Acrolein Causes Inhibitor κB-independent Decreases in Nuclear Factor κB Activation in Human Lung Adenocarcinoma (A549) Cells

Abstract

Acrolein is a highly electrophilic alpha,beta-unsaturated aldehyde to which humans are exposed in various situations. In the present study, the effects of sublethal doses of acrolein on nuclear factor kappaB (NF-kappaB) activation in A549 human lung adenocarcinoma cells were investigated. Immediately following a 30-min exposure to 45 fmol of acrolein/cell, glutathione (GSH) and DNA synthesis and NF-kappaB binding were reduced by more than 80%. All parameters returned to normal or supranormal levels by 8 h post-treatment. Pretreatment with acrolein completely blocked 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced activation of NF-kappaB. Cells treated for 1 h with 1 mM diethyl maleate (DEM) showed a 34 and 53% decrease in GSH and DNA synthesis, respectively. DEM also reduced NF-kappaB activation by 64% at 2 h post-treatment, with recovery to within 22% of control at 8 h. Both acrolein and DEM decreased NF-kappaB function approximately 50% at 2 h after treatment with TPA, as shown by a secreted alkaline phosphatase reporter assay. GSH returned to control levels by 8 h after DEM treatment, but proliferation remained significantly depressed for 24 h. Interestingly, DEM caused a profound decrease in NF-kappaB binding, even at doses as low as 0.125 mM that had little effect on GSH. Neither acrolein nor DEM had any effect on the levels of phosphorylated or nonphosphorylated inhibitor kappaB-alpha (IkappaB-alpha). Furthermore, acrolein decreased NF-kappaB activation in cells depleted of IkappaB-alpha by TPA stimulation in the presence of cycloheximide, demonstrating that the decrease in NF-kappaB activation was not the result of increased binding by the inhibitory protein. This conclusion was further supported by the finding that acrolein modified NF-kappaB in the cytosol prior to chemical dissociation from IkappaB with detergent. Together, these data support the conclusion that the inhibition of NF-kappaB activation by acrolein and DEM is IkappaB-independent. The mechanism appears to be related to direct modification of thiol groups in the NF-kappaB subunits.