title: Regulation of xanthine oxidoreductase protein expression by hydrogen peroxide and calcium.
abstract: OBJECTIVE
  We have previously demonstrated that endothelial xanthine oxidase (XO) levels are dependent on the NADPH oxidase. We postulated that H2O2 may modulate the irreversible conversion of xanthine dehydrogenase (XDH) to XO and sought to examine mechanisms involved.
  
  
  RESULTS
  H2O2 (100 micromol/L) decreased bovine aortic endothelial cell (BAEC) XDH protein expression, and metabolic labeling studies indicated that H2O2 stimulated conversion of XDH to XO. The decline in XDH was mimicked by the reactive oxygen species (ROS) generating compounds SIN-1 and Menadione, as well as by stimulating BAECs with angiotensin II (200 nmol/L). BAPTA-AM prevented the decline in XDH by H2O2, indicating that it was calcium-dependent. In keeping with calcium acting downstream of H2O2, the calcium ionophore A23187 (1 micromol/L) caused XDH-to-XO conversion, and this was not prevented by the antioxidants. In addition, XDH-to-XO conversion was blocked by 2-APB and NO donors and induced by thapsigargin and M-3M3FBS, implicating phospholipase C and endoplasmic reticulum calcium stores in this process.
  
  
  CONCLUSIONS
  Endothelial XO and XDH expression are strongly dependent on H2O2 and calcium. Stimulation of XDH conversion to XO may represent a feed-forward mechanism whereby H2O2 can stimulate further production of ROS.
authors.affiliation: Division of Cardiology, Emory University, 101 Woodruff Cir, WMB 319, Atlanta, GA 30322, USA.
authors.forename: J Scott
authors.initials: JS
authors.lastname: McNally
authors.forename: Archana
authors.initials: A
authors.lastname: Saxena
authors.forename: Hua
authors.initials: H
authors.lastname: Cai
authors.forename: Sergey
authors.initials: S
authors.lastname: Dikalov
authors.forename: David G
authors.initials: DG
authors.lastname: Harrison
mesh_terms: D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000166:cytology / Q000201:enzymology*; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D007476:Ionophores / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism; D016877:Oxidants / Q000494:pharmacology*; D013481:Superoxides / Q000378:metabolism; D010738:Type C Phospholipases / Q000378:metabolism; D014968:Xanthine Dehydrogenase / Q000378:metabolism; D014969:Xanthine Oxidase / Q000378:metabolism*
chemical_list: D007476:Ionophores; D016877:Oxidants; D013481:Superoxides; D009569:Nitric Oxide; D000001:Calcimycin; D006861:Hydrogen Peroxide; D014968:Xanthine Dehydrogenase; D014969:Xanthine Oxidase; D010738:Type C Phospholipases; D002118:Calcium