Lipopolysaccharide-Induced Heme Oxygenase-1 Expression in Human Monocytic Cells Is Mediated via Nrf2 and Protein Kinase C

Abstract

Monocytes play a key role in mobilization of the immune response during sepsis. In response to LPS, monocytes produce both proinflammatory mediators and regulatory proteins that counteract the inflammation and oxidative stress. In murine macrophages, LPS stimulates expression of heme oxygenase 1 (HO-1), a cytoprotective enzyme that catalyzes the degradation of heme. The HO-1 5′-untranslated region, similarly to other cytoprotective genes, contains antioxidant-response elements (AREs) that can bind the transcription factor NF-E2-related factor 2 (Nrf2). At present, the role of Nrf2 in LPS-induced HO-1 expression in monocytic cells has not been investigated. In this study, LPS induced HO-1 mRNA and protein expression in human monocytes and THP-1 cells. Nrf2 translocated from the cytosol to the nucleus in response to LPS and bound to the ARE site in the human HO-1 promoter. In addition, a dominant negative Nrf2 mutant inhibited LPS-induced HO-1 mRNA expression but not TNF-α mRNA expression in THP-1 cells. Ro-31-8220, a pan-protein kinase C (PKC) inhibitor, and Go6976, a classical PKC inhibitor, blunted LPS-induced HO-1 mRNA expression in monocytes and THP-1 cells. Both PKC inhibitors also blocked LPS-induced Nrf2 binding to the ARE. These results indicate that LPS-induced HO-1 expression in human monocytic cells requires Nrf2 and PKC.

Expression of heme oxygenase‐1 in human leukemic cells and its regulation by transcriptional repressor Bach1

“…LPS is known to affect HO-1 expression in leukemic cell lines and monocytes. (19,(22)(23)(24) To understand the regulatory mechanism of HO-1 expression in leukemic cells, we compared the effect of LPS on HO-1 expression between the U937 cell line and CD14 + primary monocytes. LPS upregulated HO-1 in U937 cells, but this upregulation was not associated with an increase or decrease in Nrf2 or Bach1 levels in the whole cell lysates ( Fig.…”

“…(13)(14)(15)(16)(17)(18) Nrf2 plays an essential role in HO-1 gene regulation in human monocytes. (19,20) Tumor necrosis factor (TNF)-dependent HO-1 induction is mediated by the activation of Nrf2 in human myelomonocytic leukemic cell lines.(11) In contrast, we have previously shown that TNF suppresses HO-1 expression in peripheral monocytes by accelerating mRNA decay without affecting transcription activity.(21) Moreover, LPS positively or negatively regulates HO-1 expression in human and rodent monocytes and the human myelomonocytic leukemic cell line, THP-1. (19,(22)(23)(24) Bach1 is known to play an important role in cellular homeostasis.…”

“…(21) Moreover, LPS positively or negatively regulates HO-1 expression in human and rodent monocytes and the human myelomonocytic leukemic cell line, THP-1. (19,(22)(23)(24) Bach1 is known to play an important role in cellular homeostasis. (25) As the affinity of Bach1 for MARE is higher than that of any activator, Bach1 occupies the element and shuts off HO-1 expression under normal conditions.…”

“…(19,20) Tumor necrosis factor (TNF)-dependent HO-1 induction is mediated by the activation of Nrf2 in human myelomonocytic leukemic cell lines.…”

“…(13)(14)(15)(16)(17)(18) Nrf2 plays an essential role in HO-1 gene regulation in human monocytes. (19,20) Tumor necrosis factor (TNF)-dependent HO-1 induction is mediated by the activation of Nrf2 in human myelomonocytic leukemic cell lines. (11) In contrast, we have previously shown that TNF suppresses HO-1 expression in peripheral monocytes by accelerating mRNA decay without affecting transcription activity.…”