Abstract 865: Cytoplasmic polyadenylation element binding protein 2 splice variants have opposing functions in the epithelial to mesenchymal transition pathway

Abstract

Abstract Alternative splicing of cytoplasmic polyadenylation element binding protein 2 (CPEB2) generates two isoforms, CPEB2B and CPEB2A, through inclusion/exclusion of exon 4, respectively, in mature mRNA. We previously reported that CPEB2B is essential to establish anoikis resistance (AnR), and promotes metastasis using in vivo orthotopic models. In contrast, CPEB2A decreases AnR and metastatic transformation. In the current studies, we examined the function of CPEB2 isoforms using next generation sequencing analysis of downstream signaling pathways. We found that CPEB2B expression upregulated AnR in breast cancer cells and induced key genes/proteins in the epithelial to mesenchymal transition (EMT) and hypoxic response (hypoxia inducible factor 1α (HIF1α)-dependent) pathways. Inhibition of either TWIST1 or HIF1α reduced the CPEB2B-mediated AnR in cells ectopically expressing CPEB2B, confirming a link between CPEB2 alternative splicing and the induction of the EMT/hypoxia pathways. We then extended our findings, and demonstrated that CPEB2 alternative splicing induced de novo translation of both HIF1α and TWIST1, whereas CPEB2A decreased translation of these factors. Furthermore, CPEB2 isoforms were found to modulate differential polyadenylation site selection of the TWIST1 3’UTR and competed for binding to HIF1α and TWIST1 3’UTR cytoplasmic polyadenylation element (CPE) site sequences. These results demonstrate that CPEB2A and CPEB2B modulate the translation of factors in the EMT/hypoxia pathways in an opposing fashion via differential polyadenylation site selection and subsequent translation. Citation Format: James T. DeLigio, Charles E. Chalfant, Margaret A. Park. Cytoplasmic polyadenylation element binding protein 2 splice variants have opposing functions in the epithelial to mesenchymal transition pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 865. doi:10.1158/1538-7445.AM2017-865