Redox Regulation of p38 MAPK Activation and Expression of ICAM-1 and Heme Oxygenase-1 in Human Alveolar Epithelial (A549) Cells

Abstract

We have explored the potential role of redox events in p38 mitogen-activated protein kinase (MAPK) activation and their relevance to the inducible expression of intercellular adhesion molecule-1 (ICAM-1) and heme oxygenase-1 (HO-1) in A549 cells. Tumor necrosis factor-α (TNFα) and hydrogen peroxide (H₂O₂) both activated p38, but only TNFα activated nuclear factor-κB (NF-κB). N-Acetyl-L-cysteine (20 mM) inhibited both H₂O_2- and TNFα-induced p38 phosphorylation (14 ± 7 and 37 ± 4% of control, respectively). The mitochondrial complex I and III inhibitors, rotenone and antimycin A, and allopurinol partially inhibited H₂O₂- but not TNFα-induced p38 activation. However, rotenone and antimycin A augmented intracellular oxidative stress measured by dichlorofluorescein fluorescence. TNFα, but not H₂O₂, induced ICAM-1 in A549 cells, which was attenuated by a proteasome inhibitor, but not by the p38 MAPK inhibitor SB203580. In contrast, hemin and hemoglobin, but neither TNFα nor H₂O₂, caused efficient HO-1 expression. However, hemin had no effect on p38 activation and SB203580 did not influence hemin-induced HO-1 protein expression. Collectively, these data suggest that p38 is a cytokine- and oxidative stress-responsive pathway in A549 cells. Whereas NF-κB appears crucial in ICAM-1 induction, p38 activation itself is not sufficient to confer HO-1 expression and may not be involved in HO-1 and ICAM-1 induction in A549 cells. Antioxid. Redox Signal. 7, 14–24.