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Absence of β-Catenin Alteration in Hepatic Tumors Induced by p-Nitroanisole in Crj:BDF1 Mice
Masahiko Kushida1,
Sigetoshi Aiso2,
Keiichirou Morimura1,
Min Wei1,
Hideki Wanibuchi1,
Kasuke Nagano2 and
Shoji Fukushima1
1 Department of Pathology, Osaka City University Medical School, Abeno-ku, Osaka 545-8585, Japan
2 Division of Pathology, Japan Bioassay Research Center, Hadano, Kanagawa 257-0015, Japan
Correspondence: Address correspondence to: Shoji Fukushima, Department of Pathology, Osaka City University Medical School, 1-4-3, Asahi-machi, Abeno-ku, Osaka, Japan, 545-8585; e-mail:fukuchan{at}med.osaka-cu.ac.jp
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Abstract
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In the present study, β-catenin localization in hepatocellular neoplasms and hepatoblastomas, induced by oral administration of p-Nitroanisole (pNA) in Crj:BDF1 for 2 years, was evaluated by immunohistochemistry along with genetic alterations in exon 2 of β-catenin by the polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) approach. Genomic DNA was isolated from paraffin sections of a total of 53 liver tumors. Immunohistochemical analysis revealed no abnormal accumulation of the β-catenin protein in any of the cases. No mutations (0/13), 20% silent mutations (3/15) and 8% silent plus 12% functional mutations (2 + 3/25), not in the multiple phosphorylation sites of β-catenin, were observed in hepatocellular adenomas, carcinomas and hepatoblastomas, respectively. The results indicate that β-catenin does not play an important role in development of hepatic tumors induced by pNA in Crj:BDF1 mice.
Key Words: β-Catenin alteration • p-Nitroanisol carcinogenicity • mouse liver tumors Abbreviations: pNA, p-Nitroanisole • HCA, hepatocellular adenoma • HCC, hepatocellular carcinoma • HB, hepatoblastoma • PCR-SSCP, polymerase chain reaction-single strand conformation polymorphism
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Introduction
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β-catenin is an essential contributor to Wnt signaling which plays roles in intercellular adhesion, signal transduction and gene transcription (Cadigan and Nusse, 1997; Nelson and Nusse, 2004), acting in concert with other components of the pathway, such as adenomatous polyposis coli (APC) protein, glycogen synthase kinase 3β (GSK-3β) and Axin (Munemitsu et al., 1995; Rubinfeld et al., 1996; Aberle et al., 1997; Hart et al., 1998; Ikeda et al., 1998). There are multiple phosphorylation sites (codons 33, 37, 41 and 45) in exon 2 (corresponding to exon 3 in man (Nollet et al., 1996)) of theβ-catenin gene in the mouse that prevent the normal degradation and result in enhanced signaling (Kim et al., 2005). Immunohistochemical analysis of β-catenin has revealed accumulation of β-catenin in the cytoplasm and/or nucleus in tumors, instead of at the cell membrane, this occurring as a result of functional mutations in APC (Morin et al., 1997; Munemitsu et al., 1995; Rubinfeld et al., 1997) and Axin (Kikuchi, 2000) as well as β-catenin (Morin et al., 1997; Rubinfeld et al., 1997).
β-catenin mutations in human hepatocellular carcinomas (HCCs) are reported to be relatively frequent (Nhieu et al., 1999). In hepatoblastomas (HBs), the most common malignant hepatic neoplasms in children (Koesters and von Knebel Doeberitz, 2003), protein accumulation in the cytoplasm and/or nucleus has been reported to highly correlate with somatic mutations of β-catenin (Blaker et al., 1999; Jeng et al., 2000; Wei et al., 2000; Park et al., 2001; Koch et al., 2004; Udatsu et al., 2001). In the mouse, relationship between alterations in the β-catenin signaling pathway and chemically induced hepatocellular neoplasms and HBs has also been investigated, but the results have been conflicting. Chemically induced hepatocellular adenomas (HCAs) and HCCs in 2 studies had mutations in exon 2 of β-catenin (Hayashi et al., 2003; Huang et al., 2003), but were lacking in another investigation (Aydinlik et al., 2001). Concerning HBs, there have been many reports of high percentages of gene mutations and abnormal localization of β-catenin (de La Coste et al., 1998; Devereux et al., 1999; Anna et al., 2000, 2003; Hayashi et al., 2003), but we earlier found no change in N,N-Dimethylformamide-induced HBs in mice (Kakuni et al., 2004).
Recently we obtained interesting samples of hepatocellular neoplasms in a 104-week mouse study of the carcinogenicity of p-Nitroanisole (pNA), an intermediate used in the manufacture of p-Anisidine, a raw material for dyes and pharmaceuticals, directed by the Japan Bioassay Research Center (Japan Bioassay Research Center, 2005). Production of pNA in Western Europe was 5,800 tons in 1978 and 5,300 tons in 1983 (GDCh-Advisory Commitiee on Existing Chemicals of Enviromnental Relevance, 1993) and global production is now about 10,000 t/year, Japan importing about 400 tons in 2002 (Japan Bioassay Research Center, 2005; GDCh-Advisory Committee on Existing Chemicals of Enviromnental Relevance, 1993). In the Ames test pNA is mutagenic (Shimizu and Yano, 1986) and its LD50 with oral administration is about 1.7 g/kg in mice and 2.6 g/kg in rats (GDCh-Advisory Commitiee on Existing Chemicals of Enviromnental Relevance, 1993).
The present study was conducted to assess whether β-catenin mutations and protein accumulation might be features of pNA-induced mouse hepatocellular neoplasms, with a combined immunohistochemical and polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) approach.
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Materials and Methods
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Tumor Samples
Samples of mouse liver tumors, induced in a 104 week mouse carcinogenicity study of pNA, were obtained from Japan Bioassay Research Center as paraffin-embedded tissue. Briefly, the study employed a total of four-hundred Crj:BDF1 mice (Males: 200, Females: 200), purchased from Charles River Japan (Kanagawa, Japan) and divided into 4 weight-matched groups, each consisting of 50 mice of both sexes. Three different dose levels of 5000, 10000 and 20000 ppm pNA in  -irradiation-sterilized CRF-1 powdered diet (Oriental Yeast Co., Tokyo, Japan) were administered at libitum for 104 weeks. Livers were then removed from the euthanized mice, fixed with 10% neutral-buffered formalin and routinely processed for paraffin embedding. Histological diagnoses were determined with 4-µm-thick H&E stained sections (Japan Bioassay Research Center, 2005). We selected typical non-necrotic and non-autolytic neoplasms from scheduled or moribund sacrifice male animals in pNA treatment groups for the present analysis. The numbers of HCAs, HCCs and HBs were 13, 15, and 25, respectively. Mice were cared in accordance with Guide for the Care and Use of Laboratory Animals, and the study was approved by the ethics committee of the Japan Bioassay Research Center.
Immunohistochemistry
The localization of β-catenin protein was detected with an anti- mouse β-catenin antibody (Clone: 14, Transduction laboratories Inc., Lexington, KY, USA), and a VECTASTAIN elite ABC kit (Vector Laboratories, Inc., Burlingame, CA, USA). Normal liver tissue, adjacent to lesions, was employed as the positive control for β-catenin immunohistochemical staining.
DNA Preparation
DNA for PCR-SSCP was prepared from paraffin-embedded sections using a microdissection approach, as described previously (Yamamoto et al., 1995). Briefly, serial sections adjacent to those used for immunohistochemical study were prepared at a thickness of 5–10 µm, deparaffinized and placed in DNase free water. Using a fine needle, appropriate amounts of neoplasmic lesions were dissected out under a microscope and collected in 20–50 µL of protein lysis buffer containing 0.1 mg/mL proteinase K. Samples were initially digested at 37°C over night, and then underwent phenol/chloroform DNA extraction, and ethanol precipitation. The resulting DNA pellets were diluted with distilled water for PCR.
PCR-SSCP
PCR-SSCP analysis was carried out on PCR products of β-catenin exon 2 (corresponds to exon 3 in the human gene (Nollet et al., 1996)), which contains the GSK-3βphosphorylation sites (de La Coste et al., 1998). The sequences of the intronic PCR primers flanking the borders of exon 2 were: BCAT-1F, 5'-TACAGGTAGCATTTTCAGTTCAC-3'; Ctnnb m-R1; 5'-CACTCAGGGAAGGAGCTGTG-3'and Ctnnb m-F2; 5'-CCACCACCACAGCTCCTT-3'; BCAT-2R: 5'-TAGCTTCCAAACACAAATGC-3' (de La Coste et al., 1998). PCR-SSCP was performed using non-radioisotopic SSCP analysis as described previously (Takahashi-Fujii et al., 1994). The primers were designed with a 5'FITC label. Hot start PCR was carried out in a 20 µL of reaction volume using AmpliTaq Gold (Perkin-Elmer Cetus Instruments, Norwalk, CT, USA) under the following conditions: initial preheating at 94°C for 9 min to achieve enzymatic activity followed by 40 cycles of denaturing (94°C) for 1 min, annealing (58°C) for 1 min and extension (72°C) for 1 min using Gene Amp PCR system 9700 (Perkin-Elmer Cetus Instruments). Five microliters of each PCR product were mixed with 20 µL of stop solution (95% formamide, 20 mM EDTA), denatured for 3 min at 95 0176C, immediately put on ice for 10 min then loaded (3 µL/lane) onto 0.5xMDE gels, with or without glycerol. Gels were run at 8 W for 16 h (with glycerol) or at 4 W for 16 h (without glycerol) at room temperature. After electrophoresis, gels were visualized using an FMBIO II Multi-View fluorescent image analyzer (Takara SHUZO CO., Shiga, Japan). The patterns of single-strand DNA bands were compared with those from normal control mouse DNA (from liver) to check for the presence of any mobility-shifted bands. Small areas of gels corresponding to the position of mobility shift bands were cut out, immersed in 400 µL distilled H2O and shaken overnight to elute the DNA. Fifteen microliters of each extracted DNA solution were amplified by PCR using the no-labeled same sequence primers used in PCR-SSCP.
Direct DNA Sequencing
DNA sequencing was carried out for both strands using a Big Dye Terminator cycle sequencing Ready Reaction kit (ABI PRISM, Applied Biosystems, CA, USA) on a Genetic Analyzer (ABI PRISM 3100, Applied Biosystems, CA, USA).
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Results
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Histopathology and Immunohistochemistory for β-Catenin in Mouse Liver
Histological sections from liver of mice were examined. Figure 1 shows histological features of an HCA, an HCC and an HB induced by pNA (Fig. A, C, E). HBs in this study were characterized by small round to elongated cells with scant basophilic cytoplasm (Figure 1).
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Figure 1 Histological appearance of hepatocellular tumors and immunohistochemical analysis of β-catenin in livers of Crj:BDF1 mouse treated with pNA for 2 years. (A, C, E) show representative hepatocellular adenoma (A), hepatocellular carcinoma (C) and hepatoblastoma (E) lesions in treated male mice. H&E staining. (B, D, F) Immunohistochemistry for β-catenin. (B) hepatocellular adenoma, (D) hepatocellular carcinoma and (F) hepatoblastoma. (All figures; x 200)
Note. (A) and (B), (C) and (D), (E) and (F) are serial liver sections.
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The immunohistochemical analysis was used to identify the localization of β-catenin protein. Immunohistochemical analysis revealed membrane staining of β-catenin in normal liver cells, HCAs and HCCs (Figure 1B, D). In HBs, β-catenin staining was also detected in membranes, but its intensity was weak (Figure 1F). No abnormal cytoplasmic or nuclear staining was exhibited by any of the neoplasms.
PCR-SSCP
Immunohistochemical analysis raised the question whether β-catenin gene mutations occurred in mice liver tumors, as there were no abnormal accumulations of the β-catenin protein in any of the cases. To determine β-catenin gene mutations occurred, DNA was extracted from mice liver tumors and analyzed by PCR-SSCP. Typical results of PCR-SSCP followed by direct DNA sequencing was shown in Table 1 and Figure 2. In HCAs, no β-catenin mutations were detected. In HCCs, the mutation frequency was 20% (3/15), all the mutations being silent and present at the third base of codons 16, 35, or 70. The mutation frequency in HBs was 20% (5/25), comprising 8% silent (2/25) and 12% functional mutations (3/25) (Table 1, Figure 2). The silent mutations were C to T and A to G transitions in codons 46 and 76, respectively. Mutations with amino acid change were observed in codons 49, 51, 67 and 72. One mutation was a transversion and the others were transitions. None occurred in or adjacent to the four known regulatory phosphorylation sites (codons 33, 37, 41, and 45).
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Figure 2 Examples of β-catenin mutations in hepatocellular neoplasms and hepatoblastomas from Crj:BDF1 mice exposed to p-nitroanisole. (A) Results of screening DNA from pNA-induced liver neoplasms by SSCP. Lanes 1–4, DNA samples from hepatocellular adenomas; Lanes 5–10, DNA samples from hepatocellular carcinomas; Lane 11–18, DNA samples from hepatoblastomas. The mobility shifts (arrows) are representative of β-catenin mutations. (B) Mutations in the β-catenin gene in liver tumors. (B-1) CCG to CCA mutation without amino acid change at codon 16 in a hepatocellular carcinoma. (B-2) Normal sequence of codon 16. (B-3) GAG to AAG mutation at codon 67 leading to Gly Lys in a hepatoblastoma. (B-4) Normal sequence of codon 67.
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Discussion
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In the present immunohistochemical study, we demonstrated no abnormal localization of β-catenin protein in three types of liver neoplasms, HCAs, HCCs and HBs, induced by pNA in Crj:BDF1 males. Furthermore, PCR-SSCP analysis of β-catenin exon 2 revealed no mutations observed in any of the multiple phosphorylation sites of the gene. It has been reported that functional abnormalities of both β-catenin and other Wnt signal components, which interfere with the degradation of β-catenin, result in its accumulation in the cell cytoplasm and translocation into the nucleus (Morin et al., 1997; Rubinfeld et al., 1997). Therefore, the absence of abnormal accumulation of β-catenin in cytoplasm and/or nucleus indicated functional normality of the Wnt signal pathway in our neoplasms. Furthermore, the lack of genetic abnormalities in the multiple-phosphorylation sites of β-catenin exon 2 supports our immunohistochemical results in indicating that β-catenin does not play an important role in hepatic tumors, particularly HBs, induced by pNA in the Crj:BDF1 mouse.
There are many reports of high percentages of HBs with gene mutation and abnormal localization of β-catenin in mice (de La Coste et al., 1998; Devereux et al., 1999; Anna et al., 2000, 2003; Hayashi et al., 2003), in contrast to our previous (Kakuni et al., 2004) and present studies. The root causes are unclear, but it is likely that specificity regarding inducing compounds and strains of mice is involved. pNA is an example of a genotoxic carcinogen (Shimizu and Yano, 1986), generally considered to interact with DNA in their target organ cells, resulting in DNA damage and finally causing genetic alterations that are considered to be irreversible (Butterworth, 1990). Even if chemicals are genotoxic, however, some studies have indicated that the involvement of β-catenin in tumor formation varies with the chemical. For example, the mutation frequencies in exon 2 of the β-catenin gene in HCAs and HCCs induced by diethanolamine (Hayashi et al., 2003), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (Huang et al., 2003) and diethylnitrosamine (Aydinlik et al., 2001) in mice were 32, 12.5, and 0%, respectively. All these three compounds are genotoxic carcinogens. Therefore, the absence of β-catenin gene mutations in present study provides further evidence that β-catenin gene mutations are not essential for liver tumor formation in the mouse. Several reports revealed that liver tumors might evolve through ras-dependent or ras-independent pathways (de La Coste et al., 1998; Devereux et al., 1999; Aydinlik et al., 2001; Hayashi et al., 2003). These reports indicated the H-ras mutations to be few or absent when β-catenin gene mutations were frequent and vice versa. Furthermore, the pathway appears to depend on the chemical. To elucidate the genetic mechanisms involved in the pNA case, analysis of H-ras mutations is needed in future investigations.
While high percentages of carcinogen-induced HBs have been found with gene mutations and abnormal localization of β-catenin, in the majority of cases B6C3F1 mice were used (de La Coste et al., 1998; Devereux et al., 1999; Anna et al., 2000, 2003; Hayashi et al., 2003). We employed Crj:BDF1 mice in our previous (Kakuni et al., 2004) and present study and there may be clear strain differences in gene mutations induced by carcinogens. Buchmann et al. (1991) demonstrated a 56% incidence rate for mutations of the H-ras gene in liver tumors induced by N-nitrosodiethylamine, but none in equivalent lesions due to this carcinogen in C57BL/6 mice. Incidence rates of H-ras mutations in both spontaneously developed and urethan-induced liver tumors were found to be more than 50% in C3H and B6C3F1 mice but only 7–9% in Balb/c mice (Dragani et al., 1991). Furthermore, there is a clear strain dependence regarding K-ras mutations in ethylnitrosourea-induced lymphomagenesis (Shimada et al., 2003).
In conclusion, liver neoplasms induced by pNA in Crj:BDF1 mouse appear to completely lack functional abnormalities in β-catenin, and our results raise a possibility that there is a β-catenin-independent pathway for development of HBs, as well as hepatocellular adenomas and carcinomas.
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Acknowledgments
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This investigation was supported by a grant from the Japanese Ministry of Health, Labour and Welfare. We thank Dr. Taijiro Matsushima (Japan Bioassay Research Center) for kindly providing the samples of mice liver tumors. We acknowledge the expert technical support of Kaori Touma for histotechnology, Masayo Imanaka for biochemical analysis, and Mari Dokoh, Yuko Onishi and Yoko Shimada for their help during preparation of this manuscript.
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References
|
|---|
- Aberle, H, Bauer, A, Stappert, J, Kispert, A, & Kemler, R. (1997). Beta-catenin is a target for the ubiquitin-proteasome pathway. Embo J, 16, 3797-804[CrossRef][Web of Science][Medline]
[Order article via Infotrieve]
- Anna, CH, Iida, M, Sills, RC, & Devereux, TR. (2003). Expression of potential beta-catenin targets, cyclin D1, c-Jun, c-Myc, E-cadherin, and EGFR in chemically induced hepatocellular neoplasms from B6C3F1 mice. Toxicol Appl Pharmacol, 190, 135-45[CrossRef][Web of Science][Medline]
[Order article via Infotrieve]
- Anna, CH, Sills, RC, Foley, JF, Stockton, PS, Ton, TV, & Devereux, TR. (2000). Beta-catenin mutations and protein accumulation in all hepatoblastomas examined from B6C3F1 mice treated with anthraquinone or oxazepam. Cancer Res, 60, 2864-8[Abstract/Free Full Text]
- Aydinlik, H, Nguyen, TD, Moennikes, O, Buchmann, A, & Schwarz, M. (2001). Selective pressure during tumor promotion by phenobarbital leads to clonal outgrowth of beta-catenin-mutated mouse liver tumors. Oncogene, 20, 7812-6[CrossRef][Web of Science][Medline]
[Order article via Infotrieve]
- Blaker, H, Hofmann, WJ, Rieker, RJ, Penzel, R, Graf, M, & Otto, HF. (1999). Beta-catenin accumulation and mutation of the CTNNB1 gene in hepatoblastoma. Genes Chromosomes Cancer, 25, 399-402[CrossRef][Web of Science][Medline]
[Order article via Infotrieve]
- Buchmann, A, Bauer-Hofmann, R, Mahr, J, Drinkwater, NR, Luz, A, & Schwarz, M. (1991). Mutational activation of the c-Ha-ras gene in liver tumors of different rodent strains: correlation with susceptibility to hepatocarcinogenesis. Proc Natl Acad Sci USA, 88, 911-5[Abstract/Free Full Text]
- Butterworth, BE. (1990). Consideration of both genotoxic and nongenotoxic mechanisms in predicting carcinogenic potential. Mutat Res, 239, 117-32[CrossRef][Web of Science][Medline]
[Order article via Infotrieve]
- Cadigan, KM, & Nusse, R. (1997). Wnt signaling: a common theme in animal development. Genes Dev, 11, 3286-305[Free Full Text]
- de La Coste, A, Romagnolo, B, Billuart, P, Renard, CA, Buendia, MA, Soubrane, O, Fabre, M, Chelly, J, Beldjord, C, Kahn, A, & Perret, C. (1998). Somatic mutations of the beta-catenin gene are frequent in mouse and human hepatocellular carcinomas. Proc Natl Acad Sci USA, 95, 8847-51[Abstract/Free Full Text]
- Devereux, TR, Anna, CH, Foley, JF, White, CM, Sills, RC, & Barrett, JC. (1999). Mutation of beta-catenin is an early event in chemically induced mouse hepatocellular carcinogenesis. Oncogene, 18, 4726-33[CrossRef][Web of Science][Medline]
[Order article via Infotrieve]
- Dragani, TA, Manenti, G, Colombo, BM, Falvella, FS, Gariboldi, M, Pierotti, MA, & Della Porta, G. (1991). Incidence of mutations at codon 61 of the Ha-ras gene in liver tumors of mice genetically susceptible and resistant to hepatocarcinogenesis. Oncogene, 6, 333-8[Web of Science][Medline]
[Order article via Infotrieve]
- GDCh-Advisory Commitiee on Existing Chemicals of Environmental Relevance. (1993). p-Nitroanisole (1-Methoxy-4-nitrobenzene). Stuttgart, German: S. Hirzel Verlag
- Hart, MJ, de los Santos, R, Albert, IN, Rubinfeld, B, & Polakis, P. (1998). Downregulation of beta-catenin by human Axin and its association with the APC tumor suppressor, beta-catenin and GSK3 beta. Curr Biol, 8, 573-81[CrossRef][Web of Science][Medline]
[Order article via Infotrieve]
- Hayashi, SM, Ton, TV, Hong, HH, Irwin, RD, Haseman, JK, Devereux, TR, & Sills, RC. (2003). Genetic alterations in the Catnb gene but not the H-ras gene in hepatocellular neoplasms and hepatoblastomas of B6C3F1 mice following exposure to diethanolamine for 2 years. Chem Biol Interact, 146, 251-61[CrossRef][Web of Science][Medline]
[Order article via Infotrieve]
- Huang, H, Ushijima, T, Nagao, M, Sugimura, T, & Ohgaki, H. (2003). Beta-catenin mutations in liver tumors induced by 2-amino-3,4-dimethylimidazo[4,5-f]quinoline in CDF1 mice. Cancer Lett, 198, 29-35[CrossRef][Web of Science][Medline]
[Order article via Infotrieve]
- Ikeda, S, Kishida, S, Yamamoto, H, Murai, H, Koyama, S, & Kikuchi, A. (1998). Axin, a negative regulator of the Wnt signaling pathway, forms a complex with GSK-3beta and beta-catenin and promotes GSK-3beta-dependent phosphorylation of beta-catenin. Embo J, 17, 1371-84[CrossRef][Web of Science][Medline]
[Order article via Infotrieve]
- Japan Bioassay Research Center. (2005). Results for carcinogenicity test of p-Nitroanisole in Mice and Rats. (in Japanese). βhttp://www.mhlw.go.gp/shingi/2005/03/s330-10e.html
 .[CrossRef][Web of Science][Medline]
[Order article via Infotrieve] - Jeng, YM, Wu, MZ, Mao, TL, Chang, MH, & Hsu, HC. (2000). Somatic mutations of beta-catenin play a crucial role in the tumorigenesis of sporadic hepatoblastoma. Cancer Lett, 152, 45-51[CrossRef][Web of Science][Medline]
[Order article via Infotrieve]
- Kakuni, M, Senoh, H, Morimura, K, Wanibuchi, H, Takaba, K, Nagano, K, & Fukushima, S. (2004). Absence of b-catenin mutations in mouse hepatoblastomas induced by N,N-dimethylformamide. J Toxicol Pathol, 93, 261-5
- Kikuchi, A. (2000). Regulation of beta-catenin signaling in the Wnt pathway. Biochem Biophys Res Commun, 268, 243-8[CrossRef][Web of Science][Medline]
[Order article via Infotrieve]
- Kim, Y, Sills, RC, & Houle, CD. (2005). Overview of the molecular biology of hepatocellular neoplasms and hepatoblastomas of the mouse liver. Toxicol Pathol, 33, 175-80[Abstract/Free Full Text]
- Koch, A, Weber, N, Waha, A, Hartmann, W, Denkhaus, D, Behrens, J, Birchmeier, W, von Schweinitz, D, & Pietsch, T. (2004). Mutations and elevated transcriptional activity of conductin (AXIN2) in hepatoblastomas. J Pathol, 204, 546-54[CrossRef][Web of Science][Medline]
[Order article via Infotrieve]
- Koesters, R, & von Knebel Doeberitz, M. (2003). The Wnt signaling pathway in solid childhood tumors. Cancer Lett, 198, 123-38[CrossRef][Web of Science][Medline]
[Order article via Infotrieve]
- Morin, PJ, Sparks, AB, Korinek, V, Barker, N, Clevers, H, Vogelstein, B, & Kinzler, KW. (1997). Activation of beta-catenin-Tcf signaling in colon cancer by mutations in beta-catenin or APC. Science, 275, 1787-90[Abstract/Free Full Text]
- Munemitsu, S, Albert, I, Souza, B, Rubinfeld, B, & Polakis, P. (1995). Regulation of intracellular beta-catenin levels by the adenomatous polyposis coli (APC) tumor-suppressor protein. Proc Natl Acad Sci USA, 92, 3046-50[Abstract/Free Full Text]
- Nelson, WJ, & Nusse, R. (2004). Convergence of Wnt, beta-catenin, and cadherin pathways. Science, 303, 1483-7[Abstract/Free Full Text]
- Nhieu, JT, Renard, CA, Wei, Y, Cherqui, D, Zafrani, ES, & Buendia, MA. (1999). Nuclear accumulation of mutated beta-catenin in hepatocellular carcinoma is associated with increased cell proliferation. Am J Pathol, 155, 703-10[Abstract/Free Full Text]
- Nollet, F, Berx, G, Molemans, F, & van Roy, F. (1996). Genomic organization of the human beta-catenin gene (CTNNB1). Genomics, 32, 413-24[CrossRef][Web of Science][Medline]
[Order article via Infotrieve]
- Park, WS, Oh, RR, Park, JY, Kim, PJ, Shin, MS, Lee, JH, Kim, HS, Lee, SH, Kim, SY, Park, YG, An, WG, Jang, JJ, Yoo, NJ, & Lee, JY. (2001). Nuclear localization of beta-catenin is an important prognostic factor in hepatoblastoma. J Pathol, 193, 483-90[CrossRef][Web of Science][Medline]
[Order article via Infotrieve]
- Rubinfeld, B, Albert, I, Porfiri, E, Fiol, C, Munemitsu, S, & Polakis, P. (1996). Binding of GSK3beta to the APC-beta-catenin complex and regulation of complex assembly. Science, 272, 1023-6[Abstract]
- Rubinfeld, B, Robbins, P, El-Gamil, M, Albert, I, Porfiri, E, & Polakis, P. (1997). Stabilization of beta-catenin by genetic defects in melanoma cell lines. Science, 275, 1790-2[Abstract/Free Full Text]
- Shimada, Y, Nishimura, M, Kakinuma, S, Ogiu, T, Fujimoto, H, Kubo, A, Nagai, J, Kobayash, K, Tano, K, Yoshinaga, S, & Bhakat, KK. (2003). Genetic susceptibility to thymic lymphomas and K-ras gene mutation in mice after exposure to X-rays and N-ethyl-N-nitrosourea. Int J Radiat Biol, 79, 423-30[CrossRef][Web of Science][Medline]
[Order article via Infotrieve]
- Shimizu, M, & Yano, E. (1986). Mutagenicity of mono-nitrobenzene derivatives in the Ames test and rec assay. Mutat Res, 170, 11-22[CrossRef][Web of Science][Medline]
[Order article via Infotrieve]
- Takahashi-Fujii, A, Ishino, Y, Kato, I, & Fukumaki, Y. (1994). Rapid and practical detection of beta-globin mutations causing beta-thalassemia by fluorescence-based PCR-single-stranded conformation polymorphism analysis. Mol Cell Probes, 8, 385-93[CrossRef][Web of Science][Medline]
[Order article via Infotrieve]
- Udatsu, Y, Kusafuka, T, Kuroda, S, Miao, J, & Okada, A. (2001). High frequency of beta-catenin mutations in hepatoblastoma. Pediatr Surg Int, 17, 508-12[CrossRef][Web of Science][Medline]
[Order article via Infotrieve]
- Wei, Y, Fabre, M, Branchereau, S, Gauthier, F, Perilongo, G, & Buendia, MA. (2000). Activation of beta-catenin in epithelial and mesenchymal hepatoblastomas. Oncogene, 19, 498-504[CrossRef][Web of Science][Medline]
[Order article via Infotrieve]
- Yamamoto, S, Masui, T, Murai, T, Mori, S, Oohara, T, Makino, S, Fukushima, S, & Tatematsu, M. (1995). Frequent mutations of the p53 gene and infrequent H- and K-ras mutations in urinary bladder carcinomas of NON/Shi mice treated with N-butyl-N-(4-hydroxybutyl)nitrosamine. Carcinogenesis, 16, 2363-8[Abstract/Free Full Text]
Toxicologic Pathology, Vol. 34, No. 3,
237-242 (2006)
DOI: 10.1080/01926230600695474
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Abstract
Introduction