title: UVB-induced 1,25(OH)2D3 production and vitamin D activity in intestinal CaCo-2 cells and in THP-1 macrophages pretreated with a sterol Delta7-reductase inhibitor.
abstract: Epidermal keratinocytes are able to produce 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] and induce vitamin D activity upon UVB irradiation. To find out whether this property is keratinocyte specific, we investigated this characteristic in two other cell types, namely intestinal CaCo-2 cells and the macrophage-like differentiated THP-1 cells. THP-1 macrophages and preconfluent CaCo-2 cells contain the vitamin D receptor (VDR), possess 25-hydroxylase (CYP2R1 and CYP27A1) and 1alpha-hydroxylase (CYP27B1) activity, and survive the low UVB doses essential for vitamin D3 photoproduction. Upon irradiation, 24-hydroxylase (CYP24) mRNA is induced in both cell types pretreated with the sterol Delta7-reductase inhibitor BM15766 whereby the 7-dehydrocholesterol (7-DHC) content was increased. Transfection studies in CaCo-2 cells with a vitamin D response element-containing construct revealed the involvement of the VDR in this UVB-dependent CYP24 induction. The CYP24 inducing activity in BM15766-pretreated UVB-irradiated CaCo-2 cells and THP-1 macrophages was identified as 1,25(OH)2D3 by combined high-performance liquid chromatography radioimmunoassay. Addition of vitamin D binding protein to the CaCo-2 cells attenuated UVB-induced CYP24 induction suggesting the possibility of a paracrine or autocrine role for the photoproduced 1,25(OH)2D3. In conclusion, preconfluent CaCo-2 cells and THP-1 macrophages are able to induce vitamin D activity upon UVB irradiation and hence combine all parts of the vitamin D photoendocrine system, a characteristic which is therefore not keratinocyte specific.
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: Lut
authors.initials: L
authors.lastname: Overbergh
authors.forename: Geert
authors.initials: G
authors.lastname: Carmeliet
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: D018938:Caco-2 Cells / Q000187:drug effects; D002460:Cell Line; D002470:Cell Survival / Q000528:radiation effects; D002762:Cholecalciferol / Q000378:metabolism; D003684:Dehydrocholesterols / Q000378:metabolism; D004307:Dose-Response Relationship, Radiation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000166:cytology / Q000187:drug effects / Q000528:radiation effects*; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects*; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000037:antagonists & inhibitors; D010879:Piperazines / Q000494:pharmacology*; D013250:Steroid Hydroxylases / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects; D014466:Ultraviolet Rays / Q000009:adverse effects*; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000378:metabolism* / Q000494:pharmacology; D014809:Vitamin D-Binding Protein / Q000528:radiation effects; D065668:Vitamin D3 24-Hydroxylase
chemical_list: D003684:Dehydrocholesterols; D004791:Enzyme Inhibitors; D010879:Piperazines; D014809:Vitamin D-Binding Protein; C118756:dihydroxy-vitamin D3; D014807:Vitamin D; D002762:Cholecalciferol; C047457:BM 15766; C016705:7-dehydrocholesterol; D013250:Steroid Hydroxylases; D065668:Vitamin D3 24-Hydroxylase; D044925:Oxidoreductases Acting on CH-CH Group Donors; C019995:7-dehydrocholesterol reductase