title: HER2 induced EMT and tumorigenicity in breast epithelial progenitor cells is inhibited by coexpression of EGFR.
abstract: The members of the epidermal growth factor receptor (EGFR) kinase family are important players in breast morphogenesis and cancer. EGFR2/HER2 and EGFR expression have a prognostic value in certain subtypes of breast cancer such as HER2-amplified, basal-like and luminal type B. Many clinically approved small molecular inhibitors and monoclonal antibodies have been designed to target HER2, EGFR or both. There is, however, still limited knowledge on how the two receptors are expressed in normal breast epithelium, what effects they have on cellular differentiation and how they participate in neoplastic transformation. D492 is a breast epithelial cell line with stem cell properties that can undergo epithelial to mesenchyme transition (EMT), generate luminal- and myoepithelial cells and form complex branching structures in three-dimensional (3D) culture. Here, we show that overexpression of HER2 in D492 (D492(HER2)) resulted in EMT, loss of contact growth inhibition and increased oncogenic potential in vivo. HER2 overexpression, furthermore, inhibited endogenous EGFR expression. Re-introducing EGFR in D492(HER2) (D492(HER2/EGFR)) partially reversed the mesenchymal state of the cells, as an epithelial phenotype reappeared both in 3D cultures and in vivo. The D492(HER2/EGFR) xenografts grow slower than the D492(HER2) tumors, while overexpression of EGFR alone (D492(EGFR)) was not oncogenic in vivo. Consistent with the EGFR-mediated epithelial phenotype, overexpression of EGFR drove the cells toward a myoepithelial phenotype in 3D culture. The effect of two clinically approved anti-HER2 and EGFR therapies, trastuzumab and cetuximab, was tested alone and in combination on D492(HER2) xenografts. While trastuzumab had a growth inhibitory effect compared with untreated control, the effect of cetuximab was limited. When administered in combination, the growth inhibitory effect of trastuzumab was less pronounced. Collectively, our data indicate that in HER2-overexpressing D492 cells, EGFR can behave as a tumor suppressor, by pushing the cells towards epithelial differentiation.
authors.affiliation: Stem Cell Research Unit, Biomedical Center, University of Iceland, Reykjavik, Iceland.|Department of Laboratory Haematology, Landspitali University Hospital, Reykjavik, Iceland.
authors.forename: S
authors.initials: S
authors.lastname: Ingthorsson
authors.affiliation: Department of Tumor Biology, Institute for Cancer Research, Oslo University Hospital, The Norwegian Radium Hospital, Oslo, Norway.|Cancer Stem Cell Innovation Center, Oslo University Hospital, The Norwegian Radium Hospital, Oslo, Norway.
authors.forename: K
authors.initials: K
authors.lastname: Andersen
authors.affiliation: Stem Cell Research Unit, Biomedical Center, University of Iceland, Reykjavik, Iceland.|Department of Laboratory Haematology, Landspitali University Hospital, Reykjavik, Iceland.
authors.forename: B
authors.initials: B
authors.lastname: Hilmarsdottir
authors.affiliation: Department of Tumor Biology, Institute for Cancer Research, Oslo University Hospital, The Norwegian Radium Hospital, Oslo, Norway.|Cancer Stem Cell Innovation Center, Oslo University Hospital, The Norwegian Radium Hospital, Oslo, Norway.|K.G. Jebsen Centre for Breast Cancer Research, Institute for Clinical Medicine, University of Oslo, Oslo, Norway.
authors.forename: G M
authors.initials: GM
authors.lastname: Maelandsmo
authors.affiliation: Stem Cell Research Unit, Biomedical Center, University of Iceland, Reykjavik, Iceland.|Department of Laboratory Haematology, Landspitali University Hospital, Reykjavik, Iceland.|Department of Pharmacology and Toxicology, University of Iceland, Reykjavik, Iceland.
authors.forename: M K
authors.initials: MK
authors.lastname: Magnusson
authors.affiliation: Stem Cell Research Unit, Biomedical Center, University of Iceland, Reykjavik, Iceland.|Department of Laboratory Haematology, Landspitali University Hospital, Reykjavik, Iceland.
authors.forename: T
authors.initials: T
authors.lastname: Gudjonsson
mesh_terms: D001943:Breast Neoplasms / Q000473:pathology*; D063646:Carcinogenesis; D049109:Cell Proliferation; D000066630:Ectopic Gene Expression; D004847:Epithelial Cells / Q000473:pathology; D058750:Epithelial-Mesenchymal Transition; D066246:ErbB Receptors / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D014411:Neoplastic Stem Cells / Q000473:pathology*; D010641:Phenotype; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism*
chemical_list: D066246:ErbB Receptors; D018719:Erb-b2 Receptor Tyrosine Kinases