Modulation of Runx2 Activity by Estrogen Receptor-α: Implications for Osteoporosis and Breast Cancer

Abstract

The transcription factors Runx2 and estrogen receptor-alpha (ERalpha) are involved in numerous normal and disease processes, including postmenopausal osteoporosis and breast cancer. Using indirect immunofluorescence microscopy and pull-down techniques, we found them to colocalize and form complexes in a ligand-dependent manner. Estradiol-bound ERalpha strongly interacted with Runx2 directly through its DNA-binding domain and only indirectly through its N-terminal and ligand-binding domains. Runx2's amino acids 417-514, encompassing activation domain 3 and the nuclear matrix targeting sequence, were sufficient for interaction with ERalpha's DNA-binding domain. As a consequence of the interaction, Runx2's transcriptional activation activity was strongly repressed, as shown by reporter assays in COS7 cells, breast cancer cells, and late-stage MC3T3-E1 osteoblast cultures. Metaanalysis of gene expression in 779 breast cancer biopsies indicated negative correlation between the expression of ERalpha and Runx2 target genes. Selective ER modulators (SERM) induced ERalpha-Runx2 interactions but led to various functional outcomes. The regulation of Runx2 by ERalpha may play key roles in osteoblast and breast epithelial cell growth and differentiation; hence, modulation of Runx2 by native and synthetic ERalpha ligands offers new avenues in selective ER modulator evaluation and development.

Prolactin and oestrogen synergistically regulate gene expression and proliferation of breast cancer cells

“…PRL was previously found to regulate RUNX2 expression in human pre-osteoblast cells (Seriwatanachai et al 2009), and a direct interaction between ER and RUNX2 was reported to influence RUNX2-mediated transcription (Khalid et al 2008). RUNX2 is involved in tumour invasion and especially bone metastasis (Pratap et al 2006).…”

The Gene for Aromatase, a Rate-Limiting Enzyme for Local Estrogen Biosynthesis, Is a Downstream Target Gene of Runx2 in Skeletal Tissues

“…Together, these findings strongly suggest that Runx2 expression in osteoblasts renders these cells competent to produce functional anabolic steroids that stimulate osteoblast function. More interestingly, the local production of estrogen in bone may be related to the Runx2-mediated transactivation function because ER-␣ interacts directly with Runx2 and modulates its transcriptional function in the presence of estrogen (13). Results from this and previous studies indicate a Runx2-aromatase-estrogen axis that may be controlled by negative-and positive-feedback mechanisms.…”

“…Furthermore, Runx2 was recently shown to control the expression of GPR30/GPER, which represents a nongenomic cell surface receptor for estrogen that is essential for osteoblast proliferation in cell culture (47). Although accumulating evidence implicates a functional association of Runx2 with estrogen signaling (13,21,45,48), Runx2 has not been directly shown to control estrogen biosynthesis. Aromatase is a rate-limiting enzyme in the conversion of testosterone into estrogen and plays a pivotal role in estrogen synthesis.…”

Screening and functional microarray analysis of differentially expressed genes related to osteoporosis

“…A mutant ESR1 gene has been found to result in reduced BMD in humans (Smith et al, 1994) and mice (Delhon et al, 2009). In addition, the ESR1 gene is also positively correlated with the expression of the IGF1 (insulin-like growth factor 1) gene (Mendez et al, 2006) and Runx2 (Khalid et al, 2008), another important osteogenic growth factor that enhances the function of osteoblasts and prevents osteoblastic apoptosis. In the estrogen receptor signaling pathway, ESR1 positively regulates the activation of MAPK3 (Levin, 2003), which increases the activation of the nucleus ESR1-estrogen dimer (Likhite et al, 2006).…”