Kras In Pancreas Research Articles

Autophagy contributes to the initiation of pancreatic cancer

The pancreatic adenocarcinoma initiation results from the interaction of genetic events combined with multiple other factors. Among the genetic alterations that contribute to the pathogenesis of this disease, the mutation of the KRAS oncogene is required but not sufficient to trigger this cancer. Pancreatitis, an inflammatory disease, facilitates and accelerates the transformation of pancreatic cells when the KRAS oncogene is mutated. Of note, the repertoire of molecular mediators of pancreatitis which are responsible of the promotion of KRAS-mediated transformation is not completely defined. Importantly, autophagy has been proposed as one of the cellular mechanisms contributing to pancreatic carcinogenesis, especially in the initial phases, in which the oncogene KRAS appears to play its leading role. In addition, autophagy is strongly induced during pancreatitis. Although some aspects of autophagy in pancreatic cancer development are not completely established, we can affirm that overexpression of VMP1, an inducer of autophagy which is specifically activated in pancreas during pancreatitis, improves the development of pancreatic precancerous lesions PanINs when the oncogene KRAS is mutated. In addition, inhibition of the autophagic flux with chloroquine inhibits the KRAS pro-tumor effect in the pancreas. In conclusion, activation of expression of VMP1 improves the pro-tumor role of KRAS in pancreas.

Abstract IA12: Oncogenic KRAS and the inflammatory microenvironment in pancreatic cancer

Abstract Pancreatic cancer -one of the deadliest human malignancies- is preceded by precursor lesions, most commonly Pancreatic Intraepithelial Neoplasia (PanIN). PanINs are characterized by changes in the epithelial architecture, and by the accumulation of a fibroinflammatory stroma. Oncogenic mutation in Kras are almost invariably associated with invasive pancreatic cancer (1-3) and often detected in PanIN lesions (4). Expression of oncogenic Kras in the mouse pancreas recapitulates the step-wise progression of the human disease (5). We have previously published a genetically engineered mouse model that allows inducible, tissue specific and reversible expression of oncogenic Kras in the pancreas, the iKras* mouse (6). By taking advantage of the reversible nature of oncogenic Kras expression in this model, we were able to address the role of this oncogene in PanIN and cancer maintenance. First, we showed that inactivation of oncogenic Kras at the PanIN stage leads to regression of the lesions and recovery of the pancreatic parenchyma. Then, by crossing iKras* mice with a mouse conditionally expressing a mutant form of the tumor suppressor p53 (7), we generated a model of metastatic pancreatic cancer, the iKras*p53* mouse(8). Inactivation of oncogenic Kras* in iKras*p53* mice bearing invasive tumors and metastases led to tumor regression, albeit without complete eradication of the malignant cells. Taking advantage of the reversible nature of oncogenic Kras expression in our model, we have undertaken to investigate the effect of modulating epithelial Kras expression on the tumor stroma. We have previously shown that the extensive myofibroblast population surrounding PanINs and invasive cancer depends on epithelial Kras for its proliferation, active status and maintenance. Recently, we have started characterizing the changes in immune cells infiltrating the pancreas during the PanIN stage. The induction of acute pancreatitis leads to extensive immune infiltration both in wild-type and iKras* mice. However, in wild type animals the immune infiltration is transient, and coincides with the dynamics of tissue repair. In contrast, in iKras* mice the immune infiltration is sustained over time. Moreover, the nature of the infiltrating cells is different in iKras* mice, with increased CD4+ T cells, and immature myeloid cells and fewer CD8+ T cells. This infiltration of immune cells is dependent on oncogenic Kras over time, as inactivation of Kras expression leads to a reduction in the number of inflammatory cells over time. While the nature of infiltrating immune cells over pancreatic carcinogenesis has been characterized before (9), the function of each specific subset is not fully understood. CD4 T cells are prevalent within the Kras-mutant pancreas, and include immune-suppressive cells such as regulator T cells and Th17 cells. Thus, we hypothesized that CD4+ T cells are required in pancreatic cancer. By genetically ablating CD4 T cell in iKras* mice (thus generating iKras*;CD4-/- animals) we determined that CD4 T cells are required for PanIN formation. Furthermore, we showed that CD4+ T cells promote pancreatic carcinogenesis by inhibiting the anti-tumor activity of CD8 + T cells. Thus, our results indicate that a potential anti-cancer immune response is inhibited by CD4+ T cells in response to signals derived from Kras mutant epithelial cells. Given the potential of immune-modulation as part of pancreatic cancer therapy, we plan to follow up on our initial observations by identifying the epithelial signals that modulate the immune response in pancreatic cancer.

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

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.