We recently identified adenosine monophosphate-activated protein kinase (AMPK) as a novel inducer of heme oxygenase-1 (HO-1) and surprisingly found that compound C (6-[4-(2-piperidin-1-yl-ethoxy)-phenyl]-3-pyridin-4-yl-pyrazolo[1,5-a] pyrimidine), a cell-permeable inhibitor of AMPK, could also elevate HO-1 suggesting other AMPK-independent actions for this agent. In this study, we investigated the biochemical mechanism by which compound C stimulates HO-1 expression in human endothelial cells (ECs) and determined the biological significance of the induction of HO-1 by compound C in these cells. Compound C stimulated a concentration- and time-dependent increase in HO-1 expression and an increase in HO-1 promoter activity that was abrogated by mutating the antioxidant responsive elements (AREs) in the HO-1 promoter or by overexpressing a dominant negative mutant of NF-E2-related factor 2 (Nrf2). Compound C also stimulated Nrf2 expression this was associated with an increase in the production of reactive oxygen species and with a decline in intracellular glutathione levels. Interestingly, the glutathione donor N-acetyl-l-cysteine or the NADPH oxidase inhibitor apocynin blocked the induction of HO-1 by compound C. Finally, compound C stimulated EC death and this was potentiated by silencing HO-1 expression and reversed by the administration of CO, biliverdin, or bilirubin. In conclusion, this study demonstrates that compound C stimulates HO-1 gene expression in human vascular endothelium via the activation of the Nrf2/ARE signaling pathway to counteract compound C-mediated cell death. The ability of compound C to induce HO-1 expression may contribute to the pleiotropic actions of this agent and suggest caution when using compound C to probe for AMPK functions.
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