UVB-induced production of 1,25-dihydroxyvitamin D3 and vitamin D activity in human keratinocytes pretreated with a sterol delta7-reductase inhibitor

J Cell Biochem. 2006 May 1;98(1):81-92. doi: 10.1002/jcb.20756.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Calcitriol / biosynthesis*
  • Cell Line, Transformed
  • Epidermis / drug effects
  • Epidermis / enzymology
  • Epidermis / metabolism
  • Epidermis / radiation effects
  • Humans
  • Keratinocytes / drug effects
  • Keratinocytes / enzymology
  • Keratinocytes / metabolism*
  • Keratinocytes / radiation effects*
  • Oxidoreductases Acting on CH-CH Group Donors / antagonists & inhibitors*
  • Oxidoreductases Acting on CH-CH Group Donors / metabolism
  • Piperazines / pharmacology*
  • Ultraviolet Rays*
  • Vitamin D / biosynthesis*

Substances

  • Piperazines
  • Vitamin D
  • BM 15766
  • Oxidoreductases Acting on CH-CH Group Donors
  • 7-dehydrocholesterol reductase
  • Calcitriol