Human estrogen receptor alpha gene is a target of Runx2 transcription factor in osteoblasts

The RUNX/CBFβ Complex in Breast Cancer: A Conundrum of Context

Dissecting and identifying the major actors and pathways in the genesis, progression and aggressive advancement of breast cancer is challenging, in part because neoplasms arising in this tissue represent distinct diseases and in part because the tumors themselves evolve. This review attempts to illustrate the complexity of this mutational landscape as it pertains to the RUNX genes and their transcription co-factor CBFβ. Large-scale genomic studies that characterize genetic alterations across a disease subtype are a useful starting point and as such have identified recurring alterations in CBFB and in the RUNX genes (particularly RUNX1). Intriguingly, the functional output of these mutations is often context dependent with regards to the estrogen receptor (ER) status of the breast cancer. Therefore, such studies need to be integrated with an in-depth understanding of both the normal and corrupted function in mammary cells to begin to tease out how loss or gain of function can alter the cell phenotype and contribute to disease progression. We review how alterations to RUNX/CBFβ function contextually ascribe to breast cancer subtypes and discuss how the in vitro analyses and mouse model systems have contributed to our current understanding of these proteins in the pathogenesis of this complex set of diseases.

Estrogen Receptor α Regulates Dlx3-Mediated Osteoblast Differentiation

Estrogen receptor α (ER-α), which is involved in bone metabolism and breast cancer, has been shown to have transcriptional targets. Dlx3 is essential for the skeletal development and plays an important role in osteoblast differentiation. Various osteogenic stimulators and transcription factors can induce the protein expression of Dlx3. However, the regulatory function of ER-α in the Dlx3 mediated osteogenic process remains unknown. Therefore, we investigated the regulation of Dlx3 and found that ER-α is a positive regulator of Dlx3 transcription in BMP2-induced osteoblast differentiation. We also found that ER-α interacts with Dlx3 and increases its transcriptional activity and DNA binding affinity. Furthermore, we demonstrated that the regulation of Dlx3 activity by ER-α is independent of the ligand (estradiol) binding domain. These results indicate that Dlx3 is a novel target of ER-α, and that ER-α regulates the osteoblast differentiation through modulation of Dlx3 expression and/or interaction with Dlx3.

Role of RUNX2 in Breast Carcinogenesis

RUNX2 is a transcription factor playing the major role in osteogenesis, but it can be involved in DNA damage response, which is crucial for cancer transformation. RUNX2 can interact with cell cycle regulators: cyclin-dependent kinases, pRB and p21Cip1 proteins, as well as the master regulator of the cell cycle, the p53 tumor suppressor. RUNX2 is involved in many signaling pathways, including those important for estrogen signaling, which, in turn, are significant for breast carcinogenesis. RUNX2 can promote breast cancer development through Wnt and Tgfβ signaling pathways, especially in estrogen receptor (ER)-negative cases. ERα interacts directly with RUNX2 and regulates its activity. Moreover, the ERα gene has a RUNX2 binding site within its promoter. RUNX2 stimulates the expression of aromatase, an estrogen producing enzyme, increasing the level of estrogens, which in turn stimulate cell proliferation and replication errors, which can be turned into carcinogenic mutations. Exploring the role of RUNX2 in the pathogenesis of breast cancer can lead to revealing new therapeutic targets.

The prognostic significance of RUNX2 and miR-10a/10b and their inter-relationship in breast cancer

Background

The major cancer related mortality is caused by metastasis and invasion. It is important to identify genes regulating metastasis and invasion in order to curtail metastatic spread of cancer cells.

Methods

This study investigated the association between RUNX2 and miR-10a/miR-10b and the risk of breast cancer relapse. Expression levels of RUNX2 and miR-10a/b in108 pairs of tumor and non-tumor tissue of breast cancer were assayed by quantitative PCR analysis and evaluated for their prognostic implications.

Results

The median expression levels of RUNX2 and miR-10b in tumor tissue normalized using adjacent non-tumor tissue were significantly higher in relapsed patients than in relapse-free patients. Higher expression of these three genes were significantly correlated with the hazard ratio for breast cancer recurrence (RUNX2: 3.02, 95% CI = 1.50 ~ 6.07; miR-10a: 2.31, 95% CI = 1.00 ~ 5.32; miR-10b: 3.96, 95% CI = 1.21 ~ 12.98). The joint effect of higher expression of all three genes was associated with a hazard ratio of 12.37 (95% CI = 1.62 ~ 94.55) for relapse. In a breast cancer cell line, RUNX2 silencing reduced the expression of miR-10a/b and also impaired cell motility, while RUNX2 overexpression elicited opposite effects.

Conclusions

These findings indicate that higher expression of RUNX2 and miR-10a/b was associated with adverse outcome of breast cancer. Expression levels of RUNX2 and miR-10a/b individually or jointly are potential prognostic factors for predicting breast cancer recurrence. Data from in vitro studies support the notion that RUNX2 promoted cell motility by upregulating miR-10a/b.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-014-0257-3) contains supplementary material, which is available to authorized users.

Estrogen Receptor α (ERα) and Estrogen Related Receptor α (ERRα) are both transcriptional regulators of the Runx2-I isoform

Runx2 is a master regulator of bone development and has also been described as an oncogene. Estrogen Receptor α (ERα) and Estrogen Related Receptor α (ERRα), both implicated in bone metabolism and breast cancer, have been shown to share common transcriptional targets. Here, we show that ERα is a positive regulator of Runx2-I transcription. Moreover, ERRα can act as a transcriptional activator of Runx2-I in presence of peroxisome proliferator activated receptor gamma coactivator-1 alpha (PGC-1α). In contrast, ERRα behaves as a negative regulator of Runx2-I transcription in presence of PGC-1β. ERα and ERRα cross-talk via a common estrogen receptor response element on the Runx2-I promoter. In addition, estrogen regulates PGC-1β that in turn is able to modulate both ERα and ERRα transcriptional activity.

Sequential expression of osteoblast phenotypic genes during medullary bone formation and resorption in estrogen-treated male Japanese quails

Medullary bone is formed reticularly in the bone marrow cavity of the long bones of female birds. Although this bone matrix contains fewer collagen fibers and more acid mucopolysaccharides than cortical bone, it is not clear that the expression pattern of osteoblast phenotypic genes during bone remodeling. Therefore, 17β-estradiol (E2)-treated male Japanese quails were used to examine the temporal expression patterns of osteoblast phenotypic genes, and to simultaneously confirm the morphological changes occurring in the bone marrow cavity during medullary bone formation and resorption. After E2 treatment, bone lining cells proliferated and developed into mature osteoblasts that had intense alkaline phosphatase (ALP) activity. These cells began to form medullary bone that contained acid mucopolysaccharides and tartrate-resistantacid phosphatase. Runt-related gene 2 (Runx2) mRNA was stably expressed throughout the process. The expression of both ALP and type I collagen mRNAs increased initially, and then rapidly decreased after day 7, while osteoclasts began to resorb medullary bone at day 5. The expression of bone matrix-related genes peaked at day 5, and suddenly decreased at day 7, except for osteopontin. Taken together with these results, the expression patterns of bone matrix-related genes during the later stages might be related to osteoclast activity. Additionally, the constant expression of Runx2 during bone formation and resorption suggested that osteoprogenitor cells always exist in the bone marrow cavity. Therefore, the expression patterns of these genes and the characteristics of bone matrix might extremely be related to the quick remodeling of medullary bone.

Opposing effects of Runx2 and estradiol on breast cancer cell proliferation: in vitro identification of reciprocally regulated gene signature related to clinical letrozole responsiveness

PURPOSE

To assess the clinical significance of the interaction between estrogen and Runx2 signaling, previously shown in vitro.

EXPERIMENTAL DESIGN

MCF7/Rx2(dox) breast cancer cells were treated with estradiol and/or doxycycline to induce Runx2, and global gene expression was profiled to define genes regulated by estradiol, Runx2, or both. Anchorage-independent growth was assessed by soft-agar colony formation assays. Expression of gene sets defined using the MCF7/Rx2(dox) system was analyzed in pre- and on-treatment biopsies from hormone receptor-positive patients undergoing neoadjuvant letrozole treatment in two independent studies, and short-term changes in gene expression were correlated with tumor size reduction or Ki67 index at surgery.

RESULTS

Reflecting its oncogenic property, estradiol strongly promoted soft-agar colony formation, whereas Runx2 blocked this process suggesting tumor suppressor property. Transcriptome analysis of MCF7/Rx2(dox) cells treated with estradiol and/or doxycycline showed reciprocal attenuation of Runx2 and estrogen signaling. Correspondingly in breast cancer tumors, expression of estradiol- and Runx2-regulated genes was inversely correlated, and letrozole increased expression of Runx2-stimulated genes, as defined in the MCF7/Rx2(dox) model. Of particular interest was a gene set upregulated by estradiol and downregulated by Runx2 in vitro; its short-term response to letrozole treatment associated with tumor size reduction and Ki67 index at surgery better than other estradiol-regulated gene sets.

CONCLUSION

This work provides clinical evidence for the importance of antagonism between Runx2 and E2 signaling in breast cancer. Likely sensing the tension between them, letrozole responsiveness of a genomic node, positively regulated by estradiol and negatively regulated by Runx2 in vitro, best correlated with the clinical efficacy of letrozole treatment.

Slug gene expression supports human osteoblast maturation

This study aims to define the function of Slug transcription factor in human normal osteoblasts (hOBs). To date, Slug is considered exclusively a marker of malignancy in bone tissue. Here, we identified, for the first time, a role for Slug in hOBs using a knockdown approach. We demonstrated that Slug is positively correlated with osteoblast markers, including Runx2, osteopontin, osteocalcin, Collagen type 1, Wnt/beta-catenin signaling mediators, and mineral deposition. At the same time, Slug silencing potentiates the expression of Sox-9, a factor indispensable for chondrogenic development. These data, with the finding that Slug is in vivo recruited by the promoters of Runx2 and Sox-9 genes, suggest that, in hOBs, Slug may act both as positive and negative transcriptional regulator of Runx2 and Sox-9 genes, respectively. In summary, our results support the hypothesis that Slug functions as a novel regulator of osteoblast activity and may be considered a new factor required for osteoblast maturation.

Nuclear factor-kappaB regulates estrogen receptor-alpha transcription in the human heart

Estrogen receptor (ER)-mediated effects have been associated with the modulation of myocardial hypertrophy in animal models and in humans, but the regulation of ER expression in the human heart has not yet been analyzed. In various cell lines and tissues, multiple human estrogen receptor alpha (hERalpha) mRNA isoforms are transcribed from distinct promoters and differ in their 5'-untranslated regions. Using PCR-based strategies, we show that in the human heart the ERalpha mRNA is transcribed from multiple promoters, namely, A, B, C, and F, of which the F-promoter is most frequently used variant. Transient transfection reporter assays in a human cardiac myocyte cell line (AC16) with F-promoter deletion constructs demonstrated a negative regulatory region within this promoter. Site-directed mutagenesis and electrophoretic mobility shift assays indicated that NF-kappaB binds to this region. An inhibition of NF-kappaB activity by parthenolide significantly increased the transcriptional activity of the F-promoter. Increasing NF-kappaB expression by tumor necrosis factor-alpha reduced the expression of ERalpha, indicating that the NF-kappaB pathway inhibits expression of ERalpha in human cardiomyocytes. Finally, 17beta-estradiol induced the transcriptional activity of hERalpha promoters A, B, C, and F. In conclusion, inflammatory stimuli suppress hERalpha expression via activation and subsequent binding of NF-kappaB to the ERalpha F-promoter, and 17beta-estradiol/hERalpha may antagonize the inhibitory effect of NF-kappaB. This suggests interplay between estrogen/estrogen receptors and the pro-hypertrophic and inflammatory responses to NF-kappaB.

The osteogenic transcription factor runx2 controls genes involved in sterol/steroid metabolism, including CYP11A1 in osteoblasts

Steroid hormones including (1,25)-dihydroxyvitamin D3, estrogens, and glucocorticoids control bone development and homeostasis. We show here that the osteogenic transcription factor Runx2 controls genes involved in sterol/steroid metabolism, including Cyp11a1, Cyp39a1, Cyp51, Lss, and Dhcr7 in murine osteoprogenitor cells. Cyp11a1 (P450scc) encodes an approximately 55-kDa mitochondrial enzyme that catalyzes side-chain cleavage of cholesterol and is rate limiting for steroid hormone biosynthesis. Runx2 is coexpressed with Cyp11a1 in osteoblasts as well as nonosseous cell types (e.g. testis and breast cancer cells), suggesting a broad biological role for Runx2 in sterol/steroid metabolism. Notably, osteoblasts and breast cancer cells express an approximately 32-kDa truncated isoform of Cyp11a1 that is nonmitochondrial and localized in both the cytoplasm and the nucleus. Chromatin immunoprecipitation analyses and gel shift assays show that Runx2 binds to the Cyp11a1 gene promoter in osteoblasts, indicating that Cyp11a1 is a direct target of Runx2. Specific Cyp11a1 knockdown with short hairpin RNA increases cell proliferation, indicating that Cyp11a1 normally suppresses osteoblast proliferation. We conclude that Runx2 regulates enzymes involved in sterol/steroid-related metabolic pathways and that activation of Cyp11a1 by Runx2 may contribute to attenuation of osteoblast growth.

ERalpha and AP-1 interact in vivo with a specific sequence of the F promoter of the human ERalpha gene in osteoblasts

Estrogen-responsive genes often have an estrogen response element (ERE) positioned next to activator protein-1 (AP-1) binding sites. Considering that the interaction between ERE and AP-1 elements has been described for the modulation of bone-specific genes, we investigated the 17-beta-estradiol responsiveness and the role of these cis-elements present in the F promoter of the human estrogen receptor alpha (ERalpha) gene. The F promoter, containing the sequence analyzed here, is one of the multiple promoters of the human ERalpha gene and is the only active promoter in bone tissue. Through electrophoretic mobility shift (EMSA), chromatin immunoprecipitation (ChIP), and re-ChIP assays, we investigated the binding of ERalpha and four members of the AP-1 family (c-Jun, c-fos, Fra-2, and ATF2) to a region located approximately 800 bp upstream of the transcriptional start site of exon F of the human ERalpha gene in SaOS-2 osteoblast-like cells. Reporter gene assay experiments in combination with DNA binding assays demonstrated that F promoter activity is under the control of upstream cis-acting elements which are recognized by specific combinations of ERalpha, c-Jun, c-fos, and ATF2 homo- and heterodimers. Moreover, ChIP and re-ChIP experiments showed that these nuclear factors bind the F promoter in vivo with a simultaneous occupancy stimulated by 17-beta-estradiol. Taken together, our findings support a model in which ERalpha/AP-1 complexes modulate F promoter activity under conditions of 17-beta-estradiol stimulation.

Prolactin decreases expression of Runx2, osteoprotegerin, and RANKL in primary osteoblasts derived from tibiae of adult female rats

Hyperprolactinemia caused by physiological or pathological conditions, such as those occurring during lactation and prolactinoma, respectively, results in progressive osteopenia. The underlying mechanisms, however, are controversial. Prolactin (PRL) may directly attenuate the functions of osteoblasts, since these bone cells express PRL receptors. The present study therefore aimed to investigate the effects of PRL on the expression of genes related to the osteoblast functions by using quantitative real-time PCR technique. Herein, we used primary osteoblasts that were derived from the tibiae of adult rats and displayed characteristics of differentiated osteoblasts, including in vitro mineralization. Osteoblasts exposed for 48 h to 1000 ng/mL PRL, but not to 10 or 100 ng/mL PRL, showed decreases in the mRNA expression of Runx2, osteoprotegerin (OPG), and receptor activator of nuclear factor κB ligand (RANKL) by 60.49%, 72.74%, and 87.51%, respectively. Nevertheless, PRL did not change the RANKL/OPG ratio, since expression of OPG and RANKL were proportionally decreased. These concentrations of PRL had no effect on the mRNA expression of osteocalcin and osteopontin, nor on mineralization. High pathologic concentrations of PRL (1000 ng/mL) may downregulate expression of genes that are essential for osteoblast differentiation and functions. The present results explained the clinical findings of hyperprolactinemia-induced bone loss.

Evaluation of chemokine and cytokine profiles in osteoblast progenitors from umbilical cord blood stem cells by BIO-PLEX technology

We have used cytokine protein array to analyze the secretion of cytokines from an osteoblastic clone derived from human umbilical cord blood mesenchymal stem cells (MSCs) cultured in an osteogenic differentiation medium. The analysis demonstrated the unexpected ability of osteoblast committed cells and their early progenitors to produce significant amounts of a range of soluble immune mediators without in vitro exposure to clinically relevant bacterial pathogens. The cells were expanded and their osteogenic potential analyzed over 45 days of culture was revealed by the expression of osteoblast-specific markers (alkaline phosphatase and Runx2), and by matrix mineralization. Over this culture period, the cells secreted particularly high levels of IL-8, MCP-1 and VEGF, but did not express IL-2, IL-7, IL-17, eotaxin, G-CSF and IFN-gamma. These findings should encourage the use of human umbilical cord blood as a potential stem cells source for bone regeneration.