The role of p44/42 mitogen-activated protein kinase (MAPK) in the expression of intercellular adhesion molecule-1 (ICAM-1) in NCI-H292 cells, a human bronchial epithelial cell line, was analyzed. Treatment with the protein kinase C (PKC) activator 12-O-tetradecanoylphorbol 13-acetate (TPA) (16.2 nM) or interferon-γ (IFN-γ) (100 U/ml) induced phosphorylation of p44/42 MAPK. The MEK inhibitor U0126 (0.1 to 10 μM) enhanced the TPA-induced ICAM-1 expression but not the IFN-γ-induced one. U0126 also enhanced the ICAM-1 expression induced by two other PKC activators teleocidin (22.5 nM) and aplysiatoxin (14.9 nM). Furthermore, PD98059 (0.5 to 50 μM), another MEK inhibitor, enhanced the TPA-induced ICAM-1 expression as well. The inhibitor of p38 MAPK SB203580 did not affect the TPA-induced ICAM-1 expression. BAY11-7082, an inhibitor of nuclear factor κB (NF-κB) activation, and MG132, a 26S proteasome inhibitor, reduced the TPA-induced ICAM-1 expression but not the IFN-γ-induced one. TPA partially decreased the level of IκB-α and the reduction was further augmented by U0126 in a concentration-dependent manner. These findings suggested that, in NCI-H292 cells, p44/42 MAPK suppresses PKC activator-induced NF-κB activation, thus negatively regulating the PKC activator-induced ICAM-1 expression but not the IFN-γ-induced one.
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