A 50 kDa protein present in conditioned medium of COLO-16 cells stimulates cell spreading and motility, and activates tyrosine phosphorylation of Neu/HER-2, in human SK-BR-3 mammary cancer cells

Inhibition of breast cancer cell growth and invasiveness by dual silencing of HER-2 and VEGF

Overexpression of HER-2 accounts for approximately 25% of all breast cancer cases, while 87.7% of HER-2 positive breast cancers are associated with upregulated VEGF. The objective of this study is to explore the combination therapy of blocking HER-2 and VEGF expressions simultaneously using siRNA. This is the first report to examine the effect of dual silencing of HER-2 and VEGF genes on tumor growth and invasiveness. We have designed nine HER-2 siRNAs and ten VEGF siRNAs, and identified potent siRNA which can silence the target gene up to 75-83.5%. The most potent HER-2 and VEGF siRNAs were used to conduct functional studies in HER-2 positive breast cancer cells. Tumor invasiveness properties including cell morphology change, in vitro migration, cell spreading, and adhesion to ECM were evaluated. In addition, cell proliferation and apoptosis were examined after the siRNA treatment. Our data demonstrated for the first time that HER-2 siRNA could inhibit cell migration and invasion abilities. Combination of HER-2 and VEGF siRNAs exhibited synergistic silencing effect on VEGF. Both HER-2 siRNA and VEGF siRNA showed significant inhibition on cell migration and proliferation. HER-2 siRNA also demonstrated dramatic suppression on cell spreading and adhesion to ECM, as well as induction of apoptosis. Dual silencing of HER-2 and VEGF exhibited significant cell morphology change, and substantial suppression on migration, spreading, cell adhesion, and proliferation. Our observations suggested that HER-2 positive breast cancer may be more effectively treated by dual inhibition of HER-2 and VEGF gene expressions using siRNA.

Roles for neuregulins in human cancer

The human epidermal growth factor (EGF) receptor (HER) family of receptor tyrosine kinases has frequently been implicated in cancer. Apart from overexpression or mutation of these receptors, also the aberrant autocrine or paracrine activation of HERs by EGF-like ligands may be important in cancer progression. Neuregulins constitute a family of EGF-like ligands that bind to HER3 or HER4, preferably forming heterodimers with the orphan receptor HER2. Mesenchymal neuregulin typically serves as a pro-survival and pro-differentiation signal for adjacent epithelia. Disruption of the balance between proliferation and differentiation, because of autocrine production by the epithelial cells, increased sensitivity to paracrine signals or disruption of the spatial organization, may lead to constitutive receptor activation, in the absence of receptor overexpression. Consequently, the analysis of ligand expression and/or activated receptors in tumor samples may broaden the group of patients that can benefit from targeted therapies.

c-erbB-2 as a target for immunotherapy

The c-erbB-2 proto-oncogene encodes a 185 kDa transmembrane Type 1 tyrosine kinase receptor whose amplification and/or overexpression has been linked with poor prognosis in a variety of cancers. The oncoprotein has been suggested to play a key role in tumour cell invasion, motility and metastasis, and in responsiveness to therapeutic agents. Over-expression of c-erbB-2 therefore identifies an important subset of patients with a high probability of relapse, but low probability of response to certain conventional therapies. The cell surface location of the oncoprotein, its stability of expression and low levels in normal adult tissues render it an attractive target for immunotherapeutic intervention. Although a 'self' antigen, there is evidence that c-erbB-2 p185 can induce both humoral and cell-mediated immune responses in cancer patients. Approaches to exploit p185 as an immunotherapeutic target include vaccination with peptides, plasmid DNA or vectors (viruses/bacteria) carrying the gene; with cytokines, co-stimulatory factors and superantigens being evaluated as adjuvants. Many monoclonal antibody (mAb)-based strategies are also in clinical development. Monoclonal antibodies can serve multiple functions; direct inhibition of c-erbB-2 activity, recruitment of host effector mechanisms and direct or indirect delivery of toxic payloads. Clinical trials in patients with late stage disease have shown that many of these approaches are safe, feasible and relatively non-toxic, and, in some cases, objective responses have been seen. As with all immunotherapy, the greatest benefit is likely to be obtained in patients with minimal residual disease in an adjuvant setting; such studies are awaited with interest.

The heregulin/human epidermal growth factor receptor as a new growth factor system in melanoma with multiple ways of deregulation

In a screening for new growth factors released by melanoma cells, we found that the p185-phosphorylating capacity of a medium conditioned by a melanoma cell line was due to the secretion of heregulin, a ligand for the human epidermal growth factor receptor (HER) family of receptor tyrosine kinases. Expression of heregulin, including a new isoform, and secretion of functionally active protein was found in several cell lines. Receptor activation by heregulin, either autocrine or paracrine, resulted in a potent growth stimulation of both melanocytes and melanoma cells. Heregulin receptor HER3 and coreceptor HER2 were the main receptors expressed by these cells. Nevertheless, none of the cell lines in our panel overexpressed HER2 or HER3. In contrast, loss of HER3 was found in two cell lines, whereas one cell line showed loss of functional HER2, both types of deregulations resulting in unresponsiveness to heregulin. This implies the heregulin/HER system as a possible important physiologic growth regulatory system in melanocytes in which multiple deregulations may occur during progression toward melanoma, all resulting in, or indicating, growth factor independence.

Marked intratumoral heterogeneity of c-myc and cyclinD1 but not of c-erbB2 amplification in breast cancer

Intratumoral heterogeneity mirrors subclonal diversity and might affect treatment response. To investigate molecular heterogeneity of primary breast cancer specimens, we determined the amplification status of growth regulatory genes (c-erbB2, topoisomerase IIalpha, c-myc, and cyclinD1) in macroscopically and microscopically separate areas of individual tumors (n = 21). Using laser-assisted microdissection and quantitative PCR, we found marked intratumoral heterogeneity with different patterns for each gene. Molecular heterogeneity in amplification pattern could be demonstrated between both macroscopically (0.5 to several centimeters) and microscopically (10 to several hundred micrometers) distant tumor areas. C-erbB2 amplification proved to be the most stable amplification in individual tumors, with heterogeneity occurring in only 36% of amplified cases. By contrast, amplification of c-myc and cyclinD1 revealed varying patterns in the vast majority of amplified cases (100% and 83%). The constancy of c-erbB2 amplification underlines its presumed importance in breast cancer biology. We conclude that the molecular heterogeneity of breast cancer as evidenced in this study requires thorough and representative sampling of different tumor areas when the biologic significance of somatic mutations is considered. Patterns of heterogeneity can be used to trace the clonal evolution within different compartments of an individual tumor.

Cell biology of lymphatic metastasis. The potential role of c-erbB oncogene signalling

Lymphatic metastases are an important indicator of the malignancy of epithelial cancers. Empirical clinical observations associating specific genetic abnormalities with tumour progression, allied with basic laboratory investigations, are providing not only improved prognostic and diagnostic opportunities, but also a detailed understanding of the molecular machinery of metastasis. One such association--between the c-erbB oncogene family and metastasis--has proved particularly instructive. Functional links between over-expression (and occasionally mutational activation) of c-erbB-1 (EGFR) and c-erbB-2 and specific phenotypes of metastatic cells have been elucidated. Activated c-erbB oncogenes potentiate tumour cell adhesion to endothelial cells and upregulate VEGF, potentially facilitating angiogenesis and vascular invasion. In addition, cells over-expressing these oncogenes frequently show aberrant cell-cell and cell-matrix interactions, mediated by changes in integrin and cadherin function. Thirdly, both EGFR and c-erbB-2 signalling can significantly upregulate specific matrix metalloproteinases, key enzymes involved in angiogenesis and invasion. Finally, c-erbB receptors linked to the actin cytoskeleton and highly expressed on invadopodia, are thought to assist cell migration. Taken together, these observations suggest that such receptors can act as "master switches" in metastasis, whose activation co-ordinately controls events normally utilised in development, now subverted by the metastatic cell. As such, they represent ideal targets for therapeutic intervention.

C-erbB-2/ HER-2 upregulates fascin, an actin-bundling protein associated with cell motility, in human breast cancer cell lines

The over-expression of c-erbB-2/ HER-2, a receptor tyrosine kinase, correlates with poor prognosis in patients with breast and ovarian cancer. In the human breast cancer cell line, MDA-MB-435, c-erbB-2 over-expression results in increased chemoinvasion and higher metastatic properties in nude mice. However, the mechanisms by which c-erbB-2 increases the malignant potential of cells remains unclear. We have determined that over-expression of c-erbB-2 in MDA-MB-435 cells, and in some additional breast cancer cell lines, is associated with graphic increases in mRNA and protein levels of the actin bundling protein fascin. Heightened fascin expression has been observed in other systems to result in greatly increased cell motility, and indeed, our work employing semi-automated time-lapse microscopy demonstrates that MDA-MB-435 cells over-expressing c-erbB-2 exhibit significantly heightened cellular dynamics and locomotion, while visualization of bundled microfilaments within fixed cells revealed enhanced formation of dendritic-like processes, microspikes and other dynamic actin based structures. To address the means by which c-erbB-2 over-expression might result in elevated fascin levels, we identified multiple perfect match TCF and NF-kappaB consensus sites in fascin's promoter and first intron, which appeared consistent with the greater endogenous transcriptional activities of TCF and NF-kappaB in c-erbB-2 over-expressing MDA-MB-435 cells. While such transcriptional modulation may occur in the context of the intact gene/chromatin, subsequent tests using reporter constructs did not support involvement of these signaling pathways. In conclusion, highly increased fascin levels were observed in MDA-MB-435 over-expressing c-erbB-2, likely contributing to these cells' altered actin dynamics, and increased cell motility and malignancy. Studies in progress aim to discern the means by which c-erbB-2 over-expression leads to transcriptional activation of the fascin gene.

Pathogenesis of Paget's disease: epidermal heregulin-alpha, motility factor, and the HER receptor family

BACKGROUND AND METHODS

In Paget's disease of the breast, the epidermis of the nipple is infiltrated by large neoplastic cells of glandular origin. It has been hypothesized that the spread of Paget cells through the nipple epidermis is induced by a motility factor that acts via the HER2/NEU receptor. To test this hypothesis, we characterized and purified a motility factor released by keratinocytes and identified its target receptors in specimens from patients with Paget's disease and in SK-BR-3 breast adenocarcinoma cells, which overexpress HER2/NEU.

RESULTS

We isolated the motility factor from keratinocyte-conditioned medium and sequenced tryptic peptides. These sequences were used to identify the motility factor as heregulin-alpha, which is released by skin keratinocytes. Heregulin-alpha induces spreading, motility, and chemotaxis of SK-BR-3 cells, as does motility factor. Motility factor activities of heregulin-alpha are inhibited by monoclonal antibody AB2, directed against the extracellular domain of HER2/NEU, which blocks the binding of heregulin-alpha. We used in situ hybridization to show that normal epidermal cells produce heregulin-alpha messenger RNA and that heregulin receptors, HER3 and/or HER4, as well as their coreceptor HER2/NEU, are expressed by Paget cells.

CONCLUSIONS

Heregulin-alpha is a motility factor that is produced and released by normal epidermal keratinocytes and thus plays a key role in the pathogenesis of Paget's disease. Paget cells express heregulin receptors HER2/NEU, as well as HER3 and/or HER4, both of which function as a co-receptor of HER2/NEU. Binding of heregulin-alpha to the receptor complex on Paget cells results in the chemotaxis of these breast cancer cells, which eventually migrate into the overlying nipple epidermis.

Complexity of signal transduction mediated by ErbB2: clues to the potential of receptor-targeted cancer therapy

The erbB2 oncogene belongs to the type I trans-membrane tyrosine kinase family of receptors. Its medical importance stems from its widespread over-expression in breast cancer. This review will focus on the signal transduction through this protein, and explains how the overexpression of erbB2 may result in poor prognosis of breast cancer, and finally it will summerize our current understanding about the therapeutic potential of receptor-targeted therapy in breast cancer. ErbB2 does not have any known ligand which is able to bind to it with high affinity. However the kinase activity of erbB2 can be activated without any ligand, if it is overexpressed, and by heteroassociation with other members of the erbB family (erbB1 or epidermal growth factor receptor, erbB3 and erbB4). This interaction substantially increases the efficiency and diversity of signal transduction through these receptor complexes. In addition, erbB2 forms large scale receptor clusters containing hundreds of proteins. These receptor islands may take part in recruiting cytosolic factors which relay the signal towards the nucleus or the cytoplasm. Overexpression of erbB2 was linked to higher transforming activity, increased metastatic potential, angiogenesis and drug resistence of breast tumor in laboratory experiments. As a corollary of these properties, erbB2 amplification is generally thought to be associated with a poor prognosis in breast cancer patients. These early findings lead to the development of antibodies that down-regulate erbB2. Such a therapeutic approach has already been found effective in experimental tumor models and in clinical trials as well. Further understanding of the importance of erbB2 and growth factor receptors in the transformation of normal cells to malignant ones may once give us a chance to cure erbB2 over-expressing breast cancer.

Internalization of the E-cadherin/catenin complex and scattering of human mammary carcinoma cells MCF-7/AZ after treatment with conditioned medium from human skin squamous carcinoma cells COLO 16

Cytokines and other paracrine or autocrine factors functionally modulate the invasion-suppressor and signal-transducing E-cadherin/catenin complex. We have used conditioned medium from human squamous carcinoma COLO 16 cells (CM COLO 16) as a source of such factors to modulate the E-cadherin/catenin complex in human breast carcinoma MCF-7 cells. CM COLO 16 induces scattering of MCF-7/AZ, but not of MCF-7/6 cells on tissue culture plastic substratum, and reduces aggregation of MCF-7/AZ cells in suspension. Insulin-like growth factor I counteracts this reduction of aggregation. Confocal laser scanning microscopy of immunocytochemical stainings shows loss of the honeycomb pattern of E-cadherin, alpha-catenin and beta-catenin, and internalization of those elements. Cell surface biotinylation shows a decrease in membrane-bound E-cadherin. Immunoprecipitation and cell fractionation show that the composition of the complex is maintained. Interleukin-1, interleukin-6, granulocyte-monocyte colony stimulating factor, stem cell factor, scatter factor/hepatocyte growth factor and transforming growth factor-beta, added separately to MCF-7/AZ cells, could not mimic the effects of CM COLO 16. Neither could we find evidence that the 80 kDa extracellular fragment of E-cadherin is implicated in scattering of MCF-7/AZ cells. This fragment is present in CM COLO 16, but it is also produced by the MCF-7/AZ cells themselves, even at higher levels. Our data point toward cytoplasmic internalization induced by paracrine factors as one of the downregulating mechanisms for the E-cadherin/catenin complex.

Involvement of the c-erbB-2 oncogene product in the EGF-induced cell motility of SK-OV-3 ovarian cancer cells

The epidermal growth factor (EGF) induces the rapid formation of dendritic processes and the dissociation of SK-OV-3 ovarian cancer cells. The SK-OV-3 cell line is characterized by over-expression of the c-erbB-2 oncogene product (p185(c-erbB-2)). To investigate the role of p185(c-erbB-2) in cell motility, a c-erbB-2-specific single-chain antibody was expressed in SK-OV-3 cells using a retroviral expression vector. Eight individual clones expressing the single chain antibody were isolated. These clones have prominent retention of the cell-surface p185(c-erbB-2). The EGF-induced morphologic changes and cell motility of the single-chain-antibody-expressing clones were strongly inhibited, as observed in cell dissociation and in transmigration experiments. However, the suppression of p185(c-erbB-2) does not inhibit the motility signal elicited by 12-O-tetradecanoyl-phorbol-13-acetate. These data indicate that the c-erbB-2 oncogene product is essential to mediate the motility signal of EGF to SK-OV-3 ovarian cancer cells. The enhancement of tumor-cell motility may be partially responsible for the unfavorable prognosis of ovarian cancer with over-expression of c-erbB-2.

Generation of a monoclonal antibody directed against a human cell substrate adhesion molecule and the expression of the antigen in human tissues

Cell substrate adhesion is a prerequisite for invasion and the subsequent formation of metastases. Therefore, we designed monoclonal antibodies (MAbs) against epitopes on the extracellular cell membrane domain of SK-BR-3 cells. One of the antibodies, called MAb 14C5, binds to an extracellular epitope of a plasma membrane antigen of SK-BR-3 and MCF-7 human breast cancer cells. This MAb 14C5 is able to inhibit cell substrate adhesion, not only on culture-treated plastic but also on host tissue, and therefore prevents invasion and metastases. We evaluated the tissue distribution of the 14C5 antigen by immunohistochemistry. The antigen is specifically overexpressed in 64% of invasive ductal adenocarcinomas of the breast (n = 33), in all investigated cases of invasive squamous cell carcinoma (n = 7) and in 40% of basocellular carcinomas of the skin (n = 5). The 14C5 molecule is located on the cell membrane of the carcinoma cells. However, when the tumor is characterized by a highly invasive phenotype, 65% of the cases also show an extensive stromal expression on the fibroblasts between the tumor cells (n = 71). This stromal expression is caused by the presence of the 14C5 antigen on the membrane of the adjacent fibroblasts. In normal tissues as well as in the stroma surrounding in situ carcinomas of the breast (n = 15), no expression of the 14C5 antigen occurred. A 90-kDa protein was purified from lysates of human breast cancer cells using a 14C5 MAb Sepharose column and is considered as the antigen recognized by the MAb 14C5.

c-neu oncoprotein in developing rostral cerebral cortex: relationship to epidermal growth factor receptor

The c-neu oncoprotein, p185c-neu, is a transmembrane tyrosine kinase that shares structural similarities with the receptor for epidermal growth factor (EGFr). We used immunoblots, immunoprecipitation, and immunohistochemistry 1) to test the hypothesis that p185c-neu and EGFr are coordinately expressed in central nervous system tissue and 2) to assess the spatiotemporal expression of both the c-neu oncoprotein and EGFr in the rostral cerebral cortex. In nondenaturing gels, anti-c-neu antibody identified high molecular weight proteins (about 300-400 kDa) that were reduced by EDTA to a molecular weight of 180-200 kDa. Sodium dodecylsulfate polyacrylamide gel electrophoresis broke down this protein into an array of smaller peptides, which were expressed prenatally, transiently during the first three postnatal weeks, or in the adult. Perinatally, c-neu immunoreactivity was evident in subplate neurons, ascending processes of neurons in the cortical plate, and ventricular zone cells. During the second postnatal week, cells throughout cortex expressed somatodendritic immunostaining, but, in the adult, c-neu immunoreactivity was expressed only by pyramidal neurons in layer V and by glia in the white matter and ependyma. EGFr-positive proteins behaved in the nondenaturing gels as did c-neu-positive oncoproteins, suggesting that both proteins naturally formed dimers. This contention was supported by the EGFr-or c-neu immunolabeling of tissue that was previously immunoprecipitated with anti-c-neu or anti-EGFr, respectively. The pattern of EGFr immunolabeling in the developing and mature cortex was virtually identical to that described for c-neu immunoreactivity. Cortical neurons express the c-neu oncoprotein and EGFr, probably as heterodimers. The specific immunolabeling of layer V neurons in the adult cortex with anti-c-neu and anti-EGFr suggests that the p185c-neu ligand and EGF regulate the activity of corticofugal systems. The expression of different c-neu- and EGFr-positive peptides is developmentally defined and may be related to specific ontogenetic events.

c-erbB-2 anti-sense phosphorothioate oligodeoxynucleotides inhibit growth and serum-induced cell spreading of P185c-erbB-2-overexpressing ovarian carcinoma cells

Overexpression of the c-erbB-2 proto-oncogene product (p185c-erbB-2) occurs frequently in different types of human cancer and is correlated with a significantly decreased survival in ovarian cancer patients. The effect of c-erbB-2 anti-sense phosphorothioate oligodeoxynucleotides (S-ODNs) was examined on the ovarian cancer cell line SK-OV-3. p185c-erbB-2 levels were specifically reduced by a single-dose application of 5 microM c-erbB-2 anti-sense S-ODNs. This was accompanied by a 60% inhibition of anchorage-dependent cell growth. More strikingly, c-erbB-2 anti-sense S-ODNs almost completely abrogated serum-induced cell spreading. A control of complementary sense oligodeoxynucleotides did not show significant inhibitory effects on cell growth or on cell spreading. The inhibition of cell spreading was imitated by a monoclonal antibody (9G6) targeting the extracellular domain of p185c-erbB-2 and by the tyrosine kinase inhibitor erbstatin. The inhibitory activity of these 2 compounds was lost after a few hours, while the inhibition of serum-induced cell spreading by anti-sense S-ODNs was still present after 24 hr. Our results show that c-erbB-2 anti-sense S-ODNs effectively inhibit the mitogenic and spreading activity of p185c-erbB-2 in ovarian cancer cells. Thus, anti-sense strategies have the potential of providing new strategies for the therapy of ovarian cancer.

neu overexpression correlates with extent of disease in large cell ductal carcinoma in situ of the breast

In a retrospective study of ductal carcinoma in situ (DCIS) of the breast, the expression of the neu oncogene was determined immunohistochemically in 76 women treated by local excision or mastectomy. The histopathological features, including the extent of the lesion, histological subtype, cell type, and number of mitoses, were related to neu overexpression. Immunopositivity was found only in DCIS of large cell type, where it correlated with extent of disease but not with mitotic rate. Our findings, together with previous experimental evidence, suggest that this relationship is a consequence of the effect of the neu protein on cell motility.

The neu-oncogene: more than a prognostic indicator?

Overexpression of the neu-protein, evidenced as membrane staining by immunohistochemistry, is detected in approximately 20% of invasive duct cell carcinomas, in approximately 50% of in situ duct cell carcinomas, and in almost 100% of cases of Paget's disease. Apart from a growth stimulatory effect, the molecule plays an important role in cell motility of tumor cells by the activity of a motility factor, which acts as a specific ligand for the neu-protein. The motility factor induces chemotaxis of neu-overexpressing breast cancer cells. The motility function of the neu-protein may lead to an increased metastatic potential of neu-overexpressing breast tumors. Also in Paget's disease of the breast, a motility factor secreted by epidermal keratinocytes attracts the neu-overexpressing Paget's cells by chemotaxis and leads to invasion of the epidermis by the tumor cells.