Opening of Chloride Channels by 1α,25-Dihydroxyvitamin D3 Contributes to Photoprotection against UVR-Induced Thymine Dimers in Keratinocytes

UVR produces vitamin D in skin, which is hydroxylated locally to 1 alpha,25-dihydroxyvitamin D-3 (1,25(OH)(2)D-3). 1,25(OH)(2)D-3 protects skin cells against UVR-induced DNA damage, including thymine dimers, but the mechanism is unknown. As DNA repair is inhibited by nitric oxide (NO) products but facilitated by p53, we examined whether 1,25(OH)(2)D-3 altered the expression of nitrotyrosine, a product of NO, or p53 after UVR in human keratinocytes. 1,25(OH)(2)D-3 and the nongenomic agonist 1 alpha,25-dihydroxylumisterol(3) reduced nitrotyrosine 16 hours after UVR, detected by a sensitive whole-cell ELISA. p53 was enhanced after UVR, and this was further augmented in the presence of 1,25(OH)(2)D-3. DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid), a chloride channel blocker previously shown to prevent 1,25(OH)(2)D-3-induced chloride currents in osteoblasts, had no effect on thymine dimers on its own but prevented the 1,25(OH)(2)D-3-induced protection against thymine dimers. Independent treatment with DIDS, at concentrations that had no effect on thymine dimers, blocked UVR-induced upregulation of p53. In contrast, reduction of nitrotyrosine remained in keratinocytes treated with 1,25(OH)(2)D-3 and DIDS at concentrations shown to block decreases in post-UVR thymine dimers. These results suggest that 1,25(OH)(2)D-3-induced chloride currents help protect from UVR-induced thymine dimers, but further increases in p53 or reductions of nitrotyrosine by 1,25(OH)(2)D-3 are unlikely to contribute substantially to this protection. Journal of Investigative Dermatology (2013) 133, 776-782; doi:10.1038/jid.2012.343; published online 27 September 2012