Abstract
Introduction: Our laboratory has discovered a protein, BP1, which is a transcription factor of the homeobox gene family activated in 89% of the tumors of African American women (AAW) compared with 57% of the tumors of Caucasian American women (CW). High level BP1 expression has been shown to be associated with aggressive and larger tumors. Tumors of AAW are generally more aggressive – higher grade, larger, more frequently estrogen receptor (ER) negative, and more proliferative – than those of CW, resulting in an almost 50% higher mortality rate. Preliminary data suggest that BP1 is involved in the epithelial to mesenchymal transition (EMT) which is associated with the transdifferentiation of malignant epithelial cells to mesenchymal cells; BP1 up-regulates the Twist gene, an inducer of EMT. We hypothesize that EMT may be more frequent in tumors of AAW than CW, and that an important mechanism of EMT is via activation of BP1.
Materials and Methods: Cell lines engineered to overexpress BP1 were compared with controls with respect to EMT characteristics using Western blot analysis, confocal microscopy, and migration assays. Breast cancer cell lines derived from the tumors of AAW and CW were characterized with respect to BP1 and EMT markers using Western blots. Selected AA or CW cell lines are being analyzed using microarrays to attempt to identify pathways that may differ between them. Several cell lines will be treated with siBP1 to reduce BP1 or used to overexpress BP1, followed by microarray analysis to identify EMT-related and other pathways dysregulated by BP1 in AAW or CW. Tumor tissues from six AAW and from six CW, matched for age and stage of breast cancer, were immunostained to determine differential expression of BP1 and/or EMT markers, including E-cadherin (ECA), vimentin (VIM), and smooth muscle actin (SMA).
Results: (a) EMT. MCF7 cells overexpressing BP1 exhibit increased Twist and decreased E-cadherin (an epithelial marker), while Hs578T cells overexpressing BP1 show increased Twist, as well as vimentin and fibronectin (mesenchymal markers). Overexpression of BP1 also leads to increased migration of Hs578T cells. (b) Cell line analysis. We have analyzed five AAW cell lines and five CW cell lines; interestingly, in both types of cells, two were epithelial, one was mesenchymal, and two were not classifiable. Microarray analysis is underway. MDA-MB 157 and HCC70 cells, derived from tumors of AAW, and Hs578T, MCF7, and MDA-MB-231cells, derived from tumors of CW, were identified as candidates to perform siBP1 knock-down and microarray analysis. Upon siBP1 treatment of MDA-MB-231cells, vimentin expression decreased, further support for regulation of EMT by BP1. (c) Clinical Studies. The nuclear membrane area was stained most intensely for BP1, nucleus > cellular membrane > cytoplasm. Nuclear and cytoplasmic staining for BP1 tended to be less for CW than AAW and membrane ECD was less in CW than AAW. VIM and SMA were not informative. Additional cases are being studied.
Conclusions: Our data support the hypothesis that BP1 overexpression upregulates EMT in breast cancer cells by directly stimulating Twist expression. If EMT is more prevalent in tumors of AAW than CW, genes expressed during the transition would make good targets for therapy, with the possibility of reducing or preventing metastases. If BP1 is a regulator of EMT in patients, there would be a strong rationale for targeting BP1 using small molecule inhibitors, siBP1 or other approaches.
Citation Information: Cancer Epidemiol Biomarkers Prev 2011;20(10 Suppl):B32.
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