Abstract 5503: Interplay between the transcription factors PRRX1 and FOXM1 in pancreatic cancer

Abstract

Abstract Introduction: We have identified previously the Paired Related Homeobox 1 gene (Prrx1) as a key regulator of embryonic ductal development, acinar-to-ductal metaplasia (ADM) and pre-cancerous lesion (PanIN)/pancreatic ductal adenocarcinoma (PDAC) progression (Reichert M. et al Genes & Dev 2013). We discovered an isoform switch between PRRX1A and PRRX1B occurring in EMT-MET plasticity in pancreatic tumorigenesis (EMT) and metastatic colonization of the liver (MET) (Takano S. et al Genes & Dev 2016). The transcription factor FOXM1 is also implicated in EMT of pancreatic cancer cells. Interestingly, both transcription factors, FOXM1 and PRRX1, are overexpressed in PDAC. The aim of this study was to investigate if PRRX1, specifically its isoforms, might interact with FOXM1, to regulate gene transcription in pancreatic cancer. Methods: Experiments were performed in human pancreatic cancer cells (PANC1, MIA PaCa2 and BxPC3), and HEK293T cells. Epitope-tagged PRRX1 and FOXM1 proteins (wild type or deletion mutants) were either transiently or stably expressed in these cells. Immunoprecipitation and western blot were performed to evaluate potential interaction between PRRX1 and FOXM1. As a functional readout, the TnC and 6xFOXM1 luciferase reporters were used to measure Tenascin C and FOXM1 transcriptional activities. Results: Immunoprecipitation of tagged-PRRX1 or endogenous FOXM1 showed co-binding of both PRRX1 isoforms (A and B) with FOXM1 in pancreatic cancer cells. We further characterized this interaction using deletion mutants of PRRX1 C-terminal region, FOXM1 binds to the 200-222 amino acid region of PRRX1. Similarly, using deletion mutants of the FOXM1 N-terminal region we mapped PRRX1 binding to the winged helix DNA binding domain of FOXM1. Interestingly, we also observed co-binding of HA-tagged PRRX1A with either Flag-tagged PRRX1A or PRRX1B suggesting homo and heterodimerization of the PRRX1 isoforms. Next, we found that co-expression of PRRX1 and FOXM1 cooperatively induced transcriptional activity of a known PRRX1 target gene, Tenascin C. Furthermore, co-expression of PRRX1A and FOXM1 cooperatively induced FOXM1 transcriptionnal activity. FOXM1 has been reported to regulate Wnt signaling in glioblastomas (Zhang N. et al. Cancer Cell 2011). Given the importance of Wnt signaling in early pancreatic carcinogenesis, we observed co-binding of PRRX1 and FOXM1 with beta-catenin. Conclusion: Our results provides new insights in the interaction of PRRX1 and FOXM1 with functional activation of FOXM1 mediated transcriptional activity, and potential regulation of the Wnt pathway. Citation Format: Benoit Marchand, Maximilian Reichert, Meredith A. Collins, Anil K. Rustgi. Interplay between the transcription factors PRRX1 and FOXM1 in pancreatic cancer [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 5503. doi:10.1158/1538-7445.AM2017-5503