Cutaneous squamous cell carcinoma (CSCC) is a kind of malignant tumor originated from keratinocytes within the epidermis and its appendages. Its etiology and pathogenesis are complex and unclear. The incidence of CSCC is increasing in the whole world, which makes the research on its pathogenesis increasing day by day. Epigenetics does not change genome sequence, but regulates gene expression by DNA methylation, histone modification, noncoding RNA, chromatin remodeling and so on. Its reversible and stable genetic characteristics will provide a new idea for the study of pathogenesis of CSCC.

Objective:To establish a xenograft model of cutaneous squamous cell carcinoma (CSCC) in nude mice, and to explore mechanisms underlying synergistic induction and promotion of CSCC in nude mice by ultraviolet radiation and human papillomavirus (HPV) infection.Methods:The human CSCC A431 cells were divided into 3 groups, namely HPV16 E6 overexpression group (LV-OE-HPV16 E6 group) transfected with adenovirus-mediated HPV16 E6 gene, empty vector group transfected with empty adenovirus vectors, and blank control group remaining untransfected. Using serum-free Dulbecco′s modified Eagle′s medium (DMEM) , A431 cells in the empty vector group and LV-OE-HPV16 E6 group were prepared into single-cell suspensions, which were subcutaneously inoculated into the left buttocks of SKH-1 nude mice separately, namely empty vector group ( n = 16) and LV-OE-HPV16 E6 group ( n = 16) . Tumor growth was observed and recorded for the mice every 3 days. When the tumor size reached 150 mm 3, the modeling was considered successful. After successful modeling, 8 mice in each group were irradiated with ultraviolet light at a dose of 1 440 mJ·cm -2·d -1 for 12 minutes each time, the other 8 mice in each group received no ultraviolet radiation, that is to say, all the 32 mice were divided into 4 groups: empty vector group, empty vector + UV group, LV-OE-HPV16 E6 group, and LV-OE-HPV16 E6 + UV group. After 4-week radiation, these nude mice were sacrificed, tumor weight and volume were measured, a tumor growth curve was drawn, immunohistochemistry study, Western blot analysis and real-time fluorescence-based quantitative PCR (qRT-PCR) were conducted to determine the protein and mRNA expression of Wnt1 and β-catenin in CSCC tissues collected from nude mice, respectively. For normally distributed measurement data, analysis of variance was used for intergroup comparisons, and least significant difference- t test for multiple comparisons; for non-normally distributed measurement data, rank sum test was used for intergroup comparisons. Results:Compared with the empty vector group (2.20 ± 0.24 g) , the tumor weight significantly increased in the empty vector + UV group (2.90 ± 0.36 g, t = 4.39, P < 0.001) , LV-OE-HPV16 E6 group (3.19 ± 0.32 g, t = 6.77, P < 0.001) , and LV-OE-HPV16 E6 + UV group (4.41 ± 0.18 g, t = 20.11, P < 0.001) ; the tumor volume was also significantly higher in the empty vector + UV group (1 033.12 ± 400.15 mm 3, t = 1.90, P < 0.001) , LV-OE-HPV16 E6 group (1 119.21 ± 447.57 mm 3, t = 2.21, P < 0.001) , and LV-OE-HPV16 E6 + UV group (1 464.29 ± 409.98 mm 3, t = 4.22, P < 0.001) than in the empty vector group (688.94 ± 319.31 mm 3) . Immunohistochemical study showed no significant difference in the protein expression of Wnt1 and β-catenin among the 4 groups ( F = 0.76, 0.71, respectively, both P > 0.05) ; Western blot analysis showed significant differences in the protein expression levels of Wnt1 and β-catenin among the 4 groups ( F = 16.74, 49.90, respectively, both P < 0.05) , which were significantly higher in the LV-OE-HPV16 E6 + UV group than in the empty vector group, empty vector + UV group and LV-OE-HPV16 E6 group (all P < 0.05) . qRT-PCR showed a significant difference in the mRNA expression of Wnt1 and β-catenin among the 4 groups ( F = 7.77, 8.38, respectively, both P<0.05) , and the LV-OE-HPV16 E6 + UV group showed significantly increased Wnt1 mRNA expression levels compared with the empty vector group, empty vector + UV group and LV-OE-HPV16 E6 group (all P < 0.05) . Conclusion:Ultraviolet radiation and HPV infection showed synergistic effect on the induction and promotion of CSCC.