TRANSFECTED HUMAN LIVER CYTOCHROME-P-450 HYDROXYLATES VITAMIN-D ANALOGS AT DIFFERENT SIDE-CHAIN POSITIONS

A full-length cDNA for the human liver mitochondrial cytochrome P-450 CYP27 was cloned from a human hepatoma HepG2 cDNA library and then sub cloned into the mammalian expression vector pSG5. When CYP27 cDNA was transfected into COS-1 transformed monkey kidney cells along with adre nodoxin cDNA, transfected cells revealed a 10- to 20-fold higher vitam in D3-25-hydroxylase activity than nontransfected cells. Transfected c ells were capable of 25-hydroxylation of vitamin D3, 1alpha-hydroxyvit amin D3 and 1alpha-hydroxydihydrotachysterol3. In each case they also showed the ability to 26(27)-hydroxylate the cholesterol-like (D3) sid e chain. The relative rates of 25- and 26(27)-hydroxylation of 1alpha- hydroxyvitamin D3 approximately mimicked the ratio of products observe d in HepG2 cells. Vitamin D2 and 1alpha-hydroxyvitamin D2, both with t he ergosterol-like side chain, were 24- and 26(27)-hydroxylated by CYP 27. The rate of side-chain 24-, 25-, or 26(27)-hydroxylation was great er for 1alpha-hydroxylated vitamin D analogs than for their nonhydroxy lated counterparts. We conclude that CYP27 is capable of 24-, 25-, and 26(27)-hydroxylation of vitamin D analogs and that the nature of prod ucts is partially dictated by the side chain of the substrate. This wo rk has revealed that the cytochrome P-450 CYP27 may be important in th e metabolism of vitamin D analogs used as drugs.