CO Induces Nrf2-Dependent Heme Oxygenase-1 Transcription by Cooperating with Sp1 and C-Jun in Rat Brain Astrocytes

Upregulation of heme oxygenase 1 (HO-1) by carbon monoxide (CO) delivered by CO-releasing molecules (CORMs) may be utilized as a therapeutic intervention for neurodegenerative diseases. This study was to delineate the two putative anti-oxidant response elements (AREs) in modulating HO-1 gene by participating with its promoter elements in rat brain astrocytes (RBA-1). CORM-2-induced HO-1 expression was mediated through superoxide, p38 mitogen-activated protein kinase(MAPK), extracellular signal-regulated protein kinases 1 and 2 (Erk1/2), protein tyrosine kinase 2 (Pyk2), platelet-derived growth factor receptor (PDGFR), and phosphatidylinositol 3'-kinase (PI3K/Akt), revealed by the pharmacological inhibitors or knockdown of these signaling molecules. CORM-2-enhanced HO-1 promoter activity was inhibited by co-transfection with small interfering RNA (siRNA) of c-Jun, specificity protein 1 (Sp1), or nuclear factor-erythroid 2-related factor 2 (Nrf2). Immunoprecipitation assay showed that CORM-2 increased the association of nuclear Nrf2 with Sp1 and c-Jun. Furthermore, chromatin immunoprecipitation (ChIP) assay confirmed that Nrf2, Sp1, and c-Jun are associated with the proximal ARE binding site on HO-1 promoter, suggesting that Nrf2/Sp1/c-Jun cooperations are key transcription factors modulating HO-1 expression. Mechanistically, CORM-2-induced ARE promoter activity was reduced by the inhibitors of reactive oxygen species (ROS), p38 MAPK, Pyk2, MAPK/ERK kinases 1 and 2 (MEK1/2), PDGFR, and PI3K/Akt or the siRNAs of c-Jun, SP1, and Nrf2. These findings suggested that CORM-2 increases formation of c-Jun, Sp1, and Nrf2 complex and binding with ARE1 binding site, which is mediated through both ROS/p38 MAPK and Pyk2-dependent PDGFR/PI3K/Akt/Erk1/2 pathways, resulting in HO-1 expression in RBA-1 cells.