Phosphorylation of E-box binding USF-1 by PI3K/AKT enhances its transcriptional activation of the WBP2 oncogene in breast cancer cells.

WW domain binding protein 2 (WBP2), a transcriptional coactivator, plays a vital role in breast tumorigenesis. It positively regulates estrogen receptor, Hippo, and Wnt pathways, which subsequently enhance the transcription of downstream target genes contributing to cancer. Understanding the regulation of the expression and activity of WBP2 oncoprotein has implication in cancer therapy. We have previously reported that WBP2 is regulated at the post-translational and post-transcriptional levels. However, its regulation at the transcriptional level is not known. In this study, the minimal promoter region of WBP2 that is critical for its transcription was identified. The E-box motif in the WBP2 promoter was demonstrated to be essential for its transcription. The E-box binding protein upstream stimulatory factor 1 (USF-1) was discovered to be a key transcription factor for WBP2 by yeast one-hybrid analysis and was validated through reporter and chromatin immunoprecipitation assays and tandem mass spectrometry, which also suggested that USF-1 acts by regulating a network of genes, in addition to WBP2, associated with cell movement, proliferation, cell-cycle, and survival cellular processes. USF-1 is overexpressed in majority of the breast cancer cell lines and tissues tested, and has profound effects on cancer cell proliferation. USF-1-mediated transcription of WBP2 was demonstrated to be inducible by insulin, which led to AKT-mediated phosphorylation of USF-1 that modulated its ability to bind to the WBP2 promoter and activate its transcription. This study sheds new light onto the regulation of the WBP2 oncogene at the transcriptional level by a novel oncogenic transcription factor, USF-1. USF-1 is a potential drug target for treatment of WBP2-positive breast cancer.-Ramos, A., Miow, Q. H., Liang, X., Lin, Q. S., Putti, T. C., Lim, Y. P. Phosphorylation of E-box binding USF-1 by PI3K/AKT enhances its transcriptional activation of the WBP2 oncogene in breast cancer cells.