Catalytic inactive heme oxygenase-1 protein regulates its own expression in oxidative stress

Free Radic Biol Med. 2008 Mar 1;44(5):847-55. doi: 10.1016/j.freeradbiomed.2007.11.012. Epub 2007 Dec 4.


Heme oxygenase-1 (HO-1) catalyzes the degradation of heme and forms antioxidant bile pigments as well as the signaling molecule carbon monoxide. HO-1 is inducible in response to a variety of chemical and physical stress conditions to function as a cytoprotective molecule. Therefore, it is important to maintain the basal level of HO-1 expression even when substrate availability is limited. We hypothesized that the HO-1 protein itself could regulate its own expression in a positive feedback manner, and that this positive feedback was important in the HO-1 gene induction in response to oxidative stress. In cultured NIH 3T3 cells, transfection of HO-1 cDNA or intracellular delivery of pure HO-1 protein resulted in activation of a 15-kb HO-1 promoter upstream of luciferase as visualized by bioluminescent technology and increased HO-1 mRNA and protein levels. These effects were independent of HO activity because an enzymatically inactive mutant form of HO-1 similarly activated the HO-1 promoter and incubation with HO inhibitor metalloporphyrin SnPP did not affect the promoter activation. In addition, HO-1-specific siRNA significantly reduced hemin and cadmium chloride-mediated HO-1 induction. Furthermore, deletion analyses demonstrated that the E1 and E2 distal enhancers of the HO-1 promoter are required for this HO-1 autoregulation. These experiments document feed-forward autoregulation of HO-1 in oxidative stress and suggest that HO-1 protein has a role in the induction process. We speculate that this mechanism may be useful for maintaining HO-1 expression when substrate is limited and may also serve to up-regulate other genes to promote cytoprotection and to modulate cell proliferation.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blotting, Western
  • Cadmium Chloride / pharmacology
  • Catalysis
  • Cell Proliferation
  • Cells, Cultured
  • Gene Expression Regulation, Enzymologic*
  • Heme Oxygenase-1 / antagonists & inhibitors
  • Heme Oxygenase-1 / physiology*
  • Hemin / pharmacology
  • Luciferases / metabolism
  • Metalloporphyrins / pharmacology
  • Mice
  • Mitogen-Activated Protein Kinases / metabolism
  • Mutation / genetics
  • NIH 3T3 Cells
  • Oxidative Stress / physiology*
  • Promoter Regions, Genetic
  • RNA, Small Interfering / pharmacology
  • Rats
  • Regulatory Elements, Transcriptional
  • Transcriptional Activation


  • Metalloporphyrins
  • RNA, Small Interfering
  • Hemin
  • Luciferases
  • Heme Oxygenase-1
  • Mitogen-Activated Protein Kinases
  • Cadmium Chloride