title: 25-hydroxyvitamin D3-1alpha-hydroxylase is expressed in human vascular smooth muscle cells and is upregulated by parathyroid hormone and estrogenic compounds.
abstract: BACKGROUND
  1,25(OH)2 vitamin D3 exerts multiple effects in human vascular smooth muscle cells (VSMCs). We therefore tested the possibility that VSMCs possess an endogenous 25-hydroxyvitamin D3-1alpha-hydroxylase system, the final enzyme in the biosynthetic pathway of 1,25(OH)2D3.
  
  
  RESULTS
  We assessed the expression and activity of 25-hydroxyvitamin D3-1alpha-hydroxylase by real-time polymerase chain reaction and the conversion of 25(OH)D3 into 1,25(OH)2D3. First, 25-hydroxyvitamin D3-1alpha-hydroxylase mRNA was identified in cultured VSMCs by real-time polymerase chain reaction. Second, in cells treated daily (3 days) with parathyroid hormone (66 nmol/L), estradiol-17beta (30 nmol/L), raloxifene (3 micromol/L), and the phytoestrogens genistein (3 micromol/L), biochainin A (3 micromol/L), and 6-carboxy biochainin A (30 nmol/L), 25-hydroxyvitamin D3-1alpha-hydroxylase mRNA increased by 43+/-13%, (P<0.05) 7+/-24% (P=NS), 176+/-28% (P<0.01), 65+/-11% (P<0.05), 152+/-24% (P<0.01), and 71+/-9% (P<0.05), respectively. Third, production of 1,25(OH)2D3 from 25(OH)D3 was seen with a Km of 25 ng/mL and increased dose dependently after treatment with parathyroid hormone, genistein, and the phytosetrogen derivative 6-carboxy biochainin A. Estradiol-17beta and biochainin A also increased the generation of 1,25(OH)2D3 by 40+/-23% (P<0.05) and 55+/-13% (P<0.05), respectively.
  
  
  CONCLUSIONS
  We provide here the first evidence for the expression of an enzymatically active 25(OH)D3-1alpha-hydroxylase system in human VSMCs, which can be upregulated by parathyroid hormone and estrogenic compounds. Because exogenous vitamin D inhibits VSMC proliferation, the role of this system as an autocrine mechanism to curb changes in VSMC proliferation and phenotype is a subject for future investigation.
authors.affiliation: Institute of Endocrinology, Metabolism and Hypertension, Tel Aviv Sourasky Medical Center ,and Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
authors.forename: Dalia
authors.initials: D
authors.lastname: Somjen
authors.forename: Yosef
authors.initials: Y
authors.lastname: Weisman
authors.forename: Fortune
authors.initials: F
authors.lastname: Kohen
authors.forename: Batya
authors.initials: B
authors.lastname: Gayer
authors.forename: Rona
authors.initials: R
authors.lastname: Limor
authors.forename: Orly
authors.initials: O
authors.lastname: Sharon
authors.forename: Niva
authors.initials: N
authors.lastname: Jaccard
authors.forename: Esther
authors.initials: E
authors.lastname: Knoll
authors.forename: Naftali
authors.initials: N
authors.lastname: Stern
mesh_terms: D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase / Q000235:genetics*; D019898:Autocrine Communication; D002117:Calcitriol / Q000096:biosynthesis; D049109:Cell Proliferation; D004305:Dose-Response Relationship, Drug; D004967:Estrogens / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D007700:Kinetics; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000201:enzymology* / Q000378:metabolism; D010281:Parathyroid Hormone / Q000494:pharmacology*; D012333:RNA, Messenger / Q000032:analysis; D014469:Umbilical Arteries / Q000166:cytology; D015854:Up-Regulation / Q000187:drug effects*
chemical_list: D004967:Estrogens; D010281:Parathyroid Hormone; D012333:RNA, Messenger; D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase; D002117:Calcitriol