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UVB‐induced 1,25(OH) 2 D 3 production and vitamin D activity in intestinal CaCo‐2 cells and in THP‐1 macrophages pretreated with a sterol Δ 7 ‐reductase inhibitor
Author(s) -
Vantieghem Katleen,
Overbergh Lut,
Carmeliet Geert,
De Haes Petra,
Bouillon Roger,
Segaert Siegfried
Publication year - 2006
Publication title -
journal of cellular biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.028
H-Index - 165
eISSN - 1097-4644
pISSN - 0730-2312
DOI - 10.1002/jcb.20910
Subject(s) - calcitriol receptor , autocrine signalling , caco 2 , vitamin d and neurology , chemistry , paracrine signalling , vitamin , keratinocyte , hacat , cell culture , reductase , macrophage , biochemistry , microbiology and biotechnology , cell , biology , receptor , enzyme , endocrinology , in vitro , genetics
Epidermal keratinocytes are able to produce 1,25‐dihydroxyvitamin D 3 [1,25(OH) 2 D 3 ] 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 1α‐hydroxylase (CYP27B1) activity, and survive the low UVB doses essential for vitamin D 3 photoproduction. Upon irradiation, 24‐hydroxylase (CYP24) mRNA is induced in both cell types pretreated with the sterol Δ 7 ‐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) 2 D 3 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) 2 D 3 . 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. J. Cell. Biochem. © 2006 Wiley‐Liss, Inc.