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Adams JS, Beeker TG, Hongo T, Clemens TL: Constitutive expression of a vitamin D 1-hydroxylase in a myelomonocytic cell line: a model for studying 1,25-dihydroxyvitamin D production in vitro. J Bone Miner Res. 1990 Dec;5(12):1265-9.
The capacity of the v-myc-transformed, chicken myelomonocytic cell line HD-11 to metabolize 25-hydroxyvitamin D3 (25-OHD3) was examined. HD-11 cells produced and secreted a metabolite of 25-OHD3 that was bound with high affinity by receptor for 1,25-dihydroxyvitamin D3 [1,25-(OH) 2D3]. On normal-phase HPLC, this metabolite cochromatographed with authentic 1,25-(OH) 2D3 in both hexane- and methylene chloride-based solvent systems. The 25-OHD3 1-hydroxylation reaction was substrate saturable with a Km of 73 nM 25-OHD3 and a maximal velocity of 167 fmol per 10 (6) cells per h. This reaction was inhibited by ketoconazole, a recognized inhibitor of cytochrome P450 mixed-function oxidases including the authentic, renal 25-OHD3 1-hydroxylase. On the other hand, HD-11 cell 1,25-(OH) 2D3 production was not affected by the antioxidant DPPD, a known inhibitor of free radical-generated 1,25-(OH) 2D3. In addition to synthesizing 1,25-(OH) 2D3, this monocyte-macrophage cell line also has the potential to be a target for the hormone; HD-11 cells express high-affinity receptor for 1,25-(OH) 2D3 (Kin = 0.06 nM). |
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