Adhesion systems in embryonic epithelial-to-mesenchyme transformations and in cancer invasion and metastasis

Expression of E-Cadherin in breast carcinomas and its association with other biological markers - a prospective study

CONTEXT

E-cadherin (E-CD) is an important cell adhesion molecule in normal epithelial cells and has been shown to be an invasion tumor suppressor gene.

MATERIALS AND METHODS

Various clinicopathological parameters like age, family history, tumor stage, histological grade, lymph node status and other biological markers were also analyzed. Present study reveals E-CD expression in 65 cases of breast cancer including 41 (63%) cases of pure infiltrating ductal carcinoma (IDC), 11 (16.9%) of pure infiltrating lobular carcinoma (ILC); another 10 (15.3%) of mixed ductal/lobular type, and remaining 3 (4.6%) miscellaneous types.

RESULTS

Negative E-CD expression was noticed more in advancing age groups (P = 0.01). About 59.2% cases showing negative E-CD expression had family history of breast and/or other cancers. E-CD expression was found significantly higher in cases of pure IDC (55.5%) than in pure ILC cases (18.1%) (P = 0.04). Eleven (68.7%) of the total 16 high-grade IDC cases, revealed negative expression. Both cases of comedo carcinoma revealed negative expression. Three (30%) out of 10 mixed cases revealed negative expression in both ductal and lobular areas, while in remaining 7 cases, positvity was seen in ductal areas only. Invasive cribriform and medullary carcinoma revealed a stronger expression, while negative staining was observed in sweat gland carcinoma. E-CD re-expression was noticed in lymph node tumor deposits. A direct association of E-CD expression with ER expression and an inverse association with that of p53 were also observed (P = 0.001), (P = 0.04).

CONCLUSIONS

E-CD expression is useful, but limited, in differentiating IDCs from ILCS. Its negative expression correlates with certain poor prognostic parameters reflecting its use as a marker for invasive cancers. It re-expresses at metastatic sites.

Cholera toxin-induced alteration of the phenotype and behaviour of an ovarian carcinoma cell line, SR8

Cholera toxin (CT) has been reported to cause a variety of effects on several different cell types. Recently, CT has been shown to increase the susceptibility of ovarian carcinoma cells to cytotoxicity mediated by a variety of effector cells (natural killer, lymphokine-activated killer cells and tumour-associated lymphocytes derived from ascites of ovarian cancer patients) of both autologous and allogenic background. In the present study, CT demonstrated several effects on a newly established ovarian carcinoma line (SR8)1 when added to the culture medium at a concentration of 12.5 ng/mL for 2 days. Cholera toxin altered SR8 morphology to a uniform polygonal cellular shape, with less cell dispersion than the non-CT treated cells. Cholera toxin prolonged the population doubling time by approximately 10 h. The CT-treated SR8 cells exhibited reduced epidermal growth factor receptor expression (39 versus 50%), and increased carbohydrate antigen 125 expression (45 versus 2%) in both immunocytochemical and quantitative flow cytometric analyses. These changes in morphology and tumour marker expression were reversible when CT was removed from the culture. The CT-treated SR8 cells showed reduced capacity to generate tumours in female nude mice in comparison with non-CT treated cells, which produce both subcutaneous and intraperitoneal xenografts with local invasion in an animal model. Cytogenetic analysis of the cell line SR8 before and during treatment with CT showed no new clonal rearrangements. The possible mechanisms involved and the influence of CT on the biological behaviour of ovarian tumour cells are discussed.

Regulated binding of PTP1B-like phosphatase to N-cadherin: control of cadherin-mediated adhesion by dephosphorylation of beta-catenin

Cadherins are a family of cell-cell adhesion molecules which play a central role in controlling morphogenetic movements during development. Cadherin function is regulated by its association with the actin containing cytoskeleton, an association mediated by a complex of cytoplasmic proteins, the catenins: alpha, beta, and gamma. Phosphorylated tyrosine residues on beta-catenin are correlated with loss of cadherin function. Consistent with this, we find that only nontyrosine phosphorylated beta-catenin is associated with N-cadherin in E10 chick retina tissue. Moreover, we demonstrate that a PTP1B-like tyrosine phosphatase associates with N-cadherin and may function as a regulatory switch controlling cadherin function by dephosphorylating beta-catenin, thereby maintaining cells in an adhesion-competent state. The PTP1B-like phosphatase is itself tyrosine phosphorylated. Moreover, both direct binding experiments performed with phosphorylated and dephosphorylated molecules, and treatment of cells with tyrosine kinase inhibitors indicate that the interaction of the PTP1B-like phosphatase with N-cadherin depends on its tyrosine phosphorylation. Concomitant with the tyrosine kinase inhibitor-induced loss of the PTP1B-like phosphatase from its association with N-cadherin, phosphorylated tyrosine residues are retained on beta-catenin, the association of N-cadherin with the actin containing cytoskeleton is lost and N-cadherin-mediated cell adhesion is prevented. Tyrosine phosphatase inhibitors also result in the accumulation of phosphorylated tyrosine residues on beta-catenin, loss of the association of N-cadherin with the actin-containing cytoskeleton, and prevent N-cadherin mediated adhesion, presumably by directly blocking the function of the PTP1B-like phosphatase. We previously showed that the binding of two ligands to the cell surface N-acetylgalactosaminylphosphotransferase (GalNAcPTase), the monoclonal antibody 1B11 and a proteoglycan with a 250-kD core protein, results in the accumulation of phosphorylated tyrosine residues on beta-catenin, uncoupling of N-cadherin from its association with the actin containing cytoskeleton, and loss of N-cadherin function. We now report that binding of these ligands to the GalNAcPTase results in the absence of the PTP1B-like phosphatase from its association with N-cadherin as well as the loss of the tyrosine kinase and tyrosine phosphatase activities that otherwise co-precipitate with N-cadherin. Control antibodies and proteoglycans have no such effect. This effect is similar to that observed with tyrosine kinase inhibitors, suggesting that the GalNAcPTase/proteoglycan interaction inhibits a tyrosine kinase, thereby preventing the phosphorylation of the PTP1B-like phosphatase, and its association with N-cadherin. Taken together these data indicate that a PTP1B-like tyrosine phosphatase can regulate N-cadherin function through its ability to dephosphorylate beta-catenin and that the association of the phosphatase with N-cadherin is regulated via the interaction of the GalNAcPTase with its proteoglycan ligand. In this manner the GalNAcPTase-proteoglycan interaction may play a major role in morphogenetic cell and tissue interactions during development.

Experimental induction of epithelial-mesenchymal interconversions

Under some in vitro conditions, such as exposure to collagen, growth factors and related molecules, and agents affecting DNA methylation, a cell phenotype shift can be observed from an epithelial to a mesenchymal state of differentiation. The reverse process, a mesenchymal-to-epithelial conversion can likewise be obtained by certain experimental manipulations. In some instances the change is fully reversible by removing the inducer substances, but in others the conversion appears to be stable and irreversible. Only a partial modulation of the cell phenotype is often seen, but sometimes a complete switch to a new phenotype occurs, and morphological, biochemical and functional characteristics of the parent cells can be abrogated. In some in vivo models development of sarcomatous tumours can be seen in animals transplanted with several types of carcinoma, and it is possible that in some of these experiments an epithelial-to-mesenchymal conversion has occurred too. In normal embryonic development as well as in pathological lesions including tissue repair, tumour invasion, and some malignant biphasic tumours, changes similar to the ones observed in experimental epithelial-mesenchymal interconversion seem to take place. Therefore, it is conceivable that experimentally-induced phenotype conversions reflect an inherent potential of cells, and that under some experimental circumstances normally silent genetic programs for epithelial or mesenchymal differentiation are activated, thus recapitulating a phenomenon that occurs in physiopathological circumstances in vivo.

EGF receptor in neoplasia and metastasis

EGFR is a member of the tyrosine kinase family of cell surface receptors with a wide range of expression throughout development and in a variety of different cell types. The receptor can transmit signals to cells: i) upon interaction with ligands such as EGF, TGF alpha, amphiregulin or heparin binding EGF, ii) upon truncation or mutation of extracellular and/or intracellular domains, iii) upon amplification of a basal receptor activity (in the absence of ligand) through cooperation with other cellular signaling pathways or nuclear events (e.g. expression of v-erbA). The activated EGFR can exert pleiotropic functions on cells, depending on their tissue origin and state of differentiation. Under certain conditions it can also contribute to neoplasia and development of metastases. Such conditions can exist upon aberrant receptor/ligand expression and activation (e.g. in the wrong cell; at the wrong time; in the wrong amounts). Aberrant signalling can also occur through constitutive EGFR activation. Oncogenic potential of EGFR has been demonstrated in a wide range of experimental animals. EGFR is also implicated in human cancer, where it may contribute both to the initiation (glioblastoma) and progression (epithelial tumors) of the disease. EGFR may influence key steps in the processes of tumor invasion and dissemination. Involvement of EGFR in tumor spread may indicate a potential use of this receptor as a target for antimetastatic therapy.

Autocrine factors, type IV collagenase secretion and prostatic cancer cell invasion

Motility factors play a major role in tumor cell invasion and metastases. The biochemical properties of various motility factors; the receptor mediated mechanism of action; the role of microtubules; the potential influence of oncogenes; and the influence of motility factors on type IV collagenase secretion and invasion are discussed. We report on expression of a 70 kDa motility factor, termed invasion stimulating factor (ISF), in human prostatic PC-3 sublines. Boyden chamber chemotactic assays and measurements of type IV collagenase synthesis and secretion suggest that an ISF-receptor dependent mechanism influences tumor cell invasion and protease secretion. Taken together, the evidence that autocrine motility factors play an essential role in tumor cell invasion and metastases is compelling.