UMLS:C0033036 - FACTA Search

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Query: UMLS:C0033036 (APC)
10,214 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The wnt signal transduction pathway is involved in many differentiation events during embryonic development and can lead to tumor formation after aberrant activation of its components. The cytoplasmic component beta-catenin is central to the transmission of wnt signals to the nucleus: in the absence of wnts beta-catenin is constitutively degraded in proteasomes, whereas in the presence of wnts beta-catenin is stabilized and associates with HMG box transcription factors of the LEF/TCF family. In tumors, beta-catenin degradation is blocked by mutations of the tumor suppressor gene APC (adenomatous polyposis coli), or of beta-catenin itself. As a consequence, constitutive TCF/beta-catenin complexes are formed and activate oncogenic target genes. This review discusses the mechanisms that silence the pathway in cells that do not receive a wnt signal and goes on to describe the regulatory steps involved in the activation of the pathway.
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PMID:Biochemical interactions in the wnt pathway. 1065 74

Our early work using the first array and imaging methods for the quantitative analysis of the expression of 4000 cDNA sequences suggested that modulation of mitochondrial gene expression was a factor in determining whether colonic epithelial cells displayed a differentiated or transformed phenotype. We have since dissected a pathway in which mitochondrial function is a key element in determining the probability of cells undergoing cell-cycle arrest, lineage-specific differentiation, and cell death. Moreover, this pathway is linked to signaling through beta-catenin-Tcf, but in a manner that is independent of effects of the APC gene on beta-catenin-Tcf activity. Utilization of unique mouse genetic models of intestinal tumorigenesis has confirmed that mitochondrial function is an important element in generation of apoptotic cells in the colon in vivo and has demonstrated that modulation of cell death may be involved in intestinal tumor progression rather than initiation. Normal spatial and temporal patterns of cell proliferation, differentiation, and apoptosis in the colonic mucosa are determined by developmentally programmed genetic signals and external signals generated by homo- and heterotypic cell interactions, humoral agents, and lumenal contents. Mitochondrial function may play a pivotal role in integrating these signals and in determining probability of cells entering different maturation pathways. How this is accomplished is under investigation using high-density cDNA microarrays.
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PMID:Cellular mechanisms of risk and transformation. 1066 79

Although tumor suppressor genes continue to be discovered, the most recent advances have been made in attributing new and exciting functions to existing ones - such as the apparent role of VHL as a regulator of proteolysis. Great insights have also come from piecing genes together into pathways and networks. For instance the discovery that cyclin D1 is regulated by beta-catenin/Tcf-4 allows us to tie the APC pathway to the RB pathway and cell cycle control. Similarly, tumor suppressor genes have been fitted together with oncogenes into the various pathways that regulate apoptosis such that tumor suppressor function is now attributed to some of the basic components of the apoptotic machinery, such as caspases and Apaf-1. The great pace at which mouse models of tumorigenesis continue to advance our knowledge of tumor suppressor gene function has led us to look anew at the role of genes such as TCF-1 and SMAD-3 in human cancer. Finally, the realisation that different growth regulatory pathways give rise to generic signals suggests that future work may lie in integrating the signals from different pathways and in understanding the importance of protein levels to cellular function.
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PMID:Tumor suppressor genes. 1067 86

It is not clear whether APC mutations are sufficient for early colorectal adenomas to grow or whether additional mutations at other loci are required. We previously have screened 210 early colorectal adenomas from familial adenomatous polyposis patients for mutations and allelic loss at APC. Here, we determined whether allelic loss at APC had any effect on the nearby alpha-catenin gene. However, loss on 5q in familial adenomatous polyposis adenomas rarely extended as far as alpha-catenin, and no differences in alpha-catenin protein expression were found in tumors that showed loss encompassing both APC and alpha-catenin. We then screened all 210 tumors for mutations at candidate loci other than APC (K-ras, beta-catenin, and allelic loss at 1p33-p35 and 1p36) and for microsatellite instability (MSI). Each of these loci has been implicated previously in early colorectal tumorigenesis. One tumor harbored a beta-catenin mutation and another MSI, but none showed K-ras mutation or allelic loss at 1p33-p35 or 1p36. These data support the following hypotheses derived from sporadic colorectal tumors: beta-catenin mutations are generally an alternative to mutations at APC, MSI is not usually an early phenomenon in colorectal tumorigenesis, and K-ras mutations are more typical of large- and moderate-sized adenomas. Contrary to some previous reports, chromosome 1p allelic loss is infrequent in very early adenomas. APC mutations are generally sufficient for colorectal tumors to grow to about 1-cm diameter, although chance mutations at other loci can provide these early colorectal adenomas with a selective advantage, and some colorectal tumors may develop along a pathway not involving APC.
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PMID:APC mutations are sufficient for the growth of early colorectal adenomas. 1068 34

Cancer is a genetic disease. The unstable genome of cancer cells causes tumour progression through multiple alterations in suppressor and promoter genes, leading to loss of homeostatic and gain of oncogenic functions. Invasion is the critical step in the acquisition of malignancy. It implicates a continuous molecular conversation of the cancer cells with other cells and with the extracellular matrix in which adhesion molecules are crucial. One of these, E-cadherin, is discussed in the present review. E-cadherin is a transmembrane glycoprotein that forms a complex with cytoplasmic proteins, termed catenins because they link E-cadherin to the actin cytoskeleton. E-cadherin/catenin-mediated intercellular adhesion and communication is mainly homophylic homotypic. There is compelling evidence from experiments in vitro as well as in vivo to accept that the E-cadherin/catenin complex acts as an invasion suppressor. The mechanism of this action is not only through cell-cell adhesion but also through transduction of signals to the cell's motility system. In the replication error positive human colon cancer cell line HCT-8, the alpha E-catenin gene CTNNA1 is an invasion suppressor gene. Here, the transition from the non-invasive to the invasive state was prevented by introduction into the unstable non-invasive cells of either an extra CTNNA1 or a wild type hMSH6 mismatch repair gene. beta-catenin also participates at a complex which comprises the adenomatous polyposis cancer protein APC. In colorectal cancer, mutation of either APC or beta-catenin is oncogenic. Downregulation of the E-cadherin/catenin complex may occur in several ways amongst which are gene mutations, methylation of 5'CpG dinucleotides within the promotor region of E-cadherin, tyrosine phosphorylation of beta-catenin, cell surface expression of proteoglycans sterically hindering E-cadherin and proteolytic release of fragments from the extracellular part of E-cadherin. Upregulation of the E-cadherin/catenin complex has been realized with a series of agents, some of which can be used therapeutically. In most human gastrointestinal cancers the E-cadherin/catenin or related complexes are disturbed and this underscores their pivotal role in the progression of these tumours. Mutations of the E-cadherin gene, including germline mutations, occur in diffuse gastric carcinoma, CpG methylation around the promotor region of E-cadherin in hepatocellular carcinomas and mutations of the APC tumour suppressor gene or in the beta-catenin oncogene in most colorectal cancers. The literature agrees about the disturbance of immunohistochemical patterns of E-cadherin and catenin expression in gastrointestinal cancers. Conflicting opinions do, however, exist about the prognostic value of such immunohistochemical aberrations. We doubt that immunohistochemistry of E-cadherin or catenins add prognostic value to the already used histological grading systems. In our opinion the major benefit from understanding of the E-cadherin/catenin-mediated pathways of invasion will be the development of new anti-invasive treatment strategies.
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PMID:The role of the E-cadherin/catenin complex in gastrointestinal cancer. 1069 69

beta-Catenin plays essential roles in cell adhesion, by associating with cadherins, and as a signaling molecule, by interacting with the Tcf/LEF-1 family of transcription factors. In order to study the protein-protein interactions of beta-catenin in living cells, we fused it to green fluorescent protein (GFP). GFP-beta-catenin was incorporated into cell junctions but also accumulated in the nucleus, where it formed rod-like structures. The carboxyl-terminal armadillo repeats of GFP-beta-catenin were sufficient for nuclear localization, but formation of rods required the armadillo repeats and sequences in both the amino- and the carboxyl-terminal domains. Rod formation was prevented by coexpression of N-cadherin, APC, and Tcf-4, which bind to the armadillo repeats of beta-catenin, but not by coexpression of alpha-catenin, although alpha-catenin expression did prevent accumulation of beta-catenin in the nucleus. Interestingly, when alpha-catenin, beta-catenin, and Tcf-4 were coexpressed they colocalized in the nucleus, and this correlated with a decrease in beta-catenin/Tcf-dependent transcriptional activity. These results indicate that binding of beta-catenin to Tcf-4 overrides the function of alpha-catenin to sequester beta-catenin in the cytoplasm and suggest that alpha-catenin can regulate beta-catenin signaling in the nucleus.
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PMID:Analysis of beta-catenin aggregation and localization using GFP fusion proteins: nuclear import of alpha-catenin by the beta-catenin/Tcf complex. 1069 36

Wnt/beta-catenin signaling is frequently activated in cancer cells by stabilizing mutations of beta-catenin or loss-of-function mutations of the APC tumor suppressor gene. We have analysed the role of beta-catenin in the pathogenesis of hepatoblastoma (HB), an embryonic liver tumor occurring mainly in children under 2 years of age. Sequence analysis of the beta-catenin NH2-terminal domain in 18 epithelial and mixed HBs revealed missense mutations in the GSK3beta phosphorylation motif or interstitial deletions in 12 tumors (67%). In the remaining cases, no truncating mutation of APC could be evidenced. Immunohistochemical analysis of beta-catenin in 11 HBs demonstrated nuclear/cytoplasmic accumulation of the protein in all tumors analysed, with predominant nuclear beta-catenin immunostaining in undifferentiated cells. Membranous beta-catenin localization was preserved only in fetal-type tumoral hepatocytes and was associated with E-cadherin expression. Moreover, we show that beta-catenin is aberrantly overexpressed in a large spectrum of tumor components, including hepatocyte-like cells at various differentiation stages and heterologous elements such as squamous, osteoid and chrondroid tissues, and in occasional other mesenchymally-derived cells. These data strongly suggest that activation of beta-catenin signaling is an obligatory step in HB pathogenesis, and raise the possibility that it interferes with developmental signals that specify different tissue types at early stages of hepatic differentiation.
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PMID:Activation of beta-catenin in epithelial and mesenchymal hepatoblastomas. 1069 19

The Wnt signaling pathway is essential for development and organogenesis. Wnt signaling stabilizes beta-catenin, which accumulates in the cytoplasm, binds to 1-cell factor (TCF; also known as lymphocyte enhancer-binding factor, LEF) and then upregulates downstream genes. Mutations in CTNNB1 (encoding beta-catenin) or APC (adenomatous polyposis coli) have been reported in human neoplasms including colon cancers and hepatocellular carcinomas (HCCs). Because HCC5 tend to show accumulation of beta-catenin more often than mutations in CTNNB1, we looked for mutations in AXIN1, encoding a key factor for Wnt signaling, in 6 HCC cell lines and 100 primary HCC5. Among the 4 cell lines and 87 HCC5 in which we did not detect CTNNB1 mutations, we identified AXIN1 mutations in 3 cell lines and 6 mutations in 5 of the primary HCCs. In cell lines containing mutations in either gene, we observed increased DNA binding of TCF associated with beta-catenin in nuclei. Adenovirus mediated gene transfer of wild-type AXINI induced apoptosis in hepatocellular and colorectal cancer cells that had accumulated beta-catenin as a consequence of either APC, CTNNB1 or AXIN1 mutation, suggesting that axin may be an effective therapeutic molecule for suppressing growth of hepatocellular and colorectal cancers.
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PMID:AXIN1 mutations in hepatocellular carcinomas, and growth suppression in cancer cells by virus-mediated transfer of AXIN1. 1070 Jan 76

beta-catenin regulates cadherin-mediated cell-cell adhesion and also functions as a signaling molecule. In this study, we examined the expression pattern of E-cadherin, alpha-catenin and beta-catenin in 22 cases of esophageal squamous-cell carcinoma by Western-blot analysis. Expression of E-cadherin, alpha-catenin and beta-catenin was lower in carcinomas than in normal esophageal mucosa in 4 cases (18.2%) for E-cadherin, 6 cases (27.3%) for alpha-catenin and 9 cases (40.9%) for beta-catenin. Expression of beta-catenin was not always correlated with that of E-cadherin. Over-expression of beta-catenin was observed in 3 cases (13.6%). Of 3 cases that presented with over-expression of beta-catenin, 2 showed cytoplasmic staining by immunohistochemistry. Nuclear localization of beta-catenin was observed in one case that had higher beta-catenin level in tumor tissue (1.4-fold higher than normal mucosa). The genomic DNA sequences of the beta-catenin and the APC gene were analyzed. No mutation of the beta-catenin gene was observed in any cases. Silent mutation of the APC gene was found in all the cases that showed over-expression or nuclear localization of the beta-catenin protein. These results indicate that alterations of the cadherin-catenin complex may play an important role in a sub-set of esophageal carcinogenesis. Furthermore, it is suggested that beta-catenin over-expression is not caused by genetic alteration of either the beta-catenin or the APC gene.
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PMID:Alteration of beta-catenin expression in esophageal squamous-cell carcinoma. 1070 91

Like sporadic colorectal cancers, ulcerative colitis (UC)-related cancers are thought to evolve through a multistep progression pathway. The genomic alterations important in sporadic colorectal carcinogenesis are well characterized, with loss of APC function being a frequent and early event. However, the genomic alterations in UC-related carcinogenesis are yet unclear and the role of APC is controversial. In this study genomic alterations in UC-related cancers, dysplasias and nondysplasias were assessed by comparative genomic hybridization (CGH). Alterations of the APC/beta-catenin pathway were evaluated by immunohistochemistry. 32 cases of UC-related cancers (14 with synchronous dysplasias and nondysplasias) and 42 sporadic cancers were matched by UICC stage. CGH was performed using DOP-PCR amplification after microdissection. Expression of beta-catenin, E-cadherin and APC were detected by immunohistochemistry in paraffin sections. Chromosomal alterations were present in 90% of the sporadic and 94% of the UC-related cancers. 86% of the UC-related dysplasias and 36% of the nondysplasias showed changes by CGH. Chromosome 5q was lost in 56% of UC-related cancers and 36% of the dysplasias but in only 26% of the sporadic cancers. Other frequent alterations in both cancer groups were loss of 18q, 8p, 17p, and gain of 8q and 20q. Immunohistochemistry showed a decrease of membranous and an increase of cytoplasmic expression of E-cadherin and beta-catenin in UC-related and sporadic cancers. APC expression was significantly decreased in both tumor types. Clonal chromosomal alterations occur early in UC-related tumor progression. UC-related and sporadic cancers share a set of common clonal abnormalities. The frequent loss of 5q and the altered expression of APC, beta-catenin, and E-cadherin proteins in UC-related cancers indicate a critical role of the APC/beta-catenin pathway in UC-related carcinogenesis.
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PMID:[Molecular carcinogenesis in ulcerative colitis-associated and sporadic colorectal carcinoma--differences and similarities]. 1071 3

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