Protein Kinase B/AKT, a serine/threonine kinase with three isoforms (AKT1-3), is downstream of phosphatidylinositol 3-kinase (PI3K), and signals through the phosphorylation and subsequent activation or inhibition of downstream substrates, such as mammalian target of rapamycin complex 1 (mTORC1) or glycogen synthase kinase 3 beta (GSK-3?), respectively. The AKT1 isoform is predominantly recognized for regulation of cell survival, growth, and proliferation, due to its constitutive activation in pancreatic cancers (e.g., islet cell carcinoma and pancreatic adenocarcinoma). The progression of pancreatic ductal adenocarcinoma (PDAC), the most lethal common cancer, is initiated by activation mutations of the KRas oncogene. This leads to additional molecular changes, such as activation of the AKT1 oncogene, which drives PDAC progression and tumor formation. By mating transgenic mice with activation of KRas (Pdx- Cre;LSL-KRasG12D) and mice with activation of AKT1 (Pdx- Tta;TetO-MyrAKT1) we were able to produce mice with two activated oncogenes (AKT1Myr/KRasG12D) for comparative studies. Kaplan-Meier survival curves, histology, and genomic/proteomic analysis were used to characterize the incidence and frequency of histological (e.g. presence of mucin-4 in pancreatic intraepithelial neoplasms) and genetic (e.g. loss of tumor suppressors p16Ink4a and p19Arf) alterations known to commonly occur in human pancreatic cancer, as well as delineate the role of AKT1 in accelerating pancreatic tumor progression and metastasis. We determined that AKT1Myr/KRasG12D mice, unlike other PDAC mouse models, accurately mimic the human PDAC progression molecularly, structurally, and temporally. Interestingly, the AKT1Myr and AKT1Myr/KRasG12D models both exhibit a pre-tumor, diabetic phenotype. While, AKT1 hyperactivation in various cancers has been thoroughly studied, its role in glucose metabolism has been noted, but comparatively overlooked. As early as the 1900s a relationship between diabetes and pancreatic cancer has been proposed. With 80% of PDAC patients suffering from hyperglycemia or diabetes prior to diagnosis, one prevailing theory is that new onset diabetes is an early marker for pancreatic cancer. This is also supported by experimental and clinical studies, such as the resolution of diabetes with tumor removal and the induction of hyperglycemia with the implantation of cancer cell lines. To better understand the role of AKT1 and its hyperactivation in glucose metabolism, AKT1Myr mice were characterized via metabolic (e.g. glucose/insulin tolerance test) and histological (e.g. immunohistochemistry) studies. Beginning at weaning, 3 weeks of age, the glucose intolerant AKT1Myr mice exhibited non-fasted hyperglycemia, which progressed to fasted hyperglycemia by 5 months of age. The glucose intolerance was attributed to a fasted hyperglucagonemia, and hepatic insulin resistance detectable by reduced phosphorylation of the insulin receptor following insulin injection into the inferior vena cava. Additionally, AKT1Myr/KRasG12D mice currently being studied, appear to display a more severe diabetic phenotype, with fasted hyperglycemia noticeable at an earlier age, fasted hyperglucagonemia, polyuria, muscle wasting, and bloating. Treatment of both models with doxycycline diet, to turn-off the transgene, caused attenuation of the non-fasted and fasted hyperglycemia, thus affirming AKT1 hyperactivation as the trigger. These newly revealed roles of AKT1, along with future studies of these mouse models, will better delineate the molecular mechanisms responsible for the individual and joint roles of AKT1 and KRas in pancreatic cancer oncogenesis, the initiation of cancer associated diabetes, and the association of these two diseases.
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Doctor of Philosophy (Ph.D.)
College of Medicine
Burnett School of Biomedical Sciences
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Albury-Warren, Toya, "Diabetes Phenotypes in Transgenic Pancreatic Cancer Mouse Models" (2015). Electronic Theses and Dissertations, 2004-2019. 5145.