Research article
Regulation of breast cancer metastasis by Runx2 and estrogen signaling: the role of SNAI2
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* Corresponding authors: Nyam-Osor Chimge chimgee@usc.edu - Baruch Frenkel frenkel@usc.edu
1 Department of Biochemistry & Molecular Biology, Keck School of Medicine of the University of Southern California, 2250 Alcazar Street, Los Angeles, CA 90033 USA
2 Institute for Genetic Medicine, Keck School of Medicine of the University of Southern California, 2250 Alcazar Street, Los Angeles, CA 90033 USA
3 Department of Orthopedic Surgery, Keck School of Medicine of the University of Southern California, 1200 N. State Street, Los Angeles, CA 90033 USA
4 Bioinformatics Service Program, Norris Medical Library, University of Southern California, 2003 Zonal Ave, Los Angeles, CA 90089 USA
5 Department of Medicine, Keck School of Medicine of the University of Southern California, 1441 East Lake Ave, Los Angeles, CA 90033 USA
6 Will Rogers Institute Pulmonary Research Center, Keck School of Medicine of the University of Southern California, 2020 Zonal Avenue, Los Angeles, CA 90033 USA
Breast Cancer Research 2011, 13:R127 doi:10.1186/bcr3073
Published: 9 December 2011Abstract
Introduction
In contrast to its role in breast cancer (BCa) initiation, estrogen signaling has a protective effect in later stages, where estrogen receptor (ER)α loss associates with aggressive metastatic disease. We asked whether the beneficial effect of estrogen signaling in late-stage BCa is attributable to the recently reported estrogen-mediated antagonism of the pro-metastatic transcription factor Runx2.
Methods
MCF7/Rx2dox breast cancer cells were engineered with a lentivirus expressing Runx2 in response to doxycycline (dox). Cells treated with dox and/or estradiol (E2) were subjected to genome-wide expression profiling, RT-qPCR analysis of specific genes, and Matrigel™ invasion assays. Knockdown of genes of interest was performed using lentiviruses expressing appropriate shRNAs, either constitutively or in response to dox. Gene expression in BCa tumors was investigated using a cohort of 557 patients compiled from publicly available datasets. Association of gene expression with clinical metastasis was assessed by dichotomizing patients into those expressing genes of interest at either high or low levels, and comparing the respective Kaplan-Meier curves of metastasis-free survival.
Results
Runx2 induced epithelial-mesenchymal transition (EMT) evidenced by acquisition of a fibroblastic morphology, decreased expression of E-cadherin, increased expression of vimentin and invasiveness. Runx2 stimulated SNAI2 expression in a WNT- and transforming growth factor (TGF)β-dependent manner, and knockdown of SNAI2 abrogated the pro-metastatic activities of Runx2. E2 antagonized the pro-metastatic activities of Runx2, including SNAI2 upregulation. In primary BCa tumors, Runx2 activity, SNAI2 expression, and metastasis were positively correlated, and SNAI2 expression was negatively correlated with ERα. However, the negative correlation between SNAI2 and ERα in bone-seeking BCa cells was weaker than the respective negative correlation in tumors seeking lung. Furthermore, the absence of ERα in primary tumors was associated with lung- and brain- but not with bone metastasis, and tumor biopsies from bone metastatic sites displayed the unusual combination of high Runx2/SNAI2 and high ERα expression.
Conclusions
E2 antagonizes Runx2-induced EMT and invasiveness of BCa cells, partly through attenuating expression of SNAI2, a Runx2 target required for mediating its pro-metastatic property. That ERα loss promotes non-osseous metastasis by unleashing Runx2/SNAI2 is supported by the negative correlation observed in corresponding tumors. Unknown mechanisms in bone-seeking BCa allow high Runx2/SNAI2 expression despite high ERα level