The Requirement of GLI Transcriptional Activity in KRAS-Induced Pancreatic Neoplasia

Abstract

Background and Aim: Kras mutations are detected in 90% of human pancreatic ductal adenocarcinoma (PDAC) and are believed to be the critical oncogenic event during pancreatic tumorigenesis. However, the downstream transcriptional mechanisms by Kras in pancreatic cancer still remain poorly understood. Recent In Vitro studies suggested that Gli transcriptional factors, the intracellular mediator of Hedgehog signaling, are important for Kras activity in human PDAC cell lines. However, a requirement for Gli activation in pancreatic malignancy has not been demonstrated In Vivo. Here we carried out both loss-of-function and gain-offunction genetic analyses to establish the functional significance of Gli transcriptional activation in Kras-Induced pancreatic tumorigenesis using genetically modified mouse models. Methods: We utilized a conditional Rosa26 allele of Gli3T, R26-Gli3T. Gli3T is a dominant repressor of Gli3 that blocks Gli transcriptional activation. The R26-Gli3T mice were crossed to the Ptf1a-Cre;LDL-KrasG12D mice, a mouse model that allows pancreatic-specific Kras activation and tumor formation. A cohort of Ptf1a-Cre;LDL-KrasG12D;R26-Gli3T mice was generated and monitored for pancreatic tumor development. For Gli gain of function studies, we ectopically expressed Gli1 along with oncogenic Kras in mouse pancreas to determine whether Gli1 cooperates with Kras to promote tumorigenesis. Results: Our results showed that Gli3T expression caused a severe growth defect and loss of tumorigenicity in human PDAC cell lines. More importantly, the mice carrying Gli3T along with oncogenic Kras failed to develop PanIN lesions, in contrast to the mice with Kras activation alone. Mice expressing Gli1 along with activated Kras in pancreas also showed marked acceleration of tumor formation. Furthermore, our gene expression profiling identified a distinct transcriptional program mediated by Gli proteins in pancreatic tumor cells. Conclusions: Gli transcriptional activation not only accelerates pancreatic tumorigenesis in cooperation with Kras, but is also required for Kras-induced tumorigenesis In Vivo.