Opening of Chloride Channels by 1α,25-Dihydroxyvitamin D 3 Contributes to Photoprotection against UVR-Induced Thymine Dimers in Keratinocytes

Abstract

UVR produces vitamin D in skin, which is hydroxylated locally to 1α,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 1α,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.

Vitamin D and Death by Sunshine

“…Image analysis showed reduced nuclear staining for thymine dimers in UV-irradiated skin cells treated with 1,25D in culture [28,38,51,52], in mouse skin [29,39,52], ex vivo human skin [43] and human skin in vivo [40]. Reduced thymine dimers in UV-exposed keratinocytes in the presence of 1,25D was also reported using an entirely different method, the Comet assay, which uses a specific enzyme to cut DNA at the site of the relevant lesion [44,53]. Reduced nuclear staining for UV-induced 8-oxo-dG by 1,25D was observed in mouse skin [44] and ex vivo human skin [43].…”

Novel vitamin D compounds and skin cancer prevention

“…Thymine dimers are also reduced in irradiated skin cells in the presence of the low calcaemic rapid acting cis -locked non-genomic analogs, 1α,25(OH) 2 -lumisterol 3 (JN) and 1α,25(OH) 2 -7-dehydrocholesterol (JM) in vitro 85 , 87 , 94 , 95 and in mouse skin, 62 and also by the transcriptionally active hybrid QW 85 , 95 …”

“…Photoprotection against thymine dimers by 1,25(OH) 2 D 3 and Bufalin in human keratinocytes. DNA damage was assessed using a monoclonal antibody to thymine dimers, 182 immunohistochemistry and image analysis as previously described 89 , 94 at 3 h after UV irradiation, in human keratinocytes treated with vehicle, 1,25(OH) 2 D 3 or three concentrations of bufalin and expressed as positively stained nuclei as a percent of total nuclei. The graph illustrates pooled data from a minimum of four independent experiments.…”

“…A reduction in thymine dimers (TD) by 1,25(OH) 2 D 3 has also been demonstrated by an entirely different method in irradiated keratinocytes by digestion with the site specific DNA repair enzyme T4 endonuclease IV for CPDs in the comet assay 94 , 98 …”

Vitamin D Supplementation Does Not Improve the Severity or the Resolution of Ultraviolet B-Induced Acute Erythema

“…Calcitriol [1α,25-dihydroxyvitamin D 3 or 1,25(OH) 2 D 3 ] may enhance keratinocyte [8][9][10][11][12][13] , melanocyte [13] and fibroblast [10,13] survival after UVR exposure by reducing UV-induced promutagenic DNA damage like cyclobutane pyrimidine dimers [8][9][10][11][12][13] , 8-oxo-7,8-dihydro-2-deoxyguanosine [9,14] , 3-nitrotyrosine, and 8-nitroguanosine [9,15,16] , which are mutagenic and are markers of inflammation and carcinogenesis. Moreover, 1,25(OH) 2 D 3 could also influence the upregulation of p53, allowing improvement of DNA repair [13] .…”