The Hedgehog signaling pathway is silent in the pancreas, both during development and in the adult organ. Pathological conditions such as pancreatitis have been linked to expression of one of the pathway ligands, Sonic Hedgehog, and activation of the pathway. The main downstream transcriptional mediators of the Hedgehog pathway are Gli transcription factors. Sonic Hedgehog is also expressed Pancreatic Epithelial Neoplasia or PanIN, the most common precursor lesion to pancreatic cancer. There is strong evidence of a paracrine role of Sonic Hedgehog, produced by the tumor epithelial cells, on the surrounding cells of mesenchymal origin such as fibroblasts. On the other hand, Gli activity is not confined to the mesenchymal compartment, but it is also present in the epithelial cells. In the epithelial cells, the Gli1 transcription factor is activated in a Hedgehog-independent manner. Similarly, in pancreatitis, epithelial Gli activity appears to be required for tissue repair. It is the aim of this proposal to understand the role of Gli activity in the different cell compartment in pancreatic disease. In the First Aim, we will be performing a detailed characterization of the expression and function of Gli1 in pancreatitis and tissue repair.
Our Second Aim will be to study Gli expression and function during PanIn formation. Finally, in the Third Aim, we will address the role of downstream effectors of Gli in pancreatitis and pancreatic cancer. The Hedgehog signaling pathway is an attractive therapeutic target and new inhibitors of the pathway are currently been tested in the clinic for Basal Cell carcinoma and medulloblastoma. The inhibitors that are currently available block the pathway at the level of Smoothened, a transmembrane protein that transduces the Hedgehog signal. Therefore, these inhibitors do not have an effect on Gli activity that is regulated in a Hedgehog-ligand independent manner, and they cannot inhibit Gli activity. Moreover, recent evidence has indicated that inhibition at the level of Smoothened is linked with the appearance of mutant forms of Smoothened that are no longer sensitive to the drug. The long-term goal of this proposal is to devise new strategies to inhibit Gli activity in pancreatic cancer. Significance: Although several studies have addressed different aspects of Hedgehog signaling in pancreatic carcinogenesis, we do not, at this point, know whether activation of this pathway is a limiting and required event in pancreatic carcinogenesis. The overarching goal of this proposal is understand whether Hedgehog inhibition has potential therapeutic efficacy in the treatment of pancreatic cancer, and how to target this disease. Since Hedgehog signaling is reported to mediate tumor-stroma interactions in pancreatic cancer, we will study the nature of the stromal feedback to the tumor with the goal to identify new therapeutic targets.
Pancreatic cancer is a horrific disease with a very dismal prognosis. It constitutes the fourth leading cause of cancer death in the US, and its yearly mortality equals the diagnosis rate. Novel therapeutic options for this disease are sorely needed, and they are likely to result from new insights on the biology of this disease. The Hedgehog signaling pathway involved in cancer of several organs, including the pancreas. Inhibitors of the pathway are currently in clinical therapy for basal cell carcinoma. Although several studies have addressed different aspects of Hedgehog signaling in pancreatic carcinogenesis, we do not, at this point, know whether activation of this pathway is a limiting and required event in pancreatic carcinogenesis. Our studies aim at understanding how the Hedgehog signaling pathway promotes pancreatic carcinogenesis, and whether it would constitute a promising therapeutic target for this disease.
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