Extracellular calcium and calcium sensing receptor function in human colon carcinomas: promotion of E-cadherin expression and suppression of beta-catenin/TCF activation

Ca(2+) has chemopreventive activity against colon cancer, albeit its mechanisms of action are not understood. In this study, we showed that four different human colon carcinoma cell lines (FET, SW480, MOSER, and CBS) expressed the human parathyroid calcium sensing receptor (CaSR) and that a function of extracellular Ca(2+) and the CaSR in these cells was the promotion of E-cadherin expression and suppression of beta-catenin/T cell factor activation. We also found that human colonic crypt epithelial cells expressed the CaSR, and histologically differentiated carcinomas (i.e., where three-dimensional, crypt-like structures were present) expressed less receptor by comparison, whereas an almost complete loss of CaSR expression was observed in undifferentiated tumors. These results suggest that extracellular Ca(2+) and the CaSR may function to regulate the differentiation of colonic epithelial cells and that disruption of this ligand receptor system may contribute to abnormal differentiation and malignant progression. In addition, the promotion of E-cadherin and suppression of beta-catenin/T cell factor may be an important mechanism underlying the chemopreventive action of Ca(2+) in colon cancer.     

Upregulation of calcium-sensing receptor and mitogen-activated protein kinase signalling in the regulation of growth and differentiation in colon carcinoma

In the present study, we demonstrate that Ca2+-induced growth inhibition and induction of differentiation in a line of human colon carcinoma cells (CBS) is dependent on mitogen-activated protein (MAP) kinase signaling and is associated with upregulation of extracellular calcium-sensing receptor (CaSR) expression. When CBS cells were grown in Ca2+-free medium and then switched to medium supplemented with 1.4 mM Ca2+, proliferation was reduced and morphologic features of differentiation were expressed. E-cadherin, which was minimally expressed in nonsupplemented medium, was rapidly induced in response to Ca2+ stimulation. Sustained activation of the extracellular signal-regulated kinase (ERK) occurred in Ca2+-supplemented medium. When an inhibitor of ERK activation (10 microM U0126) was included in the Ca2+-supplemented culture medium, ERK-activation did not occur. Concomitantly, E-cadherin was not induced, cell proliferation remained high and differentiation was not observed. The same level of Ca2+ supplementation that induced MAP kinase activation also stimulated CaSR upregulation in CBS cells. A clonal isolate of the CBS line that did not upregulate CaSR expression in response to extracellular Ca2+ was isolated from the parent cells. This isolate failed to produce E-cadherin or undergo growth inhibition/induction of differentiation when exposed to Ca2+ in the culture medium. However, ERK-activation occurred as efficiently in this isolate as in parent CBS cells or in a cloned isolate that underwent growth reduction and differentiation in response to Ca2+ stimulation. Together, these data indicate that CaSR upregulation and MAP kinase signalling are both intermediates in the control of colon carcinoma cell growth and differentiation. They appear to function, at least in part, independently of one another.     

Decreased E-cadherin augments beta-catenin nuclear localization: studies in breast cancer cell lines

We showed that the YMB-1-derived breast cancer cell line YMB-S, which proliferates in suspension without aggregation, exhibits complete loss of cell-cell adhesion despite the presence of E-cadherin-catenin complex and expression of free beta-catenin in the cytoplasm. Here, we describe beta-catenin gene regulation, interaction with E-cadherin, immunocytochemical localization, and their relation to growth rate in the YMB-1-derived cell line YMB-A, which forms tight junctions and displays anchorage-dependent growth. YMB-A cells proliferated more slowly than YMB-S cells. E-cadherin and APC gene product expression in YMB-A cells was significantly higher than that in YMB-S cells, whereas expression of beta-catenin, MUC1, and c-myc was lower in YMB-A cells than in YMB-S cells. According to immunocytochemical analysis, beta-catenin in YMB-A cells displayed membranous or submembranous localization, indicating that beta-catenin is mostly tethered to E-cadherin. Inhibition of E-cadherin expression in YMB-A cells by an antisense oligonucleotide did not change expression of whole cell beta-catenin protein, but increased nuclear beta-catenin protein level, c-myc expression, and cell growth rate. These results suggest that decreased expression of E-cadherin and APC and increased amount of beta-catenin in YMB-S cells lead to accumulation of beta-catenin in the nucleus, activate beta-catenin-LEF/TCF signaling pathway, and trigger c-myc proto-oncogene expression. c-Myc overexpression in breast cancer may be related to activated Wnt independent beta-catenin-LEF/TCF signaling.     

Calcium, calcium-sensing receptor and colon cancer

There is much evidence that dietary Ca(2+) loading reduces colon cell proliferation and carcinogenesis in humans and rodents, but during carcinogenesis it becomes ineffective or even tumor-promoting. We are beginning to see how Ca(2+) balances the continuous massive cell production in colon crypts by driving the terminal differentiation and eventually the apoptosis of the cells mainly on the mucosal surface, and how this Ca(2+) control is lost during colon carcinogenesis. The rapid proliferation of the transit-amplifying (TA) progeny of the colon stem cells is driven by the so-called "Wnt" signaling mechanism, which involves the stimulation of proliferogenic genes such as those for c-Myc and cyclin D1 and the silencing of the gene for the cell cycle-stopping p21(Cip1/WAF1) protein by nuclear beta-catenin*Tcf-4 complexes. TA cells avoid mitotic damage and premature apoptosis by expressing the protein survivin. It appears that TA cell cycling stops and terminal differentiation starts when the cells reach a higher level in the crypt where there is enough lumenal Ca(2+) to stimulate the expression and activation of CaSRs (Ca(2+)-sensing receptors), the signals from which stimulate the expression of E-cadherin. Along with this, the APC (adenomatous polyposis coli) protein appears and some of it enters the nucleus. There it makes the TA cells susceptible to the eventual apoptotic balancing by stopping survivin expression and the beta-catenin*Tcf-4 complex from driving further cell cycling by releasing beta-catenin from the nucleus, and delivering it to cytoplasmic APC*axin*GSK-3beta complexes for ultimate proteasomal destruction. Cytoplasmic beta-catenin is then prevented from returning to the nucleus by either being intercepted and destroyed by APC*axin*GSK-3beta complexes or locked by the emerging E-cadherin into membrane adherens junctions which tie the cell into the sheet of proliferatively shut-down cells with APC-dependent cytoskeletons moving to the mouth of the crypt and onto the flat mucosal surface. A common first step in sporadic colon carcinogenesis is the loss of functional APC which disorients upwardly directed migration and causes the retention of nuclear beta-catenin and proliferogenic beta-catenin*Tcf-4 complexes as well as genomic instability. Eventually the balance between cell proliferation and terminal differentiation and death is radically tipped in favour of proliferation by the appearance of apoptosis-resistant, survivin-expressing clones of Ca(2+)-insensitive cells which are locked into the proliferative, mutation-prone mode because of CaSR-disabling gene mutations which prevent the stimulation of E-cadherin expression and terminal differentiation.     

Calcium and calcium sensing receptor modulates the expression of thymidylate synthase, NAD(P)H:quinone oxidoreductase 1 and survivin in human colon carcinoma cells: promotion of cytotoxic response to mitomycin C and fluorouracil

Ca(2+) and the cell-surface calcium sensing receptor (CaSR) constitute a novel and robust ligand/receptor system in regulating the proliferation and differentiation of colonic epithelial cells. Here we show that activation of CaSR by extracellular Ca(2+) (or CaSR agonists) enhanced the sensitivity of human colon carcinoma cells to mitomycin C (MMC) and fluorouracil (5-FU). Activation of CaSR up-regulated the expression of MMC activating enzyme, NAD(P)H:quinone oxidoreductase 1 (NQO-1) and down-regulated the expression of 5-FU target, thymidylate synthase (TS) and the anti-apoptotic protein survivin. Cells that were resistant to drugs expressed little or no CaSR but abundant amount of survivin. Disruption of CaSR expression by shRNA targeting the CaSR abrogated these modulating effects of CaSR activation on the expression of NQO1, TS, survivin and cytotoxic response to drugs. It is concluded that activation of CaSR can enhance colon cancer cell sensitivity to MMC and 5-FU and can modulate the expression of molecules involved in the cellular responses to these cytotoxic drugs.     

乳腺癌组织中E-cadherin、β-catenin及cyclin D1表达的相关性研究

背景与目的上皮性钙粘素(E-cadherin)通过连接素(catenins)与细胞骨架相连介导细胞同质粘附反应,β-catenin除与E-cadherin结合介导细胞粘附反应外,还作为Wnt信号转导通路的重要成分与肿瘤发生密切相关。本研究通过检测乳腺癌组织中E-cadherin、β-catenin及cyclinD1的表达,探讨E-cadherin、β-catenin在乳腺癌发生、发展中的意义。方法采用免疫组织化学SP法检测60例乳腺癌组织中E-cadherin、β-catenin、cyclinD1的表达。结果乳腺癌组织中有29例(48.3%)E-cadherin、18例(30.0%)β-catenin正常表达,28例(46.7%)cyclinD1过度表达。E-cadherin正常表达病例中,31.0%(9/29)的病例呈现cyclinD1过度表达,而E-cadherin异常表达病例中,61.3%(19/31)的病例呈现cyclinD1过度表达,E-cadherin异常表达与cyclinD1的过度表达有显著的正相关性(rs=0.303,P<0.05)。有42例癌组织表现出β-catenin的异常表达,其中57.1%(24/42)的病例出现cyclinD1的过度表达,而β-catenin正常膜表达病例中,22.2%(4/18)的病例呈现cyclinD1的过度表达。β-catenin的异常表达与cyclinD1的过度表达有显著的正相关性(rs=0.321,P<0.05)。结论E-cadherin和β-catenin的异常表达可能通过促使或激活cyclinD1的过度表达导致乳腺癌的发生和发展。     

Significance of E-cadherin/beta-catenin complex and cyclin D1 in breast cancer

E-cadherin and beta-catenin are important epithelial adhesion molecules in normal epithelium. Loss of E-cadherin - beta-catenin adhesion is an important step in the progression of many epithelial malignancies. beta-catenin plays also a role in intracellular signaling and can function as an oncogene when binds to the T-cell factor 4 (Tcf4)-binding site in the promotor region of cyclin D1 and transactivates genes after translocation to the nucleus. We evaluated the immunohistochemical expression pattern of E-cadherin, beta-catenin in relationship with cyclin D1 overexpression, tumor stage, clinicopathologic parameters and patient survival in 128 mammary infiltrating duct carcinomas. The expression of E-cadherin/beta-catenin complex and beta-catenin/cyclin D1 double staining with confocal scanning laser microscope was evaluated. There were aberrant expressions in 78% of E-cadherin, 79% of beta-catenin, and 66% of cyclin D1 in breast cancer. There was correlation of aberrant expression of E-cadherin or beta-catenin with lymph node metastasis, survival rate, and survival length. However, there was no correlation of cyclin D1 overexpression with aberrant expression of E-cadherin or beta-catenin. No death was found in normal expression of beta-catenin, however lowest survival (50%) was found in nuclear beta-catenin expression. There was correlation of overexpression of cyclin D1 with survival rate and survival length. The highest survival rate and survival length were found in membranous normal beta-catenin expression group, however significant decrement of survival length was found in the groups of aberrant expression one or both of E-cadherin or/and beta-catenin. These results suggest that aberrant expression of E-cadherin, beta-catenin, and cyclin D1 may be involved in tumor metastasis, and analysis of the degree or the pattern of E-cadherin, beta-catenin, cyclin D1, and E-cadherin/beta-catenin complex may be good prognostic markers of mammary infiltrating duct carcinoma.     

hFRNK基因转移对结肠癌细胞中E-钙黏素/β-连环素复合物的影响

目的研究hFRNK基因对结肠癌细胞Colo320WT中E-钙黏素（E-cadherin）／β-连环素（β-catenin）复合物的影响。方法利用AdEasy^TM系统在大肠肝菌内同源重组构建表达人FRNK基因的腺病毒载体pAdhFRNK。脂质体转染pCR3．1／GR质粒于结肠癌细胞Colo320中,G418筛选出稳定表达CCK-2R的阳性克隆,RT-PCR鉴定。用10^-8 mol／L胃泌素干预Colo320WT细胞12 h和pAdhFRNK体外感染Colo320WT细胞2 d后,再用10^-8 mol／L的胃泌素干预细胞12 h,然后用免疫共沉淀观察TX-100可溶性部分和不溶性部分的E-cadherin和β-catenin的表达。利用细胞化学方法观察E-cadherin和β-catenin在Colo320WT细胞中的分布情况。结果在胃泌素干预12 h后的TX-100可溶性部分中,E-cadherin和β-catenin的表达量明显降低,而TX-100不溶解部分表达增加。pAdhFRNK感染胃泌素干预后的细胞,在TX-100可溶性部分中,E-cadherin和β-catenin的表达量增加,而TX-100不溶性部分中表达降低。细胞化学方法显示,E-cadherin和β-catenin在胃泌素干预12 h后,由胞膜向胞内和胞核转移,而胃泌素干预pAdhFRNK感染后的细胞中,两者分布又逆转。结论hFRNK基因可明显对抗外源性胃泌素引起Colo320WT细胞中E-cadherin和β-catenin的分布异常,其机制可能是通过阻断FAK磷酸化及其通路而实现。     

Nifedipine synergizes with calcium in activating the calcium sensing receptor, suppressing the expression of thymidylate synthase and survivin and promoting sensitivity to fluorouracil in human colon carcinoma cells

We have previously reported that activation of the G protein coupled calcium-sensing receptor (CaSR) by extracellular Ca(2+) down-modulates the expression of thymidylate synthase (TS) and survivin and promotes sensitivity to fluorouracil in human colon carcinoma cells. Here, we report for the first time that the cardiac drug nifedipine acted synergistically with Ca(2+) in CaSR activation and in the induction of intracellular Ca(2+). Nifedipine in combination with Ca(2+) significantly down-modulated the expression of TS and survivin and promoted sensitivity to 5-FU above and beyond the level achievable with Ca(2+) alone. Nifedipine by itself, however, had no effect on the suppression of TS or survivin or sensitivity to 5-FU. The action of Ca(2+) or in combination with nifedipine was entirely CaSR dependent as the aforementioned effects did not occur in CaSR knocked down cells. siRNAs targeting TS or survivin or both could mimic the effect of CaSR activation in promoting sensitivity to 5-FU. We conclude that nifedipine acts in synergy with Ca(2+) in activating CaSR and in promoting sensitivity to 5-FU by down modulating the expression of TS and survivin. G-protein coupled CaSR has the potential of serving as a target for improving therapeutic outcome in colon cancer.     

Increased beta-catenin expression and nuclear translocation accompany cellular hyperproliferation in vivo

Beta-catenin performs critical roles in development and cellular adhesion. More recently, an oncogenic role has been described. In colon cancer, decreased E-cadherin/beta-catenin association is causally linked to increased beta-catenin-regulated gene expression and increased cellular division. Whether the same pathway is active in native epithelia remains unknown. To address this question, we used the transmissible murine colonic hyperplasia model to measure changes in beta-catenin abundance, nuclear partitioning, target gene (c-myc and cyclin D1) expression, and subcellular distribution. Colonocyte hyperproliferation was associated with a 4.3 +/- 0.56 (SD)-fold increase in total cellular beta-catenin protein content, whereas modest changes in gamma-catenin and E-cadherin expression were recorded. The beta-catenin signal increased before changes in mucosal crypt length, a gross index of cellular proliferation/apoptosis. Beta-catenin detected in Triton X-100-soluble (cytosolic) cellular fractions was enriched 4.3 +/- 0.9 (SD)-fold, whereas a modest decrease of 0.9 +/- 0.09 (SD)-fold was recorded in Triton X-100-insoluble (cytoskeletal) fractions. After these changes, nuclear beta-catenin partitioning increased 2.4 +/- 0.4 (SD)-fold, accompanied by 2.5 +/- 0.4- and 4.0 +/- 0.8-fold (SD) increases in cellular c-myc and cyclin D1 levels, respectively. Thus, increased cellular cytosolic and nuclear beta-catenin levels were associated with increased beta-catenin target protein expression. Significant alterations in beta-catenin subcellular distribution were also recorded immunohistochemically. Apical/lateral junctional labeling was observed in normal crypts with increased lateral membrane staining within the upper regions. During transmissible murine colonic hyperplasia, these gradients were dissipated, and basilar plaques were formed within a subset of basal crypt cells. These findings predict that an oncogenic signaling mechanism related to non-E-cadherin-bound beta-catenin is active in hyperproliferating native colonocytes and is similar to that recorded during the early stages of colon carcinogenesis.     

c-Myc-induced chemosensitization is mediated by suppression of cyclin D1 expression and nuclear factor-kappa B activity in pancreatic cancer cells.

PURPOSE: Pancreatic cancer is a highly aggressive disease that remains refractory to various chemotherapeutic agents. Because the proto-oncogene c-myc can modulate apoptosis in response to cytotoxic insults and is commonly overexpressed in pancreatic cancer, we investigated the value of c-myc as a potential modulator of cellular response to various chemotherapeutic agents. EXPERIMENTAL DESIGN: Stable overexpression or small interfering RNA (siRNA)-mediated knockdown of c-myc and restoration of cyclin D1 were done in the Ela-myc pancreatic tumor cell line. Cell viability after cisplatin treatment of c-myc-overexpressing, control, and siRNA-transfected cells was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and drug-induced apoptosis was measured by DNA fragmentation, sub-G(1), and poly(ADP-ribose) polymerase cleavage analyses. Protein expression profile after cisplatin treatment was determined by Western blotting and DNA binding activity of nuclear factor-kappaB was examined by electrophoretic mobility shift assay. RESULTS: Ectopic overexpression of c-myc in murine and human pancreatic cancer cell lines, Ela-myc and L3.6pl, respectively, resulted in increased sensitivity to cisplatin and other chemotherapeutic drugs. Increased sensitivity to cisplatin in c-myc-overexpressing cells was due, in part, to the marked increase in cisplatin-induced apoptosis. Conversely, down-regulation of c-myc expression in stable c-myc-overexpressing cells by c-myc siRNA resulted in decreased sensitivity to cisplatin-induced cell death. These results indicate an important role of c-myc in chemosensitivity of pancreatic cancer cells. The c-myc-induced cisplatin sensitivity correlated with inhibition of nuclear factor kappaB activity, which was partially restored by ectopic cyclin D1 overexpression. CONCLUSIONS: Our results suggest that the c-myc-dependent sensitization to chemotherapy-induced apoptosis involves suppression of cyclin D1 expression and nuclear factor kappaB activity.     

Extracellular calcium as a candidate mediator of prostate cancer skeletal metastasis

Prostate cancer almost exclusively metastasizes to skeletal sites, indicating that the bone provides a favorable microenvironment for its localization and progression. A natural yet understudied factor in bone that could facilitate tumor localization is elevated extracellular calcium ([Ca2+]o). The present study found that elevated [Ca2+]o (2.5 mmol/L) enhanced proliferation of skeletal metastatic prostate cell lines (PC-3 and C4-2B), but not the nonskeletal metastatic, epithelial-derived prostate cell line LNCaP. The proliferative effect of elevated [Ca2+]o was associated with higher expression of the calcium-sensing receptor (CaSR), a heterotrimeric G-protein-coupled receptor that is the predominant cell-surface sensor for [Ca2+]o. Knockdown of the CaSR via RNA interference reduced cell proliferation in vitro and metastatic progression in vivo. CaSR signaling in PC-3 cells was evaluated by measuring the elevated [Ca2+]o-dependent inhibition of cyclic AMP accumulation, induced by either prostaglandin E2 or forskolin. Elevated [Ca2+]o stabilized expression of cyclin D1, a protein required for cell cycle transition. Furthermore, elevated [Ca2+]o triggered activation of the Akt signaling pathway and enhanced PC-3 cell attachment. Both pertussis toxin (a G-protein inhibitor) and LY294002 (an inhibitor of Akt signaling) reduced cell attachment. These data suggest that elevated [Ca2+]o following increased bone remodeling could facilitate metastatic localization of prostate cancer via the CaSR and the Akt signaling pathway. Taken together, [Ca2+]o is a candidate mediator of prostate cancer bone metastasis.     

Expression of E-cadherin reduces bcl-2 expression and increases sensitivity to etoposide-induced apoptosis

Expression of Bcl-2 is important in determining cancer cell resistance to chemotherapy. However, it is not clear whether cell-cell interactions regulate Bcl-2 expression. Using rat breast carcinoma cells selected for loss of hormone responsiveness, we found that parental E-cadherin-expressing cells (E cells) were more sensitive to etoposide-induced apoptosis than hormone-non-responsive cells (F cells), which failed to express E-cadherin. Expression of beta-catenin and pp120 src substrate proteins, which associate with E-cadherin, was unaffected. To determine whether re-expression of E-cadherin in F cells would restore etoposide sensitivity, F cells were transfected with an expression vector coding for the mouse E-cadherin gene. Stable clonal isolates expressing E-cadherin (F. Cad) showed increased sensitivity to etoposide treatment compared with control clones (F.Neo). Expression of E-cadherin resulted in a redistribution of beta-catenin from the cytoskeletal/nuclear fraction to the cytoplasmic/membrane fraction of the cells. E-cadherin-expressing clones also showed reduced invasion through basement membrane. Etoposide-induced apoptosis was characterized by morphological changes (nuclear blebbing) and DNA fragmentation. Induction of CPP32-like caspase activity was also observed in F.Cad transfectants but not F.Neo cells. Unlike F cells, F.Cad transfectants were not able to express Bcl-2, but transient transfection of bcl-2 resulted in re-expression and resistance to etoposide treatment. Therefore, E-cadherin may negatively regulate Bcl-2 expression by altering the availability of nuclear beta-catenin. Loss of E-cadherin in invasive tumor cells may lead to increased Bcl-2 expression and resistance to chemotherapeutic drugs.     

Modulation of cyclin D1 expression in human tumoral parathyroid cells: effects of growth factors and calcium sensing receptor activation

The study investigated cyclin D1 regulation by growth factors and calcium sensing receptor (CaSR) in human tumoral parathyroid cells. Basic fibroblast and epidermal growth factors increased cyclin D1 and phosphorylated extracellular signal-regulated kinases (pERK1/2) levels that were both efficiently inhibited by CaSR agonists. By contrast, in growth factors-free medium cyclin D1 levels were either unaffected or stimulated by CaSR activation independently from ERK1/2 pathway. Transforming growth factor beta (TGFbeta) reduced cyclin D1 levels in the majority of tumors, this effect being not influenced by CaSR activation and menin expression levels. In conclusion, in parathyroid tumors cyclin D1 expression was modulated by growth factors and CaSR activation. These data further support the oncogenic role of cyclin D1, which resulted to be target for stimulation by bFGF and EGF and inhibition by CaSR and TGFbeta signalling in the parathyroid.     

Truncation of the extracellular region abrogrates cell contact but retains the growth-suppressive activity of E-cadherin

E-cadherin has been demonstrated to induce growth suppression and decrease the invasiveness of cancer cells and thus has been proposed to be a tumor suppressor gene. The ability of E-cadherin to mediate cell-cell contact and contact inhibition presumably accounts for its antitumor effects, which are attributed to the extracellular domain of the protein. Here we report that blocking the ability of E-cadherin to mediate contact inhibition by either antagonistic antibodies or expression of a mutant form of E-cadherin with the extracellular region deleted does not abrogate growth suppression. Transfection of the E-cadherin gene into the human prostate cancer cell line TSU.Pr-1 induced cell-cell contact formation, growth suppression, and redistribution of beta-catenin to the cell membrane. Treatment of the E-cadherin transfectant (CAD) with blocking antibodies disrupted cell-cell contact formation but did not influence the growth rate, suggesting that cell-cell interaction is not required for E-cadherin-mediated growth suppression. Similarly, transfection of an E-cadherin construct in which the NH2-terminal (extracellular) region was deleted did not allow cell-cell contact formation but induced growth suppression. In contrast, transfection of an E-cadherin construct in which the COOH-terminal (cytoplasmic) region was deleted did not induce suppression but promoted cell contact formation. In cells expressing E-cadherin lacking the cytoplasmic region, beta-catenin was evenly distributed in the cytoplasm. By contrast, in cells expressing E-cadherin lacking the extracellular region, beta-catenin was cell membrane associated. Growth suppression was always associated with the localization of beta-catenin to the cell membrane. The redistribution of beta-catenin from the cytoplasm to the cell membrane initially suggested the involvement of the Wnt signaling pathway in regulating cell growth. However, only small differences in beta-catenin/T-cell factor signaling were detected in control and E-cadherin-expressing cells, suggesting that the Wnt pathway is not involved. Taken together, these findings suggest that E-cadherin-induced growth inhibition may not be solely attributed to contact inhibition but may involve the redistribution of beta-catenin from the cytoplasm to the cell membrane, and this redistribution may affect growth pathways independent of T-cell factor.