Regulation of breast cancer metastasis by Runx2 and estrogen signaling: the role of SNAI2

Abstract

IntroductionIn 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.MethodsMCF7/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.ResultsRunx2 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.ConclusionsE2 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

miR-218 Directs a Wnt Signaling Circuit to Promote Differentiation of Osteoblasts and Osteomimicry of Metastatic Cancer Cells

“…In addition, a growing number of miRs have been revealed as signatures for different diseases including cancers (46 -48). Although miR-218 functions as a tumor-suppressive "oncomiRNA" to suppress certain cancers (49,50), elevated miR-218 expression has also previously been associated with estrogen receptor positive breast tumors indicating a possible role in certain breast cancer phenotypes (51,52). Consistent with latter findings, miR-218 promotes metastasis-related molecular properties in MDA-MB-231 aggressive breast cancer cells.…”

“…miR-218 was reported to function as a tumor suppressor through regulation of the Slit-Robo pathway in some cancers, but not others (49). The Slit2 gene harboring miR-218 is expressed in metastatic breast cancer cells and is associated with metastasis to brain, but not to bone (50), whereas both Wnt signaling and estrogen are linked to bone metastasis (22,52). These results suggest that the expression of the two forms of miR-218 arising from its host genes serve different biological functions than their host genes in osteoblasts and breast cancer cells.…”

Hormone-Sensing Mammary Epithelial Progenitors: Emerging Identity and Hormonal Regulation

“…The expression of RUNX2 is negatively correlated with ERα expression, and this has been implicated as a mechanism by which ERα promotes maintenance of a differentiated epithelial phenotype by antagonising the EMT-inducing effect of RUNX2 [158]. Transplantation of Runx2-/-mouse mammary buds into immunocompromised recipient mouse fat pads demonstrated that RUNX2 is not required for mammary outgrowth but Runx2-/-outgrowths exhibit defective alveologenesis during late pregnancy (>18 days post coitum- [157]).…”

Differential Effects of RUNX2 on the Androgen Receptor in Prostate Cancer: Synergistic Stimulation of a Gene Set Exemplified by SNAI2 and Subsequent Invasiveness

“…RUNX2, best known for its roles in skeletal development (13, 14), has also been implicated in carcinogenesis, including the promotion of breast and prostate cancer metastasis (8, 15–20). RUNX2 activity in PCa is negatively regulated by PTEN through a FOXO1-dependent mechanism (21), RUNX2 expression progressively increases during PCa development in the PTEN conditional knockout mouse model (22) and its immunoreactivity is higher in human PCa than in prostatic intraepithelial neoplasia (PIN) and normal prostate epithelium (16, 23, 24).…”