Investigating GLI transcription factors as regulators of the pancreatic cancer microenvironment

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PROJECT SUMMARY/ABSTRACT Pancreatic cancer is a deadly human malignancy, with a five-year survival rate of 11%. Further, the incidence of pancreatic cancer is rising and is projected to be the second-leading cause of cancer-related death in the United States by 2030. The increasing occurrence of this disease, combined with the lack of effective treatments, creates an urgent need to better understand the factors that contribute to the progression of pancreatic cancer, and to develop improved therapies that will tangibly benefit human health. One pathway that has been implicated in pancreatic cancer for nearly twenty years is the Hedgehog (HH) signaling pathway. Initial work demonstrated that HH ligand expression increases during pancreatic cancer progression, while more recent studies have found that tumor-derived HH ligands signal in a paracrine fashion to activate HH signaling in pancreatic fibroblasts. As with many efforts to treat pancreatic cancer, clinical trials with HH pathway inhibitors have proven ineffective, or actually sped disease progression. However, work from our laboratories has identified three novel findings regarding the role of HH signaling in pancreatic cancer progression: First, we have found that the levels of HH signaling can determine whether HH signaling promotes or inhibits pancreatic tumor growth; Second, we have recently discovered that HH pathway inhibition can alter the fibroblast composition in the pancreatic cancer microenvironment; Third, our data indicate that HH pathway inhibition dramatically alters immune composition, through altered fibroblast-immune crosstalk. Together, these data suggest that an improved understanding of the role of HH signaling in the pancreatic cancer microenvironment, including HH-dependent fibroblast-immune crosstalk will provide an opportunity to advance the development of more effective pancreatic cancer treatment options. In this proposal, we will investigate the role of glioma-associated proteins (GLIs), a family of three proteins (GLI1-3) that are the transcriptional effectors of the HH signaling pathway, in pancreatic cancer progression. Specifically, we will use novel pancreatic fibroblast cell lines lacking Gli1, Gli2 or Gli3 individually and in combination to investigate the consequences on pancreatic tumor growth in co-transplantation assays. We will also investigate Gli deletion in vivo using two different Cre driver alleles (PdgfraCreER and Gli1CreER) in a novel, FlpO-driven mouse model of pancreatic cancer progression. Further, we will investigate GLI- dependent effects on fibroblast-immune crosstalk through assessment of macrophage and T cell migration, polarization and function. Finally, we will define GLI transcriptional targets in pancreatic fibroblasts both in vitro and in vivo, in the normal pancreas and in the context of pancreatic cancer, using a novel set of epitope-tagged knock-in alleles. This work will advance our understanding of the role of HH/GLI signaling in pancreatic cancer.