The RNA-Binding Protein HuR Posttranscriptionally Regulates the Protumorigenic Activator YAP1 in Pancreatic Ductal Adenocarcinoma

Abstract

Yes-associated protein 1 (YAP1) is indispensable for the development of mutant <i>KRAS</i>-driven pancreatic ductal adenocarcinoma (PDAC). High <i>YAP1</i> mRNA is a prognostic marker for worse overall survival in patient samples; however, the regulatory mechanisms that mediate its overexpression are not well understood. <i>YAP1</i> genetic alterations are rare in PDAC, suggesting that its dysregulation is likely not due to genetic events. HuR is an RNA-binding protein whose inhibition impacts many cancer-associated pathways, including the "conserved YAP1 signature" as demonstrated by gene set enrichment analysis. Screening publicly available and internal ribonucleoprotein immunoprecipitation (RNP-IP) RNA sequencing (RNA-Seq) data sets, we discovered that <i>YAP1</i> is a high-confidence target, which was validated <i>in vitro</i> with independent RNP-IPs and 3' untranslated region (UTR) binding assays. In accordance with our RNA sequencing analysis, transient inhibition (e.g., small interfering RNA [siRNA] and small-molecular inhibition) and CRISPR knockout of HuR significantly reduced expression of YAP1 and its transcriptional targets. We used these data to develop a HuR activity signature (HAS), in which high expression predicts significantly worse overall and disease-free survival in patient samples. Importantly, the signature strongly correlates with <i>YAP1</i> mRNA expression. These findings highlight a novel mechanism of YAP1 regulation, which may explain how tumor cells maintain <i>YAP1</i> mRNA expression at dynamic times during pancreatic tumorigenesis.