More than 1.2 million new cases of non-melanoma skin cancer, including squamous cell carcinoma and basal cell carcinoma, are diagnosed annually in the United States, and the lifetime risk for skin cancer exceeds the lifetime risk for all other cancers combined. Ultraviolet (UV) radiation is considered as the main cause of non-melanoma skin cancer. The current paradigm for prevention against UVB-induced skin cancer is application of general antioxidant products, which is inadequate because it is based on incomplete understanding of the role of oxidative stress in cancer development. The overall goal of this research is to gain an in-depth understanding of the mechanism by which superoxide radical/anion (O2·- ) in mitochondria contributes to metabolic switch during UVB carcinogenesis and to test the concept that a targeted antioxidant approach can prevent skin cancer. Our preliminary data demonstrate that the expression of manganese containing superoxide dismutase (MnSOD) is suppressed in histologically normal skin at preneoplastic stage, which results in increased superoxide production and increased synthesis of uncoupling proteins (UCPs). Furthermore, knockdown of UCPs suppresses lactate production and increases ATP levels. Thus, adaptation to increased superoxide production by induction of UCPs is likely the critical step leading to the Warburg effect. We also have found that exposure to UVB causes nitration and inactivation of MnSOD, and activation of prosurvival autophagy responses. Co-immunoprecipitation of nitrated MnSOD identified members of the Chaperone-Mediated Autophagy (CMA) pathway, which supports the role of CMA in selective degradation of nitrated proteins. Based on these novel findings, we propose that O2·- is a critical driver of metabolic alteration in UVB carcinogenesis that promotes cancer development and progression. Specific Aim 1 will test the hypothesis that O2·- triggers an uncoupling protein (UCP)-dependent metabolic switch. Specific Aim 2 will test the hypothesis that MnSOD is a critically important target of UVB-induced peroxynitrite (OONO- ) that leads to activation of autophagy responses. Specific Aim 3 will test the concept that UVB-induced O2·- and OONO- are critical mediators that promote UV carcinogenesis. We will use molecular genetic approach coupled with proteomics to identify UCP transcriptomes and stable-isotope-resolved metabolomics to identify pathways leading to preneoplastic metabolic alterations. We will use well- characterized mimetics of MnSOD to test the concept that mechanistically targeted antioxidants can prevent UV carcinogenesis. The relationship between UV radiation and energy metabolism remains unknown. The results from this study will close that knowledge gap and will provide valuable insights into the metabolic vulnerabilities that are amenable to cancer prevention.

The overall goal of this research is to gain a comprehensive understanding of the mechanism by which superoxide radical/anion (O2·-) in mitochondria contributes to metabolic switch during UVB carcinogenesis and to obtain valuable in-depth insights into the metabolic vulnerabilities that are amenable to cancer prevention. The results achieved from this study will have the potential to fundamentally change the practice of chemoprevention of UV-induced skin cancer.