Abstract 806: Modeling human UV-induced skin cancer through genetic manipulation of Src-kinases and Srcasm
Authors: Yang Xiaoping , Shankar Sheila , Maeno Hiroshi , Gober Micheal , Marshall Christine , Dentchev Tzvete , Seykora John 
Published: August 2015

UV-induced skin cancer is the most common form of cancer and its incidence continues to increase. Novel in vivo models that mimic human UV-induced skin cancer are needed to further studies and evaluate new therapies. Keratinocyte growth is regulated through oncogenic signals from EGFR and Src-family tyrosine kinases (SFKs); these tyrosine kinases are primary drivers of keratinocyte growth in UV-induced skin cancer. At the proteomic level, activated EGFR and SFKs are negatively regulated by Srcasm which targets activated tyrosine kinases for lysosomal degradation. Studies have shown that SFK activity is increased and Srcasm levels are decreased in human cutaneous squamous cell carcinomas and related precancerous lesions. We hypothesized that genetic downregulation of Srcasm by gene deletion or lentivirally mediated shRNA knockdown would promote oncogenic signaling and keratinocyte growth thereby promoting UV-induced skin cancer. To test this hypothesis Srcasm null mice and Srcasm lentiviral knockdown in human keratinocytes were generated and studied. Western blotting of epidermal lysates from Srcasm null mice demonstrates that loss of Srcasm promotes activation of EGFR and Src kinases and decreases levels of p53, NICD and p21. Activation of the canonical Erk1/2, STAT-3 and PDK-1 oncogenic pathways also was seen in Srcasm null keratinocytes. The epidermis of Srcasm null mice exhibits a higher Ki-67 index of 8.7 +/- 2.0 compared to 1.5 +/- 1.1 in controls (p&lt;0.001). UVB irradiation (500 mJ/cm2 × 15 doses) produced precancerous lesions in Srcasm null mice resembling human actinic keratoses but not in controls; the precancerous lesions show an increased Ki-67 index and activation of Src kinases, STAT-3 and PDK-1. Acute UVB irradiation (1200 mJ/cm2 × 1 dose) of Srcasm null mice induced prominent erythema, epidermal necrosis and a prominent increase in the TUNEL-positive index (14.0 vs 1.3). Srcasm knockdown in human keratinocytes accelerated keratinocyte growth 130%; it also increased levels of EGFR and accelerated the kinetics of EGFR and MAPK activation in response to EGF stimulation. In human keratinocytes, Srcasm knockdown accelerated cell growth post-UV exposure which could promote neoplasia. These data show that loss of Srcasm is associated with increased oncogenic signaling, impaired p53 function and keratinocyte proliferation. Loss of Srcasm promotes keratinocyte proliferation post-UV exposure leading to the early stages of UVB-induced cutaneous neoplasia.

Citation Format: Xiaoping Yang, Sheila Shankar, Hiroshi Maeno, Micheal Gober, Christine Marshall, Tzvete Dentchev, John Seykora. Modeling human UV-induced skin cancer through genetic manipulation of Src-kinases and Srcasm. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 806. doi:10.1158/1538-7445.AM2015-806