Abstract 59: The pioneer transcription factor FOXA2 regulates integrin alpha 1 expression controlling prostate cancer bone colonization

Introduction. Approximately 30,000 men will die from prostate cancer (PCa) in 2018. When localized and detected early, it has a low rate of progression and metastasis, with successful treatment. However, some patients may progress to a more lethal castrate-resistant PCa. While this occurs, frequent bone metastases will arise, and patient prognosis typically falls to 3-5 years due to lack of therapy available. The purpose of this study was to unveil the mechanisms of PCa bone colonization, allowing us to identify novel targeted therapies to prevent and treat PCa. Methods. Gene expression profiling studies revealed a subset of metastatic PCa samples express the pioneer forkhead transcription factor, FOXA2. Consistently, we found FOXA2 abundance in a sample set of human PCa bone metastases, which may suggest a functional role for FOXA2. Protein analysis of common PCa cell lines revealed high levels of FOXA2 in aggressive bone metastatic PCa PC3 cells. To understand the role of FOXA2 in PCa metastasis, FOXA2 was stably knocked down in PC3 cells. Results. PC3 cells with FOXA2 knocked down (FOXA2-KD) failed to generate in vivo bone destruction following intra-tibial injection contradictory to their parental cell line. To elucidate how FOXA2 is orchestrating these changes, we assessed the expression of all integrins and observed that loss of FOXA2 decreased mRNA and protein expression of the collagen-I binding integrin α1. Furthermore, we found FOXA2-KD decreased PC3 cells’ adhesion, spreading, and downstream Integrin α1 signaling cascades on collagen-I (a major component of bone ECM) coated surfaces. Additionally, a neutralizing antibody to integrin α1 was administered to PC3 Control cells, prompting the same adhesion pattern, solidifying that this integrin is critical to collagen-I adherence. Through ChIP analysis, we learned that FOXA2 directly regulates the ITGA1 gene promoter. Lastly, we overexpressed integrin α1 in PC3 FOXA2-KD cells and rescued the adherence properties. Conclusions. Taken together, the FOXA2-controlled expression of integrin α1 resulted in changes to adherence, spreading, and integrin signaling, providing a mechanism for how PCa cells colonize the bones. Funding: This research is supported by DOD grant (W81XWH-12-1-0212), NIH grants (R03 CA212567 and R01 CA226285), LSUHSC startups (FWCC and Office of Research) to XY, and Carroll Feist Pre-doctoral Fellowship to ZC. Citation Format: Zachary M. Connelly, Shu Yang, Nazih Khater, A. Wayne Orr, Renjie Jin, David Degraff, Colm Morrissey, Eva Corey, Robert Matusik, Xiuping Yu. The pioneer transcription factor FOXA2 regulates integrin alpha 1 expression controlling prostate cancer bone colonization [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 59.