Mouse tumor models are most useful when they reproduce as many known molecular lesions as possible, so as to most accurately portray the body's physiological response to tumorigenesis. With somatic cell engineering (Sleeping Beauty/SB), we can recapitulate multiple lesions simultaneously with ease and scale not possible by other means. Hepatocellular carcinoma is the third leading cause of cancer worldwide, with increasing incidence due to a number of epidemiologic and biologic reasons, such as obesity. Moreover, the liver is a frequent depot for metastases originating from solid tumors arising in other organs as well. We have developed oncogene-initiated liver tumors which recapitulate the development and progression of hepatocellular carcinoma (HCC) and hepatocellular adenoma (HCA).
Our first Aim i s to optimize and quantitate hepatic tumor development, using reporter genes. To date, we have reproducibly generated hepatocellular adenomas (HCA) by the co-delivery of SB-AKT and SB-beta-catenin (CAT), and hepatocellular (HCC) by the co-delivery of SB-MET and SB-CAT. In contrast, individual delivery these oncogenes does not induce tumor formation. We are using a co-delivered Gaussia luciferase transposon to track tumor growth from oncogene-initiated hepatocytes to overt tumor formation. Gaussia luciferase is secreted into the blood thereby allowing for a non-invasive, quantitative measure of gene delivery and tumor development. Additionally co-delivered transposons expressing red or green fluorescent protein will be used to tag oncogene-initiated hepatocytes using tumor imaging and flow cytometric sorting.
Our second Aim i s to define the immunological contributions to AKT+CAT and MET+CAT oncogenic pathways in vivo. Using RAG1-/- immunodeficient mice, we found that these mice were significantly protected from the development of AKT+CAT (HCA) liver tumors. This finding suggests that the host immune system collaborates and provides essential contributing factors towards the development of AKT+CAT initiated HCA. In contrast, RAG1-/- mice succumbed more rapidly to tumor development when MET+CAT was used, suggesting an important role for immune-mediated surveillance of MET+CAT initiated HCC. Our ongoing studies using T cell- and B cell-deficient mice suggest that AKT+CAT induced hepatosteatosis development and overall tumor growth is dependent on B cells, but not CD4+ or CD8+ T cells. B cell deficient mice also have a dramatic reduction in hepatic steatosis, a characteristic feature underlying non-alcoholic fatty liver disease and predisposition to liver tumor development. The tumor-promoting role of B cells is controversial, but consistent with a tumor-promoting role that has been proposed for these cells in some chronic inflammatory models. We hypothesize that tumors can develop when initiating mutations are coupled with inflammatory microenvironments that enhance tumor promotion. Therefore, in the third Aim of this project, we will identify those cytokines and inflammatory networks capable of modulating AKT+CAT or MET+CAT initiated tumors. Our results from studies using immunodeficient mice have identified a critical tumor promoting role for TNFR1 and LTBetaR signaling in the AKT+CAT model, since mice deficient in these receptors or their ligands have reduced tumor growth and improved survival. B cell associated LTBeta, in particular, may therefore play an indispensable role in AKT+CAT induced HCA and hepatic steatosis. We are monitoring tumor progression in wildtype and B cell deficient mice that have been treated with LTBetaR agonistic and antagonistic LTBetaR-binding reagents. The involvement of additional B cell-derived factors will also be investigated. Additional studies with MET+CAT will be completed to investigate oncogene specific inflammatory-mediators of tumor progression to carcinoma. Collectively, the approaches described in this project will provide us with accurate pre-clinical models for HCA and HCC and facilitate the development of therapeutics that more effectively target tumorigenesis.
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