UCSF

Sunlight, vitamin D and skin cancer form a controversial brew. While too much sunlight exposure causes skin cancer, it is the major source of vitamin D from skin. We propose that these processes can be balanced. Vitamin D signalling (VDS) protects against skin cancer as demonstrated by the susceptibility of the skin to tumor formation in VDR null mice and protection from UVB-induced mutations when VDR agonists are administered. The question is how is protection afforded. Previously, we have focused on the Wnt/β-catenin/hedgehog and DNA damage repair (DDR) pathways. As VDR regulates hundreds of genes with thousands of VDR response elements (VDRE) throughout the genome, and many VDREs are in non-coding regions, we decided to explore long non-coding RNAs (lncRNA). LncRNAs are mRNA-like transcripts ranging from 200 bases ~100 kb lacking significant open reading frames. They are aberrantly expressed in human cancers and involved in a spectrum of tumorigenic/metastatic processes (cell proliferation/apoptosis/angiogenesis). We discovered that VDS regulated the expression of certain lncRNAs in a manner consistent with VDS protection against skin cancer. Given the huge variation in genes actively regulated by 1,25(OH)2 D from different cell types, it is conceivable that our results could apply to personalized medicine based on the distinctive lncRNA profiles. These lncRNAs could also serve as skin cancer biomarkers secreted into the blood or urine via exosomes as demonstrated in other cancer types (breast, prostate). Modulation of lncRNA profile by VDS may also provide insight into regulating pathways such as Wnt/ß-catenin and hedgehog.