Catalytic inactive heme oxygenase-1 protein regulates its own expression in oxidative stress.
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.
D000818:Animals; D015153:Blotting, Western; D019256:Cadmium Chloride / Q000494:pharmacology; D002384:Catalysis; D049109:Cell Proliferation; D002478:Cells, Cultured; D015971:Gene Expression Regulation, Enzymologic; D051547:Heme Oxygenase-1 / Q000037:antagonists & inhibitors / Q000502:physiology*; D006427:Hemin / Q000494:pharmacology; D008156:Luciferases / Q000378:metabolism; D008665:Metalloporphyrins / Q000494:pharmacology; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D041681:NIH 3T3 Cells; D018384:Oxidative Stress / Q000502:physiology*; D011401:Promoter Regions, Genetic; D034741:RNA, Small Interfering / Q000494:pharmacology; D051381:Rats; D050436:Regulatory Elements, Transcriptional; D015533:Transcriptional Activation
D008665:Metalloporphyrins; D034741:RNA, Small Interfering; D006427:Hemin; D008156:Luciferases; D051547:Heme Oxygenase-1; D020928:Mitogen-Activated Protein Kinases; D019256:Cadmium Chloride