An internal enhancer regulates heme- and cadmium-mediated induction of human heme oxygenase-1.
Heme oxygenase-1 (HO-1) catalyzes the rate-limiting step in heme degradation, releasing iron, carbon monoxide, and biliverdin. Induction of HO-1 is an adaptive and beneficial response in renal and nonrenal settings of tissue injury. The purpose of this study was to characterize the regulation of the human HO-1 gene in renal proximal tubule and aortic endothelial cells in response to heme and cadmium. Evaluation of multiple human HO-1 promoter-reporter constructs up to -9.1 kb demonstrated only a partial response to heme and cadmium. In an effort to mimic endogenous stimulus-dependent levels of HO-1 induction, we evaluated the entire 12.5 kb of the human HO-1 gene, including introns and exons, in conjunction with a -4.5-kb human HO-1 promoter and observed significant heme- and cadmium-mediated induction of the reporter gene, suggesting the presence of an internal enhancer. Enhancer function was orientation independent and required a region between -3.5 and -4.5 kb of the human HO-1 promoter. Our studies identified a novel enhancer internal to the human HO-1 gene that, in conjunction with the HO-1 promoter, recapitulates heme- and cadmium-mediated induction of the endogenous HO-1 gene. Elucidation of the molecular regulation of the human HO-1 gene will allow for the development of therapeutic strategies to manipulate HO-1 gene expression in pathological states.
Hill-Kapturczak
Nathalie
N
Department of Medicine, Div. of Nephrology, Hypertension, and Transplantation, Univ. of Florida, Gainesville, FL 32610, USA.
Sikorski
Eric
E
Voakes
Christy
C
Garcia
Jairo
J
Nick
Harry S
HS
Agarwal
Anupam
A
D001011:Aorta / Q000166:cytology; D002104:Cadmium / Q000494:pharmacology*; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000166:cytology / Q000201:enzymology; D004742:Enhancer Elements, Genetic / Q000235:genetics*; D004790:Enzyme Induction / Q000187:drug effects*; D006418:Heme / Q000378:metabolism / Q000494:pharmacology*; D006419:Heme Oxygenase (Decyclizing) / Q000235:genetics*; D051547:Heme Oxygenase-1; D019382:Human Growth Hormone / Q000235:genetics; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000201:enzymology*; D008565:Membrane Proteins; D011401:Promoter Regions, Genetic / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects
D008565:Membrane Proteins; D002104:Cadmium; D019382:Human Growth Hormone; D006418:Heme; C496541:HMOX1 protein, human; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1