Mapping the cellular and molecular heterogeneity of normal and malignant breast tissues and cultured cell lines

Patricia J Keller,Lisa M Arendt,Ainsley D Jones,Amy F Lin,Theresa A Dimeo,Stephen P Naber,Jenny A Rudnick,Hannah Gilmore,Charlotte Kuperwasser,Roger A Graham,Ina Klebba,Stuart Schnitt,Douglas M Jefferson

doi:10.1186/bcr2755

Abstract

IntroductionNormal and neoplastic breast tissues are comprised of heterogeneous populations of epithelial cells exhibiting various degrees of maturation and differentiation. While cultured cell lines have been derived from both normal and malignant tissues, it remains unclear to what extent they retain similar levels of differentiation and heterogeneity as that found within breast tissues.MethodsWe used 12 reduction mammoplasty tissues, 15 primary breast cancer tissues, and 20 human breast epithelial cell lines (16 cancer lines, 4 normal lines) to perform flow cytometry for CD44, CD24, epithelial cell adhesion molecule (EpCAM), and CD49f expression, as well as immunohistochemistry, and in vivo tumor xenograft formation studies to extensively analyze the molecular and cellular characteristics of breast epithelial cell lineages.ResultsHuman breast tissues contain four distinguishable epithelial differentiation states (two luminal phenotypes and two basal phenotypes) that differ on the basis of CD24, EpCAM and CD49f expression. Primary human breast cancer tissues also contain these four cellular states, but in altered proportions compared to normal tissues. In contrast, cultured cancer cell lines are enriched for rare basal and mesenchymal epithelial phenotypes, which are normally present in small numbers within human tissues. Similarly, cultured normal human mammary epithelial cell lines are enriched for rare basal and mesenchymal phenotypes that represent a minor fraction of cells within reduction mammoplasty tissues. Furthermore, although normal human mammary epithelial cell lines exhibit features of bi-potent progenitor cells they are unable to differentiate into mature luminal breast epithelial cells under standard culture conditions.ConclusionsAs a group breast cancer cell lines represent the heterogeneity of human breast tumors, but individually they exhibit increased lineage-restricted profiles that fall short of truly representing the intratumoral heterogeneity of individual breast tumors. Additionally, normal human mammary epithelial cell lines fail to retain much of the cellular diversity found in human breast tissues and are enriched for differentiation states that are a minority in breast tissues, although they do exhibit features of bi-potent basal progenitor cells. These findings suggest that collections of cell lines representing multiple cell types can be used to model the cellular heterogeneity of tissues.

Highlights

Normal and neoplastic breast tissues are comprised of heterogeneous populations of epithelial cells exhibiting various degrees of maturation and differentiation
We wanted to determine whether these markers could be used to classify luminal and basal breast cancer cell lines, many of which have been previously classified on the basis of gene expression profiling [7,31]
Using a panel of 16 cancer lines we found that all breast cancer cell lines contained a population of CD44+ cells regardless of tumor subtype

Summary

Introduction

Normal and neoplastic breast tissues are comprised of heterogeneous populations of epithelial cells exhibiting various degrees of maturation and differentiation. Breast cancer cell lines are commonly used in xenograft models for drug discovery and in the assessment of pre-clinical experimental therapeutic efficacy. Despite their crucial role for rational drug discovery and development and in understanding molecular pathophysiology of cancer, their ability to accurately reflect phenotypes of tumors remains controversial. Several studies have suggested that cell lines exhibit a narrow range of genetic profiles, harbor genetic alterations due to adaptation of tissue culture environment, and are poor predictors of in vivo sensitivity to drug efficacy [1,2,3]. Cell line-derived gene signatures can correctly classify human tumor samples [6,7,10], suggesting that despite their acquired ability to grow in vitro, and acquired mutations following adaptation to culture conditions, cell lines continue to share many of the molecular and genetic features of the primary breast cancers from which they were derived

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Discussion

Conclusion