Activation of the Mouse Heme Oxygenase-1 Gene by 15-Deoxy-Δ12,14-Prostaglandin J2Is Mediated by the Stress Response Elements and Transcription Factor Nrf2

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Abstract
The mechanism of heme oxygenase-1 (ho-1) gene activation by 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) was examined. 15d-PGJ2 stimulated expression of HO-1 mRNA and protein and of a mouse ho-1 gene promoter/luciferase fusion construct (HO15luc) in a dose-dependent manner in mouse hepatoma (Hepa) cells. HO15luc expression was not effected by troglitazone, a peroxisome proliferator-activated receptor-γ (PPAR-γ) ligand, but induction by 15d-PGJ2 was abrogated by the antioxidant N-acetylcysteine. The primary 15d-PGJ2 responsive sequences were localized to a 5′ distal enhancer (E1) and identified as the stress-response element, previously shown to mediate ho-1 activation by several agents, including heme and heavy metals. Treatment of Hepa cells with 15d-PGJ2 stimulated stress-response element-binding activity as judged by electrophoretic mobility shift assays. Antibody "supershift" experiments identified NF-E2 related factor 2 (Nrf2), but not Fos, Jun, or activating transcription factor/cyclic AMP response element binding protein transcription factors, within the 15d-PGJ2-induced complexes. Similarly, a dominant-negative mutant of Nrf2, but not of c-Jun or c-Fos, abrogated 15d-PGJ2-stimulated E1 transcription activity. Finally, prior induction of HO-1 in RAW264.7 mouse macrophages by 15d-PGJ2 attenuated cell death caused by diesel exhaust particle extracts. These results demonstrate that induction of mouse HO-1 expression by 15d-PGJ2 is independent of PPAR-γ but dependent on oxidative stress, is regulated by the oxidative stress-activated transcription factor Nrf2, and provides cytoprotective activity.