Transcriptional control of the heme oxygenase gene in mouse M1 cells during their TPA-induced differentiation into macrophages

It has long been known that heme oxygenase (HO) is a key enzyme in heme catabolism and recently it was also found to acts as an oxidative stress protein to produce carbon monoxide (CO), which has similar actions to those of nitrogen monoxide (NO). Therefore, we examined transcriptional control of the HO gene in mouse M1 (myeloleukemia) cells during their differentiation into macrophages. Since the promoter region of this gene is known to have a TPA-responsive element (TRE), its expression might be regulated by a C- kinase signal transduction pathway. Then we investigated the activation of the HO gene after treatment of M1 cells with TPA and inhibitors of C- kinase. When M1 cells were treated with TPA, they differentiated into macrophage-like cells. Upon treatment with TPA, H₂O₂ was produced first, the nuclear proto-oncogenes fos and jun were activated, and then the HO gene was activated. The extent of transcriptional activation of the fos, jun, and HO genes in M1 cells treated with TPA was reduced by a specific inhibitor of C-kinase and a scavenger of oxygen radicals. When M1 cells were treated with H₂O₂, essentially the same level of transcription of the HO gene was observed, but the extent of transcriptional activation of the fos and jun genes was about half of the treatment with TPA. Super-shift assays using the TRE of the HO gene revealed that the Fos and Jun proteins from nuclei of M1 cells treated with TPA bound to the TRE, and same assays using DNA with the NF-κB motif also revealed that the active NF-κB protein from M1 cells treated with H₂O₂ or TPA also bound to the corresponding motif. These results strongly suggest that the HO gene in M1 cells is activated by TPA through a production of H₂O₂, an oxidative activation pathway of NF-κB, and a signal-transduction pathway that involves C-kinase during the differentiation of macrophages that occurs upon treatment with TPA.