Rationale: Patients with diabetes are at higher risk than the general population of developing cancer of the urinary tract, liver, pancreas, colon, endometrium and kidney. Diabetes and hyperglycemia are associated with enhanced production of reactive oxygen species and induce DNA damage by several mechanisms. 8-Oxodeoxyguanine (8-oxodG) a major form of oxidative DNA damage has been implicated in early carcinogenesis. The DNA repair enzyme that recognizes and excises 8-oxodG is 8- oxoG-DNA glycosylase (OGG1). Deficiency in OGG1 has important functional consequences, compromising the ability of cells to repair DNA. Indeed, loss of heterozygosity at the OGG1 allele was found in human renal clear cell carcinoma (RCC) identifying loss of OGG1 function as a possible contributor to tumorigenesis in the kidney. Our preliminary data show that 8-oxodG levels are increased in kidney tissue of diabetic animal and human. In addition, we found that mutation in Ser326, the active site of OGG1 enzyme is increased in DNA blood samples from diabetic patients. One of the tumor suppressor genes involved in renal carcinogenesis is tuberous sclerosis gene (TSC2), which encodes tumor suppressor protein, tuberin. Eker rats harboring mutations in TSC2 develop spontaneous renal tumors at a very high incidence. We showed also that loss of function of the tumor suppressor gene, tuberous sclerosis complex 2 (TSC2), which encodes the protein tuberin, is associated with loss of function and mutations of OGG1 gene and accumulation of significant amounts of 8-oxodG in animal and human kidney tissues. Certain agonists activate PI-3 kinase and Akt, which stimulate tuberin phosphorylation resulting in its inactivation. Our preliminary studies show that incubation of rat renal proximal tubular cells (the cell origin of renal cell carcinoma) in high glucose results in increased reactive oxygen species (ROS) enhanced tuberin phosphorylation and decreased OGG1 expression. We also find that tuberin phosphorylation is increased in kidneys of diabetic rat. This is associated with increased levels of 8-oxodG. We have screened 500 kidney tumors from RCC patients and found that 25% of them has a history with diabetes. The mechanism(s) by which patients with diabetes are predisposed to cancer are not known. Hypothesis: We hypothesize that the increased production of ROS in diabetic subjects phosphorylates and inactivates tuberin, activates mTORC1 and/or mTORC2 resulting in downregulation of the DNA repair enzyme 8-oxoG-DNA glycosylase (OGG1) and accumulation of 8-oxodG. 8-OxodG enhances mutagenesis and predisposes the kidney and other organs to cancer. To explore our hypothesis we propose the following specific aims:
SPECIFIC AIM 1 : To determine the mechanism by which high glucose down-regulates OGG1 in proximal tubular cells, the cell origin of renal cell carcinoma.
SPECIFIC AIM 2 : To explore the effect of diabetes on the rate of development and severity as well as on the mutation frequency of renal cell carcinoma in the TSC-2 heterozygous rat and OGG1-/- mouse models.
SPECIFIC AIM 3 : To determine the levels of oxidative DNA damage (8-oxodG), OGG1 (protein, activity and mRNA) expression, the incidence of Ser326 mutation in OGG1, and levels of Akt, tuberin, S6K phosphorylation and downstream signals of mTOR in kidney tissue from patients with diabetes, patients with kidney cancer as well as patients with kidney cancer and diabetes.
The renal cell carcinoma (RCC) is one of the most lethal kidney cancers and is the sixth leading cause of cancer deaths. Every year approximately 40,000 Americans are diagnosed with RCC including military personnel, their family members, and U.S. Veteran population. More than 12,000 deaths in the United States are caused by RCC. Patients with diabetes are at higher risk than the general population of developing certain malignancies including kidney. Cancer contributes approximately 13% to mortality in diabetic patients. In Texas, an estimated of 1.9 million persons have been diagnosed with diabetes. The increasing the incidence of diabetes in our population will increase the risk of solid tumors including RCC. Our goal is to identify the mechanism by which diabetes accelerate tumor formation in kidney and other organs and validate 8-oxodG and OGG1 mutation(s) as new biomarkers for screening the diabetic subjects for early detection of cancer.
