Extended UVB Exposures Alter Tumorigenesis and Treatment Efficacy in a Murine Model of Cutaneous Squamous Cell Carcinoma

DNA-PKcs Mediates An Epithelial-Mesenchymal Transition Process Promoting Cutaneous Squamous Cell Carcinoma Invasion And Metastasis By Targeting The TGF-β1/Smad Signaling Pathway

Purpose

DNA-dependent protein kinase catalytic subunit (DNA-PKcs) has attracted extensive attention in various types of malignant tumors. However, the role of DNA-PKcs in cutaneous squamous cell carcinoma (cSCC) development has not been elucidated. In this study, we investigated the role of DNA-PKcs in cSCC and the molecular mechanisms of TGF-β1-induced cSCC progression mediated by DNA-PKcs.

Methods

We performed bioinformatic analysis and RT-PCR to examine the DNA-PKcs expression level in cSCC. Then, we downregulated DNA-PKcs using a DNA-PK-specific inhibitor or small interfering RNA (siRNA) to explore the effects of DNA-PKcs on SCL-1 cell migration and invasion. To further investigate the mechanism by which DNA-PKcs promotes cSCC progression, TGF-β1 and the TGF-β receptor (TGF-βR) I/II dual inhibitor LY2109761 were used to examine whether DNA-PKcs participates in TGF-β1/Smad signaling.

Results

DNA-PKcs expression was upregulated in cSCC. DNA-PK inhibition or expression knockdown resulted in inhibited migration and invasion and altered epithelial-mesenchymal transition (EMT) marker expression patterns in SCL-1 cells. Importantly, TGF-β1 mediated EMT induction in cSCC cells, and DNA-PKcs was identified as a TGF-β1-responsive gene. TGF-β1 promoted DNA-PKcs transcription, and DNA-PKcs enhanced the TGF-β1-induced EMT program involved in cSCC invasion and metastasis by phosphorylating Smad3.

Conclusion

This study is the first to show that DNA-PKcs mediates EMT to promote cSCC aggressiveness by targeting the TGF-β1/Smad signaling pathway, which provides insight into how DNA-PKcs impacts cSCC progression and identifies a new therapeutic target.

ADA-07 Suppresses Solar Ultraviolet-Induced Skin Carcinogenesis by Directly Inhibiting TOPK

Cumulative exposure to solar ultraviolet (SUV) irradiation is regarded as the major etiologic factor in the development of skin cancer. The activation of the MAPK cascades occurs rapidly and is vital in the regulation of SUV-induced cellular responses. The T-LAK cell-originated protein kinase (TOPK), an upstream activator of MAPKs, is heavily involved in inflammation, DNA damage, and tumor development. However, the chemopreventive and therapeutic effects of specific TOPK inhibitors in SUV-induced skin cancer have not yet been elucidated. In the current study, ADA-07, a novel TOPK inhibitor, was synthesized and characterized. Pull-down assay results, ATP competition, and in vitro kinase assay data revealed that ADA-07 interacted with TOPK at the ATP-binding pocket and inhibited its kinase activity. Western blot analysis showed that ADA-07 suppressed SUV-induced phosphorylation of ERK1/2, p38, and JNKs and subsequently inhibited AP-1 activity. Importantly, topical treatment with ADA-07 dramatically attenuated tumor incidence, multiplicity, and volume in SKH-1 hairless mice exposed to chronic SUV. Our findings suggest that ADA-07 is a promising chemopreventive or potential therapeutic agent against SUV-induced skin carcinogenesis that acts by specifically targeting TOPK. Mol Cancer Ther; 16(9); 1843-54. ©2017 AACR.

Role of vitamin D3 in modulation of ΔNp63α expression during UVB induced tumor formation in SKH-1 mice

ΔNp63α, a proto-oncogene, is up-regulated in non-melanoma skin cancers and directly regulates the expression of both Vitamin D receptor (VDR) and phosphatase and tensin homologue deleted on chromosome ten (PTEN). Since ΔNp63α has been shown to inhibit cell invasion via regulation of VDR, we wanted to determine whether dietary Vitamin D₃ protected against UVB induced tumor formation in SKH-1 mice, a model for squamous cell carcinoma development. We examined whether there was a correlation between dietary Vitamin D₃ and ΔNp63α, VDR or PTEN expression in vivo in SKH-1 mice chronically exposed to UVB radiation and fed chow containing increasing concentrations of dietary Vitamin D₃. Although we observed differential effects of the Vitamin D₃ diet on ΔNp63α and VDR expression in chronically irradiated normal mouse skin as well as UVB induced tumors, Vitamin D₃ had little effect on PTEN expression in vivo. While low-grade papillomas in mice exposed to UV and fed normal chow displayed increased levels of ΔNp63α, expression of both ΔNp63α and VDR was reduced in invasive tumors. Interestingly, in mice fed high Vitamin D₃ chow, elevated levels of ΔNp63α were observed in both local and invasive tumors but not in normal skin suggesting that oral supplementation with Vitamin D₃ may increase the proliferative potential of skin tumors by increasing ΔNp63α levels.