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Query: UMLS:C0699790 (colon cancer)
 28,837 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To clarify the molecular mechanisms of human carcinogenesis associated with abnormal Wnt/wingless signaling, we searched for genes the expression of which was significantly altered by introduction of wild-type AXIN1 into LoVo colon cancer cells. By means of a cDNA microarray, we compared expression profiles of LoVo cells infected with either adenoviruses expressing wild-type AXIN1 (Ad-Axin) or those expressing a control gene (Ad-LacZ). Among the genes showing altered expression, the ectodermal-neural cortex 1 (ENC1) gene was down-regulated in response to Ad-Axin. The promoter activity of ENC1 was elevated approximately 3-fold by transfection of an activated form of beta-catenin together with wild-type T-cell factor (Tcf)4 in HeLa cells. Semiquantitative reverse transcription-PCR experiments revealed that expression of ENC1 was increased in more than two-thirds of 24 primary colon cancer tissues that we examined compared with corresponding noncancerous mucosae. Introduction of exogenous ENC1 increased the growth rate of HCT116 colon cancer cells in serum-depleted medium. In other experiments, overexpression of ENC1 in HT-29 colon cancer cells suppressed the usual increase of two differentiation markers, in response to treatment with sodium butyrate, a differentiation-inducible agent. These data suggest that ENC1 is regulated by the beta-catenin/Tcf pathway and that its altered expression may contribute to colorectal carcinogenesis by suppressing differentiation of colonic cells.
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PMID:Up-regulation of the ectodermal-neural cortex 1 (ENC1) gene, a downstream target of the beta-catenin/T-cell factor complex, in colorectal carcinomas. 1169 83

Accumulation of the Wnt pathway effector beta-catenin is a hallmark of a number of cancers, including colon cancer. As beta-catenin accumulates in the cell, it forms a complex with Tcf family transcription factors and activates the transcription of several critical genes involved in cell proliferation. Because Tcf4 is the predominant Tcf factor present in colon cancer cells, drugs that specifically disrupt the beta-catenin-Tcf4 complex could be useful in treating colon cancers. Earlier structural and biochemical studies demonstrated that the central region of the beta-catenin binding domain of Tcf is essential for anchoring Tcf to beta-catenin via two conserved lysines in beta-catenin (called the charged 'buttons'). Here we report the crystal structure of a beta-catenin-Tcf4 complex at 2.0 A resolution. Our structural and mutagenesis studies show that Tcf4 docks specifically to beta-catenin using several distinct conformations in its essential central region. These conformations allow different glutamate residues in the central region of Tcf4 to form a salt bridge with the same critical charged button, Lys 312 of beta-catenin. We propose that this interaction may be the first event in beta-catenin-Tcf4 recognition.
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PMID:Tcf4 can specifically recognize beta-catenin using alternative conformations. 1171 75

Genetic studies have identified mutations in key regulators of the Wnt/beta-catenin pathway in a variety of cancers, most frequently in colon cancers. However, whether the pathway is activated in clinical cancer samples is not easily determined, and therefore it is useful to find markers that could be surrogates to show activation of the Wnt/beta-catenin pathway. Gene expression profiles were analyzed in SW620, a colon cancer cell line in which beta-catenin levels are stabilized as a consequence of truncated adenomatous polyposis coli and were compared with profiles of the same cells transfected with antisense oligodeoxynucleotides. Treatment of cells with beta-catenin antisense oligodeoxynucleotides resulted in a decrease in the levels of axin2 and human naked cuticle (hnkd) mRNAs. Interestingly, the proteins encoded by both of these mRNAs are known inhibitors of the beta-catenin pathway. In 30 human cell lines derived from different origins, axin2 and hnkd were expressed only in human colon cancer cell lines that are known to have activating mutations in the Wnt/beta-catenin pathway. Further, levels of both axin2 and hnkd mRNA were also found to be elevated in about 65% of laser microdissected cells from human colon tumors compared with laser microdissected cells of normal morphology from the same patient samples. The increased expression of axin2 and hnkd correlated with truncations in adenomatous polyposis coli in the same patient samples. These results reveal that it is possible to detect activation of a carcinogenic pathway in human cancer samples with specific markers.
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PMID:Elevated expression of axin2 and hnkd mRNA provides evidence that Wnt/beta -catenin signaling is activated in human colon tumors. 1175 46

WNT signaling pathway is implicated in embryogenesis as well as in carcinogenesis. We have previously cloned and characterized Frizzled-1 (FZD1), FZD2, FZD3, FZD4, FZD5, FZD6, FZD7, FZD8, and FZD10, encoding seven-transmembrane-type WNT receptors. Here, expression of FZD10 mRNA in various types of human cancer and effects of FZD10 mRNA microinjection into Xenopus early embryos were investigated. Northern blot analyses revealed relatively high-level expression of 4.0-kb FZD10 mRNA in cervical cancer cell lines HeLa S3, SKG-I, SKG-IIIa, and in a glioblastoma cell line A-172. Matched tumor/normal expression array analysis revealed significant up-regulation of FZD10 mRNA in 2 cases of primary colon cancer. Function of FZD10 was next investigated by using Xenopus axis duplication assay, in which positive regulators of the WNT - beta-catenin - TCF signaling pathway induce axis duplication. Injection of wild-type FZD10 mRNA into the ventral marginal zone of 4-cell-stage Xenopus embryos induced partial axis duplication in 40% of embryos. Ventral injection of Thr579Ala FZD10 mRNA or Val581Leu FZD10 mRNA with mutations in the C-terminal Ser/Thr-X-Val motif also induced partial axis duplication in about 40% of embryos. Furthermore, ventral injection of FZD10 mRNA significantly augmented the potential of co-injected Xenopus wnt-8 (Xwnt-8) mRNA to induce complete axis duplication. These results suggest that up-regulation of FZD10 mRNA in several types of human cells might lead to carcinogenesis through activation of the beta-catenin - TCF signaling pathway synergistically with some class of WNTs.
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PMID:Frizzled-10, up-regulated in primary colorectal cancer, is a positive regulator of the WNT - beta-catenin - TCF signaling pathway. 1178 18

Mutation of the adenomatous polyposis coli and beta-catenin genes in colon cancer leads to constitutive activation of transcription from promoters containing binding sites for Tcf/LEF transcription factors. We have constructed adenoviruses with Tcf binding sites in the early promoters, in order to target viral replication to colon tumours. Tcf regulation of the E1A promoter confers a 100-fold selectivity for cells with activated wnt signalling in viral burst and cytopathic effect assays. p300 is a coactivator for beta-catenin, and E1A inhibits Tcf-dependent transcription through sequestration of p300, but mutation of the p300 binding site in E1A leads to a 10-fold reduction in cytopathic effect of all of the Tcf-regulated viruses. When Tcf sites are inserted in the E1A, E1B, E2 and E4 promoters the viruses show up to 100 000-fold selectivity for cells with activated wnt signalling.
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PMID:Adenoviruses with Tcf binding sites in multiple early promoters show enhanced selectivity for tumour cells with constitutive activation of the wnt signalling pathway. 1189 66

Accumulation of beta-catenin in cytoplasm and nuclei is frequently observed in a wide variety of tumors arising, for example, in the colon, liver, uterus, or brain. In association with Tcf/LEF transcription factors, beta-catenin regulates expression of genes involved in the Wnt/wingless signaling pathway, but the precise mechanisms are unclear. Here we report evidence that the claudin-1 (CLDNI) gene is one of the genes regulated by beta-catenin. Not only did expression of CLDN1 decrease significantly in response to reduction of intracellular beta-catenin by adenovirus-mediated transfer of wild-type APC into the APC-deficient colon cancer cells, but also two putative Tcf4 binding elements in the 5' flanking region of CLDN1 were confirmed to be responsible for activating its transcription. We documented increased expression of CLDN1 in all 16 primary colorectal cancers we examined, compared with adjacent noncancerous mucosae. Furthermore, immunohistochemical staining demonstrated that claudin-1 was weakly stained at apical boarder of lateral membrane of noncancerous epithelial cells and that it was strongly stained at all cell-cell boundaries and in the cytoplasms of cancer cells. Our results imply that claudin-1 is involved in the beta-catenin-Tcf/LEF signaling pathway, and that increased expression of claudin-1 may have some role in colorectal tumorigenesis.
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PMID:Involvement of claudin-1 in the beta-catenin/Tcf signaling pathway and its frequent upregulation in human colorectal cancers. 1193 10

The oncogenic protein beta-catenin is overexpressed in many cancers, frequently accumulating in nuclei where it forms active complexes with lymphoid enhancer factor-1 (LEF-1)/T-cell transcription factors, inducing genes such as c-myc and cyclin D1. In normal cells, nuclear beta-catenin levels are controlled by the adenomatous polyposis coli (APC) protein through nuclear export and cytoplasmic degradation. Transient expression of LEF-1 is known to increase nuclear beta-catenin levels by an unknown mechanism. Here, we show that APC and LEF-1 compete for nuclear beta-catenin with opposing consequences. APC can export nuclear beta-catenin to the cytoplasm for degradation. In contrast, LEF-1 anchors beta-catenin in the nucleus by blocking APC-mediated nuclear export. LEF-1 also prevented the APC/CRM1-independent nuclear export of beta-catenin as revealed by in vitro assays. Importantly, LEF-1-bound beta-catenin was protected from degradation by APC and axin in SW480 colon cancer cells. The ability of LEF-1 to trap beta-catenin in the nucleus was down-regulated by histone deacetylase 1, and this correlated with a decrease in LEF1 transcription activity. Our findings identify LEF-1 as key regulator of beta-catenin nuclear localization and stability and suggest that overexpression of LEF-1 in colon cancer and melanoma cells may contribute to the accumulation of oncogenic beta-catenin in the nucleus.
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PMID:Lymphoid enhancer factor-1 blocks adenomatous polyposis coli-mediated nuclear export and degradation of beta-catenin. Regulation by histone deacetylase 1. 1198 4

Somatic cell gene targeting was used to create an isogenic set of human colon cancer cells that differs only in the presence or absence of their endogenous activated beta-catenin oncogene. Affymetrix Genechip expression profiling of parental cells and gene-targeted derivatives identified numerous novel genes whose expression was dependent on the presence of oncogenic beta-catenin. The transforming growth factor-beta family member bone morphogenetic protein 4 (BMP4), whose receptor is mutated in a rare inherited gastrointestinal cancer predisposition syndrome, was the most highly differentially expressed gene. Additional experiments revealed that the oncogenic allele of beta-catenin specifically is absolutely required for BMP4 expression and secretion by human cancer cells and that BMP4 is overexpressed and secreted by human colon cancer cells with mutant adenomatous polyposis coli genes. These data identify the presence of regulatory interactions between the Wnt and BMP signaling pathways in cancer pathogenesis, providing an intriguing connection between the sporadic and inherited forms of a common human malignancy.
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PMID:Oncogenic beta-catenin is required for bone morphogenetic protein 4 expression in human cancer cells. 1201 47

A novel phosphorylation-specific antibody (alphapbeta-catenin) was generated against a peptide corresponding to amino acids 33-45 of human beta-catenin, which contained phosphorylated serines at positions 33 and 37. This antibody is specific to phosphorylated beta-catenin and reacts neither with the non-phosphorylated protein nor with phosphorylated or non-phosphorylated plakoglobin. It weakly interacts with S33Y beta-catenin but not with the S37A mutant. pbeta-catenin is hardly detectable in normal cultured cells and accumulates (up to 55% of total beta-catenin) upon overexpression of the protein or after blocking its degradation by the proteasome. Inhibition of both GSK-3beta and the proteasome resulted in a rapid (t1/2=10 minutes) and reversible reduction in pbeta-catenin levels, suggesting that the protein can undergo dephosphorylation in live cells, at a rate comparable to its phosphorylation by GSK-3beta. pbeta-catenin interacts with LEF-1, but fails to form a ternary complex with DNA, suggesting that it is transcriptionally inactive. Immunofluorescence microscopy indicated that pbeta-catenin accumulates in the nuclei of MDCK and BCAP cells when overexpressed and is transiently associated with adherens junctions shortly after their formation. pbeta-catenin only weakly interacts with co-transfected N-cadherin, although it forms a complex with the ubiquitin ligase component beta-TrCP. SW480 colon cancer cells that express a truncated APC, at position 1338, contain high levels of pbeta-catenin, whereas HT29 cells, expressing APC truncated at position 1555, accumulate non-phosphorylated beta-catenin, suggesting that the 1338-1555 amino acid region of APC is involved in the differential regulation of the dephosphorylation and degradation of pbeta-catenin.
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PMID:Regulation of S33/S37 phosphorylated beta-catenin in normal and transformed cells. 1207 67

A major obstacle to obtaining more detailed insights into the diversity of phenotypic and molecular changes occurring in colon cancer cells is the lack of low-passage colon cancer cell lines, which would still closely reflect the phenotype of the colon cancer cells in vivo. Here, we characterize eight novel, low passage number human colon carcinoma cell lines, originating from colorectal cancers extensively characterized in the clinics. All cell lines closely resemble the original tumors with respect to phenotype, markers and detectable genetic changes. Cell morphology and marker expression is highly variable, ranging from fully polarized cells correctly expressing all basolateral epithelial markers, to cells with mesenchymal characteristics and a complete loss of polarity due to delocalization or loss of junction complex proteins. The alterations in phenotype and epithelial marker expression correspond to changes already detectable in the primary tumor in vivo. Seven of the cell lines show chromosomal instability, while one cell line is characterized by microsatellite instability. p53 associated with K-ras mutations were detected in three cell lines. Hitherto non-described E-cadherin mutations were found at both alleles in one cell line whereas in another cell line the E-cadherin protein was down-regulated. A stabilizing beta-catenin mutation (S45F) appears in the same cell line that carried the mutated E-cadherin gene. Six cell lines carried APC mutations, which in five of the lines led to an activated beta-catenin/Tcf/LEF signaling pathway. In accordance with beta-catenin/Tcf/LEF activation, the cell lines show increased migration and invasiveness. Our results show that the characterized, low-passage cell lines mirror the diversity of the individual tumors from which they were derived. Through molecular analyses of these cell lines we demonstrate that tumorgenicity events are much more diverse in human colon cancer than expected, despite the common origin of the tumors from a small patient group with similar tumor grading and clinical prognosis.
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PMID:Novel colon cancer cell lines leading to better understanding of the diversity of respective primary cancers. 1209 41


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