Exposure of eukaryotic cells to a variety of reactive-oxygen-intermediate (ROI)-mediated sources of cellular injury, including heavy metals and UV radiation, induces the expression of heat-shock (HS) and stress-related genes among which is a 32–34kDa protein identified as inducible haem oxygenase-1 (HO-1). We previously showed that tobacco smoke (TS), a potent source of oxidants leading to oxidative stress, induces both HS proteins (HSPs) and HO-1 in normal human monocytes. Here we investigated the induction mechanisms of human HO-1 gene expression by TS in the human premonocytic line U937. Northern blotting and flow cytometry revealed a dose- and time-dependent induction of HO-1 mRNA and protein by TS. In order to clarify the role of transacting factors in this induction, electrophoretic mobility-shift analysis was performed with nuclear extracts from control, TS-, cadmium (Cd)- or H2O2-exposed cells, incubated with consensus elements and binding sites of the promoter region of HO-1[heat-shock factor (HSF), nuclear factor κB (NF-κB) and activator protein-1 (AP-1)] and the cadmium-responsive element (CdRE) isolated by Takeda, Ishizawa, Sato, Yoshida and Shibahara [(1994) J. Biol. Chem. 269, 22858–22867]. We report an inhibition of NF-κB activation by TS, no effect on AP-1 and a strong activation of CdRE-binding activity, whereas cadmium chelation from TS only partially prevented HO-1 induction. H2O2 also activated the CdRE-binding activity, and pretreatment with N-acetyl-l-cysteine, which replenishes the intracellular levels of GSH, suppressed, in TS-treated cells, both the CdRE-binding activity and the increased HO-1 expression.

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Present address: INSERM U332, ICGM (Institut Cochin de Génétique Moléculaire), 22 rue Méchain, 75014 Paris, France