EpCAM overexpression prolongs proliferative capacity of primary human breast epithelial cells and supports hyperplastic growth

Gilbert Spizzo,Guenther Gastl,Agnieszka Martowicz,Johannes Rainer,Julien Lelong,Gerold Untergasser

doi:10.1186/1476-4598-12-56

Abstract

IntroductionThe Epithelial Cell Adhesion Molecule (EpCAM) has been shown to be strongly expressed in human breast cancer and cancer stem cells and its overexpression has been supposed to support tumor progression and metastasis. However, effects of EpCAM overexpression on normal breast epithelial cells have never been studied before. Therefore, we analyzed effects of transient adenoviral overexpression of EpCAM on proliferation, migration and differentiation of primary human mammary epithelial cells (HMECs).MethodsHMECs were transfected by an adenoviral system for transient overexpression of EpCAM. Thereafter, changes in cell proliferation and migration were studied using a real time measurement system. Target gene expression was evaluated by transcriptome analysis in proliferating and polarized HMEC cultures. A Chicken Chorioallantoic Membrane (CAM) xenograft model was used to study effects on in vivo growth of HMECs.ResultsEpCAM overexpression in HMECs did not significantly alter gene expression profile of proliferating or growth arrested cells. Proliferating HMECs displayed predominantly glycosylated EpCAM isoforms and were inhibited in cell proliferation and migration by upregulation of p27KIP1 and p53. HMECs with overexpression of EpCAM showed a down regulation of E-cadherin. Moreover, cells were more resistant to TGF-β1 induced growth arrest and maintained longer capacities to proliferate in vitro. EpCAM overexpressing HMECs xenografts in chicken embryos showed hyperplastic growth, lack of lumen formation and increased infiltrates of the chicken leukocytes.ConclusionsEpCAM revealed oncogenic features in normal human breast cells by inducing resistance to TGF-β1-mediated growth arrest and supporting a cell phenotype with longer proliferative capacities in vitro. EpCAM overexpression resulted in hyperplastic growth in vivo. Thus, we suggest that EpCAM acts as a prosurvival factor counteracting terminal differentiation processes in normal mammary glands.

Highlights

The Epithelial Cell Adhesion Molecule (EpCAM) has been shown to be strongly expressed in human breast cancer and cancer stem cells and its overexpression has been supposed to support tumor progression and metastasis
In clear contrast to all tumor samples analyzed, normal polarized epithelia had a strict localization of EpCAM on the basolateral membrane
In vitro cultivated human mammary epithelial cells (HMECs) were negative for EpCAM in the immunofluorescence analysis (Figure 1B), low transcript levels could be detected by qPCR analysis

Summary

Introduction

The Epithelial Cell Adhesion Molecule (EpCAM) has been shown to be strongly expressed in human breast cancer and cancer stem cells and its overexpression has been supposed to support tumor progression and metastasis. Effects of EpCAM overexpression on normal breast epithelial cells have never been studied before. EpCAM ( known as 17-1A, GA733-2, KSA, ESA, and EGP-40) is a homophilic, calcium-independent cell adhesion molecule of 39–42 kDa [1,2] expressed on most normal and cancerous epithelial tissues, cancer stem cells, embryonic stem cells and germ cells [3,4,5]. EpCAM has been shown to be expressed on normal epithelial cells in situ at intercellular basolateral interfaces [1]. EpCAM−/− mice die in uterus at embryonic day 12, are developmentally delayed and display prominent placental abnormalities [7]

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