Fatty acid transduction of nitric oxide signaling: nitrolinoleic acid mediates protective effects through regulation of the ERK pathway

In vivo and in vitro studies revealed that nitroalkenes serve as protective mediators in the lung by inducing the cytoprotective enzyme heme oxygenase-1 (HO-1). Nitrolinoleic acid (LNO 2) increased HO-1 mRNA, protein, and activity in cultured pulmonary epithelial cells treated with 5 to 50 μM LNO 2 and in lungs of rats injected intraperitoneally with 2.6 mg/kg LNO 2 twice daily for 20 days. Western blotting revealed that HO-1 protein increased significantly within 4 h of in vitro LNO 2 addition and was preceded by an increase in HO-1 mRNA, consistent with transcriptional regulation of HO-1 expression by LNO 2. LNO 2 also dephosphorylated and activated eukaryotic initiation factor 2α, a key translational regulatory protein, indicating that increased translation may also contribute to LNO 2-induced increases in HO-1. Exposure of cells to LNO 2 activated ERK and JNK, as evidenced by increased phosphorylation. Downstream targets of ERK and JNK, Elk-1 and c-Jun, respectively, were also phosphorylated in response to LNO 2 exposure. However, inhibitor studies revealed that only the ERK pathway is necessary for the LNO 2-mediated increase in HO-1 mRNA and protein. These data reveal that LNO 2 induces pulmonary epithelial HO-1 expression and downstream adaptive responses to inflammation via both transcriptional and translational regulatory mechanisms.