Different mutation status of the beta-catenin gene in carcinogen-induced colon, brain, and oral tumors in rats

Loss of FOXN3 in colon cancer activates beta-catenin/TCF signaling and promotes the growth and migration of cancer cells

Aberrant activation of beta-catenin/TCF is a hallmark of colon cancer. How the functions of nuclear localized beta-catenin are regulated is not fully understood. Here, it was found that FOXN3 (Forkhead box N3) was down-regulated in colon cancer tissues. Forced expression of FOXN3 inhibited the growth, migration and invasion of colon cancer cells, while knocking down the expression of FOXN3 promoted the growth, migration, invasion and metastasis of colon cancer cells. FOXN3 bind to beta-catenin and inhibited beta-catenin/TCF signaling by blocking the interaction between beta-catenin and TCF4. Taken together, these data demonstrated the suppressive roles of FOXN3 in the progression of colon cancer, and indicated that restoring the functions of FOXN3 would be a novel therapeutic strategy for colon cancer.

β-catenin in oral cancer: an update on current knowledge

β-Catenin is a multiple function protein. These functions derive from its interactions with other cell proteins, both on the cell membrane, in the cytoplasm and in the nucleus. β-Catenin forms a complex with the adhesion molecule E-cadherin, promoting cell-cell adhesion and thereby preventing the cell dissociation that is required for cancer invasion and progression mechanisms. There is also a dynamic pool of cytoplasmic β-catenin that serves as connection between the extracellular microenvironment and the nucleus. Cytoplasmic β-catenin acts as a transcription factor for the nucleus in the canonical Wnt pathway, activating the transcription of various genes. Structural or functional alterations of β-catenin can promote cancer progression. This review addresses the current knowledge on the implications of β-catenin in the development of oral cancer.

Gel-based nonradioactive single-strand conformational polymorphism and mutation detection: limitations and solutions

Single-strand conformation polymorphism (SSCP) for screening mutations/single-nucleotide polymorphisms (SNPs) is a simple, cost-effective technique, saving an expensive exercise of sequencing each and every polymerase chain reaction product and assisting in choosing only the amplicons of interest with expected mutations. The principle of detection of small changes in DNA sequences is based on changes in single-strand DNA conformations. The changes in electrophoretic mobility that SSCP detects are sequence dependent. The limitations faced in SSCP range from routine polyacrylamide gel electrophoresis (PAGE) problems to the problems of resolving mutant DNA bands. Both these problems can be solved by controlling PAGE conditions and by varying physical and environmental conditions such as pH, temperature, voltage, gel type and percentage, addition of additives or denaturants, and others. Despite much upgrading of the technology for mutation detection, SSCP remains the method of choice to analyze mutations and SNPs in order to understand genomic variations, both spontaneous and induced, and the genetic basis of diseases.

The cycad genotoxin MAM modulates brain cellular pathways involved in neurodegenerative disease and cancer in a DNA damage-linked manner

Methylazoxymethanol (MAM), the genotoxic metabolite of the cycad azoxyglucoside cycasin, induces genetic alterations in bacteria, yeast, plants, insects and mammalian cells, but adult nerve cells are thought to be unaffected. We show that the brains of adult C57BL6 wild-type mice treated with a single systemic dose of MAM acetate display DNA damage (O⁶-methyldeoxyguanosine lesions, O⁶-mG) that remains constant up to 7 days post-treatment. By contrast, MAM-treated mice lacking a functional gene encoding the DNA repair enzyme O⁶-mG DNA methyltransferase (MGMT) showed elevated O⁶-mG DNA damage starting at 48 hours post-treatment. The DNA damage was linked to changes in the expression of genes in cell-signaling pathways associated with cancer, human neurodegenerative disease, and neurodevelopmental disorders. These data are consistent with the established developmental neurotoxic and carcinogenic properties of MAM in rodents. They also support the hypothesis that early-life exposure to MAM-glucoside (cycasin) has an etiological association with a declining, prototypical neurodegenerative disease seen in Guam, Japan, and New Guinea populations that formerly used the neurotoxic cycad plant for food or medicine, or both. These findings suggest environmental genotoxins, specifically MAM, target common pathways involved in neurodegeneration and cancer, the outcome depending on whether the cell can divide (cancer) or not (neurodegeneration). Exposure to MAM-related environmental genotoxins may have relevance to the etiology of related tauopathies, notably, Alzheimer's disease.

Databases applicable to quantitative hazard/risk assessment--towards a predictive systems toxicology

The Workshop on The Power of Aggregated Toxicity Data addressed the requirement for distributed databases to support quantitative hazard and risk assessment. The authors have conceived and constructed with federal support several databases that have been used in hazard identification and risk assessment. The first of these databases, the EPA Gene-Tox Database was developed for the EPA Office of Toxic Substances by the Oak Ridge National Laboratory, and is currently hosted by the National Library of Medicine. This public resource is based on the collaborative evaluation, by government, academia, and industry, of short-term tests for the detection of mutagens and presumptive carcinogens. The two-phased evaluation process resulted in more than 50 peer-reviewed publications on test system performance and a qualitative database on thousands of chemicals. Subsequently, the graphic and quantitative EPA/IARC Genetic Activity Profile (GAP) Database was developed in collaboration with the International Agency for Research on Cancer (IARC). A chemical database driven by consideration of the lowest effective dose, GAP has served IARC for many years in support of hazard classification of potential human carcinogens. The Toxicological Activity Profile (TAP) prototype database was patterned after GAP and utilized acute, subchronic, and chronic data from the Office of Air Quality Planning and Standards. TAP demonstrated the flexibility of the GAP format for air toxics, water pollutants and other environmental agents. The GAP format was also applied to developmental toxicants and was modified to represent quantitative results from the rodent carcinogen bioassay. More recently, the authors have constructed: 1) the NIEHS Genetic Alterations in Cancer (GAC) Database which quantifies specific mutations found in cancers induced by environmental agents, and 2) the NIEHS Chemical Effects in Biological Systems (CEBS) Knowledgebase that integrates genomic and other biological data including dose-response studies in toxicology and pathology. Each of the public databases has been discussed in prior publications. They will be briefly described in the present report from the perspective of aggregating datasets to augment the data and information contained within them.

An animal model for the rapid induction of tongue neoplasms in human c-Ha-ras proto-oncogene transgenic rats by 4-nitroquinoline 1-oxide: its potential use for preclinical chemoprevention studies

Oral squamous cell carcinoma is one of the most common human neoplasms, and prevention of this malignancy requires a better understanding of its carcinogenesis process. To this end, we tried to establish an animal model using the human c-Ha-ras proto-oncogene-carrying transgenic (Tg) rats and the carcinogen 4-nitroquinoline 1-oxide (4-NQO). 4-NQO (20 p.p.m.) was administered to Tg and non-Tg rats for 8 weeks in their drinking water, and then the occurrence of tongue carcinogenesis was compared during the experimental period of 22 weeks. In addition, we determined the DNA ploidy in tongue lesions and examined the immunohistochemical expression of five biomarkers such as cyclin D1, glutathione S-transferase placental form, cyclooxygenase (COX)-2, inducible nitric oxide synthase (iNOS) and beta-catenin. Next, the cancer chemopreventive effects of nimesulide, pioglitazone and a synthetic geranylated derivative, which have been reported to be inhibitors of tongue carcinogenesis, were examined in Tg rats treated with 4-NQO. Either during or after treatment with 4-NQO in the drinking water, tongue dysplasia and tumors were observed on the tongues of both Tg and non-Tg rats, with a greater incidence and multiplicity in Tg rats. Histopathologically, squamous cell dysplasia, papilloma and carcinoma with or without invasion were present in the tongue. Immunohistochemistry revealed that expression levels against five biomarkers increase with disease progression, and the changes correlated with those of the DNA ploidy pattern. Interestingly, a strong expression of COX-2, iNOS and beta-catenin was observed on the invasive front of squamous cell carcinomas. A subsequent chemoprevention study using Tg rats showed that the chemicals tested suppressed the occurrence of tongue carcinomas when they were administered after 4-NQO-exposure. These results may thus indicate that our 4-NQO-induced Tg rat tongue carcinogenesis model simulates many aspects of human oral carcinogenesis and it can be applied for an analysis of oral cancer development while also helping to identify potentially effective cancer chemopreventive agents against oral cancer.

Expression of Catenin family members CTNNA1, CTNNA2, CTNNB1 and JUP in the primate prefrontal cortex and hippocampus

Members of the catenin family of proteins are thought to play a major role in the folding and lamination of the cerebral cortex. We have used in situ hybridization to determine the cellular expression patterns of four members of this family, Alpha-E-, Alpha-N-, Beta-, and Gamma-catenins (CTNNA1, CTNNA2, CTNNB1, and JUP respectively) in the adult primate dorsolateral prefrontal cortex (DLPFC) and hippocampus. CTNNA2, CTNNB1, and JUP mRNAs were detected in all layers of the DLPFC and in all neuronal subregions of the hippocampal formation, however CTNNA1 mRNA, coding for an 'epithelial' specific catenin, was not detected in any region of the cortex or hippocampus. CTNNA2, a 'neuronal-specific' catenin, and CTNNB1 mRNAs were abundant in both DLPFC and hippocampus, with a distinct neuronal localization. CTNNA2 mRNA was concentrated in both granular/stellate cells and large pyramidal cell bodies, while CTNNB1 expression was more strongly associated with granular cell bodies throughout the DLPFC, with expression in pyramidal cells confined mainly to cortical Layers III and VI. CTNNA2 and CTNNB1 mRNAs were also abundant in the granule cells of the dentate gyrus and pyramidal cells of Ammon's horn, apparently co-expressed in the same neurons. JUP mRNA was rather diffusely localized in the DLPFC without the distinct laminar patterns seen for CTNNA2 and CTNNB1 but was distinctly localized in the granule cells of the dentate gyrus and pyramidal cells of Ammon's horn. These studies demonstrate a distinct neuronal pattern of gene expression for catenin family members in primate brain structures characterized by high degrees of folding and strong lamination. The high level expression of these transcripts supports the notion of a major role for catenins even in the adult brain. Such an understanding is also important in view of the multiple interactions that catenins have with many other proteins in the adult and ageing brain. This may also have implications for understanding the pathogenesis of neurodegenerative diseases such as Alzheimer's disease, as well as emerging neuronal stem cell therapies.

Invasion and metastasis of oral cancer cells require methylation of E-cadherin and/or degradation of membranous beta-catenin

The extent of lymph node metastasis is a major determinant in the prognosis of oral squamous cell carcinoma (OSCC). Abnormalities of cell adhesion molecules are known to play an important role in invasion and metastasis of cancer cells through the loss of cell-to-cell adhesion. In this study, we isolated highly invasive clones from an OSCC cell line established from a lymph node metastasis by using an in vitro invasion assay method and compared the abnormalities of cell adhesion molecule E-cadherin and beta-catenin in these cells. The isolated, highly invasive clones showed significant invasive capacity and reduction of E-cadherin and membranous beta-catenin protein in comparison with parent cells. We found that reduced expression of E-cadherin was due to methylation of its promoter region. In fact, most invasive and metastatic area of OSCCs showed reduced expression and methylation of E-cadherin. Moreover, we found that reduced expression of membranous beta-catenin was due to its protein degradation. Reduced expression of membranous beta-catenin was also found frequently in invasive and metastatic areas of OSCCs. In summary, invasion and metastasis of OSCC cells require methylation of E-cadherin and/or degradation of membranous beta-catenin. In addition, we suggest that the method of isolation of highly invasive clones may be useful for studies aimed at discovering novel genes involved in invasion and metastasis.

Histological and immunohistochemical observations of mucin-depleted foci (MDF) stained with Alcian blue, in rat colon carcinogenesis induced with 1,2-dimethylhydrazine dihydrochloride

The usefulness of mucin-depleted foci (MDF), which have recently been proposed as a new preneoplastic biomarker in rat colon carcinogenesis, was histologically investigated in rat colonic tissues treated with 1,2-dimethylhydrazine dihydrochloride (DMH). The relationship among aberrant crypt foci (ACF), MDF and beta-catenin accumulated crypts (BCAC) was examined by comparing the corresponding computer-captured images. Twelve male F344 rats were given DMH s.c. at a dose of 40 mg/kg body weight, once a week for 2 weeks, and randomly divided into two groups. Rats in group 1 were given normal drinking water, while those in group 2 were given drinking water containing indomethacin (IND) at 16 ppm for 6 weeks. All animals were sacrificed 8 weeks after the first DMH treatment. The resected colons were fixed in 10% formalin, and stained with Alcian blue for observation of ACF and MDF. Histological and immunohistochemical analysis revealed that the numbers of ACF, MDF and overlapping lesions in group 2 (treated with IND) were significantly decreased, compared with those in group 1. The number of BCAC in group 2 was also significantly lower than that in group 1. The reduction (61.5%) of MDF by IND was much greater than that (29.3%) of ACF. Analyses of the computer-captured images indicated that MDF had more frequent dysplastic changes and overexpression of beta-catenin than did ACF. MDF having over 4 crypts or MDF with the appearance of ACF corresponded well to BCAC. These results suggest that MDF may be useful as an early biomarker in colon carcinogenesis.

Dietary sodium gluconate protects rats from large bowel cancer by stimulating butyrate production

Butyrate has an antitumorigenic effect on colorectal cancer cell lines. Dietary sodium gluconate (GNA) promotes butyrate production in the large intestine. Accordingly, we examined the effect of dietary GNA on tumorigenesis in the large intestine in rats. Male Fisher-344 rats (n = 32) were divided into 4 groups: 2 diets (with or without 50 g GNA/kg basal diet) x 2 treatments (with or without carcinogen administration). Colonic tumors were induced by 3 intraperitoneal injections of azoxymethane (15 mg/kg body wt, 1 time/wk) and dietary deoxycholic acid (2 g/kg basal diet). The experiment was conducted for 33 wk except for a few rats. Ingestion of GNA increased cecal butyrate concentration at the end of experiment (P < 0.01). No tumor development occurred in the untreated groups. Ingestion of GNA decreased the incidence of tumors in rats administered the carcinogen (37.5 vs. 100%, P < 0.05). Ingestion of GNA also decreased the mean number of tumors per rat (0.5 +/- 0.8 vs. 2.8 +/- 1.5, P < 0.01). beta-Catenin accumulation and TdT-mediated dUTP nick end labeling (TUNEL) positive cells in tumors were histochemically examined. The results of this study suggested that the antitumorigenic effect of GNA may involve the stimulation of apoptosis through enhanced butyrate production in the large intestine.

Preclinical models for chemoprevention of colon cancer

Colon cancer is the second leading cause of cancer incidence and death in the USA in 2002. Specific genetic defects have been identified which cause hereditary colon cancers in humans. In addition, a number of intestinal luminal risk factors for colon cancer have been described. This information has been exploited to develop experimental cell and rodent models which recapitulate features of human colon cancer. In this chapter, we will discuss the strengths and limitations of these models to further our understanding of basic mechanisms of colon carcinogenesis and to develop strategies for colon cancer chemoprevention.

beta-Catenin mutations and nuclear accumulation during progression of rat stomach adenocarcinomas

Aberrant Wnt/beta-catenin signaling caused by mutations in exon 3 of the beta-catenin gene has been identified in a number of human malignancies, including stomach cancer. However, studies of mutation frequency have yielded conflicting results, and timing during progression remains largely unknown. In this study, we utilized an animal model to address this question. A total of 20 ACI male rats were treated with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in the drinking water and 22 induced differentiated adenocarcinomas were histopathologically and immunohistochemically evaluated for beta-catenin localization. Fourteen tumors (63.6%) that showed homogeneous low-grade morphology, preserving cell polarity, were found to harbor beta-catenin protein on the cell membranes (M). Eight tumors exhibited regions of high-grade morphology among areas with low-grade morphology, and they were characterized by denser cell growth and loss of cell polarity. Among these 8 tumors, 4 (18.2%) showed cytoplasmic localization (C) of beta-catenin in small regions. The remaining 4 tumors (18.2%) contained more dysplastic regions that displayed nuclear (N) beta-catenin staining. Analysis of DNA obtained by microdissection demonstrated that all of 4 regions with C staining and 20 with M staining, as well as 17 samples of surrounding normal mucosa (S) had wild-type beta-catenin. In contrast, all of 3 regions with N staining featured mutations (3 of 3 = 100%; N vs. C, P < 0.05; N vs. M and N vs. S, P < 0.001, Fisher's exact test) in exon 3, at glycine 34, threonine 41, and serine 45, which affected phosphorylation sites. In conclusion, beta-catenin mutations appear to be associated with the late progression stage of adenocarcinoma development in rat stomach carcinogenesis, in contrast to the case of colorectal cancers, in which mutations appear to occur in the early stages.

Changing expression of E- and P-cadherin during rat tongue carcinogenesis induced by 4-nitroquinoline 1-oxide

BACKGROUND

Oral squamous cell carcinoma (SCC) develops from pre-malignant lesions, but the role of cell adhesion molecules such as E-cadherin (E-CD) and P-cadherin (P-CD) in the pre-malignant stage has not been elucidated.

METHODS

The expression of E-CD and P-CD was examined immunohistochemically and biochemically in a 4-nitroquinoline 1-oxide (4NQO)-induced rat model of carcinogenesis.

RESULTS

The expression of E-CD in the pre-malignant stage was the same as that in the normal epithelium. The expression of P-CD was even throughout the prickle cell layer in the dysplasia stage. E-CD and P-CD were expressed in essentially the same locations in SCC and in the pre-malignant stage. P-CD expression was very strong in the pre-malignant stage, compared to that in normal epithelium.

CONCLUSIONS

Aberrant P-CD expression in E-CD-positive cells may play a crucial role in the progression of the pre-malignant stage of 4NQO-induced carcinogenesis, and may activate mechanisms responsible for cell proliferation.

No involvement of beta-catenin gene mutation in gastric carcinomas induced by N-methyl-N-nitrosourea in male F344 rats

The agent N-methyl-N-nitrosourea (MNU) is a direct acting carcinogen and induces well-differentiated adenocarcinoma on the rat gastric mucosa. In this study, 27 histopathologically verified gastric carcinomas induced in male F344 rats were analyzed for mutations in the N-terminal phosphorylation sites (codons 1-51) of the beta-catenin gene by using polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP) assays. In parallel studies, the specific localization of the beta-catenin protein was also examined by immunohistochemical analysis. No mutations in the beta-catenin gene were found in any of 27 gastric carcinomas induced by MNU. Immunohistochemical analysis resulted in the beta-catenin protein to be localized in the plasma membrane but cytoplasmic and/or nuclear accumulation of beta-catenin was not identified in any of these carcinomas. These results suggest that mutations in the beta-catenin gene are less contributory to the development of rat gastric carcinomas induced by MNU. This animal model may provide a system for evaluating the mechanism of human gastric carcinogenesis that is not associated with beta-catenin gene mutations.

Expression of beta-catenin in rat oral epithelial dysplasia induced by 4-nitroquinoline 1-oxide

The aim of this study was to evaluate whether beta-catenin accumulation is useful for diagnosing the malignant potential of oral precancerous lesions. We investigated oral epithelial dysplasia adjacent to early cancer induced by 4-nitroquinoline 1-oxide in rats. Localization of beta-catenin and cell proliferation were detected immunohistochemically, and exon 3 of the beta-catenin gene was analyzed. Accumulation of beta-catenin in the cytoplasm and nucleus was evident in 10 of 16 dysplasia lesions. Since almost all of the dysplastic lesions in these rats transformed to invasive cancer, beta-catenin accumulation may contribute to the early stage of carcinogenesis. The Ki-67 labeling index was significantly higher in dysplasia and early cancer than in no change. However, there were no significant differences between the expression patterns of beta-catenin protein, suggesting that other proliferation pathways are involved in the early stage of tumor development in addition to beta-catenin accumulation. No mutations of exon 3 of the beta-catenin gene were detected in any of the dysplasia or early cancer lesions. These findings suggested that beta-catenin accumulation in the cytoplasm and nucleus without mutation of exon 3 is an early event during carcinogenesis in this tongue cancer model.