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

Abstract

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.

The emerging roles of WBP2 oncogene in human cancers

“…Our lab further showed that USF-1 phosphorylation/ activation is necessary for its transcriptional activation of WBP2 expression and the former was mediated by the PI 3 K/Akt pathway in response to insulin stimulation [51]. Taken together with the previous findings that WBP2 positively regulates PI 3 K/Akt pathway, the presence of a positive feedback loop between PI 3 K/Akt and WBP2 is envisaged to drive cancer processes.…”

“…Since WBP2 protein is well established to be overexpressed in breast cancer [13], we reasoned the transcription factors that drive WBP2 expression would have contributed to this phenotype, at least in part. Testing this hypothesis led to the identification of upstream factor-1 (USF-1) as a novel, oncogenic transcription factor for WBP2 [51]. ChIP experiments showed that USF-1 drives WBP2 transcription by binding to the E-box of WBP2 promoter, resulting in an increase of WBP2 transcript, protein level, and breast cancer cell proliferation [51] ( Fig.…”

“…Testing this hypothesis led to the identification of upstream factor-1 (USF-1) as a novel, oncogenic transcription factor for WBP2 [51]. ChIP experiments showed that USF-1 drives WBP2 transcription by binding to the E-box of WBP2 promoter, resulting in an increase of WBP2 transcript, protein level, and breast cancer cell proliferation [51] ( Fig. 3).…”

Hippo/MST blocks breast cancer by downregulating WBP2 oncogene expression via miRNA processor Dicer

“…3a, iii). Knockdown of USF-1, the transcription factor of WBP2 23 was used as the positive control. This suggest regulation of WBP2 by MST at the post-transcriptional/ translational level.…”

WBP2 Negatively Regulates Hippo Pathway By Competitively Binding To WWC3 With LATS1 To Promote The Malignant Phenotype Of Non-Small Cell Lung Cancer

“…In hepatocellular carcinoma, micro non-coding RNA (miRNA) can affect the malignant phenotype of hepatocellular carcinoma cells by downregulating the expression of WBP2 [31]. The transcription factor USF1 can promote the transcription of WBP2 by binding to the E-box region of the WBP2 promoter [32]. ITCH also attenuated CD4 T-cell proliferation in mice by limiting WBP2 protein stability [33].…”