Abstract LB-203: The mRNA binding protein Human Antigen R (HuR, ELAVL1) is a novel regulator in pancreatic ductal adenocarcinoma metastatic progression and persistence
Authors: McCarthy Grace A. , Jain Aditi , Brown Samantha Z. , Yeo Charles J. , Brody Jonathan 
Published: September 2020

Abstract
Pancreatic ductal adenocarcinoma (PDAC) is the third leading cause of cancer-related death with a five-year survival rate of 10%. Yet, for the majority of patients who present with metastatic burden (50-60%), this rate drops to a mere 3%. Systemic chemotherapeutic regimens such as FOLFIRINOX or gemcitabine abraxane, have only shown marginal efficacy in delaying tumor growth and metastatic progression. Thus, there is a dire need for more robust treatment options to effectively target metastatic PDAC. Work by Iacobuzio-Donahue et al. and others have interrogated genetic drivers of patient metastases. They have demonstrated through genomic sequencing of matched primary and metastatic tumors that no single genetic event can account for driving metastasis. Therefore, metastatic progression is most likely driven by mechanisms beyond genomic mutations. Our lab has characterized one such alternative, the RNA binding protein Human Antigen R (HuR). HuR is a major regulator of pleiotropic gene regulation in response to demands from the pancreatic tumor microenvironment (e.g. nutrient deprivation, hypoxia). HuR generally stabilizes and enhances the translation of pro-survival mRNA transcripts (e.g., PIM1, IDH1, WEE1, DCK, PARG, etc.). Outside of this role, published data has implicated HuR to regulate epithelial-to-mesenchymal transition diving genes (e.g. SNAI1, PLAU, CTTNB1, MMP9) necessary for migration and invasion. We have been able to demonstrate that HuR is important for the migration and invasion of PDAC cells, in vitro. Through use of short hairpin RNA and CRISPR technology, inhibition of HuR decreased the ability of PDAC cells to migrate and invade in a transwell assay. Additionally, both knockdown and knockout of HuR slowed wound healing and colony formation. To evaluate the role of HuR in metastasis in vivo, we utilized a luciferase-expressing humanized PDAC orthotopic model to monitor tumor growth and spread. Either parental or HuR knockout luciferase-expressing PDAC cells were injected into the tail of the pancreas of NRG mice. A month after tumor engraftment, the majority of mice bearing parental tumors harbored liver and lung metastases (liver-5/5, lung 4/5) while HuR knockout tumor-bearing mice showed little to no evidence of metastasis (liver 2/4, lung 0/4). Employing ribonucleoprotein immunoprecipitation assays identified metastatic-associated mRNA transcripts bound to HuR (i.e., CTNNB1 (beta-catenin) and YAP1 mRNAs). Validation of these findings demonstrated that silencing or knocking out HuR induces a robust loss of beta-catenin and YAP1 expression (p&lt;0.001). Ongoing work will further uncover known and novel pathways that HuR is modulating for the pro-metastatic phenotype often seen in PDAC. Taken together, these data supports our continuing work of developing novel therapeutic strategies to target HuR in PDAC.
Citation Format: Grace A. McCarthy, Aditi Jain, Samantha Z. Brown, Charles J. Yeo, Jonathan Brody. The mRNA binding protein Human Antigen R (HuR, ELAVL1) is a novel regulator in pancreatic ductal adenocarcinoma metastatic progression and persistence [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-203.