[Vitamin D and the skin: new aspects and perspectives].

Vitamin D (calciferol) is under clinical investigation for the treatment of psoriasis. Vitamin D was previously solely regarded as a key substance in hormonal calcium homeostasis, a view that is no longer tenable. The human receptor for the biologically active metabolite 1,25-dihydroxyvitamin-D3 was cloned in 1988. Sequence analyses revealed that it was a member of the nuclear steroid hormone receptor family. This family of gene-regulatory DNA-binding proteins includes the oestrogen, progesterone, glucocorticoid, mineralocorticoid, thyroxine (T-3) and retinoic acid receptors. Vitamin D receptors have been identified in a variety of tissues primarily unrelated to calcium metabolism. The skin and the immune system are some of the most interesting new targets. In vitro 1,25-dihydroxyvitamin-D3 inhibits proliferation and induces differentiation of keratinocytes. Furthermore, this hormone has potent immunomodulatory functions.