Adherens junctions (AJs; also called the zonula adherens) are critical for the establishment and maintenance of epithelial layers, such as those lining organ surfaces. AJs mediate adhesion between cells, communicate a signal that neighboring cells are present, and anchor the actin cytoskeleton. In serving these roles, AJs regulate normal cell growth and behavior. At several stages of embryogenesis, wound healing, and tumor cell metastasis, cells form and leave epithelia. This process, which involves the disruption and reestablishment of epithelial cell-cell contacts, may be regulated by the disassembly and assembly of AJs. AJs may also function in the transmission of the 'contact inhibition' signal, which instructs cells to stop dividing once an epithelial sheet is complete. As reviewed by Peifer M. (1993), the AJ is a multiprotein complex assembled around calcium-regulated cell adhesion molecules called cadherins (i.e. E-cadherin). Cadherins are transmembrane proteins: the extracellular domain mediates homotypic adhesion with cadherins on neighboring cells, and the intracellular domain interacts with cytoplasmic proteins that transmit the adhesion signal and anchor the AJ to the actin cytoskeleton. These cytoplasmic proteins include the alpha-, beta-, and gamma-catenins.
There is evidence that a loss of function in E-cadherin and/or one or more collaborating proteins contributes to increased proliferation, invasion, and metastasis in breast cancer (and other solid tumors). Associations have been found between loss of E-cadherin expression and dedifferentiation, grade (Gamallo C. et al., 1993), metastasis (Oka H. et al., 1993), and decreased patient survival duration.
Cell lines:
- By immunofluorescence, E-cadherin was found in BT-483, MDA-MB-175-VII, MCF-7, ZR-75-B, T-47D, BT-474, and MDA-MB-361 breast cancer cell (BCC) lines, but not in MDA-MB-468, SK-BR-3, CAMA-1, MDA-MB-453, -134, -436, -435, -231, BT-549, Hs578T, and MCF-7/Adr (doxorubicin-resistant) BCC lines. E-cadherin expression was directly correlated with
ER,
ZO-1, and desmoplakin I+II expression, inversely correlated with
vimentin expression and
in vitro invasiveness of BCC (Sommers C.L. et al., 1994).
- Analyses of expression, genetic mutation, and promoter methylation of E-cadherin was examined in 10 commonly used BCC lines. Five BCC lines (BT-474, MCF-7, MDA-MB-361, MDA-MB-468, and T-47D) expressed E-cadherin, at mRNA and protein levels, and were genetically normal. Five others (SK-BR-3, 600 MPE, MDA-MB-134 IV, CAMA1, and MDA-MB-435) did not express CDH1 (neither at protein or, except for 600 MPE cells, at mRNA levels); in SK-BR-3, the E-cadherin gene was deleted from exon 12 through the promoter; exon 6 was deleted in MDA-MB-134 IV; 600 MPE carried a 21-bp deletion in the splicing acceptor site for exon 9; CAMA1 seemed to have been inactivated through promoter methylation. No explanation was found for the inactivation of E-cadherin in MDA-MB-435 (Hiraguri S. et al., 1998).
- The treatment of breast tumor cells in a three-dimensional culture with a
beta 1 integrin antibody caused a reversion of the malignant phenotype and increased E-cadherin expression (Weaver V.M. et al., 1997).
- EMT/6 mouse mammary carcinoma cells that lack E-cadherin were transfected with an exogenous E-cadherin expression vector. E-cadherin expression in EMT/6 cells resulted in tighter adhesion of multicellular spheroids and a reduced proliferative fraction in three-dimensional culture. In addition to increased cell-cell adhesion, E-cadherin expression also resulted in dephosphorylation of the retinoblastoma protein, an increase in the level of the cyclin-dependent kinase inhibitor p27(kip1) and a late reduction in
cyclin D1 protein. Exposure to E-cadherin-neutralizing antibodies in three-dimensional culture simultaneously prevented adhesion and stimulated proliferation of E-cadherin transfectants as well as a panel of human colon, breast, and lung carcinoma cell lines that express functional E-cadherin. To test the importance of p27 in E-cadherin-dependent growth inhibition, E-cadherin-positive cells were engineered to express inducible p27. By forcing expression of p27 levels similar to those observed in aggregated cells, the stimulatory effect of E-cadherin-neutralizing antibodies on proliferation could be inhibited (St Croix B. et al., 1998).
- Treatment of MDA-MB-468 BCC line with epidermal growth factor (EGF) inhibited cellular aggregation but did not affect either the levels of E-cadherin or catenin expression nor the association of catenins (
beta-catenin, plakoglobin/gamma-catenin, or p120(cas)) with E-cadherin. However, EGF treatment of the MDA-MB-468 BCC line dissociated actin, alpha-actinin, and vinculin from the E-cadherin-catenin complex, and this coincided with a robust phosphorylation of
beta-catenin, plakoglobin/gamma-catenin, and p120(cas) on tyrosine residues. Inactivation of the
EGF receptor in serum-treated MDA-MB-468 cells with either a function-blocking antibody or
EGF receptor kinase inhibitors mimicked the effects of serum starvation by stimulating both cellular aggregation and assembly of E-cadherin complexes with vinculin and actin (Hazan R.B. and Norton L., 1998).
- A decreased expression of
MUC1 was found to induce E-cadherin-mediated adhesion of the YMB-S and ZR-75-1S BCC normally proliferating in suspension culture without aggregation (Kondo K. et al., 1998). In YMB-S BCC, the anticancer agent adriamycin was able to induce E-cadherin-mediated cell-cell adhesion by increasing expression of E-cadherin and beta-catenin and decreasing expression of
MUC1 during breast cancer cell apoptosis induced by this drug (Yang S. et al., 1999).
- MDA-MB-435S BCC transfected with wild-type E-cadherin showed an epitheloid morphology, while all MDA-MB-435S cells expressing mutant E-cadherin exhibited more irregular cell shapes. Cells expressing E-cadherin mutated in exon 8 showed the most scattered appearance, whereas cells with deletion of exon 9 had an intermediate state. Mutant E-cadherins were localized to the lateral regions of cell-to-cell contact sites. Additionally, both exon 8-mutated E-cadherins showed apical and perinuclear localization, and actin filaments were drastically reduced. MDA-MB-435S cells with initial calcium-dependent cell aggregation exhibited decreased aggregation and, remarkably, increased cell motility, when mutant E-cadherin was expressed. It was concluded that these E-cadherin mutations may not simply affect cell adhesion but may act in a trans-dominant-active manner, i.e. lead to increased cell motility (Handschuh G. et al., 1999).
- The phenotypic characteristics of 2 tumor cell lines (BC-H1 and BC-K1) established from bone marrow of patients with breast cancer were studied by immunocytochemistry, flow cytometry, and RT-PCR. Both cell lines expressed E-cadherin,
vimentin, cytokeratins (including
component 18), alpha 5-,
alpha V-,
beta 1-, and
beta 3- integrin subunits,
ICAM-1,
MCAM, LFA-3 (CD58), and
CD44s (but not
CD44v5,
v6,
v7/8). BC-H1 also expressed
ErbB2 (not found in BC-K1), and
MAGE-4 (but not MAGE-1, -2, -3/6, -12; BC-K1 was not tested). The expressed molecules might be potential candidates for novel therapeutic targets (Putz E. et al., 1999).
- In cultured BCC, the heterogeneous methylation of E-cadherin promoter was found to be dynamic, varying from allele to allele and shifting in relation to the tumor microenvironment. Following invasion
in vitro, which favors diminished E-cadherin expression, the density of promoter methylation markedly increased. When BCC were cultured as spheroids, which requires homotypic cell adhesion, promoter methylation decreased dramatically, and E-cadherin was reexpressed. These data suggest that the methylation associated with E-cadherin loss in human breast cancer is heterogeneous and unstable. Such epigenetic plasticity might contribute to the dynamic, phenotypic heterogeneity that drives metastatic progression (Graff J.R. et al., 2000).
Tumors:
- Low E-cadherin expression is found in half of infiltrating ductal carcinoma (Gamallo C. et al., 1993; Moll R. et al., 1993; Rasbridge S.A. et al., 1993).
- Lobular carcinomas were shown to contain a high frequency of E-cadherin mutations, resulting in decreased or absent expression (Berx G. et al., 1995b; De Leeuw W.J.F. et al., 1997).
- In an immunohistochemical study of breast tumor samples, the proportion of tumors with reduced or lost E-cadherin expression increased significantly from pure intraductal carcinomas (20%, 4 of 20) through invasive ductal (IDCs; 52%, 124 of 239) to recurrent carcinomas (64%, 18 of 28; chi square test for trend, P = .004). Invasive lobular carcinomas (ILCs) and IDCs differed from each other in their E-cadherin expression. None of the ILCs (n=55) retained normal E-cadherin expression in contrast to 48% (115 of 239) of the IDCs. In 259 primary IDCs, reduced E-cadherin expression was associated with high histologic grade (chi square test for trend, P < .001), negative
estrogen receptor status (ER; Fisher's exact test; P = .042), and marginally with axillary node involvement (Fisher's exact test, P = .063). In a subset of 109 primary IDC patients whose clinical follow-up was available (median follow-up 51 months), reduced E-cadherin expression was associated with shortened disease-free survival (DFS; Mantel-Cox test, P = .027) (Siitonen S.M. et al., 1996).
- Loss of E-cadherin expression in breast tumors may occur through mutation (Berx G. et al., 1996), promoter methylation (Graff J.R. et al., 1995), and/or transcriptional down-regulation.
- The expression of P-cadherin, E-cadherin, and N-cadherin, and alpha-catenin and beta-catenin was investigated in 183 cases of invasive breast carcinoma by immunohistochemistry on paraffin sections. P-cadherin was positive in 95 cases and negative in 88 cases of breast carcinoma. Positive P-cadherin expression in breast carcinoma showed a strong correlation with poor patient prognosis. Expression of N-cadherin, alpha-catenin, and beta-catenin did not correlate with patient survival. In ductal carcinomas, positive P-cadherin expression correlated with a higher histologic grade. In contrast, expression of E-cadherin was low in high grade ductal carcinomas but negative tumors were uncommon. Negative or low E-cadherin expression did not correlate with poor survival. In lobular carcinomas, E-cadherin expression frequently was negative or low, and P-cadherin always was negative (Peralta Soler A. et al., 1999).
- From a study of 40 human lobular breast cancers, it was concluded that loss of heterozygosity (LOH) at chromosome 16q is the most frequent chromosome alteration and E-cadherin is a typical tumour suppressor gene in lobular breast cancer (Huiping C. et al., 1999).
- E-cadherin expression was evaluated by immuno-histochemistry in a combined panel of 214 breast cancers enriched in hereditary cases (176 sporadic cases and 38
BRCA1-associated breast cancers). Following multivariate statistical analysis using a logistic regression model, only 2 parameters were significantly associated with loss of E-cadherin expression: lobular histological type, in agreement with previous results, and syncytial growth pattern (Jacquemier J. et al., 1999).
- It has been suggested that the heterogeneous loss of E-cadherin expression in primary human breast cancers reflects a heterogeneous pattern of promoter region methylation, which begins early prior to invasion (Graff J.R. et al., 2000).
- Protein expression of p53,
bcl-2, p21,
cyclin D1,
E-cadherin, alpha-catenin,
beta-catenin, and gamma-catenin was investigated in both primary tumours and metastatic lesions from 34 breast cancer patients by immunohistochemistry (IHC) using monoclonal antibodies. Metastatic tissue showed a different expression profile from the primary tumour in most patients. The most significant finding was the re-expression of
E-cadherin, alpha-catenin, and
beta-catenin, and increased down-regulation of gamma-catenin, in metastatic lesions (Bukholm I.K. et al., 2000).
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