A Functional Screen in Human Cells Identifies UBF2 as an RNA Polymerase II Transcription Factor That Enhances the β-Catenin Signaling Pathway

Abstract

β-Catenin signaling plays an important role in the development of many organisms and has a key part in driving the malignant transformation of epithelial cells comprising a variety of cancers. β-Catenin can activate gene expression through its association with transcription factors of the lymphoid enhancer factor 1 (LEF-1)/T-cell factor (TCF) family. We designed a screen in human cells to identify novel genes that activate a β-catenin-LEF/TCF-responsive promoter and isolated the high-mobility group box transcription factor, UBF2. UBF1 and UBF2 are splice variants of a common precursor RNA. Although UBF1 has been shown to activate RNA polymerase I-regulated genes, the function of UBF2 has remained obscure. Here, we show for the first time that both UBF1 and UBF2 activate RNA polymerase II-regulated promoters. UBF2 associates with LEF-1, as shown by coimmunoprecipitation experiments, and potentiates transcriptional activation stimulated by LEF-1/β-catenin from a synthetic promoter with multimerized LEF/TCF binding sites and a natural cyclin D1 promoter with consensus LEF/TCF binding sites. Downregulation of endogenous UBF expression using an RNA interference approach reduces transcriptional activation of a β-catenin-LEF/TCF-responsive promoter by means of overexpressed β-catenin, further implicating UBF as a transcriptional enhancer of the β-catenin pathway.

ACKNOWLEDGMENTS

We thank Jacqueline Saleh and Jolene Andrews for flow cytometry, Peter Reavey and M. Draper for several cDNA libraries, M. Lee for sharing reagents and ideas, Mei Xin for establishing the luciferase assay, and the ACGC sequencing facility for HTP sequencing and clustering of genes. We especially thank A. Arnold and R. Pestell for cloning the cyclin D1 promoter and O. Tetsu and F. McCormick for generously sharing their pGL3 cyclin D1 reporter constructs. We thank A. Roy, L. Comai, J. Cherry, and M. Lee for critical reading of the manuscript. A special thank you is due to Lori Rosenthal for generating figures at ARRCO Medical Art & Design.