Abstract
IntroductionNuclear accumulation of β-catenin is important for cancer development and it is found to overlap with p68 (DDX5) immunoreactivity in most breast cancers, as indicated by both clinical investigations and studies in cell lines. In this study, we aim to investigate the regulation of p68 gene expression through β-catenin/transcription factor 4 (TCF4) signaling in breast cancer.MethodsFormalin-fixed paraffin-embedded sections derived from normal human breast and breast cancer samples were used for immunohistochemical analysis. Protein and mRNA expressions were determined by immunoblotting and quantitative RT-PCR respectively. Promoter activity of p68 was checked using luciferase assay. Occupancy of several factors on the p68 promoter was evaluated using chromatin immunoprecipitation. Finally, a syngeneic mouse model of breast cancer was used to assess physiological significance.ResultsWe demonstrated that β-catenin can directly induce transcription of p68 promoter or indirectly through regulation of c-Myc in both human and mouse breast cancer cells. Moreover, by chromatin immunoprecipitation assay, we have found that both β-catenin and TCF4 occupy the endogenous p68 promoter, which is further enhanced by Wnt signaling. Furthermore, we have also established a positive feedback regulation for the expression of TCF4 by p68. To the best of our knowledge, this is the first report on β-catenin/TCF4-mediated p68 gene regulation, which plays an important role in epithelial to mesenchymal transition, as shown in vitro in breast cancer cell lines and in vivo in an animal breast tumour model.ConclusionsOur findings indicate that Wnt/β-catenin signaling plays an important role in breast cancer progression through p68 upregulation.Electronic supplementary materialThe online version of this article (doi:10.1186/s13058-014-0496-5) contains supplementary material, which is available to authorized users.
Highlights
Nuclear accumulation of β-catenin is important for cancer development and it is found to overlap with p68 (DDX5) immunoreactivity in most breast cancers, as indicated by both clinical investigations and studies in cell lines
The results indicate that there is a probable correlation for β-catenin and transcription factor 4 (TCF4) with p68 in the cancer cell lines
Our results indicate that p68 expression is quite low in MCF-7 cells as compared to highly metastatic MDA-MB 231 and mouse 4T1 cells with reduced expression or absence of E-cadherin, which is corroborated with the previous findings in breast tumours and cell lines [35]
Summary
Nuclear accumulation of β-catenin is important for cancer development and it is found to overlap with p68 (DDX5) immunoreactivity in most breast cancers, as indicated by both clinical investigations and studies in cell lines. We aim to investigate the regulation of p68 gene expression through β-catenin/transcription factor 4 (TCF4) signaling in breast cancer. Epigenetic silencing of the Wnt antagonists secreted Frizzled-related proteins (sFRPs) and Wnt inhibitory factor-1 (WIF-1) leads to aberrant regulation of Wnt/β-catenin signaling in both primary breast tumours and cell lines [15,16,17]. P68 has been implicated in a wide range of biological processes, and early studies of this protein indicate its possible involvement in the regulation of proliferation and organ differentiation [22]. Serum-induced p68 expression in Swiss 3 T3 fibroblasts is involved in cellular proliferation and connected to organ differentiation and maturation of the foetus [37]
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