title: De-orphanization of cytochrome P450 2R1: a microsomal vitamin D 25-hydroxilase.
abstract: The conversion of vitamin D into an active ligand for the vitamin D receptor requires 25-hydroxylation in the liver and 1alpha-hydroxylation in the kidney. Mitochondrial and microsomal vitamin D 25-hydroxylase enzymes catalyze the first reaction. The mitochondrial activity is associated with sterol 27-hydroxylase, a cytochrome P450 (CYP27A1); however, the identity of the microsomal enzyme has remained elusive. A cDNA library prepared from hepatic mRNA of sterol 27-hydroxylase-deficient mice was screened with a ligand activation assay to identify an evolutionarily conserved microsomal cytochrome P450 (CYP2R1) with vitamin D 25-hydroxylase activity. Expression of CYP2R1 in cells led to the transcriptional activation of the vitamin D receptor when either vitamin D2 or D3 was added to the medium. Thin layer chromatography and radioimmunoassays indicated that the secosteroid product of CYP2R1 was 25-hydroxyvitamin D3. Co-expression of CYP2R1 with vitamin D 1alpha-hydroxylase (CYP27B1) elicited additive activation of vitamin D3, whereas co-expression with vitamin D 24-hydroxylase (CYP24A1) caused inactivation. CYP2R1 mRNA is abundant in the liver and testis, and present at lower levels in other tissues. The data suggest that CYP2R1 is a strong candidate for the microsomal vitamin D 25-hydroxylase.
authors.affiliation: Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas 75390, USA.
authors.forename: Jeffrey B
authors.initials: JB
authors.lastname: Cheng
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Motola
authors.forename: David J
authors.initials: DJ
authors.lastname: Mangelsdorf
authors.forename: David W
authors.initials: DW
authors.lastname: Russell
mesh_terms: D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase / Q000737:chemistry; D000595:Amino Acid Sequence; D000818:Animals; D053493:Cholestanetriol 26-Monooxygenase; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics; D000072467:Cytochrome P450 Family 2; D006801:Humans; D051379:Mice; D008861:Microsomes / Q000201:enzymology*; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000032:analysis; D013250:Steroid Hydroxylases / Q000737:chemistry / Q000235:genetics*; D065668:Vitamin D3 24-Hydroxylase
chemical_list: D012333:RNA, Messenger; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D000072467:Cytochrome P450 Family 2; C506833:CYP2R1 protein, human; C506831:CYP27A1 protein, human; D053493:Cholestanetriol 26-Monooxygenase; C506832:Cyp27a1 protein, mouse; C585549:CYP24A1 protein, human; C585550:Cyp24a1 protein, mouse; D065668:Vitamin D3 24-Hydroxylase; D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase