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Title: UVB-induced production of 1,25-dihydroxyvitamin D3 and vitamin D activity in human keratinocytes pretreated with a sterol Delta7-reductase inhibitor
Authors: Vantieghem, Katleen ×
Kissmeyer, Anne-Marie
De Haes, Petra
Bouillon, Roger
Segaert, Siegfried #
Issue Date: May-2006
Publisher: A.R. Liss
Series Title: Journal of Cellular Biochemistry vol:98 issue:1 pages:81-92
Abstract: The skin fulfills an important role in the vitamin D photo-endocrine system. Epidermis is not only the site of vitamin D3 photoproduction. In addition, epidermal keratinocytes contain the vitamin D receptor (VDR) and possess 25-hydroxylase and 1alpha-hydroxylase activity indicating that all components of the vitamin D system are present. We investigated whether these components cooperate in inducing vitamin D activity upon treatment with physiological UVB doses. Upon irradiation, 24-hydroxylase mRNA was induced in keratinocytes pretreated with a sterol Delta7-reductase inhibitor (BM15766) whereby the 7-dehydrocholesterol content increased by 300-fold. Transfection experiments with a vitamin D response element containing construct confirmed VDR-dependent gene activation. Furthermore, the UVB-dependent induction of 24-hydroxylase was blocked by the cytochrome-P450 inhibitor ketoconazole. The 24-hydroxylase inducing photoproduct was transferable to unirradiated keratinocytes by medium and cellular homogenates of UVB-irradiated, BM15766-pretreated cells and was identified as 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] by high-performance liquid chromatography with tandem mass spectrometric detection. Addition of vitamin D binding protein blunted UVB-induced 24-hydroxylase suggesting the possibility of a paracrine or autocrine role for 1,25(OH)2D3. In conclusion, epidermal keratinocytes can produce vitamin D3, convert it to 1,25(OH)2D3 and respond to it upon UVB irradiation in the absence of exogenous 7-dehydrocholesterol and therefore contain a unique and complete photo-endocrine vitamin D system.
URI: 
ISSN: 0730-2312
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Laboratory of Dermatology
Clinical and Experimental Endocrinology
Laboratory of Dermatoimmunology (+)
× corresponding author
# (joint) last author

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