Clear cell renal cell carcinoma (ccRCC) is a serious health concern for military personnel, particularly males beyond 40 years of age, including military veterans. According to The Defense Medical Epidemiology Database for 1995-2004 the incidence of RCC specifically for military members after the 4th decade of life is dramatically increased to 8.5 as compared to 1.5 cases per 100,000 person-years of the overall incidence. Our laboratory studies molecular pathways regulated by the von Hippel-Lindau (VHL) protein, the most frequently lost tumor suppressor in ccRCC. During the previous funding period we have published important data regarding the role of autophagy in growth of ccRCC. This competitive renewal builds on these substantial observations. Autophagy is a homeostatic function by which cells process their own organelles and proteins in order to eliminate defective molecules and to recycle nutrients. During tumor growth many cancers become addicted to autophagy as a source of nutrients. Moreover, autophagy is activated by different cancer therapies, causing resistance to treatments, and promoting use of autophagic inhibitors, chloroquine derivatives in combination therapies. MAP1LC3s (LC3) are essential proteins for the formation of an autophagosome. In our recently published work and preliminary results, we show that two LC3 paralogs, LC3B and LC3C, have opposite effects on growth of ccRCC. LC3B-dependent autophagy promoted growth of tumors formed by RCC cells with lost VHL, while LC3C-dependent autophagy was tumor suppressive and absent in VHL(-) cells. This proposal focuses on investigations to understand the activity of LC3C-dependent autophagy. Most importantly, we found that LC3C, but not LC3B, autophagic program targets of degradation enzymes of oxidative (rate limiting enzyme, glucose 6-phosphate dehydrogenase, G6PD) and non-oxidative (transketolase, TKT) pentose phosphate pathway (PPP). The effect of LC3C is specific for PPP and does not affect the glycolytic pathway. This important cancer pathway produces ribose-5-phophate for the production of nucleic acids and NADPH for the lipid synthesis and reduction of glutathione, all resulting in enhanced cell survival and growth. The importance of our data is further supported by unsupervised analysis published by KIRC TCGA, which showed significant correlation between levels of G6PD, TKT and poor outcome in ccRCC. The leading hypothesis for this proposal is that loss of VHL through indction of HIF reduces LC3C, permitting activation of PPP to support tumor growth.
In Aim 1 we will determine the molecular mechanism by which VHL induces LC3C gene expression. Our working hypothesis is that HIF suppresses LC3C by inducing expression of repressing transcription factors.
In Aim 2 we will determine the role of LC3C in the activities of the oxidative and non-oxidative branches of PPP in controlling nucleic acid synthesis and generation of NADPH using genetic and metabolomics approaches.
In Aim 3 we will determine the role of the oxidative and non-oxidative branches of PPP in orthotopic xenograft tumor growth and expression of PPP enzymes in human kidney-ccRCC specimens.
In Aim 4 we will determine the molecular mechanism by which LC3C, but not LC3B, specifically targets TKT and G6PD for autophagic degradation. Our working hypothesis, supported by preliminary data is that the specificity of LC3C effects is mediated by the LC3C C-terminal peptide.
Renal cancer is a serious health concern for military personnel, particularly those beyond 40 years of age, and for military veterans. Renal cancer accounts for 2% to 3% of all adult malignancies in the US, with 63,920 new cases and 13,800 deaths reported in 2014. The Defense Medical Epidemiology Database for 1995-2004 analyzed that the incidence of renal cancer specifically for military members after the 4th decade of life it is quite dramatically increased to 8.5 as compared to 1.5 cases per 100,000 person-years of the unadjusted incidence. In addition, renal cancer occurs almost twofold more frequently in males than in females and approximately 80% of military personnel are males. Cigarette smoking leads to a 47% increase in risk for renal cancer relative to nonsmokers, and the relative risk correlated positively with the number of cigarettes smoked per day. Smoking represents an important health issue for military personnel. It is currently estimated that 30% of active military personne and 74.2% (+/- 0.7%) of veterans are smokers or have smoked at some point in their lives.