Beta-catenin mutations in cell lines established from human colorectal cancers

Genetic and protein markers related to in situ growth and multiplicity in small sporadic colorectal adenomas

BACKGROUND

Some early genetic events in the development of colorectal adenomas are known, but their relationship to in vivo growth characteristics is uncertain. This study compared in situ size changes and other clinicopathological variables with selected genetic and protein markers.

METHODS

56 adenomas (< or = 10 mm) from 39 patients were analysed for APC, CTNNB1 and K-ras mutations, allelic imbalance on 1p and 18q, microsatellite instability and immunohistochemical expression of HLA-DR, BAX, BCL-2 and Ki-67. For 42 of the adenomas, in situ growth was measured over 3 years. The total number of polyps in each patient was recorded.

RESULTS

K-ras was mutated in 8/56 adenomas. None of the regressing adenomas revealed such mutations, compared to 20% in those that maintained or increased their size. Multivariate linear regression analysis showed that tumour growth was higher in females compared to males, and was even higher in the presence of a K-ras mutation. APC mutations were found in 37/56 adenomas. CTNNB1 mutations were found in 2/19 adenomas without APC mutation. Deletions of 1p were found in 12/56 adenomas and, seemingly, most frequent in patients with few tumours. The most frequently expressed protein was BAX (33/41), but neither this nor the other proteins showed associations with an in situ growth pattern.

CONCLUSION

The multivariate linear regression model showed that patient gender and the presence of K-ras mutation had significant effects on tumour growth. The lack of the proliferative stimulus resulting from a K-ras mutation may contribute to the process of adenoma regression.

Exchange of catenins in cadherin-catenin complex

beta-Catenin is an intracellular multifunctional protein. In complex with the transmembrane adhesive receptor E-cadherin, it becomes plasma membrane-associated and mediates intercellular adhesion. A cytosolic pool of beta-catenin interacts with DNA-binding proteins and participates in signal transduction. To reveal the possible cross-talk between these two pools, we studied whether beta-catenin is exchanged between its free and cadherin-bound states. We found that pulse-labeled beta-catenin replaces the beta-catenin bound to the cell surface prebiotinylated E-cadherin immediately after synthesis. Approximately 25% of all pulse-labeled beta-catenin destined for E-cadherin associates with this protein via this mechanism. The rest of the newly synthesized beta-catenin arrives at the plasma membrane in a complex with the E-cadherin precursor. Immediately after arrival, this beta-catenin pool is transferred to the prebiotinylated E-cadherin. beta-Catenin released from E-cadherin may participate in new exchange cycles. This beta-catenin exchange is strongly affected in cells that contain mutations in the tumor suppressor gene APC. This process may contribute significantly to both cell-cell adhesion and beta-catenin-dependent signaling.

CpG island methylation is a common finding in colorectal cancer cell lines

Tumour cell lines are commonly used in colorectal cancer (CRC) research, including studies designed to assess methylation defects. Although many of the known genetic aberrations in CRC cell lines have been comprehensively described, no studies have been performed on their methylation status. In this study, 30 commonly used CRC cell lines as well as seven primary tumours from individuals with hereditary nonpolyposis colorectal cancer (HNPCC) were assessed for methylation at six CpG islands known to be hypermethylated in colorectal cancer: hMLH1, p16, methylated in tumour (MINT-)-1, -2, -12 and -31. The cell lines were also assessed for microsatellite instability (MSI), ploidy status, hMLH1 expression, and mutations in APC and Ki-ras. Methylation was frequently observed at all examined loci in most cell lines, and no differences were observed between germline-derived and sporadic cell lines. Methylation was found at MINT 1 in 63%, MINT 2 in 57%, MINT 12 in 71%, MINT 31 in 53%, p16 in 71%, and hMLH1 in 30% of cell lines. Overall only one cell line, SW1417, did not show methylation at any locus. Methylation was found with equal frequency in MSI and chromosomally unstable lines. MSI was over-represented in the cell lines relative to sporadic CRC, being detected in 47% of cell lines. The rate of codon 13 Ki-ras mutations was also over three times that expected from in vivo studies. We conclude that CpG island hypermethylation, whether acquired in vivo or in culture, is a ubiquitous phenomenon in CRC cell lines. We suggest that CRC cell lines may be only representative of a small subset of real tumours, and this should be taken into account in the use of CRC cell lines for epigenetic studies.

Nuclear accumulation of beta-catenin protein in Wilms' tumours

The wnt-signalling pathway plays an important role during both normal kidney development and Wilms' tumourigenesis. Activation of this pathway involves stabilization, intracellular accumulation, and nuclear translocation of the beta-catenin protein and may be caused by specific mutations in the beta-catenin gene itself. Such mutations have been found in about 15% of Wilms' tumours. This study has analysed the intracellular levels and subcellular distribution of beta-catenin protein in 36 primary Wilms' tumour specimens and has correlated these results with the mutational status of the beta-catenin gene. Immunohistochemistry detected faint cytoplasmic and strong membranous expression of beta-catenin protein in the epithelial compartment of all tumours examined. In contrast, nuclear immunoreactivity for beta-catenin was detected in 9 of 9 Wilms' tumours containing a mutation of the beta-catenin gene and in 15 of 27 Wilms' tumours without detectable beta-catenin mutation. Nuclear positivity, in each case, was found to be very strong, but was usually present only in a fraction of cells ranging from 5% to 10%. Among the different histological subcompartments, blastemal and mesenchymal cell nuclei preferentially stained positive, whereas cells of epithelial differentiation displayed nuclear localization of beta-catenin protein in only a single case. Furthermore, nuclear positive cells were found in Wilms' tumours of all stages and in tumours of both favourable and unfavourable histology. These data support the idea that activation of the wnt-signalling pathway is a key oncogenic step in Wilms' tumourigenesis and that it probably involves transcriptional activation of critical target genes, carried out by beta-catenin protein in the nucleus. The fact that nuclear immunoreactivity specific for beta-catenin was detected in a significant number of Wilms' tumours in the absence of beta-catenin mutations suggests that genetic defects affecting other members of the wnt-signalling pathway may contribute to the development of Wilms' tumours in those cases.

Analysis of chromosomal instability in human colorectal adenomas with two mutational hits at APC

In vitro data show that the adenomatous polyposis coli (APC) protein associates with the mitotic spindle and that mouse embryonic stem cells with biallelic Apc mutations are karyotypically unstable. These findings led to suggestions that APC acts in chromosomal segregation and that APC inactivation leads to chromosomal instability (CIN). An alternative hypothesis based on allelic loss studies in colorectal adenomas proposes that CIN precedes and contributes to genetic changes at APC. We determined whether colorectal adenomas with two mutations at APC show features consistent with these models by studying 55 lesions (average size 5 mm; range 1-13 mm) from patients with familial adenomatous polyposis. A variety of methods was used depending on available material, including flow cytometry, comparative genomic hybridization, and loss of heterozygosity (LOH) analysis. Selected adenomas were assessed for proliferative activity by Ki-67 immunocytochemistry. Seventeen of 20 (85%) tumors were diploid, two were near-diploid, and one was hypotetraploid. Just one (near-diploid) tumor showed increased proliferative activity. LOH was found occasionally on chromosome 15q (2 of 49 tumors), but not on chromosome 18q (0 of 48). In 20 adenomas, LOH at APC was associated with loss at 5q but not 5p markers, with the former encompassing a minimum of 20 Mb. However, three of these lesions analyzed by comparative genomic hybridization displayed normal profiles, suggesting, together with other data, that the mechanism of LOH at APC is probably somatic recombination. Our results therefore do not support the hypothesis that CIN precedes APC mutations in tumorigenesis. Regarding the model in which APC mutations lead directly to CIN, if APC mutations do have this effect in vivo, it must be subtle. Alternatively, CIN associated with APC mutations might be essentially an in vitro phenomenon.

Beta-catenin-mediated transactivation and cell-cell adhesion pathways are important in curcumin (diferuylmethane)-induced growth arrest and apoptosis in colon cancer cells

The development of nontoxic natural agents with chemopreventive activity against colon cancer is the focus of investigation in many laboratories. Curcumin (feruylmethane), a natural plant product, possesses such chemopreventive activity, but the mechanisms by which it prevents cancer growth are not well understood. In the present study, we examined the mechanisms by which curcumin treatment affects the growth of colon cancer cells in vitro. Results showed that curcumin treatment causes p53- and p21-independent G(2)/M phase arrest and apoptosis in HCT-116(p53(+/+)), HCT-116(p53(-/-)) and HCT-116(p21(-/-)) cell lines. We further investigated the association of the beta-catenin-mediated c-Myc expression and the cell-cell adhesion pathways in curcumin-induced G(2)/M arrest and apoptosis in HCT-116 cells. Results described a caspase-3-mediated cleavage of beta-catenin, decreased transactivation of beta-catenin/Tcf-Lef, decreased promoter DNA binding activity of the beta-catenin/Tcf-Lef complex, and decreased levels of c-Myc protein. These activities were linked with decreased Cdc2/cyclin B1 kinase activity, a function of the G(2)/M phase arrest. The decreased transactivation of beta-catenin in curcumin-treated HCT-116 cells was unpreventable by caspase-3 inhibitor Z-DEVD-fmk, even though the curcumin-induced cleavage of beta-catenin was blocked in Z-DEVD-fmk pretreated cells. The curcumin treatment also induced caspase-3-mediated degradation of cell-cell adhesion proteins beta-catenin, E-cadherin and APC, which were linked with apoptosis, and this degradation was prevented with the caspase-3 inhibitor. Our results suggest that curcumin treatment impairs both Wnt signaling and cell-cell adhesion pathways, resulting in G(2)/M phase arrest and apoptosis in HCT-116 cells.

A novel role for p120 catenin in E-cadherin function

Indirect evidence suggests that p120-catenin (p120) can both positively and negatively affect cadherin adhesiveness. Here we show that the p120 gene is mutated in SW48 cells, and that the cadherin adhesion system is impaired as a direct consequence of p120 insufficiency. Restoring normal levels of p120 caused a striking reversion from poorly differentiated to cobblestone-like epithelial morphology, indicating a crucial role for p120 in reactivation of E-cadherin function. The rescue efficiency was enhanced by increased levels of p120, and reduced by the presence of the phosphorylation domain, a region previously postulated to confer negative regulation. Surprisingly, the rescue was associated with substantially increased levels of E-cadherin. E-cadherin mRNA levels were unaffected by p120 expression, but E-cadherin half-life was more than doubled. Direct p120-E-cadherin interaction was crucial, as p120 deletion analysis revealed a perfect correlation between E-cadherin binding and rescue of epithelial morphology. Interestingly, the epithelial morphology could also be rescued by forced expression of either WT E-cadherin or a p120-uncoupled mutant. Thus, the effects of uncoupling p120 from E-cadherin can be at least partially overcome by artificially maintaining high levels of cadherin expression. These data reveal a cooperative interaction between p120 and E-cadherin and a novel role for p120 that is likely indispensable in normal cells.

Pro-apoptotic actions of exisulind and CP461 in SW480 colon tumor cells involve beta-catenin and cyclin D1 down-regulation

Exisulind and its analogues are inhibitors of cyclic GMP phosphodiesterases (PDEs) that have been shown to activate and induce protein kinase G, resulting in the induction of apoptosis in colon cancer cells. These drugs also reduce beta-catenin protein levels and decrease cyclin D1 mRNA levels in SW480 cells. Herein we report on studies pertaining to exisulind regulation of beta-catenin levels and activity in colon tumor cells. Exisulind and its higher-affinity PDE analogues, (Z)-5-fluoro-2-methyl-(4-pyridylidene)-3-(N-benzyl)-indenylacetamide hydrochloride (CP461) and (Z)-1H-indene-3-acetamide, 5-fluoro-2-methyl-N-(phenylmethyl)-1-[(3,4,5-trimethoxyphenyl)methylene] (CP248), reduced beta-catenin, including the nuclear beta-catenin in SW480 cells (EC(50) approximately 200 microM, 1 microM, and <1 microM, respectively). The 50% reduction of beta-catenin was seen in 8-14 hr. There was no change in beta-catenin mRNA. Exisulind-induced beta-catenin reduction was blocked by the proteasomal inhibitor MG132 (Z-leu-Leu-Leu-CHO), indicating that the effect of exisulind involved ubiquitin-proteasomal degradation. A consequence of reduced beta-catenin in SW480 cells was that exisulind, CP461, and CP248 caused a concentration- and time-dependent decrease in cyclin D1 levels (EC(50) approximately 300 microM, 1 microM, and <1 microM, respectively) in 4 hr. The effect was via decreased cyclin D1 mRNA levels. Exisulind-induced degradation of beta-catenin was not blocked by the inhibition of caspase-3 activity and/or apoptosis, and some SW480 cells showed a reduction in beta-catenin levels before the appearance of early apoptosis indicators. Expression of the N-terminal 170 amino acid fragment of beta-catenin reduced the effects of beta-catenin degradation, cyclin D1 reduction, and the apoptosis response to exisulind. These results indicate that exisulind-induced beta-catenin degradation precedes the induction of apoptosis and that the down-regulation of inappropriate beta-catenin-activated genes accounts in part for the pro-apoptotic effects of exisulind and CP461 in colon tumor cells.

Beta-catenin mutations correlate with over expression of C-myc and cyclin D1 Genes in bladder cancer

PURPOSE

We hypothesized that over expression of c-myc and cyclin D1 genes is transcriptionally activated by beta-catenin mutation independent of gene amplification in bladder cancer. To test this hypothesis we investigated the relationship of beta-catenin mutation to c-myc and cyclin D1 mRNA with special reference to the changes in copy number of the 2 genes.

MATERIALS AND METHODS

Genomic DNA and total RNA were extracted from 59 bladder cancer specimens and from 31 histologically normal specimens of bladder mucosa. We performed beta-catenin deletion screening by polymerase chain reaction (PCR) using primers spanning exons 3 (including the glycogen synthase kinase-3beta consensus motif), 5 and 6. Mutational changes in beta-catenin in exons 3, 5 and 6 were detected by each PCR-single strand conformational polymorphism analysis followed by direct DNA sequencing. mRNA expression and copy numbers of c-myc and cyclin D1 were determined by semiquantitative reverse transcriptase-PCR and competitive genomic PCR.

RESULTS

Missense mutations of beta-catenin found in grade 3 bladder cancer were involved in the consensus motif of glycogen synthase kinase-3beta in exon 3. These cancers showed strong intracellular accumulation of beta-catenin and intense expression of c-myc and cyclin D1 mRNA compared with samples lacking the beta-catenin mutation. When grade 3 cancers were compared, expression levels of c-myc and cyclin D1 mRNA were still higher in those with versus without the beta-catenin mutation. In bladder cancers with beta-catenin mutations copy numbers of the c-myc and cyclin D1 genes did not amplify.

CONCLUSIONS

Bladder cancer harboring a beta-catenin mutation may represent aggressive biological behavior with enhanced proliferating activity. These findings are important for understanding the role of beta-catenin mutation in the pathogenesis of bladder cancer.

Regulation of epithelial cell migration and tumor formation by beta-catenin signaling

Cell migration requires precise control, which is altered or lost when tumor cells become invasive and metastatic. beta-catenin plays a dual role in this process: as a member of adherens junctions it is essential to link cadherins to the cytoskeleton thereby allowing tight intercellular adhesion, and as a member of the Wnt-signaling pathway, beta-catenin is translocated into the nucleus and serves together with the LEF1/TCF-transcription factors to drive gene expression necessary for the epithelial-to-mesenchymal transition (EMT). Activated beta-catenin signaling has been implicated in the genesis of a variety of tumors. Here we demonstrate a pivotal function for beta-catenin signaling in epithelial cell migration and tumorigenesis. Hepatocyte growth factor (HGF) and epidermal growth factor (EGF) induce beta-catenin signaling under conditions where they stimulate cell motility. Ectopic expression of either stabilized beta-catenin or a regulatable form of activated beta-catenin induces cell migration in different cell types and cooperates with EGF and HGF in this process. Activation of beta-catenin signaling induces expression of the new target gene osteopontin during migration. Cells expressing stabilized beta-catenin also exhibit significantly increased capability to form tumors in a nude mouse xenograft model. The data suggest that a critical threshold of beta-catenin signaling, activated by cooperative mechanisms, may be important during the EMT and tumorigenesis.

Beta-catenin immunohistochemistry separates mesenteric fibromatosis from gastrointestinal stromal tumor and sclerosing mesenteritis

Although separating gastrointestinal stromal tumor (GIST) from mesenteric fibromatosis and sclerosing mesenteritis is clinically important, this distinction sometimes poses problems for practicing pathologists. In the STI571 (Gleevec, Imatinib) era, the problem may be further compounded when protocol-driven staining for CD117 (c-kit) is performed on spindle cell proliferations presenting in the bowel wall and mesentery using an antibody known to react with the majority of mesenteric fibromatoses when other antibodies are more specific. Because most mesenteric fibromatoses have mutations in the pathway and hence have abnormal nuclear accumulation of beta-catenin protein, we studied beta-catenin expression among a panel of other immunohistochemical stains to distinguish mesenteric fibromatosis, GIST, and sclerosing mesenteritis. Examples of gastrointestinal stromal tumors (GIST, 11), sclerosing mesenteritis (5), and mesenteric fibromatosis (10) were retrieved from the archives of our institutions. Cases were studied with an immunohistochemical panel consisting of CD117, beta-catenin, CD34, smooth muscle actin, desmin, keratin, and S-100 protein. Cases were scored as "negative," "focally positive," or "diffusely positive." In evaluating beta-catenin, nuclear accumulation was required. GIST all had CD117 (11 of 11, diffuse) and CD34 (11 of 11, diffuse) with variable actin (5 of 11, focal) and negative desmin, keratin, S-100 protein. All GIST lacked beta-catenin (0 of 11). Mesenteric fibromatosis had CD117 (6 of 10, 3 focal, 3 diffuse), typically expressed more weakly than in GIST, actin (5 of 9, focal), and desmin (3 of 8, focal) in keeping with myofibroblastic differentiation but lacked CD34, S-100, and keratin. CD117 staining was not eliminated by use of a non-avidin-biotin technique. Nuclear beta-catenin was detected in 9 of 10 fibromatoses, including one case associated with familial adenomatous polyposis. Two of five sclerosing mesenteritis cases focally expressed CD117. None of the sclerosing mesenteritis cases had nuclear beta-catenin. Sclerosing mesenteritis cases were otherwise fibroblastic and myofibroblastic with focal actin in 5 of 5 and negative desmin, keratin, and S-100 protein but one had CD34 (1 of 5, focal). With increasing protocol-driven interest in evaluating bowel wall and mesenteric spindle cell lesions using CD117 (c-kit) antibodies, it is important for practicing pathologists to be aware that lesions other than GISTs are likely to express this antigen using certain antibodies. beta-Catenin staining identifies lesions that are, instead, mesenteric fibromatoses.

Variable nuclear localization of alpha-catenin in colorectal carcinoma

The E-cadherin/catenin complex plays a major role in epithelial cell-cell adhesion. Both beta-catenin and gamma-catenin bind directly to the cytoplasmic domain of E-cadherin whereas alpha-catenin links the bound beta-catenin or gamma-catenin to the actin microfilament network of the cellular cytoskeleton. Significant changes in the expression and/or structure of members of the complex can occur in neoplasia. Several studies have reported on the nuclear localization of beta- and gamma-catenin and on their role in influencing the transcriptional activity of several proto-oncogenes. The cellular localization of alpha-catenin has not been studied in detail. The aim of this study was to investigate the cellular localization of alpha-catenin in colorectal carcinoma both in vitro and in vivo and to assess whether it might be relevant to tumor behavior. The expression of alpha-catenin was examined in a panel of colorectal carcinoma cell lines (SW480, SW620, HCT116, HT29, and Caco-2) using a combination of immunohistochemistry, confocal fluorescence microscopy, and Western blotting. The expression of alpha-catenin was also studied by immunohistochemistry in 15 sporadic colorectal adenomas, 30 sporadic colorectal adenocarcinomas, and their 13 lymph node metastases. From familial adenomatous polyposis patients, 20 adenomas and 5 adenocarcinomas were studied. Nuclear localization of alpha-catenin was detected in the colorectal carcinoma cell lines when the cells were dispersed rather than confluent. alpha-catenin was not detected in the nuclei in any of the sporadic or familial adenomas. However, it was detected in one sporadic and one familial adenocarcinoma but not in any of the lymph node deposits. alpha-catenin can localize to the nuclei of colorectal tumor cells, and this may be related to lack of perception of connection to adjacent cells.

Targeted inactivation of CTNNB1 reveals unexpected effects of beta-catenin mutation

Inactivating mutations of the adenomatous polyposis coli gene (APC) or activating mutations of the beta-catenin gene (CTNNB1) initiate colorectal neoplasia. To address the biochemical and physiologic effects of mutant beta-catenin, we disrupted either the mutant or wild-type CTNNB1 allele in a human colorectal cancer cell line. Cells with only wild-type beta-catenin had decreased colony-forming ability when plated at low density, although their growth was similar to that of parental cells when passaged under routine conditions. Immunohistochemistry and cell-fractionation studies suggested that mutant beta-catenin activity was distinguished primarily by cellular localization and not by protein degradation. Surprisingly, we found mutant beta-catenin bound less well to E-cadherin than did wild-type beta-catenin, and the membranous localization of wild-type and mutant beta-catenin was accordingly distinct. These findings pose several challenges to current models of APC/beta-catenin function.

Protection against anoikis and down-regulation of cadherin expression by a regulatable beta-catenin protein

beta-Catenin signaling plays a key role in a variety of cellular contexts during embryonic development and tissue differentiation. Aberrant beta-catenin signaling has also been implicated in promoting human colorectal carcinomas as well as a variety of other cancers. To study the molecular and cellular biological functions of beta-catenin in a controlled fashion, we created a regulatable form of activated beta-catenin by fusion to a modified estrogen receptor (ER) ligand binding domain (G525R). Transfection of tissue culture cells with expression vectors encoding this hybrid protein allows the signal transduction function of beta-catenin to be induced by the synthetic estrogen, 4-hydroxytamoxifen, leading to regulated activation of a beta-catenin-lymphocyte enhancer-binding factor-dependent reporter gene as well as induction of endogenous cyclin D1 expression. The activation of ER-beta-catenin signaling rescues RK3E cells from anoikis and correlates with an increased phosphorylation of mitogen-activated protein kinase. The inhibition of anoikis by ER-beta-catenin can be abolished by a mitogen-activated protein kinase pathway inhibitor, PD98059. Evidence is also provided to show that ER-beta-catenin down-regulates cadherin protein levels. These findings support a key role for activated beta-catenin signaling in processes that contribute to tumor formation and progression.

Deregulated expression of the human tumor marker CEA and CEA family member CEACAM6 disrupts tissue architecture and blocks colonocyte differentiation

Human carcinoembryonic antigen (CEA) and the CEA family member CEACAM6 (formerly nonspecific cross-reacting antigen [NCA]) function in vitro, at least, as homotypic intercellular adhesion molecules and, in model systems, can block the terminal differentiation and anoikis of several different cell types. We have recently demonstrated that the increased cell surface levels of CEA and CEACAM6 in purified human colonocytes from freshly excised, well to poorly differentiated colon carcinomas are inversely correlated with the degree of cellular differentiation. Thus, deregulated expression of CEA/CEACAM6 could directly contribute to colon tumorigenesis by the inhibition of terminal differentiation and anoikis. Evidence against this view includes the common observation of increased CEA/CEACAM6 expression as normal colonocytes differentiate in their migration up colonic crypt walls. We report here the direct effects of deregulated overexpression of CEA/CEACAM6, at levels observed in colorectal carcinomas, on the differentiation of two human colonic cell lines, SW-1222 and Caco-2. Stable transfectants of both of these cell lines that constitutively express 10- to 30-fold higher cell surface levels of CEA/CEACAM6 than endogenous levels failed to polarize and differentiate into glandular structures in monolayer or 3D culture or to form colonic crypts in a tissue architecture assay in nude mice. In addition, these transfectants were found to exhibit increased tumorigenicity in nude mice. These results thus support the contention that deregulated overexpression of CEA and CEACAM6 could provide a tumorigenic contribution to colon carcinogenesis.

Cancer genetics and their application to individualised medicine

One of the great challenges of basic research is to translate scientific discoveries into the improved treatment of patients. For colorectal cancer, our increased understanding of the molecular aetiology of the disease has not yet been paralleled by an improvement in patient care. However, several new approaches are on the verge of clinical implementation. Technical advances such as real-time polymerase chain reaction (PCR) and microarray techniques coupled to insight in the molecular pathways in colorectal cancer makes it possible to develop new clinical tools for the diagnosis, classification and treatment of patients. The ultimate goal of the incorporation of cancer genetics into the clinical treatment of patients is individualised medicine; therapeutic strategies based on the molecular taxonomy of tumours and individually constructed for each patient.

Sphingoid bases and ceramide induce apoptosis in HT-29 and HCT-116 human colon cancer cells

Complex dietary sphingolipids such as sphingomyelin and glycosphingolipids have been reported to inhibit development of colon cancer. This protective role may be the result of turnover to bioactive metabolites including sphingoid bases (sphingosine and sphinganine) and ceramide, which inhibit proliferation and stimulate apoptosis. The purpose of the present study was to investigate the effects of sphingoid bases and ceramides on the growth, death, and cell cycle of HT-29 and HCT-116 human colon cancer cells. The importance of the 4,5-trans double bond present in both sphingosine and C(2)-ceramide (a short chain analog of ceramide) was evaluated by comparing the effects of these lipids with those of sphinganine and C(2)-dihydroceramide (a short chain analog of dihydroceramide), which lack this structural feature. Sphingosine, sphinganine, and C(2)-ceramide inhibited growth and caused death of colon cancer cells in time- and concentration-dependent manners, whereas C(2)-dihydroceramide had no effect. These findings suggest that the 4,5-trans double bond is necessary for the inhibitory effects of C(2)-ceramide, but not for sphingoid bases. Evaluation of cellular morphology via fluorescence microscopy and quantitation of fragmented low-molecular weight DNA using the diphenylamine assay demonstrated that sphingoid bases and C(2)-ceramide cause chromatin and nuclear condensation as well as fragmentation of DNA, suggesting these lipids kill colon cancer cells by inducing apoptosis. Flow cytometric analyses confirmed that sphingoid bases and C(2)-ceramide increased the number of cells in the A(0) peak indicative of apoptosis and demonstrated that sphingoid bases arrest the cell cycle at G(2)/M phase and cause accumulation in the S phase. These findings establish that sphingoid bases and ceramide induce apoptosis in colon cancer cells and implicate them as potential mediators of the protective role of more complex dietary sphingolipids in colon carcinogenesis.

Role of beta-catenin/T-cell factor-regulated genes in ovarian endometrioid adenocarcinomas

In various cancers, inactivating mutations in the adenomatous polyposis coli or Axin tumor suppressor proteins or activating mutations in beta-catenin's amino-terminal domain elevate beta-catenin levels, resulting in marked effects on T-cell factor (TCF)-regulated transcription. Several candidate beta-catenin/TCF-regulated genes in cancer have been proposed. Expression of a few of these genes has been studied in primary human cancers, but most studies have focused on colon cancers and not on other cancer types that harbor mutational defects in adenomatous polyposis coli, AXIN, or beta-catenin. Mutations leading to beta-catenin deregulation are found in nearly half of ovarian endometrioid adenocarcinomas (OEAs). We report here on the expression of 6 candidate beta-catenin/TCF-regulated genes in a panel of 44 primary OEAs, more than a third of which carry demonstrable defects in beta-catenin regulation. Using quantitative assays of gene expression, we found significantly elevated expression of the MMP-7, CCND1 (Cyclin D1), CX43 (Connexin 43), PPAR-delta, and ITF2 genes in OEAs with deregulated beta-catenin. This correlation was not observed for c-myc, another putative beta-catenin/TCF-regulated gene. Immunohistochemical studies confirmed that overexpression of cyclin D1 and MMP-7 was highly associated with nuclear accumulation of beta-catenin and mutational defects of the Wnt/beta-catenin/TCF-signaling pathway. Our findings indicate cyclin D1, MMP-7, connexin 43, PPAR-delta, and ITF-2, likely play important roles in the pathogenesis of those OEAs that manifest defects in beta-catenin regulation.

Deregulated expression of the human tumor marker CEA and CEA family member CEACAM6 disrupts tissue architecture and blocks colonocyte differentiation

Human carcinoembryonic antigen (CEA) and the CEA family member CEACAM6 (formerly nonspecific cross-reacting antigen [NCA]) function in vitro, at least, as homotypic intercellular adhesion molecules and, in model systems, can block the terminal differentiation and anoikis of several different cell types. We have recently demonstrated that the increased cell surface levels of CEA and CEACAM6 in purified human colonocytes from freshly excised, well to poorly differentiated colon carcinomas are inversely correlated with the degree of cellular differentiation. Thus, deregulated expression of CEA/CEACAM6 could directly contribute to colon tumorigenesis by the inhibition of terminal differentiation and anoikis. Evidence against this view includes the common observation of increased CEA/CEACAM6 expression as normal colonocytes differentiate in their migration up colonic crypt walls. We report here the direct effects of deregulated overexpression of CEA/CEACAM6, at levels observed in colorectal carcinomas, on the differentiation of two human colonic cell lines, SW-1222 and Caco-2. Stable transfectants of both of these cell lines that constitutively express 10- to 30-fold higher cell surface levels of CEA/CEACAM6 than endogenous levels failed to polarize and differentiate into glandular structures in monolayer or 3D culture or to form colonic crypts in a tissue architecture assay in nude mice. In addition, these transfectants were found to exhibit increased tumorigenicity in nude mice. These results thus support the contention that deregulated overexpression of CEA and CEACAM6 could provide a tumorigenic contribution to colon carcinogenesis.

An insight into the genetic pathway of adenocarcinoma of the small intestine

BACKGROUND

Although the adenoma to carcinoma pathway in colorectal cancer is well described, the mechanisms of carcinogenesis in the small intestine remain unclear.

AIMS

The aim of this study was to investigate candidate genes in the genetic pathway of adenocarcinoma of the small intestine.

SUBJECTS AND METHODS

A total of 21 non-familial, non-ampullary adenocarcinomas of the small intestine were analysed. DNA was extracted from formalin fixed paraffin wax embedded tissue using standard techniques. The replication error (RER) status was determined by amplification of BAT26. The mutation cluster region (MCR) of the adenomatous polyposis coli (APC) gene was screened using polymerase chain reaction single strand conformational polymorphism and direct sequencing. Immunohistochemistry was performed on formalin fixed paraffin wax embedded tissue using monoclonal antibodies for hMLH1, hMSH2, beta-catenin, E-cadherin, and p53.

RESULTS

Fourteen male and seven female patients with a median age of 64 years (range 21-85) presented with adenocarcinoma of the duodenum (10), jejunum (7), and ileum (4). One cancer (5%) was found to be RER+, and all tumours stained positive for hMLH1 and hMSH2. No mutations were detected in the MCR of the APC gene. beta-Catenin showed increased nuclear expression with loss of membranous staining in 10 cancers (48%). Absent or decreased membrane expression of E-cadherin was found in eight cancers (38%). Strong staining of p53 was found in the nucleus of five cancers (24%).

CONCLUSION

We did not detect mutations in the MCR of the APC gene, and this suggests that adenocarcinoma of the small intestine may follow a different genetic pathway to colorectal cancer. Abnormal expression of E-cadherin and beta-catenin was common and reflects an early alternative to APC in this pathway in which mutations may be found in adenocarcinoma of the small intestine.

Beta-catenin--a linchpin in colorectal carcinogenesis?

An important role for beta-catenin pathways in colorectal carcinogenesis was first suggested by the protein's association with adenomatous polyposis coli (APC) protein, and by evidence of dysregulation of beta-catenin protein expression at all stages of the adenoma-carcinoma sequence. Recent studies have, however, shown that yet more components of colorectal carcinogenesis are linked to beta-catenin pathways. Pro-oncogenic factors that also release beta-catenin from the adherens complex and/or encourage translocation to the nucleus include ras, epidermal growth factor (EGF), c-erbB-2, PKC-betaII, MUC1, and PPAR-gamma, whereas anti-oncogenic factors that also inhibit nuclear beta-catenin signaling include transforming growth factor (TGF)-beta, retinoic acid, and vitamin D. Association of nuclear beta-catenin with the T cell factor (TCF)/lymphoid enhancer factor (LEF) family of transcription factors promotes the expression of several compounds that have important roles in the development and progression of colorectal carcinoma, namely: c-myc, cyclin D1, gastrin, cyclooxygenase (COX)-2, matrix metalloproteinase (MMP)-7, urokinase-type plasminogen activator receptor (aPAR), CD44 proteins, and P-glycoprotein. Finally, genetic aberrations of several components of the beta-catenin pathways, eg, Frizzled (Frz), AXIN, and TCF-4, may potentially contribute to colorectal carcinogenesis. In discussing the above interactions, this review demonstrates that beta-catenin represents a key molecule in the development of colorectal carcinoma.

Genetics of colorectal cancer: hereditary aspects and overview of colorectal tumorigenesis

Familial adenomatous polyposis and hereditary non-polyposis colorectal cancer are dominantly inherited conditions with 100% and 80% life-time risk of developing colorectal cancer, respectively. The genetic mutations responsible for these two conditions lie in the adenomatous polyposis coli (APC) and mismatch repair genes. These same genes also play a key role in the formation of sporadic colorectal cancers, which arise on a background of a similar spectrum of mutations to the hereditary cancers. This article examines the genetic mechanisms underlying the hereditary colorectal cancers, as well as genetic predisposition to colorectal cancer in the general population in the absence of a clear-cut genetic syndrome. Colorectal cancer arises as the cumulative effect of multiple mutations within the cell, allowing it to escape growth and regulatory control mechanisms. This step-wise progression of mutations facilitates the histological transition from normal mucosa to adenoma to carcinoma. The latter part of this paper focuses on the key genetic events underlying this process and provides an overview of the genetic mechanisms responsible for colorectal tumorigenesis.

Genetics--cellular basis

Colorectal carcinogenesis is a multistep process during which the specialised epithelial cells of intestinal mucosa surface (e.g. colonocytes) accumulate a series of genetic and epigenetic events which lead to a perturbation of their normal cellular functions and turnover. This review will address the mechanisms and biological effects of these abnormalities on the growth control, differentiation, adhesion and survival of the colonocytes.

Evolution of colorectal cancer: change of pace and change of direction

This review compiles evidence for an alternative to the classical adenoma-carcinoma sequence in the evolution of colorectal cancer. It is suggested that between 30 and 50 of colorectal cancers are not initiated by mutation of the tumor suppressor gene APC, but through the epigenetic silencing of genes implicated in the control of differentiation, cell cycle control and DNA repair proficiency. The precursor polyps are often characterized by a serrated architecture, and include hyperplastic polyps, admixed polyps and serrated adenomas. The alternative pathway is heterogeneous and may culminate in cancers showing low or high level DNA microsatellite instability (MSI-L and MSI-H, respectively), and in cancers that are microsatellite stable (MSS). Cancers showing DNA MSI may be characterized by an accelerated evolution. Cancers in hereditary non-polyposis colorectal cancer show features of both classical (adenoma and APC mutation) and alternative pathways (rapid evolution, MSI-H and lack of chromosomal instability).

Cell type- and promoter-dependent modulation of the Wnt signaling pathway by sodium butyrate

The Wnt signaling pathway modulates the transcription of genes linked to proliferation, differentiation and tumor progression. beta-Catenin-Tcf (BCT)-dependent Wnt signaling is influenced by the short-chain fatty acid sodium butyrate, which induces growth arrest and/or maturation of colonic carcinoma cells. We have compared the effects of sodium butyrate on BCT-dependent signaling in 2 colon carcinoma cell lines that differ in their physiologic response to butyrate, with SW620 cells responding to butyrate by undergoing terminal differentiation and apoptosis, and HCT-116 cells undergoing reversible growth arrest, but no significant apoptotic cell death. Furthermore, these colon carcinoma cell lines differ in their mechanism of Wnt pathway activation, with adenomatous polyposis coli (APC) mutant SW620 cells having high levels of BCT complexes and APC wild-type HCT-116 cells having mutant beta-catenin, low levels of BCT complexes and correspondingly higher levels of free Tcf. We have demonstrated that in SW620 cells, butyrate downregulates BCT-dependent expression of the Tcf-TK, matrilysin and cyclin D1 promoters, whereas in HCT-116 cells, butyrate upregulates expression of these promoters. Cotransfection with expression vectors that interfere with the Wnt pathway suggests that butyrate enhances BCT complex-DNA binding. Butyrate reduces the expression of Tcf4 in HCT-116 cells, consistent with the induction by butyrate of Tcf-repressible promoters in these cells. These findings indicate that sodium butyrate modulates the Wnt pathway in SW620 and HCT-116 cells in a different manner and that these differences have consequences for promoter activity that may influence the physiologic response to butyrate.

Regulation and possible function of beta-catenin in human monocytes

In this study, we demonstrate that adherence factors, serum constituents, LPS, and zymosan are capable of inducing a cellular accumulation of beta-catenin in human monocytes. Whereas adherence-dependent accumulation of beta-catenin can be blocked by wortmannin, an inhibitor of phosphatidylinositol 3-kinase, accumulation induced by the remaining stimuli cannot be prevented by inhibition of phosphatidylinositol 3-kinase, implying the involvement of beta-catenin in other not yet described signal transduction pathways. A role of beta-catenin in adherence-dependent processes by interacting with classical cadherins can be excluded as we could not detect cadherins in monocytes. To test whether it is possible that beta-catenin interacts with LEF/TCF (lymphoid enhancer factor/T cell factor) transcription factors, we studied the expression of this protein family. TCF-4 was identified as the LEF/TCF transcription factor present in human monocytes. However, neither cellular induction of beta-catenin nor cotransfection experiments with beta-catenin conducted in the monocytic cell line THP-1 resulted in the activation of a LEF/TCF-dependent promoter, suggesting the requirement of additional signals. Concurrent with this suggestion, we found that LPS and zymosan, two physiological inducers of beta-catenin, caused an increase in the expression of genes that are positively regulated by beta-catenin.

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

Mutations in the region corresponding to the N-terminal phosphorylation sites (codons 1-51) of the rat beta-catenin gene (Ctnnb1) were investigated in rat colon tumors induced by 1-hydroxyanthraquinone (1-HA) plus methylazoxymethanol (MAM) acetate, by using polymerase chain reaction (PCR)-single-strand conformation polymorphism (SSCP) analysis. The beta-catenin gene was also screened for mutations in rat brain and oral tumors induced by ethyl nitrosourea (ENU) and 4-nitroquinoline 1-oxide (4-NQO), respectively. In colon tumors, beta-catenin gene mutations were found in two of three adenomas (67%) and 26 of 28 adenocarcinomas (93%), with a total incidence of 90% (28 of 31 adenomas plus adenocarcinomas). Eight (29%) were (34)G-->T (second position), eight (29%) were (32)G-->A (first position), five (18%) were (34)G-->A (first position), five (18%) were (41)C-->T (second position), one (4%) was (34)G-->A (second position), and one (4%) was (32)A-->G (second position), mutations, resulting in the substitutions of Gly(34)-->Val, Asp(32)-->Asn, Gly(34)-->Arg, Thr(41)-->Ile, Gly(34)-->Glu, and Asp(32)-->Gly, respectively. The (34)G-->T (second position) mutations found in this study were unique compared to those found in other carcinogen-induced rat colon carcinogenesis models. In contrast, beta-catenin gene mutations were not found in either the brain or oral tumors. These results suggest that mutations in the beta-catenin gene in rat tumors occur in specific tissues or organ sites and in a carcinogen-specific manner. Thus, the mutation spectrum in the beta-catenin gene is organ- and chemical carcinogen-specific.

Progressive changes in adherens junction structure during intestinal adenoma formation in Apc mutant mice

The C57BL/6J-Min/+ (Min/+) mouse bears a mutant Apc gene and therefore is an important in vivo model of intestinal tumorigenesis. Min/+ mice develop adenomas that exhibit loss of the wild-type Apc allele (Apc(Min/-)). Previously, we found that histologically normal enterocytes bearing a truncated Apc protein (Apc(Min/+)) migrated more slowly in vivo than enterocytes with either wild-type Apc (Apc(+/+)) or with heterozygous loss of Apc protein (Apc(1638N)). To study this phenotype further, we determined the effect of the Apc(Min) mutation upon cell-cell adhesion by examining the components of the adherens junction (AJ). We observed a reduced association between E-cadherin and beta-catenin in Apc(Min/+) enterocytes. Subcellular fractionation of proteins from Apc(+/+), Apc(Min/+), and Apc(Min/-) intestinal tissues revealed a cytoplasmic localization of intact E-cadherin only in Apc(Min/+), suggesting E-cadherin internalization in these enterocytes. beta-Catenin tyrosine phosphorylation was also increased in Apc(Min/+) enterocytes, consistent with its dissociation from E-cadherin. Furthermore, Apc(Min/+) enterocytes showed a decreased association between beta-catenin and receptor protein-tyrosine phosphatase beta/zeta (RPTPbeta/zeta), and Apc(Min/-) cells demonstrated an association between beta-catenin and receptor protein-tyrosine phosphatase gamma. In contrast to the Apc(Min/+) enterocytes, Apc(Min/-) adenomas displayed increased expression and association of E-cadherin, beta-catenin, and alpha-catenin relative to Apc(+/+) controls. These data show that Apc plays a role in regulating adherens junction structure and function in the intestine. In addition, discovery of these effects in initiated but histologically normal tissue (Apc(Min/+)) defines a pre-adenoma stage of tumorigenesis in the intestinal mucosa.

Studies on human colon cancer gene APC by targeted expression in Drosophila

Mutations in human Adenomatous Polyposis Coli (APC) gene are associated with both familial and sporadic colorectal tumors. APC is known to down regulate beta-catenin levels, a transducer of Wnt signaling. The aim of this study is to provide transgenic Drosophila expressing either full-length or truncated forms of human APC (hAPC) protein and methods for using them in functional genomics and drug screening. Consistent with its biochemical properties, targeted expression of either full-length hAPC or its beta-catenin binding domain alone negatively regulated the function of the beta-catenin homologue, Armadillo (Arm) and thereby, inhibited Wnt/Wg signaling during fly development. hAPC inhibited Arm function even in the absence of GSK-3beta activity, although the latter was required to mediate the degradation of Arm. Consistent with this, hAPC suppressed the phenotypes induced by the over-expression of degradation-resistant forms of Arm. Subsequently, using hAPC-induced eye phenotypes as the assay in a suppressor-enhancer screen, we have identified two new loci in Drosophila, which modulate Wnt/Wg signaling. In addition, an anti-colon cancer drug, indomethacin, specifically enhanced hAPC-induced phenotypes.

beta-catenin expression in pilomatrixomas. Relationship with beta-catenin gene mutations and comparison with beta-catenin expression in normal hair follicles

BACKGROUND

beta-catenin functions in signal transduction in the Wnt signalling pathway, which has recently been implicated in hair follicle (HF) morphogenesis. beta-catenin gene mutations affecting exon 3 have been reported in a high percentage of human pilomatrixomas. However, the expression pattern of beta-catenin in human HFs and pilomatrixomas has not been reported.

OBJECTIVES

To analyse immunohistochemically the expression pattern of beta-catenin in normal anagen HFs and in 40 human pilomatrixomas.

METHODS

In 11 of these tumours we also studied exon 3 beta-catenin gene mutations by polymerase chain reaction and direct sequencing. As these mutations have been related to a replication error (RER) phenotype in other tumour types, we explored whether or not this association also occurs in pilomatrixomas.

RESULTS

beta-catenin was expressed in the cell membranes of the outer and inner root sheaths and in matrix cells located at the base and periphery of the HF bulb. However, central matrix cells that differentiate into cortical cells, cortical and cuticular cells expressed beta-catenin in the nucleus, suggesting a role in signal transduction. In addition, some fibroblasts of the dermal papilla also showed nuclear expression of beta-catenin. All 40 analysed pilomatrixomas showed intense nuclear and cytoplasmic beta-catenin expression in proliferating matrix (basaloid) cells. In areas of maturation, transitional cells mainly showed cytoplasmic and membranous expression of beta-catenin, while only a few cells retained nuclear expression. Shadow or ghost cells did not show beta-catenin expression. Three of 11 tumours (26%) had beta-catenin mutations. All three had the same heterozygote mis-sense mutation: a G to T change affecting the first nucleotide at codon 32 (D32Y). None of the 11 tumours studied had a positive RER phenotype.

CONCLUSIONS

Present and previous studies suggest that the Wnt/beta-catenin/Tcf-Lef pathway is activated in normal matrix cells of the HF to induce differentiation to the hair shaft. Additionally, the beta-catenin mutation in matrix cells of the HF stabilizes beta-catenin protein, which translocates into the nucleus, where it activates of gene transcription together with lymphoid enhancer factor-1 producing pilomatrixoma. These mutations occur without an underlying defect in DNA mismatch repair.

Extensive characterization of genetic alterations in a series of human colorectal cancer cell lines

A number of genetic alterations have been described in colorectal cancers. They include allelic losses on specific chromosomal arms, mutations of oncogenes, tumor suppressor genes and mismatch repair genes, microsatellite instability in coding repeat sequences of target genes and methylation defects in gene promoters. Since these alterations have been reported by different groups on different tumors and cell lines, the complete repertoire of genetic alterations for any given tumor sample remains unknown. In the present study, we analysed a series of 22 colorectal cancer cell lines for 31 different genetic alterations. We found significant correlations between mutational profiles in these colorectal cell lines associated with differences in mismatch repair status. This panel of colon cancer cell lines is representative of the genetic heterogeneity occurring in sporadic colorectal carcinoma. Our results may prove to be very useful for understanding the different biological pathways involved in the development of colon cancer, and for groups studying cellular biology and pharmacology on the same cell lines.

Protein phosphatase 2A and its B56 regulatory subunit inhibit Wnt signaling in Xenopus

Wnt signaling increases beta-catenin abundance and transcription of Wnt-responsive genes. Our previous work suggested that the B56 regulatory subunit of protein phosphatase 2A (PP2A) inhibits Wnt signaling. Okadaic acid (a phosphatase inhibitor) increases, while B56 expression reduces, beta-catenin abundance; B56 also reduces transcription of Wnt-responsive genes. Okadaic acid is a tumor promoter, and the structural A subunit of PP2A is mutated in multiple cancers. Taken together, the evidence suggests that PP2A is a tumor suppressor. However, other studies suggest that PP2A activates Wnt signaling. We now show that the B56, A and catalytic C subunits of PP2A each have ventralizing activity in Xenopus embryos. B56 was epistatically positioned downstream of GSK3beta and axin but upstream of beta-catenin, and axin co-immunoprecipitated B56, A and C subunits, suggesting that PP2A:B56 is in the beta-catenin degradation complex. PP2A appears to be essential for beta-catenin degradation, since beta-catenin degradation was reconstituted in phosphatase-depleted Xenopus egg extracts by PP2A, but not PP1. These results support the hypothesis that PP2A:B56 directly inhibits Wnt signaling and plays a role in development and carcinogenesis.

Superficial fibromatoses are genetically distinct from deep fibromatoses

Whereas deep fibromatoses (abdominal, extra-abdominal, mesenteric) display locally aggressive behavior, superficial fibromatoses typically remain small and less likely to recur despite essentially identical morphology. Somatic beta-catenin or APC gene mutations have been reported in < or =74% of sporadic deep fibromatoses and in virtually 100% of Gardner syndrome-associated fibromatoses, whereas genetic events in superficial fibromatoses remain less well characterized. We performed immunohistochemical staining for beta-catenin on 29 superficial fibromatoses (22 palmar, 5 plantar, 1 penile, and 1 infantile digital fibromatosis) and 5 deep fibromatoses. Mutations of beta-catenin and APC genes were analyzed in cases of superficial fibromatoses by direct DNA sequencing of the beta-catenin gene on Exon 3 encompassing the GSK-3 36 phosphorylation region and of the APC gene on the mutation cluster region. Nuclear accumulation of beta-catenin was present in 86% (25/29) of superficial fibromatosis cases ranging from 5 to 100% of nuclei (mean, 13%; median, 10%), though in a minority of nuclei in most examples. Deep fibromatoses had 60 to 100% nuclear staining in all five cases. No somatic mutations of beta-catenin or APC genes were identified in any of the superficial fibromatoses. In contrast to deep fibromatoses, superficial fibromatoses lack beta-catenin and APC gene mutations; the significance of focal nuclear beta-catenin accumulation is unclear. This difference may account inpart for their divergent clinical manifestations despite their morphologic resemblance to deep fibromatoses.

Mutations of the beta- and gamma-catenin genes are uncommon in human lung, breast, kidney, cervical and ovarian carcinomas

Beta-catenin forms complexes with Tcf and Lef-1 and functions as a transcriptional activator in the Wnt signalling pathway. Although recent investigations have been focused on the role of the adenomatous polyposis coli (APC)/ beta-catenin/Tcf pathway in human tumorigenesis, there have been very few reports on mutations of the beta-catenin gene in a variety of tumour types. Using PCR and single-strand conformational polymorphism analysis, we examined 93 lung, 9 breast, 6 kidney, 19 cervical and 7 ovarian carcinoma cell lines for mutations in exon 3 of the beta-catenin gene. In addition, we tested these same samples for mutations in the NH2-terminal regulatory region of the gamma-catenin gene. Mutational analysis for the entire coding region of beta-catenin cDNA was also undertaken in 20 lung, 9 breast, 5 kidney and 6 cervical carcinoma cell lines. Deletion of most beta-catenin coding exons was confirmed in line NCI-H28 (lung mesothelioma) and a silent mutation at codon 214 in exon 5 was found in HeLa (cervical adenocarcinoma). A missense mutation at codon 19 and a silent mutation at codon 28 in the NH2-terminal regulatory region of the gamma-catenin gene were found in H1726 (squamous cell lung carcinoma) and H1048 (small cell lung carcinoma), respectively. Neither deletions nor mutations of these genes were detected in the other cell lines examined. These results suggest that beta- and gamma-catenins are infrequent mutational targets during development of human lung, breast, kidney, cervical and ovarian carcinomas.

APC senses cell-cell contacts and moves to the nucleus upon their disruption

The adenomatous polyposis coli (APC) tumor suppressor protein is involved in the Wnt/wingless pathway, modulating beta-catenin activity. We report the development of a highly specific, chemically synthesized oligobody (oligonucleotide-based synthetic antibody), directed against the N-terminal region of APC. Using this reagent, we found that within 16 h of disrupting HT-29 cell-cell contacts by harvesting cells with trypsin/EDTA treatment and replating, APC was translocated from the cytoplasm to the nucleus. Five days after plating the cells, when the cells had returned to their normal confluent phenotype and cell-cell contacts were reestablished, APC returned to the cytoplasm. These results suggest that APC functions as part of a "sensor" system, and responds to the loss of cell-cell contacts by moving to the nucleus, and returning to the cytoplasm when the contacts are fully restored.

E-, N- and P-cadherin, and alpha-, beta- and gamma-catenin protein expression in normal, hyperplastic and carcinomatous human prostate

The expression of E-, N- and P-cadherin, alpha-, beta- and gamma-catenin, and actin was studied by immunohistochemistry, ELISA, and Western blot analysis in normal prostates, and in the prostates of men with benign prostatic hyperplasia and men with prostatic carcinoma, in order to evaluate their possible role in the pathogenesis of these diseases. Present results reveal that the immunophenotype of hyperplastic prostates differs from those of both normal and carcinomatous prostates in the intracellular distribution (observed by immunohistochemistry) and the intensity (measured by ELISA) of immunoreactions to cadherins, catenins, and actin. Hyperplastic prostates differ form normal prostates in the weaker immunoreaction to the three cadherin types, the two catenins, and actin, as well as in the intracellular distribution of P-cadherin, beta- and gamma-catenin, and actin. Differences between benign prostatic hyperplasia and prostatic carcinoma are less marked because hyperplastic prostates differ from carcinomatous prostates only in the weaker immunoreactions to P-cadherin, and alpha-catenin. The most remarkable findings in this study were: (1) alpha-catenin production was elevated in prostatic carcinoma in comparison with benign prostatic hyperplasia and normal prostate; and (2) P-cadherin expression in benign prostatic hyperplasia is reduced with regard to those of normal and carcinomatous prostates. It may be concluded that a decreased immunoreaction to cadherins, catenins, and actin, as well as changes in the intracellular distribution of actin in prostatic cells are not necessarily suggestive of malignancy, because these alterations are also present in BPH, and thus, the loss of cadherin-catenin-mediated adhesion alone is not sufficient to establish an invasive phenotype.

beta-Catenin expression pattern, beta-catenin gene mutations, and microsatellite instability in endometrioid ovarian carcinomas and synchronous endometrial carcinomas

beta-Catenin gene mutations and microsatellite instability (MI) have been reported in endometrioid ovarian carcinomas. In colon but not endometrial cancer, beta-catenin gene mutations are associated with a replication error phenotype and MI. In this study the authors investigate whether beta-catenin mutations and MI are two independent oncogenic pathways in endometrioid ovarian carcinomas. They also evaluate the usefulness of these molecular markers in determining the primary origin of simultaneous tumors in the ovary and endometrium. This study was performed on 26 patients diagnosed with primary endometrioid ovarian carcinoma, five of whom also had pathologically diagnosed primary synchronous endometrioid endometrial carcinoma. Immunohistochemical and molecular analyses indicated that there were 25 primary ovarian tumors with four primary synchronous endometrial cancers and one ovarian metastasis of a primary endometrial carcinoma. All studies were performed on formalin-fixed, paraffin-embedded tissue samples. The beta-catenin expression pattern (nuclear vs. membranous) was analyzed immunohistochemically. Mutations in exon 3 of the beta-catenin gene were studied by polymerase chain reaction, single-strand conformational polymorphism, and direct sequencing. MI status was established by studying BAT-26 and BAT-25 mononucleotide repeats. In the group with 21 single ovarian tumors, 18 (85%) had beta-catenin nuclear expression, eight (38%) had beta-catenin gene mutations (always associated with beta-catenin nuclear expression), and four (19%) had MI. Only one case (5%) had both beta-catenin gene mutations and MI. The mutations affected one of the serine/threonine residues targeted for phosphorylation by glycogen synthase kinase-3beta or adjacent residues. At codon 32, a GAC-to-TAC (D32Y) change was found; at codon 33, two TCT-to-TGT (S33C) changes were found; at codon 37, three TCT-to-TTT (S37F) changes and one TCT-to-TGT (S37C) change were found; and, lastly, one ACC-to-GCC change at codon 41 (T41A) was detected. Four of the 25 endometrioid ovarian carcinomas (16%) had an associated synchronous endometrial carcinoma. There was a higher percentage of beta-catenin mutations (n = 3, 75%) in synchronous ovarian carcinomas than in single ones, although with a similar percentage of MI (n = 1, 25%). beta-catenin mutations were S37C in two cases and D32G in one. One of the four endometrial carcinomas showed an S33C beta-catenin mutation, and two carcinomas had MI. None of the four tumors had both beta-catenin gene mutation and MI. beta-catenin gene mutations were always associated with a nuclear beta-catenin expression pattern, whereas MI was associated with a membranous pattern. In one patient both the ovarian and the endometrial carcinomas had beta-catenin gene mutations, in another patient both tumors showed MI, whereas in the remaining two patients the ovarian carcinomas showed beta-catenin gene mutations and the endometrial carcinomas showed MI. To summarize, the results of this study suggest that beta-catenin mutations and MI could represent two independent pathways in endometrioid ovarian carcinomas because they occur simultaneously very infrequently (in 5% of these cases). beta-catenin mutations are always associated with a nuclear beta-catenin expression pattern, whereas cases with a replication error -plus phenotype showed no abnormal beta-catenin subcellular localization. The study of the beta-catenin expression pattern, beta-catenin mutations, and MI, together with conventional clinicopathologic findings, could aid in distinguishing between the metastatic or independent origin of simultaneous endometrioid ovarian and endometrial carcinomas. Tumors with identical immunohistochemical and molecular features should therefore be considered to have a common origin.

Specific down-regulation of an engineered human cyclin D1 promoter by a novel DNA-binding ligand in intact cells

Cyclin D1 is expressed at abnormally high levels in many cancers and has been specifically implicated in the development of breast cancer. In this report we have extensively analyzed the cyclin D1 promoter in a variety of cancer cell lines that overexpress the protein and identified two critical regulatory elements (CREs), a previously identified CRE at -52 and a novel site at -30. In vivo footprinting experiments demonstrated factors binding at both sites. We have used a novel DNA-binding ligand, GL020924, to target the site at -30 (-30-21) of the cyclin D1 promoter in MCF7 breast cancer cells. A binding site for this novel molecule was constructed by mutating 2 bp of the wild-type cyclin D1 promoter at the -30-21 site. Treatment with GL020924 specifically inhibited expression of the targeted cyclin D1 promoter construct in MCF7 cells in a concentration-dependent manner, thus validating the -30-21 site as a target for minor groove-binding ligands. In addition, this result validates our approach to regulating the expression of genes implicated in disease by targeting small DNA-binding ligands to key regulatory elements in the promoters of those genes.

The PEA3 subfamily of Ets transcription factors synergizes with beta-catenin-LEF-1 to activate matrilysin transcription in intestinal tumors

The matrix metalloproteinase matrilysin (MMP-7) is expressed in the tumor cells of a majority of mouse intestinal and human colonic adenomas. We showed previously that matrilysin is a target gene of beta-catenin-Tcf, the transcription factor complex whose activity is thought to play a crucial role in the initiation of intestinal tumorigenesis. Here we report that overexpression of a stable mutant form of beta-catenin alone was not sufficient to effect expression of luciferase from a matrilysin promoter-luciferase reporter plasmid. However, cotransfection of the reporter with an expression vector encoding the PEA3 Ets transcription factor, or its close relatives ER81 and ERM, increased luciferase expression and rendered the promoter responsive to beta-catenin-LEF-1 as well as to the AP-1 protein c-Jun. Other Ets proteins could not substitute for the PEA3 subfamily. Luciferase activity was induced up to 250-fold when PEA3, c-Jun, beta-catenin, and LEF-1 were coexpressed. This combination of transcription factors was also sufficient to induce expression of the endogenous matrilysin gene. Furthermore, all matrilysin-expressing benign intestinal tumors of the Min mouse expressed a member of the PEA3 subfamily, as did all human colon tumor cell lines examined. These data suggest that the expression of members of the PEA3 subfamily, in conjunction with the accumulation of beta-catenin in these tumors, leads to coordinate upregulation of matrilysin gene transcription, contributing to gastrointestinal tumorigenesis.

beta-Catenin mutation in rat colon tumors initiated by 1,2-dimethylhydrazine and 2-amino-3-methylimidazo[4,5-f]quinoline, and the effect of post-initiation treatment with chlorophyllin and indole-3-carbinol

Carcinogens 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and 1,2-dimethylhydrazine (DMH) induce colon tumors in the rat that contain mutations in beta-catenin, but the pattern of mutation differs from that found in human colon cancers. In both species, mutations affect the glycogen synthase kinase-3beta consensus region of beta-catenin, but whereas they directly substitute critical Ser/Thr phosphorylation sites in human colon cancers, the majority of mutations cluster around Ser33 in the rat tumors. Two dietary phytochemicals, chlorophyllin and indole-3-carbinol, given post-initiation, shifted the pattern of beta-catenin mutations in rat colon tumors induced by IQ and DMH. Specifically, 17/39 (44%) of the beta-catenin mutations in groups given carcinogen plus modulator were in codons 37, 41 and 45, and substituted critical Ser/Thr residues directly, as seen in human colon cancers. None of the tumors from groups given carcinogen alone had mutations in these codons. Interestingly, many of the mutations that substituted critical Ser/Thr residues in beta-catenin were from a single group given DMH and 0.001% chlorophyllin, in which a statistically significant increase in colon tumor multiplicity was observed compared with the group given DMH only. These tumors had marked over-expression of cyclin D1, c-myc and c-jun mRNA and c-Myc and c-Jun proteins were strongly elevated compared with tumors containing wild-type beta-catenin. The results indicate that the pattern of beta-catenin mutations in rat colon tumors can be influenced by exposure to dietary phytochemicals administered post-initiation, and that the mechanism might involve the altered expression of beta-catenin/Tcf/Lef target genes.

Altered distribution of beta-catenin, and its binding proteins E-cadherin and APC, in ulcerative colitis-related colorectal cancers

The beta-catenin pathway plays a central role in transcriptional signaling and cell-cell interactions in colonic epithelium. Alterations of the expression of beta-catenin, and its binding partners E-cadherin and the adenomatous polyposis coli protein (APC), are frequent events in sporadic colorectal cancer. Ulcerative colitis (UC)-related cancers originate in a field of chronic inflammation and therefore may have different alterations in the beta-catenin pathway than sporadic cancers. To test this hypothesis, expression and subcellular localization of beta-catenin, E-cadherin, and APC were detected by immunohistochemistry in paraffin sections from 33 UC-related and 42 sporadic colorectal cancers. Although beta-catenin and E-cadherin expression were predominantly limited to the lateral cell membrane in normal colonic epithelium, both tumor groups showed an overall shift from membranous to cytoplasmic expression for these proteins. An increase in nuclear localization of beta-catenin and a decrease in cytoplasmic APC expression also were seen in both cancer groups compared with normal epithelium. Abnormal beta-catenin expression was more closely linked to E-cadherin alterations in UC-related cancers than in sporadic cancers. In contrast, abnormal beta-catenin expression was more closely linked to APC alterations in sporadic cancers than in UC-related cancers. These data suggest that alterations of the beta-catenin pathway are important in both UC-related and sporadic colorectal cancers. However, differences in the expression patterns of beta-catenin, E-cadherin, and APC between UC-related and sporadic colorectal cancers suggest that the specific alterations in this pathway may differ in these two cancer groups.

beta- Catenin mutations and aberrant nuclear expression during endometrial tumorigenesis

To clarify the possible role of aberrant beta-catenin expression during endometrial tumorigenesis, a total of 199 cases of endometrial carcinomas (endometrioid type), as well as 37 cases of simple/complex and 32 of atypical hyperplasias, was consecutively investigated for immunohistochemistry, along with 141 normal endometrial samples distant from carcinomas. Of 199 carcinoma cases, 73 tumours as well as 44 normal samples were also analysed using a combination of RT-PCR and Southern blot hybridization, Western blot, and mutation gene assays. Cell membrane beta-catenin immunoreactivity showed a stepwise decrease from normal, through atypical hyperplasia, to grade 3 carcinomas. In contrast, the nuclear accumulation in atypical hyperplasias and grade 1 or 2 tumours was higher than in simple/complex hyperplasias. Mutations in exon 3 of the beta-catenin gene involving codons 33, 34, 37, 41, and 45 were observed in 16 (22.9%) of 70 endometrial carcinomas, as well as 3 (12.5%) of 24 atypical hyperplasias, the results being significantly related to low membrane and high nuclear immunoreactivity but not relative mRNA expression levels, suggesting that the gene mutations may be closely associated with changes in subcellular distribution. In addition to significant association between beta-catenin mutation and low grade histological malignancy (P = 0.048), the mutations were detected in none of 15 and 13 (26%) of 50 tumours with or without lymph node metastasis, the difference being significant (P = 0.027). These findings suggest that beta-catenin abnormalities may play an important role in a relatively early event during the endometrial hyperplasia-carcinoma sequence.

Analysis of beta-catenin mutations and alpha-, beta-, and gamma-catenin expression in normal and neoplastic human pituitary tissues

The cadherin-catenin system mediates Ca(2+)-dependent cell-cell adhesion, and genetic alterations in these molecules play a significant role in multistage carcinogenesis. Mutations in the beta-catenin gene, mostly affecting exon 3, have been detected in malignant cell lines and in primary tumors. Immunohistochemical abnormalities in alpha-, beta-, and gamma-catenin have been reported in malignant and benign tumors, and nuclear localization of beta-catenin has been associated with mutations in exon 3 of this gene. Mutational analysis of exon 3 of the beta-catenin gene was undertaken by polymerase chain reaction (PCR) and sequencing using genomic DNA extracted from frozen tissues, including 4 normal pituitaries, 22 pituitary adenomas, and one pituitary carcinoma. Frozen sections from these cases were used for immunohistochemical detection of beta-catenin. We also analyzed immunohistochemical expression of alpha-, beta-, and gamma-catenin by paraffin sections from 154 pituitary tumors, including 148 adenomas and 6 carcinomas. Genomic DNA was extracted from paraffin sections of 2 gonadotroph tumors showing nuclear staining for beta-catenin and was used for PCR and sequencing of exon 3 of the beta-catenin gene. No mutations in exon 3 of the beta-catenin gene were found in any of the 23 cases analyzed by PCR and sequencing. In addition, the 2 cases studied by paraffin section immunohistochemistry, with nuclear staining for beta-catenin, were negative for mutations in this exon. Normal pituitary expressed all three catenin proteins. Immunostaining usually showed a membranous pattern of reactivity and was generally stronger in normal pituitary than in the adjacent adenomas. Stains for alpha-catenin were positive in fewer tumors than for beta-catenin. The lowest frequency immunopositive tumors and the weakest immunostaining was for gamma-catenin. All medically treated prolactinomas were negative for gamma-catenin, whereas treated growth hormone adenomas were less often positive for both alpha- and gamma-catenin than for untreated tumors. The percentage of positive cases for beta-catenin was the same in these two groups. Most pituitary carcinomas were negative for both alpha- and gamma-catenin but were beta-catenin positive. These results indicate that (i) mutations in exon 3 of the beta-catenin gene are uncommon in pituitary tumors, and (ii) expression of alpha-, beta-, and gamma-catenin is decreased in pituitary adenomas compared to normal pituitary tissues.

Prognostic value of the preserved expression of the E-cadherin and catenin families of adhesion molecules and of beta-catenin mutations in synovial sarcoma

This study addresses the immunohistochemical expression of the E-cadherin and catenin families and mutations of the beta-catenin gene detected by PCR-SSCP in synovial sarcoma. Immunohistochemical analysis was performed for 72 cases, with follow-up data available on 62. The prognostic value of the expression of these proteins was evaluated. Reduced immunoreactivity for E-cadherin and alpha-catenin was significantly correlated with a poor survival rate (p=0.0040 and 0.0053, respectively). According to multivariate analysis, low AJC stage (stages I and II: p<0.0001), the preservation of alpha-catenin expression (p=0.0001), and a low necrotic rate (<50%: p=0.0139) were independent favourable prognostic factors. Widespread aberrant staining of beta-catenin protein within cytoplasm and/or nuclei was observed in 28 cases (38.9%) and was significantly correlated with poor survival (p=0.0122). In addition, there was a trend towards a correlation between widespread aberrant staining of beta-catenin and the MIB-1 labelling index (p=0.0535). Mutational analysis of exon 3 of the beta-catenin gene was performed for 49 cases. Nucleotide sequencing analysis revealed that four (8.2%) contained point mutations (three in codon 32, GAC to TAC; one in codon 37, TCT to TTT). Survival data were available for three out of four cases with beta-catenin mutations; two of these patients died within 1 year (died of disease at 6 and 11 months, respectively). These results suggest that E-cadherin and alpha-catenin undertake important roles as intercellular adhesion molecules; their preserved expression is associated with a better overall survival rate in synovial sarcoma and may have prognostic value. Abnormal levels of beta-catenin, with or without mutation, could contribute to the development and progression of synovial sarcoma, through increasing the proliferative activity of the tumour cells.

Insulin-like growth factor 1 regulates the location, stability, and transcriptional activity of beta-catenin

The insulin-like growth factor (IGF) type 1 receptor is required for growth, transformation, and protection from apoptosis. IGFs can enhance cell migration, which is known to be influenced via regulation of the E-cadherin/beta-catenin complex. We sought to investigate whether IGF-1 modulated the interaction between E-cadherin and beta-catenin in human colorectal cancer cells. We used the C10 cell line, which we established and have previously shown to lack adenomatous polyposis coli, E-cadherin, or beta-catenin mutations. We found that IGF-1 stimulation enhanced tyrosine phosphorylation of two proteins, beta-catenin and insulin-receptor substrate 1, which formed a complex with E-cadherin. Tyrosine phosphorylation of beta-catenin was accompanied by rapid (<1 min) dissociation from E-cadherin at the plasma membrane, followed by relocation to the cellular cytoplasm. IGF-1 also enhanced the stability of beta-catenin protein. Despite this, we observed no enhancement of transcriptional activity in complex with T-cell factor 4 (Tcf-4) in human embryonic kidney 293 cells treated with IGF-1 or insulin alone. IGF-1 did, however, enhance transcriptional activity in combination with lithium chloride, an inhibitor of glycogen synthase kinase 3 beta, which also stabilizes beta-catenin. In conclusion, we have shown that IGF-1 causes tyrosine phosphorylation and stabilization of beta-catenin. These effects may contribute to transformation, cell migration, and a propensity for metastasis in vivo.

Mutational analysis of the CTNNB1 and APC genes in uterine endometrioid carcinoma

Despite recent studies, the molecular genetic events responsible for the development of uterine endometrioid carcinoma (UEC) remain incompletely characterized. Mutations in the beta-catenin (CTNNB1) gene have been recently reported in a small percentage of UECs and in the endometrioid variant of ovarian carcinoma suggesting that the Wnt signal transduction pathway is involved in the development of female genital tract tumors with endometrioid morphology. The Wnt pathway is a critical pathway in the development of colorectal cancer (CRC) with mutations occurring in the beta-catenin (CTNNB1) or adenomatous polyposis coli (APC) genes in 10 to 15% and 85% of cases, respectively. Because UEC and CRC share other molecular genetic alterations and histologic features and previous studies of UEC have not reported an analysis of the APC gene, we chose to further elucidate the role of the Wnt pathway in UEC. To this end, we analyzed 32 cases of UEC for mutations of the CTNNB1 and APC genes. Mutations of CTNNB1 were present in six of 32 (18%) cases: four grade 1 carcinomas, one grade 2, and one grade 3 carcinoma. Five missense mutations were identified, three involving Ser/Thr phosphorylation sites and two adjacent to a Ser phosphorylation site. One case contained a deletion encompassing codons 34 to 37, which includes a Ser phosphorylation site. No mutations resulting in truncation of the APC protein were found. Our results support a role for the Wnt signaling pathway via mutation of CTNNB1, but not APC, in the development of a subset of UECs.

Altered expression of beta-catenin, inducible nitric oxide synthase and cyclooxygenase-2 in azoxymethane-induced rat colon carcinogenesis

Activation of the beta-catenin/T cell factor-mediated transcription pathway through mutations of the APC or beta-catenin gene is suggested to play an important role in colon carcinogenesis and there is great interest in the target genes. We have described the frequent mutation and an altered cellular localization of beta-catenin in rat colon adenocarcinomas induced by azoxymethane (AOM), along with up-regulation of inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2. In the present study, the relation between beta-catenin alteration and expression of iNOS and COX-2 in AOM-induced rat colon carcinogenesis was examined in hyperplastic and dysplastic type aberrant crypt, adenoma and adenocarcinoma samples. K-ras gene mutations were also investigated. Mutation analysis by the PCR-single strand conformation polymorphism method and direct sequencing demonstrated the beta-catenin gene to be mutated in two of three dysplastic aberrant crypt foci (ACF), two of six adenomas and 20 of 26 adenocarcinomas, while K-ras was mutated in seven of 10 hyperplastic ACF and seven of 26 adenocarcinomas. Immunohistochemical staining showed an alteration in cellular localization of beta-catenin in all dysplastic ACF, adenomas and adenocarcinomas examined. iNOS expression was also observed in all but one of the lesions in which beta-catenin alterations were observed. Neither iNOS expression nor beta-catenin alterations were observed in any hyperplastic ACF. COX-2 expression in stromal elements was found even in normal colon mucosa and increased in adenomas and adenocarcinomas, while epithelial cells were only positive in large adenocarcinomas. These results show that beta-catenin alterations may be related to induction of iNOS expression, these being early events in AOM-induced colon tumorigenesis which may play important roles in causing dysplastic changes.

alpha-catenin inhibits beta-catenin signaling by preventing formation of a beta-catenin*T-cell factor*DNA complex

alpha-Catenin and beta-catenin link cadherins to the cytoskeleton at adherens junctions. beta-Catenin also associates with members of the T-cell factor (Tcf) family of transcription factors, and mutations in beta-catenin lead to activation of Tcf-dependent transcription and increased cell growth. Although the loss of alpha-catenin expression can also promote cell growth, the role of endogenous alpha-catenin in beta-catenin signaling is unclear. Here we show that loss of alpha-catenin expression in a colon cancer cell line correlates with increased Tcf-dependent transcription. The presence of alpha-catenin in colon cancer cell nuclei suggests that it inhibits transcription directly, and, in agreement with this, ectopic expression of alpha-catenin in the nucleus represses Tcf-dependent transcription. Furthermore, recombinant alpha-catenin disrupts the interaction between the beta-catenin.Tcf complex and DNA. We conclude that alpha-catenin inhibits beta-catenin signaling in the nucleus by interfering with the formation of a beta-catenin. Tcf.DNA complex.