ATM Suppresses SATB1-Induced Malignant Progression in Breast Epithelial Cells

Ellen Ordinario,Joe W Gray,Terumi Kohwi-Shigematsu,Paul T Spellman,Yoshinori Kohwi,Saori Furuta,Hye-Jung Han,Mina J Bissell,Lakshmi R Jakkula,Laura M Heiser,Francis Rodier,Judith Campisi

doi:10.1371/journal.pone.0051786

Abstract

SATB1 drives metastasis when expressed in breast tumor cells by radically reprogramming gene expression. Here, we show that SATB1 also has an oncogenic activity to transform certain non-malignant breast epithelial cell lines. We studied the non-malignant MCF10A cell line, which is used widely in the literature. We obtained aliquots from two different sources (here we refer to them as MCF10A-1 and MCF10A-2), but found them to be surprisingly dissimilar in their responses to oncogenic activity of SATB1. Ectopic expression of SATB1 in MCF10A-1 induced tumor-like morphology in three-dimensional cultures, led to tumor formation in immunocompromised mice, and when injected into tail veins, led to lung metastasis. The number of metastases correlated positively with the level of SATB1 expression. In contrast, SATB1 expression in MCF10A-2 did not lead to any of these outcomes. Yet DNA copy-number analysis revealed that MCF10A-1 is indistinguishable genetically from MCF10A-2. However, gene expression profiling analysis revealed that these cell lines have significantly divergent signatures for the expression of genes involved in oncogenesis, including cell cycle regulation and signal transduction. Above all, the early DNA damage-response kinase, ATM, was greatly reduced in MCF10A-1 cells compared to MCF10A-2 cells. We found the reason for reduction to be phenotypic drift due to long-term cultivation of MCF10A. ATM knockdown in MCF10A-2 and two other non-malignant breast epithelial cell lines, 184A1 and 184B4, enabled SATB1 to induce malignant phenotypes similar to that observed for MCF10A-1. These data indicate a novel role for ATM as a suppressor of SATB1-induced malignancy in breast epithelial cells, but also raise a cautionary note that phenotypic drift could lead to dramatically different functional outcomes.

Highlights

Normal breast epithelial cells acquire malignant phenotypes through multiple genomic and microenvironmental modifications [1,2,3]
base-unpairing regions (BURs) of specific gene loci are tethered to a protein complex comprising SATB1, which serves as an architectural platform to recruit transcriptional regulators and chromatin remodeling proteins to alter the epigenetic states of target gene loci [9,10]
Quantitative RT-PCR and immunoblot analyses showed that endogenous SATB1 levels were very low to undetectable in all immortalized non-tumorigenic cell lines tested in contrast to its detectable expression in metastatic human breast cancer cell lines, MDA-MB-231 and BT549 (Fig. 1A)

Summary

Introduction

Normal breast epithelial cells acquire malignant phenotypes through multiple genomic and microenvironmental modifications [1,2,3]. SATB1, thereby, regulates a large number of genes by folding chromatin into loops [11] and promotes growth and metastasis of breast tumors by reprogramming chromatin organization and altering the transcription of up to 1000 genes [5]. This ‘genome organizing’ activity of SATB1 is critical for changes in cellular functions such as T cell differentiation [12,13], T cell activation [11], postnatal cortical development [14], X-chromosome inactivation [15], epidermal differentiation [16] and progression of breast tumors to metastasis [5]

Methods

Results

Conclusion