Abstract 4264: PI3K/Akt/mTOR signaling modulation in solar UV-induced skin carcinogenesis.

Basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) are the most common types of cancers. Since most BCC and SCC develop on sun-exposed areas of the body, chronic sun exposure is considered the main etiologic factor of these tumors. In vitro and in vivo studies have identified PI3K/Akt/mTOR signaling pathway as a solar light-activated pathway. However, little work has been done on studying the expression profiles of this pathway in humans. In the study herein, we evaluate the modulation of solar light-activated PI3K/Akt/mTOR signaling pathway in normal human skin and solar simulated light (SSL)-irradiated human skin to determine the expression profiles of upstream and downstream phosphorylated proteins Akt (Ser473), mTOR (Ser2448), S6 ribosomal protein (Ser235/236), and 4E-BP1 (Thr37/46). The study population consisted of individuals 18 years or older in general good health with skin types II-III. SSL irradiation at 2, 2.5, and 3 times minimal erythema dose (MED) were applied to unexposed skin. Punch biopsies were taken at baseline, 5 minutes, 1 h, 5 h, and 24 h post-irradiation and immediately fixed in 10% formalin. Tissues were evaluated by immunohistochemistry for the expression of phosphorylated proteins. Proliferating cell nuclear antigen (PCNA) and cleaved caspase 3 (Asp175) were evaluated as markers for keratinocyte proliferation and apoptosis, respectively. Induction of phosphorylated Akt was seen at 5 hours with a 2-fold increase in expression when compared to baseline. Expression of phosphorylated mTOR gradually increased with a peak at 24 hours (3-fold). Significant induction of phosphorylated S6 ribosomal protein was seen at 1 h (3-fold), 5 h (7-fold), and 24 h (10-fold) post SSL irradiation. Induction of phosphorylated 4E-BP1 was limited to the 24 h time point with an increase of 2-fold when compared to baseline. Our data corroborate in vitro and in vivo studies finding, which allow for better understanding of the expression profile patterns of phosphorylated proteins in the PI-3 kinase/Akt/mTOR pathway during exposure of physiological relevant solar-simulated light. Identification of key proteins in this pathway could lead to the use of these proteins as biomarkers and/or specific targets for the prevention and control of skin tumors. Citation Format: Yira Bermudez, Steve P. Stratton, Clara Curiel-Lewandrowski, Chengcheng Hu, George T. Bowden, Kathylynn Saboda, David S. Alberts, Janine G. Einspahr. PI3K/Akt/mTOR signaling modulation in solar UV-induced skin carcinogenesis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4264. doi:10.1158/1538-7445.AM2013-4264