title: Dietary phosphorus transcriptionally regulates 25-hydroxyvitamin D-1alpha-hydroxylase gene expression in the proximal renal tubule.
abstract: Synthesis of the hormone 1,25-dihydroxyvitamin D, the biologically active form of vitamin D, occurs in the kidney and is catalyzed by the mitochondrial cytochrome P450 enzyme, 25-hydroxyvitamin D-1alpha-hydroxylase (1alpha-hydroxylase). We sought to characterize the effects of changes in dietary phosphorus on the kinetics of renal mitochondrial 1alpha-hydroxylase activity and the renal expression of P450c1alpha and P450c24 mRNA, to localize the nephron segments involved in such regulation, and to determine whether transcriptional mechanisms are involved. In intact mice, restriction of dietary phosphorus induced rapid, sustained, approximately 6- to 8-fold increases in renal mitochondrial 1alpha-hydroxylase activity and renal P450c1alpha mRNA abundance. Immunohistochemical analysis of renal sections from mice fed the control diet revealed the expression of 1alpha-hydroxylase protein in the proximal convoluted and straight tubules, epithelial cells of Bowman's capsule, thick ascending limb of Henle's loop, distal tubule, and collecting duct. In mice fed a phosphorus-restricted diet, immunoreactivity was significantly increased in the proximal convoluted and proximal straight tubules and epithelial cells of Bowman's capsule, but not in the distal nephron. Dietary phosphorus restriction induced a 2-fold increase in P450c1alpha gene transcription, as shown by nuclear run-on assays. Thus, the increase in renal synthesis of 1,25-dihydroxyvitamin D induced in normal mice by restricting dietary phosphorus can be attributed to an increase in the renal abundance of P450c1alpha mRNA and protein. The increase in P450c1alpha gene expression, which occurs exclusively in the proximal renal tubule, is due at least in part to increased transcription of the P450c1alpha gene.
authors.affiliation: Department of Pediatrics, University of California, San Francisco, California 94143, USA.
authors.forename: Martin Y H
authors.initials: MY
authors.lastname: Zhang
authors.forename: Xuemei
authors.initials: X
authors.lastname: Wang
authors.forename: Jonathan T
authors.initials: JT
authors.lastname: Wang
authors.forename: Nathalie A
authors.initials: NA
authors.lastname: Compagnone
authors.forename: Synthia H
authors.initials: SH
authors.lastname: Mellon
authors.forename: Jean L
authors.initials: JL
authors.lastname: Olson
authors.forename: Harriet S
authors.initials: HS
authors.lastname: Tenenhouse
authors.forename: Walter L
authors.initials: WL
authors.lastname: Miller
authors.forename: Anthony A
authors.initials: AA
authors.lastname: Portale
mesh_terms: D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase / Q000096:biosynthesis* / Q000235:genetics*; D000818:Animals; D015153:Blotting, Western; D002467:Cell Nucleus / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects* / Q000235:genetics; D007150:Immunohistochemistry; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000201:enzymology*; D007700:Kinetics; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008928:Mitochondria / Q000201:enzymology; D009399:Nephrons / Q000378:metabolism; D016226:Phosphorus, Dietary / Q000008:administration & dosage*; D012333:RNA, Messenger / Q000096:biosynthesis; D015533:Transcriptional Activation / Q000502:physiology
chemical_list: D016226:Phosphorus, Dietary; D012333:RNA, Messenger; D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase