beta-catenin signalling modulates proliferative potential of human epidermal keratinocytes independently of intercellular adhesion.
(25/5919)
We found that cultured human keratinocytes with high proliferative potential, the putative epidermal stem cells, expressed a higher level of noncadherin-associated beta-catenin than populations enriched for keratinocytes of lower proliferative potential. To investigate the physiological significance of this, a series of beta-catenin constructs was introduced into keratinocytes via retroviral infection. Full-length beta-catenin and a mutant containing only nine armadillo repeats had little effect on proliferative potential in culture, the full-length protein being rapidly degraded. However, expression of stabilised, N-terminally truncated beta-catenin increased the proportion of putative stem cells to almost 90% of the proliferative population in vitro without inducing malignant transformation, and relieved the differentiation stimulatory effect of overexpressing the E-cadherin cytoplasmic domain. Conversely, beta-catenin lacking armadillo repeats acted as a dominant negative mutant and stimulated exit from the stem cell compartment in culture. The positive and negative effects of the beta-catenin mutants on proliferative potential were independent of effects on cell-cycle kinetics, overt terminal differentiation or intercellular adhesion, and correlated with stimulation or inhibition of transactivation of a TCF/LEF reporter in basal keratinocytes. We conclude that the elevated level of cytoplasmic beta-catenin in those keratinocytes with characteristics of epidermal stem cells contributes to their high proliferative potential. (+info)
Frequent mutation and nuclear localization of beta-catenin in anaplastic thyroid carcinoma.
(26/5919)
Beta-catenin is an ubiquitously expressed cytoplasmic protein that has a crucial role in both E-cadherin-mediated cell-cell adhesion and as a downstream signaling molecule in the wingless pathway. Stabilization of beta-catenin followed by nuclear translocation and subsequent T-cell factor/lymphoid-enhancing factor-mediated transcriptional activation has been proposed as an important step in oncogenesis. Stabilization may occur through activating mutations in exon-3 at the phosphorylation sites for ubiquitination and degradation of beta-catenin. Immunohistochemical subcellular localization of beta-catenin and mutational analysis of exon-3 of the beta-catenin gene by single-strand conformational polymorphism followed by DNA sequencing was performed on 37 samples from 31 patients with anaplastic thyroid carcinoma. Immunofluorescent staining showed nuclear localization in 15 (42%) of the 36 samples examined. Nucleotide sequencing of mobility shifts detected by single-strand conformational polymorphism revealed somatic alterations in 19 (61%) of the 31 patients analyzed. We conclude that mutations in beta-catenin are common in anaplastic thyroid cancer and that they may activate transcription, as illustrated by frequent nuclear localization of the protein. These findings support the idea that beta-catenin acts as an oncogene and contributes to the highly aggressive behavior of this tumor. (+info)
Beta-catenin mutations are frequent in hepatocellular carcinomas but absent in adenomas induced by diethylnitrosamine in B6C3F1 mice.
(27/5919)
Activating mutations in the region of the beta-catenin gene corresponding to the NH2-terminal phosphorylation sites of glycogen synthetase kinase 3beta have been causally implicated in carcinogenesis. In this study, the beta-catenin exon 3 was examined in hepatic lesions induced by diethylnitrosamine in B6C3F1 mice. PCR and DNA sequencing detected seven beta-catenin mutations in 13 samples dissected from hepatocellular carcinoma tissues, but none in 14 hepatic adenomas. All of the mutations were found in codon 41 encoding a threonine residue, one of the possible glycogen synthetase kinase-3beta phosphorylation sites. Although beta-catenin protein was immunohistochemically stained mainly on the cell membrane in preneoplastic hepatocytic foci and most adenomas, as observed in normal hepatocytes, it was detected in the cytoplasm and nuclei in addition to the cell membrane, indicating stabilization of the protein in HCCs. This shift in staining was observed not only in tumors with mutations, but also in examples lacking exon 3 mutations. Our data demonstrate that beta-catenin alterations may be important for malignant progression during multistep hepatic carcinogenesis in mice. (+info)
T cell factor-activated transcription is not sufficient to induce anchorage-independent growth of epithelial cells expressing mutant beta-catenin.
(28/5919)
N-terminal mutations in beta-catenin that inhibit beta-catenin degradation are found in primary tumors and cancer cell lines, and increased beta-catenin/T cell factor (TCF)-activated transcription in these cells has been correlated with cancer formation. However, the role of mutant beta-catenin in cell transformation is poorly understood. Here, we compare the ability of different N-terminal mutations of beta-catenin (DeltaN131, DeltaN90, DeltaGSK) to induce TCF-activated transcription and anchorage-independent growth in Madin-Darby canine kidney epithelial cells. Expression of DeltaN90 or DeltaGSK beta-catenin increased TCF-activated transcription but did not induce significant anchorage-independent cell growth. In contrast, deletion of the alpha-catenin-binding site in DeltaN131 beta-catenin reduced TCF-activated transcription, compared with that induced by DeltaN90 or DeltaGSK beta-catenin, but significantly enhanced anchorage-independent cell growth. (+info)
Tcf-1-mediated transcription in T lymphocytes: differential role for glycogen synthase kinase-3 in fibroblasts and T cells.
(29/5919)
Beta-catenin is the vertebrate homolog of the Drosophila segment polarity gene Armadillo and plays roles in both cell-cell adhesion and transduction of the Wnt signaling cascade. Recently, members of the Lef/Tcf transcription factor family have been identified as protein partners of beta-catenin, explaining how beta-catenin alters gene expression. Here we report that in T cells, Tcf-1 also becomes transcriptionally active through interaction with beta-catenin, suggesting that the Wnt signal transduction pathway is operational in T lymphocytes as well. However, although Wnt signals are known to inhibit the activity of the negative regulatory protein kinase glycogen synthase kinase-3beta (GSK-3beta), resulting in increased levels of beta-catenin, we find no evidence for involvement of GSK-3beta in Tcf-mediated transcription in T cells. That is, a dominant negative GSK-3beta does not specifically activate Tcf transcription and stimuli (lithium or phytohemagglutinin) that inhibit GSK-3beta activity also do not activate Tcf reporter genes. Thus, inhibition of GSK-3beta is insufficient to activate Tcf-dependent transcription in T lymphocytes. In contrast, in C57MG fibroblast cells, lithium inactivates GSK-3beta and induces Tcf-controlled transcription. This is the first demonstration that lithium can alter gene expression of Tcf-responsive genes, and points to a difference in regulation of Wnt signaling between fibroblasts and lymphocytes. (+info)
Relationship of beta-catenin and Bcl-2 expression to sulindac-induced regression of intestinal tumors in Min mice.
(30/5919)
Non-steroidal anti-inflammatory drugs (NSAIDs) can cause regression of early intestinal tumors and although this is believed to involve cyclooxygenase-2 and apoptosis, the molecular mechanisms remain unclear. Cytoplasmic and nuclear beta-catenin are overexpressed in many of these lesions and Bcl-2, which inhibits apoptosis, may also be elevated during the course of intestinal tumorigenesis. We recently showed that sulindac causes regression of 70-80% of small intestinal tumors in Min/+ mice within 4 days, but does not have the same impact on colonic lesions; after 20 days of treatment the tumor load stabilizes at 10-20% of that in untreated animals. The aim of this study was to determine if NSAID-induced regression of intestinal adenomas might be associated with changes in beta-catenin or Bcl-2 expression. Intestinal tumors from Min/+ mice were harvested after treatment with sulindac for 2, 4 or 20 days and evaluated for expression of beta-catenin and Bcl-2 using immunohistochemistry. There was a > or = 50% decrease in beta-catenin (P = 0.001) and diminishing Bcl-2 (P = 0.019) in small intestinal tumors harvested between 2 and 4 days of treatment when compared with untreated controls. In contrast, small intestinal tumors from animals treated for 20 days were not significantly different from untreated controls. Colonic tumors expressed higher levels of Bcl-2 than those from the small intestine and did not show any significant changes in either Bcl-2 or beta-catenin expression after treatment. Results suggest that modulation of aberrant beta-catenin expression occurs during NSAID-induced regression of intestinal adenomas and that Bcl-2 may confer resistance to these effects. (+info)
Differential expression of prostaglandin endoperoxide H synthase-2 and formation of activated beta-catenin-LEF-1 transcription complex in mouse colonic epithelial cells contrasting in Apc.
(31/5919)
Mutations in Apc underlie the intestinal lesions in familial adenomatous polyposis and are found in >85% of sporadic colon cancers. They are frequently associated with overexpression of prostaglandin endoperoxide H synthase-2 (PGHS-2) in colonic adenomas. It has been suggested that Apc mutations are linked mechanistically to increased PGHS-2 expression by elevated nuclear accumulation of beta-catenin-Tcf-LEF transcription complex. In the present study, we show that PGHS-2 is differentially expressed in mouse colonic epithelial cells with distinct Apc status. Cells with a mutated Apc expressed markedly higher levels of PGHS-2 mRNA and protein and produced significantly more prostaglandin E2 than cells with normal Apc. Using electrophoretic mobility shift assays, we demonstrate that DNA-beta-catenin-LEF-1 complex formation is differentially induced in these two cell lines in an Apc-dependent manner. Our data indicate that the differential induction of beta-catenin-LEF-1 complex correlates closely with differential expression of PGHS-2. These findings support the hypothesis that the differential expression of PGHS-2 is mediated through the proposed beta-catenin/Tcf-LEF signaling pathway. (+info)
p120(ctn) acts as an inhibitory regulator of cadherin function in colon carcinoma cells.
(32/5919)
p120(ctn) binds to the cytoplasmic domain of cadherins but its role is poorly understood. Colo 205 cells grow as dispersed cells despite their normal expression of E-cadherin and catenins. However, in these cells we can induce typical E-cadherin-dependent aggregation by treatment with staurosporine or trypsin. These treatments concomitantly induce an electrophoretic mobility shift of p120(ctn) to a faster position. To investigate whether p120(ctn) plays a role in this cadherin reactivation process, we transfected Colo 205 cells with a series of p120(ctn) deletion constructs. Notably, expression of NH2-terminally deleted p120(ctn) induced aggregation. Similar effects were observed when these constructs were introduced into HT-29 cells. When a mutant N-cadherin lacking the p120(ctn)-binding site was introduced into Colo 205 cells, this molecule also induced cell aggregation, indicating that cadherins can function normally if they do not bind to p120(ctn). These findings suggest that in Colo 205 cells, a signaling mechanism exists to modify a biochemical state of p120(ctn) and the modified p120(ctn) blocks the cadherin system. The NH2 terminus-deleted p120(ctn) appears to compete with the endogenous p120(ctn) to abolish the adhesion-blocking action. (+info)