title: UVB-induced production of 1,25-dihydroxyvitamin D3 and vitamin D activity in human keratinocytes pretreated with a sterol delta7-reductase inhibitor.
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.
authors.affiliation: Laboratory for Experimental Medicine and Endocrinology (LEGENDO), Gasthuisberg, Katholieke Universiteit Leuven, Leuven, Belgium.
authors.forename: Katleen
authors.initials: K
authors.lastname: Vantieghem
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Kissmeyer
authors.forename: Petra
authors.initials: P
authors.lastname: De Haes
authors.forename: Roger
authors.initials: R
authors.lastname: Bouillon
authors.forename: Siegfried
authors.initials: S
authors.lastname: Segaert
mesh_terms: D002117:Calcitriol / Q000096:biosynthesis*; D002461:Cell Line, Transformed; D004817:Epidermis / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism / Q000528:radiation effects; D006801:Humans; D015603:Keratinocytes / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism* / Q000528:radiation effects*; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000037:antagonists & inhibitors* / Q000378:metabolism; D010879:Piperazines / Q000494:pharmacology*; D014466:Ultraviolet Rays; D014807:Vitamin D / Q000096:biosynthesis*
chemical_list: D010879:Piperazines; D014807:Vitamin D; C047457:BM 15766; D044925:Oxidoreductases Acting on CH-CH Group Donors; C019995:7-dehydrocholesterol reductase; D002117:Calcitriol