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Experimental Therapeutics, Preclinical Pharmacology |
National Research Council Canada, Biotechnology Research Institute, Montréal, Québec, H4P 2R2 Canada and Department of Biochemistry, McGill University, Montréal, Québec, Canada [A-E. A., C. Y., M. O-M.]; and Lady Davis Institute for Medical Research of the Sir Mortimer B. Davis-Jewish General Hospital, Departments of Medicine and Oncology, and McGill Center for Translational Research in Cancer, Montréal, Québec, H3T 1E2 Canada [M. A. A-J.]
| ABSTRACT |
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| INTRODUCTION |
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, has also been demonstrated in human carcinomas and cell lines, suggesting a possible role for an EGF-R/TGF-
autocrine loop in human carcinogenesis (3
, 4) . This autocrine signaling loop and the overexpression of EGF-R have both been demonstrated in human lung cancer cells (5
, 6)
. Anti-EGF-R-inactivating antibodies bind to EGF-R with high affinity, block the binding of EGF-R with its ligands, reduce phosphorylation of EGF-R, and inhibit the growth of epidermoid, prostate, colon, and gastric cancer cells (7, 8, 9, 10)
. Accordingly, it has been suggested that inhibitors of EGF-R tyrosine kinase are potentially useful as therapeutic agents in the treatment of these cancers (11
, 12)
. E-cadherin is a cell-cell adhesion molecule that connects epithelial cells via homotypic calcium-dependent interactions (13) . Decreased E-cadherin expression or function correlates with an enhanced aggressiveness and invasiveness of many carcinomas (14) . Previous studies have revealed an inverse relationship between EGF-R activation and E-cadherin expression patterns in human oesophageal, cutaneous squamous carcinoma, and breast cancer cells (15, 16, 17) .
In this study, we examined the effects of the ligand-blocking anti-EGF-R mAb LA1 on selected parameters of human lung cancer cell lines and NHBE cells. These cell lines were chosen because of their particular levels of EGF-R expression. Both the H322 and NHBE lines express comparable amounts of EGF-R, whereas none is detectable in H661 cells. We found that treatment with the LA1 antibody induces the up-regulation of E-cadherin expression, induces morphological change, inhibits cell proliferation, and reduces the constitutive activation of EGF-R in H322 and NHBE cells. This is the first demonstration that a blockade of EGF-R by an antibody results in differentiation and the up-regulation of E-cadherin. Our results suggest possible therapeutic roles for EGF-R-blocking antibodies in the treatment of invasive lung carcinomas by their ability to up-regulate the expression of cell adhesion molecules such as E-cadherin.
| MATERIALS AND METHODS |
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Growth Assay
Growth curves were established by measuring the incorporation of [3H]methylthymidine into the acid insoluble fraction of cellular extracts. Briefly,
2 x 104 cells were plated in either 2 ml of KSFM (NHBE) or 2 ml of DMEM 5% FBS (H322 and H661) into individual wells of 12-well tissue culture plates. One day later, the medium was changed either with fresh medium (control) or medium with various concentrations of anti-EGF-R mAb (0.1, 0.5, 1, and 2 µg/ml; LA1; mouse monoclonal IgG1 reacts with external domain of EGF-R; Upstate Biotechnology, Inc.). Mouse anti-IgG1 (1 µg/ml; Becton Dickinson Canada, Inc.) was used as control for the effects of mAb LA1. Cells were allowed to grow for 3 days after treatment. [3H]methylthymidine (1 µCi/ml; Amersham Corp.) was added during the last 2024-h period. After multiple washings in cold PBS, 10% trichloroacetic acid, and 95% ethanol, the plates were allowed to dry for 2 h. Cells were solubilized in 2% SDS, and the radioactivity was quantitated by liquid scintillation mixture (ICN Biomedical, Inc). The experimental points were determined in triplicates.
Morphological changes were examined by phase-contrast microscopy using 2 x 104 cells cultured in 2 ml of KSFM (NHBE) or 2 ml of DMEM 5% FBS (H322 and H661). One day later, the medium was changed either with fresh medium (control) or medium with 1 µg/ml of anti-EGF-R mAb LA1. Mouse anti-IgG1 (1 µg/ml) was used as control for the effects of mAb LA1. The cells were examined every day for 3 days.
Clonogenic Assay
H322, H661, and NHBE cells (5 x 103) were placed in medium containing 0.5% agar with 1 µg/ml LA1 mAb or 1 µg/ml mouse anti-IgG1 as control and plated over a layer of medium containing 0.7% agar. The cultures were examined every 12 days for 2 weeks.
Immunoblot Analysis
Equal amounts of protein (25 µg) were subjected to electrophoresis through a 7.5% SDS-PAGE gel and transferred to a nitrocellulose membrane (Xymotech). The membrane was blocked overnight in PBS containing 3% dried milk. The membrane was then probed for 2 h at room temperature with anti-EGF-R mAb LA1 (Upstate Biotechnology, Inc.), washed three times with PBS, and incubated for 1 h with a rabbit antimouse IgG coupled to alkaline phosphatase (Canadian Life Technologies, Inc.), followed by alkaline phosphatase substrate detection (Vector Laboratories, Inc.).
Cell Lysis and Immunoprecipitation
Cells were grown with or without 1 µg/ml LA1 antibody. Cells were washed with cold PBS and lysed on ice for 30 min in lysis buffer [120 mM Tris-HCl (pH 7.4), 135 mM Nacl, 1 mM EDTA, 1% NP40, and 0.1% SDS] supplemented with the tyrosine-phosphatase inhibitor sodium orthovanadate (1 mM) and the protease inhibitors aprotinin (10 ng/ml) and PMSF (1 mM). Nuclei and insoluble material were removed by centrifugation at 13000 x g for 10 min at 4°C. Equal amounts of protein (300 µg) were precipitated with anti-EGF-R mAb (clone EGF-R; Amersham Canada Ltd.) and protein G-Sepharose (Pharmacia) overnight at 4°C. Immune complexes were separated by SDS-PAGE and immunoblotted with antiphosphotyrosine mouse mAb 4G10 (Upstate Biotechnology, Inc.)
Immunofluorescence Staining and Flow Cytometric Analysis
Cells were grown with or without 1 µg/ml LA1 antibody for 72 h and washed with PBS. Cells were then harvested by trypsinization, washed, and fixed in 3.7% formaldehyde for 10 min. Fixed cells were hydrated in PBS, permeabilized with 0.05% Triton X-100 for 1 min, and treated with an anti-E-cadherin mAb (Uvomorulin; ICN Biomedical, Inc.) for 60 min, as previously described (18)
. Finally, cells were washed and resuspended in 1 ml of PBS. All steps were carried out at 4°C after trypsinization. A minimum of 1 x 104 cells was analyzed using a FAC-Scan flow cytometer (Beckman Coulter).
| RESULTS AND DISCUSSION |
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, heparin-binding EGF-like factor, and ß-cellulin) induce the epithelial-fibroblastoid conversion of an immortalized human bronchial epithelial cell line (HBE4-E6E7). These ligands induce a loss of, or a reduction in, the expression of the cell-cell adhesion molecules E-cadherin and desmoplakin. This is accompanied by an overexpression of intermediate filament proteins of mesenchymal cells.5
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E-cadherin Expression Is Regulated by the Anti-EGF-R mAb LA1
In epithelial tissues, E-cadherin is required for the assembly of cells into multiple layers, as well as the establishment and maintenance of an epithelial phenotype (22
, 23)
. There is evidence that E-cadherin also acts as a suppressor of tumor invasion and metastasis (14
, 24)
. Recent studies have reported that the activation of some receptor tyrosine kinases, including EGF-R, affects the adhesive function of E-cadherin via the ß-catenin pathway (25
, 26)
. We treated H322, H661, and NHBE cells with the LA1 antibody to determine whether the inhibition of EGF-R activation by a neutralizing mAb affects E-cadherin expression patterns. All three cell lines were treated with LA1 antibody for 3 days and examined using immunofluorescence staining with an anti-E-cadherin mAb and flow cytometric analysis. Untreated cells, as well as those treated with 1 µg/ml mouse anti-IgG1 cells, were shown to express low levels of E-cadherin. In contrast, significantly and reproducibly high levels of E-cadherin were expressed in H322 and NHBE cells treated with LA1 mAb. No effect was observed in H661 cells (Fig. 5)
, which do not express the EGF-R. Results similar to those obtained using immunofluorescent staining were obtained using Western blot analysis with an anti-E-cadherin mAb in the same cell lines (data not shown).
The EGF-R is expressed in high levels in the majority of human lung carcinomas and cell lines (5 , 6) . We report here that normal NHBE and tumorigenic H322 human lung cell lines express comparable levels of EGF-R, whereas tumorigenic H661 cells express no detectable EGF-R. We examined the effects of an anti-EGF-R mAb, LA1, on these cell lines. The neutralization of EGF-R by this mAb was found to induce differentiation, inhibit proliferation, and induce the overexpression of E-cadherin only in the cell lines that express EGF-R. We observed that the LA1 antibody up-regulates E-cadherin expression in an immortalized human bronchial epithelial cell line.5 Other studies have shown that anti-EGF-R mAbs are capable of inhibiting growth of epidermoid, prostatic, colon, and gastric cancer cells (7, 8, 9, 10) . In addition, anti-EGF-R mAbs have previously been shown to induce G1 arrest and up-regulate the cyclin-dependent kinase inhibitor p27KIP1 in prostatic cancer cell lines (8 , 27) .
Although EGF-R is overexpressed in several other types of human cancers, it is not known whether blocking EGF-R in these cell-types results in an up-regulation of E-cadherin expression similar to the effect we observe in lung cancer cells. Preliminary experiments in human breast MDA-MB-231, epidermis cancer A431, and lung cancer H460 cell lines treated with the blocking EGF-R mAb LA1, confirm our observed up-regulation of E-cadherin expression.6 A recent study of the human breast cancer cell line MDA-MB-468, by Hazan and Norton (28) , shows that inactivation of EGF-R induces the interaction of E-cadherin adhesion complexes with the actin-based cytoskeleton. These authors also demonstrated a large increase in cell aggregation after monoclonal anti-EGF-R treatment, but did not show an up-regulation of E-cadherin expression.
Our study is the first evidence demonstrating that treatment with an EGF-R-inactivating mAb induces differentiation to a more epithelial phenotype and up-regulates the expression of E-cadherin in normal and tumorigenic human lung cells. This observation is significant in light of the fact that a key event in carcinogenesis and metastasis is the down-regulation of cell-cell adhesion molecules, such as E-cadherin. Potential therapeutic strategies involving the up-regulation of E-cadherin by EGF-R-blocking antibodies must consider the effect we show on normal cells. Studies where control animals have been treated with anti-EGF-R mAbs have not indicated any resulting pathogenesis and suggest that these agents may not hinder normal cells in vivo (12) . Finally, our results imply that the induction of E-cadherin expression by EGF-R-blocking antibodies represents a possible therapeutic strategy in the case of invasive carcinomas.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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1 Studies conducted in M. A. A-J.s laboratory were supported by the Medical Research Council and the National Cancer Institute of Canada. ![]()
2 To whom requests for reprints should be addressed, at Biotechnology Research Institute, 6100 Royalmount Avenue, Montréal, Québec, H4P 2R2 Canada. Phone: (514) 496-6142; Fax: (514) 496-5143; E-mail: ala-eddin.al-moustafa{at}nrc.ca ![]()
3 The abbreviations used are: EGF-R, epidermal growth factor receptor; TGF-
, transforming growth factor-
; E-cadherin, epithelial cadherin glycoprotein; mAb, monoclonal antibody; NHBE, normal human bronchial epithelial; FBS, fetal bovine serum; KSFM, keratinocyte-SFM. ![]()
4 A-E. Al Moustafa, B. P. Roc, and M. OConnor-McCourt, unpublished data. ![]()
5 A-E. Al Moustafa and M. OConnor-McCourt, Epithelial-fibroblastoid cell conversion of an immortalized human bronchial epithelial cell line by epidermal growth factor (EGF) family members, submitted for publication. ![]()
6 A-E. Al Moustafa and M. OConnor-McCourt, unpublished data. ![]()
Received 8/20/98; revised 12/ 2/98; accepted 12/ 7/98.
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in human non-small cell lung cancers. J. Formos. Med. Assoc., 96: 579-585, 1997.[Medline]
-mediated epidermal growth factor receptor activation. J. Cancer Res. Clin. Oncol., 122: 328-334, 1996.[Medline]
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