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.     

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.     

Src family kinase inhibitor PP2 restores the E-cadherin/catenin cell adhesion system in human cancer cells and reduces cancer metastasis.

The E-cadherin/catenin cell adhesion system is often down-regulatedin epithelial tumors. This is thought to play an important role in cancer invasion and metastasis. Restoring this system may enable suppression of the metastatic spread of cancer. This study examined the effect of Src family kinase inhibitor PP2 on E-cadherin-mediated cell-cell adhesion and metastatic potentials. In cell aggregation assays, PP2 stimulated the aggregation of colon, liver, and breast cancer cells. In vitro cultures of cancer cells showed that PP2 induced strong cell-cell contact. Immunoblot analysis showed that PP2 enhanced E-cadherin/catenin expression and that increased E-cadherin/catenin proteins were strongly associated with the actin cytoskeleton. Northern blot studies indicated that the observed increase of E-cadherin/catenin protein content was due to their increased gene expression. After the spleens of severe combined immunodeficient mice were inoculated with cancer cells, treatment with PP2 for 3 weeks markedly reduced the rate of liver metastasis, compared with the control counterparts. Our data demonstrate that PP2 can activate the functioning of the E-cadherin-mediated cell adhesion system, which is associated with the suppression of metastasis in cancer cells. Thus, selective inhibition of Src activation may be potentially useful in the prevention of cancer metastasis.     

Ras Farnesylation Inhibitor FTI-277 Restores the E-Cadherin/Catenin Cell Adhesion System in Human Cancer Cells and Reduces Cancer Metastasis

The E-cadherin/catenin cell adhesion system is often down-regulated in epithelial tumors. This is thought to play an important role in cancer invasion and metastasis, and restoration of this system may suppress metastatic spread of cancer. In this study, the effects of a Ras farnesylation inhibitor (FTI-277) on E-cadherin-mediated cell-cell adhesion and metastatic potential were examined. In cell aggregation assays, FTI-277 stimulated aggregation of colon, liver and breast cancer cells. In vitro cultures of cancer cells showed that FIT-277 induced strong cell-cell contact. Immunoblotting analysis showed that FTI-277 increased E-cadherin/catenin (α, β and γ) expression and strongly stabilized E-cadherin/catenin with the actin cytoskeleton. Northern blotting studies indicated that the observed increase in the E-cadherin/catenin protein content was due to increased expression of their genes. After inoculation of the spleens of mice with severe combined immunodeficiency (SCID) with cancer cells, FTI-277 treatment for 3 weeks markedly reduced splenic primary tumor growth and the rate of liver metastasis compared with control counterparts. Our data demonstrate that FTI-277 can activate functioning of the E-cadherin-mediated cell adhesion system, which is associated with suppression of cancer cell metastasis. Therefore, selective inhibition of Ras activation may be useful for preventing cancer metastasis.     

Involvement of nectin in the localization of IQGAP1 at the cell-cell adhesion sites through the actin cytoskeleton in Madin-Darby canine kidney cells

IQGAP1, a putative downstream target of the Rho family small G proteins, Cdc42 and Rac, localizes at adherens junctions (AJs) in epithelial cells. It has been suggested that IQGAP1 localizes at AJs through its binding to beta-catenin, and negatively regulates the E-cadherin-mediated cell-cell adhesion. Nectin is a Ca(2+)-independent, immunoglobulin-like cell-cell adhesion molecule that localizes at AJs. Nectin is associated with E-cadherin through their respective cytoplasmic tail-binding proteins, afadin and catenins, and involved in the formation of AJs cooperatively with E-cadherin. Here we investigated a role of nectin in the localization of IQGAP1 at AJs. Ca(2+) chelation from the medium causes disruption of the E-cadherin-mediated cell-cell adhesion, but not the nectin-based cell-cell adhesion, in Madin-Darby canine kidney (MDCK) cells. IQGAP1 remained at the residual nectin-based cell-cell adhesion sites where the E-cadherin immunofluorescence signal disappeared. Restoration of Ca(2+) in the medium causes re-accumulation of E-cadherin to the residual nectin-based cell-cell adhesion sites to re-form AJs. Nectin inhibitors inhibit this re-accumulation of E-cadherin to re-form AJs by impairing the nectin-based cell-cell adhesion. The nectin inhibitors also reduced the localization of IQGAP1 at the cell-cell adhesion sites. When MDCK cells were incubated with microbeads coated with the extracellular fragment of nectin that interacts with cellular nectin, IQGAP1 also accumulated at the bead-MDCK cell contact sites. The accumulation of IQGAP1 at the cell-cell adhesion sites was inhibited by actin filament-disrupting agents, latrunculin A and cytochalasin D. These results indicate that nectin is involved in the localization of IQGAP1 at AJs through the actin cytoskeleton.     

Anti-tumor effect of the anti-KL-6/MUC1 monoclonal antibody through exposure of surface molecules by MUC1 capping

Human polymorphic epithelial mucin (MUC1) is a heavily glycosylated large protein that is frequently overexpressed on the surface of many human adenocarcinomas. Studies using monoclonal antibodies (mAb) identified MUC1 as a tumor-associated antigen that has been intensely studied as a target for cancer immunotherapy. We previously identified a mouse IgG(1) mAb that recognizes a sialylated sugar chain, designated as KL-6, classified in 'Cluster 9 (MUC1)'. Using the anti-KL-6 mAb, we investigated antitumor effects of anti-MUC1 mAb on breast cancer cell lines expressing MUC1 abundantly. We showed that anti-KL-6 mAb induced capping of MUC1 and facilitated E-cadherin-mediated cell-cell interaction in the breast cancer cell lines YMB-S and ZR-75-1S, which proliferate in suspension culture without aggregation. Moreover, anti-KL-6 mAb enhanced the cytotoxic activity of lymphokine-activated killer cells. These results indicate that the capping of MUC1 restores cell surface proteins, such as adhesion molecules and tumor antigens, to work in cell-cell interactions, leading to inhibition of tumor proliferation due to cell-cell adhesion and increased accessibility to effector cells that are needed to kill tumor cells.     

Ras farnesylation inhibitor FTI-277 restores the E-cadherin/catenin cell adhesion system in human cancer cells and reduces cancer metastasis.

The E-cadherin/catenin cell adhesion system is often down-regulated in epithelial tumors. This is thought to play an important role in cancer invasion and metastasis, and restoration of this system may suppress metastatic spread of cancer. In this study, the effects of a Ras farnesylation inhibitor (FTI-277) on E-cadherin-mediated cell-cell adhesion and metastatic potential were examined. In cell aggregation assays, FTI-277 stimulated aggregation of colon, liver and breast cancer cells. In vitro cultures of cancer cells showed that FTI-277 induced strong cell-cell contact. Immunoblotting analysis showed that FTI-277 increased E-cadherin/catenin (alpha, beta and gamma) expression and strongly stabilized E-cadherin/catenin with the actin cytoskeleton. Northern blotting studies indicated that the observed increase in the E-cadherin/catenin protein content was due to increased expression of their genes. After inoculation of the spleens of mice with severe combined immunodeficiency (SCID) with cancer cells, FTI-277 treatment for 3 weeks markedly reduced splenic primary tumor growth and the rate of liver metastasis compared with control counterparts. Our data demonstrate that FTI-277 can activate functioning of the E-cadherin-mediated cell adhesion system, which is associated with suppression of cancer cell metastasis. Therefore, selective inhibition of Ras activation may be useful for preventing cancer metastasis.     

Collagen type I induces disruption of E-cadherin-mediated cell-cell contacts and promotes proliferation of pancreatic carcinoma cells

Pancreatic cancer is characterized by its invasiveness, early metastasis, and the production of large amounts of extracellular matrix (ECM). We analyzed the influence of type I collagen and fibronectin on the regulation of cellular adhesion in pancreatic cancer cell lines to characterize the role of ECM proteins in the development of pancreatic cancer. We show that collagen type I is able to initiate a disruption of the E-cadherin adhesion complex in pancreatic carcinoma cells. This is due to the increased tyrosine phosphorylation of the complex protein beta-catenin, which correlates with collagen type I-dependent activation of the focal adhesion kinase and its association with the E-cadherin complex. The activation and recruitment of focal adhesion kinase to the E-cadherin complex depends on the interaction of type I collagen with beta1-containing integrins and an integrin-mediated activation of the cellular kinase Src. The disassembly of the E-cadherin adhesion complex correlates with the nuclear translocation of beta-catenin, which leads to an increasing expression of the beta-catenin-Lef/Tcf target genes, cyclin D1 and c-myc. In addition to that, cells grown on collagen type I show enhanced cell proliferation. We show that components of the ECM, produced by the tumor, contribute to invasiveness and metastasis by reducing E-cadherin-mediated cell-cell adhesion and enhance proliferation in pancreatic tumor cells.     

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。     

Abnormal expression and function of the E-cadherin-catenin complex in gastric carcinoma cell lines.

Dysfunction of the cadherin-catenin complex, a key component of adherens junctions, is thought to confer invasive potential to cells. The aim of this study is to examine the expression and function of the E-cadherin/catenin complex in gastric carcinoma cell lines. Expression of E-cadherin, alpha, beta and gamma-catenin and p120ctn, and of the adenomatous polyposis coli protein (APC), together with function of the cadherin-catenin complex was examined in a panel of gastric carcinoma cell lines, using immunocytochemistry, Western blotting and a cell-cell aggregation assay. Protein interactions were examined by sequential immunoprecipitation and immunoblotting with antibodies to E-cadherin, alpha, beta and gamma-catenin, p120ctn and APC. Abnormalities of E-cadherin, alpha- and beta-catenin expression, were associated with disturbance of E-cadherin-catenin complex composition, loss of membranous localization and loss of calcium-dependent aggregation in six gastric carcinoma cell lines. APC protein expression and interaction with beta-catenin was preserved in five cell lines. We demonstrate frequent abnormalities of expression and function of E-cadherin and catenins, and associated disturbance of E-cadherin-mediated intercellular adhesion in gastric carcinoma cell lines. These findings support the tumour suppressor role of the E-cadherin and its contribution to the development and progression of the neoplastic phenotype in gastric carcinoma.     

Inverse relationship between E-cadherin and p27Kip1 expression in renal cell carcinoma

The cell-cell adhesion system plays a pivotal role in the maintenance of tissue structure and cell-cell communication. E-cadherin is a major adhesion protein of the epithelial cells, and E-cadherin expression may be involved in the regulation of cell proliferation or differentiation. To address the relationship between cell-cell adhesion and cell proliferation, we focused on the alteration of p27Kip1 (p27), a cyclin-dependent kinase inhibitor, by E-cadherin-mediated adhesion. In an immunohistochemical study of 76 cases of renal cell carcinoma (RCC), the p27-labeling index (LI) was 67% in E-cadherin-reduced RCC, but only 28% in E-cadherin-preserved RCC. E-cadherin-expressing cells rarely expressed p27 in various cancers including those of the breast, colon, liver and prostate. In a subconfluent monolayer culture, the E-cadherin levels were increased steadily in the E-cadherin positive RCC cell line ACHN, whereas the p27 levels were decreased. Subsequent exposure of ACHN cells to the E-cadherin-specific function-blocking antibody reduced the growth associated with the increase in p27 and the decrease in phosphorylated epidermal growth factor receptor (EGFR). In the E-cadherin negative RCC cell line Caki-1, these effects were not observed. These results suggest that E-cadherin-mediated adhesion may be involved in the contact stimulation for cell proliferation in part through the downregulation of p27 and the activation of EGFR in human cancers.     

Dominant-negative E-cadherin alters adhesion and reverses contact inhibition of growth in breast carcinoma cells

Cadherins play a crucial role in epithelial morphogenesis and mediate intercellular adhesion. These receptors bind catenins and are involved in signal transduction pathways that regulate cell growth and apoptosis, and are frequently down-regulated in invasive and metastatic carcinomas. In order to assess the role of E-cadherin in cell adhesion and growth, we transfected MCF-7 cells, a human breast cancer cell line, with a dominant-negative construct of E-cadherin (H-2kd-E-cad). The dominant-negative form of E-cadherin disrupted cell-cell adhesion of monolayer cells and induced an epithelial-to-fibroblastic conversion without any significant change in integrin profiles. Whereas control cells rapidly formed multicellular aggregates that tightly compacted into spheroids, dominant-negative transfected cells failed to compact and remained as loosely-associated cells. The transfectants exhibited down-regulation and redistribution of endogenous E-cadherin as well as increased levels of alpha- and beta-catenin. Importantly, the H-2kd-E-cad-transfected cells, when grown as multicellular aggregates, showed an increase in cell proliferation rate, compared to control cells. Overall, these observations suggest that in breast carcinoma, disruption of E-cadherin and catenin function modulates both cell-cell adhesion and permits escape from cell-cell contact-involved inhibition of cell growth.     

Type I collagen and divalent cation shifts disrupt cell-cell adhesion, increase migration, and decrease PTHrP, IL-6, and IL-8 expression in pancreatic cancer cells

Background: We have shown in FG pancreatic cancer cells that α₂β₁ integrin-mediated type I collagen adhesion decreases parathyroid hormone-related protein (PTHrP), inerleukin-6 (IL-6), and interleukin-8 (IL-8) expression, decreases the localization of E-cadherin and β-catenin in cell-cell contacts, increases cell migration, and increases glycogen synthase kinase 3 (GSK3) and protein kinase B (PKB/Akt) phosphorylation states relative to α₅β₁ integrin-mediated fibronectin (Fn) adhesion. Aim of the Study: To extend our observations in FG cells to other pancreatic cancer cell lines, and to determine whether E-cadherin-mediated cell-cell adhesion and its downstream effectors were functionally involved in the ECM-mediated regulation of PTHrP, IL-6, and IL-8. Methods: We used standard biochemical techniques to determine ECM-specific differences in E-cadherin and β-catenin localization, GSK3 and PKB/Akt phosphorylation, haptokinetic cell migration, and cytokine expression in pancreatic cancer cells. We also conducted functional studies using pharmacological inhibitors for GSK3 and PKB/Akt, as well as elevated Mg²⁺/Ca²⁺ ratios similar to pancreatic juice, and examined their effects on cytokine expression. Results: Differences in E-cadherin and β-catenin localization along with GSK3 and PKB/Akt phosphorylation occur in multiple pancreatic cancer cell lines, resulting in differences in ECM-mediated haptokinesis and cytokine expression that are generally consistent with previous observations in FG cells. Our functional studies also suggest that E-cadherin-mediated cell-cell adhesion and downstream effectors are involved in PTHrP, IL-6, and IL-8 expression. Conclusions: These data indicate that α₂β₁ integrin-mediated type I collagen adhesion disrupts cell-cell adhesion architecture, resulting in increased migration and decreased PTHrP, IL-6, and IL-8 expression in pancreatic cancer cells.     

Csk defines the ability of integrin-mediated cell adhesion and migration in human colon cancer cells: implication for a potential role in cancer metastasis

Progression of human colon cancer is often associated with elevated expression and activity of the Src family tyrosine kinase (SFK). SFK is ordinarily in equilibrium between inactive and primed states by a balance of negative regulatory kinase Csk and its counteracting tyrosine phosphatase(s), both of which act on the regulatory C-terminal tyrosine of SFK. To evaluate the contribution of the regulatory system of SFK in cancer progression, we here modulated the equilibrium status of SFK by introducing wild-type or dominant-negative Csk in human epithelial colon cancer cells, HCT15 and HT29. Overexpression of wild-type Csk induced decreased SFK activation, increased cell-cell contacts mediated by E-cadherin, decreased the number of focal contacts and decreased cell adhesion/migration and in vitro invasiveness. Conversely, expression of a dominant-negative Csk resulted in elevated SFK activation, enhanced phosphorylation of FAK and paxilllin, enhanced cell scattering, an increased number of focal contacts, dramatic rearrangement of actin cytoskeleton and increased cell adhesion/migration and in vitro invasiveness. In these scattered cells, however, localization, expression and phosphorylation of either E-cadherin or beta-catenin were not significantly affected, suggesting that the E-cadherin-mediated cell-cell contact is indirectly regulated by SFK. Furthermore, all these events occurred absolutely dependent on integrin-mediated cell adhesion. These findings demonstrate that Csk defines the ability of integrin-SFK-mediated cell adhesion signaling that influences the metastatic potential of cancer cells.     

Cadherin dysfunction in a human cancer cell line: possible involvement of loss of alpha-catenin expression in reduced cell-cell adhesiveness.

A human lung cancer cell line, PC 9, was analyzed to elucidate the molecular mechanisms of dysfunction of cadherin-mediated cell-cell adhesion in cancer. Although PC 9 cells strongly expressed E-cadherin at the cell membrane, which was indistinguishable immunochemically from functional E-cadherin, they did not show tight cell-cell adhesion and had reduced E-cadherin-mediated aggregation activity. Immunoprecipitation with E-cadherin and Western blot analysis revealed that PC 9 cells did not express alpha-catenin, a cadherin-associated protein, suggesting that this was the cause of the cadherin dysfunction in the cell line. In addition, Northern and Southern blot analyses disclosed homozygous deletion of part of the alpha-catenin gene, which might have resulted in the loss of alpha-catenin expression in PC 9 cells.     

Regulation of squamous cell carcinoma antigen production by E-cadherin mediated cell-cell adhesion in squamous cell carcinoma cell line

Squamous cell carcinoma antigen (SCCA) is a useful tumor marker for diagnosis and management of squamous cell carcinoma. It is well known that cell-cell adhesion is important for progression of cancer. However, it is not clarified whether cell-cell adhesion affects SCCA production in squamous cell carcinoma. The present study was, therefore, undertaken to investigate whether E-cadherin-mediated cell-cell adhesion affects SCCA production in squamous cell carcinoma of the uterine cervix. SKG-IIIa cells or CaSki cells, cervical squamous cell carcinoma cell lines, were treated with anti-E-cadherin antibodies (1 microg/ml) up to 72 h. The cells were dissociated, and SCCA content in the cytosol and SCCA mRNA levels were significantly decreased compared to the control group treated with mouse IgG. Secondly, the signaling pathway for SCCA production mediated by E-cadherin was examined. Phosphatidylinositol (PI) 3-kinase is a well-known mediator of E-cadherin-mediated biological events. The treatment with a PI 3-kinase inhibitor suppressed SCCA production in SKG-IIIa cells. It is concluded that E-cadherin mediated cell-cell adhesion maintains SCCA production through PI 3-kinase in squamous cell carcinoma.     

Transactivation of E-cadherin is not involved in the activity of EGF receptor in colorectal carcinoma cells

In epithelial cells, the cell surface glycoprotein E-cadherin is a key molecule in the establishment of cell-cell adhesion. In addition to its contribution to cell adhesion, E-cadherin was found to induce ligand-independent activation of the EGF receptor (EGFR), likely as a result of their co-clustering. As it has also been reported that ligand activation of the overexpressed EGFRs disturb E-cadherin-mediated cell-cell adhesion, we analyzed E-cadherin-EGFR interactions and their consequences in A431 cells and in two colorectal cancer cell lines using immunoblotting and analyzes of several protein kinase activities. Activation of the PI3-K/Akt/GSK-3 signaling pathway upon EGF treatment that we observed in the analyzed cells indicates that EGFRs are functional even in the colorectal cancer cells containing a low density of EGFRs. The transactivation of EGFR by E-cadherin did not occur either in the colorectal cancer cells tested or in A431 cells containing a high density of both EGFRs and E-cadherin on their surface. This observation suggests that high amounts of both molecules on the surface of tumour cells did not predetermine ligand-independent activation of EGFRs.     

Heterogeneity of MUC1 expression by human breast carcinoma cell lines in vivo and in vitro

Increased expression of the epithelial mucin MUC1 has been linked to tumor aggressiveness in human breast carcinoma. Recent studies have demonstrated that overexpression of MUC1 interferes with cell-substrate and cell-cell adhesion by masking cell surface integrins and E-cadherin. Additionally, the cytoplasmic tail of MUC1 is involved in signal transduction and interactions with catenins. In the present study, we have examined the in vitro expression of MUC1 mRNA and protein in a panel of 14 human breast cancer cell lines using northern blotting, western blotting, immunocytochemistry, and flow cytometry. Considerable variability of expression was noted not only between cell lines but also within several individual lines. Many cell lines such as BT 20, KPL-1, and T47D expressed abundant MUC1 whilst others such as MDA-MB-231 and MCF-7 showed intermediate expression, and MDA-MB-435 and MDA-MB-453 expressed very low levels. Low levels of MUC1 expression were associated with decreased expression of cytokeratin and increased expression of vimentin. Additionally, 12 of the cell lines were established as xenografts in immunocompromised (SCID) mice, and MUC1 expression in both the primary tumors as well as metastases was assessed immunohistochemically. In general, in vivo expression mirrored in vitro expression, although there was reduced in vivo expression in T47D and ZR-75-1 xenografts. Although we showed no correlation between tumorigenicity or metastasis and MUC1 expression, this study will assist development of experimental models to assess the influence of MUC1 of on breast cancer progression.