Abstract A34: CELF1 is a central node in post-transcriptional regulatory programs underlying EMT and metastasis in breast epithelial cells
Authors: Chaudhury Arindam , Cheema Shebna , Fachini Joseph M. , Kongchan Natee , Lu Guojun , Simon Lukas M. , Wang Tao , Mao Sufeng , Rosen Daniel G. , Ittmann Michael M. , Hilsenbeck Susan G. , Shaw Chad A. , Neilson Joel R. 
Published: May 2017

Abstract
The importance of translational regulation in tumorigenesis and metastasis is increasingly appreciated. We have leveraged polyribosomal profiling to prospectively and functionally define translational regulatory programs underlying the epithelial to mesenchymal transition (EMT), one of the early manifestations of metastasis, in breast epithelial cells. Our approach identified scores of mRNAs both enriched and depleted from polyribosomal fractions in mesenchymal cells as compared to their epithelial counterparts. Computational analysis of the 3' untranslated regions (UTRs) of mRNAs enriched in polysomal fractions derived from the mesenchymal state revealed enrichment of a distinct GU-rich cis-element within these mRNA transcripts. Strikingly, while relative representation of these GU-rich-containing transcripts at the level of bulk mRNA were generally decreased in mesenchymal cells, the protein encoded by each of these mRNAs was dramatically increased. 3' UTRs from affected transcripts conferred similar regulation upon a fluorescent reporter gene dependent upon the presence of the GU-rich element within the 3' UTR sequence. Several of the translationally upregulated transcripts were necessary and/or sufficient for the EMT program. We next identified the CELF1 protein as a common regulator of these mRNA transcripts, demonstrating direct binding of the CELF1 protein to affected transcripts dependent upon the presence of the GU-rich element within their 3' UTRs. CELF1 was itself necessary and sufficient for EMT in several distinct in vitro models as well as for metastatic colonization in vivo. Analysis of publicly available transcriptomic data revealed no increase in the relative expression of CELF1's regulatory targets or CELF1 itself in human breast cancer. We demonstrate that the CELF1 gene product is itself post-translationally regulated during EMT, and that CELF1 protein, but not mRNA, is significantly overexpressed in human breast cancer tissues and correlates with disease progression. Cumulatively, our data present an eleven component genetic pathway, invisible to transcriptional profiling approaches, in which the CELF1 protein functions as a central node controlling translational activation of genes driving EMT and ultimately tumor metastasis in human breast cancer.
Citation Format: Arindam Chaudhury, Shebna Cheema, Joseph M. Fachini, Natee Kongchan, Guojun Lu, Lukas M. Simon, Tao Wang, Sufeng Mao, Daniel G. Rosen, Michael M. Ittmann, Susan G. Hilsenbeck, Chad A. Shaw, Joel R. Neilson. CELF1 is a central node in post-transcriptional regulatory programs underlying EMT and metastasis in breast epithelial cells. [abstract]. In: Proceedings of the AACR Special Conference on Translational Control of Cancer: A New Frontier in Cancer Biology and Therapy; 2016 Oct 27-30; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2017;77(6 Suppl):Abstract nr A34.