Trends in Endocrinology & Metabolism
ReviewVitamin D 1α-Hydroxylase
Section snippets
The Vitamin D Biosynthetic Enzymes are Mitochondrial Forms of Cytochrome P450
The vitamin D 25-hydroxylase, the 1α-hydroxylase and the 24-hydroxylase are all type I (mitochondrial) cytochrome P450 enzymes, which function as oxidases and use electrons from NADPH and molecular oxygen3, 4. For catalysis by a type I P450 enzyme, electrons from NADPH are first taken up by a flavoprotein, ferredoxin reductase, which is bound to the inner mitochondrial membrane. Ferredoxin reductase passes the electrons to ferredoxin, an iron–sulfur protein that is either loosely associated
Vitamin D 25-Hydroxylase
The hepatic 25-hydroxylase was initially thought to be a microsomal enzyme, and it was not until it was cloned that its subcellular location was agreed upon. Studies of bile acid 26-hydroxylation led to the cloning of vitamin D 25-hydroxylase. A mitochondrial P450 enzyme that had bile acid 26-hydroxylase activity was isolated from rabbit liver and cloned. Three groups used similar techniques to purify rat liver mitochondrial vitamin D 25-hydroxylase6, 7, 8, 9, 10. Screening of
Vitamin D 24-Hydroxylase
Vitamin D 24-hydroxylase was cloned by purifying P450c24 from renal mitochondria, raising a polyclonal antiserum, and screening a rat kidney cDNA expression library18. This facilitated the cloning of the rat gene19 and the human cDNA and gene20, 21. Studies with the purified rat renal enzyme18 and with cells expressing the transfected human cDNA20 show that P450c24 can catalyze the 24-hydroxylation of either 25OHD or 1,25(OH)2D. The conversion of 1,25(OH)2D to 1,24,25(OH)3D, which is inducible
Vitamin D 1α-Hydroxylase
Although the 25- and 24-hydroxylases were cloned in 1990 and 1991, the 1α-hydroxylase was not cloned until the second half of 1997, when four independent groups using different approaches reported the cloning of the mouse, rat and human vitamin D 1α-hydroxylase, P450c1α (25, 26, 27, 28, 29, 30). This work has been reviewed in greater detail elsewhere31. The cloning of P450c1α was very difficult, primarily because there is very little P450c1α protein in the kidney. Although physiological
The Molecular Genetics of 1α-Hydroxylase deficiency
We then studied the P450c1α genes in 19 more patients from 17 families from multiple ethnic groups40. These patients all had the typical findings of 1α-hydroxylase deficiency: hypocalcemia, hypophosphatemia, high serum alkaline phosphatase and PTH concentrations, normal 25OHD concentrations, low 1,25(OH)2 D concentrations, radiographic evidence of rickets and a therapeutic response to physiological replacement doses of 1,25(OH)2D. Because the P450c1α gene is small, we could PCR amplify the
Regulation of P450c1α
Renal 1α-hydroxylase activity and P450c1α mRNA are stimulated by PTH, insulin-like growth factor I (IGF-I), hypocalcemia and hypophosphatemia, and suppressed by hypercalcemia, hyperphosphatemia and 1,25(OH)2D (28, 29, 45). The stimulatory effect of PTH on 1α-hydroxylase activity appears to require both the cAMP-dependent protein kinase A (PKA) and protein kinase C (PKC) pathways. The induction by PTH (and cAMP) occurs, at least in part, at the transcriptional level and the suppression by
Acknowledgements
The work discussed here was supported by National Institute of Health grants DK37922 (to WLM), DK42154 (to WLM), DK/AR54433 (to AAP), and by grants from the March of Dimes Birth Defects Foundation (to WLM and AAP).
References (49)
Normal and abnormal regulation of 1,25(OH)2D synthesis
Am. J. Med. Sci.
(1988)Cytochrome b5 augments the 17,20 lyase activity of human P450c17 without direct electron transfer
J. Biol. Chem.
(1998)Cloning structure, and expression of the mitochondrial cytochrome P-450 sterol 26-hydroxylase, a bile acid biosynthetic enzyme
J. Biol. Chem.
(1989)Purification and characterization of vitamin D 25-hydroxylase from rat liver mitochondria
J. Biol. Chem.
(1988)Hydroxylations in biosynthesis of bile acidsisolation of a cytochrome P-450 from rabbit liver mitochondria catalysing 26-hydroxylation of C-27 steroids
J. Biol. Chem.
(1984)Molecular cloning of cDNA for vitamin D3 25-hydroxylase from rat liver mitochondria
FEBS Lett.
(1990)- et al.
Characterization of human sterol 27-hydroxylase. A mitochondrial cytochrome P-450 that catalyses multiple oxidation reaction in bile acid biosynthesis
J. Biol. Chem.
(1991) Partial deletion of the gene encoding sterol 27-hydroxylase in a subject with cerebrotendinous xanthomatosis
J. Lipid Res.
(1996)A possible genetic defect in 25-hydroxylation as a cause of rickets
J. Pediatr.
(1994)Cloning, structure and expression of a cDNA encoding vitamin D3 25-hydroxylase
Biochem. Biophys. Res. Commun.
(1997)
Cloning and expression of cDNA encoding 25-hydroxyvitamin D3 24-hydroxylase
FEBS Lett.
Cloning of the human 1α‴25-dihydroxyvitamin D3-24-hydroxylase gene promoter and identification of two vitamin D-responsive elements
Biochim. Biophys. Acta
Molecular cloning of cDNA and genomic DNA for human 25-hydroxyvitamin D3 1α-hydroxylase
Biochem. Biophys. Res. Commun.
Genetic disorders of vitamin D biosynthesis
Endocrinol. Metab. Clin. North Am.
Genetics of vitamin D 1α-hydroxylase deficiency in 17 families
Am. J. Hum. Genet.
Two novel 1α-hydroxylase mutations in French-Canadians with vitamin D dependency rickets type I
Kidney Int.
The promoter of the 25-hydroxyvitamin D3 1α-hydroxylase gene confers positive and negative responsiveness to PTH, calcitonin and 1α,25 (OH)2D3
Biochem. Biophys. Res. Commun.
Metabolism of 1,25-dihyroxy vitamin D3
Physiol. Rev.
P450 genesstructure, evolution and regulation
Annu. Rev. Biochem.
P-450 cytochromesstructure and function
Adv. Enzymol. Relat. Areas Mol. Biol.
25-Hydroxylation of vitamin D by a cytochrome P-450 from rabbit liver mitochondria
J. Biochem.
Purification and characterization of a hepatic mitochondrial cytochrome P450 active in aflatoxin B1 metabolism
Biochemistry
A cDNA encoding a rat mitochondrial cytochrome P450 catalysing both the 26-hydroxylations of cholesterol and 25-hydroxylation of vitamin D3gonadotropic regulation of the cognate mRNA in ovaries
DNA Cell Biol.
Inborn errors in bile acid biosynthesis and storage of sterols other than cholesterol
Cited by (73)
The activating enzymes of vitamin D metabolism (25- and 1α-hydroxylases)
2023, Feldman and Pike's Vitamin D: Volume One: Biochemistry, Physiology and DiagnosticsVitamin D new therapy for breast cancer prevention
2022, Oncogenic Viruses: Volume 2: Medical Applications of Viral Oncology ResearchThe Activating Enzymes of Vitamin D Metabolism (25- and 1α-Hydroxylases)
2018, Vitamin D: Fourth EditionGenetic Disorders Of Vitamin D Synthesis and Action
2018, Genetics of Bone Biology and Skeletal Disease: Second EditionGenetic Diseases of Vitamin D Metabolizing Enzymes
2017, Endocrinology and Metabolism Clinics of North AmericaCitation Excerpt :VDDR-1A is the classic and most prevalent form of pseudovitamin D deficiency rickets or hereditary vitamin D–resistant rickets. It is caused by recessive loss-of-function mutations in the CYP27B1 gene encoding 25-(OH)D3-1α-hydroxylase.21,47–51 Numerous patients and CYP27B1 mutations have been reported (see Fig. 2C).