HOXB7, a Homeodomain Protein, Is Overexpressed in Breast Cancer and Confers Epithelial-Mesenchymal Transition

Abstract

Epithelial-mesenchymal transition (EMT) is increasingly recognized as a mechanism whereby cells in primary noninvasive tumors acquire properties essential for migration and invasion. Microarray analyses of microdissected epithelial cells from bone metastasis revealed a HOXB7 overexpression that was 3-fold higher than in primary breast carcinomas and 18-fold higher compared with normal breast. This led us to investigate the role of HOXB7 in neoplastic transformation of breast cells. Expression of HOXB7 in both MCF10A and MadinDarby canine kidney (MDCK) epithelial cells resulted in the acquisition of both phenotypic and molecular attributes typical of EMT. Loss of epithelial proteins, claudin 1 and claudin 7, mislocalization of claudin 4 and E-cadherin, and the expression of mesenchymal proteins, vimentin and A-smooth muscle actin, were observed. MDCK cells expressing HOXB7 exhibited properties of migration and invasion. Unlike MDCK vector-transfected cells, MDCK-HOXB7 cells formed highly vascularized tumors in mice. MDCK-HOXB7 cells overexpressed basic fibroblast growth factor (bFGF), had more active forms of both Ras and RhoA proteins, and displayed higher levels of phosphorylation of p44 and p42 mitogen-activated protein kinase (MAPK; extracellular signal-regulated kinases 1 and 2). Effects initiated by HOXB7 were reversed by specific inhibitors of FGF receptor and the Ras-MAPK pathways. These data provide support for a function for HOXB7 in promoting tumor invasion through activation of Ras/Rho pathway by up-regulating bFGF, a known transcriptional target of HOXB7. Reversal of these effects by HOXB7-specific siRNA further suggested that these effects were mediated by HOXB7. Thus, HOXB7 overexpression caused EMT in epithelial cells, accompanied by acquisition of aggressive properties of tumorigenicity, migration, and invasion.

The HOXB7 protein renders breast cancer cells resistant to tamoxifen through activation of the EGFR pathway

“…Prolonged endocrine therapy is often associated with an increase in expression of receptor tyrosine kinases such as EGFR/HER2, which, together with activation of ER-dependent gene transcription and aberrant growth/apoptosis, leads to endocrine resistance (12). In addition, epithelial-mesenchymal transition (EMT) has been observed in tamoxifen-resistant MCF-7 cells (13), similar to our report of EMT in MCF10A-HOXB7 cells (6). Because of the striking similarity in phenotype between prolonged endocrine therapy-primed TAMresistant models and our HOXB7-overexpressing cells, we explored the hypothesis that HOXB7 is a mediator of anti-estrogen resistance.…”

“…The role of HOX genes in breast cancer development is largely unexplored. Recently, we identified HOXB7 through microarray analysis as one of the genes whose expression was significantly elevated in both the primary cancer and distant metastasis (6). HOXB7 overexpression promoted cell proliferation in SKBR3 breast cancer cells that acquired the ability to grow as robustly vascularized xenografts in immunodeficient mice (7).…”

“…HOXB7 overexpression promoted cell proliferation in SKBR3 breast cancer cells that acquired the ability to grow as robustly vascularized xenografts in immunodeficient mice (7). In culture, HOXB7 transformed mammary epithelial cells, MCF10A, and promoted epithelial/mesenchymal transition and invasion in a variety of cell lines through activation of the RHO/RAC pathway (6).…”

Tumor suppressor p16 INK4A is necessary for survival of cervical carcinoma cell lines

“…For example, HOXC10 overexpression is associated with increased invasion and the transition of cervical high-grade squamous intraepithelial lesions to cervical squamous cell carcinoma (28). HOXB7 mediates aspects of epithelial-to-mesenchymal transition in breast cancer, promotes proliferation in oral cancer, and is associated with progression and development of metastases in lung cancer (29)(30)(31). In addition, germ-line HOXB13 mutations have been linked to an increased prostate cancer risk (32).…”

shRNA Mediated RHOXF1 Silencing Influences Expression of BCL2 but not CASP8 in MCF-7 and MDA-MB-231 Cell Lines

“…Many of them have been shown to be aberrantly expressed in different cancers (Wu et al, 2006). As they have critical roles in regulation of cellular functions such as apoptosis, receptor signaling, differentiation, motility and angiogenesis, alteration of their expression can be important for both tumorigenesis and cancer suppression, depending on the situation (Shah and Sukumar, 2010).…”