Activation of sonic hedgehog (Shh) signaling occurs in the majority of pancreatic ductal adenocarcinomas. Here we investigate the mechanisms by which Shh contributes to pancreatic tumorigenesis. We find that Shh expression enhances proliferation of pancreatic duct epithelial cells, potentially through the transcriptional regulation of the cell cycle regulators cyclin D1 and p21. We further show that Shh protects pancreatic duct epithelial cells from apoptosis through the activation of phosphatidylinositol 3-kinase signaling and the stabilization of Bcl-2 and Bcl-X L. Significantly, Shh also cooperates with activated K-Ras to promote pancreatic tumor development. Finally, Shh signaling enhances K-Ras-induced pancreatic tumorigenesis by reducing the dependence of tumor cells on the sustained activation of the MAPK and phosphatidylinositol 3-kinase/Akt/mTOR signaling pathways. Thus, our data suggest that Shh signaling contributes to tumor initiation in the pancreas through at least two mechanisms and additionally enhances tumor cell resistance to therapeutic intervention. Collectively, our findings demonstrate crucial roles for Shh signaling in multiple stages of pancreatic carcinogenesis.K-ras ͉ mouse model ͉ pancreatic cancer ͉ Shh P ancreatic cancer is the fourth leading cause of cancer-related deaths in the United States, with Ϸ30,000 new cases annually (1, 2). Pancreatic ductal adenocarcinoma (PDAC) arises from precursor lesions called pancreatic intraepithelial neoplasia (PanIN), which are believed to be induced by the transformation of the epithelial cells of the small intercalated and intralobular ducts (3). PanIN lesions are characterized by specific histologic changes to the duct epithelium that correlate with the accumulation of alterations in the KRAS2 oncogene and loss of the INK4A (PanIN 1 and 2), TP53 (PanIN 2-3), and MADH4 (PanIN 3)

Hepatocellular carcinoma (HCC) is a leading cause of cancerrelated death worldwide. HCC patients frequently present with disease that has metastasized to other regions of the liver, the portal vein, lymph nodes, or lungs, leading to poor prognoses. Therefore, model systems that allow exploration of the molecular mechanisms underlying metastasis in this disease are greatly needed. We describe here a metastatic HCC model generated after the somatic introduction of the mouse polyoma virus middle T antigen to mice with liver-specific deletion of the Trp53 tumor suppressor locus and show the cell autonomous effect of p53 loss of function on HCC metastasis. We additionally find that cholangiocarcinoma also develops in these mice, and some tumors display features of both HCC and cholangiocarcinoma, suggestive of origin from liver progenitor cells. Concomitant loss of the Ink4a/Arf tumor suppressor locus accelerates tumor formation and metastasis, suggesting potential roles for the p16 and p19 tumor suppressors in this process. Significantly, tumor cell lines isolated from tumors lacking both Trp53 and Ink4a/Arf display enhanced invasion activity in vitro relative to those lacking Trp53 alone. Thus, our data illustrate a new model system amenable for the analysis of HCC metastasis. [Cancer Res 2007;67(16):7589-96]

The presence of distant metastases is a common finding on diagnosis of pancreatic cancer; however, the mechanisms underlying the dissemination of this tumor type remain poorly understood. Loss of the p53 tumor suppressor protein has been associated with tumor progression and metastasis in several tumor types including pancreatic ductal adenocarcinoma. Here, we describe the generation of a progressive and metastatic pancreatic cancer mouse model after the somatic and sporadic delivery of avian retroviruses encoding the mouse polyoma virus middle T antigen to elastase-tv-a transgenic mice with a pancreas-specific deletion of the Trp53 tumor suppressor locus. In this model, the tumors metastasize most frequently to the liver, consistent with human pancreatic carcinomas. Analysis of metastatic lesions demonstrated that concomitant loss of the Ink4a/Arf locus was not required for metastasis; however, pancreas-specific deletion of a single Ink4a/Arf allele cooperated with Trp53 deletion in a haploinsufficient manner to accelerate tumor development. Thus, our findings illustrate the potential role of p53 loss of function in pancreatic tumor progression, demonstrate the feasibility of modeling pancreatic cancer metastasis after somatic and sporadic oncogene activation, and indicate that our model may provide a useful experimental system for investigation of the molecular mechanisms underlying pancreatic cancer progression and metastasis. Pancreatic cancer is the fourth-leading cause of cancerrelated mortalities in the United States, with ϳ32,000 deaths annually.1 The median survival after diagnosis is 6 months, and the 5-year survival rate is only 5%. These statistics reflect the advanced stage at which most pancreatic tumors are identified, exemplified by extra-pancreatic invasion and metastasis to the liver and peritoneum, and the resistance of pancreatic cancers to conventional chemotherapeutic intervention. 2,3 Thus, understanding the factors that contribute to pancreatic tumor progression and metastasis is important in combating this disease.Mouse models are attractive experimental systems for exploring the genesis and behavior of human malignancies, and as a result, several mouse models for pancreatic cancer have been generated using transgenic approaches.2,4,5 These models, although valuable, were restricted in several respects including the expression of the oncogene throughout pancreatic development. Indeed, in some of the published models mice die shortly after birth, or perinatally, with architecturally abnormal pancreata. 6 Further, because all cells of a particular lineage within the pancreas express the transgene, tumors arise in an environment of aberrant intercellular signaling, unlike the scenario of sporadic tumor development in humans, in which tumor cells are surrounded by genetically normal cells.To address these issues, we recently generated a mouse model for pancreatic cancer using the RCAS-TVA gene delivery system. 7 This system allows the sporadic postnatal delivery of oncogene-bearing avian ret...