Epigenetic Silencing of THY1 Tracks the Acquisition of the Notch1-EGFR Signaling in a Xenograft Model of CD44+/CD24low/CD90+ Myoepithelial Cells.

Micaela Montanari,Luigi Coppola,Sabino De Placido,Felicia Leccia,Rossella Lauria,Roberto Bianco,Bianca Maria Veneziani,Enrico V Avvedimento,Maria Rita Carbone,Mario Giuliano,Grazia Arpino,Meghana V Trivedi,Agostina Nardone,Corrado Garbi

doi:10.1158/1541-7786.mcr-17-0324

Abstract

The surface glycoprotein THY is a marker of myoepithelial precursor cells, which are basal cells with epithelial-mesenchymal intermediate phenotype originating from the ectoderm. Myoepithelial precursor cells are lost during progression from in situ to invasive carcinoma. To define the functional role of Thy1-positive cells within the myoepithelial population, we tracked Thy1 expression in human breast cancer samples, isolated THY1-positive myoepithelial progenitor cells (CD44+/CD24low/CD90+), and established long-term cultures (parental cells). Parental cells were used to generate a xenograft model to examine Thy1 expression during tumor formation. Post-transplantation cell cultures lost THY1 expression through methylation at the THY1 locus and this is associated with an increase in EGFR and NOTCH1 transcript levels. Thy1-low cells are sensitive to the EGFR/HER2 dual inhibitor lapatinib. High THY1 expression is associated with poorer relapse-free survival in patients with breast cancer. THY1 methylation may track the shift of bipotent progenitors into differentiated cells. Thy1 is a good candidate biomarker in basal-like breast cancer. IMPLICATIONS: Our findings provide evidence that THY1 expression is lost in xenografts due to promoter methylation. Thy1-low cells with increased EGFR and Notch1 expression are responsive to target therapy. Because DNA methylation is often altered in early cancer development, candidate methylation markers may be exploited as biomarkers for basal-like breast cancer.

Highlights

The human breast gland is a ductal tree covered with a monolayer of polarized epithelial cells whose basal surface lies on contractile myoepithelial cells that are confined by the basement membrane and surrounded by an interstitial stroma
Phycoerythrin-conjugated mAbs against CD10, CD29, CD49f, CD61, and fluorescein isothiocyanate (FITC)-conjugated mAbs against CD49b, CD90, CD227, CD324, and CD326 were from BD Biosciences and BD Pharmingen; PE-conjugated mAbs against CD133 were from Miltenyi Biotec; Alexa Fluor 647–conjugated mAbs against CD24 and PE-Cy7–conjugated mAbs against CD44 were from BioLegend
To evaluate whether Thy1 expression was stable in cells sorted for stem features, we measured THY1 messenger RNA in stabilized cultures

Summary

Introduction

The human breast gland is a ductal tree covered with a monolayer of polarized epithelial cells whose basal surface lies on contractile myoepithelial cells that are confined by the basement membrane and surrounded by an interstitial stroma. Note: Supplementary data for this article are available at Molecular Cancer Research Online (http://mcr.aacrjournals.org/). Interest in basal cells was stimulated after molecular gene profiling divided breast cancer into five intrinsic subtypes, one of which displays basal-like gene expression [2]. Basal-like breast cancers are generally aggressive [3] and most are triple-negative, that is, they test negative for estrogen receptor (ER), progesterone receptor (PgR), and HER2 Treatment of patients with basal-like triple-negative breast cancer (TNBC) is challenging because of the heterogeneity of the disease and the absence of well-defined druggable targets [5]

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