatocyte cell proliferation in response to partial hepatectomy (31,32), the previous observations and others indicate that HGF can also function as a growth suppressor in hepatocarcinoma cells (33,34). This suggests that the influence of peroxisome proliferators on expression of genes encoding peroxisomal fatty acid metabolizing enzymes and cell cycle control proteins could be prevented in the presence of higher levels of HGF. In this work, this hypothesis was examined using two different transgenic mouse lines overexpressing HGF, and the role of the PPAR
in modulating HGF down-regulation was studied using PPAR
-null mice.
Two different transgenic mouse lines overexpressing either mouse or human HGF were used in these studies. The mouse line expressing human HGF (hHGF) was generated as previously described and was under transcriptional control of the albumin promoter (35,36). The mouse line expressing mouse HGF (mHGF) was generated as described previously and was under transcriptional control by a metallothionein promoter (37). Overexpression of HGF is considerably different between the two HGF transgenic mouse lines based on serum HGF concentrations. Serum concentration of HGF in hHGF transgenic mice is ~2-fold higher than that of controls (23 ng/ml) (38), while serum concentration of HGF in the mHGF transgenic mice is ~4-fold higher than that of controls (16.4 ng/ml) (39). For both transgenic mouse lines, male mice were used as described below. Mice were housed in a temperature and light controlled environment (25°C, 12 h light/dark cycle) and provided food and water ad libitum. Pelleted mouse chow was prepared (Bioserv, Frenchtown, NJ) containing either 0.0 or 0.1% [4-chloro-6-(2,3-xilidino)-pyrimidynylthio]acetic acid (WY-14,643; ChemSyn Science Laboratories, Lenexa, KS) and fed for 7 days. After this, mice were killed by overexposure to carbon dioxide, livers were weighed and immediately frozen in liquid nitrogen for further analysis.
Total RNA was extracted from liver samples using TRIZOL® reagent (Gibco Life Technologies, Gaithersburg, MD) following the manufacturer's instructions. RNA (10 µg) from individual mice were electrophoresed on a 1% agarose gel containing 0.22 M formaldehyde and transferred to a nylon membrane in 20x SSC. RNA was fixed to the membrane by baking at 80°C for 1 h. Membranes were hybridized with cDNA probes for peroxisomal acyl-CoA oxidase (AXO), bifunctional enzyme (BIEN) and thiolase (THIOL) and microsomal cytochrome P450 4A1 (CYP4A1). Additionally, cDNA probes for mouse cyclin dependent kinase-1 and -4 (CDK1, CDK4) and mouse HGF were used. The probes for northern analysis were previously described (17,19,39). After hybridization, the membranes were washed in 2x SSC twice and subsequently exposed to a PhosphoImager screen for 124 h. Image recording and analysis was performed using a Molecular Dynamics Storm 860 PhosphoImager and Image Quantification (v4.2a) software.
Mean body weight was significantly lower in hHGF mice fed WY-14,643 for one week compared with controls (Table I
). Mean body weight was also lower in mHGF mice fed WY-14,643 than in controls although this effect was not statistically significant (Table I
). This may be due to the low number of animals examined since feeding peroxisome proliferators typically causes weight loss due to increased oxidation of fatty acids. Loss of body weight is consistent with previous reports and is likely due to increased oxidation of fatty acids as a result of increased expression of mRNAs encoding peroxisomal and microsomal fatty acid metabolizing enzymes as shown below. Mean liver weight was significantly increased in both strains of HGF transgenic mice compared with controls (~2-fold greater than control liver weight, Table I
). Increased liver weight as a result of treatment with peroxisome proliferators is consistent with previous reports and indicates that in addition to peroxisome proliferation, increased hepatic cell proliferation resulted from feeding WY-14,643 to HGF transgenic mice (Table I
).
Hepatic levels of mRNAs encoding peroxisomal and microsomal fatty acid metabolizing enzymes were increased in both HGF transgenic mouse lines compared with controls (Figure 1
). Liver levels of mRNAs encoding AXO, BIEN, THIOL and CYP4A1 were higher in mice fed Wy-14,643 than in controls (Figure 1
), consistent with an induction of peroxisome proliferation and increased oxidation of fatty acids. Additionally, levels of mRNAs encoding CDK-1 and CDK-4 in liver were higher in both lines of HGF transgenic mice fed WY-14,643 compared with untreated controls (Figure 1
), consistent with increased hepatocyte cell proliferation known to occur in response to peroxisome proliferators. To verify higher expression of HGF, analysis of mRNA encoding both the endogenous and transgenic HGF transcripts was performed. Consistent with previous reports (28,29), endogenous mRNA encoding HGF in liver was significantly lower in both lines of HGF transgenic mice fed WY-14,643 compared with controls (Figure 2
). Interestingly, the level of mRNA encoding the human transgenic mRNA was substantially lower as a result of WY-14,643 feeding, while the level of mRNA encoding the mouse transgenic mRNA was significantly higher as a result of WY-14,643 feeding (Figure 2
). Thus, expression of HGF is apparently reduced by WY-14,643 in the hHGF transgenic mouse similar to endogenous HGF expression, while expression of transgenic HGF is apparently increased by the same treatment in the mHGF transgenic mice. This is likely due to differences in transcriptional alterations resulting from the different promoters driving HGF expression in the two different models. This suggests that the metallothionein promoter may be responsive to peroxisome proliferators, consistent with a previous report showing induction of metallothionein mRNA in liver tumors from rats treated with these chemicals (40). However, analysis of the metallothionein promoter (41) revealed no consensus PPREs.

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Fig. 1. Effect of WY-14,643 on hepatic peroxisomal and microsomal RNA levels in HGF transgenic mice. Northern blot analysis of liver RNA from transgenic mice expressing the human (hHGF) or murine (mHGF) HGF transcripts fed control (Con) or WY-14,643-containing diet (WY) using the specified cDNA probes. Each lane represents the RNA from an individual mouse.
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Fig. 2. Endogenous and transgenic HGF mRNA in transgenic mouse liver. Northern blot analysis of liver RNA from transgenic mice expressing the human (hHGF) or murine (mHGF) HGF transcripts fed control (Con) or WY-14,643-containing diet (WY) using a mouse HGF cDNA probe. Each lane represents the RNA from an individual mouse.
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To determine the role of PPAR
in modulating HGF expression, male mice, Sv/129 wild-type or PPAR
-null (17) were fed either the control diet or one containing 0.1% WY-14,643 for 1 week. Mice were killed by overexposure to carbon dioxide and livers weighed and immediately frozen in liquid nitrogen until further analysis. Samples of liver were prepared for northern and western analysis as previously described (19). Northern analysis was performed as described above. Protein (50 µg) were electrophoresed by SDSPAGE and transferred to nitrocellulose membranes by electroblotting. An anti-HGF antibody (Santa Cruz Biotechnologies, Santa Cruz, CA) was used as the primary antibody followed by incubation with an anti-mouse horseradish peroxidaseconjugated secondary antibody. Immunoreactive protein was detected by ECL (Amersham Pharmacia Biotech, Piscataway, NJ). Recombinant human HGF was used as a positive control (Sigma Chemical Company, St Louis, MO).
As previously reported (28,29), northern analysis of liver RNA from wild-type mice showed that mRNA encoding HGF was significantly lower in WY-treated mice than untreated controls (Figure 3
). The lower level of HGF mRNA was not found in WY-treated PPAR
-null mice (Figure 3
). Consistent with RNA analysis, western blot analysis showed significantly lower levels of HGF in wild-type mice fed WY-14,643 for 1 week compared with controls and this effect was not observed in PPAR
-null mice treated with WY-14,643 (Figure 2
). These results provide definitive evidence that down-regulation of HGF requires a functional PPAR
.
As a naturally occurring liver cytokine, HGF is thought to be responsible for the hepatic regenerative response to injury, promoting proliferation of liver parenchymal cells (31,32). However, while HGF functions as a growth factor in healthy liver cells, it is also reported to act as a tumor suppressor by inhibiting growth of neoplastic and preneoplastic cells obtained from rats treated with WY-14,643 in soft agar (28,30). Additional in vivo support for an inhibitory role of HGF in tumor formation has also been reported in genetic- and chemically-induced carcinogenic rodent models (36,42). Administration of WY-14,643 causes significant reductions of hepatic HGF in rodents and was hypothesized to be causally related to the mechanisms underlying increased cell proliferation, peroxisome proliferation and liver tumors induced by these chemicals (28,29). The data presented in this study suggest that high levels of HGF found in the mHGF mice have no influence in preventing the hyperplastic response resulting from exposure to the non-genotoxic carcinogen WY-14,643. Both HGF transgenic mouse lines showed a significant increase in liver weight after administration of WY-14,643 despite the presence of `supplemental' HGF as a result of transgene expression. The lack of influence on the hyperplastic response by HGF is further supported by the observation that mRNA for genes encoding proteins involved in cell replication and cell cycle control are significantly elevated in HGF transgenic mice fed WY-14,643 compared with controls. In contrast to the observed inhibitory effect of HGF in preventing cell proliferation of neoplastic cells in c-myc transgenic mice (36) or rats treated with diethylnitrosamine (42), these results show that two different lines of HGF transgenic mice are not refractory to the pleiotropic response resulting from short-term treatment with peroxisome proliferators.
A related hypothesized mechanism thought to contribute to peroxisome proliferator induced liver cancer is increased intracellular accumulation of H2O2 resulting from the induction of acyl-CoA oxidase that may lead to oxidative damage to DNA (24,25). While HGF did not prevent hepatocyte cell replication resulting from WY-14,643, it was also possible that this growth factor could inhibit peroxisome proliferation related to increased H2O2 production. These results demonstrate that `supplemental' HGF was not able to prevent peroxisome proliferation induced by acute administration of WY-14,643 as assessed by mRNA level of AXO. In addition to the increase in liver weight which is associated with this effect, higher hepatic levels of mRNAs encoding peroxisomal and microsomal fatty acid metabolizing enzymes were also elevated in HGF transgenic mice fed WY-14,643. Combined, the pleiotropic response typically observed with acute administration of WY-14,643 was not reduced or inhibited in either transgenic HGF mouse line, suggesting that HGF is not capable of preventing the hepatocarcinogenic effect of these chemicals. While WY-induced repression of transgenic mRNA in the hHGF mice suggest that HGF expression is lower in this model, mRNA levels of transgenic mHGF was substantially higher as a result of WY feeding demonstrating that this model is appropriate to test the hypothesis that exogenous HGF would prevent WY-induced hepatic cell proliferation.
Repression of HGF by peroxisome proliferators requires a functional PPAR
since decreased HGF mRNA and protein is not found in livers from PPAR
-null mice fed WY-14,643. This provides support for the idea that decreased liver HGF contributes to the signalling pathways involved in the pleiotropic response resulting from peroxisome proliferators. Whether or not this is due to a direct interaction between PPAR
and a PPRE in the HGF promoter, or other downstream events associated with PPAR
activation can not be determined from this work. However, since the pleiotropic response resulting from WY-14,643 including increased cell proliferation and peroxisome proliferation were not prevented in HGF transgenic mice which have a functional PPAR
, the significance of decreased HGF expression in the mechanism of action of peroxisome proliferation is uncertain.
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Notes
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6 To whom correspondence should be addressed at: Department of Veterinary Science, Center for Molecular Toxicology, 226 Fenske Laboratory, The Pennsylvania State University, University Park, PA 16802, USA Email: jmp21{at}psu.edu 
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Acknowledgments
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The authors gratefully acknowledge Dr Debra Wolgemuth for providing the CDK cDNA probes, and Camilla Hendrych and Dae-Joon Kim for their technical assistance. Supported in part by Hungarian National Scientific Research Foundation No. F030382, Hungarian Scientific Council of Health 01078/98 and Bolyai Scientific Foundation (A.K.).
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References
|
---|
-
Gottlicher,M., Widmark,E., Li,Q. and Gustafsson,J.A. (1992) Fatty acids activate a chimera of the clofibric acid-activated receptor and the glucocorticoid receptor. Proc. Natl Acad. Sci. USA, 89, 46534657.[Abstract]
-
Issemann,I., Prince,R.A., Tugwood,J.D. and Green,S. (1993) The peroxisome proliferator-activated receptor:retinoid X receptor heterodimer is activated by fatty acids and fibrate hypolipidaemic drugs. J. Mol. Endocrinol., 11, 3747.[Abstract]
-
Rao,M.S., Musunuri,S. and Reddy,J.K. (1992) Dehydroepiandrosterone-induced peroxisome proliferation in the rat liver. Pathobiology, 60, 8286.[ISI][Medline]
-
Elcombe,C.R. (1985) Species differences in carcinogenicity and peroxisome proliferation due to trichloroethylene: a biochemical human hazard assessment. Arch. Toxicol., 8 (suppl.), 617.
-
Warren,J.R., Lalwani,N.D. and Reddy,J.K. (1982) Phthalate esters as peroxisome proliferator carcinogens. Environ. Health Perspect., 45, 3540.[ISI][Medline]
-
Desvergne,B. and Wahli,W. (1999) Peroxisome proliferator-activated receptors: nuclear control of metabolism. Endocr. Rev., 20, 649688.[Abstract/Free Full Text]
-
Reddy,J.K., Rao,S. and Moody,D.E. (1976) Hepatocellular carcinomas in acatalasemic mice treated with nafenopin, a hypolipidemic peroxisome proliferator. Cancer Res., 36, 12111217.[Abstract]
-
Reddy,J.K. and Rao,M.S. (1977) Malignant tumors in rats fed nafenopin, a hepatic peroxisome proliferator. J. Natl Cancer Inst., 59, 16451650.[ISI][Medline]
-
Reddy,J.K., Rao,M.S., Azarnoff,D.L. and Sell,S. (1979) Mitogenic and carcinogenic effects of a hypolipidemic peroxisome proliferator, [4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio]acetic acid (Wy-14,643), in rat and mouse liver. Cancer Res, 39, 152161.[ISI][Medline]
-
De La Iglesia,F.A., Lewis,J.E., Buchanan,R.A., Marcus,E.L. and McMahon,G. (1982) Light and electron microscopy of liver in hyperlipoproteinemic patients under long-term gemfibrozil treatment. Atherosclerosis, 43, 1937.[ISI][Medline]
-
Blumcke,S., Schwartzkopff,W., Lobeck,H., Edmondson,N.A., Prentice,D.E. and Blane,G.F. (1983) Influence of fenofibrate on cellular and subcellular liver structure in hyperlipidemic patients. Atherosclerosis, 46, 105116.[ISI][Medline]
-
Gariot,P., Barrat,E., Drouin,P., Genton,P., Pointel,J.P., Foliguet,B., Kolopp,M. and Debry,G. (1987) Morphometric study of human hepatic cell modifications induced by fenofibrate. Metabolism, 36, 203210.[ISI][Medline]
-
Hanefeld,M., Kemmer,C. and Kadner,E. (1983) Relationship between morphological changes and lipid-lowering action of p-chlorphenoxyisobutyric acid (CPIB) on hepatic mitochondria and peroxisomes in man. Atherosclerosis, 46, 239246.[ISI][Medline]
-
Law,M.R., Thompson,S.G. and Wald,N.J. (1994) Assessing possible hazards of reducing serum cholesterol. Br. Med. J., 308, 373379.[Abstract/Free Full Text]
-
Huttunen,J.K., Heinonen,O.P., Manninen,V., Koskinen,P., Hakulinen,T., Teppo,L., Manttari,M. and Frick,M.H. (1994) The Helsinki Heart Study: an 8.5-year safety and mortality follow-up [see comments]. J. Int. Med., 235, 3139.[ISI][Medline]
-
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., Tugwood,J. and Wahli,W. (1998) Do peroxisome proliferating compounds pose a hepatocarcinogenic hazard to humans? Regul. Toxicol. Pharmacol., 27, 4760.[ISI]
-
Lee,S.S., Pineau,T., Drago,J., Lee,E.J., Owens,J.W., Kroetz,D.L., Fernandez-Salguero,P.M., Westphal,H. and Gonzalez,F.J. (1995) Targeted disruption of the
isoform of the peroxisome proliferator-activated receptor gene in mice results in abolishment of the pleiotropic effects of peroxisome proliferators. Mol. Cell. Biol., 15, 30123022.[Abstract]
-
Peters,J.M., Cattley,R.C. and Gonzalez,F.J. (1997) Role of PPAR
in the mechanism of action of the nongenotoxic carcinogen and peroxisome proliferator Wy-14,643. Carcinogenesis, 18, 20292033.[Abstract]
-
Peters,J.M., Aoyama,T., Cattley,R.C., Nobumitsu,U., Hashimoto,T. and Gonzalez,F.J. (1998) Role of peroxisome proliferator-activated receptor
in altered cell cycle regulation in mouse liver. Carcinogenesis, 19, 19891994.[Abstract]
-
Hardwick,J.P., Song,B.J., Huberman,E. and Gonzalez,F.J. (1987) Isolation, complementary DNA sequence and regulation of rat hepatic lauric acid
-hydroxylase (cytochrome P-450LA
). Identification of a new cytochrome P-450 gene family. J. Biol. Chem., 262, 801810.[Abstract/Free Full Text]
-
Reddy,J.K., Goel,S.K., Nemali,M.R., Carrino,J.J., Laffler,T.G., Reddy,M.K., Sperbeck,S.J., Osumi,T., Hashimoto,T., Lalwani,N.D. and Rao,M.S. (1986) Transcription regulation of peroxisomal fatty acyl-CoA oxidase and enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase in rat liver by peroxisome proliferators. Proc. Natl Acad. Sci. USA, 83, 17471751.[Abstract]
-
Gulick,T., Cresci,S., Caira,T., Moore,D.D. and Kelly,D.P. (1994) The peroxisome proliferator-activated receptor regulates mitochondrial fatty acid oxidative enzyme gene expression. Proc. Natl Acad. Sci. USA, 91, 1101211016.[Abstract/Free Full Text]
-
Rininger,J.A., Wheelock,G.D., Ma,X. and Babish,J.G. (1996) Discordant expression of the cyclin-dependent kinases and cyclins in rat liver following acute administration of the hepatocarcinogen [4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio] acetic acid (WY14,643). Biochem. Pharmacol., 52, 17491755.[ISI][Medline]
-
Reddy,J.K. and Rao,M.S. (1989) Oxidative DNA damage caused by persistent peroxisome proliferation: its role in hepatocarcinogenesis. Mutat. Res., 214, 6368.[ISI][Medline]
-
Fahl,W.E., Lalwani,N.D., Watanabe,T., Goel,S.K. and Reddy,J.K. (1984) DNA damage related to increased hydrogen peroxide generation by hypolipidemic drug-induced liver peroxisomes. Proc. Natl Acad. Sci. USA, 81, 78277830.[Abstract]
-
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]
-
Roberts,R.A. (1996) Non-genotoxic hepatocarcinogenesis: suppression of apoptosis by peroxisome proliferators. Ann. NY Acad. Sci., 804, 588611.[ISI][Medline]
-
Motoki,Y., Tamura,H., Morita,R., Watanabe,T. and Suga,T. (1997) Decreased hepatocyte growth factor level by Wy-14,643, non-genotoxic hepatocarcinogen in F-344 rats. Carcinogenesis, 18, 13031309.[Abstract]
-
Motoki,Y., Tamura,H., Watanabe,T. and Suga,T. (1999) Wy-14,643, a peroxisome proliferator, inhibits compensative cell proliferation and hepatocyte growth factor mRNA expression in the rat liver. Cancer Lett., 135, 145150.[ISI][Medline]
-
Suga,T., Motoki,Y., Tamura,H. and Watanabe,T. (2000) Involvement of hepatocyte growth factor on hepatocarcinogenesis induced by peroxisome proliferators. Cell Biochem. Biophys., 32, 221228.[ISI]
-
Nakamura,T., Teramoto,H. and Ichihara,A. (1986) Purification and characterization of a growth factor from rat platelets for mature parenchymal hepatocytes in primary cultures. Proc. Natl Acad. Sci. USA, 83, 64896493.[Abstract]
-
Nakamura,T., Nawa,K. and Ichihara,A. (1984) Partial purification and characterization of hepatocyte growth factor from serum of hepatectomized rats. Biochem. Biophys. Res. Commun., 122, 14501459.[ISI][Medline]
-
Shiota,G., Rhoads,D.B., Wang,T.C., Nakamura,T. and Schmidt,E.V. (1992) Hepatocyte growth factor inhibits growth of hepatocellular carcinoma cells. Proc. Natl Acad. Sci. USA, 89, 373377.[Abstract]
-
Shiota,G., Kawasaki,H., Nakamura,T. and Schmidt,E.V. (1994) Inhibitory effect of hepatocyte growth factor against FaO hepatocellular carcinoma cells may be associated with changes of intracellular signalling pathways mediated by protein kinase C. Res. Commun. Mol. Pathol. Pharmacol., 85, 271278.[ISI][Medline]
-
Shiota,G., Wang,T.C., Nakamura,T. and Schmidt,E.V. (1994) Hepatocyte growth factor in transgenic mice: effects on hepatocyte growth, liver regeneration and gene expression. Hepatology, 19, 962972.[ISI][Medline]
-
Santoni-Rugiu,E., Preisegger,K.H., Kiss,A., Audolfsson,T., Shiota,G., Schmidt,E.V. and Thorgeirsson,S.S. (1996) Inhibition of neoplastic development in the liver by hepatocyte growth factor in a transgenic mouse model. Proc. Natl Acad. Sci. USA, 93, 95779582.[Abstract/Free Full Text]
-
Jhappan,C., Stahle,C., Harkins,R.N., Fausto,N., Smith,G.H. and Merlino,G.T. (1990) TGF
overexpression in transgenic mice induces liver neoplasia and abnormal development of the mammary gland and pancreas. Cell, 61, 11371146.[ISI][Medline]
-
Shiota,G. and Kawasaki,H. (1998) Hepatocyte growth factor in transgenic mice. Int. J. Exp. Pathol., 79, 267277.[ISI][Medline]
-
Takayama,H., La Rochelle,W.J., Anver,M., Bockman,D.E. and Merlino,G. (1996) Scatter factor/hepatocyte growth factor as a regulator of skeletal muscle and neural crest development. Proc. Natl Acad. Sci. USA, 93, 58665871.[Abstract/Free Full Text]
-
Eagon,P.K., Teepe,A.G., Elm,M.S., Tadic,S.D., Epley,M.J., Beiler,B.E., Shinozuka,H. and Rao,K.N. (1999) Hepatic hyperplasia and cancer in rats: alterations in copper metabolism. Carcinogenesis, 20, 10911096.[Abstract/Free Full Text]
-
Kelly,E.J., Sandgren,E.P., Brinster,R.L. and Palmiter,R.D. (1997) A pair of adjacent glucocorticoid response elements regulate expression of two mouse metallothionein genes. Proc. Natl Acad. Sci. USA, 94, 1004510050.[Abstract/Free Full Text]
-
Liu,M.L., Mars,W.M. and Michalopoulos,G.K. (1995) Hepatocyte growth factor inhibits cell proliferation in vivo of rat hepatocellular carcinomas induced by diethylnitrosamine. Carcinogenesis, 16, 841843.[Abstract]
Received November 29, 2000;
accepted February 13, 2001.